Schlumberger

Performance Report: North Sea Milling/Sidetrack Debris Management: MAGNOSTAR Tools Extract 1200 lb of Debris

Challenge: A North Sea operator required a solution for a complex clean-up prior to sidetracking and drilling the 6-in. section to 14,728 ft (4490 m) MD. The operation would entail milling the tubing stump above the 7-in. production packer and then milling and retrieving the old hydraulically set production packer. The clean-up also would include a drift run while scraping inside the 7-in. liner whipstock setting area. Afterwards, the whipstock would be set, window milled and the 6-in. OD rat hole drilled. The final step before drilling the 6-in. sidetrack would be jetting the BOP stack.

Solution: Upon request, M-I SWACO SPECIALIZED TOOLS designed a series of assemblies to manage debris on the multiple runs for this project, comprising: 1. Milling: Three 7-in. MAGNOSTAR magnets (one with a row of magnets removed to create a dedicated flow channel) were positioned above the BHA, while one 9 ⅝-in. MAGNOSTAR tool was positioned just below the wellhead 2. BOP Jetting: 9-in. OD Jetting Sub, 9 ⅝-in. WELL PROTECTOR tool, 9 ⅝-in. MAGNOSTAR magnet placed below the BOP 3. Window milling: Three 7-in. MAGNOSTAR magnets. One 9 ⅝-in. MAGNOSTAR magnet positioned immediately above the 7-in. liner top; two 9 ⅝-in. MAGNOBACK magnets at the wellhead and a 1 x 13 ⅜-in. MAGNOBACK tool placed inside the marine riser. The operator and M-I SWACO agreed to a number of objectives, including assessing the effectiveness of debris extraction tools during the casing milling operation. The primary aim was to mechanically remove residual milled tubing and casing exit debris and minimize potential internal BOP damage. A surface stack inspection and testing of the BOP would verify any damage with any remaining debris inside the BOP compared with that from conventional milling work. The final objective was to minimize the risk of bit damage by removing downhole milled debris prior to drilling the 6-in. sidetrack.

Result: The 18 total runs made with the clean-up assemblies recovered a cumulative 2727 lb (1,196 kg) of wet debris that was weighed at the well site. An analysis of the debris in the M-I SWACO Field Support Laboratory in Aberdeen categorized 44% of the sample as metallic debris on a dry basis. Consequently, 1200 lb (545.5 kg) of ferrous material was gathered on the downhole magnets versus 1480 lb (672.7 kg) theoretical weight of the metal milled, for 81% total retrieval. In addition, 101 lb of metal were trapped and retrieved on the ditch magnets, resulting in 1301 lb (591.4 kg) or 88% of theoretical. A further confirmation that the MAGNOSTAR assemblies were pulling out a high percentage of the estimated debris generated is the minimal swarf recovery on the three BOP jetting runs.

A total of 18 milling runs were conducted using the designed milling assembly of three 7-in. MAGNOSTAR magnets and the 9 ⅝-in. MAGNOSTAR tool. The designed jetting assembly was utilized on three BOP jetting trips while two whipstock/window milling runs also were performed successfully as designed. After the old production packer was milled up, it was found the tubing underneath had been cut far higher than expected. This resulted in a prolonged milling and fishing operation to remove the tubing stump. The mother bore was sidetracked and 6-in. hole drilled to TD without encountering any milled debris. Afterwards, a liner clean-up was completed without incident.


Download: North Sea Milling / Sidetrack Debris Management: MAGNOSTAR Tools Extract 1,200 lb of Debris (0.57 MB PDF)

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