Synthesis And Performance Evaluation Of Liquid-solid Phase Change Turnaround Fracturing Fluid

In recent years,the volume fracturing technology has become the mainstream technology of reservoir transformation,and the steering fracturing technology emerged.In order to form a fracture network system with created and natural fracture penetrating each other and improve the stimulation results,the high permeability channel and the original fracture is plugged by using diverting agent during the hydraulic fracturing process to enhance the net stress of the bottom hole and hydraulic fracture,which is greater than the fracture pressure of the weak part in the old fracture.As a very important treatment agent,fracturing diverting agent plays an important role in plugging old fractures and relocating new fractures.However,the traditional diverting agent has the disadvantages of complex construction,damage to reservoir,uncontrollable gelling time and incomplete backflow.Based on the investigation of supramolecular gel materials,the structure monomers were optimized.A turnaround fracturing fluid with advantages of controllable gel breaking time,automatic breaking of glue,and little damage to the reservoir is synthesized with the multi component gel system constructed by the synergistic action of various non covalent bonds among molecules.In addition,the influence of temperature and proportioning on the performance of fracturing fluid was studied by experiment,and the fracturing fluid and temporary plugging steering was evaluated by laboratory tests to optimize the turnaround fracturing fluid suitable for North China Oilfield and conduct field tests.The main conclusions are as follows:(1)?-cyclodextrin was first selected as the main molecule to synthesize liquid-solid phase change fracturing fluid.By controlling the proportion of crosslinking agent and evaluating of rheological experiment in laboratory,the most suitable fracturing fluid system for the medium and low temperature formation conditions was derived,that is,the fracturing fluid system with the proportion of 2%crosslinking agent.(2)The experiment shows that the viscosity of the fracturing fluid is 160 m Pa·s at the shear rate of 170s^-1.It is showed that the fracturing fluid has good compatibility with the formation environment,great ability of sand suspension,good temperature and shear resistance,core damage rate of about 10%,and gel breaking completely without residue.(3)The turnaround fracturing fluid has great plugging effect for created and natural fracture within 1mm with more than 99%plugging rate and with diverting ability.(4)The turnaround fracturing fluid was applied to the secondary sanding process of well Y in Huabei Oilfield.The pump pressure increased by 5 MPa after injecting into the formation.New fractures were opened and fracture height was in controlled.The average daily liquid and oil production of a single well are 12.35 t and5.09 t,respectively.It shows that the turnaround fracturing fluid meets the requirements of field operation and has good adaptability,which is of great significance for improving oil recovery by diverting fracturing.