Sedimentary Facies Of The Longwangmiao Formation In The Eastern Sichuan Basin And Its Relationship With Reservoirs

In this paper,the Lower Cambrian Longwangmiao Formation of South Sichuan Basin is focused as the research object.Based on carbonate sedimentology,carbonate reservoir geology and other related disciplines,combined with core,slice identification and analysis data of eight Cambrian outcrops and four Cambrian drillings,as well as a large number of literature investigation,stratigraphy,sedimentary facies and reservoir characteristics of Longwangmiao Formation are analyzed.Based on the above achievements,the relationship between sedimentary facies and reservoir development is summarized.In the study of the formation,the layers of the top of Longwangmiao Formation have contacted with the layers of the bottom of the overlying Gaotai formation and underlying Canglangpu formation as the parallel unconformity.The top and bottom boundaries of Longwangmiao formation are clear.The main types of rocks of Longwangmiao Formation are grain dolostone,crystal grain dolostone,grain limestone,crystal grain limestone,dolomitic limestone and gypsum rock.In the lateral direction,the strata can be well correlated in the basin scale.On the plane,the Stratigraphic thickness has little difference in study area.Besides,the strata distributes steady.The strata in northwest is thicker than the strata in southeast,which shows a southwest-northeast trending.In the study of sedimentary facies,the main types of sedimentary facies of Longwangmiao Formation are restricted platform,open platform and platform edge,which can be further divided into lagoon,platform beach,beach sea,and subfacies.Among these,the restricted platform is most widely developed.In the vertical direction,Longwangmiao Formation obviously has upward shallowing and granularity coarsening sequences,which can constitute sedimentary sequencese of lagoon-platform beach.In the lateral direction,Longwangmiao Formation sediments occurred in a gentle slope depositional environment,which are divided into restricted platform,open platform and platform edge from northwest to southeast.Platform edge mainly developed in the southeast area.On the plane,all the facies are distributed in a southwest-northeast trending.In the study of reservoirs,the main types of reservoir rocks are grain dolostone(mainly include dolarenite and oolitic dolostone),silt-sized crystalline doloston,grain limestone(mainly include oolitic limestone)and cloud limestone.The main types of reservoir space are intergranular dissolved pores,intragranular dissolved pores,intercrystalline(dissolved)pores,moldic pores,vugs and fractures.Among these,intergranular dissolved pores and intragranular dissolved pores are most widely developed.And the the reservoir is a typical pore type and pore-fracture reservoir with low porosity and low permeability.Based on the study of the reservoir distribution,reservoirs can be bad correlated in the basin scale,and reservoirs distributes limitedly.Based on the above research results,sedimentation provided the geological background for the reservoir development.The sedimentary differentiation makes the reservoirs different in the early action,which may decide on the distribution pattern of the reservoir under certain conditions.Besides,the development of the reservoirs is closely related to sedimentary sequence.Reservoirs mainly develops in the upper part of upward shallow sequence.Finally,reservoirs developed in different sedimentary environments have different reservoir performance.The sandy beach microfacies and oolitic beach microfacies are conducive to the development of the reservoirs.And the cloud lagoon is following.