SPE-181305-MS A Novel Technique for Generation of Accurate Capillary Pressure (Pc) Curves from Conventional Logs and Routine Core Data and new Pc Endpoint Functions after Considering the Sedimentary Environment and Pore Throat Size Distribution Shape (PTSDS) Mohsen FazelAlavi, Petrocarbon; Mina FazelAlavi, Kansas Geological Survey (KGS); and Maryam FazelAlavi, Petrocarbon
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SPE-181305-MS
A Novel Technique for Generation of Accurate Capillary Pressure (Pc)
Curves from Conventional Logs and Routine Core Data and new Pc
Endpoint Functions after Considering the Sedimentary Environment and
Pore Throat Size Distribution Shape (PTSDS)
Mohsen FazelAlavi, Petrocarbon; Mina FazelAlavi, Kansas Geological Survey (KGS); and
Maryam FazelAlavi, Petrocarbon
Overview
Reservoir zonation based on the linear relationship between FZI and 1/ (Swir.φ),
(Fazelalavi et al. 2014)
Correlation of endpoints of Pc curves (Pe and Swir) with different rock properties
Effect of pore size distribution on Pc curves
1st Pc Model - Brooks and Corey model after modification
2nd Pc Model – Normalized Pc (Pcn) relation with normalized non-wetting phase
saturation (Snwn)
Sw prediction in well A3 by 1st Pc model
Sw prediction in well A3 by 2nd Pc model
Slide 2
SPE-181305-MS • A Novel Technique for Generation of Accurate Capillary Pressure (Pc) Curves • Mina Fazelalavi
Slide 3
SPE-181305-MS • A Novel Technique for Generation of Accurate Capillary Pressure (Pc) Curves • Mina Fazelalavi
Reservoir Zonation
FZI (core) and 1/(Swi*Phi) (log) are plotted vs. depth and zones with similar
pore size distribution are delineated (Fazelalavi et al. 2014)
Best correlation is obtained when 1) reservoir rocks are classified 2) Swir is
correlated to Reservoir quality Index (RQI)
Correlations of Swir with other rock properties such as k, FZI, DRT, HUs, and
Phi are more inferior relative to RQI. Table below shows R2 of Swir correlation
with different rock properties
Irreducible Water Saturation (Swir) Correlation
Reservoir Zone RQI k FZI Phi
1 0.85 0.85 0.72 0.34
2 0.87 0.82 0.67 0.04
3 0.95 0.93 0.89 0.08
4 0.86 0.84 0.67 0.24
5 0.88 0.87 0.82 0.13
6 0.91 0.86 0.91 0.02
Average 0.88 0.86 0.78 0.10
Slide 5
SPE-181305-MS • A Novel Technique for Generation of Accurate Capillary Pressure (Pc) Curves • Mina Fazelalavi
Swir Correlation with RQI
Reservoir rock is first classified based on FZI and 1/(Sw*Phi), (Fazelalavi et al.
2014)
Swir correlation with RQI is found: Swir = a*𝑅𝑄𝐼𝑏
A distinct Swir correlation is found for every zone of the reservoir
y = 0.031x-0.895
R² = 1
0.000
0.100
0.200
0.300
0.400
0.500
0.600
0.700
0.800
0.000 0.100 0.200 0.300 0.400
Irre
du
cib
le W
ate
r Sa
tura
tio
n, F
r
Reservoir Quality Index (RQI)
Zone 1
y = 0.022x-0.63
R² = 0.9955
0.000
0.050
0.100
0.150
0.200
0.000 0.050 0.100 0.150 0.200Sw
i, Fr
Reservoir Quality Index (RQI)
Zone 2
Slide 6
SPE-181305-MS • A Novel Technique for Generation of Accurate Capillary Pressure (Pc) Curves • Mina Fazelalavi
Relationship between Pc Entry pressure (Pe) and RQI
A strong correlation exists between Winland R35 and RQI in each zone: R35= aRQIb
Pore throat radius (Re) at entry pressure (Pe) is proportional to Winland R35: Re = C1*R35
A function for Re in terms of RQI is found for each zone: Re = C1*a* RQIb
Therefore, Pe can be expressed in terms of RQI for each zone: Pe = (2σ2cosθ) /(Re)
Residual Oil Saturation Correlation
Residual Oil saturation is needed for imbibition Pc curves
When SCAL data is available:Sor = e× RQIf
When SCAL data is not available (Pentland et al. 2010) :
Sor = 0.012 Soi2 + 0.474 Soi
Effect of Pore Size Distribution on Pc Curves
Figure 19: Pore throat size distribution
– Single Modal
Figure 20: Capillary pressure curve by
mercury injection –Single Modal
One Pc equation accurately
predicts water Saturation in a
single modal pore size
distribution
Similar pore size distributions
are delineated by reservoir
zonation (Slide 3)
Constant C1 (Re = C1*a*
RQIb) depends on degree of
sorting
Irreducible water saturation
function based on RQI depends
on degree of sorting
0
0
1
10
100
1000
0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1
Pc,
psi
Sw, v/v
Pc Lab
Predicted Pc
Figure 21: Pore throat size distribution
in a carbonate Sample – Bi--Modal
In a bi-modal pore
size distribution, one
Pc equation can
predict water
saturation for all Pc
values
In this case, two
models are needed
Effect of Pore Size Distribution on Pc Curves
Figure 23: Core Capillary pressure –
Bi-Modal Sample and Pc Prediction by
a Single Model
Son
Swn
Lambda is obtained by plotting Pcn versus normalized water saturation (Swn) on log-log scale
1st Pc Model
Brooks and Corey Model after Modification
Slide 11
SPE-181305-MS • A Novel Technique for Generation of Accurate Capillary Pressure (Pc) Curves • Mina Fazelalavi
Well A3 – Zone 1: Correlation between Pcn and Swn
(Modified Brook and Core Model)
Capillary pressure at log depth
was calculated from FWL and fluid
densities
Pcn and Swn were calculated at
each depth and they were plotted
to obtain Lambda in Pc equations
Lambda is the negative of the
reciprocal of slope
2nd Pc Model- Drainage Pc curves
Pcn Relation with Normalized Non-wetting Phase Saturation (Snwn)
Pcn = Pc/Pe
Snwn= (1-Sw)/ (1-Swir) Eq.21
Pcn is plotted against Snwn and following equation is found:
Snwn = (1 – a ×Pe/Pc) × (1- (Pe/Pc) b) Eq.22
Combining the equations 21 & 22 and after rearranging result in: