Study On Micro-pore Structure Of South-eastern Sulige Gas Field In Ordos Basin

Now it is difficult for low permeability reservoirs to have an economic production effect, even the same gas region has different development degree and different development difficulty. The reason consists in different micro-pore structure rather than low permeability that makes low permeability reservoir different form high permeability reservoir. The characteristics of Sulige gas field, such as low abundance, low porosity, low permeability and low well yield, makes huge cost of investment and increases the difficulty for developing. Based on the achievements of predecessors, this study utilizes conventional and unconventional methods to analyze the sedimentary facie and petrology in He-8reservoir Sulige gas field in both microcosmic and macroscopical ways, but mainly focuses on micro-pore structure. The main conclusions of this study are presented as follows:(1)The sedimentary facie in He-8reservoir is braided river delta front sub-facie which mainly developed underwater distributary channel and distributary inter-channel bay. Horizontal bedding, grain of small sand bedding and massive bedding are developed in rock stratum.(2) The major rock type of the reservoir is mainly medium and coarse debris-quartz sandstone or quartz-debris sandstone. The debris fragments consist of quartz and metamorphic debris. Interstitial materials mainly includes kaolinite, illite, ferrocalcite, siliceous. Dissolution makes dissolved pore so developed.(3) The main space and chief pore types in He-8reservoir are dissolved debris pore and intercrystalline pore, feldspar dissolved pore, microfissure and intergranular pore.The pore assembly types mainly comprise dissolved pore-intergranular pore and intercrystalline pore-dissolved pore. The type of throats includes control shape throat as wellas punctual throat, laminated throat and curved lamellar throat.(4) The experimental results and analysis of high pressure mercury penetration demonstrate that a few big pores and throats in this region that increase the connectivity while the sorting is poor in whole the area. The capillary pressure curve towards left-and-down part as a whole with poor plateau phase. Most mercury intrusion comes with double peak. The relativity between both medium radius, max pore-throat radius and physical property is highly verified. The contribution curve of pore-throat-to-permeability demonstrates that0.04μm is the limitation radius for effective pore and throat.(5) The experimental results and analysis of constant pressure mercury indicates that the average radius of pore in this region is stable while the average radius of throat is unstable. Porosity is mainly controlled by throat radius and the space of pore and throat.Through the comparison of sample5and sample7concludes that it is the distribution range of throat radius virtually determines permeability rather than the magnitude of throat radius.Generally, the micro-pore structure essentially determines the physical property of reservoir and big radius pore and throat increase the reserving space in reservoir. The ability to flow is determined by the reasonable distribution of both pore and throat.