Groundbreaking gas source rock correlation research based on the application of a new experimental approach for adsorbed gas

Abstract

Many years of experimentation have led to the development and improvement of equipment and methods used to make gas source rock correlations. By crushing samples using a ball mill and directly collecting adsorbed gases in the absence of aqueous media under high vacuum conditions, most possible interference factors, such as atmospheric pollution, crushing-induced pyrolysis, and gas collection by aqueous media are eliminated. This greatly enhances the volume percentage of hydrocarbon gas in the acquired adsorbed gases, with maxima up to more than 80%. The actual measurement of carbon isotopic series can be carried out to such an extent as to be δ13C1-δ13C5. A preliminary study using newly established equipment and methods has indicated the following. (1) The carbon isotopic composition of ethane in adsorbed gases on hydrocarbon source rocks can be used to distinguish the types of source rocks. This is consistent with results obtained by using organic geochemical parameters for source rocks, and illustrates that it is highly feasible to use the carbon isotopic composition of ethane in natural gases as a parameter for distinguishing the types of source rocks. (2) The thermal evolution degree (Ro) of hydrocarbon-source rocks calculated in terms of the carbon isotopic composition of methane in adsorbed gases on hydrocarbon source rocks agrees well with the vitrinite reflectance actually measured in the source rocks. This confirms the reliability of the relationship between the carbon isotopic composition of methane in natural gases and the thermal evolution degree determined using statistics. (3) Finally, a direct gas source correlation method for natural gases has been established, and the expression of log Ro vs. δ13C1 established in terms of actually measured δ13C1 values of methane in absorbed gases. Ro values of hydrocarbon source rocks have been established as well, thus creating favorable conditions for precise oil-and-gas source correlations in exploration areas. © 2012 The Author(s).