Study On The Fracture Initiation And Propagation For Horizontal Well Fracturing

The domestic fracturing effect of the horizontal wells is not ideal presently, and one of the reasons is that the fracture formation mechanism is not well understanded and the fracture initiation and propagation law are not deeply studied on in the horizontal wells especially.Using the logging and fracturing information in XueCha district of YanChang Oil field,the following data is calculated such as Poisson ratio 0.18, Young's modulus 23.7GPa, minimum level earth stress 20.6MPa and maximum level earth stress 33.6 MPa. In this base, the interspace model considering the hole is set up and the mathematic simulation is brought into production with the finite element method. It is thought that the fracturing pressure is mainly affected by the minimum level earth stress, impacted obviously by wellbore orientation, perforation orientation and perforation density and indistinctly influenced by the perforation length and diameter. It is forecasted that the fracturing pressure of XuePing 1 well is 35MPa. Based on two-dimensional and three-dimensional crack propagation models that have existed and considering the impact of some factors such as pressure drop gradient of the crack height to the crack extension, the improved model of quasi three-dimensional crack extension is founded and the numerical method is given.It is thought that the fracture height increases obviously when the delivery rate is increased and the fracture height is increasing continuously when the fracture length increases.When the fracture half length is more than 130m,the augmentation of the fracture height is swelling. Without considering the vertical size of the crack and perforated completion and based on the maximum tensile stress criterion and Lagrange Multiplier method, the turing model of the crack near wellbore is founded. The calculated result indicates that there exists the the frature turning near wellbore and when wellbore orientation increases, the distance of the fracture turning finishing away from wellbore continuously decreases. It is believed that when the wellbore vertical with the maximum horizontal earth stress is optimal.