17. Special Applications

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TAMU - Pemex

Well Control

Lesson 17

Special Well ControlApplications


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Special Well Control

Applications

Underbalanced Drilling

Well Control in Unconventional Hole

Programs

Casing and Cementing Operations


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These are wells where the ECD is

intentionally kept below theformation pore pressure.


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Reasons for UBD

Minimize formation damage

Faster penetration rates

Longer bit life and fewer trips

Eliminate one or more casing strings


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Reasons for UBD

Reduced risk of lost circulation

Reduced risk of differential sticking

Lower mud costs

Earlier oil sales


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Air and Natural Gas Drilling

Mist and Foam Drilling

Underbalanced Drilling w/Mud


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Simplified Air

Drilling System


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Using the

Choke to

Control

Pressures inWell Control

and in UBD


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Well Control

Equipmentfor Air or

Natural Gas

Drilling


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RotatingHead used

in Air

Drilling


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Air and Natural

Gas Drilling

Compressor at

surface

Drillpipe Float

Gas in drillstring

Friction

These make DP

gauge unreliable

for BHP

determination

Casing gauge

is used topredict BHP

zT

D

csp

g

epp3.53

K

!

How do you

determineBHP?


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zTD

csp

g

epp 3.53K

!


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zT3.53

D

cssh

g

epp

K

!


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Mist drilling may be used when small

water flows would cause mud rings

with air or natural gas drilling.

Water is injected downstream of the

compressors until the air is nearly

saturated with water vapor.


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Foam drilling can tolerate still more

water than mist.

Foams are generated by shearing

water and gas together with a

foaming surfactant and bentonite or

polymers added for betterhole

cleaning.


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Underbalanced Drilling with Mud

Air can be injected into the mud stream

to lighten the mud column.

One way is to inject at the standpipe


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Air Injection

Options


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Used to determine volume of air to inject:Reduce 9.0 lb/gal mud to 5.0 lb/gal effective density at TD

9.0 5.0 = 4.0

Vm

VeVm Ve lb/gal

Ve lb/gal

5.0


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Mud

Simulator


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Tz77.2

pK!


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UBD with Weighted Mud


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Annulus isfilled with

heavy mud

as DP is

being

pulled outof hole


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Unconventional Wellbores

and Drilling Practices

Horizontal and ERD Wells

Slim-Hole Applications

Coil-Tubing Operations


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Horizontal and ERD Wells

For Horizontal and ERD Wells the window for

acceptable mud weights narrows.

The high angle reduces frac pressure,lowering the maximum mud weight allowed

Hole collapse increases the minimum mud

weight.

Mud weight may limit the length of the lateral


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NOTE Same TVD, but ERD well has smaller

MW window, and higher ECD.


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9,642

KOP10,000


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Heel

Terminus


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Additional Pressure Concerns

in Horizontal Wells

Cuttings beds require high annularvelocity

Surge and Swab pressures higher


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Lessoverbalance

during trip

(pSWAB = 10.3 * 3

= 31 psi

Circulating while

POH can offset

swab pressure


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Additional Pressure

Concerns

ERD wells more prone to kicks and lost

circulation (smallerMW window)

SICP lower for ERD

Gas migration less of a problem


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Fig. 6.15Surface

Pressure

Relationship

for a

Horizontal

Well closed in

on a kick

SIDPP = SICP


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Gas trappedin washouts

reduces

migration


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Vertical height remains

constant in lateral section


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Slim-Hole Applications

High annular friction during circulation

Small pit gains yield long vertical heightof kick fluid resulting in high SICP


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Coil-Tubing Operations

Continuous, non-jointed pipe which is

stored on a reel and transported to awellsite to perform a specific

operation


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Fig 6.19

Coiled Tubing

stuffing box


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Coiled Tubing


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CT growth with time


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Casing and Cementing

Operations

Running the Casing

Cementing the Casing

The Annular Flow Problem

LinerTop Tests


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Running the Casing Operator should replace upper DP

rams with casing rams.

SIP could result in large upward forces

on the large diameter casing.

Large diameter casing results in highsurge and swab pressures.


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Comparison of surge/swab

pressures for casing vs. DP


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Cementing the Casing

pbh = pch + ph +(pf+- (pss +(pa

pbh = BHP

pch

= choke backpressure

ph = HSP

(pf = circulating friction pressure

(pss = surge or swab pressures

(pa = pressure resulting from fluid

acceleration


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Fig. 6.34

Downhole

Pressures

associatedwith a

Cement Job


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Cementing Consideration Spacer density and volume

High viscosities

U-tubing of cement slurries

Freefall of cement

Flash setting of cement


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Effect of bridged

annulus on wellbore

pressures whilecementing

Cement

Cement

may

flash-

set


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Fig. 6.36

Effect ofCement

Channeling

on

Hydrostatic

PressuresHigher

Cement

Hydrostatic


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The Annular Flow Problem

The transition period between

development of gel strength and

setting sometimes allows flow

High gel strength cement can

support the HSP of mud column

above and allow flow into the cement

Gas may then percolate upward


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Fig. 6.37 Cement

Gel Strength

Development andHSP Reduction

with TimeFormation Pressure

No gas migration if

gel strength exceeds500 lbf/100 sq/ft


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17. Special Applications

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