Idealized Shale Sorption Isotherm Measurements To Determine Pore Capacity, Pore Size Distribution, and Surface Area

Abstract

One potential method for mitigating the impacts of anthropogenic CO2-related climate change is the sequestration of CO2 in depleted geological gas and oil formations, including shale. The accurate characterization of the heterogeneous material properties of shale, including pore capacity, surface area, pore-size distributions, and composition is needed to understand the potential storage capacities of shale formations. Powdered idealized shale samples were created to explore reduction of the complications in characterization of pore capacity that arise from the heterogeneous rock composition and pore sizes ranging over multiple orders of magnitude. The idealized shales were created by mechanically mixing incremental amounts of four essential powdered components by weight and characterized with low pressure gas adsorption/desorption isotherms. The first two components, organic carbon and phyllosilicates (such as clays, micas, and chlorite), have been shown to be the most important components for CO2 uptake in shales. Organic carbon was represented by kerogen isolated from a Silurian shale, and phyllosilicate groups were represented by powdered illite from the Green River shale formation. The remainder of the idealized shale was composed of equal parts by weight of SiO2 to represent quartz and CaCO3 to represent carbonate components. Three idealized sample groups were prepared to be approximately 10, 30, and 55% illite by weight. Each of the sample groups consisted of four samples, incrementing the percent kerogen from 1.5 to 6%. Eagle Ford, Baltic, and Barnett shale sorption measurements were used to validate the idealized sample methodology. The sorption isotherms were measured volumetrically using low pressure N2 (77 K) and Ar (87 K) adsorbates on Quantachrome Autosorb IQ2. Both idealized and validation samples were outgassed using a standardized procedure that produced repeatable results while minimizing changes to the material properties of the shale. The idealized sample results indicated a positive linear correlation with increasing total organic carbon and pore capacity. This work is essential toward the development of predictive models weighted and scaled by the corresponding mineral compositional description of the reservoir.

Comprehensive Review about Methane Adsorption in Shale Nanoporous Media

“…However, as discussed above, the working mechanisms for these two approaches are different. In addition, whole shale samples containing both organic and inorganic matters have been widely used to measure adsorption capacity. ,,, While there have been experimental works separating various constituents in shale samples to measure gas adsorption in each of them, , a precise control of PSD cannot be achieved. As methane adsorption in shale nanoporous media strongly depends on rock type and PSD, it is imperative to combine the macroscopic experimental measurements with the microscopic molecular modeling and simulation approaches which can explicitly consider fluid–fluid and fluid–surface interactions.…”

“…On the other hand, the rock heterogeneity (organic and inorganic matters) in shale media adds another layer of difficulty, as most interpretation methods are built upon homogeneous rock properties (such as wettability). There have been attempts to separate different rocks in shale , to provide a better interpretation of rock properties. In addition, the nonuniform pore geometries in shale media indicate that the experiences from nanoporous media with a uniform pore geometry cannot be directly applied.…”

Impact of Degassing Time and Temperature on the Estimation of Pore Attributes in Shale

“…Shales, previously looked upon as “source rocks”, have received unprecedented research focus since their development as “unconventional petroleum systems”. − Further, the fact that shales are also being studied to be one of the preferred options for CO 2 sequestration has warranted more efforts for characterizing their fundamental attributes, viz., gas storage capacity, nature of porous structures, kinetics of hydrocarbon generation, etc. − The primary factor that controls the petroleum generation and/or gas storage in shales is the nature of the organic matter present within them. ,− Although clay minerals have also been identified as the other significant component in shale reservoirs, their complete role in storage and transport still presents certain ambiguity. Several researchers have extensively used the low-pressure gas adsorption (LPGA) technique using N 2 and CO 2 to comprehend the complexity of pore attributes of shales. − …”

The Role of Microfabric and Laminae on Pore Structure and Gas Transport Pathways of Marine Shales from Sichuan Basin, China

“…To characterize the complex pore structure, innovative approaches are implemented to obtain information about the nanometer-to micrometer-sized pore systems of shales [4][5][6][7][8]. A variety of organic matter-hosted and inorganic matter-related pores with pore size ranging from micropore (<2 nm, IUPAC classification) to mesopore (2-50 nm, IUPAC classification) to macropore (>50 nm, IUPAC classification) have been reported in shales [9][10][11]. Pore structure characteristics (morphology, porosity, pore size distribution, and specific surface area) of shales are found to be associated with rock composition, total organic carbon (TOC) content, maturity, and other geological factors [12][13][14][15][16].…”