Schlumberger

Case Study: Gulf of Mexico: WELL SCAVENGER Vacuum Debris Removal Tool Cleans Up on Shelf Milling Job

Challenge: The operator had run in the hole (RIH) with an 8 ½-in. roller cone bit and drilled up the 200 ft (61 m) cement plug on top of the cast iron bridge plug (CIBP), which was set at 1000 ft (305 m). During the process, a bit cone was left in the hole. The job was in 170 ft (52 m) of water, with the wellhead and casing removed to 23 ft (7 m) below the mud line (BML). The well consisted of 9 ⅝-in. casing at 53.5 lbs/ft, with a casing I.D. of 8.535-in. set at 706 ft (215 m). The plan was to mill up the cone and CIBP. After an attempt with a bladed junk mill failed, the client sought a solution for removing the bit cone from the wellbore in a single trip that also would entail running a burning shoe to burn over the CIBP.

Solution: The M-I SWACO Specialized Tools group recommended incorporating the WELL SCAVENGER tool in a specially designed BHA. It was believed this assembly would create a reverse flow scenario below the WELL SCAVENGER tool, thus pulling the bit cone and generated milling debris into the finger basket, cable fingers and ultimately the WELL SCAVENGER debris chamber. Consequently, the leading edge of the shoe would mill up fresh iron, thereby allowing the job to be completed faster and more effectively, without interference from the bit cone. To ensure the cone would not be an issue and to remove the debris while simultaneously burning over the CIBP, M-I SWACO proposed a BHA comprising a wash over shoe dressed with a smooth O.D., a rough I.D. and a rough leading edge; a wash pipe extension dressed with two rows of finger baskets and inserted with cable fingers; a triple bushing sub; cross over and a 7 ⅞-in. WELL SCAVENGER, dressed with a 0.075-in. jet cup spacer. This BHA would leave 16.45 ft (5 m) between the bottom of the WELL SCAVENGER and the leading edge of the shoe.

Result: Despite the inferior lifting properties of the seawater drilling fluid, the BHA, featuring the WELL SCAVENGER tool, removed the bit cone, as well as all debris created by burning over the CIBP. As a result, the operator was able to run in the hole and retrieve the remaining mandrel and dog knot without interference from any debris or junk, thus saving the time and cost of additional trips.

The operator had run the hole (RIH) with an 8 1/2-in. roller cone bit and drilled up the 200 ft (61 m) cement plug on top of the cast iron bridge plug (CIBP), which was set at 1000 ft (305 m). During the process, a bit cone was left in the hole. The job was in 170 ft (52 m) of water, with the wellhead and casing removed to 23 ft (7 m) below the mud line (BML).


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