Application of Perforate, Wash, and Cement (PWC) Technology for Annular Remediation in Deepwater Well Abandonment

Abstract To achieve zonal isolation during well abandonment, all the zones with flow potential must be isolated from each other through the installation of permanent barrier(s), both inside and outside the casing (wall-to-wall), for caprock restoration. The conventional approach for installing a permanent barrier in an uncemented casing or a poorly cemented one is through casing milling, cement squeeze, or casing cut and pull operation. However, casing milling is time consuming, expensive, and complex, especially for deepwater operations, due to the associated risks of swarf to the subsea BOPs and flow lines. Cement squeeze operation is a best-endeavor approach, as the fluids will typically take the path of least resistance and may not achieve the cement lift required for permanent isolation behind the casing. The probability of success (PoS) with the casing cut and pull approach in the open hole section is low due to the possibility of formation collapse and sagged barite behind the casing. Perforate, Wash, and Cement (PWC) technology has been established globally as an efficient and cost-effective solution for annular remediation. During the Bonga deepwater field mid-life plug and abandonment campaign in Q2 2024, the first deployment of PWC technology in the field demonstrated significant cost and time savings compared to conventional methods. The PWC strategy involves using TCP guns to perforate the casing at the target interval, followed by deploying specialized PWC tools to wash out debris and place cement slurry in the annulus and wellbore to achieve rock-to-rock isolation. This approach reduced the well abandonment complexity and achieved significant cost savings for WELL-B operations. This paper discusses the extensive work that led to the successful deployment of PWC technology for the placement of an annular barrier across a 9 5/8" casing on Well-B in the Bonga deepwater field, the first of its kind in Nigeria for well abandonment. This demonstrates the potential for broader application and further optimization in well abandonment operations.