Research On Middle Permian Reservoir In Western Sichuan

This paper focused on the Qixia-Maokou Formation of Middle Permian in Western Sichuan Basin.Relied on the professional theories of Geology and Petroleum Geology,based on the experience of predecessors,and ombined with the regional geological background,this paper discussed the diagenesis,the characteristics of stratigraphic,sedimentary facies and reservior petrology and physical property of the Middle Permian Qixia-Maokou Formation in Western Sichuan.The controlling factors of reservoir development in Middle Permian are revealed and the favorable exploration areas are predicted.In the study of the stratum,based on the partition scheme which divided the formation of Permian in Sichuan Basin into three parts,combining the outcrop characteristics of several observed field profiles with the drilling core characteristics and electrical logging curves,the stratigraphic boundary is determined,and on this basis,the vertical and horizontal and plane distribution laws of Permian strata in the study area are analysed through stratigraphic correlation.In terms of sedimentary facies,on the basis of previous studies,the sedimentary model of Middle Permian Formation in the study area is divided into homogeneous platform model that contains both platform and gentle slope which steepen at the far end according to the sedimentary facies markers.The homogeneous platform is consist of four types of subfacies,which are equiclinal platform margin,shallow gentle slope,deep gentle slope and slope-basin,and their sedimentary characteristics are described in this paper.Finally,the distribution of sedimentary facies in the Middle Permian can be obtained by vertical and horizontal comparison referring to the classification criteria of sedimentary facies in typical well profile.Reservoir research shows that the rock types of Middle Permian reservoirs in Western Sichuan are mainly granular limestone,grain dolomite and dolomitic leopard porphyry,and the reservoir space is mainly intergranular(karst)pore,karst cave and fracture.The overall physical property of the study area is poor,with porosity less than 2%and permeability less than 0.0 lmD.It belongs to low porosity and low permeability reservoir.However,the reservoir has strong heterogeneity,and there are high porosity and high permeability zones locally,which may be related to the development of dissolution fractures and caves.According to the type of reservoir space and its combination characteristics,the reservoir types of Middle Permian in Western Sichuan are divided into three types:porous,fractured,fractured and porous-fractured reservoirs.In terms of diagenesis,the main diagenesis types of Middle Permian in North Sichuan can be divided into constructive diagenesis and destructive diagenesis,the former mainly includes recrystallization,dolomitization and dissolution,and the latter mainly includes cementation and compaction and compaction.The main controlling factors for the development of Middle Permian reservoirs in Western Sichuan are sedimentation,diagenesis and tectonic movement.Sedimentary facies have laid the material foundation for reservoir formation.Among them,shallow high-energy beach microfacies in platform margin and low-energy point-beach microfacies in shallow and gentle slope are favorable zones for reservoir development.Dolomitization in platform margin shoal determines the formation of high-quality reservoirs.Diagenesis leads to the formation of secondary pore,which is the most important factor to control reservoir development.Intergranular pore formed by recrystallization and dissolution pore formed by dissolution transformation are the main reservoir space of Middle Permian reservoir.Fractures superimposed by multi-stage tectonic movements improve the connectivity of reservoirs and effectively improve the permeability of reservoirs.Based on the study of sedimentary facies,diagenesis and reservoirs,the most favorable exploration areas are identified in the areas of Kuangshanliang-Shuangyushi,Jiulongshan-Yuanba,Langzhong and Laoguanmiao in northwestern Sichuan;Zhougongshan-Hanwangchang in the southwestern Sichuan is a more favorable exploration area;Jiuxunping-Yanziyan-Tongkou is a favorable area for reservoir development.