Three-dimensional in-situ stress prediction based on pre-stack rock mechanics parameter inversion:A case study of shale gas in Changning block
Compared with conventional oil and gas reservoirs,shale gas reservoirs have inferior physical properties and ul-tra-low porosity and permeability.The key to large-scale exploitation lies in applying horizontal well volume fracturing technolo-gy.In recent years,many development practices have proved that the fracturing effect of horizontal wells is obviously affected by In-situ stress.The study shows that when the horizontal wells are drilled along the perpendicular direction of the maximum hor-izontal principal stress or oblique at an angle greater than 60°,and the stress difference coefficient is small,it generates complex induced fractures.In this paper,the Changning shale gas block is selected to study the application of 3D in-situ stress prediction technology based on seismic method in horizontal well development.Based on the structural information(seismic interpretation of horizon and fault),rock mechanics information(velocity,density,Young's modulus and Poisson's ratio)predicted by seismic method,the appropriate model method is optimized,and the model parameters(Biot coefficient,tectonic stress coefficient a and b,lo cal strain coefficient A and B,etc.)are calibrated to predict the maximum and minimum horizontal principal stress,stress difference coefficient and in-situ stress direction.Through studying the regional stress mechanism of the shale gas in Changning block and analyzing the micro-seismicity monitoring results of three horizontal wells,the reliability of the 3D in-situ stress pre-diction results in this paper is verified.In the design of horizontal wells,the stress direction,heterogeneity and stress difference coefficient should be comprehensively considered to obtain favorable fracturing effect.
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