Copyright

by

Ochiagha Victor Ananaba

2007

Experimental Study On The Effect Of The Internal Design On The

Performance Of Down hole Gas Separators

by

Ochiagha Victor Ananaba, B.Eng.

Thesis

Presented to the Faculty of the Graduate School of

The University of Texas at Austin

in Partial Fulfillment

of the Requirements

for the Degree of

MASTER OF SCIENCE IN ENGINEERING

The University of Texas at Austin

December 2007

Experimental Study On The Effect Of The Internal Design On The

Performance Of Down hole Gas Separators

Approved by Supervising Committee:

Augusto L. Podio (Supervisor)

Paul Bommer

Dedication

To God Almighty.

To my loving and supporting parents Sir Emeka & Lady Nnenne Ananaba.

To my siblings, Nnem, Ugochukwu, Ugwunwanyi, Ogbugo & Amah (Papa).

To the woman that will be my wife.

v

Acknowledgements

I specifically want to thank my supervisor Dr. Augusto Podio for his continuous

support and encouragement through this research project. Under his supervision I have

greatly improved my knowledge and skills in the areas of petroleum production engineering

and artificial lift systems. It is an honor to have him as my supervisor and to be his friend.

I wish to thank Dr. Paul Bommer for the time that he took inside his very busy

schedule to read and review my thesis.

I will not forget to thank our Lab. Technician and my friend Tony Bermudez whose

support in maintaining and constructing my laboratory models made certain that I finished

my experiments in good time with high levels of accuracy.

I wish to thank Glenn Banm, Harry Linnemeyer, Ehiwario M., Acholem K., Ojifini

R., Elekwachi K. and Don Sorrell who were there to help whenever I needed assistance.

My special thanks go to our amiable graduate coordinator Cheryl Kruzie. I would not

be in UT if not for her kind and honest counseling.

Finally I would like to thank the companies that supported this research, Echometer

Company, ConocoPhillips, Yates Petroleum and Chevron. The comments and suggestions

from James McCoy, Lynn Rowland, John Patterson and Gabriel Diaz helped in shaping my

research.

I worked with Renato Bohorquez in the early days of this research and it was great.

Ochiagha Victor Ananaba

December 2007

vi

ABSTRACT

Experimental Study On The Effect Of The Internal Design On The

Performance Of Down hole Gas Separators

Ochiagha Victor Ananaba, M.S.E.

The University of Texas at Austin, 2007

Supervisor: Augusto L. Podio

The re-design of the internal geometry of static down hole gas separators directly

affects the gas liquid separation performance.

This thesis describes experimental results obtained after changing the dip tube design

from the conventional straight design to a helical design. Typically, a static down hole gas

separator with a conventional straight dip tube design depends on gravity to induce density

difference in the flowing wellbore fluid which causes gas liquid separation to occur. Thus,

the device is known as a gravity driven down hole gas separator.

vii

This research compared the experimental results and visual observations from

gravity driven down hole gas separators to that of static down hole gas separators with

helical dip tube designs known as static centrifugal down hole gas separators.

The visual observations showed that not only did the driving mechanisms for gas

liquid separation inside static centrifugal down hole separators include gravity it also

incorporated other means such as induced centrifugal forces that greatly improved overall

gas liquid separation. The 6 inch/second threshold downward superficial liquid velocity

generally regarded as the industry rule of thumb for down hole gas separators was

increased to 10 inch/second. In field units this is a 200 BPD increase in liquid production.

This research also studied the effect of increasing outer diameter of gravity driven

down hole gas separators from 3inches (2.75 ID) to 4inches (3.75 ID). The results

showed that liquid handling capacity increased by over 90% due to favorable flow regimes

observed inside the separator. However, critical examination of gas liquid separation

performances of both 3 inch OD and 4 inch OD separators in terms of downward liquid

superficial velocity reveal that gas liquid separation results are similar. It was concluded

therefore that downward superficial liquid velocity is a reliable parameter in the design of

down hole gas separators and that all gravity driven separators regardless of separator

outer diameter will operate in similar fashion except at different liquid flow rates.

Bubble rise experiment performed in this research project gave a range of 1 100 cp

as region of applicability for the results discussed in this thesis.

viii

Table of Contents

Acknowledgment v

Abstract...vi

List of Tables ........................................................................................................ xii

List of Figures ...................................................................................................... xiii

CHAPTER 1 1

Introduction ..............................................................................................................1 1.1 OBJECTIVE ..........................................................................................1 1.2 LITERATURE REVIEW ......................................................................3

1.2.1 PATENTED STATIC CENTRIFUGAL DOWN HOLE GAS SEPARATORS ...........................................................................15

1.2.1.1 GAS ANCHOR - PATENT No 3128719 .................................15 1.2.1.2 Continuous Flow Down hole gas separator for

Progressive Cavity Pumps - Patent No 5902378 .........................17 1.2.2 ACTIVE TYPE CENTRIFUGAL DOWN HOLE GAS

SEPARATORS ...........................................................................20 1.2.2.1 Liquid Gas Separator Unit - Patent No 3887342 .............20 1.2.2.2 Liquid Gas Separator Apparatus - Patent No 4481020 ...21 1.2.2.4 Apparatus for separating gas and solids from well fluids -

Patent No 6382317 B1 .................................................................24

CHAPTER 2 28

Experimental Facility And Procedure ....................................................................28 2.1 EXPERIMENTAL FACILITIES.........................................................28 2.2 DESCRIPTION OF EXPERIMENTAL FACILITIES .......................28 2.3 LABORATORY TEST WELL ............................................................32

2.3.1 LABORATORY INSTRUMENTS ............................................34 2.3.1.1 LIQUID FLOW MEASUREMENTS ................................34 2.3.1.2 GAS FLOW MEASUREMENT ........................................35

ix

2.3.2.2 PRESSURE MEASUREMENT ........................................37 2.4 EXPERIMENTAL PROCEDURE ......................................................38 2.5 SEPARATOR PERFORMANCE DISPLAY ......................................39 2.6 DOWN HOLE GAS SEPARATOR DESIGNS ..................................44

2.6.1 ECHOMETER (3X1), ECHOMETER (3X1.5), ECHOMETER (4x1), ECHOMETER (4X1.5), ECHOMETER (4X1.75) ..........44

2.6.2 PATTERSON (3X1), PATTERSON (3X1.5), PATTERSON (4x1), PATTERSON (4X1.5), PATTERSON (4X2) ..................47

2.6.3 TWISTER ...................................................................................48 2.6.3.1 ECHOMETER-TWISTER ..........................................52 2.6.3.2 PATTERSON TWISTER .........................................53

CHAPTER 3 55

Analysis Of Experimental Results .........................................................................55 3.1 EFFECT OF HELICAL DIP TUBE DESIGN ....................................55

3.1.1 PERFORMANCE RESULTS FOR THE TWISTER SEPARATOR .............................................................................56

3.1.2 PERFORMANCE RESULTS FOR ECHOMETER TWISTER SEPARATOR .............................................................................58

3.1.3 PERFORMANCE RESULTS FOR PATTERSON TWISTER SEPARATOR .............................................................................61

3.2 COMPARISON OF PERFORMANCES OF HELICAL DIP TUBE GAS SEPARATORS TO STRAIGHT DIP TUBE GAS SEPARATOR63 3.2.1 COMPARISON OF ECHOMETER-TWISTER AND

ECHOMETER (3X1) GAS SEPARATORS ..............................63 3.2.2 COMPARISON OF PATTERSON-TWISTER AND

PATTERSON (3X1) GAS SEPARATORS ...............................73 3.2.3 EFFECT OF THE NUMBER OF DIP TUBE TWISTS ON

STATIC CENTRIFUGAL SEPARATORS ...............................78 3.2.4 ANALYSIS OF STATIC CENTRIFUGAL SEPARATOR

DESIGNS. ...................................................................................84 3.3 EFFECT OF INTERIOR AND EXTERIOR FLOW AREAS ON

SEPARATOR PERFORMANCE ........................................................88 3.3.1 EFFECT OF CHANGING INTERIOR AND EXTERIOR

ANNULAR AREA FOR ECHOMETER GAS SEPARATORS90

x

3.3.2 EFFECT OF CHANGING INTERIOR AND EXTERIOR ANNULAR AREA FOR PATTERSON GAS SEPARATORS103

3.4 DIP TUBE LENGTH EFFECTS ..............................................116 3.5 PERFORMANCE OF ECHOMETER (3X1) GAS SEPARATOR

WITH STANDING VALVE INCLUDED BETWEEN GAS SEPARATOR AND TUBING RETURN LINE (PUMP INTAKE) .119 3.5.1 ECHOMETER (3X1) AND ECHOMETER (3X1) WITH

