Distribution Of Channel Sand Bodies In The Shaximiao Formation In The Gong 115H High-density Three-dimensional Area In Central Sichuan And Favorable Targets For Exploration

Channel sandstone of Shaximiao formation in Sichuan Basin is a key but challenging area of tight oil and gas exploration and development in recent years.The vertical and horizontal distribution of sand bodies is disordered,making them difficult to be depicted accurately.Secondly,strong heterogeneity of sand bodies has negative effect on the evaluation of reservoir characteristics.Thirdly,forming conditions of the reservoir is poor as the result of limited hydrocarbon generating capacity.——That is to say,finding sand bodies is not sufficient to find reservoirs,finding reservoirs are not sufficient to find oil and gas reservoirs as well.This paper takes Shaximiao formation in Gong115H well area in central Sichuan as an example.Based on the study of the genetic types of sand bodies,the spatial distribution of sand bodies is precisely depicted by method combining high density three-dimensional seismic coherence analysis with geology.Meanwhile,the characteristics and horizontal distribution of channel sand reservoirs are studied using limited coring data.Finally,the characteristics of industrial wells in channel sand reservoirs are summarized through the dissection of typical industrial oil wells,and favorable exploration targets are put forward further more.The conclusions are as follows:(1)There are two genetic types of sand bodies,sheet sand and channel sand,in the Shaximiao Formation.Sheet sand is developed in the range of 60-100 meters above the bottom of Shaximiao under lacustrine sedimentary environment.Sheet sand has lithology of grey siltstone and thin single layer thickness(generally 1-4 m)with stable horizontal development and sheet distributed sand bodies.Channel sand is developed in the middle and upper part of Sha 1 member and Sha 2 member under flood sedimentary environment.Channel sand has lithology of gray medium to fine siltstone and thick single layer(generally 5-40 m)with unstable horizontal and vertical development,zonal distributed sand bodies and direction of NE-SW.(2)The average porosity of channel sand reservoirs in Shaximiao Formation is 6%?10%,which should be classified as low porosity and permeability reservoirs.These reservoirs have electrical characteristics of low gamma,high acoustic wave and relatively high resistivity,and response characteristics of them on seismic profiles are mainly characterized by strong amplitude and lenticular reflection.Channel sand Reservoirs have unstable vertical and horizontal developments with porosity 6%,single layer thickness 5 m as the lower limit of the reservoirs,and mainly distributed in the middle of Gong115 wellblock.(3)The characteristics of industrial wells in channel sand reservoirs are as follows:the target of well location is near Gong1 fault,the reservoirs are well developed,and the relationship between Gong1 fault and sand body configuration is good in profile.According to the geological characteristics of channel sand reservoir,three favorable exploration zones and two well location targets are selected.