Page 214 - Well Logging and Formation Evaluation

204 Well Logging and Formation Evaluation

Using the equations presented in Chapter 4 and solving for h (the height
above FWL) yields:

h = [ { ( S w - S wirr ) a] - ( 1 b) k ( f ) } ( [ rho w - rho h ) 3 281 0 433* . * . ] (13.4.1)

where:
h = the height above FWL, in m
S w = log-derived saturation (fraction)
S wirr = irreducible water saturation (fraction)
a, b = Leverett J fitting constants
k = permeability, in md
f= porosity (fraction)
rho w = water density, in g/cc
rho h = hydrocarbon density, in g/cc.

It would be necessary to derive an empirical relationship for the height
between the OWC (or GWC) and FWL and to have a log-derivable param-
eter (such as permeability from the poroperm relationship). In Figure
13.4.1 is a hypothetical example of a well drilled close to an FWL, using
the log-derived saturation to estimate the depth of the FWL.
In the figure, production from neighboring fields was known to cause
a variation in the FWL. Entry height between the FWL and OWC was

X00 x500 x1000 x1500 x2000 x2500
Measured depth (ft)
X00

X50
Wellbore

X100
TVD
(ft) Predicted FWL
X150

X200
Figure 13.4.1 Calculating the Position of the Free Water Level While Drilling