STANDING VALVE COMPARED. .......................................123 3.5.2 ANALYSIS OF PRESSURE DROP FOR ECHOMETER (3X1)

AND ECHOMETER (3X1) WITH STANDING VALVE ......125 3.6 FLOW REGIMES INSIDE THE DOWN HOLE GAS

SEPARATORS ..................................................................................126

CHAPTER 4 133

Bubble Rise Experiments .....................................................................................133 4.1 APPARATUS USED IN BUBBLE RISE EXPERIMENTS .............134 4.2 PROPERTIES OF FLUIDS USED IN THE EXPERIMENT ...........136

4.2.1 TEST FOR NEWTONIAN CHARACTERISTICS OF FLUIDS136 4.2.2 DETERMINING THE VISCOSITY OF TEST FLUIDS IN

ASSOCIATION WITH WATER AT ROOM TEMPERATURE138 4.2.2.1 TEST DATA FOR GLYCERIN IN ASSOCIATION WITH

WATER ....................................................................................139 4.2.2.2 TEST DATA FOR CORN SYRUP IN ASSOCIATION

WITH WATER .........................................................................140 4.3 ANALYSIS OF RESULTS FROM BUBBLE RISE EXPERIMENTS141

CHAPTER 5 145

Conclusions and Recommendations ....................................................................145 5.1 CONCLUSIONS...............................................................................145

5.1.1 CONCLUSIONS FROM COMPARISONS OF GRAVITY DRIVEN SEPARATORS AND STATIC CENTRIFUGAL GAS SEPARATORS .........................................................................146

5.1.2 THE EFFECT OF INCREASING SEPARATOR OUTER DIAMETER FOR GRAVITY DRIVEN SEPARATORS .......147

5.1.3 CONCLUSIONS FROM BUBBLE RISE EXPERIMENT ....149

xi

5.2 GENERAL DESIGN GUIDE ...........................................................149 5.3 RECOMMENDATIONS AND FUTURE WORK ..........................150

Appendix A ..........................................................................................................152

Schematics of the Echometer Separators .............................................................152

Appendix B ..........................................................................................................155

Schematics of the Patterson Separators ...............................................................155

Appendix C ..........................................................................................................159

Original data files .................................................................................................159

Nomenclature .......................................................................................................160

Abbreviations .......................................................................................................161

References ............................................................................................................163

Vita .165

xii

List of Tables

Table 2-1 - Sample Excel Spreadsheet for continuous flow test .......................................... 41

Table 2-2 Echometer gas separators configuration ............................................................ 44

Table 2-3 Patterson Separator Configuration ...................................................................... 46

Table 4-1 Dimensions of bubble rise experiment apparatus ........................................... 134

Table 4-2 Fluid Properties used in bubble rise experiment ............................................. 135

Table 4-3 Test data for glycerin in association with water ............................................... 138

Table 4-4 - Test data for corn syrup in association with water ....................................... 139

xiii

List of Figures

Figure 1-1 - Centrifugal Separator(Kobylinski et al) ................................................................ 8

Figure 1-2 - Gas flow through centrifugal separator (Kobylinski et al) ................................ 9

Figure 1-3 - Reverse-flow separator (Kobylinski et al) .......................................................... 10

Figure 1-4 Collar-Size down hole gas separator (McCoy and Podio10) ....................... 12

Figure 1-5- Down-hole gas separator (Patterson and Leonard11) ........................................ 14

Figure 1-6 - Jongbloed et al12 ..................................................................................................... 17

Figure 1-7 Static Centrifugal Separator by Obrejanu Marcel13 .......................................... 19

Figure 1-8 Invention by Bunnelle P14.................................................................................... 21

Figure 1-9 - Centrifugal Separator by Kobylnski et al ........................................................... 23

Figure 1-10 Invention by Powers Maston15 ......................................................................... 24

Figure 1-11 Invention by Delwin Cobb16 ............................................................................. 26

Figure 1-12 Cross section (3) in Figure 1-11 .................................................................... 26

Figure 2-1 Schematic of experimental test facility .............................................................. 30

Figure 2-2 Laboratory facility ................................................................................................. 30

Figure 2-3 Laboratory test well .............................................................................................. 31

Figure 2-4 Laboratory Well .................................................................................................... 32

Figure 2-5 Turbine flow meter and valve between pump and mixer ............................... 33

Figure 2-6 - - ITT Barton floco positive displacement meter .............................................. 34

Figure 2-7 - Fisher Porter Flow Rator tube ............................................................................. 35

Figure 2-8 - Thermodynamic Omega Air Flow Meter .......................................................... 36

Figure 2-9 - Sample Performance plot for Patterson (3X1) in continuous flow ............... 42

Figure 2-10 Echometer (3 X1.5) gas separator design ....................................................... 45

Figure 2-11- Echometer entry port geometry ......................................................................... 45

Figure 2-12 Echometer (4X1.75) gas separator design ...................................................... 45

Figure 2-13 4 inch OD Patterson Separator Design .......................................................... 47

Figure 2-14 3 inch OD Patterson Separator Design .......................................................... 47

Figure 2-15 Twister Separator (Bohorquez) ........................................................................ 50

Figure 2-16 Twister Connection ............................................................................................ 50

xiv

Figure 2-17 Diagrammatic of the forces acting in a static centrifugal separator ............ 51

Figure 2-18 Echometer - Twister .......................................................................................... 52

Figure 2-19 Patterson - Twister ............................................................................................. 53

Figure 3-1- Twister results in field units .................................................................................. 56

Figure 3-2 - Twister result in terms of superficial velocities ................................................. 57

Figure 3-3 Echometer - Twister result in terms of superficial velocities ......................... 58

Figure 3-4 Echometer - Twister results in field units ......................................................... 59

Figure 3-5 - Patterson - Twister result in terms of superficial velocities ............................ 60

Figure 3-6 - Patterson - Twister results in field units ............................................................. 61

Figure 3-7 Comparison of Echometer Twister and Echometer (3X1) results in terms

of superficial velocity .................................................................................................................. 64

Figure 3-8- Comparison of Echometer Twister and Echometer (3X1) results in Field

Units .............................................................................................................................................. 65

Figure 3-9 - Pressure Drop between the entry ports and pump intake for Echometer

Twister and Echometer (3X1); Casing Pressure (Pc) = 10 13psi ...................................... 66

Figure 3-10 Pressure measurements during the tests ......................................................... 67

Figure 3-11 Pressure drop for Echometer-Twister and Echometer (3X1) at constant

gas rates; Pc = 10 13 psi .......................................................................................................... 68

Figure 3-12- Pressure drop for Echometer-Twister and Echometer (3X1) at constant

liquid rates; Pc = 10 13 psi ...................................................................................................... 71

Figure 3-13 - Comparison of Patterson Twister and Patterson (3X1) results in terms of

superficial velocity ....................................................................................................................... 72

Figure 3-14 - Comparison of Echometer Twister and Echometer (3X1) results in Field

Units .............................................................................................................................................. 73

Figure 3-15 - Pressure Drop between the entry ports and pump intake for Patterson

Twister and Patterson (3X1) separators; Casing Pressure (Pc) = 10 13psi ...................... 74

Figure 3-16 Pressure drop for Patterson-Twister and Patterson (3X1) at constant gas

rates; Pc = 10 13 psi ................................................................................................................. 75

xv

Figure 3-17 - Pressure drop for Patterson-Twister and Patterson (3X1) at constant liquid

rates; Pc = 10 13 psi ................................................................................................................. 76

Figure 3-18 Patterson-Twister (2 twits) ................................................................................. 77

Figure 3-19 - Patterson Twister (2 twists) results in terms of superficial velocities ....... 78

Figure 3-20 - Patterson Twister (2 twists) gas separator results in field units ................ 79

Figure 3-21 - Comparison of Patterson Twister (4 twists) and Patterson Twister (2

twists) results in superficial velocity terms ................................................................................ 80

Figure 3-22 - Comparison of Patterson Twister (4 twists) and Patterson Twister (2

twists) results in Field Units ........................................................................................................ 81

Figure 3-23 - Pressure drop between the entry ports and pump intake for Patterson

Twister 2 twists and 4 twists gas separators; Casing Pressure (Pc) = 10 -13 psi.................... 82

Figure 3-24 Comparison of results for all static centrifugal separators in terms of

superficial velocities .................................................................................................................... 84

Figure 3-25 - Comparison of results for all static centrifugal separators in field units ..... 85

Figure 3-26 - Pump Liquid Fraction for Static Centrifugal Separators at 10 in/sec ......... 86

Figure 3-27 - Echometer (4X1) and Echometer (3X1) results compared in field units ... 90

Figure 3-28 - Echometer (4X1.5) and Echometer (3X1.5) results compared in field units

