Organic geochemical applications to the exploration for source-rock reservoirs – A review

Source-rock reservoirs are fine-grained petroleum source rocks from which liquid and gaseous hydrocarbons may be produced following fracture stimulation. A major factor that allows such a source rock to function well as a reservoir is its organic matter – specifically the quantity, quality and thermal maturity of that organic matter as it occurs within the source-rock reservoir. Here we review the published literature to assess the current status of geochemical measurement and data interpretation of organic matter in these reservoirs, and how workers have applied this information in the exploration for this reservoir type. Our focus is on the chemical and geochemical characteristics of source-rock reservoirs, with emphasis on the isotopic and molecular characteristics of their hydrocarbon fluids and solid organic matter. Special consideration is given to geochemical analytical methods particularly appropriate to the organic matter in this reservoir type. Our discussions of published studies focus on three areas: (a) source rock characteristics – organic matter quantity, quality and maturity; (b) thermally-induced cracking of kerogen, oil, condensate and gas; and (c) natural gas stable carbon isotopic anomalies often observed in shale plays. Conceptual approaches and practical applications are addressed in equal measure, and our assessment of future directions and unsolved problems is provided.