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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