Small-diameter Shockwave Hydraulic Oscillator for Passability and Milling
The well is a Longmaxi Formation production horizontal well with an approximately 5904 ft lateral section and around 145 ℃ bottomhole temperature. Severe casing deformation reduced the minimum casing ID to approximately 3.07 in, creating clear limits for conventional tool passability, weight transfer, and long-lateral reach.
Challenge
After the initial plug-milling interval, severe casing deformation restricted the ability of the larger tool string to continue into the remaining section. The long lateral also increased friction, reduced weight transfer, complicated toolface control, and placed higher demands on debris transport during plug milling.
Tool String
The operation used 2 in coiled tubing with 2-1/8 in connectors, check valves, hydraulic disconnect, hydraulic Jar, small-diameter Shockwave hydraulic oscillator, positive displacement motor, and concave-bottom mill. The small-diameter Shockwave hydraulic oscillator helped reduce friction and improve tool-string movement through the deformed casing and long lateral.
Operation
The earlier 2.875 in OD milling BHA removed 6 dissolvable plugs. Based on the casing deformation and passability limit, the operation then switched to the 2-1/8 in small-diameter tool string to mill the remaining 13 dissolvable plugs. Field operation used approximately 400 L/min flow rate, about 26 MPa wellhead pressure, and about 45 MPa circulating pressure.
Result Review
The well completed 19 dissolvable plug milling operations and wellbore cleanout, establishing the unobstructed path required for subsequent production. The case shows how a small-diameter Shockwave hydraulic oscillator can work with a CT milling tool string to improve passability, reach, and operating continuity in severe casing deformation and long-lateral conditions.