Chapter 7.2 Lifting Capacity of Drilling Fluids

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1InternalPCB – 4223 DRILLING HYDRAULICS SEMESTER- JANUARY 2015

BY . ASIF ZAMIR

UNIVERSITI TEKNOLOGI PETRONAS

PETROLEUM ENGINEERING DEPARTMENT

Chapter 7.2

• Fluid Velocity in Annulus

• Particle Slip Velocity

• Particle Reynolds Number

• Friction Coefficient

• Example

• Iterative Solution Method

• Alternative Solution Method

• API RP 13D Method


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Historically, when an operator felt that the hole was not being cleared of cuttings at a satisfactory rate, he would:

Increase the circulation rate

Thicken the mud(increase YP/PV)


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More recent analysis shows that:

Turbulent flow cleans the hole better.

Pipe rotation aids cuttings removal.

With water as drilling fluid, annular velocities of 100-125 ft./min are generally adequate (vertical wells)


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5

A relatively “flat” velocity profile is

better than a highly pointed one.

Mud properties can be modified to

obtain a flatter profile in laminar flow

e.g., decrease n

InternalPCB – 4223 DRILLING HYDRAULICS SEMESTER- JANUARY 2015

BY . ASIF ZAMIR



Drilled cuttings typically have a density of about 21 lb/gal.

Since the fluid density is less than 21 lb/gal the cuttings will tend to settle, or ‘slip’ relative to the drilling mud.

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s lipf luidpart ic le VVV

Density & Velocity

slipV

partic leVf luid

_

V


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Velocity Profile

The slip velocity can be reduced by modifying the mud properties such that the velocity profile is flattened:

Increase the ratio (YP/PV)(yield point/plastic viscosity) or

Decrease the value of n


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Plug Flow

Plug Flow is good for hole cleaning. Plug flow refers to a “completely” flat velocity profile.

The shear rate is zero where the velocity profile is flat.


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Newtonian Fluids:

The terminal velocity of a small spherical particle settling (slipping) through a Newtonian fluid under Laminar flow conditions is given by STOKE’S LAW:

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2

sfss

d)(138v


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Where

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cp viscosity, fluid

in particle, of diameterd

lbm/gal fluid, of density

lbm/gal particle, solid of density

ft/s velocity, slipv

s

f

s

s

2

sfss

d)(138v


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Stokes’ Law gives acceptable accuracy for a particleReynolds number < 0.1

For Nre > 0.1 an empirical friction factor

may be used.

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ssf

Re

dv928N


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What forces act on a settling particle?

Non-spherical particles

experience relatively higher drag

forces


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Sphericities for Various Particle Shapes

Shape Sphericity

0.58 20rh

0.87 2rh

0.83 rh

0.59 r/3h

0.25 r/15h

Cylinders

0.73 3*2*

0.77 2**

Prism

0.81 Cube

0.85 Octahedron

1.00 Sphere


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Particle Reynolds Number

In field units,

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189.1

f

sss

f

dv

Based on real cuttings


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1. Calculate the flow velocity.

2. Determine the fluid n and K values.

3. Calculate the appropriate viscosity (apparent viscosity).

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4. Calculate the corresponding Particle Reynolds

number.


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Slip Velocity Calculation (using Moore’s Correlation)

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Slip Velocity Calculation (using Moore’s graph)


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Reference

Chapter 4, Applied Drilling Engineering by

Chapter 5, Drilling Engineering by J.J. Azar and

G. Robello Samuel.


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Documents

Chapter 7.2 Lifting Capacity of Drilling Fluids