Pore Characterization and Inner Adsorption Mechanism Investigation for Methane in Organic and Inorganic Matters of Shale

Abstract

The pore characterization and the adsorption property for gas shale have been studied widely due to the vigorous exploration of shale gas reservoirs. However, for a particular shale sample, few research studies have focused on the pore characterizations and inner adsorption mechanisms for different types of pores in organic and inorganic matters. In this research, a low-pressure N 2 /CO 2 adsorption method with a novel analysis and a simplified local density (SLD) method with a particular regression were utilized to investigate the pore characteristics and inner adsorption mechanisms for methane in organic micropores and inorganic micropores and nonmicropores. Effective pore characterizations were acquired for these three types of pores. Furthermore, based on the obtained adsorption proportion of each type of pore to the total adsorption of all the pores, the adsorptions in inorganic micropores and nonmicropores were both essential and nonnegligible. Organic micropores are more competitive than inorganic micropores for adsorption owing to their stronger fluid−wall interaction. Due to the variation in density distribution in the pores, excess adsorption possesses positive and negative relationships with micropore size at high and low pressures, respectively, and slightly negative relationship with nonmicropore size. Besides, strong solid−solid molecule interactions and small pores could bring about a high sensitivity of adsorption to the specific surface area (SSA).

Comprehensive Review about Methane Adsorption in Shale Nanoporous Media

“…Moreover, the kerogen pore surface is not smooth, carrying varying degrees of surface roughness. Kuila and Prasad recommended the use of consistency criteria proposed by Rouquerol et al Moreover, as the BET model only provides qualitative estimation of surface area, it should be used with cautions for quantitative computation of the average pore diameter , by combining the BET surface area and total pore volume.…”

“…58 The geophysical properties of shale rocks have been generally characterized by total organic carbon (TOC) analysis, 59−61 rock-eval pyrolysis, 62−65 and X-ray diffraction (XRD) experiments 66−69 to determine the TOC content, thermal maturity, and chemical compositions. Generally, the adsorbed methane amount has a positive correlation with the TOC content in shale samples, 23,70,71 while clay minerals can also significantly contribute to shale gas adsorption. 23 In addition, experimental studies have reported that methane adsorption in shale significantly decreases due to the presence of moisture.…”

“…The geophysical properties of shale rocks have been generally characterized by total organic carbon (TOC) analysis, − rock-eval pyrolysis, − and X-ray diffraction (XRD) experiments − to determine the TOC content, thermal maturity, and chemical compositions. Generally, the adsorbed methane amount has a positive correlation with the TOC content in shale samples, ,, while clay minerals can also significantly contribute to shale gas adsorption . In addition, experimental studies have reported that methane adsorption in shale significantly decreases due to the presence of moisture. ,,, On the other hand, the burial depth of shale reservoirs generally ranges from 800 to 7000 m, − leading to a temperature gradient from 20 to 30 K/km ,, and a pressure gradient around 100–150 bar/km, ,− resulting in typical shale reservoir temperature and pressure up to 450 K ,, and 700 bar, − respectively.…”

Experimental Investigation about Gas Transport in Tight Shales: An Improved Relationship between Gas Slippage and Petrophysical Properties

“…Shale samples analyzed in this study were collected from the Upper Ordovician Wufeng Formation (O 3 w) and the Lower Silurian Longmaxi Formation (S 1 l) in Sichuan Basin. The Upper Ordovician Wufeng-Lower Silurian Longmaxi (O 3 w-S 1 l) shales are one of the most productive shale gas formations in China. − The Upper Ordovician Wufeng Formation was deposited in a deep-water shelf sedimentary environment, which was a benefit for the preservation of organic matter. Kinds of graptolite fossil were identified from the shales of Wufeng Formation. , The Longmaxi Formation was deposited from a deep-water shelf to a shallow-water shelf environment.…”

Modeling Water Imbibition and Penetration in Shales: New Insights into the Retention of Fracturing Fluids

“…Spontaneous imbibition is related to the capillary rise of a wetting liquid. 14 Because of the extremely fine pore sizes, 15 the capillary pressures of the partially saturated shale matrix are very high, 16 causing fracturing water infiltration into the rock matrix. At the same time, the hydraulic fracturing operation creates a network of interconnected fractures that exposes a great surface area of the rock.…”