Challenging Through-Tubing Intervention Succeeds Despite Extreme Well Conditions

Abstract The subject well, located onshore in the Kingdom of Saudi Arabia, had approximately 9,000 ft of 2.00-in coiled tubing lost in the wellbore, and was requiring thru-tubing intervention to recover the parted string and subsequently abandon the well. The string was lost following a failed cementing operation that left the string stuck due to 2,000 ft of cement inadvertently setting in the coiled tubing-production tubing annulus. Additionally, the lost coiled tubing had an inconel fiber optic cable (IFC) running through it, which presented an additional challenge in recovering the tubing from the wellbore. Downhole conditions were extreme, with 42% hydrogen sulfide and 10% carbon dioxide emitting from the wellbore. Operational conditions were also a major constraint, as the drive fluid was mud with 16% solids content, along with mud which had "packed off" in the coiled tubing-wellbore annulus. These factors created great challenges, and meticulous planning and execution was required to prevent critical well-control problems throughout the intervention operation. The operation began with a rig-less coiled tubing operation to polish the top of the "fish" and permit access for a fishing assembly to begin recovery of the string. This was followed by the deployment of a workover rig to provide a more effective and time-efficient platform to recover the string. Following the string recovery, the 4.5-inch heavy-walled tubing required severing to commence the abandonment process. This paper will describe the challenging operation to recover the coiled tubing from the wellbore and sever the heavy-walled tubular, with all cautionary measures taken to mitigate well-control hazards and avoid lost-time safety incidents. The operation was concluded with most of the string recovered without any lost-time incidents. More than 62 runs were conducted, both rig-less and rig-supported, with the IFC coiled tubing string being recovered in 100- to 500-foot sections. Despite the heavy mud and high solids content, the heavy-walled tubular was cut successfully using a hydraulic cutter, which allowed for its subsequent recovery. Given the extremely sour down-hole conditions, along with the multiple challenging operational factors, this case presents an application with a unique set of unconventional circumstances which usually prohibit the successful recovery of lost strings. This case also demonstrates how careful planning, round-the-clock technical support and effective execution were the cornerstones of a successful intervention with extremely challenging conditions.