........................................................................................................................................................ 91

Figure 3-29 - Echometer (4X1.75) results in field units ........................................................ 93

Figure 3-30 Comparison of results of all Echometer gas separators in terms of

superficial velocity ....................................................................................................................... 94

Figure 3-31 - Pump Liquid Fraction for Echometer Separators at 6 in/sec ...................... 96

Figure 3-32 - Pump Liquid Fraction for Echometer Separators at 10in/sec ..................... 97

Figure 3-33 Comparison of all Echometer 4 inch OD separator results in field units . 98

Figure 3-34 - Pressure drop between the entry ports and pump intake for Echometer 4

inch OD gas separators for 2 phase gas liquid flow; Casing Pressure (Pc) = 10 -13 psi . 100

Figure 3-35 - Pressure drop between the entry ports and pump intake all tested

Echometer gas separators; Casing Pressure (Pc) = 10 -13 psi ............................................ 101

Figure 3-36 - Patterson (4X1) and Patterson (3X1) results compared in field units ....... 103

xvi

Figure 3-37- Patterson (4X1.5) and Patterson (3X1.5) results compared in field units .. 104

Figure 3-38 Patterson (4X1.75) results in field units ........................................................ 105

Figure 3-39 - Patterson (4X2) results in field units .............................................................. 106

Figure 3-40 - Comparison of results for all Patterson 3 inch OD and 4 inch OD

separators in superficial velocity terms .................................................................................. 107

Figure 3-41 - Pump Liquid Fraction for Patterson Separators at 6 in/sec ....................... 109

Figure 3-42 - Pump Liquid Fraction for Patterson Separators between 8 9 in/sec ..... 110

Figure 3-43 - Comparison of all Patterson 4 inch OD separator results in field units ... 112

Figure 3-44 Pressure Drop between the entry ports and pump intake for Patterson 4

inch OD gas separators; Casing Pressure (Pc) = 10 13psi ............................................... 113

Figure 3-45 - Pressure drop between the entry ports and pump intake for Patterson 4

inch OD gas separators at varying gas and liquid rates; Casing Pressure (Pc) = 10 -13psi

...................................................................................................................................................... 114

Figure 3-46 Comparison of results for Echometer (4X1.75) with 5dip tube and Echometer

(4X1.75) with 2 dip tube in superficial velocity terms ................................................................. 116

Figure 3-47 - Comparison of results for Echometer (4X1.75) with 5dip tube and Echometer

(4X1.75) with 2 dip tube in field units ...................................................................................... 117

Figure 3-48 Standing Valve Assembly ................................................................................ 119

Figure 3-49 SV joint Gas Separator Connection ........................................................... 119

Figure 3-50 Echometer (3X1) with SV result in terms of superficial velocities ........... 120

Figure 3-51 - Echometer (3X1) with SV result in field units .............................................. 121

Figure 3-52 Comparison of Echometer (3X1) with and without Standing Valve in terms

of superficial velocities ............................................................................................................. 122

Figure 3-53 - Comparison of Echometer (3X1) with and without Standing Valve in field

units ............................................................................................................................................. 123

Figure 3-54- Pressure drop between the entry ports and pump intake for Echometer

(3X1) with and without Standing Valve .................................................................................... 124

Figure 3-55 - Pressure drop between the entry ports and pump intake for Echometer

(3X1) with and without Standing Valve at varying gas and liquid rates; Pc = 10 -13 psi ... 125

xvii

Figure 3-56 Flow Regimes observed in the gas separator annular area

(courtesy Renato Bohorquez7) ................................................................................................. 126

Figure 3-57 Flow regime map for the annular space of 3 inch OD gravity driven gas separators7 127

Figure 3-58 Flow regime map for the annular space of 4 inch OD gravity driven gas separators .. 128

Figure 3-59 Flow regime map for the Twister separator annlus7 ................................... 130

Figure 3-60 Flow regime for Patterson Twister and Echometer Twister static

centrifugal separators ................................................................................................................ 131

Figure 4-1 Schematic of Laboratory Constructed Apparatus for testing bubble rise velocity ......... 134

Figure 4-4 Glycerin Rheology test ....................................................................................... 136

Figure 4-5 Glycol Rheology test .......................................................................................... 136

Figure 4-6 Corn Syrup Rheology test.................................................................................. 137

Figure 4-7 Viscosity plot for Glycerin in association with water at room temperature

...................................................................................................................................................... 138

Figure 4-8 Viscosity plot for Corn Syrup in association with water at room temperature

...................................................................................................................................................... 139

Figure 4-9 Combined viscosity plots for glycerin and corn syrup in association with

water at room temperature ...................................................................................................... 140

Figure 4-10 Examples of bubble diameter sizes measured.142 Figure 4-11 Mean bubble rise velocities in stationary liquid in an annulus ................... 143

1

Chapter 1

Introduction

1.1 OBJECTIVE

Most wells producing from mature reservoirs use artificial lift methods for oil

and gas production. Common artificial lift methods include beam pumping,

progressive cavity pumping and electric submersible pumping. All the mentioned

artificial lift systems exhibit a common problem: Gas Interference

The presence of free gas in beam pumps (sucker rod pumps) prevents the

traveling valve from opening at the appropriate time interval during the downstroke.

This is caused by the high compressibility of gas in the pump barrel. The traveling

valve may eventually open when the gas inside the barrel has been compressed

enough to overcome the fluid load on the plunger. In such a case fluid pound occurs.

In extreme cases the peak pressure of the trapped gas on the downstroke is

insufficient to overcome the hydrostatic head of the traveling valve; then the pressure

is not reduced enough on the upstroke to allow the standing valve to open and admit

new fluid. Both valves are essential stuck at a closed position and the pump refuses to

pump. This extreme case is known as gas locking.

In progressive cavity pumps (PCP) the produced liquid lubricates the rotor and

the stator so as to reduce the heat caused by friction. The presence of free gas in the

2

produced fluid reduces the lubricating function of the produced fluid so that the rotor

and stator are in direct contact. Temperature increase due to the direct contact causes

damage to the pump. In other cases gas in the produced fluid in PCP may change the

chemical composition of the elastomer in the stator of the pump which further

complicates the problem.

Electric submersible pumps (ESP) are typically used to handle high liquid flow

rates. Significant volumes of gas entering the pump especially at low intake pressures

degrade the pump performance, and dramatically reduce the head produced by the ESP.

This may prevent the pumped liquid from reaching the surface. The ESP is composed of

a down hole motor which is connected to a seal section which in turn is connected

to a centrifugal pump. It is imperative that the motor be cooled by the produced fluid

passing the outer casing. In the event that large quantities of gas pass the motor, the heat

transfer from the motor to the produced fluid will be drastically reduced, potentially

causing motor damage by overheating.

In all cases - beam pumps, PCP and ESP the pump volumetric efficiency is

reduced by the presence of gas. To combat the problem of reduced volumetric efficiency

and system damage down hole gas separators are used in conjunction with down

hole pumps.

The sole purpose of down hole gas separators* is to prevent gas from entering

into down hole pumps, or to at least reduce the quantity of gas entering into the pump

to permissible ranges where the pump efficiency is still acceptable.

Unfortunately many gas separator designs have not yielded the desired efficiency.

The widely used poorboy gas separator which depends on gravity segregation to

separate gas from liquids has become synonymous with inefficiency. * Down hole gas separators will mean the same thing as gas separators throughout this thesis

3

A thorough literature review on the subject of gas separator design was done to

study previous designs and relevant applications. Sources of information included

published technical papers, patents and thesis reports by Lisguiski, Guzman and

Bohorquez.

The scope of the present work emphasized the effect of the internal geometry

and induction of centrifugal forces on gas separator performance.

1.2 LITERATURE REVIEW

Schome 1 in February 1953 reported a field test of a down-hole gas separator in a

well in Utah. The pump volumetric efficiency obtained before the installation the down-

hole gas separator ranged between 26 and 48%. Schome1 reported that the efficiency was

increased to 70%; resulting in an increased production of 50BPD after the new gas

separator was installed. The author went on to describe some bottom-hole separator (as

it was then referred) designs and their mode of operation. All the separator designs

described in his paper depended on gravity segregation as the controlling mechanism for

efficient performance and were 30 40 ft long with 1inch suction tubes (dip tubes).

Schome1 noted that operators often faced retrieval problems when the separators were

plugged with formation debris. He attributed that to inconsistent installation techniques

and gas separator designs.

