Establishment Of Criterion For Judging Trend Of Artificial Fracture Under Natural Fracture Influence

Unconventional oil and gas resources,as alternative energy sources for conventional oil and gas resources,have important mining value.Unconventional reservoirs usually have the characteristics of low porosity and low permeability.It is necessary to use hydraulic fracturing technology to form irregular and complex network-like fractures to increase the permeability of reservoirs and increase oil and gas production.The mode of action of artificial fractures and natural fractures directly affects the fracturing effect of unconventional reservoirs.At present,conventional crack propagation criteria usually only consider the interaction between artificial fractures and natural fractures under the action of original ground stress.The factors considered are not comprehensive enough,and the results of model determination are different from the actual situation.Therefore,to carry out the interaction of unconventional reservoir artificial fractures in the process of contact with natural fractures,it is of guiding significance to establish a more perfect criterion for fracture extension determination for the overall fracturing design of reservoirs.In order to deeply study the extended extension law of reservoir fracturing fractures and the formation conditions of fracture networks,this paper uses fracture mechanics theory to analyze the extension direction of the interaction between artificial fractures and natural fractures.Cracks form a complex network of mechanical conditions.The main research content is as follows:(1)Based on the theory of elasticity and fracture mechanics,the stress distribution around natural fractures was analyzed.The full-field and near-field types of stress around natural fractures were studied separately,and a more scientific method of stress action was selected for the interaction between fractures.(2)Based on the fracture mechanics,the fracture network formation criterion was established based on the pressure drop of the fluid in the joint.Whether the natural fracture can be opened or not determines the extension trend of the fracture,through the analysis of the critical water pressure required for opening the natural fracture,the criterion for the fracture opening is established,and the criterion for the fracture interaction is established based on fracture mechanics.The influencing factors of cracks passing through natural fractures were analyzed and the reliability of the criteria was verified.(3)The controllable factors for the formation of fracture networks were analyzed.Based on the numerical simulation of the artificial crack extension process,the influence of the intersecting angle on the formation of the fracture network was analyzed.It was found that a complex fracture network was easily formed near the intersection angle of 60°.Increasing the fracture displacement can increase the complexity of the fracture network.