The Study Of Shale Gas Enrichment Pattern In The Dongyuemiao Member Of Ziliujing Formation Of Lower Jurassic In Northern Sichuan Basin, China

Tons of research data show that the shale gas resource in China is rich, and the enrichment conditions are similar with the USA.Owning to the different geological conditions, it is hard to copy the American development model, and should pay attention to geological characteristics of shale gas. The investigation of shale gas resources from Dongyuemiao member of lower Jurassic in north Sichuan basin holds that it is mainly controlled by lacustrine deposition, and contains brittle mineral. Therefore, the resource potential is well, and it may be beneficial to fracturing treatment. However, it buried so deep that has lower overall exploration degree, so the gas enrichment pattern can be researched detailed here, and find the “sweet sopt” to guiding the production.Using comprehensive research to analyse gas enrichment pattern of Dongyuemiao member in research region, the paper gets following understandings:(1) There are two types of sedimentary facies in research region: lake and lacustrine delta. The lakeshore, shallow lake and semi-deep lake facies are widely distributed.(2) To established a division standard for shale in the study area: in sandstone and limestone section, the oil and gas system is that layers continuous thickness >2m and mud-strata ratio <40%; In shale section, the oil and gas system is that layers continuous thickness >9 m and mud-strata ratio >60%.(3) The organic geochemical analysis illustrates the important information: the kerogen is primary in type III, the proportion of type II1 and II2 is high additionally; the organic matter abundance shows they are better hydrocarbon source rocks; the organic matter maturity displays in the stage of condensate-wet gas; but the gas-bearing property is inferior to the United States.(4) The shale is mainly include clay mineral and quartz, the feldspar and calcite can be found sometimes. The content of brittle mineral is more than the overall average, illustrates the shale has good brittleness, and the compressive strength is lower.(5) The physical analysis shows some informations: the shale primary developed organic pore, inorganic pore(intragranular, intergranular and intercrystalline pore), and fracture systems(macro and micro cracks); it has higher average of porosity and permeability, and porosity and permeability showed a positive correlation.(6) Research on the reservoir-forming mechanism displayed that the gas content is controlled by temperature, pressure, TOC, thermal evolution degree, mineral composition, pore and fracture, and the sedimentary facies, lithofacies, fractures and barrier layer determined shale gas enrichment. According to the above, the favorable areas can be decided in western Yuanba, southeastern Yuanba to Yilong and Northwestern Dazhou region.