Clegg2 did a thorough review of the different types of gas anchors (down-hole

gas separators) and the principles that govern most of their operation. He pointed out

that the desire of several gas separator inventors was to achieve a downward mixture

4

velocity of 0.5ft/sec (6in/sec) inside the separator dip tube annular area. A downward

mixture velocity of 0.5ft/sec is generally accepted as being below the rising (slip) velocity

of gas in low viscosity fluids. Clegg2 and McCoy3 et al described the reasons for the

inefficiency of the commonest down-hole gas separator design the poorboy separator.

The reasons for the inefficiency of the Poorboy gas separator according to the author

included the high downward liquid velocity inside the Poorboy separator and size of its

dip tube ID which the author considered as too small in diameter. The small ID dip tube

often causes excessive pressure drop inside the separator. The Shell (Schmit Jongbloed)

gas anchor formula:

gas anchor efficiency = 0.66 0.5100

(1 )wf slC P V+

1

Pwf= intake pressure at the anchor; Vsl=downward superficial velocity of liquids; C = gas anchor

constant (usually 0.2 based on laboratory data)

described by Clegg1 showed that the performance of any given size and type of gas

separator is largely dependent on the intake pressure at the anchor and the downward

superficial velocity of the fluids in the anchor. An examination on the formula done by

the author reveled that at zero pressure and zero velocity the anchor/gas separator

efficiency is 100% and that at high velocities (greater than 0.5 ft/sec) inside the gas

separator the separation efficiency is poor. Pressures above 400psig also resulted in low

efficiencies. The author however cautioned that actual experiences indicate that

separation may be significantly greater than what the formula predicts. The uncertainty in

the equation emerged from the use of the constant C which represented other

important variables such as viscosity, gas bubble size and dispersion. Laboratory results

that were not published indicated a constant of 0.2. The author warned that the

5

determination of accurate values of C is difficult for actual field conditions. Clegg2

strongly encouraged using a Natural gas anchor (installing the pump below the lowest

perforation) whenever it is feasible as is gives the greatest down-pass area for the liquid

thereby reducing the downward liquid velocity.

The work by Campbell and Brimhall4 largely focused on developing an industry

standard for determining the down-hole gas separator area; the dip tube area and the dip

tube length to be used for different liquid and gas flow rates. The objective of their

computer program was to aid in the design of a gas separator system and to evaluate the

pressure drops within the system and thus the system efficiency. The major parameters

which they noted were pivotal to gas separator design included the gas bubble velocity,

diameter of the mud anchor (down-hole gas separator), length of dip tube and the

pressure drops associated with the system. They agreed that the 0.5 ft/sec downward

liquid velocity inside the separator was a valid rule of thumb for low viscosity fluids.

The design procedure began with using Stokes Law (see Equation 2) to determine the

terminal rising velocity that a given gas bubble will achieve in a liquid for a given gas

bubble radius, liquid viscosity and density difference between the two phases.

2

1 22 ( )9

bg RU =

2

Where U = terminal velocity, ft/sec; g = 32.17 ft/sec2; L = liquid density; Ib/ft3 g = gas density,

Ib/ft3; = liquid viscosity; Ibm/(ft-sec); Rb = bubble radius (ft)

The second step used the calculated terminal velocity to calculate the area of the gas

separator (also called Mud Anchor or MA) using equation 3.

6

0.00935 LQAMAU EV

=

Where AMA = area of mud anchor, in2, QL = liquid rate,STBD

; EV = Pump efficiency

3

These calculated values are inputted into the computer program explained in

their paper to generate relationships between (1) pressure effects on gas bubble velocity

over constant viscosity and temperature (2) gas bubble velocity and diameter of the mud

anchor over different liquid flow rates (3) dip tube diameter and pressure drop in the gas

anchor over different liquid flow rates (4) pressure drop and dip tube length as a

function of liquid rate.

The results showed that gas bubbles travelled faster in smaller OD mud anchors

larger dip tube diameters yielded the smallest pressure drop and longer dip tubes had the

largest pressure drops.

Experimental results from Lisugurski5, Guzman6 and Bohorquez7 however

dispute the orders of magnitude of the results from Campbell and Brimhall4. Field

results9 based on Lisugurskis 5 thesis have shown that a 6ft long gas separator can

operate efficiently at rates which would require longer gas separator lengths if Campbell

and Brimhalls 4 results were practiced to the letter. Bohorquez7 in his work however

concluded that gas bubbles especially during the up - stroke of a sucker rod pumping

system coalesce more readily and rise faster in smaller separator annular areas compared

to larger annular areas.

Kobylinski et al 8 described the design, development and laboratory testing of a

new rotary gas separator, Figure 1-1 and Figure 1-2. The rotary gas separator is an active-

7

type centrifugal separator. Laboratory and field comparison were conducted between the

Centrifugal separator and the passive-type Reverse-flow separator, Figure 1-3.

Laboratory tests were done using water and air as test fluids in continuous flow

condition. The Reverse-flow separator uses the gravity separation mechanism for gas

liquid separation. The Centrifugal separator achieved separation of gas and liquid by the

use of cyclone and vortex technology. The characteristics of this method identified by

the authors were that the separated liquid is concentrated in the vicinity of the wall of the

separator while the gas phase concentrates at the center of the system. The authors

stated that dimensioning of the separator should be based on the equation of the

trajectory of the gas bubbles; they added that a general equation that would cover the

turbulence arising in the process is not available. Kobylinski et al8 believe that since both

bubble dimensions and proportionality constant between gas and liquid velocities are

unknown from Stokess law for laminar flow(1), reliance on experimental work for

design optimization remains the only alternative. A detailed discussion on bubble

dynamics is analyzed in the paper.

The results from the field tests8 complemented the results from the laboratory

and led to a 95% average improvement in fluid production when results from the active-

type centrifugal separators were compared to the passive-type reverse-flow separators in

tested wells. The dimensions of both the centrifugal and reverse-flow separators were

not given.

8

Figure 1-1 Centrifugal Separator Kobylinski et al

9

Figure 1-2 - Gas flow through centrifugal separator (Kobylinski et al)

10

Figure 1-3 - Reverse-flow separator (Kobylinski et al)

McCoy and Podio10 gave a detailed description of the Collar Size gas separator,

Figure 1-4. They emphasized a maximum pressure loss of PSI for friction loss in the

dip tube. The authors also highlighted the need to allow for sufficient space in the gas

11

separator annular area. According to the authors sufficient flow area should exist so that

the gas flow rate around the ports in the gas separator will allow liquid to flow or fall

into the gas separator annulus. The authors noted the necessity to balance the area

available for flow in the wellbore and that inside the gas separator. Decreasing the casing

annulus will result in increased upward gas velocity which when above 10 ft/second will

suspend some of the liquid and allow mist flow to occur. Another consequence of casing

annulus reduction and increase of gas velocity will be the prevention of liquid from

flowing into the gas separator annulus. The authors stressed the need for the use of large

ports. Large ports allow liquid from the casing to fall by gravity force into the gas

separator because the pressures inside and outside the large ports are the same.

Kobylinski et al8 in their paper also recommended that for a gas separator to operate

efficiently, it must ingest the two phase mixture with minimal pressure drop. This is

necessary to prevent additional gas breakout inside the separator. The Collar Size

separator10 had a total port area which was approximately four times the area inside the

gas separator. The gas separator length received special treatment by McCoy and Podio10

they suggested that the dip tube length extend at least 18 inches below the gas separator

inlet perforations (separator ports). They based their calculation on a gas rise velocity of

6in/sec (0.5ft/sec) and an average pumping speed of 10 strokes per minute which

translates to a pumping cycle time of 6 seconds. The authors also looked at eccentricity

of the separator. Earlier studies noted by the authors showed that liquid concentrates

where tubing is placed against the casing wall and thus advised that gas separators outer

diameter should contact the casing wall, see Figure 1-4.

In wells with some deviation McCoy and Podio10 advised that the separator

should be allowed to rest on the low side of the casing since gas tends to flow up on the

12

high side of the casing annulus by installing any tubing anchors at a distance of 60 to 90

feet shallower than the pump intake.

Figure 1-4 Collar-Size down hole gas separator (McCoy and Podio10)

Patterson and Leonard11 ran some field tests in coal-bed methane wells in

Wyoming with some changes in the down hole pump setting depth interval and for an

increase in gas separator OD. The authors noted that while the modifications were not

fully understood or tested with significant number of installations the improvements

observed warranted some discussion. The tests were conducted in two wells and are fully

described in the paper.

Patterson and Leonard11designed different gas separators used in the field tests in

a bid to achieve greater pump efficiency. The gas separators used in the tests had smaller

slot width and included vent holes and a baffle to facilitate the evolution of gas - Figure

13

1-5 . The concept according to the authors assumes that a smaller slot width will reduce

the amount of gas entering the gas separator and the vent holes will allow the gas that

enters to vent back to the casing. The slot sizes ranged from 0.3 wide by 6 long for the

3.5 OD gas separator (2 in number) to a 3/16 wide by 10 long for the 5.5 OD gas

separator (8 in number). The 5.5 OD gas separators also had three diameter holes

in the swedge (see Figure 1.1-5). Both separator designs had the same dip tube OD but

different dip tube lengths 2 inches difference. The 3.5 OD gas separator was 24 feet

long whereas the 5 OD gas separator was 26 feet long.

