Research On The Reef-shoal Reservoir Of Permian Changxing Formation In The Yuanba Area,Northeastern Sichuan Basin

With the advance of exploration and development,following Puguang and Longgang area,Yuanba area has gradually become another important natural gas production base.Because the reef-shoal reservoirs of yuanba area are very thin and of strong heterogeneity,with the further exploration,how to effectively predict the reservoir distribution gradually becomes a key problem that restricts the hydrocarbon exploration for the area.Guided by sequence stratigraphy,sedimentology,reservoir geology,and seismic sedimentology of carbonate rock,the paper taking Permian Changxing formation in the Yuanba area,northeastern Sichuan Basin as the research object,making full use of the core,drilling,logging,seismic,testing and geochemical analysis data,the fine research on sequence stratigraphy,sedimentary microfacies,main controlling factors and the distribution prediction of the reef-shoal reservoirs is carried out.Through sequence stratigraphy analysis,Permian Changxing formation is divided into 2 third-order sequences and 6 fourth-order sequences.The distribution of the reservoir is of obvious characteristics.In the vertical direction shoal mainly develops in early period while reef tends to develop in late,and on the plane the reef dominates in the north while the shoal dominates in the south.The bioclastic shoal of early period displays in flake shape,mainly distributing in the central part of gas reservoirs.The reef of late period mainly distributes in the platform edge,developing four reef belts and partial back-reef shoal facie.Reservoirs mainly develop in the reef cap and back-reef shoal facies,comprised of dolomite with dissolved pores and crystalline dolomite.The reservoirs are of high-quality reservoir developing mode,i.e.micro-facies control the development of reservoirs,in early period dissolution occurs and in late period reformation occurs.Based on fine reservoir calibration and seismic response characteristics analysis,by the means of seismic facies analysis,palaeogeomorphologic resume,and seismic attribute analysis,the distribution ofreef-shoal reservoirs are predicted.The result indicates that No.3,No.4 and No.2 reef belts are the best reservoirs,with relatively high productivity,and furthermore,the favorable target areas are selected,which are Yuanba 101 well and Yuanba 103 H well area of No.2 reef belt,Yuanba 204 well and Yuanba 205-Yuanba 29 well area of No.3reef belt,as well as Yuanba 27-Yuanba 271 well area of No.2 reef belt.