Microstructural investigation of gas shale in Longmaxi Formation, Lower Silurian, NE Sichuan Basin, China

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 N 2 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 N 2 and CO 2 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.

WITHDRAWN: Impact of Hydraulic fracturing on Mineralogy on Change in Micro and Nano Porosity and Permeability of Shales

“…Quartz, 43.2% Illite, 0.9% Kaolinite, 0.6% Chlorite, 2.5% Pyrite, 17.9% Pyrite, and 3.0% Dolomite. Although there are minor differences between the measured and the reported, the measured results are comparable to those reported [42,43]. Table 1 summarizes the results of all the shales used in this study.…”

Impact of de-ionized water on changes in porosity and permeability of shales mineralogy due to clay-swelling

“…Figure 3 a shows the average original mineralogy of Hayesville shale: 24.1% Quartz, 43.2% Illite, 0.9% Kaolinite, 0.6% Chlorite, 2.5% Pyrite, 17.9% Calcite, and 3.0% Dolomite. Although there were minor differences between the measured and the reported, the measured results were comparable to those reported 53 – 56 . Also, the treated mineralogy of Haynesville is summarized in Table 1 .…”

Sulfonic-functionalized algal/PEI beads for scandium, cerium and holmium sorption from aqueous solutions (synthetic and industrial samples)

“…For A L PEI, the adsorption isotherms can be considered a Type IIa isotherm according Rouquerol classification (with limited hysteresis loop, HL). On the opposite hand, the strong and typical hysteresis loop for adsorption/desorption branches mean that the material follows the Type IIb classification [53,54]. The hysteresis loop is associated with the socalled type B, which is described by slit shaped pores, while the original material has a more regular hysteresis loop (qualified as Type A) where the pores are generally described as cylindrical pores.…”