The test well , 43-26, had a 3.5 OD 8 long gas separator installed with a

Progressive Cavity Pump (PCP) at 1446 ft after a bucket test had been conducted.

After some months a 5.5OD gas separator was attached to the PCP in test well 43-26.

Although the well contained coal particles which got into the gas separator and starved

the pump intake some useful evaluations on the effect of increase in gas separator cross

sectional area were made from test well 43-26.

Due to gas separator design changes the inlet area of the 5.5 OD gas separator

design increased four times compared to the 3.5 OD gas separator design. The 5.5

OD gas separator annular area (gas separator annular area = gas separator ID dip tube

OD) increased by approximately 3 times over the 3.5 OD gas separator.

The field results11 showed that no gas was produced through the tubing when the

5.5 OD separator was run with the PCP in test well 43-26. Patterson and Leonard11

infer that the differences in inlet area and cross sectional area available for flow could

have had an impact on gas separation and would appear that some combination of these

differences has a grater influence on gas separation than only increasing the cross

sectional area. In another well test where a 4 OD gas separator with some modifications

to the entry slot area and separator length was compared to a 3.5 OD gas separator

14

efficiency in the same well. The authors observed that whereas the 3.5 OD gas

separator produced gas through the tubing the 4 OD gas separator did not. The authors

observed that the increase in annular area must have contributed to pump efficiency

improvement. They however speculated that the increase in length of the 4 OD

separator or the baffle design of the gas separator might also have aided to the

improvement. The authors suggested that more field tests be done and visual modeling

experiments be evaluated with different geometries and configurations to better

understand the reason(s) behind the improvements. Patterson and Leonard11 made other

related conclusions in the paper which dealt with; downward liquid velocity, essence of

vent holes, position of the inlet of the gas separator relative to the perforations and the

age old theory that placing the intake of the pump below the perforated interval creates

an effective natural gas anchor (gas separator).

Figure 1-5- Down-hole gas separator (Patterson and Leonard11)

15

Guzman6 experimentally determined that placing the gas separator inlet at about

3feet below the lowest perforation results in natural separation that yields total gas

liquid separation. A gas separator is not needed in such cases as long as the annular liquid

downward velocity is less than 6 inches per second.

Guzman6 also suggested that the ports area should be equal the gas separator

annular area so that the superficial liquid velocity does not control the flow regime inside

the separator. The use of vent holes in the design of Patterson and Leonard11 in the

experiments conducted by in continuous flow Guzman6 showed that the vent holes do

not improve gas separation. The author suggested the use of single row slots instead of

multiple rows. He however noted that for the decentralized wells the results might be

difficult to predict due to well eccentricity10.

Several centrifugal gas separators have been patented over the years. Most of the

patented arts require the invention have moving parts whereas some do not. The next

sections will initially describe the parts and mode of operation of patented static

centrifugal separators and finally do same for active patented centrifugal separators

1.2.1 PATENTED STATIC CENTRIFUGAL DOWN HOLE GAS

SEPARATORS

1.2.1.1 GAS ANCHOR - PATENT No 3128719

The invention (Figure 1-6) by Jongbloed et al12 in 1964 relates to a gas anchor

consisting of a cylindrical housing sealed at the bottom, at least one sheet metal helix

accommodated in the housing, and a tube (14), one side of which communicates with

the space underneath the sheet metal helix. According to the invention, a discharge

16

conduit is centrally positioned in the housing, the conduit is provided with openings,

preferably near the side of the sheet metal helix facing the bottom of the housing (19),

the gas discharge conduit (17) and the sheet, communicates with the outside of the

housing through the opening (21) that is above the supply openings (20).

In a reported experimental arrangement in which the outer diameter of the

helical channels was 7.5 cm (gas anchor ID = 3 inches), mixtures of varying gas/oil

ratios were supplied to a gas anchor according to the invention. The quantity of oil

passing the separator was from 1 1.5 cu. meters per hour (151 BPD 226 BPD).

When fluid mixtures (dispersions) having gas oil ratios of between 5 and 20

were supplied, the gas/oil ratio of the mixture flowing through conduit (14) was less

than 0.01.

This invention has no moving parts.

17

Figure 1-6 - Jongbloed et al12

1.2.1.2 Continuous Flow Down hole gas separator for Progressive Cavity Pumps - Patent No 5902378

This apparatus invented by Obrejanu Marcel13 in 1999 is a gas separator which

can be attached to the suction of a down hole pump to remove gas from the liquid

being pumped prior to the liquid entering the pump inlet. The separator has an elongate

18

housing having an annular chamber with guides which direct the liquid gas mixture to

flow in an annular path from the inlet to the outlet end. During this flow centrifugal

forces act to displace the gas content to the central region from which it is removed via a

separate central gas outlet so that liquid delivered to the pump inlet is greatly reduced in

its gas content.

In operation, the separator is attached in a coaxial fashion via sub (14) to the

lower end of a progressive cavity pump. In a gaseous environment the liquid will contain

dissolved gases and will enter the chamber (15) under formation pressure through the

inlet ports (16). When the pump is operated the reduction in pressure as a result of the

pump suction will cause some of the dissolved gas to come out of solution. The gas

liquid mixture is drawn upwardly within the tubular housing (12) and upon encountering

the helical flights (20) is guided thereby to move in a helical path. The centrifugal forces

created in the liquid as a result of the helical flow act to reduce the gas content of the

peripherally outer region of the flow and increase the gas content of the central region of

the flow. The angular momentum created in the liquid flow by the flights (20) is

maintained as the liquid moves upwardly into the expansion chamber (23). In this

chamber the cross sectional area of the flow passage is expanded as a result of the

termination of the flights (20), the tapering and termination of the spindle (17), and the

outwards flare of the inner wall of the tubular housing (12), the combined effects of

these resulting in a marked reduction in pressure of the liquid flow thus enhancing the

gas separation effect. The centrifugal force in the rotating liquid is effective to confine

the separated gas to the axial region of the chamber which rises above the rounded top

end (22) of the spindle. The separated gas flow through the axial exit passage (26) to the

exterior of the sub (14) where they can be released into the well bore, or if so desired

delivered to the surface through a separate conduit.

19

This separator has no moving parts within the separating chamber. To force the

liquid into the chamber the separator depends on both hydrostatic head and the pressure

drawdown created by the action of the PCP mounted above. Another interesting feature

about the invention is that multiple separation chambers could be attached just below

(18) for a two stage separation process before the liquid enters into the pump.

This separator design is currently been manufactured in commercial quantity in

Canada.

Figure 1-7 Static Centrifugal Separator by Obrejanu Marcel13

20

1.2.2 ACTIVE TYPE CENTRIFUGAL DOWN HOLE GAS SEPARATORS

1.2.2.1 Liquid Gas Separator Unit - Patent No 3887342

The unit was invented by Bunnelle P14 in 1975. The inventor claims that the unit

when tested in the laboratory could handle high liquid flow capacity of about 82 gallons

per minute (2730 BPD) at zero discharge pressure (pressure head generated by the unit)

and that this rate is slightly reduced to 70 GPM when a 26 ft3/min (37440 CFD) gas is

introduced into the unit. The test fluids where air and water.

The separator unit operates as follows. As motor shaft (58) revolves at a constant

rate impeller shaft (26) and impeller (16) likewise revolve. The impeller draws a liquid

gas mixture through intake openings (32a), into the chamber (12a). As this liquid gas

mixture moves upwardly within chamber 12a, the revolving impeller vanes (20) impart a

compound motion to it. Impeller vane segments (20b) impel the mixture primarily

upwardly through chamber (12a), while vane segments (20a) primarily impart circular

motion to the upwardly moving mixture, thereby centrifuging the liquid component of

the mixture of the mixture outwardly away from the impeller hub (18) and causing

undissolved gas present in the liquid to move inwardly toward the hub (18). The

separated liquid flows up through discharge channels (100) into discharge element

chamber (72a). The separated gas forms a liquid free gas column around hub, the

column of gas moves upwardly into discharge element chamber 86a from where the gas

flows into inlets (96b) and through gas conducting channels (96) to discharge outlets

(96a) in nearly vertical, upward directions. The channel outlets discharge discrete high

velocity gas streams of separated gas that are substantially upwardly directed to promote

21

upward movement of the discharged gas within a wellbore where the separated unit is

situated.

