Logging Evaluation Of Longmaxi Formation Shale Gas Reservoirs In Weiyuan Area, Sichuan Basin

The shale gas resources of the Longmaxi Formation in Weiyuan area of the Sichuan Basin are rich and have great potential for exploration and development,and shale is buried than 3000m and belongs to deep shale.Nowdays,shale gas reservoirs in the study area have a relatively low level of research and understanding,especially in the comprehensive evaluation of reservoir logging and better methods of shale gas reservoir evaluation have not been formed,because of the limit of logging and core data.So this paper evaluates shale gas reservoir in the study area comprehensively by characteristics of mineral,organic matter content,porosity,saturation,gas-bearing properties and so on and a set of suitable evaluation method of shale gas reservoir is formed to provide theoretical guidance and technical support in exploration and development of shale gas.Taking the deep shale of the Longmaxi Formation in Weiyuan as an example,the characteristics of the mineral composition of the shale gas reservoir in the study area were clarified.According to the X diffraction analysis,shale of the study area is mainly composed of clay,quartz,feldspar,calcite and pyrite and so on,among which the content of clay and quartz are the largest.Multi-mineral composition model calculates shale mineral content and porosity by uranium natural gamma,sonic,density,neutron and photoelectric absorption section index,and the result of calculation is good.Shale brittleness index is calculated by mineral composition method according to quartz and carbonate and the result shows that the brittleness of the Longmaxi Formation becomes better and the fracture strength can be enhanced from top to bottom.The type of hydrocarbon source rocks in the study area are mainly I,and the degree of thermal evolution is high,which is in a higher than mature stage according to test data.with a high degree of thermal evolution and a high degree of high degree.According to the density logging,triporosity logging and natural gamma ray spectrometry logging to establish two models to achieve the total organic carbon content(TOC)calculation.The density logging is used to calculate total organic carbon content by principle of core scale and cross-plot diagram,and the calculated results are in good agreement with the core TOC and the correlation is 0.81,which meets the requirements of the interpretation accuracy.Meanwhile,BP neural network technology is used to calculate total organic carbon content by triporosity logging and uranium,and the correlation of the calculated results is 0.88 and the calculation results are better than the density logging.The calculation models of free gas,adsorbed gas and total gas content about shale gas reservoir are constructed.Then,the water saturation is calculated by Simandoux equation and a calculation model of the free gas is established by relationship between porosity,saturation and the free gas.This paper put forward the double L-DA composite model that is suitable to calculate the adsorption gas content of deep shale according to shale gas adsorption characteristics and related computing models,and a series of relevant parameters are fitted by the isothermal adsorption experiments.In the end,the calculation model of the total gas content is established by free gas and adsorbed gas.