Porosity Heterogeneity Analysis Using Confocal Laser Scanning Microscopy (CLSM)

Abstract

High levels of heterogeneity in many shale and other tight reservoirs have raised concerns about the validity and relevance of RCA measurements from core plugs and high-resolution imaging techniques like Scanning Electron Microscopy. Although the measurements may be precise, they may not accurately describe the range of formation properties that exist within a given sample. In a recent study of shale and other tight reservoirs, including reservoirs in the Williston Basin, Powder River Basin, Anadarko Basin, and Permian Basin, we developed a technique to address this issue using Confocal Laser Scanning Microscopy (CLSM). The samples are prepared with a fluorescent dye and imaged in 3D, at a lateral resolution of 350 nanometers and a vertical resolution of 500 nanometers. The resulting porosity volumes are analyzed using binary image analysis techniques. These techniques allow us to determine the porosity heterogeneity in vertical and horizontal directions, provide a heterogeneity index on a sample (facies) level, and to quantify the pore size distribution across a thin section. We found that a significant pore size and porosity distribution heterogeneity is present at the thin section (core plug) scale. Both pore size and porosity distribution heterogeneity are highly facies dependent. The fact that routine core plug measurements are insensitive to heterogeneity at this scale explains the difficulties in using average porosity values in these formations to predict reservoir behavior and to reliably calibrate wireline logs. Our findings quantify the small-scale porosity heterogeneities that are below the resolution of RCA, which have a significant impact on how we evaluate formations using core data.

AAPG Datapages/Search and Discovery Article #90357 ©2019 AAPG Rocky Mountain Section Meeting, Cheyenne, Wyoming, September 15-18, 2019