Study On Micro Geological Feature Of Tight Sandstone Gas Reservoir At Eastern Part Of Sulige Gas Field, Ordos Basin

He8and Shan1formation of upper palaeozoic at the eastern part of Sulige gas field, Ordos basin have the feature of ahead tight and accumulation later without a unified water-gas interface. Micro pore structure feature controlling the favorable reservoir distribution results in low gas saturation, poor property and pretty much difficult development et at. Because of lacking relative deep study of micro geological feature at the study area, this paper is based on a serious of core analysis experiments including cast thin section, image pore, particle size analysis, scanning electronic microscope, high pressure mercury intrusion, gas-water relative flow experiments and currently advanced constant-rate mercury intrusion, nuclear magnetic resonance, all of which characterize micro geological features after core observation and then selection of representative samples. Detailed characteristics of reservoir space and micro fluid flow are analyzed to provide comprehensive classification and evaluation of sandstone with micro geological basis, which leads to the following results:(1) Reservoir space is complex and classified by pore formation principles as residual intergranular pore, dissolved pore, intercrystalline pore and micro cracks et al which mainly consists of debris dissolution and intercrystalline pore and less either feldspar or tuffaceous dissolved pore.;(2) Complex pore-throat structure which mainly consists of Ⅲ and Ⅲ class with poorer structure, more uni-pore type, larger amounts of micro pores has the pore radius around80-210μm and throat radius around0.2-1.8μm with relative large discrepancy. The permeability of reservoir depends on the configuration of pore and throat which mainly controls reservoir;(3) The moveable fluid saturation varies a lot (8.48%-32.67%) and is low as a whole (averagely21.67%), which is divided into IV and V classes. The gas-water relative flow curves are classified into Ⅰ, Ⅱ, Ⅳ, Ⅴ classes and along this sequence it is becoming more obvious that the ratio of gas and water relative permeability declining, synchronously flow range of two phase narrowing, irreducible water saturation increasing, capability of fluid flow turning bad correspond with the accretion of water saturation;(4) On the microscopic scale reservoir permeable radius is divided into moveable, transition and immoveable sections which correspond with the radius ranges:0.25μm,0.1-0.25μm,<0.1μm respectively. Transition section is controlled mainly by pore and moveable section can be controlled by pore-throat and pore respectively. The poorer the pore and throat structure is, the more narrow the moveable section of pore dominance is;(5) From aspects of micro geological features reservoir quality can be divided into four classes. The discrepancy of reservoir quality depends on the diagenesis intensity. The distribution of pore-throat radius dominates the initial water saturation and then gas relative permeability, moveable fluid saturation and recoverable reserve. I class has high and stable production and Ⅱ class has low and stable production, both of which should be developed with main interest. Ⅲ class has low production and IV class has little industrial potential, both of which have developed potential.