Figure 1-8 Invention by Bunnelle P14

1.2.2.2 Liquid Gas Separator Apparatus - Patent No 4481020

This centrifugal liquid-gas separator is same as described in earlier section (see

Figure 1-1). Here the mode of operation is briefly summarized with an explanatory

pictorial shown in Figure 1-9.

In operation the pump, separator apparatus (Figure 1-9) and motor are

submerged down hole within a liquid gas well fluid mixture. The liquid - gas enters

the intake ports (54) of the intake head (18) through a perforated or slotted member

22

(100) which assists in filtering debris from the fluid mixture. From the intake ports, the

fluid mixture enters the inducer (48) which pressurizes the fluid mixture and supplies it

to the centrifugal separator (50) via transition region (52). The transition region, which is

designed to provide a uniform rate of change through in flow direction and velocity to

the fluid mixture, conveys the fluid mixture smoothly to the centrifugal separator while

minimizing pressure loss. At the outlet end of the transition region, the tangential

velocity of the fluid approaches angular velocity of the centrifugal separator vanes and

the axial velocity of the fluid approaches the flow through velocity of the apparatus.

Liquid gas separation occurs at the inlet of the centrifugal separator region and

continues throughout its length. The liquid section is supplied to the pump through (86),

while the separated gas is vented via gas vents (90) into the space between the well casing

and the separator.

The rotary motion to the inducer and extending vanes are supplied by an

attached motor (20)

23

Figure 1-9 - Centrifugal Separator by Kobylnski et al

1.2.2.3 Recirculating Gas Separator for Electrical Submersible Pumps - Patent

No 4981175

This invention by Powers Maston15 in 1991(Figure 1-10) is a modification of

Lee et al (Figure 1-9). The inventor claims that by including a recirculating means (56)

for recirculating a portion of the discharged liquid from the discharge outlet (50) back to

the separator chamber (46) the gas oil ratio in the separator becomes substantially

lower than a gas to liquid ratio of well fluid entering the well fluid intakes (48). The

recirculating means includes all of the following:

1. Extraction chamber (60)

24

2. Liquid injection chamber (62)

3. Conduit (64)

A drive motor will be needed to extend an upward motion to drive all the

separator mechanisms.

Figure 1-10 Invention by Powers Maston15

1.2.2.4 Apparatus for separating gas and solids from well fluids - Patent No

6382317 B1

The apparatus invented by Delwin E. Cobb16 Figure 1-11, is designed to separate

gas and solids from well fluids in a wellbore.

25

The gas and solids are removed from the well fluids in two separate steps by two

separate spirals, one spiral for the gas (66) and a separate spiral for the solids (70). An

upper gas spiral is positioned below the openings (60) in the outer tubular housing (44)

and a separate lower spiral spaced axially from the upper gas spiral is provided for the

solids. The spirals are positioned in the annulus between the outer tubular housing and

the inner flow tube (46). The spirals provide a helical flow and are spaced axially from

each other at a distance. The gas accumulates in the swirl chamber (80) between the

spirals and is librated from the liquid. The gas normally exists as large bubbles through

an inner gas annulus (72). The liquid flows downwardly in a helical path to the solids

spiral.

The solids, such as sand are separated from the well fluid by the solids spiral and

fall by gravity into the mud anchor or other suitable collection area. The liquid then

flows upwardly in the flow tube (46) to be pumped for flow to a surface location.

This invention makes use of induced centrifugal motion and gravity to separate

gas and solids from wellbore fluids.

The invention has no moving parts.

26

Figure 1-11 Invention by Delwin Cobb16

Figure 1-12 Cross section (3) in Figure 1-11

27

The research reported in this thesis extended the experiments of Kobylinski et al8

and the theory behind the inventions of Jongbloed et al12 and Obrejanu13 in the sense of

using gravity, agitation and centrifugal forces as physical mechanisms to obtain improved

gas liquid separation. The difference between this research and Kobylinski et al8 is in

the use of different experimental procedure, experimental facilities and most importantly

that the centrifugal down hole gas separator must have no moving parts; it must be

static similar to the inventions of Jongbloed et al12 and Obrejanu13.

This research also investigated experimentally the points raised by Patterson and

Leonard11 in terms of the effect of the increase in the gas separator annular area and

improvement in pump efficiency. Visual observation as Patterson and Leonard11

suggested was used to capture the separation mechanism(s) in the production

engineering laboratory at University of Texas at Austin as described in the next chapter.

28

Chapter 2

Experimental Facility and Procedure

This chapter fully describes the facilities, equipment and procedure used in

acquiring laboratory data used throughout this research. The down hole gas separators

used for the purposes of this experimental study are described in detail.

2.1 EXPERIMENTAL FACILITIES

The separator designs were installed in a laboratory well model and tested over a

range of 120 900 BPD of water and air rates between 13 115 MSCFD. The input

into the experimental test system was water and air at pre - determined rates Qg and Qw;

the output from the system included the pressures at the entry ports, tubing pressure and

the gas flow-rate through the dip tube of the separator. The inputs and outputs are

combined in a mathematical model to calculate the pump liquid fraction (pump

efficiency) of the separator relative to particular input values.

This chapter describes the facilities at The University of Texas Production

Laboratory and the procedure used to input and acquire data.

2.2 DESCRIPTION OF EXPERIMENTAL FACILITIES

Figure 2-1 and Figure 2-2 show schematic and overview pictures of the

production laboratory facility used for testing down-hole gas separator designs. The test

facility is a closed loop system with manually controlled valves for fluid flow control.

Water was pumped in a loop into and out of a 3 - phase separator into the well (Figure

29

2-3) Air was supplied to the system by a compressed air line. Water and air meet at the

mixer before entering into the well. The hoses lead the mixture from the manifold

through the casing perforations into the well. Water is returned to the 3 phase

separator through a return a line. Air that passes through the dip tube is carried with the

water into the 3 phase separator and the rest rises up the casing.

30

Figure 2-1 Schematic of experimental test facility

31

Figure 2-2 Laboratory facility

Figure 2-3 Laboratory test well

32

2.3 LABORATORY TEST WELL

The bottom parts of the well are made of clear acrylic pipe to allow observation

of the gas and liquid phases inside the separator. Figure 2-3 shows close up pictures of

the laboratory well. Figure 2-4 shows the full laboratory well picture, notice that the

down hole gas separator is placed below the down hole pump. All the laboratory

tests were conducted with the gas separator situated in such position. The down-hole gas

separator components are positioned in the laboratory well as they would in a real well.

The mud anchor is the outer barrel of the separator. The mud anchor entry ports or

inlets allow water and some of the air to flow into the separator. The dip tube is the

small diameter tube inside the separator. The water flows down in the separator annular

area to the dip tube suction. Then the water flows up through the dip tube to the tubing

intake shown in Figure 2-4.

The bottom part of the casing has an ID of 6 inches. The upper part is PVC pipe

that extends to the rooftop of the Petroleum Engineering building at the University of

Texas, approximately 80ft. as seen in Figure 2-4. The bottom section of the casing has

several perforations, 31/64 inch in diameter, distributed at different positions. This way

it is possible to vary the relative location of the down-hole separator entry ports with

respect to the perforations.

33

Figure 2-4 Laboratory Well

Ports Pressure gauge (P2)

Casing Pressure gauge (P1)

Tubing Pressure gauge (P3)

Location of the separator

34

2.3.1 LABORATORY INSTRUMENTS

The instruments used in the conducting all the tests used for this research are

shown below. The functions that they performed are also explained.

2.3.1.1 LIQUID FLOW MEASUREMENTS

Figure 2-5 is a photo of the Daniel MRT97 turbine flow meter, used to measure

the water flow rate, installed in the liquid loop before the mixer. The water flow was

controlled by the valve in the same picture.

Figure 2-5 Turbine flow meter and valve between pump and mixer

The ITT Barton Floco positive displacement meter (ITT Barton, model 308K)

was used only for reference. It is installed between the turbine flow meter and the mixer.

35

Figure 2-6 - - ITT Barton floco positive displacement meter

2.3.1.2 GAS FLOW MEASUREMENT

The air flow into the mixer was controlled with the Fisher Porter flowrator tube

and the valve shown in Figure 2-7. The flowrator tube displays the airflow as a

percentage of the maximum flow rate, 16416 CFD. The percentages used in the tests

were 10, 20, 30, 60 and 90. The pressure in the compressed air line was measured by a

pressure transducer to convert the actual air flow rate to standard conditions using the

ideal gas law since working pressure of less than 100psi and laboratory temperature,

allowed assuming a Z factor in the vicinity of 1.0.

