The conditions and modelling of hydrocarbon accumulation in tight sandstone reservoirs: A case study from the Jurassic Shaximiao formation of western Sichuan Basin, China

Complex tight sandstone reservoirs from the Jurassic Shaximiao Formation on the eastern slope of western Sichuan Basin of China, have the characteristics of narrow channels, thin sandbodies with poor physical properties, strong reservoir heterogeneity, high water saturation, and low productivity of individual wells. The exploration and development of these complex tight sandstone gas reservoirs from the Jurassic Shaximiao Formation of the study area are faced with a huge challenge. The key factors controlling natural gas enrichment is unclear, and it is especially difficult to predict high-yield enrichment zones. Based on the data of drilling wells, cores, logs, and experiments, the methods of organic geochemistry analysis, carbon and oxygen isotope analysis and homogeneous temperature analysis of fluid inclusions are applied, to conduct the conditions and modelling of hydrocarbon accumulation in tight sandstone reservoirs from the Jurassic Shaximiao Formation of the study area. The gas source in the Jurassic Shaximiao Formation of the study area has been analysed based on the previous works. The reservoir characteristics and transportation system have been determined, high porosity and permeability of sandstones from the Js3 sand group, with an average porosity of 9.52%, and an average permeability of 0.376 x 10-3 & mu;m2. Five evolution types of the assembly of the faults and sandbodies can be divided in the study area. The timing of hydrocarbon accumulation from the Jurassic Shaximiao Formation of the study area is determined as three periods on the basis of experienced tectonic movements. It is revealed that the hydrocarbon accumulation of the Jurassic Shaximiao Formation of the study area is mainly controlled by the high-quality reservoir, structure characteristics, fault system and evolution of the assembly of faults and sandbodies, and the pathways of channel sandbodies. The sandstones of high porosity and permeability contacted with listric faults and ramp-flat faults of low dip angle or some minor faults, located in the high point of structure, with the evolution of the assembly of faults and sandbodies of type #i and type #ii, leading to the formation of multiple traps in reservoirs laterally and an amount of natural gas in these sandstones. The channel sandbodies going through the high-potential area (i.e., syncline area) is effectively configured with the source rock faults, it is difficulty for a long-distance hydrocarbon accumulation. Based on the petroleum geological conditions and the main controlling factors of hydrocarbon accumulation, the dynamic hydrocarbon accumulation model from the Jurassic Shaximiao Formation of the study area has been established. These research conclusions can provide the theoretical foundation for predicting the high-yield enrichment zones of the study area.