The Evaluation Of Chang 7 Shale Gas Reservoir Characteristics In The South Of Ordos Basin

The study is based on the reservoir of Chang 7 formation, the south of Ordos Basin.By collecting and researching the large number of geological data in the study area, and making full use of field outcrops, drilling, logging, well logging and thin section analysis data, SEM, organic geochemistry and a variety of analysis methods. The paper systematically studied the southern Ordos Basin, and comprehensive evaluation the reservoir characteristics of Chang 7 formation.Research shows that the Chang 7 formation is half deep lake- deep lake facies, it is the favorable facies of rich organic shale development. The thickness of dark mud shale in the study area is larger, and the distribution is stable. By using the lithology, lithofacies and X-ray diffraction of whole rock analysis, we have found out that the dark mud stone of Chang 7 formation is basically iron fine silty mud, fine silt stone, iron mud stone, carbonaceous shale, and mostly fine silty coarse silt. The clastic composition are mainly quartz, feldspar, mica, and a small amount of acidic extrusive rock, metamorphic rock and other debris. Brittleness mineral content is high, just as the Barnett shale in American. The dark mud stone of Chang 7 formation contain highly organic matter, the hydrocarbon potential is much more higher than the ordinary mud stone.Organic carbon content between 0.88 to 25.46%, with an average content of 4.96%. Type of Kerogen in type Ⅱ. Vitrinite reflectance between 0.52-1.13 %, into the hot oil and gas phase catalysis. By scanning electron microscopy revealed Chang 7 shale pore types to intergranular corrosion pores and micropores. Chang 7 shale porosity distribution in the range between 0.5%-3.5 %,with average value of 1.82%; Permeability less than 0.01×10-3μm2. More exploration wells in the study area in the Chang 7 shale gas test show abnormal, gas for the pyrolysis of organic origin, mode of occurrence adsorption state, free and dissolved coexist. Drilling coring measured gas content greater than 2m3/t, containing gas is affected by multiple factors.According to the conditions of shale gas accumulation, and the standard of shale gas reservoir evaluation, this paper is using the three parameters: the thickness of dark mudstone, total organic carbon(TOC) and organic matter maturity(Ro). and other related parameters to predict the favorable target area of shale gas in Chang 7 formation, and provide the reference to the exploration and development in other regions.