Characterizing Unconventional Reservoirs: an Informal Mudstone and Shale Classification Based on Core

Milner, Mary¹, Barbara Marin², and David Handwerger^1
1TerraTek, a Schlumberger Company, Salt Lake City, UT
²TerraTek, a Schlumberger Company, Houston, TX

     Reservoir characteristics of shales and mudstones are strongly influenced by the three parameters: 1) depositional mineralogy, 2) organic content and maturity, and 3) matrix composition. These parameters also affect log response and mechanical properties. A suite of analytical methods developed to measure these parameters has led to an informal classification of shales and mudstones based on core measurements. This ‘shale toolkit' ideally includes core description and geology, thin section petrology, X-ray diffraction, scanning electron microscopy, and geochemistry. With data thus gathered, a three-layered classification of shales and mudstones is possible. Layer one, depositional mineralogy, considers the ratio of different sized detrital materials, and mimics in concept most traditional classification schemes for fine-grained clastic rocks. Layer two considers organic content as an essential component, and characterizes its abundance, source and thermal history. Layer three characterizes the composition of the shale or mudstone matrix, that is, material less than 4 microns (clay). In general, observations identify three common matrix mineralogies resulting from a combination of original (depositional) and diagenetic elements. Siliceous mudstones, argillaceous mudstones, and calcareous/dolomitic mudstones form major subdivisions of matrix composition; several intermediate and variant compositions are also important.

AAPG Search and Discovery Article #90071 © 2007 AAPG Rocky Mountain Meeting, Snowbird, Utah