Abstract: In this study, existing oil, gas and water exploration results and information on reservoirs and fractures were used and various methods employed, including conventional borehole logging, seismology, geochemistry, and mathematical statistics. The goal of this synthesis of methodology and data was to examine the distributions and accumulation characteristics of oil and gas in the target layers in the study area. The results reveal that the Ordovician reservoirs are mainly composed of reef beach sediments. There are numerous karst caves and fractures, which control the relatively high-permeability accumulation of oil and gas. As porosity and permeability of a reservoir increase, capillary force differences between the reservoir and its surrounding rocks increase. Consequently, there is a higher probability that the reservoir contains oil and gas, and the degree of oil saturation increases. The critical capillary force for oil and gas accumulation is 2.5 MPa. Fractures in Ordovician source rocks show complicated distributions. They intersect each other to form ten oil and gas filling points, and control oil and gas accumulation near these filling points. When far away from these points, oil and gas filling becomes less intense and their yield decreases. The geochemical properties of oil and gas show regular variations. The critical distance for oil and gas accumulation is 20 km from a filling point. Under the joint control from reservoirs and fractures in source rocks, oil and gas show an accumulation mode characterizing "relatively high permeability near filling points" in which reserves are first formed near filling points in high-permeability reservoirs.

Key words: reservoir, fault, source, hydrocarbon accumulation, Ordovician, Tazhong Uplift