The Study On Yijianfang Formation Of Ordovician Reservoir Characteristics,in The Shunbei Area Of The Tarim Basin

The discovery of the Shunbei oilfield is a major breakthrough in the hydrocarbon exploration of carbonates in the Lower Paleozoic in the Tarim Basin,karst reservoir is an important reservoir type in Shunbei oilfield.Shunbei Oilfield is located in the northern part of Shuntuoguole uplift,it develop multiperiodic NE strike-slip fault,the paleo-rock caves,cave systems and pore-fractured reservoirs developed in Ordovician carbonate rocks are the main reservoir spaces.Papers research Yijianfang Group of Ordovician carbonate reservoir characteristics,in the Shunbei area,guided by carbonate reservoir geology theory,based on the absorption of previous research results and the collection,organization,and analysis of data,development of sequence stratigraphy,sedimentary facies and reservoir characteristics.Make full use of core observations,rock sheet identification,drilling,logging and seismic data,establish sedimentary facies patterns in the three-level sequence grids and sequence grids,simultaneous analysis of test data,study on Yijianfang reservoir lithology,physical properties,pores,diagenesis and evolution characteristics of reservoir space,defining the reservoir formation mechanism.Study the relationship between atmospheric freshwater karstification,hydrothermal action,fracture and reservoir formation,combined with regional geological background,tectonic evolution and petroleum geological conditions,identify the main controlling factors of reservoir development and establish the reservoir development model.The study of sequence is based on the Vail sequence,integrate previous research results,combine regional tectonic movement and sedimentary facies analysis,the Shunbei area of Ordovician is divided into two second-order sequences,SSQ1(Middle-Lower Ordovician),SSQ2(Upper Ordovician),divided into eight three-level sequences,SQ1(Penglaiba Group),SQ2(lower section of Yingshan Group),SQ3(upper section of Yingshan Group),SQ4(Yijianfang Group),SQ5(Qiaerbake Group),SQ6(Lianglitage Group),SQ7?SQ8(Sangtamu Group).The overall structure of Yijianfang Group is an open platform sediment and locally developed platform beach(reef).The Shunbei area is mainly deposited on the platform beach.Occasionally,reefs are seen.According to the lithology,the sand shoals and bioclastic shoals can be identified.Through comprehensive research on cores,lamellas,analytical tests,logging and seismic data,the results show that: the reservoir rocks of a chamber group are bright-microcrystalline grain limestone,see biomechanical limestone,siliceous rocks,occasionally dolomite;the reservoir space is intragranular pores,intergranular pores,matrix dissolved pores,karst caves,cracks;physical analysis shows that the pore permeability of the Yijianfang reservoir is poor;the diagenesis is mud crystallization,cementation,compaction and pressure dissolution,dolomitization,recrystallization,silicidation,hydrothermal action,dissolution and filling,and fracture;the diagenetic sequence is divided into four stages,near-surface diagenesis,shallow burial period,epigenetic period and post-burial period.The Yijianfang group reservoir in the Shunbei area is limestone cave-fractured reservoir.Limestone dissolving pore reservoirs are mainly formed by multiple stages of karstification.It is subdivided into high-stage karstification,low-stage karstification,and epigenetic karstification.The faults in the Shunbei area play an important role in the formation and reconstruction of the reservoir,the northeast and northwest strike-slip faults are mainly developed in the Shunbei area,the fractures communicated with the early formation of the reservoir space,the fracture also provides a channel for the rise of deep siliceous hydrothermal fluids in the hercynian period.The Yijianfang reservoirs of Ordovician in Shunbei area are mainly controlled by four factors: sequence interface,sedimentary facies,diagenesis,tectonic activity,the limestone cavernous reservoir is mainly controlled by the sequence boundary karst,there are three main types of developmental geology:the fourth-sixth sequence boundary dissolution mode,the third-order sequence boundary low-stage karst mode,and the second-order sequence boundary karst mode.