Kuqa Depression Overthrust Fault Sealing And Fluid Migration

Through the research on the development character of overthrust fault, we analyzed its sealing mechanism. We also established evaluation standard and method of fault sealing ability through the following two simulation experiment: experiment on the quantitative relationship between property of fracture zone filler and fault sealing ability; experiment on the deformation character of cream shale. Based on these work, we evaluated sealing ability of overthrust faults on several typical structure in Kuche depression. The result is that most current faults are sealed. This is the main condition for natural gas and abnormal pore pressure to preserve in Kuche depression. We have also studied fracture formation and moving period by means of growth triangle zone and equilibrium section technology. The result is that fracture formation period in diffirentt struture zone are very d'rffirent. The basic law is that from the north to the south, the fracture formation period is later and later. But the main fracture moving period is Kuche - Quaternary. Based on these research, we recovered the evolution history of overthrust faults vertical sealing ability and considered that there always have fracture activity ever since Jidike formation deposition period. But this kind of activity is not always continuous. During moving period, fault is open. During static period, fault is dosed. We established geological and mathematic model for the relief of overthrust fault and earned out simulation computation after selecting factors. The result is that pressure can be released when fault is open. But ft will take a long time for the formation pressure to be relieved to normal formation pressure. This is not enough for the superpressure in the trap to be relieved. This is the other main reason for the overpressure in Kuche depression to be preserved. We analyzed the effect of fracture in the gas deposit formation and hold that different kinds of fracture have different effect: hydrocarbon dissipation and relief effect of crossing salt bed faults that run through source rock, reservoir, and caprock; filling effect of under salt bed faults that run through source rock and reservoir; slippage faults that did not connect source rock have no effect to hydrocarbon accumulation and dissipation; adjusting faults in reservoir have effect of adjusting formations for hydrocarbon distribution. We also summed up four kinds of faults combination transportation model: the model that under salt bed fault and crossing salt bed fault are connected by faults; the model that under salt bed fault and crossing salt bed fault are connected by reservoir, the model that under salt bed fracture and crossing salt bed fracture are connected by reservoir and breakthrough faults at the top of the trap; single crossing salt bed model. We studied gas deposit formation process of several typical structure in Kuche depression by these models. Failure wells were also analyzed. The result is that the first and second model are favorable to gas deposits formation. The third model can not formbig gas deposit because breakthrough faults developed at the top of the trap. The fourth model are very drfficuft to form gas deposit because the short of gas filing passage. Based on these research, we analyzed gas deposit formation character of Kuche depression and concluded three kinds of gas deposit formation model. They are: Kela 2 model, Kela 3 model; Tuzfluoke model. The models are important guide for next step exploration in Kuche depression.