sCore: A Classification scheme for Organic Mudstones based on Bulk Mineralogy.

Helena Gamero-Diaz, Camron Miller, and Richard Lewis
Schlumberger, Dallas

In recent years, operators have produced large quantities of hydrocarbon from organic shale reservoirs. Horizontal drilling and multi-stage stimulations, targeting sections with superior reservoir and completion quality, have been proven as key to their development. Organic mudstones are fine-grained sedimentary rocks with total organic content above 1.5% that typically consist of complex mineralogy that may be heterogeneous at very small scales. Although numerous cores have been studied and described, there is no published mineralogy-based classification scheme for these rocks. This paper defines a methodology for creating a detailed mineralogy-based description for organic mudstones using core and geochemical log data. The proposed classification scheme is based on a ternary diagram created specifically for organic mudstones. It is based on a combination of core- and log-based mineralogical relationships. The primary classes are siliceous mudstone, carbonate-rich mudstone and argillaceous mudstone. Sub-classes are based on relative amounts of these three mineral groups. A mineralogy-based classification may help provide a better understanding of depositional conditions and identify target zones for completion. A common metric for the description of organic mudstones will also facilitate comparison of such reservoirs from different areas, formations, basins, and continents. A secondary objective is to provide a log display that flags other descriptive parameters that impact reservoir quality, completion quality and/or operational efficiency. The log display presented here will provide a consistent description of the organic shale section and the input necessary for proper decision making when planning a drilling development project.

AAPG Search and Discovery Article #90152©2012 AAPG Southwest Section Meeting, Fort Worth, Texas, 19-22 May 2012