Objectives/Scope The Perforate, Wash and Cement technique has been widely implemented in the remediation of annular cement in recent years, with the application gaining increasing confidence within the Well Integrity, Plugging and Abandonment sectors. With the increase in confidence in the technique to successfully remediate annulus cement comes the evolution of the process; pushing of limitations to meet new and previously challenging plugging and abandonment projects with confidence. The first attempted and successful ‘Closed System’ type Perforate, Wash and Cement of Dual Annuli is discussed and evaluated in this paper as an effective mean for environmental plugging and abandonment. Methods, Procedures, Process For the dual annuli application to be successful, the perforation of 10-3/4" and 13-3/8" casings must be effective without damaging the 18-5/8" casing to ensure efficient hydraulic communication that allows for washing out of annular debris and placement of cement across both annuli and this was verified by a full system test of the charge. Utilizing a ‘closed system’ (cup tool) perforate, wash and cement method enables constant communication between the isolated swab cups and the annulus behind the perforated casing during the process of washing. As a result of this specific methodology, the amount of annular obstruction is visibly confirmed from surface using standpipe pressure variations long before any debris is seen at surface. The reduction in standpipe pressure over subsequent washing pass is evidence that annular debris has been removed and this is visually confirmed by debris at surface. Dual annuli washing introduces additional uncertainty regarding effectiveness of washing within the second annulus and the effectiveness of this has been verified by both Computational fluid dynamics analyses (CFD), and full scaled yard test. Results, Observations, Conclusions Large volumes of debris consisting of approximately 30% formation cuttings / metal and 70% cement were observed at surface throughout the washing sequence. Cement was efficiently placed using the ‘Pump and Pull’ method. Utilizing the ‘closed system’ benefit of the cup tool, fresh cement was placed across the entire perforated interval ensuring the highest chance of a successful cement bond. Post-execution verification was performed on the cement plug and validation of successful placement of the plug was confirmed. Volumetric analysis verified the effective placement of cement into the 10-3/4", 13-3/8" and 18-5/8" annuli.

A semi-submersible drilling rig chosen to perform the subsea well abandonment. The campaign consisted of abandoning four development wells which were completed with Horizontal Xmas Tree and having sustained casing pressure. In this paper, the methodology for performing the plug and abandonment of each well was divided into four main phases. Secure wellCut and retrieve TubingReservoir plugRemediation of sustained casing pressure The cleanliness of the Chirstmas Tree VX sealing profile is crucial before the deployment of the subsea Blowout Preventer (BOP). A modified wellhead cleaner was created for the efficient cleaning of the VX profile. Caprock restoration was implemented for the effective isolation of the zones with flow potential. Conventional section milling to remediate the sustained casing pressure was eliminated by using Perforate Wash and Cement (PWC). This technology has been widely used by Shell North Sea, where the best practices have been incorporated in the operation. This paper discusses the "first in the world" application of Dual Casing Cup Type PWC to cement across two annuli. The utilisation of the Tubing Hanger Emergency Retrieval Tool (THERT) to retrieve the Internal Tree Cap (ITC) was deemed more cost-effective as compared to the use of Subsea Test Tree (SSTT). The design of the Lower Crown Plug (LCP) that was installed in the tubing hanger incorporates an erosion plate known as flow target that was screwed onto the plug by four threads. The flow target from the first well was dislodged and is tightly wedged above the TR-SCSSSV and milling may be required to gain access below the TR-SCSSSV.

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.

Following the successful proof of concept of the closed system dual casing perforate, wash and cement for environmental plug application in 2018 (SPE-193989-MS), the same system was optimized for 2 subsea wells to isolate a gas sand behind 2 casings (9-5/8" × 13-3/8" × 16" open hole). Learning from recent operations, it was discovered that there is significant improvement achievable with specialized gun system, and refined washing and cementing parameters. Such improvement was critical to the success of the annular remediation and thus, the long-term isolation of the gas sand. The first successful closed system dual casing perforate, wash and cement for annular isolation is discussed and evaluated in this paper.