Improved pore-structure characterization in shale formations with FESEM technique

Abstract

Field emission scanning electron microscope (FESEM) is a widely used technique to examine pore structures in shale reservoirs. Prior to a FESEM scan, one must decide upon the location of sample to be viewed as well as the magnification ratio to be used, which is, however, prone to human errors. One common practice in FESEM study is that one tends to use a fixed magnification ratio for observing the pore structure on a given location of a sample. Also, the pore structure observed based on a given magnification factor cannot entirely represent the true pore structure characteristics of the shale sample, primarily due to the multi-scale heterogeneity of the shale rocks. To improve the FESEM characterization of pore structure in shale samples, we propose a methodology to reveal the multi-scale characteristics of shale samples. In this work, we propose an improved method for taking multiple FESEM images for performing more accurate characterization of the pore structures in shale samples. With the improved method, we can determine the appropriate number of FESEM images to be taken as well as the appropriate magnification ratio to be used in FESEM scan. A given magnification ratio is used throughout all the FESEM scans. This method can be used to retrieve important multiscale pore-structure characteristics of shale samples. We demonstrate the efficacy of the improved FESEM characterization technique by applying it to a shale gas formation in Sichuan basin in China.