Net Pay Cutoffs from Capillary Pressure

Andy MayFebruary 24, 2014

Cutoffs from a Capillary Pressure Model Justifying cutoffs is difficult in the absence of extensive

test data

Proper core measurements and a capillary pressure model can define reservoir rock and net pay

Cutoffs are important because all hydrocarbons-in-place are not equal

Provides a profile of the hydrocarbon/water transition zone for accurate reservoir simulation – Sw is not a constant or a simple function of porosity!

Origin of Capillary PressureSealed Open

Gas

Water

In a water-wet rock, the pressure in the water on both sides of the tube is the same.  This is the hydrostatic pressure. The gas in the left tube has a higher pressure which holds the heavier water below the gas/water interface. 

The difference between the water pressure and the gas pressure is the capillary pressure.

( )w gCp H

Capillary Pressure Well Name: CFD_11-1-1 Depth: 52.05 to 1459.1 by 0.15 meters Constraints: None

1700 1732 1764 1796 1828 1860 1892 1924 1956 1988 2020FT Pressure - PRESS (psi)

1400

1380

1360

1340

1320

1300

1280

1260

1240

1220

1200Su

bsea

TVD

- TV

DSS

(m)

RFT/FMT/MDT Plot 27 out of 9381 points plotted.

15:25:44 on 26-Jul-03

Line no: 1 Gradient: 0.432 psi/ft No. pts: 17 Fit: 0.99984

Line no: 2 Gradient: 0.380 psi/ft No. pts: 6 Fit: 0.99981

Depth: 1361.9691m

Capillary Pressure

Free Water Level

Traditional OWC

Alt OWC

Leverett's J Function

0.1

1.0

10.0

100.0

0 10 20 30 40 50 60 70 80 90 100

Water Saturation(%)

Lab Data Model

Sr = 6.5 %

Lambda = 0.68

J 100 = 0.206

Pe

Neutral Wet Example

Well Name: CFD_11-1-1 Depth: 52.05 to 1459.05 by 0.15 meters Constraints: None Curve Aliasing: Name Match: Exact; Function Match: Ignored; Version Match: Highest

1880 1892 1904 1916 1928 1940 1952 1964 1976 1988 2000 PRESS[Unknown];1 (psi)

1380

1374

1368

1362

1356

1350

1344

1338

1332

1326

1320

TVD

Sub

sea

- TVD

SS[U

nkno

wn]

;1 (m

)

11 out of 9381 points plotted. RFT/FMT/MDT Plot

Line no: 1Gradient: 0.437 psi /ft

No. pts: 3Fit: 0.99975

Line no: 2Gradient: 0.391 psi /ftNo. pts: 7Fit: 0.99950

Depth: 1361.3486m

Correlation

Gamma Ray corrected (GRCO)0 150 (API)

M.Depth (m

)

1350

1375

Resistivity

True formation resistiv ity (RT)0.2 20 (ohmm)

Raw Porosity

(RHOC)1.7 2.7 (g/cc)

(PHIN)0.6 0 (pu)

(DLTC)160 60 (us/f)

SS Porosity

(PHTNSS)0.5 0

(PHTDSS)0.5 0

(PHTSSS)0.5 0

Sw

Effective water satur ation (S WE )1 0

(SWCP)1 0 (% )

Core Data

4

5

6

7

8

9

10

11

12

13

14

15

16

17

18

1920

211310

1320

1330

1340

1350

1360

1370

General Eng.

1

sample

sample

sample

sample

Net pay Flag (PAY)0 4

1350

1375

Effective Porosity

Effectiv e porosity (PHIE)0.5 0

(BVW_USE)0.5 0

SH SS VOLC LS DOL A N

Permeability

Permeab ili ty (KMDAR)1 50000 (mD)

(MOBIL)1 50000 (cP)

Mudlog Gas

(TOTGAS)0.1 100 (none)

Ng3

Ng3_FWL

Ng3_OWC

Oil below FWL?

FWL

OWC

Corey’s Function

* b

c

PSwe

P

(1 ) *Sw Sr Swe Sr

100(1 )J

Sw Sr SrJ

J100 is the J value for the bubbling pressure(Pb) or the Pc at the critical oil-phase Saturation

Substitute (J100/J) for (Pb/Pc)

Brooks and Corey, 1966 (eq. 24)

Derived from eq. 11, Amaefule, 1988

Critical Oil Phase Saturation

0.000

0.100

0.200

0.300

0.400

0.500

0.600

0.700

0.800

0.900

1.000

0.0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1.0

Sw, fraction

Kr,

fra

ctio

n

Krw

Kro

The Sw where Kro comes off zero in drainage mode is the critical oil saturation, the point at which the oil crosses the pore system.

