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The Silurian hydrocarbon accumulation research in the southeastern Sichuan Basin lacks evidence of the hydrocarbon accumulation and destruction stages in reservoirs. Bitumen and calcite veins that were developed in the Shiniulan Formation had recorded the information of the fluid evolution in reservoirs and have important implications for fluid activities and hydrocarbon accumulation processes in the Dingshan area, southeast Sichuan Basin. Based on analysis of petrographic, trace element, fluid inclusion and laser Raman spectroscopy of the calcite veins, this research determines the timing and origin of the paleo-fluids formed the calcite veins; recovers the paleo-pressure of the methane inclusions, and reveals the petroleum system evolution and controlling factors of the Shiniulan Formation. The results indicate that two phases of calcite veins were developed in the Shiniulan Formation, and oil charging happened before the formation of the two phases of the calcite veins. The first phase of calcite veins were formed at ~127 Ma under relative reduction conditions, with the forming fluid sourcing from the diagenetic fluid of the same strata, which show brown-red cathode luminescence colors. The second phase calcite veins were formed at ~83 Ma under relative oxidation conditions, showing brown-yellow cathode luminescence colors. Oil generation peak of the Longmaxi source rocks, which were the main source of the Shiniulan reservoirs, was from ~190 Ma to ~150 Ma. Oil to gas cracking happened at ~135 Ma. The trapping pressure of methane inclusions is 51.77-57.46 MPa, and the pore fluid pressure coefficient is 1.26-1.40. Since the Yanshanian period, a series of tectonic movements have taken place in the Dingshan area, which uplifts and lead to erosion and fracturing of the Dingshan area is accounts for the destruction of the Shiniulan gas reservoirs.

Based on the understanding of the basic geological conditions of shale gas from the Upper Ordovician Wufeng Formation to the Lower Silurian Longmaxi Formation in Dingshan area of the southeastern Sichuan Basin, the occurrence, migration mode and intensity of natural gas in the shale gas system were discussed according to the results of drilling, logging, fracturing test, laboratory test and structural interpretation, moreover, a shale gas enrichment mode suitable for the study area was proposed. In shale gas systems, high-angle fractures extend for a short distance, while horizontal fractures such as bedding-parallel detachment and interlayer bedding fractures extend for a long distance. As a result, the permeability in the bedding direction is much greater than that in the vertical direction. These characteristics together determined that natural gas in shale gas system was usually transported horizontally, and sometimes both horizontally and vertically. For the Qiyueshan fault zone, the burial depth of shale reservoir and the distance to Qiyueshan fault zone are the major constrains for shale gas enrichment in the Wufeng-Longmaxi formations in the study area. The Qiyueshan fault zone is a basin-controlling fault zone with fractures and associated fractures developed, and is a shale gas escaping area. In the shallow-buried area in the southeastern part, high-angle fractures were relatively developed, by which horizontal fractures were opened. The proportion of free gas was less than 60%. A normal pressure system indicates a semi-retention area for shale gas. In the middle-to deep-buried area in the northwest, high-angle fractures were relatively undeveloped, and horizontal fractures were closed. The vertical and horizontal migrations were blocked, and most of shale gas was trapped in shale reservoirs. The proportion of free gas is more than 60%. A high-to ultra-high pressure system indicates a shale gas accumulation area.

Tectonic fractures are a significant factor for production of the Longmaxi formation in Dingshan area. The analyse of the distribution and development degree of tectonic fractures is the main research method in present-day. Based on the data of field outcrops and borehole core, the new method-binary method is put forward by rock fracture and energy value to decide tectonic fracture development. According to the method the fitting formula is offered between the relation of the value of rock fracture, energy and the fracture density. Compared the fracture density predictive value and the observed value of 15 wells, all wells relative error less than 25%. The prediction results are accurate. According to the fitting formula of fracture development and distribution in the study area are obtained. The results show that the fracture density is high as a whole of the Longmaxi formation in Dingshan area. Whole shows by south east to gradually reduce the trend of the north west. Supported the future of the oil and gas exploration to provide geological basis and guidance in Dingshan area.