Practices and Understandings of Acid Fracturing of Ultra Deep Exploratory Wells in Sichuan Basin and Its Periphery

Comparing to ordinary deep wells, the acid fracturing of deep and ultra-deep wells in Sichuan Basin and its periphery has faced the working environment of deeper wells, higher temperature, higher pressure, more complicated fluid and more complicated lithology, and it also has the problems of higher operating friction, lower discharge, smaller scale, shorter effective distance of acid solution, poor fracturing result, poor tool reliability, low operation execution success rate, high security guarantee difficulty and bad yield, thus the exploration progress is slow. By applying the latest achievements of domestic and foreign oil and gas industry and manufacturing industry, conducting the technical research combining own experiences and lessons, the new large-diameter high-strength air-tight seal pipe string is used to replace the traditional pipe string to reduce the friction and increase the discharge, the bi-directional bimetal seal which can be motivated simultaneously is used to replace the bi-directional single-metal seal to increase the wellhead capacity to achieve the capacity verifiable and maintain the long-term stability, the bi-directional anchored expansion packer is used to replace the bottom-anchored rotary pressure setting packer to reduce the probability of seal failure caused by cylinder movement due to string expansion during acid fracturing, multiple sets of shock absorber is series connected to reduce the adverse effects of detonation force, the 'four-valves-one-packer' is used to replace the 'two-valves-one-packer', the backup valves are series connected to improve the reliability of the valve function, the corrosion retarding and retarding working fluid suitable for ≥220 ℃ temperature and ≥180 MPa pressure is researched and applied, and equal emphasis are placed on two-step simultaneous operation and three-step simultaneous operation instead of the traditional emphasis on two-step simultaneous operation, thus the optimum selection method of acid fracturing process is established. The field application is progressing smoothly, and the safety guarantee ability, fracturing scale, fracturing result operation success rate have been significantly improved.