Methods and key parameters for shale gas resource evaluation

Methods and key parameters of shale gas resources evaluation are studied so as to accurately assess the potential of shale gas resources. In much-explored areas, the volume method, followed by the analogy method, is recommended for evaluation; in less-explored areas, the analogy method is recommended. The concept of “gas-bearing shale system” is put forward and taken as an evaluation unit to calculate the thickness of shale. It refers to the lithologic assemblage sealed by upper and lower tight layers in one pressure system, composed of organic carbon-rich shale and the interbeds of sandstones and carbonates, featuring the logging responses of gas-bearing shale, with tight rocks at top and bottom, and the continuous thickness of gas-bearing interval being more than 30 m and no obvious water layer. According to exploration degree and available data, different methods may be selected to calculate the thickness of gas-bearing shale system. The logging data and the content of organic carbon are used in the areas with high degree of exploration and abundant data, while field geological profile, seismic profile, depositional characteristics and other data are considered in areas with low or ultra-low degree of exploration.