Eslinger, Eric¹, Robert Everett², Scotty Tuttle³, David Dennard³
(1) Eric Geoscience, Inc. and The College of Saint Rose, Glenmont, NY
(2) Consultant, Victoria, BC
(3) Dominion E&P, Inc. (currently Mission Resources, Inc.), Houston, TX

ABSTRACT: Net Pay from Petrophysical Analysis of 29 Wilcox Wells, SW Bonus Field, Wharton County, Texas, using a Multi-Well and Multi-Dimensional Clustering Analysis Coupled with a Mineralogy-Based Forward Modeling Procedure

A petrophysical analysis was made in a ~3000 feet thick Wilcox Formation multiple-sand gas-bearing sequence in 29 wells from Southwest Bonus Field, Wharton County, Texas. A 29-well clustering analysis using RHOB, NPHI, GR, and DT was used to probabilistically assign samples in each well to ten "rock types" (5 sandstones, 3 siltstones, and 2 shales). The only well with whole core was used as a "model" well. Porosity, permeability, and water saturation profiles were determined for the model well using a forward-modeling procedure based on: 1- the clustering results; 2- the mineralogy of each cluster; 3- a database for well log responses for minerals and fluids; and 4- a published (by others) method that uses porosity, grain density, and mineralogy surface area to estimate permeability. The same inputs used for the model well were also applied to the other 28 wells.
Net pay was computed in each well using a suite of five cutoff parameters: total porosity, free porosity, permeability, bulk volume water, and water saturation. "Opportunity" was defined to be depths where net pay exists but where no perforations had been made. Total net pay (all wells) was 4382 feet and total "opportunity" was 2338 feet. Therefore, "opportunity" footage was 53% of total net pay.
The same 29 wells also were analyzed using a modification of the ECS* (Elemental Capture Spectroscopy [Schlumberger] procedure), and the resulting petrophysical profiles were similar to those obtained using the clustering and forward modeling procedure.

AAPG Search and Discovery Article #90026©2004 AAPG Annual Meeting, Dallas, Texas, April 18-21, 2004.