Drill Bit Hydraulics

8/21/2019 Drill Bit Hydraulics

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IDPT BHIPM

Well Engineering ModuleDrill Bit Hydraulics

IPM IDPT

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Lecture Contents;,

Lecture Objectives,

Basic concepts of Hydraulic,

Pressure Losses and ECD,

Bit nozzle selection,

Hydraulic optimisation.

Bit Hydraulics


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Lecture Objectives;

By the end of this lecture YOU should be able to:

Understand basic concept of bit hydraulics,

Describe various pressure losses

Factors effecting ECD

Select bit nozzles to optimize bit hydraulics

Bit Hydraulics

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Fluid Circulation:

Circulation across the bit face must be designed toremove the cuttings efficiently and also cool the bit

face,

These requirements may be satisfied byincreasing the fluid flowrate,

The increased fluid flowrate may however causeexcessive erosion of the face and premature bit

failure.

Bit Hydraulics


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Roller Cone Bit: Penetration rate is function of many parameters including:

WOB,

RPM,

Mud properties,

In order to prevent an influx of formation fluids into thewellbore, mud hydrostatic pressure should be slightlyhigher (safety margin),

Hydraulic efficiency.

Bit Hydraulics

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Hydraulic Efficiency:

The effects of increased hydraulic horsepower at the bit aresimilar to their effect on the roller cone bits,

Manufacturer often recommend a minimum flowrate in anattempt to ensure the bit face is kept clean and cutter

temperature is kept minimum,

This requirement for flowrate may adversely affectoptimization of HHP.

Bit Hydraulics


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Importance of Hydraulics;

Cuttings removal in the annulus,

Hydrostatic pressure to balance pore pressure and prevent thewellbore from collapsing,

ECD (Equivalent Circulating Density),

Surge/swab pressures during tripping,

Limitation of pump capacity ,

Optimization of the drilling process (Max HHP or Max JetImpact),

Pressure and Temperature effects.

Bit Hydraulics

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Hole Cleaning;

Annular Velocity,

Rate of penetration (ROP),

Viscosity,

Hole Angle,

Mud Weight,

Hole washout.

Bit Hydraulics


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Circulating System;

Annulus

Drill pipe

Open hole

Casing & cement

Drill collar

Mud pump

Mud pit

Drill bit

Bit Hydraulics

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Circulating System Pressure Loss;

Pressure loss through the surface equipment,

From the pump to the standpipe, kellyhose, Kelly or top

drive, to the top of the drill pipe.

Pressure loss through the drill string,

Downhole tool pressure loss:

PDM/Turbines,

Shock Subs/Jars,

MWD/LWD.

Bit nozzle pressure loss,

Annular pressure losses.

Drilling Hydraulics


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Operating Margin of Mud Pressures;

Pore

pressure

Fracture

pressure

Pressure

Depth

ECD

Mud Hydrostatic

pressure

Drilling Hydraulics

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Basic Concepts of Hydraulics;

Average fluid velocity,

Fluid velocity through the annulus V f (ft/min);

vQ

d df =

24 51

22

12

.

Fluid velocity through the drill string Vf(ft/min):

v

Q

df =

24 512

.

Q = pump rate (gpm), d2 = wellbore diameter (inch), d1 = Outer diameter of the drill string (inch), d = Inner diameter of the drill string (inch).

Drilling Hydraulics


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Reynolds Number (annulus);

( )[ ] ''2

22300 *69.8**/*69.43

N

N

qN DpDhDpDh

QEMWR

=

Laminar3000

Where:

RN , Annular Reynolds Number (dimensionless)

MW, Mud weight (lbs/gal)

Eq300 Equivalent Fann Dial reading at RPMDh, Hole Diameter (in)

Dp, Pipe diameter (in)

N, Power law N value = log (600/300 ) / log (600/300)

Drilling Hydraulics

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Critical Flow Calculations;

Critical flow rate is the rate at which the fluid profile in thesmallest annuli goes from laminar to turbulent.

It is important to maintain the flow in laminar, drilling throughmechanically unstable formations.

{ }n

n

NCc

)DpDh(..

R)DpDh(Q

=

2

1

30022

6986443

Qc, Rate of flow ,gpm

RNC , Critical Reynolds number , usually 2,000

Dh , diameter of hole in inches

Dp , diameter of pipe in inches

n, Power law n value = log (600/300 ) / log (600/300)300 , 300 RPM reading.

