The Study Of The Shale(Gas) Features In Upper Ordovician-Lower Silurian, Uplift In The Northern Of Guizhou

As one of the best source rocks in China, the Upper Ordovician WufengFormation--Lower Silurian Longmaxi Formation black shale located into thenorthern margin of Guizhou Province is generally regarded as a potential reservoir forshale gas. However, there are only few studies on the reservoir parameters. Based onthe organic geochemistry, mineralogy and adsorbed gas capacity etc., we haveconducted a systematic research on reservoir features of the black shale in the Qilongsection, southern Sichuan basin.The sedimentary environment of Wufeng-Longmaxi formation is theshallow-water shelf and deep-water shelf in turn:(1) The black shale of the Wufengformation is the deep-water shelf,(2) Guanyinqiao segment of the Wufeng formationis the shallow shelf,(3) The black shale of the bottom Longmaxi Formation is thedeep-water shelf,(4) The mudstone-limestone of the top Longmaxi Formation is theshallow-water shelf. The obvious sedimentary environment differences of the blackshale directly lead to the differences of the main organic parameters, such as TOC.The black shale enriching with high TOC distribution in the bottom of the Wufengand Longmaxi Formation is the best segment for shale gas.In the study area, the black shale of the Wufeng-Longmaxi Formation dominatedby I-II1types of kerogen, rich aboundent of organic contents (TOC range from2.0%to8.0%). Effective thickness was more than30m. Vitrinite reflectance (Ro) wasgreater than1.8%, generally in2.4%~3.6%, has been in over mature evolutionarystages. The Ro of the core region was more than1.6%(Maximum of3.6%), Tmax≥470°C.The minerals in the black shale of the Wufeng-Longmaxi Formation are mainly composed of clay minerals (illite and a small amount of chlorite, montmorillonite),quartz, feldspar, barite, gypsum and pyrite, et al. The clay content gradually wasincreased and the quartz content gradually was reduced from base to top. There is apositive correlation between the TOC and the content of quartz mineral, and anegative correlation between the TOC and the content of clay.In the study area, at the bottom of the Wufeng-Longmaxi Formation, the densityof black shale was range from2.16to2.65g/cm3, with an average of2.47g/cm3. Theporosity of black shale peaked in4%~8%, with an average of6.17%, and other rockspeaked in5%~10%, with an average of6.63%.Four pore types are recognized in the black shale of the Wufeng-LongmaxiFormation： intergranular pore, intragranular pore, fracture and organic pore.Intergranular pore and intragranular pore were the main pore types. The surface areawas between4~32m~2/g, peaked around22m~2/g.The pore volume was range from0.008ml/g to0.032ml/g, with an average of0.02ml/g. Pore size distribution ofdifferent lithology were present three-section significantly：<6nm，6~11nm，11~1000nm.In the study area, the Langmuir volume of the black shale was range from1.17to4.36cm~3/g,with an average of2.41cm~3/g. Siliceous minerals (mainly quartz) and theorganic matter in the black shale was the main internal control cause of themicroporous. At the same time, there is a positive correlation between the porevolume and the surface area of the microporous (<10nm) with the methaneadsorption, which further confirmed that the Organic matter microporous was themain factor influencing the gas content of the black shale.