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.