Research On Stress Prediction Of Shale Based On Seismic Data

Geophysical inversion is an important means of obtaining formation elastic parameters and reservoir parameters,which provides a wealth of information of the exploration and development of oil and gas fields.With the improvement of in-depth of research and requirements,geophysical inversion gradually developed from the post-stack toward the pre-stack.Particularly those AVO technology based on Zoeppritz equation,which performed a great advantages and application prospects in lithology identification,reservoir prediction and other aspects.Zoeppritz equation described the relationship between the formation elastic parameters and the reflection coefficients in isotropic medium.For different research objectives and assumptions,different forms of reflection coefficient approximation has been derived by many scholars.Based on the analysis of various approximations based on the equation,the direct inversion of the Young's modulus and Poisson's ratio of PP wave reflection coefficient approximation has been derived.Otherwise,in the model set,a detailed analysis of their accuracy has been done.At the same time,the least squares AVA inversion object equations has been derived under the Bayesian theory,and tested under different models.The profile of Young's modulus and Poisson's ratio from inversion,which characterized the degree of been cracked,has been further proofed by the micro-seismic monitoring data.Due to the presence of natural fractures,the reservoir showed some different features vary from azimuthal.After the P-wave reflection coefficient AVO approximate in TI media proposed,the analysis of azimuthal anisotropy in TI media has been developed very rapidly.The impact of the azimuth?angle and the Thomsen anisotropy parameters on reflection coefficient has been analyzed firstly based on Ruger approximation.Then,the AVAZ approximate expression of the fracture compliance component represents has been derived,and the AVAZ inversion was also been constructed under Bayesian theory.Pre-stack inversion uses partial-stack angle gathers(CRP gathers),gathers quality has a great influence on the inversion results.Therefore,we have much to do before the inversion,such as improving the SNR of the gathers,amplitude compensation varying with offset,and the NMO without stretch.Meanwhile,the conventional time-depth relationship establish,well-seismic calibration,also have to do good.Different from conventional porosity or fractured reservoirs,shale gas reservoir has a more small porosity and a lower penetration.Only by hydraulic fracturing,shale gas reservoirs can obtain a commercial productivity.The brittleness and stress distribution of the Reservoir has a great importance on the reservoir reconstruction,.From the point of view of seismic pre-stack inversion,we predicted the brittleness and stress field of the reservoir,which provided huge support for the hydraulic fracturing in technical and data.By contrasted with logging data,the inversion results correspond well;verified by the micro seismic monitoring data,the prediction of brittleness and stress field and the actual situation is more consistent.