Study On The Relationship Between The Fracture Evolution And Oil And Gas In Yubei Area

Since have made a major breakthrough in oil and gas exploration so as toaccelerate the pace on exploration，analytical study of tectonic fault zone in Yubeiarea also put forward higher requirements. Therefore, the style of the fault zone inYubei area, active times, activity intensity, and the relationship with vuggy karstreservoir development, systematic in-depth study is very necessary. In this paper,the latest application of the study area strata, earthquakes and drilling data as thebasis for a lot of seismic description work to fine and in-depth analysis the fivemain fault zone in the study area. This thesis mainly made the followingunderstanding:（1）The fracture system can be divided into3sets of structural layers, frombottom to top respectively the lower structural layer (sinian period to the middleand lower Cambrian), the middle structural layer (upper Cambrian to ordovician),the upper structure layer (carboniferous to Permian). Lower structural layers aredeveloped basement-involved steep occurrence fracture, and the basement rockshave ups and downs; the main fault zone in YuBei area developed in the middlestructural layer, there has developed the thrust nappe structure along the creamsalt rocks under the T81face, and a large number of the thrusts were testedshovel-like, more steeper on the up section,the lower part of the fault plane andCambrian paste layers are almost parallel; the main thrust in the upper structurelayer had further inheritance thrust activity only appeared in the YuBei1fault belt,the rest of the study area tectonic fault fracture has no active again, the formationjust has a slight fold deformation. Can be thought that the plasticity salt layers inthe middle Cambrian layer and the basement relief were the main geologicalfactors to control the fault zone emerged under the background of extrusion.(2) Study of the five fault zone in the Yubei area believed that most fractureare thrust fault, part of the fracture with a strike-slip characteristics, stretch faultonly developed in the middle-lower Cambrian. According to the combination offault characteristics on the bisect, tectonic style mainly include the type of thebasement involved tectonic and the cap slipped and the composite superimposed three kinds. Influenced by superposition of multiphase tectonic deformation, thefirst two structural styles are always confined in certain formations, the morefracture shows as composite superimposed tectonic style. The fracture in thestudy area are superposition of the basically basement involved and the capslipped fracture of the upper formations.(3) The five fault zone in the study area had two main evolution stages,except YuBei1fault belt (with three evolution stages): In the early caledonian,the Tarim block was in a stretch environment as a whole, mainly on normal fault,there developed some small steep normal faults in the basement in the study area;in late Caledonian-early Hercynian, was the main period of developing the capslipped thrusts, and have2-3row recoil fault development, the main thrust faultno longer Inherited activitied again later, there only had slightly deformation inthe formation on the top of the fracture. YuBei1fault belt in addition to the abovetwo stage of evolution, in the late hercynian, the main thrust fault inheritedactivitied again, the fault entered the Carboniferous-Permia formation andcontrolled the flexure deformation of the Carboniferous-Permia formation. Later,structure was stable, fracture shaped completely, all fracture without anyactivities again.(4) The fault zone in the YuBei area have a great influence on reservoirdevelopment that reflected in two aspects,(1) Near the fault zone due to thetectonic fracture effect where produced a large number of cracks and microcracks,due to controlled by a large number of the north east trending faults in the area,the ordovician reservoir in the YuBei aera is given priority to with crack, crack-dissolution pore,cave, oil and gas accumulation was controlled by fracture andreservoir development degree, strong heterogeneity;(2) the fracture and thedevelopment of the corresponding structural fractures connected the surface waterand the reservoir, along the fracture and the reticular cracks produced insidertype of solution pores, with the fracture evolution, Yubei area developed Calgaryto the early Hercynian three superimposed karst.(5) This paper puts forward the oil and gas accumulation patterns of theYuBei area: in middle Caledonian-early Hercynian period, in YuBei area withinthe ordovician yingshan group had developed karst reservoir, the development ofNE connected Cambrian source rocks deep and large faults play an importantrole in the process of oil and gas migration, but due to the lack of effective caprock of the ordovician reservoir, and the fracture has been extended to the surface, thus the main structural belt is given priority to with destruction and loss of oiland gas; late hercynian, Cambrian hydrocarbon source rock generated a greatquantity of hydrocarbon, the ordovician trap in the YuBei area shaped at the sametime, have a good reservoir and caprock, at this point, the early fracture activitiedagain and the formation of the new fracture become a good channel of oil and gasmigration, and accumulated into reservoir; Himalayan, faulting in the area isweak, because lack of effective hydrocarbon migration channel, could not form anatural gas reservoir.