The Study On Shale Gas Accumulation Conditionsof Qiongzhusi Formation In Jingyan-Qianwei Area

The thesis threated shale gas in Qiongzhusi formation in Jingyan-Qianwei area as the main body,studied on related factors which effected shale gas accumulating,such as shale distribution features,shale reservation characteristics and shale gas preservation conditions.Based on sedimentary facies,successive thickness,TOC,porosity,gas content,pressure coefficient and geological structure complexity,classification standards which applied on identifying shale gas enrichment in study area had been established,and the type of favorable areas had been divided.?1?According to ancient extinct life fossils,drilling,logging and testing data,Qiongzhusi formation in Jingyan-Qianwei area were mainly judged as wide marine-continental shelf sedimentary faces.Among the Qiongzhusi formation,the top was shallow water shelf sub-facies,the middle and the bottom both were deep water facies.Accordingly,four sets of good quality thin layer of shale which would be recognized by using well logs and seismic sections characteristics were developed in Qiangzhusi formation,Jingyan-Qianwei area?respectively 1st,2nd,3rd and 4th shale layer?.The four sets of shale were all deep water facies,which mainly distributed in the middle and the bottom of the Qiongzhusi formation.On this basis,distribution characteristics in study area of four sets of good quality layer had been forecasted by using amplitude attribute.The prediction results showed that 1st shale layer developed locally on the plane,2nd and 4th shale layers shale distributed widely on the plane,the thickness of 1st,2nd and 4th shale layer were large,3rd developed less quality on the plane relatively,and its entire thickness was thin.?2?The four sets of shale were classified according to core measuring and analyzing data,and logging data.The result showed that the average TOC of 1^st,2^nd,and 4^thh shale layer were all more than 1%,only the average TOC of 3^rdd shale layer was less than 1%.From this,four sets of shale layer were further divided by TOC.The shale layer was I type shale when its TOC was larger than 2%,the shale layer was II type shale when the TOC less than 1%,more than 2%,the shale layer was III type shale when the TOC more than 0.5%,less than 1%.The average TOC of 1^stt and 4^thh were higher relatively,the average value of 1^stt was 2.32%,and the 4^thh was 4.1%,the both were all belonged to I type shale;the average TOC of 2ⁿdd was the lowest,the value was 0.65%,which was III type shale;3^rdd shale's TOC was 1.05%,relatively low,and belonged to II type shale.According to the plane distribution features,thickness and TOC of four sets of shale layers,1^stt and 4^thh shale layer had significance for exploration.?3?The active porosity and gas content of 1st and 4th shale layer had been forecasted by core data,logging data and seismic inversion.The active porosity of 1st and 4th layer was relatively higher,the value was more than 3%,and the gas bearing was well.The average gas content of 1st layer was 3.39m³/t,and the 4th layer's gas content was 4.01m³/t averagely.?4?The fracture developmental characteristics and roof&floor condition were determined by using seismic and logging data.From this,the relationship between fracture,roof&floor condition,formational pressure and shale gas preservation conditions had been studied.Beast on fracture characteristics,roof&floor condition,pressure conditions and pressure coefficient,the evaluation criterion of shale gas preservation conditions in study area had been established,and the shale gas preservation conditions in Qiongzhusi formation in study area had been evaluated.The study area was far away fold-and-thrust belt,the fold deformation was weak,and the development of roof&floor conditions were complete and physical properties were poor,so its sealing effect was good.The roof&floor developed completely,and were all low porosity and low permeability.The roof's porosity was 0.97%,and the penetration rate was 0.034md.The floor's porosity was 0.91%,and the penetration rate was 0.19md.Hence,the seal effect of capping formation was good.The paper foresaw the formation pressure and the pressure coefficient in the study area by using Fillippone mode in formula method.Abnormal formation pressure was high which showed that shale gas had been preserved well and has not leaked out in Qiongzhusi formation in study area.?5?Finally,the classification criteria in favorable zone of Qiongzhusi formation,Jingyan-Qianwei area had been established,and 1^stt and 4^thh high-quality shale in the area had been classified based on the above-mentioned studie.