Main Controlling Factors Of Lower Paleozoic Karst Reservoir Development And Prediction Of Favorable Areas In Southern Nanpu Depression

Carbonate karst reservoirs are widely distributed and are currently the main exploration targets.Although a series of experiences and achievements have been achieved in the study of carbonate karst reservoir in Nanpu Depression in recent years,it is difficult to establish reservoir geological models and difficult to study reservoir prediction because of the complex stratigraphic contact relationship,unclear understanding of sedimentary systems,complex reservoirs and rapid changes in longitudinal and transverse physical properties.Therefore,this paper adopts the technology of casting thin slice,scanning electron microscope,laboratory analysis,combined with core,well logging,well logging,seismic data and regional geological data,the development characteristics and development models of Lower Paleozoic carbonate karst reservoirs in the southern part of Nanpu Depression are systematically studied,and karst paleogeomorphology is restored.The main controlling factors of karst reservoirs are further discussed.The high-quality reservoir prediction of karst reservoirs is carried out by wave impedance inversion,and the favorable areas of karst reservoirs are screened out by combining multi-factor comprehensive analysis and superposition mapping.To achieve a major breakthrough in oil and gas exploration and development in the southern area of Nanpu depression.The research results are as follows:The carbonate karst reservoir in Nanpu Depression mainly consists of three rock types:limestone,dolomite and karst rock.The weathered crust granular limestone and inside powdery dolomite are the most favorable rock types.The guarantee of reservoir formation is multi-episodic karst activity.The Lower Paleozoic in the southern part of Nanpu Depression mainly develops three periods of karst: Late Caledon-Early Hercynian,Indosinian-Yanshanian and Late Yanshan-early Himalayan,and the third period of karst is the most favorable.The types of karst processes are mainly supergenetic karst and burial karst.Among them,karst in supergene stage will lead to the development of pore and cave system,karst in the middle of supergene stage will further dissolve the cave,and karst in burial stage will further dissolve the karst space.The vertical karst zoning mainly includes residual layer,vertical percolation zone,upper percolation zone and lower percolation zone,among which the upper percolation zone has the best reservoir performance,followed by the vertical percolation zone.According to the karst process,the lower Paleozoic karst reservoirs in the southern part of Nanpu Depression can be divided into weathering crust reservoirs under the action of supergene karst and inside reservoirs under the action of buried karst.Weathering crust reservoirs can be divided into fault-controlled karst reservoirs and karst collapse reservoirs.In addition,according to the morphology and combination form of pores and fractures,karst reservoirs can be quantitatively divided into pore reservoirs,fracture reservoirs,fracture porosity reservoirs and fracture cavity reservoirs.The main controlling factors of Lower Paleozoic karst reservoir development in southern Nanpu Depression include lithology,diagenesis,fracture development,paleogeomorphology and karst zonation.Among them,Majiagou Formation limestone near Nanpu No.1 and No.2 fault zone and Maozhuang Formation dolomite near No.3 fault zone are conducive to reservoir development.Dolomitization,dissolution and tectonic rupture can improve reservoir performance and contribute to reservoir development.The fractures near Nanpu No.1 fault zone,No.2 fault zone and No.3 fault zone are well developed,which is conducive to reservoir development.Nanpu No.1 Buried Hill and No.2 Buried Hill are located in the paleo-geomorphic background of karst slope,and the reservoir is well developed.The porosity and fracture evaluation of Lower Paleozoic karst reservoirs in southern Nanpu Depression were carried out,and the karst reservoirs were divided into Ⅰ,Ⅱ and Ⅲreservoirs by using FMI imaging data and DSI analysis data,combined with multi-factor comprehensive analysis and superposition map,the favorable zoning of karst reservoir is further divided into three categories.The favorable area of karst reservoir is mainly located in the north of Nanpu No.1 latent mountain,close to Nanpu No.1 structural fault zone.The favorable areas of the second type of karst reservoir are mainly located in the east of Nanpu No.2 latent mountain,adjacent to the Nanpu No.2 tectonic fracture zone.Both of these favorable areas are favorable areas of weathering crust reservoir distribution,and are dominated by supergene karstification.The favorable areas of the three types of karst reservoirs are mainly located in the Nanpu No.3 burial-hill Cambrian Maozhuang Formation,close to the Nanpu No.3 tectonic fracture zone,which is a favorable area for the distribution of inside reservoirs and is dominated by buried karstification.