Study On The Deposition And Reservoir Characteristics Of The Changxing Formation In The Nanmenchang-Shibaozhai Block Of Northeastern Sichuan

As one of the important gas reservoirs in Liangping-Kaixian area,the Permian Changxing formation reef reservoir has aroused widely study among domestic scholars.Moreover,their understanding about the distribution of sedimentary facies in this area has always been different.The purpose of this paper is the Changxing formation in the Nanmenchang-Shibaozhai area in northeastern Sichuan Basin.Based on sedimentary petrology and reservoir geology,the division of stratigraphy is studied,using geology logging,well logging,core,thin sections,seismic,geochemical and outcrops data.Then develop fine research on sedimentary facies,specific determinationg the distribution of platform margin.Finally,the distribution and controlling factors of the reef-shoal reservoir have been systematically studied.This paper have practical significance in Changxing formation exploration and development within study area.Based on geology logging,well logging,core,thin sections and outcrops data,according to the differences of rock associations types,logging curves response and paleontological fossils features,objective formation can divided into three shallowing-upward cycles,namely P3ch1,P3ch2,P3ch3.Consulting the previous research achievement,the Changxing formation in the study area was divided into five major phases:shallow-gentle slope facies,deep-gentle slope facies,slope-trough facies,platform edge facies,and the open platform facies,subdivided into 6 subfacies and 12 microfacies.By analyzing sedimentary characteristics of representative individual well and connecting-well section in study area,Upper Permian Changxing reef-shoal just development of P3ch 2 and P3ch3.P3ch1 without reef-shoal deposit,its main lithology is the micritic limestone,siliceous limestone and argillaceous micritic limestone,containing calcispheres and spicule fossils.The development of reef in different sedimentary areas has distinct characteristics:the platform marginal reef developed in P3ch2 and P3ch3;reefs near the margin of platform(close to the open platform facies)only developed in P3ch2,P3ch3 not developed;open platform reef just developed in P3ch3,P3ch2 not developed.Study on bore cuttings or core thin section identification,geochemical statistical analysis,this paper hold that the highest quality reservoir rock are residual bioclastic dolomite and biohermal dolomite.The main reservoir type is ? and ? zone,reservoir porosity-permeability features of platform margin is better than open platform facies.Through reservoir control factors study,consider the sedimentary facies is the basis of reservoir formation,diagenesis is crucial of reservoir space formation and preservation.According to current trace elements and isotope data,show that the Upper Permian Changxing formation large-scale dolomitization occurred in shallow burial diagenetic environment and the dolomitization fluids comes form the overlying Lower Triassic Feixianguan seawater.Distribution characteristics of reef-shoal reservoir:on its transverse section,reservoir distributed on P3ch2 and P3ch3,P3ch1 undeveloped effective reservoir;on the plane,the platform margin facise controls the distribution of reservoir,the majority of quanlity reef-shoal reservoirs is distributed in the platform margin,the thickness of the reservoir in the open platform facise is generally thinner,the slope-trough depositional environments undeveloped reservoir.