36

Figure 2-7 - Fisher Porter Flow Rator tube

Figure 2-8 shows the Omega FMA-A2313 thermodynamic mass flow meter

installed at the top outlet of the three - phase separator. This instrument gave the most

important reading in the tests, the amount of air that enters the pump. The units on the

display are in standard liters per minute with accuracy of 1%.

37

Figure 2-8 - Thermodynamic Omega Air Flow Meter

2.3.2.2 PRESSURE MEASUREMENT

The casing pressure (see Figure 2-4) was used as a control variable for the entire

system. This pressure was set between 10 psig 13 psig for all experiments. These

pressure values correspond to the maximum liquid volume in the casing that can be

managed at the highest gas flow rates without overflowing at the top of the well model.

This value was measured using an analog pressure gauge (Ashcroft, model Q-9047).

An analog pressure gauge (Ashcroft, model Q-9047) determined the annular

casing pressure at the entry of the top ports of the down-hole gas separator Figure 2-4,

P2. This pressure is measured within a foot from the ports and this value is used as a

reference value to determine the pressure drop inside the down-hole gas separator.

The discharge pressure of the separator is considered to be equivalent to the

pump intake pressure see Figure 2-4, P3. This pressure is equivalent to the pump

intake pressure. This pressure was measured using a pressure/ vacuum gauge, calibrated

38

in psig for positive values of pressure and in inches of mercury for vacuum. One of the

applications this pressure is to determine the pressure drop that occurs between the

separator in-take (P2) and the tubing pressure/discharge pressure (P3).

2.4 EXPERIMENTAL PROCEDURE

Use Figure 2-1 to follow the step - by - step procedure shown next. Before beginning

1. Make sure that there is sufficient water in the separator using the level

control. Add water if necessary

2. Make sure that the desired ports in the manifold are open to inject flow from

the desired position relative to the down-hole gas separator entry ports

Starting the flow of fluids in the loop and setting the system in steady state

3. Turn on the pump

4. Use valve G to regulate the water flow rate. The gallons per minute read

by the turbine flow meter should approximately result in the desired BPD.

Valve G and the turbine flow meter are shown in Figure 2-5.

5. Gradually open the air flow to the desired percentage. It is usually set at

0% for the first experiment. There are three valves involved in the airflow.

First open valve D to let air in from the compressed air line. Then set the

desired percentage with valve E (seen in Figure 2-7).

39

6. Finally open valve F to let air mix with the water. Valve F should be

opened carefully. Otherwise the sudden injection of air can cause the

water to come out the top of the well.

7. By closing valve A, let water accumulate in the well until a desired bottom

hole pressure is obtained. The pressure gauge labeled BHP in Figure 2-1

indicates the bottom hole pressure. All the continuous flow tests were

run between 10 13 psi. Once the desired hydrostatic head is obtained,

regulate the flow out of the well to match the flow entering the well using

valve A. This way, the BHP and liquid level inside the three phase

separator are kept constant. This control is done throughout the test.

2.5 SEPARATOR PERFORMANCE DISPLAY

The performance plots are displayed as three Dimensional graphs, Figure 2-9.

The plots are presented both in terms of oil field units and in terms of superficial

velocities.

In terms of oil filed units the x axis represents the input liquid flow rate in

BPD entering into the well through the perforations; the y axis is the gas flow rate in

MSCFD entering the laboratory well; the z axis is the gas rate through the separator in

MSCFD. This represents the gas that would enter the pump in a real well having the

down hole gas separator installed immediately below the pump intake.

In terms of superficial velocity the x axis is labeled the superficial liquid

velocity inside the separator in inch/second. The y axis represents the superficial gas

40

velocity inside the casing annulus in inch/second and the z axis is the gas rate through

the separator in MSCFD.

The height of each dot (and/or the vertical bar) on the 3 D performance plot

corresponds to the gas rate through the separator for a given liquid and gas rate either in

terms of oil filed units or in terms of superficial velocity.

The data used in plotting the performance plots are managed with an Excel

spreadsheet, see a sample data set in Table 2-1.

The inputs for the spreadsheet include the following:

1. The actual start and end time for each conducted test

2. The casing, ports and tubing pressures (P1, P2 and P3) psi

3. The Floco meter reading (sec/0.1 bbl)

4. The input gas meter pressure (psi)

5. The measured gas rate through the separator (SLM).

The spreadsheet calculates the following;

1. The liquid input rate (BPD)

2. The gas rate (MSCFD)

3. The superficial velocities for both liquid and gas (inch/second) inside the

casing and inside the separator.

4. Gas rate through the separator (MSCFD)

41

5. The pump liquid fraction

The spreadsheet provides all the information needed to accurately study the

performance of each separator design.

All the laboratory tests conducted were run under continuous flow condition. In

this type of test the valve H is completely open so that there is constant liquid and gas

rate throughout the system.

42

Table 2-1 - Sample Excel Spreadsheet for continuous flow test

43

Figure 2-9 - Sample Performance plot for Patterson (3X1) in continuous flow

44

2.6 DOWN HOLE GAS SEPARATOR DESIGNS

Seven down hole gas separator designs were tested. Two of the four gravity driven

separators were originally constructed in 2004 and 2005 and were used with minor

modifications. The other two were constructed in 2007. The three static centrifugal

separators were constructed between summer 2006 and summer 2007.

2.6.1 ECHOMETER (3X1), ECHOMETER (3X1.5), ECHOMETER (4x1),

ECHOMETER (4X1.5), ECHOMETER (4X1.75)

The naming procedure is given as: (separator name) (separator OD x dip tube OD).

Continuous flow tests2 were run on these separators between spring 2006 and

summer 2007 for the purposes of:

a. Comparing the performance of a gravity driven separator to that of a centrifugal

separator

b. Studying the effect of increasing the separator annular area

c. Studying the pressure drop inside the separator

d. Verifying the effect of port geometry

Figure 2-10 and Figure 2-12 are pictures of the Echometer (3X1) and Echometer

(4X1) design respectively. There are two sets of four slots. Each slot is 4 inches long and 2

inches wide. The first set is located 11 inches below the separator thread and the second set

2All the continuous flow tests were conducted with fluid entering from below the separator through the bottom four perforations located adjacent the separator see Figure 2-4

45

is 16 inches below the thread. There is a distance of 24 inches between the lower slots and

the dip tube suction and 44 inches between the upper slots and the dip tube suction.

Both the 3inch and 4inch OD Echometer separators have a wall thickness of 0.125

inch so that the IDs are 2.75 inch and 3.75 inch respectively. The dip tube wall thickness is

also 0.125 inch, making the ID of the dip tube a quarter of an inch less than the dip tube

OD.

The 4 inch OD Echometer separators have the same design configurations as the 3

inch OD Echometer separators, except for larger diameter.

A summary of the Echometer separator design configurations is shown in Table 2-2

below.

Table 2-2 Echometer gas separators configuration

Separator type

Number of slots

Size of slots (WXL) (inch)

Total area of slots (in2)

Area of separator dip tube

annulus (in2)

Area of casing separator

annulus (in2)Echometer (3X1) 4 2X4 32 5.15 21.20 Echometer (3X1.5) 4 2X4 32 4.17 21.20 Echometer (4X1) 4 2X4 32 10.26 15.70 Echometer (4X1.5) 4 2X4 32 9.28 15.70 Echometer (4X1.75) 4 2X4 32 8.64 15.70

46

Figure 2-10 Echometer (3 X1.5) gas separator design

Figure 2-11- Echometer entry port geometry

Figure 2-12 Echometer (4X1.75) gas separator design

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2.6.2 PATTERSON (3X1), PATTERSON (3X1.5), PATTERSON (4x1),

PATTERSON (4X1.5), PATTERSON (4X2)

The naming principle is same as the Echometer designs. Continuous flow tests were

run concurrently for both designs between spring 2006 and fall 2007. The purpose of the

tests is same as listed for Echometer design.

The Patterson design has 16 thin and long entry slots. The slots are 1/8 inch wide

and 8 inch long. There are 0.5 in diameter vent holes. Table 2-3 is a summary of the

Patterson separator configuration.

Table 2-3 Patterson Separator Configuration

Separator type

Number of slots

Number of inch

holes

Size of slots

(WXL) (inch)

Total area of slots

(in2)

Area of separator dip tube annulus

(in2)

Area of casing separator annulus

(in2) Patterson

(3X1) 16 4 1/8 X 8 16 5.15 21.20

Patterson (3X1.5) 16 4 1/8 X 8 16 4.17 21.20

Patterson (4X1) 16 4 1/8 X 8 16 10.26 15.70

Patterson (4X1.5) 16 4 1/8 X 8 16 9.28 15.70

Patterson (4X1.75) 16 4 1/8 X 8 16 8.64 15.70

Patterson (4X2) 16 4 1/8 X 8 16 7.90 15.70

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Figure 2-13 4 inch OD Patterson Separator Design

Figure 2-14 3 inch OD Patterson Separator Design

2.6.3 TWISTER

The separator named The Twister is the first in the series of static centrifugal

separators constructed since summer 2006. The initial results of the performance of the

Twister as reported by Bohorquez7 pointed to the need for more inquests into the

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performance of static centrifugal separators based on the Echometer and Patterson separator

entry port designs.

