Evaluation of Pore Characteristics of Deeper Cambay Shale under Simulated Pre/Postsorption Conditions by CH4 and CO2 Gases

The sorption behavior of gases like CH4 and CO2 on low permeable shale plays a crucial role in the prediction and evaluation of gas reserve as well as the reservoir potential to sequestrate CO2. Shale mineralogy and pore characterization are the most prominent parameters controlling the adsorption-desorption characteristics. In this paper, characterization of older Cambay shale has been presented using nondestructive techniques, that is, XRD and FESEM coupled with energy-dispersive X-ray spectroscopy (EDS or EDX) for crystallographic structure and compositional analysis and correlated with the gas sorption capacity using low-pressure nitrogen adsorption, that is, LPNA experiment. Frenkel-Halsey-Hill (FHH) model was employed for the determination of fractal dimension of samples, which is used to obtain the spatial distribution of the pores of shale. The studied shale samples showed abundance in quartz, calcite, and birnessite with minor components like pyrite, berlinite, and siderite. The presence of calcite and birnessite can be inferred to the occurrence of minerals like manganese in samples in recognizable amounts, which adds to the fracability and brittleness of shale. FESEM images at different imaging levels confirm the existence of different minerals and the presence of intra and inter-particle pores, which also correlates with the LPNA data confirming the existence of pores at the meso and macro-levels. Samples comprise a continuous broad span of pore sizes ranging from 1.8 to 66 nm. This paper presents the sorption behavior of CO2 and CH4 gases on shale matrix which will facilitate in estimating the chances of CO2/CH4 infusion into shale as well as fracability.