Geological characteristics and exploration prospect of oil and gas from the sandstone of the Silurian Xiaoheba Formation in the Sichuan Basin, China

Abstract The sandstone of the Silurian Xiaoheba Formation in the Sichuan Basin is poorly understood and the exploration prospect is unclear. The geological characteristics of oil and gas from the aspects of sedimentation, reservoir and accumulation of the sandstone of the Xiaoheba Formation in the Sichuan Basin, as well as evaluating its exploration potential and prospect, were made possible using the data on field outcrops, exploratory wells, as well as seismic and logging data. By studying the above, the following four points are understood. (1) The sandstone of the Xiaoheba Formation in the Sichuan Basin is mainly dominated by siltstone. There are two types of sand masses: the distal sandbank sand mass of the foreland basin delta front and the thin layer sand mass intercalated with pro-delta mudstone. The two types of sand masses are widely distributed in east Sichuan. (2) The sandstone reservoir of the Xiaoheba Formation is characterized by low porosity, low permeability and extra density. The late-stage diagenesis led to the densification of the reservoir. Intervals with relatively high porosity were developed locally and satisfactory reservoirs could be developed in the period of reservoir forming. (3) The sandstone reservoir of the Xiaoheba Formation, the high-quality argillaceous hydrocarbon source rocks of the Longmaxi Formation, and the thick layer mud shale caprocks of the Hanjiadian Formation formed a set of high-quality source rocks, reservoir, and caprock accumulation assemblage. The formation and evolution of the Kaijiang paleo-uplift in eastern Sichuan were conducive to the accumulation and preservation of the sandstones of the Xiaoheba Formation. (4) The sandstone of the Xiaoheba Formation is a potential field for natural gas exploration in the Sichuan Basin. Both types of sand masses have a certain potential, among which the favorable exploration area of the sand mass of the distal sandbank is about 10 × 103 km2. The study results are of great significance for improving geological understanding and guiding natural gas exploration in this field.