Accumulations Of Natural Gases And Their Controls In The Langgu Depression

Langgu Depression is rich in natural gas resources, which makes it recently the keydirection in Huabei Oil Field. There are some fundamental problems such as indistinct genetictypes of natural gas, unknown origin source of hydrocarbon and the unavailable maincontrolling factors of accumulation are needed to be settled. Hence, these are chosen as mainissues of PhD dissertation.Various data and theories of geology, organic geochemistry and geophysics are utilizedto analyze the generated natural gas and associated crude oil. Research shows that there arefour genetic types of end-gas including biogas，low-mature gas，mature gas and coal-relatedgas. And it finds out three kinds of source-mixed gases namely mixture of biogas andlow-mature gas, low-mature gas and mature gas，coal-related gas and low-mature gas. Thisdissertation evaluates the distribution law of vari-kind natural gas and analyzes the keyelements of accumulation and their controlling factors.Research indicates different genetic natural gas accumulation is controlled byHydrocarbon source rocks evolution and Hydrocarbon generation stages. Developmentcharacteristics of the source rocks in Es4upper section, Es3lower section, Es3middle sectionand Es3upper are estimated systematically. Results demonstrate that the low-mature gas isgenerated from Es3lower section and Es4upper section of Langfang-Jiuzhou,Hupoying-Caojiawu and Gu’an effective hydrocarbon kitchens respectively. The mature gasgeneration is located in some sag. Under the Jiuzhou and Daxing fault action, part of Es3islifted to the biological action zone with the surface water invasion and then biogas namedepigenetic biogas in this dissertation is generated and accumulated in Liuquan area et al. Thecalculations of resource potential are56.42×10⁸m³of biogas （epigenetic biogas） and10.7×10¹²m³of low-mature gas respectively.Fault is another crucial controlling factor of natural gas accumulation. Analysis in faultclosure and activity indicate that SGR more than0.7can block off oil effectively and SGRmore than0.8can block off gas effectively （partly more than0.9）. Meanwhile, research onstatic elements and dynamic process, such as fault evolution, reservoir-cap combination and preservation condition et al. in downthrow side of Daxing fault, Liuquan-Caojiawu structureand Hexiwu structure establishes five different natural gas accumulation models which are themodel of self-generating and self-preserving accumulation in glutenite fan in downthrow sideEs3of Daxing fault, the model of epigenetic biogas accumulation in superficial part ofLiuquan structure, the model of low-mature gas accumulation in semideep part of Liuquanstructure, the model of complex accumulation of two-way duplex in Hexiwu structure and themodel of low-mature gas accumulation of reverse fault block in Hexiwu structure.The results of research indicate that the southwest of Liuquan-Caojiawu structure is thebeneficial exploration target to find epigenetic biogas and glutenite fan within the depth of thedownthrow side ravine and slope in Daxing fault with pressure coefficient between1.1and1.4, Hexiwu structure and reservoir-cap combination and trap formation in southern anticlinein Hupoying are beneficial exploration targets to find mature gas.