Challenge: Mill 1,500 ft of cement in 9⅝-in casing with CT in two wells with poor cement integrity and gas leak.
Solution:
Results: Reduced rig intervention costs after successful milling to prepare the well for permanent abandonment, saving the operator approximately USD 340,000 within one month between both wells.
An operator in the United Kingdom who acquired an existing asset needed to address a gas leak in two onshore wells with poor cement integrity. The operator detected a gas leak through the steel plate welded to the 20-in casing.
The wells were originally drilled to TD at 3,620 ft below the rotary table and cased with 9⅝-in casing. Based on the limited information available, the operator was unable to determine whether the casing strings were concentric in the well. Also, the 9⅝-in casing was cut at 485 ft below the rotary table to attempt to pull the casing by the previous operator. Well schematics identified a 19-ft gap in the casing string at this level and indicated a potential drop in the casing below.
The operator collaborated with SLB to create a customized solution for the gas leak. The team used a 4¾-in PDM with an 8½-in bit to mill out the abandonment plugs under pressure control with a CT unit. The 2⅞-in tool with the Jet Blaster service was then used to clean the casing side and two retrievable bridge plugs were set for each well prior to mobilizing a workover rig to abandon the wells in compliance with current Oil & Gas UK guidelines
The collaboration between SLB and the operator reduced rig intervention costs by an estimated USD 340,000 within one month. The operator also removed the existing poor-integrity cement, enabling proper abandonment of the wells per regulations.
