Of Xinjiang Santanghu Basin, Permian Tectonic Fracture Study

Santanghu basin which lies to northeast of Xinjiang province is a type of rebuilt superposition sediment basin in late Paleozoic to middle Cenozoic which superposed on the fold basement of Paleozoic orogen belt. Permian to Tertiary strata comprises sedimentary cover of the basin.the Permian strata are main gas and oil reservoir of the basin,which possesses the low porosity and low permeability characteristics and the fracture is the main reservoir space.So the study on Permian structure fracture of Santanghu basin possesses important theoretical and practical significance.This paper keeps up the research principles of integration,dynamic and synthesis,on the basis of the analysis of geology evolvement make use of seismic data, core of drilled well information,microscopic study materical,paleomagnetism materical and experiment data study elementarily the characteristics of the fractures of the Santanghu basin and the fracture effecting on the low porosity and low permeability reservoir from geology and reservoir.After study ,we get to know that:Santanghu basin came through a long period of time of geology evolution and formed the structure pattern of one depression sandwiched by two uplifts from southwest to northeast which making up of thrusting nappe belt,the center depression belt and thrust uplift belt.The center depression belt is the important oil-bearing belt of Santanghu basin and the belt lacked upper Permian and late Trias trata being the Santanghu basin uplifted and denuded.Xishanyao group in mid-Jurassic of the basin distributed mostly wide.Middle and late Jurassic to early Cretaceous the basin formed the pattern which relatively high in northern and western compound syncline.And the structure pattern controlled the distributing of remainder sediment cover.Santanghu basin developed three stage structure fracture related to structure of basin.Firstly,the fracture combination developed in the remainder Permian which effected by region compression in late Hercynian.Secondly,effected by region compression in late Yanshan stage formed fractures combination in Trias,Jurassic and late cretaceous strata. In the same time ,the structure in second stage superposed and rebuilt the Permian stratum and formed new fracture combination.Thirdly,it formed fracture combination in Permian,Trias,Jurassic and Cretaceous strata effected by the compression-strike-slip structure superposed and rebuilt process.The different stage structure fracture developed in Santanghu basin possessed megascopically inhomeogeneity which related close with folds and faults of depression belt,and the occurrence was controlled by the occurrence of the faults and parts of the fold.The fracture developed very well, mostly in direction from north to east and north to west ,and secondly from east to west .And the fracture is 0.04-2mm wide.The line density is between 0.3bar/m-5bar/m.The earlier fracture was filled by the calciteand laumontite,but they still belong to the usable fracture.The most of the Permian structure fracture is useful learned by the characters of fracture and the water displacing oil experiment. To the fracture reservoir,making use of the microcosmic model to simulating the water displacing oil phenomenon,the results show that the fracture reservoir water displacing oil in this region has the two ways of the directional and undirectoinal water displacing oil.the physical property of the matrix and the fracture characteristics are also working on the water displacing oil efficiency.The fracture characteristic is the main factor.Meanwhile,if the corrosion phenomena occurs around the fracture,the formed solution fracture is propitious to improve water displacing oil efficiency in matrix.The fracture effects porosity, permeability and heterogeneity in low permeable reservoir.The Permian structure fracture is evaluated and forecasted based of the tectonic evolvement, the interpreting of seismic section, the favorable reservoir analysis. As a result, the south thrusting nappe belt of the Tiaohu depression and Malang depression are considered as the structure fractures main region, at the same time which is the greatest reservoir.