Distribution rules, main controlling factors and exploration directions of giant gas fields in the Sichuan Basin

Abstract

Over the past decade, great progresses have been made in natural gas exploration in the Sichuan Basin, where several large gas fields (such as Anyue) have been discovered. With the increase of data and the deepening of exploration, new knowledges have been gained in geological theory, thus it is necessary to further analyze the distribution characteristics and main controlling factors of large gas fields, thus to put forward new exploration directions for large gas fields. Therefore, based on the statistics on the geological parameters of 20 large gas fields discovered in this basin, the distribution rules, formation conditions and main controlling factors of large gas fields were analyzed, and the follow-up exploration directions were proposed. The following results were achieved. (1) Large gas fields are developed in different tectonic regions in the Sichuan Basin, mostly in the low and gentle tectonic belts in the central Sichuan Basin. Large gas fields are developed in seven series of strata in longitudinal stratigraphic sequences, which are dominated by the reef-shoal large gas fields formed in the Upper Permian Changxing–Lower Triassic Feixianguan Fms. (2) There are four sets of source rocks contributing to the formation of large gas fields, mostly from the assemblage of Xujiahe Fm source rocks. (3) Reservoirs in the large gas fields are dominated by porous carbonates and tight sandstones; large gas fields are mostly structural–lithological ones and normal pressure ones. (4) The development of marine large gas fields are mainly controlled by intracratonic rifts and paleo-uplifts. The controlling effect of intracratonic rifts is mainly from three aspects, namely the hydrocarbon generation center of source rocks, high-energy facies belts on the platform edges, and lateral sealing for hydrocarbon accumulation. The controlling effect of the paleo-uplifts mainly acts from another three aspects: intra-platform high-energy facies belts, karstic dolomite reservoirs and long-term hydrocarbon accumulation. The structures of foreland basins controlled the development of the continental large gas fields from four aspects: tectonic setting, source and reservoir assemblage, trap type and fracture distribution. In conclusion, a total of 5 domains with 14 favorable zones are the follow-up exploration directions of large gas fields in the Sichuan Basin. Keywords: Sichuan Basin, Large gas field, Distribution rule, Geological feature, Main controlling factor, Intracratonic rift, Paleo-uplift, Foreland basin structure, Exploration direction