The twister design uses a wire reinforced PVC hose used as a dip tube. The hose has

a 1.028 in OD and a 0.75 in. ID. The reinforced PVC is spiraled four full turns inside the

gas separator, Figure 2-15. The hose is twirled inside the gas separator and a plate is used to

secure the hose in place.

The straight dip tubes (for example, Echometer (3X1)) used for gravity separator

designs are directly connected to the wells tubing. But for the centrifugal design the

connection to the tubing is different. Figure 2-15 is a picture of the twister connection. The

arrows show the flow path for the gas through the gas vents and the liquid through the spiral

tube connection.

In operation the gas liquid mixture enters through the three circular entry ports of

the Twister separator. The helical dip tube induces a centrifugal motion on the mixture

entering through the ports. Gas is evolved and a coalescing zone is formed. The length of

the coalescing zone depends on the gas and liquid flow rates. The liquid mass is forced to

the inner walls of the separator by centrifugal forces and the gas mass accumulates at the

center (coalescing zone). While the gas rises to the gas vents at the separator connection to

escape into the casing annulus the liquid flows down towards the dip tube suction and

thereafter into the pump by gravity forces. Figure 2-17 shows a diagrammatic of the forces

acting on the mixture as soon as it enters into the separator annulus.

Laboratory observations show that the helical dip tube induces the centrifugal

motion by virtue of its design; a bubble coalescing zone is formed in the center of the

separator; the bubbles coalesce and become bigger bubbles in the coalescing zone and thus

rise faster; the liquid momentum is reduced by the helical nature of the dip tube. This greatly

The full construction detail for the Twister is covered in the thesis report by Bohorquez, 2006.

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improved the gas pathway through the core of the separator eliminating the need for a gas

venting tube.

The operation of the twister is similar to the invention by Jongbloed et al12 since

both are static type separators. The basic difference between the two is that the twister does

not have a gas discharge conduit instead it has inclined gas vent holes at the connection head

(Figure 2-16). The Twister design also has similarity with the invention by Obrejanu13. Apart

from both separator designs been static by construction both separator designs depend on

the helical nature of the separator internal design to induce centrifugal motion and thus

centrifugal forces on the fluid flow inside the separator. The centrifugal forces induced

become the driving mechanism for gas liquid separation. The main differences between

the two are the entry port placement and gravity effects. The Twister has three entry port

circles at the top of the separator; the separator design by Obrejanu13 has the entry port at

the bottom part of the separator. The Twister depends to a significant extent on gravity for

gas liquid separation as well as on hydrostatic head to flow the mixture through the

separator. The gas separator by Obrejanu13 depends on both hydrostatic head and pressure

drawdown created by the action of the PCP to operate efficiently. Whilst the advantages of

having the entry ports at the bottom part of the gas separator is founded by density

difference; in the case of fines production the PCP rotor will erode at a faster pace causing

pre mature pump damage.

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Figure 2-15 Twister Separator (Bohorquez)

Figure 2-16 Twister Connection

Gas Vent holes

Spiral Tube Connection

52

coalescing zone

Improved gas path way

Induced centrifugal motion

Dip tube acts as baffles which reduce liquid momentum

Figure 2-17 Diagrammatic of the forces acting in a static centrifugal separator

2.6.3.1 ECHOMETER TWISTER

The Echometer Twister is a static centrifugal separator. The design is very similar

to the Twister as per the dip tube design which is helical. The major difference between the

two separator designs is the entry port geometry. While the Echometer design has four 4X2

slots the Twister has 3 circular entry ports and 4 half inch vent holes.

The main objective of constructing the Echometer Twister is to study the effect of

centrifugal forces on separation performance. A head to head comparison is made

between Echometer (3X1) and Echometer Twister to understand the controlling

mechanisms.

53

Figure 2-18 is the picture of the laboratory constructed Echometer Twister

separator.

Figure 2-18 Echometer - Twister

2.6.3.2 PATTERSON TWISTER

The Patterson Twister is the third in the series of static centrifugal separators

constructed. This separator design (Figure 2-19) has the same entry port geometry has the

Patterson (3X1). Like the Echometer Twister it was constructed to comparatively study

the effect of centrifugal forces on the previously constructed Patterson (3X1) separator

design. The Patterson Twister also has a dip tube with four full turns/twists with pitch

length of 12 14 inches lying at an angle of 45o on the inner walls of the separator.

54

Figure 2-19 Patterson - Twister

55

Chapter 3

Analysis Of Experimental Results

3.1 EFFECT OF HELICAL DIP TUBE DESIGN

These experiments studied the effect of changing the dip tube design from the

conventional straight shape to a helical form.

The designs experimentally tested include the following; The Echometer-Twister,

Patterson-Twister (2 twists and 4 twists) and the Twister, which was previously tested by

Bohorquez7.

The following parameters were examined during the experimental tests of the

separators:

Liquid input rate: up to 600 BPD

Gas flow rate: 0 MSCFD to 115 MSCFD

Superficial liquid velocity in the separator: up to 14 in/sec

Superficial gas velocity in the casing: up to 70 in/sec

Casing pressure: between 10 and 13 psi

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The performance plots for each of the static centrifugal separators are presented in

the following sections and a comparative analysis is presented thereafter so that the effects

of the change in dip tube design are effectively captured.

3.1.1 PERFORMANCE RESULTS FOR THE TWISTER SEPARATOR

Figure 3-1 and Figure 3-2 show the performance plots for the Twister separator in

continuous flow in both field units and in terms of superficial velocity. Notice that the

Twister achieved a zero gas flow rate through the separator up to a downward superficial

liquid velocity (Vsl) of 10 in/sec for all gas rates tested. This liquid rate is equivalent to 430

BPD. The area highlighted in red represents the optimum performance for the Twister

separator. Approximately no gas entered into the dip tube suction in this area for these

conditions of liquid and gas flow.

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Figure 3-1- Twister results in field units

Separator Type: TwisterOD Dip Tube = 1; Number of Slots = 3; Number of Twists = 4; Casing Pressure = 10 13 psi

Dimension of Slots =2 1 holes & 1 1.5 hole; Position of the Separator = Above the Perforations

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Figure 3-2 - Twister result in terms of superficial velocities

3.1.2 PERFORMANCE RESULTS FOR ECHOMETER TWISTER

SEPARATOR

In Figure 3-3 and Figure 3-4 the performance results for EchometerTwister

separator are shown.

Separator Type: TwisterOD Dip Tube = 1; Number of Slots = 3; Number of Twists = 4; Casing Pressure = 10 13 psi

Dimension of Slots =2 1 holes & 1 1.5 hole; Position of the Separator = Above the Perforations

59

Figure 3-3 Echometer - Twister result in terms of superficial velocities

Separator Type: Echometer - TwisterOD Dip Tube = 1; Number of Slots = 4; Number of Twists = 4; Casing Pressure = 10 13 psi

Dimension of Slots =2 X 4; Position of the Separator = Above the Perforations

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Figure 3-4 Echometer - Twister results in field units

The region highlighted in red in both plots depicts areas where it was observed that

no gas entered into the dip tube suction of the EchometerTwister separator. Notice that in

Figure 3-3 the no gas zone was established at a downward Vsl 10 inch/sec.

Separator Type: Echometer - TwisterOD Dip Tube = 1; Number of Slots = 4; Number of Twists = 4; Casing Pressure = 10 13 psi

Dimension of Slots =2 X 4; Position of the Separator = Above the Perforations

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3.1.3 PERFORMANCE RESULTS FOR PATTERSON TWISTER

SEPARATOR

Both Figure 3-5 and Figure 3-6 show the results for the PattersonTwister Separator

in continuous flow in terms of superficial velocities and in field units.

Figure 3-5 - Patterson - Twister result in terms of superficial velocities

Separator Type: Patterson - TwisterOD Dip Tube = 1; Number of Slots = 16; Number of Twists = 4; Casing Pressure = 10 13 psi

Dimension of Slots =1/8 X 8; Position of the Separator = Above the Perforations

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Figure 3-6 - Patterson - Twister results in field units

In the following sections a comparison is made between the separation performances

of EchometerTwister and Echometer (3X1) and then Patterson Twister and Patterson

(3X1) in terms of both superficial velocity and field units.

Separator Type: Patterson - TwisterOD Dip Tube = 1; Number of Slots = 16; N