Abstract:
To reveal the enrichment characteristics of shale gas in the southeastern Ordos Basin, shale samples from Yan'an exploration area were selected for geochemical tests of organic matter, rock pyrolysis, and vitrinite reflectance.At the same time, a large number of experimental methods such as thin section identification, whole rock, and clay minerals, shale gas analysis, and isothermal adsorption were carried out to discuss the main controlling factors of shale gas enrichment in Shanxi Formation in the study area.And the following research results are obtained: ①The total organic carbon(TOC) varies widely in the shale of Shanxi Formation shale, and the type Ⅲ kerogen is the main one.The average value of
Ro is 2.48%, which is in the high mature-overmature stage.②The organic carbon content, pyrolysis parameters free hydrocarbon(
S1), and pyrolysis hydrocarbon(
S2) are positively correlated with the content of desorption gas and isothermal adsorption gas.The vitrinite reflectance
Ro is positively correlated with desorption gas, residual gas, and total gas content, indicating that the abundance of organic matter and thermal evolution maturity control the content of shale gas directly.③The physical property test data of the shale reservoir show that the porosity is low, with an average of 0.77% and an average permeability of 0.039×10
-3μm
2, and the physical property is directly proportional to the shale gas content.The clay mineral content is high, ranging from 57.87% to 60.28%, mainly composed of the illite/montmorillonite mixed layer and kaolinite.With a high specific surface area, which is conducive to improving the gas adsorption capacity of shale.But the clay mineral is inversely proportional to shale gas production.④The formation excess pressure at the end of Early Cretaceous in the shan1 member is relatively high, and the excess pressure in the Yanchuan-Zhangjiatan-Yunyan-Yichuan line is above 10 MPa, which plays a decisive role in the preservation of shale gas.In conclusion, high organic matter abundance and high maturity are the basic control factors of shale gas enrichment in Shanxi Formation of Ordos Basin.Secondly, the physical properties show that the test samples have high permeability and the formation excess pressure at the end of Early Cretaceous in the shan1 member is relatively high, which provides important preservation conditions.