Single Run Plug and Abandonment Cementing Operation Across Multiple Casings

Abstract

One objective of well abandonment is to help prevent pollution to the environment from residual fluids left in the well post caprock restoration. These fluids may have been present in the annuli when well construction was commenced. They are normally removed when the casing(s) is retrieved from the well and capped with an environmental cement plug, or more recently, via perforating the casing(s) and circulating out the annuli contents prior to setting the environmental cement plug. Gaining access to the annuli is achieved via tubing conveyed perforation (TCP) guns and the charges are designed to penetrate the targeted casing(s) with sufficient entry hole diameter (EHD) without causing damage to the casing beyond. Fluid is then circulated into the annuli via the perforations with returns taken through the wellhead side outlet valves (SOVs). Cement is subsequently circulated into the annuli and a wellbore cement plug is placed above the cement retainer thereafter to form an environmental plug. This approach requires two trips, the first where the mechanical setting tool, cement retainer with TCP guns attached below is run into the well to perforate the casings and perform the cement circulation. The second trip is with a cement stinger to place a wellbore plug above the cement retainer after the Mechanical Setting Tool (MST) has been retrieved. The retrieval of the MST is required as the MST outside diameter (OD) is almost equal to the inside diameter (ID) of casing. This can cause cement swabbing and contamination if pulled through the cement plug after the placement. In this case, an alternative Bottomhole Assembly (BHA) was explored where the entire operation can be performed in a single trip. This involved the use of a hydraulically set cement retainer that comes with a slick tubing for placing the cement plug once the running tool is removed from the cement retainer. The cement slurry design was tailored to allow for additional thickening time to compensate for the single trip run. A successful trial was performed in Brunei's operations in the 3rd quarter of 2021, where the cement was placed immediately above the cement retainer after annuli fluids removal and cement circulation in the B and C annuli after perforations were completed. A single trip system with revised cement slurry design has also been trialed successfully to enable removal of residual fluids and cementing of the annuli and a wellbore cement plug to be placed in a single trip. This reduces HSE exposure to the crew and achieved significant time and cost savings.