Intervention and Abandonment - Riserless Productive Zone Abandonment Using Epoxy Resin

When an operator in the deepwater Gulf of Mexico needed to abandon a productive zone in a well with unique challenges, an innovative operation using both riserless and resin sealant technologies provided the ideal solution. The unique challenges of this well resulted in two primary project requirements: the first, which restricted use of any on-tree, through-tubing access equipment, necessitated the second, which required an isolation material to be bull-headed from surface. The first project requirement prevented the operator from installing standard, through-tubing access equipment, so the operator investigated 15K riserless pumping packages and tree interfaces. After evaluating several options for safety, compliance, availability, reliability, and service the operator selected a turn-key solution including a multi service vessel, two ROVs, two coiled-tubing down-lines, and a stand-alone dual-barrier isolation unit with emergency disconnect capability. Two tree interface locations were evaluated: a choke insert and a custom dual-valve pressure cap with a hot-stab receptacle installed on the subsea tree's flowline hub. Because the well was to be abandoned in the near future, the operator decided to remove the flowline jumper and install the custom pressure cap. The second project requirement caused the operator to seek an isolation material that would overcome three primary obstacles. First, the material must provide isolation from a small treatment volume due to unknown injection rates and pressures. Second, the isolation material must not degrade when mixed with wellbore fluids in such a way that would compromise the mechanical properties of the resulting plug, which would be pumped more than 20,000 ft during placement. Third, the isolation material must minimize the risk of bridging off while squeezing past a known obstruction in the flow path. Analysis of a resin sealant revealed that it could successfully address each of these obstacles. Previous laboratory testing had established that resins provide a 400% increase in shear bond when compared to conventional cement. Project-specific laboratory testing confirmed these results for this particular resin and application. Also, the resin's immiscibility in water-based fluids all but eliminated any concern regarding questionable plug integrity due to wellbore fluid mixing. Finally, the resin's solids-free, active composition greatly reduced the potential of bridging and not isolating the zone of interest. These properties and advantages allowed the operator to proceed with a 35 bbl treatment, confident that the small volume could be pumped into place and would provide the necessary isolation. Ultimately, wellbore isolation and emergency disconnect equipment, as well as coiled tubing down-lines, were successfully run, installed, and tested. Then the operator pumped 35 bbl of resin down the production tubing, squeezing 10 bbl into the formation and leaving the remainder in the tubing. When the resin had cured, the operator successfully pressure tested the well, both positively and negatively. The combination of two relatively novel technologies allowed the operator to overcome a unique set of challenges while staying on schedule and under budget.