Abstract: New Core-analysis Methods Applied To Permian Sandstone, Pakenham (Wolfcamp) Field, Terrell County, Texas

CLIFT, SIGRID J., and STEPHEN E. LAUBACH, Bureau of Economic Geology, The University of Texas at Austin,F. E. ABEGG, KERBY S. ASLESEN, T. MATTHEW LAROCHE, ROD G. STANLEY, Chevron USA Production Company

The objective in the study was to use new core-analysis methods to identify areas where macrofractures are open and capable of transmitting fluid. Typically, macroscopic fractures are difficult to characterize because vertical wells rarely intersect them with a frequency sufficient to obtain representative samples. New core-analysis techniques based on electronbeam-induced luminescence (scanned CL) can detect microfractures that are otherwise invisible. Together with standard petrographic techniques that estimate authigenic-cement percent volume in the rock matrix, this information can be used to determine the attributes of macrofractures. These methods are particularly powerful in cases where such fractures are not directly sampled.

A test of these methods was carried out on naturally fractured Wolfcamp A2 sandstone cores from Chevron's Mitchell 1B No. 7 and University 29 No. 1 wells, located in the Pakenham (Wolfcamp) field in the Val Verde Basin Results show that, as predicted from microfracture analyses, open fractures are lined and bridged by synkinematic quartz cement, and filled (closed) fractures are occluded by postkinematic ankerite, barite, and other minerals. Matrix postkinematic cement volumes accurately predict the location of filled fractures. These results show that microstructural analysis is a promising approach for diagnosing fracture openness and for helping to assess fracture permeability in reservoirs.

AAPG Search and Discovery Article #90936©1998 AAPG Southwest Section Meeting, Wichita Falls, Texas