Shale Lithofacies Classification And 3D Geological Model Of The 7^th Member Of Yanchang Fm. In Ganquan Area, Southeastern

It is indicated from North American shale gas exploration that lithofacies classification based on the gas content and brittleness is important for evaluation and favorable area prediction. Shale in 7th member of Yanchang Fm. is widely distributed in Ganquan area, Ordos Basin, with large thickness and high abundance of organic matter, known as the hydrocarbon source of the adjacent reservoirs. In recent years, this area was confirmed as the shale gas exploration prospect by implementing of many shale gas wells.In this paper, shale thickness distribution in 7th member of Yanchang Fm. was researched by means of logging data, including into log response of pure shale, silty shale and argillaceous siltstone. Rock pyrolysis and total organic carbon test were used to study the organic matter type and total organic carbon. Core X-ray diffraction (XRD) was detected to analyze mineralogical characteristics of shale formation. By using triaxial mechanics test, characteristics of shale mechanics were analyzed, and the brittleness was discussed by choosing the ratio of the normalized of modulus and Poisson's ratio as the brittleness index (I). Based on isothermal adsorption experiment and gas content of log interpretation, adsorbed gas, influencing factors and the proportion of different occurrence of shale gas are comprehensive researched. On these bases, shale lithofacies classification and 3D geological model are established and favorable areas were predicted. The research results are concluded as follows.(1) Organic matter types are mainly composed of type I and type ?1, Ro values range in 0.83%?1.10%. TOC content mainly ranges between 1.0% and 8%. Clay mineral is 22.5%?68%. Quartz ranges from 7.3% to 30.8%. Feldspar ranges from 5.3% to 47.5%.Carbonate and pyrite is little.(2) Total strain of shale is bellow 0.65%, and silty shale is 0.70%?0.89%. It generally shows as a "short elastic and plastic". Modulus of shale is between 13.5GPa and 23.9GPa, silty shale is 15.09GPa?25.4GPa. Poisson's ratio of shale ranges from 0.13 to 0.43, silty shale ranges in 0.18?0.32. Modulus and Poisson's ratio of different lithology have big difference.(3) Total gas content ranges from 2.18cm3/g to 5.41 cm3/g. The proportion of adsorbed gas content is between 27.8% and 87.5%; with an average of 56.1%. It was dominated by adsorbed gas in total gas content. The ratio of free gas content is 4.1%?48.2%, with average of 32.4%. The dissolved gas is relatively less.(4) Four lithofacies were classified according to three criteria:TOC data, clay mineral and brittleness index (?) in 7th member of Yanchang Fm. Then,3D geological model of lithofacies was built, and organic siliceous shale and siliceous shale were confirmed as advantageous shale lithofacies. Finally, based on advantageous lithofacies thickness, the favorable areas types were divided and predicted.