Characteristic and Dynamics Mechanism of Low Potential Controlling on Hydrocarbon Accumulation

The formation and distribution of hydrocarbon accumulation are controlled by the fluid potential in oil-bearing basin. The distribution characteristics of discovered hydrocarbon accumulation in the Jiyang superdepression show that hydrocarbon could only be accumulated in the reservoir rock where the potential varies from 2 to 100 times of the potential of the surrounding rock. A certain critical value of porosity is necessary for hydrocarbon accumulation in depth. The research also suggests that the porosity decreases and the critical formation condition of hydrocarbon accumulation changes with the burial depth. The trap in the deep burial depth should meet the condition of relatively lower potential compared with the trap in the shallow burial depth. The dynamic analysis and physical experiments also show that the premise condition of hydrocarbon accumulation in the surface of the earth is pore radii in the reservoir rock is double of that in the surrounding rock. The premise condition of hydrocarbon accumulation in the underground reservoir rock is the capillary pressure disparity higher than the sum of capillary pressure and the stratigraphic pressure in the reservoir., which suggests that the lower potential in the trap would cause the higher oil saturation and resources in the reservoir. The characteristics and dynamic analysis suggest that hydrocarbon can be accumulated in the deeper reservoir with low porosity and permeability only if the physical property of reservoir is better than that of the surrounding mudstone, which could extend the hydrocarbon exploration domain and depth. The characteristics also suggest that sand with relative low porosity and permeability can be cap rocks for sand with relatively high porosity and permeability, which could broaden the favorable exploration area in the shallow strata.