Study On Multi-fracture Competition Propagation Law Of Horizontal Well Fracturing In Shale Reservoir

In the process of multi-cluster fracturing in the horizontal section of shale reservoir,due to the existence of stress interference and weak bedding plane,there is a strong competitive expansion effect between the main fractures of multi-cluster fractures and the bedding and fracture height.However,at present,the understanding of this competitive expansion law of multi-fractures is still unclear,and the optimal fracturing parameters cannot be determined,so it is difficult to improve the fracturing effect.In this paper,the theory,experiment and numerical simulation are combined to study the multi-fracture competitive propagation law of shale horizontal well reservoir.Firstly,the variation law of tensile strength and uniaxial triaxial compressive strength of shale under different reservoir depths is clarified by indoor mechanical experiments,and the influence of stress difference and displacement on the competitive propagation law of multiple fractures is preliminarily analyzed.Secondly,the induced stress field distribution,stress interference theory and flow distribution theory during the synchronous expansion of multiple fractures are analyzed,and the competitive expansion mechanism of multiple fractures in shale reservoirs is clarified.Finally,based on the in-situ stress evaluation model,a numerical model is established to study the influence of different construction parameters and formation stress parameters on the competitive propagation law of multiple cracks.The results show that the competitive propagation effect between vertical main fractures increases first and then decreases with the increase of cluster number,displacement,horizontal in-situ stress difference and vertical in-situ stress in the fracturing section,and continues to decrease with the increase of cluster spacing.The competitive propagation effect between vertical main fractures and bedding weak surface fractures decreases first and then increases with the increase of cluster number,displacement and cluster spacing,and continues to increase with the increase of stress difference and vertical in-situ stress.When the fracturing section is three clusters,displacement is 12m~3/min,cluster spacing is 5m,stress difference is 5MPa and vertical stress is 70MPa,the competition effect between the vertical main fractures is the most obvious.When the fracturing section is four clusters,displacement is 16m~3/min,cluster spacing is 20m,stress difference is 15MPa and vertical stress is 75MPa,the competition effect between the vertical main fractures and the bedding weak surface fractures is the most obvious.The first four are the bedding weak surface fractures,and the latter is the opposite.The steering angle of the vertical main fracture increases first and then decreases with the increase of the number of clusters in the fracturing section,and continues to increase with the increase of displacement,while decreases with the increase of stress difference,vertical stress and cluster spacing.It is found that the larger the number of clusters,displacement and stress difference,the more developed the weak bedding fracture.When the number of clusters in the fracturing section is three,the displacement is 14m~3/min,the cluster spacing is 20 m,the stress difference is 5 MPa and the vertical stress is 75 MPa,the vertical fracture height is the most developed,which communicates more weak bedding planes,and the development of multiple clusters of fractures is more uniform under such displacement,cluster spacing and vertical stress.Therefore,it is suggested that the fracturing construction parameters under such conditions should be used in the field to promote the development of the main fractures and make them more uniform and communicate more.