Organic Matter in Gas Shales: Origin, Evolution, and Characterization. Origin, Evolution, and Characterization.

Abstract

Sedimentary organic matter is the source of gaseous hydrocarbons in shales. The concentration and composition of organic matter preserved during deposition and diagenesis of sediment ultimately determines the hydrocarbon generative capacity of the rock. The quantity of organic carbon is relative to the total organic carbon (TOC) content of rocks, whereas the quality is ascribed by the type of organic matter and its thermal maturity. Molecular and isotopic signatures of sedimentary organic matter determined using mass spectrometry reliably predict these geochemical attributes, and the kinetic parameters for its decomposition due to subsurface temperatures provide the quantitative estimation for the generation of hydrocarbon. The shale gas reservoirs are also its source rock; thus investigation of shale's organic properties plays an important role in the success of gas shale plays. The chapter describes the origin and evolution of organic matter in shale source rocks and basic techniques for its characterization exemplified by case histories from the potential Gondwana sedimentary basins of India, the Damodar Valley, and the Pranhita-Godavari sub-basin.