Review on hydrocarbon generation, pores formation and its methane adsorption mechanism in shale kerogen

Abstract

Now problems of shale gas development reveal that organic matter diagenesis, hydrocarbon generation process of kerogen, characteristics of methane and water occurrence in organic pores are all with complexities, which will seriously affect the desorption and production laws of shale gas. But existing research is shortage in these aspects, such as: the product characteristics of each thermal evolution stage of shale organic matter, the mechanism of hydrocarbon generation, organic pores type as well as formation mechanism. Besides, the occurrence modes of methane and water in organic pores are controversial, so further research is necessary. Literature reviews on process of kerogen formation, generation mechanism of oil/gas in shale kerogen, evolution characteristics of pores in organic matter and water distribution characteristics in pores of organic matter are conducted. During the biochemistry stage, kerogen is generated by bacterial action and condensation polymerization. Because the C-H bonds of aliphatics in kerogen release, aliphatic-intermolecular pores occur. During the thermo-catalysis stage, asphaltenes, liquid hydrocarbon and residual kerogen are generated by thermal-depolymerization, and cracking of asphalt turn out to be liquid hydrocarbon, so the marginal-oil pores (liquefied pores) form. During the thermo-cracking stage, liquid hydrocarbon crack into wet gas, and major pores in organic matter are marginal (or internal) -gas pores. During the deep high temperature stage, hydrocarbon transform into dry gas, owing to the release of C-H bonds in kerogen aromatics, pores in organic matter mainly include intermolecular pores in aromatic and gas pores. In addition, it is water that is involved in the pores of organic matter during each thermal evolution stage of shale kerogen, which shows a solid-liquid interface effect. As a theoretical basis on exploration and development of shale gas, it is valuable to obtain better understanding on production discipline of shale gas.