Experimental Study On Physical Simulation Of Complex Fractures In Shale Reservoir

The world energy shortage situation is grim,and conventional oil and gas resources have been unable to meet domestic demand.Large-scale development of shale gas can effectively ease the tense situation based on China's abundant resources.As an effective measure of increasing production,hydraulic fracturing has been widely used in the exploitation of shale gas.But different from conventional oil and gas reservoirs,there are many natural fractures in shale reservoirs,leading to complex fracture morphology after fracturing.So it is of great significance to study the crack initiation and propagation of hydraulic fracture in shale.Aiming at the above problems,this paper studied crack initiation and propagation of rock mass under complex conditions via physical experiment and numerical simulation.The main contents and conclusions of this paper are as follows.Study on the interaction mechanism between hydraulic fracture and natural fracture.The intersection of hydraulic fractures and natural fractures may lead to share crack of natural fractures,then the hydraulic fracture extends along the natural fracture surface.The hydraulic fracture may also extend along the original direction through natural fracture,or open natural crack.On the basis of the typical crack interference criterion,a more accurate hydraulic fracture criterion is proposed.Explore the experimental method of simulating shale fracturing and determine the optimal material proportioning scheme.Study on crack initiation and propagation in laboratory by hydraulic fracturing experiment.If the difference of stress and the angle of approximation are small,the hydraulic fracture is not easy to cross the natural fracture,which is easy to be captured by the natural fracture,thus changing the direction of the original extension path.If the difference of stress and the angle of approach is relatively large,the hydraulic fracture is easy to cross the natural fracture and continue to expand along theoriginal direction.As to the influence degree of crack propagation,the influence of the approach angle is the most significant,the difference of stress is the second,and the effect of pump displacement is weak.Two-dimensional numerical models of rock mass under different stress states,different bedding angles,multiple factors interacting were established by RFPA finite element software.With the increase of confining pressure difference,the hydraulic fracture gradually evolves into a single seam perpendicular to the minimum principal stress,and the fracture pressure decreases.With the increase of bedding angle,the crack initiation and propagation are more likely to be controlled by the maximum principal stress.