All-metal mud motor applied in nitrogen-foam plug milling
The well had 6165 m measured artificial bottom, 1909 m horizontal section, and 31 plugs. The job used combined liquid and nitrogen circulation to improve debris transport, while the 3 1/8 in all-metal mud motor delivered stable rotary power to the high-efficiency mill.
Challenge
Plug milling in shale gas horizontal wells requires reliable CT conveyance, downhole power delivery, debris transport, and pressure-window control. With a long horizontal section and multiple plugs, the operation also needed stable tool-string performance under nitrogen-foam circulation.
Tool string
The BHA was configured with 3 1/8 in pin connector, 3 1/8 in check valve, 3 1/8 in hydraulic disconnect, 3 1/8 in Jar, 3 1/8 in all-metal mud motor, and 4 in high-efficiency mill. The all-metal mud motor is suited for challenging circulating media such as gas-bearing and foam fluids, providing continuous rotary power to the mill.
Operation
Field operation used approximately 300 L/min inlet liquid rate, about 20 standard cubic meters of liquid nitrogen, and about 33.4 MPa circulating pressure. The outlet was controlled through 12 mm + 10 mm chokes, with about 10 MPa wellhead pressure and approximately 380 L/min outlet flow rate.
Result review
The operation completed 31 plug milling runs with total operation time of about 96 h and average milling time of about 20 min per plug. The case demonstrates the adaptability of the 3 1/8 in all-metal mud motor in nitrogen-foam plug milling and ASBR's integrated CT tool-string capability for multi-plug long-lateral operations.