Abstract
The purpose of this paper is to probe into the nature and variability in vertical microstructure within Longmaxi gas shales of well WX2, Lower Silurian, located in the NE Sichuan Basin of China. To understand the pore system of these rocks, the total porosity, pore size distribution (PSD), surface area, organic geochemistry, and mineralogy, some image analyses by electron microscopy are performed. The obtained results indicated the following. (1) Gas shales have a complex pore structure. Total porosity from helium pycnometry ranges between 0.75% and 4.62%. Total organic content ranges between 3.4 wt.% and 11 wt.%, and vitrinite reflectance measured between 2.5% and 3.1%. The gas shales are quartz and clay rich. (2) Focused ion beam milling and field emission scanning electron microscopy provide high-resolution images of pores distribution and types. Three primary types of pores, organic matter (OM)-hosted pores, mineral-hosted pores, and micro-fractures, and 11 subgroups have been recognized. (3) The N2 isotherm curves are grouped into two types, II b as well as IV a, with the hysteresis loop belonging to Type B, reflecting the morphology of slits pores, and Type A, presenting cylinder pores. Combination of N2 and CO2 isotherm curve shows bimodal in two diameter sections, 0.3–1 nm and 2–5 nm, revealing meso-pores play important role in pore volume, whereas the micro-pores have great influence on pore specific surface area. (4) Total organic carbon (TOC) is considered to be the dominant contributor to total porosity and pore types, with the proportion of OM-hosted pores following the upward decreasing tendency of TOC. In plane, pore types are controlled by sedimentary facies. The OM-hosted pores are more prevalent in deep shelf facies within lower part of shale other than upper formation, instead of shallow shelf facies.
Highlights
The successful commercial exploitation of shale gas in the U.S, has garnered significant attention and focus of the countries in the world, China
There seems to be no correlation between them, given that pores associated with clay are relatively negligible compared with OMhosted pores, which is identical with the analysis of organic matter (OM)-hosted pores dominant observation from FE-SEM pore imaging
The correlations between total gas content versus pore volume and specific surface area demonstrate good positive linear tendency as high Total organic carbon (TOC) led to high gas content and high level of OM-hosted pores existence (Figure 13-c, d)
Summary
The successful commercial exploitation of shale gas in the U.S, has garnered significant attention and focus of the countries in the world, China. WX2 has been recently drilled by Research Institute of Petroleum Exploration and Exploitation-Langfang, CNPC, in the northeastern Chongqing and high gas content (2-8m3/t) has been obtained (Liang et al 2016). This breakthrough has made lower Silurian Longmaxi shale in northeastern Sichuan Basin a focus of attention and it is regarded as the exploration target in addition to the hot spots of shale gas development in southern Sichuan Basin. Previous studies focus on the sedimentary environments, large thickness and organic richness of this area By studying the fresh cores from well WX2, this paper intends to shed light on the Longmaxi shale microstructure of NE Sichuan Basin, giving implications of controlling on amount of gas in place
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a callDisclaimer: All third-party content on this website/platform is and will remain the property of their respective owners and is provided on "as is" basis without any warranties, express or implied. Use of third-party content does not indicate any affiliation, sponsorship with or endorsement by them. Any references to third-party content is to identify the corresponding services and shall be considered fair use under The CopyrightLaw.
