Research And Application Of Seismic Prediction Method For Shale Gas Reservoir Sweet Spots

Shale gas,which boasts abundant resources and broad prospects for exploration and development,is a popular research trend and research field for exploration and development of the unconventional gas in the world.Shale gas reservoir has the characteristics of low porosity and low permeability,and its sensitivity of geophysical parameters is low.Although shale has a stable distribution in a certain range,the strong heterogeneity of shale gas reservoir brings much difficulty to reservoir prediction.Focusing on the particularity of shale gas,and the relevant factors that affecting shale gas accumulation conditions,this paper makes a systematic and comprehensive study on the research zone based on geophysical methods involving shale geophysical response characteristics and shale gas "sweet spot" evaluation index and so on.According to the analysis of geophysical response characteristics of shale gas reservoir,it is proved that the lower black shale section of Wufeng-Longmaxi formation in Changning area of Sichuan province is the best.The corresponding logging response characteristics of high quality reservoir are high gamma,low resistance,high porosity and low density;the corresponding seismic response characteristics of shale gas reservoir in the research area are reflected by the strong wave crest at the bottom of the reservoir,and the top of the first part of the dragon is reflected by the mid-strong trough.Fracture is predicted through coherent,curvature and other post-stack property fusion method,while evaluation parameters of shale reservoir brittleness are predicted through the high precision of poisson's ratio and the young's modulus data volume got by pre-stack inversion method.Based on the comprehensive research on multiple parameters,the linear relationship between TOC and the velocity ratio of the vertical and horizontal wave and its density is established.Then,through simultaneous inversion of density and vertical and horizontal wave velocity ratio before stacking,the TOC data is calculated based on the different weights.Meanwhile,the horizontal distribution characteristics of hydrocarbon showings are predicted through the establishment of the relationship between air content and the longitudinal wave impedance inversion.On the basis of well logging,geology and seismic research,a set of geophysical prediction methods for shale gas "sweet spot" reservoir is achieved,which is applicable to predicting the sweet spot marine shale gas reservoir in Changning.Good effects can be obtained through practical application,and it can provide references for the well placement during shale gas exploration and development in this region.