Seismic Prediction Of Shale Oil Reservoir Fractures In Qianjiang Depression

Most domestic shale oils with industrial production value are derived from fractured mud shale.Shale reservoirs are different from conventional reservoirs.The characteristics of low porosity and low permeability are a major difficulty in exploration and development.Therefore,cracks that can be used as oil and gas reservoirs and migration channels have become the focus of shale reservoir research.Because the seismic gather data contains information about stratigraphic fractures,the methods for predicting cracks are mostly seismic methods,such as AVO anomaly response feature analysis,coherence analysis,and curvature analysis.Coherence analysis and curvature analysis are based on the post-stack data body analysis,ignoring a lot of useful information,so the predicted crack development can not analyze the crack type but more use in the crack plane distribution prediction.The AVO technology directly uses CDP gather data for analysis.This makes full use of the rich raw information obtained by multiple coverages,but requires a certain degree of geological,logging and drilling data.In addition,the AVO crack prediction technology is a geophysical method based on strict knowledge expression and with clear geological significance.Therefore,there is a mathematical expression of the AVO anomaly response caused by cracks,which provides a theoretical basis for the quantitative prediction of cracks.In this paper,the Wangchang area of Qianjiang Depression is taken as an example.It mainly starts from three aspects: 1.The main controlling factors of crack development in Wangchang area are analyzed.It is found that the crack development in Wangchang area is mainly affected by tectonic action.2.According to the curvature analysis and coherence analysis,the crack development area is roughly determined.According to the actual logging data in the study area,the AVO forward modeling of fracture development is carried out.The forward modeling model is established to analyze the AVO response characteristics caused by cracks,which provides a basis for crack prediction.The main insights gained in this paper are as follows:1.The shale oil in the Qianjiang sag is mainly in the third member of the submerged shale,which belongs to the dense carbonate rock in the shale strata or the petroleum resources in the interlayer,which also causes the salt in the Yanchang sag oil exploration area.Interbedded mudstone and cloud shale provide hydrocarbons,self-generated and self-storing,and are characterized by salt rock zone isolation(closed system)and large amount of resources remaining in the salt rock interlayer.2.From the analysis of lithologic factors of fracture development,it is found that the tectonic fracture is greatly affected by the layer thickness,while the horizontal layered seam is greatly affected by the rock brittle mineral composition.The structural factors are found to be mainly NE and NW in the Wangchang area.The two groups of cracks in the direction are mainly controlled by the warrior anticline and the vehicle fault..3.The AVO response characteristics analysis is used to predict the cracks,and the cracks are mainly divided into vertical cracks and horizontal cracks according to the occurrence.Because the vertical fracture logging data is abundant,the longitudinal and transverse wave velocity and density of the vertical crack are directly read from the well seismic data,while the horizontal crack related data is lacking.Only the physical model can be established to calculate the longitudinal and transverse wave velocity and density.Under this premise,the sensitive factors of different types of cracks are simulated separately.It is found from the PG intersection graph that no matter what kind of crack increases with crack,the P value is negative and negative,and the G value is positive.As the positive direction increases,the reflection coefficient decreases as the incident angle increases.4.It is known that the reflection coefficient of different types of cracked media and the incident angle change curve show that the horizontal crack is the smaller the incident angle,and the larger the difference of the reflection coefficient caused by the crack,the larger the difference on the change graph is that the opening is at 0°,and the angle of incidence is higher.Larger convergence,vertical cracks do not have this trend.This provides a basis for distinguishing the type of reservoir fracture.5.The seismic properties(coherence and curvature)of the study area are analyzed,and the prediction map of the plane distribution of the fracture development is obtained.