Shale Gas Reservoir Conditions Analysis Of Middle Jurassic In The Northern Qaidam Basin

A thorough study has been performed on shale gases from the Middle Jurassic Shimengou Formation and Dameigou Formation in the northern Qaidam Basin to understand shale distribution, geochemical characteristics, buried depth, mineral composition, reservoir performance and gas-bearing.The result shows that the organic rich shale of Shimengou Formation thickness between 50~250m, wide distribution and depth difference, high abundance of organic matter, organic carbon content is generally higher, the average is 4.63%, the maximum is 17.05%, Type of organic matter in Ⅰ-Ⅱ2 main type; Dameigou Formation shale thickness between 20 ~ 100 m, organic carbon content, an average of 5.2%, up 21.76%, organic matter type to Ⅱ1-Ⅲ type-based; two shale thermal evolution of low maturity based, high maturity reached in some areas.Shimengou Formation shale, the average content of 27.6% quartz, clay minerals average of 35.7%; porosity distribution between 1.5% ~ 15.6%, with an average of 7.1% and permeability distributed in 0.003 × 10-3μm2 ~ 6.24 × 10-3μm2, an average of 0.296 × 10-3μm2. Dameigou Formation shale quartz content of 36.98% on average, 56.5% of clay minerals; porosity distribution between 1.8% ~ 9.2% with an average of 4.9% and permeability distributed in 0.002 × 10-3μm2 ~ 0.3μm2 an average of 0.185 × 10-3μm2. Shale micro pores mainly between intergranular porosity, dissolution pores, shale porosity, organic matter nanopores and endogenous crumbs body bore; more developed cracks and micro cracks based.Through field desorption experiments, straight-line method and polynomial curve fitting to Shimengou Formation shale gas test sample, the desorption gas is 0.04 ~ 0.32m3/t, the loss of volume 0.03 ~ 0.47m3/t, the residual volume of 0.04 ~ 0.08 m3/t, total gas is about 0.42 ~ 0.83m3/t. By desorbed gas methane carbon isotope analysis of desorbed gas δ13C1 Yuqia region is-80.59 ‰ ~-61.89 ‰, biogenic; Sainan desorbed gas δ13C1 is-38.4 ‰ ~-39.9 ‰, the low-temperature heat Causes of gas; Xidatan area desorbed gas δ13C1 is-40.1 ‰, low temperature thermogenic gas.Finally, the study area of shale gas reservoir geological conditions conducted a comprehensive analysis, that the study area has good shale gas reservoir conditions and predict optimized Shimengou Formation four prospective areas were Sainan prospect, Yuqia prospect, Dameigou and North Delingha prospect; Dameigou Formation two prospective areas, namely the potential prospective areas Qianxi and Dameigou prospect.