Drilling Hydraulics


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Annular Pressure Losses-Laminar; If the flow rate is below the critical Reynolds number in the

annuli the pressure loss calculation in psi/1000 ft. is:

n

n

DpDh

QDpDhAPL

+= +

)(69.8)/(75.3 12300

Q,,, Rate of flow ,gpm

APL, annular pressure loss in psi/1000 ft.Dh , diameter of hole in inches

Dp , diameter of pipe in inches

n, Power law n value = log (600/300 ) / log (600/300)300 , 300 RPM reading

Drilling Hydraulics

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Annular Pressure Losses-Turbulent;

If the flow rate is above the critical Reynolds number in theannuli the pressure loss calculation in psi/1000 ft. is:

23

2

)()(

67.163

DpDhDpDhR

QAPL

NC

=

Q,, Rate of flow ,gpm

APL, annular pressure loss in psi/1000 ft.Dh , diameter of hole in inchesDp , diameter of pipe in inches

RNC , Critical Reynolds number , usually 2,000 mud density in ppg

Drilling Hydraulics


9/13

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Equivalent circulating density (ECD);Equivalent circulating density (ECD);

ECD is the sum of the annular pressure losses / (depth xfactor), in oilfield terms as:

oa

TVD

PECD +

=

052.

ECD, in psi

pa, annular pressure lossTVD, true vertical depth in feet

original mud weight in ppg

Drilling Hydraulics

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Equivalent circulating density (ECD)

Factors affecting the ECD:

Mud density.

Annular pressure loss Pa.

Hole geometry,effective viscosity, temperature,pressure,flow rate,

Rate of penetration and cuttings size,

Hole cleaning efficiency.

Drilling Hydraulics


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Pressure loss inside a pipe; Assuming turbulent flow inside the drillstring or Reynolds

number > 2100.

LD

VfP

pp

p

=81.25

2

Pp , pipe pressure loss in lb/in2

fp , pipe friction factor Mud density in ppgV

p, average bulk velocity in pipe in ft/sec

D, internal diameter of pipe in inches

L, length of pipe in feet

Drilling Hydraulics

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Friction loss in Bit Nozzles;

[ ] 222156

n

bD

QP

=

Pb , bit pressure loss in psiQ , pump output rate in gpm

Dn , diameter of nozzles in 1/32 of an inch , mud density in ppg

Drilling Hydraulics


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Hydraulic Horsepower; HHP at bit = (Pb Q ) / 1714

Where;

HHP , hydraulic horse power,

.Pb , bit pressure loss in psi,

Q , pump output rate in gpm.

HHP at pump = (Pt Q) / 1714

Where;

HHP , hydraulic horse power,

Pt , total pressure loss in psi ( SPP),

Q , pump output rate in gpm.

Drilling Hydraulics

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Jet or Nozzle Velocity;

It is closely related to the cleaning action taking place at the bit,

It can lead to hole erosion at high velocities in fragile formation,

It is expressed as:

2

3.418

nD

QVn

=

Where:

Vn , nozzle velocity in ft/sec

Q, pump output rate in gpm

. Dn 2, sum of the square nozzle diameters in 1/32 of an inch

Drilling Hydraulics


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Jet Impact Force; The force exerted by the exiting fluid below the bit,

It is expressed as:

1930

ni

QVF =

Where:

Fi , Jet impact force in pounds,

Q, pump output rate in gpm,

Vn , nozzle velocity in ft/sec , mud density in ppg

Drilling Hydraulics

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Other Hydraulics Applications;

To calculate or estimate the settling velocities of drilledcuttings with or without pumps on,

To calculate surge and swab pressures,

To calculate safe pipe/casing running speeds,

To calculate maximum rate of penetration given the fracturegradient.

Drilling Hydraulics


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Maximum Hydraulic Horsepower

Should be adopted for use in soft to medium formations.

Maximum Jet Impact Force

Should be adopted for use in medium to hard formations.

Maximum Jet Velocity

Is based on maximum allowable surface pressure at a selectedflow rate.

Optimization of Bit Hydraulics

Calculation flow:1 After determining fluid rheology model work out carrying capacity of fluid2 Calc the Delta P for the hole using either Max HHP or JIF3 Decide on Nozzle combination4 Calculate Pump horsepower requirements

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Now YOU should be able to:

Understand basic concept of bit hydraulics

Describe various pressure losses

Describe the factors affecting ECD

Understand the process to optimize bit hydraulics

Drilling & Bit Hydraulics

Drill Bit Hydraulics

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