Dual Layer Cement Evaluation: Case Study on Casing Collapse Environment

Abstract Maintaining the integrity of the well is very crucial to extend the well's life. One of the operational nightmares is having the casing failure such as collapse in the middle of the well life. Casing collapse happened when excessive stress applied to the body of the casing from surrounding environment and it could occur due to various reasons, such as corrosion and corrosive environment, excessive pressure, geological shifts, cement issues or mechanical damage. The focus of this paper will be addressing the cementing issue that contributes to the casing collapse. While investigating the casing integrity problem, it was discovered that the only cement data available is from the drilling report. To reduce uncertainty and better assess the integrity of the well, the approach taken was to acquire the cement data to evaluate cement behind 13-3/8-inch casing and 9-5/8-inch liner. Acquiring this data is no longer a simple task as the casing has been damaged and the well is no longer in the best condition to acquire the data. Due to the urgency of this operation and the complexity of the well, the options have become very limited. Through Tubing Cement Evaluation technology (TTCE) was implemented to aid in investigating 2 layers of cement behind 13-3/8-inch and 9-5/8-inch liner simultaneously. Due to the absence of cement data, previously the top of cement (TOC) was referred to the estimated TOC in the drilling report. Therefore, the casing collapsed issue may be inter-related with the absence of cement data. TTCE uses a combination of nuclear and acoustic data technique to evaluate two layers of cement while investigating fluid movement behind the casing. The outcome of TTCE data reveals that the TOC behind the surface casing was deeper than estimated in the drilling report with indication of fluid movement from the collapse interval down to near perforated zone. By integrating Acoustic and nuclear data cement behind 13-3/8-inch casing can be evaluated even across the 9-5/8-liner interval. The absence of cement across the interval could be one of the factors that lead to casing failure. Casing collapse could have been avoided if the cement data (CBL Legacy) was available at the earlier phase by providing a crucial insight during the brainstorming process. In well operation, preserving the well integrity cannot be understated. One of the ways to maintain the well integrity is by obtaining data as much as possible. To conclude, gathering cement data aids the decision-making process in creating a mitigation plan to overcome the casing collapse issue. With more data available, the condition of the well can be easily understood in the future.