Continuous Improvement for Offshore Plug and Abandonment, a Case Study from Egypt Offshore

Abstract

Setting cement plugs is a critical operation, often not getting the required attention and potentially resulting in lost time. For example, while drilling an exploratory well offshore Egypt in the North Ras el Ash block, special attention was given early in the well's design phase to the wellbore abandonment to be executed after reaching the well target and achieving all well's objectives. As part of the continuous improvement, a detailed after-action review (AAR) took the place of the abandonment of the previous exploration well in the same field ahead of spud. All applicable lessons learned were identified and worked out in easy-to-implement steps to improve the chances of a successful abandonment meeting all company and regulatory requirements. The AAR addressed all aspects of the abandonment, including cement slurry design and laboratory testing, cement plug placement and operational rig procedures, and post-placement activities that could impact the cement plug and, in the worst case, could lead to not meeting abandonment requirements. All plugs to be verified by a positive and negative pressure test were simulated using proprietary software. The simulation results would predict the cement plug bonding to the formation or casing during and after the positive and negative tests. To overcome any damage in the sealing capability of the plug, those plugs were designed so that the slurry would expand during the cement setting phase. In addition, detailed laboratory tests were run to optimize the cement slurry design at actual downhole conditions. Special attention was given to formation pressures and possible losses or influx after cutting and retrieving the intermediate casing. Certain shales are gas-bearing formations but with very low permeability and very low capability to deliver gas to the wellbore. During the drilling phase, this is not considered a high risk and was easily managed with drilling fluids. However, while setting plugs, a small influx of gas can percolate through the cement plug creating a potential leak path. Correct placement in the field is equally important to a good design. The plug placement was simulated to minimize contamination during placement for plugs. Optimum spacer volume, underdisplacement, and the use of mechanical separators were optimized to achieve the plug and abandonment (P&A) objectives. Pull out of hole (POOH) was designed to minimize disturbance of the cement plug and circulation at top of cement (TOC) was performed without disturbing the cement/spacer interface. All the effort placed into the well abandonment during the well design phase paid out during the execution. A total of five cement plugs were planned. The plugs were tagged and tested achieving all the abandonment requirements successfully. No repeat plugs were required.