Reservoir Characterization Utilizing a Low Cost Resistivity-Porosity Crossplot and an Interactive Spreadsheet

Willard J. Guy, John H. Doveton, W. Lynn Watney, Timothy R. Carr, and Saibal Bhattacharya

In mature oil and gas producing provinces it is necessary to find a low cost, but reliable method to evaluate oil/gas field reservoirs for improving recovery. If a field has very limited core data, and production is commingled, the reservoir study will often need to rely on wireline logs of many types and from different logging companies. The challenge is to fully evaluate each well with a technique in which reservoir characterization is comparable and consistent so as not to "build" anomalies that are not really present.

A reliable technique is the "Super" Pickett plot that is an extension of the classical log-log porosity/resistivity plot. The "Super" Pickett plot is a pattern recognition tool where points are linked successively by depth and annotated with lines corresponding to bulk volume water and permeability in addition to the standard water saturation, porosity, and resistivity lines.

Subtle trends and patterns of these depth-linked series of points are used to characterize each reservoir. Color is used to display additional attributes such as gamma ray values, photo electric values, capillary pressure and lithology (RHOMAA/UMAA). The computational power and flexibility of a spreadsheet computer program is utilized with a color graphic display to expedite the characterization of complex reservoirs. Key reservoir parameters derived from this analysis are mapped using the software to portray interwell heterogeneities and evaluate continuity.

This log analysis technique can be tailored to varied, complex heterogeneous reservoirs both siliciclastics and carbonate lithology. Results provide the means to promote communication among geologists and engineers. The use of this technique is illustrated by a study of the Schaben Field in Ness County, Kansas, which is being supported by a Class II DOE grant.

AAPG Search and Discover Article #91019©1996 AAPG Convention and Exhibition 19-22 May 1996, San Diego, California