shale fluid interaction

8/10/2019 Shale Fluid Interaction

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Shale/Fluid Interactions


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Introduction

Shale instability is a costly problemfor the oil and gas industry Shale makes up over 75% of drilled

formations

Shales cause over 90% of wellbore instabilityproblems

Wellbore instability problems cost the oil

industry >> $1billion/year


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Wellbore Instability Problems

Shrunk Hole

LostCirculation

Overgauged

HoleGauged Hole

Brittle Shale

Swelling Shale

Friable Sandstone

Tensile Failure

(Breakdown)

Compressive Failure(Collapse)


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Mechanisms of Wellbore Failure

Increase in pore pressure and decrease in

effective stresses

Shales can act as leaky semi-permeable

membranes that generate an osmotic

pressure


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Transient

water and solute flux

Transient flow

Time dependent wellbore failure

Failure away from wellbore wall

Thermal effects (fully coupled)


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Use of Non-Aqueous Drilling Fluids

Advantages

Can prevent problems caused by fluid/shaleinteractions

drill-string balling

borehole instability.

Can provide excellent filtration control, lubricity andstability at high temperatures.

Disadvantages

Can result in excessive loss of mud because of lowfracture extension pressures.

Are subject to stringent environmental regulations, andcan result in costly liabilities.


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Differential Pressure

The difference between the boreholepressure and the formation pore

pressure is a driving force affectingtransfer of fluid from drilling mud toshale formations.

Increasing mud density can raise thedifferential pressure and contribute toshale hydration.


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Osmotic Potential

Chemical Potential is a driving force determined

by the relative water activities of the drilling mud

and the shale pore fluid at downhole conditions.

The chemical osmotic force and resulting transfer

of fluid is dependent upon the efficiency of the

leaky-semipermeable membrane

Hydraulic potential will compete with osmotic

potential in affecting the shale swelling.

Manipulating the concentration of drilling fluid

can control shale swelling


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Diffusion

Diffusion osmosis is determined by the differences in theconcentrations of the individual solutes in the drilling mudand in the shale pore fluid. Ions and molecules of eachspecies tend to move from the high to low concentration.

The flow of solute and associated water is dependent

upon the solute selectivity of the drilling mud/shaleinterface at downhole conditions for each individual solute.

When using a water-based mud, diffusion osmosisopposes chemical osmosis. A lightly compacted shale (high permeability shale) having

large pore throats favors diffusion, A more compacted shale favors chemical osmosis.

Higher membrane efficiency and lower permeability


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Drilling Mud / Shale Membrane System

Non-aqueous based muds (diesel, mineral, synthetic)can provide an ideal semipermeable membrane thatprevents diffusion of ions and molecules. Reduce the shale/fluid interactions

Helps to reduce shale instability problems Water-based muds do not provide an ideal semi-

permeable membrane. Leaky membrane

Shale/fluid interactions Diffusion

Hydraulic driven

Osmotic pressure


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Stresses Induced by Pore Pressure and

Formation Temperature Changes

(Yew and Liu [1992], Wang[1992],Chen[2001])

),(

13),(

1

21

),(,1

13

),(,1

1

21

,

1

13

,1

1

21

2

2

2

2

2

2

2

2

trTE

trp

pr

rtrTrdrtrT

r

E

trprdrtrpr

pr

r

rdrtrTr

E

rdrtrpr

fmf

zz

wwf

r

r

fm

f

r

r

f

ww

r

r

fm

r

r

f

rr

w

w

w

w

l M d l F Fl i


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eneral Model For Flow inShales

Transport Model

for Water

and Ions

Continuity Equations

+

Flux Equations

Activityof Water

and

Osmotic

Pressure

Coupling Coefficients

for Shale Kijor Lij

Flux of Water and Ions

Into ShalePressure and Ion

Concentration Profile

Swelling Pressures and

Osmotic Pressure


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Mathematical Model

XPo

Co

wP

dfC

y

x


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Water Activity

Suppose the water activity of the solution is a

function of solute concentration:

aw=f(Cs)


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Osmotic Pressure

For ideal solutions

S

=nRT(CS

-Cdf)

For non-ideal solutions


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Coupled Flux Equations

(De Groot [1958] & Prigogine[1968])

333231

232221

131211

KKPKI

KKPKJ

KKPKJ

s

sD

sv

v

s

sD J

C

JJ


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Continuity Equations

0x

J

t

Css

0 vJxt

oo PPc exp

01

x

J

cx

PJ

t

P vv


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Phenomenological

Coefficients

33

3113

11

K

KK

KKI 33

3213

12

K

KK

KKII

33

312321

L

LLLLI

33

322322

L

LLLLII


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Fully Coupled C-P Equations

0,,,

0,,,00,,,0

..

