The determination of the permeability distribution in a heterogeneous reservoir is the key for performance predictions. The permeability is usually evaluated from cores and/or pressure transient well tests. The determination of the permeability distribution in a heterogeneous reservoir is a complex problem because core samples and well test data are only available from very limited number of wells. At the same time, geophysical logs are available from the majority of, if not all, the wells in a reservoir. Therefore, the evaluation of permeability from well log data represents a significant technical as well as economic advantage. The evaluation of permeability in heterogeneous formations from well log data however represents a difficult problem. Generally, a simple correlation between permeability and porosity cannot be developed in heterogeneous formations, The goal of this study has been to investigate the feasibility of estimating the permeability of a heterogeneous formation utilizing geophysical well logs as well as geological interpretations.
Granny Creek Field in West Virginia has been selected for detailed evaluation in this paper. This field has produced oil from the Big Injun Formation since early the 1900's. Water flooding operations were initiated in the 1970's and currently are in progress. Well log data from a substantial number of wells, as well as core samples and/or core analysis results from a limited number of wells, were available and were collected. The core samples and the various well logs were analyzed to determine permeability and porosity. However, a reliable porosity-permeability correlation could not be developed even when the formation was subdivided into several zones based on the various geological interpretations.
A methodology was developed in this study by integrating actual well log responses (Gamma Ray, Deep Induction, and Bulk Density) and geological interpretations to subdivide the formation into several zones which led to development of a reliable correlation between bulk density and permeability. The field-wide applicability of the correlation was verified through comparison against measured permeability values. The results presented in this paper could serve as a guideline for correlating permeability with well log data in heterogeneous formations.