Challenges in Performing Coiled Tubing Zonal Isolation in a Well with Integrity Complication and the Probable Low-Cost Solutions; A Case Study in Balingian Basin

This paper discusses the common operation challenges when performing Coiled Tubing Cement Zonal Isolation in a well with integrity complications and offers probable solutions to mitigate the operational risks introduced by the well integrity issues. Our case study, well Y is situated in the shallow offshore terrain in Balingian Basin. This well was completed as a Dual String Completion Oil Producer in the year 1986. After years of production, well Y experienced multiple leaks in its production tubing, and the leaks were successfully isolated by tubing patches. During well intervention campaign, these multiple tubing patches need to be retrieved to allow Coiled Tubing to pass through the well inner diameter (ID) which leaves the well to be in a leaking condition again. A comprehensive risk assessment was conducted to identify the feasibility of performing Coiled Tubing Cement Zonal Isolation in a leaking tubing and recommended solutions to achieve a successful Zonal Isolation. Few of the vital criteria that enabled this campaign to be executed were the location of tubing leaks that were ways above the intended top of cement, the Production Packer Integrity was intact, and the use of Cement Retainer in the operation. The low-cost solutions recommended were to (1) fill up both production casing and tubing with fluid to enable Production Packer – Tubing Integrity / Cement Retainer Integrity to be evaluated appropriately, (2) use of Single Trip Cast Iron Cement Retainer to avoid difficulties in sting-in or (3) use of Modified Cement Retainer with Dual Flapper Check Valve (DFCV) and Pump Out Plug to facilitate Cement Retainer Integrity Test in case if result from solution (1) was misleading or not available. This paper therefore details all the operation approaches taken by the project team in accessing the available well data and how the integrity problems were addressed. This paper intends to guide well engineer who might face similar well integrity challenges in their intervention campaign.