4 2 drilling hydraulics

• Lecture Objectives;to: • Understand basic concept of bit hydraulics, • Describe various pressure losses • Factors effecting ECD • Select bit nozzles to optimize bit hydraulics Hydrau

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Bit Hydraulics

– Lecture Objectives,– Basic concepts of Hydraulic,– Pressure Losses and ECD,– Bit nozzle selection,

– Hydraulic optimization.

• Lecture Objectives;

to:

• Understand basic concept of bit hydraulics,

• Describe various pressure losses

• Factors effecting ECD

• Select bit nozzles to optimize bit hydraulics

Hydraulics

– Fluid Circulation:

• Circulation across the bit face must be designed to

remove the cuttings efficiently and also cool the bit face,

• These requirements may be satisfied by increasing

the fluid flowrate,

• The increased fluid flowrate may however cause

excessive erosion of the face and premature bit failure.

• Roller Cone Bit:

– Penetration rate is function of many parameters including:

• Mud properties,

wellbore, mud hydrostatic pressure should be slightly higher (safety margin),

• Hydraulic efficiency.

Hydraulics

• The effects of increased hydraulic horsepower at the bit are

similar to their effect on the roller cone bits,

• Manufacturer often recommend a minimum flowrate in an

attempt to ensure the bit face is kept clean and cutter temperature is kept minimum,

• This requirement for flowrate may adversely affect

optimization of HHP

– Cuttings removal in the annulus,– Hydrostatic pressure to balance pore pressure and prevent

the wellbore from collapsing,

– ECD (Equivalent Circulating Density),– Surge/swab pressures during tripping,– Limitation of pump capacity ,

– Optimization of the drilling process (Max HHP or Max

Jet Impact),

– Pressure and Temperature effects.

– Annular Velocity,– Rate of penetration (ROP),– Viscosity,

– Hole Angle,– Mud Weight,– Hole washout.

Drill collar

Mud pump

Mud pit

Drill bit

– 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:

Pore pressure

Fracture pressure

– Average fluid velocity,– Fluid velocity through the annulus Vf (ft/min);

300 * * 8 69 * /

* 69

N q

Dp Dh

Q E

Where:

R N , Annular Reynolds Number (dimensionless)

MW, Mud weight (lbs/gal)

E qΘ300Equivalent Fann Dial reading at3 0 0 RPM

Dh, Hole Diameter (in)

Dp, Pipe diameter (in) N’, Power law “N” value = log (Θ600 /Θ300 ) / log (600/300)

• Critical Flow Calculations;

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

– It is important to maintain the flow in laminar, drilling through mechanically unstable formations.

NC c

) Dp Dh

(

.

R )

Dp Dh

2 2

69 8

64

θ

Q c, Rate of flow ,gpm

R NC , Critical Reynolds number , usually 2,000

Dh , diameter of hole in inches

Dp , diameter of pipe in inches

• Annular Pressure Losses-Laminar;

n n

Dp Dh

Q Dp

69 8

) /(

75

300

θ

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 (Θ600 /Θ300 ) / log (600/300)

Θ300 , 300 RPM reading

• Annular Pressure Losses-Turbulent;

2 3

2

) (

) (

67

163

Dp Dh

Dp Dh

R

Q APL

⋅

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

R NC , Critical Reynolds number , usually 2,000

 ρ  mud density in ppg

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

•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.

• Pressure loss inside a pipe;

L D

25

2 ρ

P p , pipe pressure loss in lb/in 2

f p , pipe friction factor

ρ Mud density in ppg

V p , average bulk velocity in pipe in ft/sec

D, internal diameter of pipe in inches

L, length of pipe in feet

=

∆P b , bit pressure loss in psi

Q , pump output rate in gpm

D n , diameter of nozzles in 1/32 of an inch

ρ , mud density in ppg

•Hydraulic Horsepower;

– HHP at bit = ( ∆ b Q ) / 1714

• Where;

– HHP , hydraulic horse power,

– ∆ P b , bit pressure loss in psi,

– Q , pump output rate in gpm.

– HHP at pump = ( ∆ P t Q) / 1714

• Where;

– HHP , hydraulic horse power,

∆ P t , total pressure loss in psi ( SPP),

– Q , pump output rate in gpm.

• 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

n

D

Q Vn

Σ

=

– Where:

• V n , nozzle velocity in ft/sec

• Q, pump output rate in gpm

• .Σ D n 2 sum of the square nozzle diameters in 1/32 of an inch

• Jet Impact Force;

– The force exerted by the exiting fluid below the bit,

– It is expressed as:

1930

ρ

n i

QV

Where:

F i , Jet impact force in pounds,

Q, pump output rate in gpm,

V n , nozzle velocity in ft/sec

ρ , mud density in ppg

•Other Hydraulics Applications;

– To calculate or estimate the settling velocities of drilled cuttings 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 fracture gradient.

• Now YOU should be able to:

– Describe various pressure losses – Factors effecting ECD

– Select bit nozzles to optimize bit hydraulics

Hydraulics

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Bit Hydraulics

End of Lecture