| In recent years,the largest single-scale marine carbonate monolithic gas reservoir has been discovered in the Longwangmiao Formation in the central Sichuan Basin,indicating that the Longwangmiao Formation has great exploration potential.The Longwangmiao Formation in the southern Sichuan Basin also develops dolomite,but there are few pertinent studies on the sedimentary facies in the southern Sichuan area.Through investigation,core observation,identification of core cuttings,and logging and seismic data,the stratigraphic distribution,sedimentary characteristics,facies types,and plane distribution of sedimentary facies of the Longwangmiao Formation in the southern Shunan area were systematically summarized.The research shows that the Longwangmiao Formation in the area is in integrated contact with the overlying Gaotai Formation and the underlying Canglangpu Formation,and the lithology and electrical characteristics of the top and bottom of the Longwangmiao Formation are obvious,with obvious "dichotomy" characteristics inside.They have significant differences in thickness,lithology and overall electrical properties.They are divided into the upper section of the Longwangmiao Formation and the lower section of the Longwangmiao Formation from bottom to top.The lithology of the upper member of Longwangmiao Formation is mainly gray,gray white oolitic,sandy dolomite and argillaceous dolomite,and the natural gamma(GR)is straight and low;The lithology of the lower member of Longwangmiao Formation is mainly dark gray,gray limestone and dolomite,and GR is a weak tooth low value.The strata of Longwangmiao Formation are relatively stable as a whole,with little difference in stratum thickness in the east-west direction;From north to south,it is thick in the south and thin in the north.The strata of Longwangmiao Formation are relatively stable as a whole,with little difference in stratum thickness in the east-west direction;from north to south,it is thicker in the South and thiner in the north.The lithology of Longwangmiao Formation in the study area is mainly argillaceous dolomite,silty dolomite,oolitic dolomite,sandy dolomite and a small amount of algal dolomite,bioclastic dolomite,micritic limestone,argillaceous limestone,oolitic limestone,sandy limestone and a small amount of bioclastic limestone;The sedimentary facies is a restricted platform,which can be further divided into intra platform beach and inter beach sea sedimentary subfacies.The intra platform beach subfacies include sandy debris beach,oolitic beach and other microfacies,and the tidal flat subfacies include gypsum dolomite flat,limestone dolomite flat,limestone flat,mud dolomite flat,sand dolomite flat,mud dolomite flat and other microfacies;In the northern part of the region,intra platform shoals are developed,including oolitic shoals and sandy debris shoals.The water body in the south is relatively deep,which is inter beach sea or inter beach depression,with limestone flat,limestone dolomite flat and dolomite flat developed;The lower section of Longwangmiao is dominated by limestone flat and limestone dolomite flat.Small-scale granular beach is developed in the north,the water body in the upper section becomes shallow,dolomite flat is dominated in the south,and northeast southwest granular beach is widely developed in the north. |
