Quantification of the Gas-in-Place and CO2 Storage Potential of Shale Using Sorption Measurements and Modelling
Abstract
Despite major technical advances in extraction techniques, shale gas production remains inefficient, with about 90% of the original Gas-in-Place (GIP) remaining in the formation. While primary recovery methods yield suitable initial production rates, enhanced recovery using CO2 injection may be required to sustain them. In shale, natural gas is adsorbed within the pores of the organic matter and clay minerals. Understanding adsorption/desorption is key, as this dictates both production rates and the GIP. This study aims to quantify adsorption in shale at subsurface conditions and assess the effect of shale composition on sorption to estimate the recoverable and storable gas.
CO2 and CH4 high pressure adsorption isotherms have been measured using a Rubotherm Magnetic Suspension Balance at various temperatures (283-353K) and pressures (0-30 MPa) on two distinct sample-sets: (i) shales from the Bowland (UK) and Marcellus (USA) formations, and (ii) synthetic materials, including mesoporous carbon. The organic content of the shale can be used to scale the measured mesoporous carbon isotherms, confirming that the organics drive adsorption in shale and that shales are largely mesoporous. We also observe a substantial selectivity of shale towards CO2 vs. CH4, which can be exploited to enhance gas production and store CO2. The adsorption isotherms have been successfully described using a Lattice Density Functional Theory model, which uses the pore size distribution, obtained from Ar (87K) physisorption, as an input. It is thus able to provide unique insight into the pore-scale interaction between shale and supercritical fluids. The measured results have been deployed within a material balance framework to predict the GIP and CO2 storage potential. We modify the classic approach to correctly account for the volume occupied by the adsorbed phase. In this way, the conventional p/Z vs. cumulative gas production (or storage) curve becomes more useful: it maps the distinct features of the adsorption isotherm, clearly showing the contribution of adsorption and, most significantly, it provides a more reliable estimate of the original GIP, which is notably higher than the GIP from the traditional approach. Operational parameters are derived, including an optimal abandonment pressure that maximizes both recovery and storage.- Publication:
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AGU Fall Meeting Abstracts
- Pub Date:
- December 2019
- Bibcode:
- 2019AGUFMMR11A..04A
- Keywords:
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- HYDROLOGY;
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- PHYSICAL PROPERTIES OF ROCKS;
- 5114 Permeability and porosity;
- PHYSICAL PROPERTIES OF ROCKS;
- 5139 Transport properties;
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