Carbonate Reservoir Characterization Using Wireline Logs Permian Basin, West Texas
By
Chunming Xu1, Pete Richter1, W. Rex Butler1, Jonas Gournay2, Nathan Miller2
(1) Schlumberger Oilfield Services, Houston, TX (2) ExxonMobil Production Company, Houston, TX
Through an optimized workflow, small-scale heterogeneity from image and
conventional log processing is quantified with calibration
from core data.
Interwell heterogeneity is characterized through integrated 3-D visualization of
the single
well
porosity/permeability heterogeneity with seismic and production
data. A five-step methodology for quantifying primary and secondary porosity,
permeability variations, and stratigraphic rock types through interpretation of
uniquely processed image log data is proposed.
In a pilot study, thirteen wells in an oil field of Permian basin, West
Texas, were analyzed to understand the complex porosity and permeability
heterogeneity of the Permian Queen, Grayburg and San Andres Formations. Grayburg
siliciclastics and dolomites, which were generally thought to be poor
reservoirs, exhibit significant, vertical porosity heterogeneity that has not
been previously resolved by conventional wireline logs. The San Andres dolomite
reservoir, on the other hand, is characterized by porosity heterogeneity ranging
from 5-30%. Image log analyses quantify azimuthal porosity heterogeneity up to
50% as well
as small-scale permeability variations of 3-4 orders of magnitude
for different intervals having the same porosity of 15-20%. Quantification of
secondary porosity and permeability using conventional logs with
calibration
from both the core and FMI results allows a field wide evaluation of the
heterogeneity. Seven rock types were identified from image and conventional logs
through neural network process. They provided valuable stratigraphic constraints
on areal reservoir variations, especially for uncored wells. The proposed
methodology may be applicable to underutilized image log databases in other
areas, thereby potentially adding significant value to reservoir
characterization efforts.