Study On Fracture Initiation And Propagation For Horizontal Well Multistage Fracturing

Hei Dimiao Oil Layer of Da Qingzi Well Block in Jilin Oilfield belongs to typical low permeability reservoir with poor reservoir property and has no natural productivity.Through using the multistage fracturing technology,the single well control reserves and production capacity can be improved,and realized the efficient development of low permeability reservoir.The horizontal well multistage fracturing can open several fractures at the same time,and using the interference among fractures to make the fractures reversing,and thus develop complex network fractures and achieve the goal of volumetric reconstruction.This paper obtained the reservoir's rock mechanics parameters through the triaxial stress experiment,and got the value and orientation of the ground stress using differential strain analysis and paleomagnetic orientation;Based on the homogeneous and isotropic two-dimensional plane strain model,built up the calculation model of induced stress at the borehole wall under different perforation azimuth,and analyzed the influence of fracture parameters and borehole parameters on induced stress;Established the calculating model of facture's initial stress which was under the induced stress according to rock mechanics and plasto elasticity,and it took original stress,induced stress,internal pressure of well bore,leakage of fracture fluid and temperature effect have been taken into consideration;Developed the mechanical conditions of fracture diversion in horizontal well multistage fracturing,and established discriminating model for the forming conditions of complex fractures.Using the established model to calculate initial pressure of Well Black A,the results showed that average error is only 4.59%.So the induced stress cannot be ignored in the study of initiation pressure during horizontal well multistage fracturing;Using the discriminating model in the calculating process of Well Block B,the results showed that complex fractures come into being.G function fitting results showed that the model was accurate and reliable,and can be used as discriminant criteria for the forming conditions of complex fractures.The study results enrich the theoretical research of the initiation and propagation of fractures during the horizontal multistage fracturing.