陆相页岩气富集主控因素——以鄂尔多斯盆地延安探区山西组为例

    Main controlling factors of continental shale gas enrichment: A case study of Shanxi Formation in Yan'an exploration area, Ordos Basin

    • 摘要: 为揭示鄂尔多斯盆地东南部页岩及页岩气富集特征,选取延安探区页岩样品进行岩石热解、镜质体反射率、页岩解析气、等温吸附等实验分析,对研究区山西组页岩气的富集主控因素进行详细的探讨。结果表明:①有机碳总量变化范围较大,以Ⅲ型干酪根为主。镜质体反射率Ro平均值为2.39%~2.51%,处于高成熟—过成熟阶段。②有机碳含量、热解参数游离烃(S1)及热解烃(S2)均与解析气含量、等温吸附气含量呈现正相关性,镜质体反射率Ro与解析气、残余气及总含气量具正相关关系。③储层孔隙度较低,物性与页岩气含量成正比;粘土矿物含量较高,比表面积高,有利于提高页岩对气体的吸附能力,但是粘土矿物含量与页岩气产量成反比。④山1段早白垩世末期地层过剩压力较高,延川—张家滩—云岩—宜川一带的地层过剩压力基本在10 MPa以上,地层过剩压力对页岩气的保存具有决定作用。研究结果认为,页岩气的富集主控因素为高有机质丰度、高热演化程度,其次物性显示测试样品渗透率较高、早白垩世末期的地层过剩压力较大,为页岩气提供了重要的保存条件。

       

      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 0.039×10-3μm2, 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.

       

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