Study On The Vertical Propagation Model And Simulation Of Multi-layer Fracture

In the process of actual fracturing,hydraulic fractures,in addition to forming steering extension fractures in the direction of fracture length,meet with bedding and stratum interface in the direction of fracture height,which will form a variety of complex fractures,and the height of fracture extension will involve multiple strata.Therefore,whether it can accurately describe the vertical extension of fractures has become whether it can be accurate The key to predict the effective fracturing volume.In the past,scholars at home and abroad have proposed a multi formation hydraulic fracture height extension model,but because of the complexity of fracture height extension and the difficulty in obtaining relevant parameters,the existing fracture height model is too simplified,which is different from the actual hydraulic fracture height growth.In this paper,first of all,by consulting a large number of domestic and foreign papers on the fracture height of hydraulic fracturing,the extension types and laws of vertical fractures in multi-layer strata are analyzed and summarized.Based on the theory of fracture mechanics,it is found that the plastic zone at the crack tip has a significant effect on the growth of the crack height,and the effect of the plastic zone at the crack tip is expressed by solving the effective crack height.In addition,the formation fracture toughness changes obviously with the confining pressure.The relationship between the formation fracture toughness and confining pressure is expressed by the theory of elastic-plastic mechanics,which is added to the judgment of fracture height growth.According to the theory of fracture mechanics,fluid mechanics and rock mechanics,the calculation model of vertical extension net pressure,stress intensity factor at the tip of multi-layer through fracture and the influence model of special physical properties of strata on fracture height are established.Finally,the vertical extension height model of fracture is obtained,and the corresponding solution process is worked out In order to calculate and simulate the change rule of vertical fracture extension height with different influencing factors.In this paper,the fracture height growth model is compared with the former mfeh equal fracture height model,the overall height growth trend is consistent,and more factors are considered in this model to make it more consistent with the actual fracture extension.Then carry out the physical simulation experiment of true triaxial core hydraulic fracturing,analyze the experimental results,verify and supplement the theory of vertical fracture propagation height.The research results of this paper can provide reliable theoretical basis for the design of hydraulic fracture height and the prediction of post fracturing productivity.