| As typical representative of the continental shale gas, geological conditions of shale gas are developed great in the large-scale continental depression basin of the Ordos Basin. There are not only hydrocarbon discovery sandstone reservoirs, but also widespread organic-rich mudstone in Yanchang formation. The lacustrine mudstone of the Yanchang Formation is taked as target stratum. Combined geological information with experimental data, this article uses core observation and field survey. Based on the accumulation conditions, development model of continental shale gas is discussed.Taking major inland basin as background, fluvial and lacustrine facies are primary terrigenous clastic sediments in the Yanchang Formation. Controlled by the north-northeast sediment source, there are mainly developed delta front intrafacies in the researched area of Chang 9, and distributed shallow lake subfacies in southern of researched area. And controlled by the northern sediment source, there are mainly developed shallow lake and semideep-deep lacustrine subfacies in the researched area of Chang 7. The Chang 7 shale is better than Chang 9 shale in thickness and distributed stability.The Yanchang Formation lacustrine shale are mainly developed type Ⅱ1 kerogen, it has higher Organic carbon content(2.0%-3.0%) and lower maturity(0.75%-1.5%). The Chang 7 shale indicators of organic matter abundance are better than Chang 9 shale. Based on the analysis of burial history and history, the organic matter hydrocarbon-generation condition is better and intended interval reach oil-generating window in late period of Late Jurassic to early of Lower Cretaceous. The gas potential is graet in the west of researched area.The mineral composition is similar in Chang 9 shale and Chang 7 shale. It is dominated by quartz and clay mineral, carbonate content is small, and a small amount of plagioclase, potassium feldspar, siderite and pyrite. And the clay mineral is dominated by I/S mixed-layer mineral. Through the core observation of single well, bedding fractures is widespread. The shale reservoir space is inorganic-porosity. The results think that mesopores is chief pore distribution of shale.The adsorption capacity of Yanchang shales match with high-productivity shale of American according to isothermal adsorption experiment. The result of site desorption test showed that the gas content of Chang 9 shale is lower than Chang 7 shale. The ratio of free gas content to adsorbed gas content is from 0.24 to 4.38, the average value is 1.0.There are three development models of continental shale gas. First, it is shore lake facies or paludal facies in general, kerogen is mainly develops type Ⅲ, the buried depth of objective interval is shallow, and thermal evolution degree of shale is in primary stage and in gas-generating window. In the Second, it is usually shallow lake facies, kerogen is dominated by type Ⅱ-Ⅲ, the main product is oil-gas coexistence in general. The third thing is, it always distributed in semi-deep lake facies, type Ⅱ-Ⅱ kerogen is given priority, the buried depth of objective interval is deep, the thermal evolution degree of shale is in higher stage, and the product is dominated by oil-gas coexistence or cracking gas. According to the geological background, gas-generation condition, reservoir condition and gas content analysis of shale, indicate that accumulation conditions of shale gas are superior in the southwest of researched area, there are large thickness, stable distribution, enormous potential of gas-generation, high gas content and so on. The results think that shale oil and gas is symbiosis in researched area, and the ratio of gas to oil is 0.68. |
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