Controlling Effects of Poor Permeable Layers upon Accumulation and Distribution of Hydrocarbon in Inhomogeneous Sandstone Reservoir

Based on capillary pressure theory, the accumulation and distribution of hydrocarbon in inhomogeneous sandstone reservoir with complicated pore structures were analyzed. It was concluded that the accumulation and distribution of hydrocarbon in inhomogeneous reservoir were predominated by the poor permeable layers (barrier beds). The analysis demonstrated that the transition intervals would be long in inhomogeneous reservoir with moderate to low porosity and permeability. The entrapment in this kind of reservoir requested larger closure height. In the situation of limited closure, the poor permeable layers resulted in sealing process and formed non-saturated, both hydrocarbon and free water-bearing stratum with broader distribution vertically. The production ability was much limited because of the low effective permeability in the porous media with two-phase liquid system. All those features bring about a contradiction between the gas logs, well logs and the well testing. The well log responses and characteristics of this reservoir were also discussed in this paper both theoretically and by the case study. Generally, the correlation in well logs between the hydrocarbon saturation and the porosity in this formation became obscure and difficult to distinguish due to the great changes in porosity and saturation of the reservoir vertically. A case study was also presented and proved a good evidence of the above theoretical deductions.