Utility of Micro-X-Ray Computed Tomography for Analysis of Shale Reservoirs

Abstract

The fine-grained texture and heterogeneity of shale makes analysis challenging, and this difficulty is compounded by the diverse depositional, diagenetic, and structural factors that determine its properties. Accordingly, the study of shale requires a systematic, multidisciplinary approach. X-ray computed tomography (CT) is a useful tool for observing shale fabric from mesoscopic to nanoscopic scales, and micro CT, in particular, has been underutilized. Micro-CT provides a noninvasive way to image specimens in three dimensions from cm to μm scale, and this investigation explored its utility for shale analysis and the ways it can be incorporated into workflows for shale evaluation. Shale samples from several Paleozoic formations in the southeastern and south-central United States were analyzed. Qualitatively, micro-CT facilitates the characterization of a variety of depositional, biogenic, diagenetic, and structural features. The technology further provides the ability to visualize, dissect, map, and filter tomographs in three dimensions is a major asset for shale characterization. Features imaged include micron-scale rock fabric, physical and biogenic sedimentary structures, body fossils, diagenetic minerals, fractures, and microfaults. Quantitatively, data from CT proved useful for calculating volumetric percentages of mineral constituents and for determining fracture porosity. CT helped pinpoint locations where microfabric could be further resolved by ion milling and SEM analysis. SEM coupled with energy dispersive spectroscopy (EDS) was then used observe and analyze pores, mineralogy, mineral morphology, fossils, and fracture-filling cement. Data gathered from SEM analysis were essential for interpreting CT images. This research demonstrates the utility of incorporating CT analyses into geologic workflows for the evaluation of shale. By using micro-CT in combination with SEM analysis, shale properties can be evaluated from mesoscopic to nanoscopic scales, thereby informing a range of sedimentologic, structural, and petrologic interpretations.

AAPG Datapages/Search and Discovery Article #90259 ©2016 AAPG Annual Convention and Exhibition, Calgary, Alberta, Canada, June 19-22, 2016