Page 70 - Well Logging and Formation Evaluation

60 Well Logging and Formation Evaluation

where

q
J = P c [ * k ( f ) ] ( coss ( )) (4.2)
)
P c = (rho w - rho * h* .281 * .433 (4.3)
3
0
h
S wirr = irreducible water saturation
rho w = formation water density, in g/cc
rho h = hydrocarbon density, in g/cc
P c = capillary pressure, in psi
k = permeability, in md
f= porosity (as fraction)
s= interfacial tension between the hydrocarbon and water, in dynes/cm 2
q= contact angle between the hydrocarbon and water, in degrees
h = height above the free water level (FWL), in m
the constants a and b are to be fitted to the data.

Note that units are not particularly important, as long as they are used
consistently throughout. If, say, pressures are used in bars instead of psi,
the effect will be for a and b to be modified, but the results will be the
same.

4.1 CORE CAPILLARY PRESSURE ANALYSIS

The results of a SCAL program of P c measurements will usually be pre-
sented in the form of Table 4.1.1.
Note that figures in the body of the table represent S w values. Note also
that these measurements will have been performed by one of a number of
methods, none of which use actual formation fluids. Use the following
steps to generate the average J function. Let:

S wr = S w - S wirr . (4.1.1)

1. Convert the table above into a table of J vs. S wr . Set S wirr equal to 0.01
below the lowest water saturation seen anywhere in the reservoir in
cores or logs. In order to derive J, use the values for k and f in the
table. For the interfacial tension and contact angle, use the data in Table
4.1.2 depending on the type of measurement used:
2. Plot Log(J) vs. Log(S wr ). The intercept and gradient should give you
the constants a and b (Figure 4.1.1).