Tectonic Geological Characteristics And Evaluation Of Shale Gas In Luzhai Area,Guizhong Depression,Guangxi

Guizhong depression is located in the northeast of Dianqiangui basin,the east of Nanpanjiang Basin and the southeast of Qiannan depression.It is a large marine sedimentary depression formed on the basis of Guangxi movement.Through the analysis and summary of geological mapping data and oil and gas exploration and research results,combined with field investigation and indoor data analysis,this paper studies the geological structure characteristics,superimposed deformation mechanism and its impact on shale gas preservation conditions in Luzhai area.Based on the study of field geological survey and regional survey data,it is concluded that Luzhai area has experienced three stages of fold superimposed deformation: the first stage is overturned fold,which is formed by bedding extrusion;the second stage is inverted closed fold,which is superimposed across the same axis,and the hinge is inclined to nearly east-west direction,which is near NW-SE extrusion;the third stage is open fold,with nearly N-S axis lines and it is nearly EW extrusion.In addition,two stages of fault activity can be identified in the study area: the first stage is a near NE-SW thrust nappe fault formed by near NW-SE extrusion,with NW dip and 30-60 ° dip angle.The second stage is a nearly NW-SE imbricate thrust fault formed by NE-SW extrusion,with fault dip of NE or SW and dip angle of 30-50 °.The results of organic geochemical test are as follows: The TOC of the first and second members of the lower Carboniferous Luzhai formation ranges from 0.83% to10.08%,with an average of 3.16%.Ro is distributed in 0.83%-2.31%,with an average of1.22%,which belongs to over mature dry gas generation stage.The TOC of the third member of the lower Carboniferous Luzhai formation ranges from 0.42% to 2.30%,with an average of 0.938%.Ro is distributed in 0.93%-2.16%,with an average of 1.68%,which belongs to high mature wet gas generation-over mature dry gas stage.The TOC of the upper Devonian Liujiang formation ranges from 0.048% to 3.75%,with an average of1.51% and a maximum of 3.75%.Therefore,the lower Carboniferous Luzhai formation and the upper Devonian Liujiang formation are potential exploration targets for shale gas with good quality.Through the interpretation of seismic section,it is further concluded that the deep structure style in this area is mainly the fold deformation accompanied by thrust and napping extrusion,the fold deformation superimposed in the later stage and the hedging triangle structure.The hedging triangle is a stable area of structure and provides good conditions for shale gas preservation.Based on the above research,combined with the regional survey data,the roof and floor conditions,formation inclination,fault influence and burial depth of the target strata in the study area are studied,in order to evaluate the shale gas preservation conditions in the study area.It was found that the formation inclination of the core of Luzhai syncline and the north west wing area was gentle,and it was located in the stable area of structure,which is favorable for oil and gas conservation.