01

0

00

00

tPPCCx

tPPCCxxPPCCt

CB

x

CnRTKx

PKxct

P

x

CL

C

LnRT

x

PL

xt

C

s

wdfs

s

sIII

sI

s

III

s


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Assumptions & Simplifications

(Ideal Solution)

No chemical reactions

Constant temperature

LI,LII,KI,KIIare constant

1&1

2

x

C

x

P

x

P s

P P M d l


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Pore Pressure Model(Ideal Solution)

)( ijeff KfD

00

00

;,0,

;,0,;,,0

ppCCtr

ppCCtrrppCCrrt

S

wdfSw

Sw

02

t

C

cD

nRTKp

c

K

t

p S

feff

II

f

I

02

Seff

S CDt

C


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Permeability

11

kk

33

3113

11

33

321312

0

k

kkk

kkkk

p

vJ

Reflection Coefficient


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Fluxes

Solute

x

CL

C

LnRT

x

PLJ

Solventx

CnRTKx

PKJ

sI

s

IIIs

sIIIv


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Cdf/Co=0.01M/1M

0.80

0.90

1.00

1.10

1.20

1.30

0 20 40 60 80 100 120

x (mm)

PD

t=3hr

t=12hr

t=24hr

Pressure Profile Variation


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Non-Ideal Case


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Verification in the Case of

Ideally Dilute Solution

)1( SWWWW nxxxa

WSW nnnn

For ideal dilute solution:

(n is the dissociation number)

For dilute solution, it gives:


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W

S

W

S

SW

SS

n

VC

n

n

nnn

nx

W

S

SSW n

nVCnxCfa 11)(


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For nW=1 mole, V is the molar volume of pure water

SSSW nVCnxCfa 11)(

the water activity goes to 1 when CS0

nVCf S )('

nVCf

Cf

S

S )(

)('


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nVCf

Cf

S

S

)(

)('

02

2

2

2

x

C

c

nRTK

x

P

c

K

t

P sIII


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nVCf

Cf

S

S

)(

)('

0

x

CL

C

LnRT

xt

C sI

s

IIs


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Water Activity for NaCl

Solutionsy = -0.0027x 2- 0.0303x + 1

R2= 0.999

0.4

0.5

0.6

0.7

0.8

0.9

1

0 1 2 3 4 5 6

C(mol/L)

aw


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Abnormal Pressure

Cdf>Co

-0.4

-0.2

0

0.2

0.4

0.6

0.81

1.2

0 50 100 150 200

x (mm)

Pd


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Abnormal Pore Pressure

500psi

0

0.5

1

1.5

2

2.5

0 200 400 600 800 1000

x(mm)

Pd

Co=3M,

Cdf=0.01M

P P P fil A d


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Pore Pressure Profile AroundWellbore

Time=3hr Time=9hr


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Pressure Profile

Variation with Time (Cdf


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Estimating Model Input Parameters

shaleP1

C1

P2

C2

P1 P2, C1= C2 Pressure buildup KI

P1 P2, C1C2 Pressure buildup KIIRadio active tracer Deff

Experimental Data from Chevron


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Experimental Data from Chevron(R. T. Ewy 2000)

Confining Pressure

Test Fluid (WellborePressure)

Pore PressureGauge

ShaleSample

Screens or porous metalJacket

Confining PressureConfining

Pressure

Summary of Model Parameters and Their


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Summary of Model Parameters and TheirEffects on the Behavior of Pore Pressure

II

0

100

200

300

400

500

600

700

800

900

1000

0 10 20 30 40 50 60

t (hr)

P(

psi)

KI

KII

Deff


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Diffusion Coefficient

D vs CD

y = 3E-10x

2

- 1E-09x + 7E-10R2= 0.9996

0.00E+00

2.00E-10

4.00E-10

6.00E-10

8.00E-10

0 0.2 0.4 0.6 0.8 1CD

D

Pressure Profiles in a Constant Volume Swelling


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Pressure Profiles in a Constant Volume Swelling

TestPh

awdf

awsh

P

PT

P

Ph

PT

awdf aw

df

P

PT

Ph

Time t = 0 Time t =Time t8

PT, average ORPconfining

Time

Ph, average

Paverage


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Shale Properties(R. T. Ewy, 2000)

Shale

Sample

Clay

Contents

CEC(meq/100g)

Surface Area

(m2/g)

Permeability(microdarcies)

A1 20%-25% 5.3, 3.8 23, 25 1~2

A2 50%-75% 14.6, 10.8 227, 230 0.001~0.004

N1 65%-75% 16.5, 16.8 209,212,256,261

0.002~0.008


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Input Data for A2-1-G

Drilling fluid salt concentration 267g/L CaCl2

Pore fluid salt concentration 0.01M

Pressure of drilling fluid 1020 psi

Pore pressure 5 psi

KI 2.344X10-18

m3s/kg

KII -1.394X10-19

m3s/kg

Deff 8.94X10-11m2/s


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Comparison of Model with Data A2-1-G(To obtain parameters)

A2-1-G

0

100

200

300

400

500

600

700

800

900

1000

0 10 20 30 40

t (hr)

PorePressure(psi)

Experimental Data

Model fit


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Input Data for A2-2-A

Drilling fluid salt concentration 413g/L CaCl2

Pore fluid salt concentration 0.01M

Pressure of drilling fluid 955 psi

Pore pressure 50 psi

KI 2.344X10-18

m3s/kg

KII -1.394X10-19

m3s/kg

Deff 8.94X10-11m2/s


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shale fluid interaction

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