Characterization of hydrocarbon/pores generation and methane adsorption in shale organic matter
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2018 Taylor & Francis Group, LLC. The exploration and development of shale gas reservoirs has been of growing interest in the industry in recent years. It has been widely acknowledged that, during different thermal evolution stages, some characteristics including: the hydrocarbon-generation mechanism, development of organic matter pores, and methane storage/transport mechanism in organic matter/pores will affect shale gas desorption and production fundamentally. However, current research has failed to reveal them completely, which introduces large discrepancies between actual and predicted production in some shale gas reservoirs. In this paper, for the four thermal evolution stages of shale organic matter, i.e., the biochemical, thermo-catalytic, thermo-cracking and deep high temperature phases, respectively, characteristics of products generated from shale kerogen, including the form and quality of the solid frame, gas-oil ratios, and pore characteristics in organic matter (e.g., types of pores, pore wall materials) were first investigated. A new classification method for organic-matter pores was proposed. Additionally, methane absorption characteristics in shale organic matter and pores were demonstrated, the fact that water is involved during each thermal evolution phase was addressed, and current theories of solid-gas interface adsorption/desorption in the organic matter in shale were questioned. This work concluded that the system of solid-gas interface differs from actual shale reservoirs, so predicting production based on this understanding leads to significant inaccuracies. This work explained the possibility of solid-liquid interface effects in the organic matter of shale through analyzing product-generation and pore-formation mechanisms during the evolution of shale, which will directly affect potential reserves of shale. Therefore, this work should provide a basis for improving the accuracy of production predictions in actual reservoirs and should assist analysts in determining reasonable shale gas targets.