0.000

0.100

0.200

0.300

0.400

0.500

0.600

0.700

0.800

0.900

1.000

0.0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1.0

Sw, fraction

Kr,

fra

ctio

n

Krw

Kro

Imbibition Steady State Rel K

Drainage, followed by Imbibition, also steady state

Sr - Irreducible Sw "Irreducible" Water Saturation

y = 24.368x-0.4579

R2 = 0.7964

0

10

20

30

40

50

60

70

80

90

100

0.01 0.1 1 10Rmh (microns)

Wat

er S

atur

atio

n @

200

psi

Air/

Brin

e

Outlier

Sw from OBM core

Hg

Rel Perm & Porous PlateSr as a function

of Rmh

Needed to compute Swe*

0.0314 kRmh

Leverett J -Function

0.1

1

10

100

0.1 1 10 100Effective Water Saturation* (%)

J

Laboratory Sw Best Fit CurveCorey Parameters

Lambda = 1.07

λ and J100

Lambda (λ) is the inverse of the slope, usually it is between .4 and 4. Corey calls this the “pore distribution index.” A value of 1.07 indicates highly variable pore sizes.

J100 is the intercept at Swe* where Kro comes off 0 (drainage).

Sw(Kro=0, imbibition)=73, Sr=21, Swe*=66.

J100= .46

Interfacial Tension (σ)

1 2

1 1cP R R

Interfacial tension (IFT or σ) helps determine the amount of curvature between the liquids in pore space(θ). It can be measured in the laboratory. The units are dynes/cm.

In heavy oil, the value is usually 10 to 20

In light oil it is 20 to 45.

Ref: Firoozabadi & Ramey, 1988

After Leverett, 1940

0.2179cos( )Pc kJ

Effect of Roughness on θSurface roughness diminishes the apparent contact angle.Anderson, Oct. 1987, JPT

0.2179cos( )Pc kJ

Use zero in water-wet reservoirs if no other data

Higher values are appropriate in neutral to oil-wet reservoirs, purely oil-wet reservoirs or neutral wet reservoirs are likely to have effective contact angles of about 90 degrees.

Range: 0 to 140 or more.

Capillary Pressure Model vs. Data

Porous Plate Capillary Pressure Curve

1

10

100

1000

0 10 20 30 40 50 60 70 80 90 100Water Saturation(%)

Air/B

rine

Capi

llary

Pre

ssur

e (p

si)

Lab Data Fitted Curve

POROSITY (%) PERMEABILITY (mD)

23.2 49

CFD 12-1-3ST

Dongying

Schraeder Bluff Saturation vs Height

0

100

200

300

400

500

600

700

800

900

1000

0 10 20 30 40 50 60 70 80 90 100

Water Saturation (%)

1 mD10 mD15 mD20 mD30 mD40 mD100 mD800 mD

20 md

Traditional OWC

Nansen Sw vs Height

0

100

200

300

400

500

600

700

800

900

1000

0 10 20 30 40 50 60 70 80 90 100

Water Saturation (%)

Heig

ht (f

t)

100 Md800 Md

Sw Cutoff

0.000

0.100

0.200

0.300

0.400

0.500

0.600

0.700

0.800

0.900

1.000

0.0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1.0

Sw, fraction

Kr,

fra

ctio

n

Krw

KroCross

1st water

Sw (Total) cutoff = 59%91% to 99% water cut0.000

0.100

0.200

0.300

0.400

0.500

0.600

0.700

0.800

0.900

1.000

0.0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1.0Sw, fraction

fw,

frac

tion

fw

99% water cut

Sw cutoff = 59%

Schraeder Bluff Saturation vs Height

0

100

200

300

400

500

600

700

800

900

1000

0 10 20 30 40 50 60 70 80 90 100

Water Saturation (%)

1 mD10 mD15 mD20 mD30 mD40 mD100 mD800 mD

15 md

Sw = 59%

Core K vs. Core Sw Constraints: None

0.1 1 10 100 1000 10000Core Perm Ovb corr - corwkhob

0

10

20

30

40

50

60

70

80

90

100W

hole

Cor

e Sw

- co

rwsw

118 out of 5002 points plotted.

Key to symbols

NIKAITCHUQ_4

KIGUN_1

2 well crossplot. Well collection used: Unnamed Collection

RMA: CORWSW (%) = -23.0925 * (log)CORWKHOB + 90.2008 . CC: -0.924312:20:18 on 3-Nov -05

23 md

Settled on a perm cutoff of 20 md.

Capillary Pressure Summary A capillary pressure model rigorously describes

the transition zone

The model provides a check on Sw

The model provides a clear backup for cutoffs

The model provides the best way to tie log and core data and the most comprehensive way to feed petrophysics to a reservoir simulator