Upper-Assam Shale as a Gas-Shale Reservoir: Their Composition and Pore Characteristics

The success of the shale gas in the US has caused other countries to investigate the shale gas prospects that could improve their energy security. The role of shale-gas as an unconventional energy resource calls for a detailed understanding of shale as a reservoir. This study discusses two essential themes which are pertinent to the gas shale reservoir characterization and engineering, i.e pore characteristics and organic-inorganic mineral composition. Organic-rich shales from Upper-Assam of India are renowned for their hydrocarbon resources and are potential target for future shale gas exploration. But due to unpublished data and less research work, a problem persists in assessing the producibility of these shales. Details of pore characteristics were investigated by low pressure N₂-CO₂ adsorption and mercury injection method. CO₂-N₂-Hg dV/dlogr pore size-distribution data reveals that shale samples are dominated by mesopore followed by micropore and macropore. The consistency of Hg dV/dlogr plot with that of CO₂-N₂ plot suggests presence of slit shaped pores. The Hg injection curve indicates that pore radius influences the tightness and ultimately the connectivity of the samples. XRD study exhibited the clay rich nature of shale that might cause the high amount of mesopores. Rock eval data is suggestive of excellent source rock potential in the samples. It was found that a positive relation exists between the TOC, micropore volume and total porosity. This relation indicates a strong influence of organic matter on micropore volume and ultimately on the total porosity of the samples. However, a lack of correlation between clay minerals with CO₂ micropore surface area suggests that clay minerals do not contribute to the microporosity of the shales. But clay minerals positively correlate with N₂ surface area suggesting their strong influence on meso and macro-pores of shale samples.