Abstract

Exposure of production annulus with formation fluids due to tubing-casing communication is unfavorable scenario throughout well's life cycle. The communication paths are always susceptible to aggravate with the passage of time, eventually resulting in complete loss of well integrity due to failure of one of the integral well barriers and potentially causing major risk and hazards to environment and personnel. Accurate and most efficient actions are therefore required on war-foot basis to restore lost integrity.

DST of an exploratory well in South Pakistan revealed the corrosiveness of reservoir fluid (26 % CO2), therefore, completed with chrome material. Well remained shut-in due to plant capacity constraints. Soon after well commissioning, pressurized annulus was reported. Initial investigation depicted hydrocarbons in annulus, however, Distributed Temperature Sensing (DTS) was later used to accurately locate the leak path. Conventional remedial options including tubing patch and work-over were ruled out due to extreme reservoir parameters and associated high cost as well as production curtailment. Placement of Resin-Based Isolation Plug (RBIP) in annulus was found to be the most feasible option to restore well integrity.

Coiled tubing conveyed DTS was carried out in shut-in and flowing conditions that confirmed depth of leak path in completion string. Main reason of implementing this diagnostic technique was the unavailability of conventional logging tools compatible with high temperatures. DTS was run in conjunction with correlating tool (CCL) for precise depth determination with respect to completion jewelry. After exploring pros and cons of conventional remedial techniques, treatment through annulus was the only remedial option left to block the leakage path in completion string therefore, placement of RBIP on top of leak point was planned. This plug, once solidifies, restricts tubing movement due to thermal effects when exposed to production loads. Therefore, extensive stress analysis was essential to evaluate the integrity of anchored completion due to plug under various production loads throughout the well's lifecycle. With all possible risks critically assessed, RBIP along with bridging spacers was successfully poured in annulus during rig less operation. Well was kept in flowing conditions towards plant to avoid production curtailment throughout the operations. Currently, well is flowing, maintaining the necessary feed at plant and fulfilling country's gas demands with well integrity intact.

Tubing-Casing communication and pressurized annulus has become common problem and plays significant role in maintaining the reputation and progress of E&P companies. Conventional methods are readily available to rectify such problems however, there are scenarios where wellbore conditions / parameters and economic feasibility may restrain their implementation. RBIP is a new technique in restoring well integrity through annulus and is successfully implemented for the first time not only in Pakistan Petroleum Limited (PPL) but in Pakistan.

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