Coupling Relationship Between Paleokarst And Fracture Of Ordovician Reservoir In In North Tarim Basin

The fracture-vug karst reservoirs in Ordovician of Northern Tarim Basin are widely developed,which have the complicated and various reservoir space,and big difference in development scale and distribution.The production of Northern Tarim Basin such as Halahatang oilfield and Yingmai district is based on the fracture-vug reservoirs in Ordovician.Because of the considerable development of strike-slip faults in Northern Tarim Basin,the coupling relationship between the phase of fault activity and the phase of karstification greatly increased the complicated evolutionary mechanism and heterogeneity,then we have a lot of worries during the reservoirs development,so it is urgent to carry on the research of coupling relationship between faults and karstification.Guided by the modern karst and outcrops investigation,based on the certain data as cores,drilling data,logging data and high precision 3D seismic data,we identified the fracture-vug reservoirs and strike-slip faults,then subdivided the genetic types of fracture-vug reservoir,also studied the phases,levels,combined characteristics of strike-slip faults,made clear the coupling relationship between the phase of fault activity and the phase of karstification.The research not only has important practical significance to the oilfield development,but also can enrich the theory of karstification.Based on the observiation and analysis of cores and FMI images,combined with production data,reveals the reservoir space in different area of Northern Tarim Basin,the reservoir types of Halahatang oilfield include cavernous reservoirs,fractured and vuggy type reservoirs and hole-type reservoirs,the mainly reservoir space in Yingmai district is fractured and vuggy type reservoirs.Then explained and identified the faults in typical district by ant-tracking method,the result showed that the faults in Northern Tarim Basin are mainly of reverse and strike slip faults,different district has different composite pattern,and all the strike-slip faults in different phases,levels,and composite pattern had obvious control action on karstification and hydrocarbon accumulation process.Guided by the modern karst and outcrops investigation,according to the reservoirs' genetic type,scale and shape,we subdivided cavernous reservoirs into tubulose underground river,caves controlled by faults and rivers,caves controlled by faults.On the analysis of the phase of fault and fractures' activity,we subdivided fractured and vuggy type reservoirs into two types,including fracture-vug in early stage and micro fracture-vug in late stage.On the analysis of karstification and fault activity,the research result shows that the faults had an obvious control action on the process of karstification.At the beginning and middle period of the karst development,the faults mainly control the occurrence of the meteoric water karstification.At the late period of the karstification,the faults in Yingmai district offered the migration pathway for hydrothermal,the hydrothermal upwelling along the faults,and will reconstruction the fracture-vug reservoirs which formed early.Compared with hydrothermal dissolution,the hydrothermal in late Hercynian of Yingmai district played an destructive role to early fracture-vug reservoirs.On the basis of phase of fault activity and the phase of karstification in different area,through comprehensive application of multi-type and multi-scale data,under the constraint of the corresponding tectonic background and karst background,first we made clear the major controlling factors and evolutionary model of tubulose underground river,caves controlled by faults and rivers,caves controlled by faults,fracture-vug in early stage and micro fracture-vug in late stage,then established the evolutionary model in typical district in Halahatang oilfield,Yingmai 1 and Yingmai 2 wellblock.The internal district of Halahatang oilfield has two kinds of evolutionary models,include bedding karst through fault draining and interval karst through fault draining,Yingmai district mainly is fault controlling hydrothermal karst which inherit from early fault controlling karst.Different evolutionary models can explain the development pattern of fracture-vug reservoirs better.