Optimization and application of sand bailing technology for coalbed methane horizontal well

Objective and Methods Sand accumulation, pipe wall scaling and stuck pump of coalbed methane (CBM) horizontal wells lead to gas production decrease or shutdown, which seriously restrict the continuous and stable gas production. Mechanical sand bailing is an effective technology to restore and improve the gas production of CBM horizontal wells. Aiming at the problems of poor sealing of sand bailing toll string, low efficiency and sand consolidation in coalbed methane horizontal wells, the claw-type scraper tip, sand-breaking drill bit, eccentric turnover plate and mechanical rotating tool are optimized and processed. Based on the principle of horizontal well mechanical sand bailing pump, the hydraulic additional axial force is introduced into the tubular pipe mechanical model to establish the pipe-hydraulic coupling mechanical model. The optimization method of sand bailing operation parameters in horizontal wells is designed. The influence of single-stroke reciprocating cycle of sand bailing pump (T) on the fluid flow velocity in sand storage pipe and coal fines migration has been analyzed. And the opening degree of flap suction port on the axial force of hydraulic additional axial force are analyzed. Results and Conclusion The results show that the claw-type scraper tip improves the efficiency of sand bailing for horizontal well through structural optimization. Mechanical rotating tool, sand breaking bit and clip springs have been used to drill and break the pipe wall scaling. Eccentric turnover plate and ball single flow valve increase the area and sealing of sand channel. The Φ110 mm sand bailing pump can transport particles with a diameter of no more than 2.5 mm and small coal cuttings of 3-12 mm (T=60s), which effectively transport the pulverized coal particles deposited in the horizontal wellbore into the sand storage pipe. Compared with the conventional tripping, the axial force of the tubular pipe under the upward and downward conditions of the sand bailing pump increases by 906.94 N and decreased by 37.41 N, respectively, which improve the calculation accuracy of force on the sand bailing string. The field demonstration project shows that the sand bailing amount of single well and single time are increased by 1.5 and 0.9 times respectively after the optimization of sand removal tool. The average daily gas and water production are increased by 1483.7 m³ and 2.18 m³ after sand bailing, which provides technical support for high and stable production of CBM horizontal wells. This technology is suitable for horizontal well and highly-deviated well with screen completion and casing perforation completion, which has important practical significance to promote the efficient development of coalbed methane.