Study On Multi-stage Temporary Plugging Characteristics And Steering Law In Fractures Of Ultra-low Permeability Reservoirs

The temporary plugging and steering fracturing technology is one of the effective methods to improve the effect of reservoir reconstruction.At present,the temporary plugging and steering fracturing technology has been widely used in many oil fields and achieved remarkable stimulation effect.The multi-stage temporary plugging fracturing technology has become a research hotspot.However,due to the influence of many factors on the plugging of temporary plugging agent in the fracture,it is difficult to determine the plugging condition and location of temporary plugging body.Therefore,the fracture steering law under different multi-stage temporary plugging conditions still needs to be further studied.In this paper,the ultra-low permeability reservoir is taken as the research object,and the temporary plugging experiment in the fracture under 3D printing technology,real triaxial large physical model experiment and numerical simulation experiment are carried out successively.Through the temporary plugging experiment in the fracture,the real morphology of the fracturing fracture under the formation conditions is simulated,the fracture parameters are obtained,and the characteristics of the fracture and temporary plugging body in the multi-stage temporary plugging process are analyzed.The real triaxial large-scale physical model experiment shows that when the in fracture near well plugging is adopted,the sealing body with denser,tighter and greater plugging strength is formed in the fracture area,the area holding high pressure is smaller,the plugging pressure is higher,the natural fractures are fully opened after plugging,and the fracture network shape is more complex.When the plugging body appears at the joint end,the temporary plugging body is evenly laid in most areas of the joint.The temporary plugging body scattered in the joint may lead to insufficient local plugging strength,and the high-pressure accumulation area becomes larger.After plugging,only part of the natural fractures are opened,indicating that when the plugging body is uniform and dispersed,the net pressure cannot open all the natural fractures,and the ability of fracture network transformation is limited.The formation conditions are simulated by numerical simulation method,and the influence of different factors,especially the temporary plugging position,on the fracture steering law in the process of multi-stage temporary plugging fracturing is analyzed.The results show that the horizontal in-situ stress difference affects the opening of multi-stage fractures.When the direction of the maximum horizontal principal stress is close to the angle of multi-stage fractures,there is a positive correlation between them;Temporary closure of branch seam can effectively increase the original crack length;There is a critical value for the secondary steering of hydraulic fractures with low approach angle.When the angle is greater than the critical value,the secondary steering of fractures may occur;Multistage temporary plugging fracturing increases the opening capacity of micro fractures,but reduces the expansion capacity of the upper level of multistage fractures;By changing the position of the temporary plug,the pressure holding zone of the fluid pressure in the fracture can be controlled.When a point in the zone reaches the opening threshold of the nearby micro fracture,the micro fracture will open.The research on the characteristics of multi-stage temporary plugging in fractures and the steering law of ultra-low permeability reservoirs,especially the experimental results of different plugging positions leading to different fracture patterns,provides theoretical basis and technical support for guiding the field fracturing construction design.