Research On Fault Sealing Characteristics Of Xicaogu Tectonic Belt,Shulu Depression,Southern Jizhong

The study area is Xicaogu tectonic belt located in the south of Shulu depression with “nose shape” structural configuration.The traps in the area are mainly sealed by fault systems in which the hanging walls are confirm by coring that they contain faults breccia and shale smear with sealing ability.Caprock and interlayers in different classes resulted from various sedimentary environments divide the study area into several oil systems isolated to each other with different OWC,which means the oil possibility of these traps are different.The oil reservoirs in study area distribute in narrow strip shapes along the faults and the OWCs or Hydrocarbon column height in these oil reservoirs varies because of lateral fault sealing ability.The thesis identifies traps,seals and interlayers,divides the reservoirs into high resolution oil-water units,and determines the OWCs in each oil system as well as hydrocarbon column height according to well logs and reservoir data.A quantitative evaluation mode about lateral fault sealing ability is also established based on shale gouge ratio(SGR)and across fault pressure difference(AFPD)due to high resolution division of oil-water units: lateral fault sealing ability will be strengthen while SGR increasing;and the floor level for SGR of lateral fault sealing ability is 16%.For practical application in oil fields,fault throw-hydrocarbon column height evaluation mode is also set up: effective hydrocarbon accumulation of Xicaogu tectonic belt will occur when the fault throw exceed 25 m.In the process of setting up lateral sealing ability,there are influences caused by the amplitude of fault trap,hydrocarbon injection and tectonic reactivity during the latter part of hydrocarbon accumulation: when the amplitude of fault trap is small but the hydrocarbon injection is plenty,the evaluation results will be smaller than the ability actually;when the tectonic trap reacts during the latter part of hydrocarbon accumulation but hydrocarbon injection is little,the hydrocarbon in traps will redistribute which will also made the evaluation results smaller than the ability actually.