Reviving the Production Potential of a Severely Damaged, Subhydrostatic Gas Well Using a Novel Solids-Free Acid Diverter System: Case Study from the Middle East

Abstract A gas well that produced from a carbonate reservoir developed tubing-casing annulus communication above the polished bore receptacle (PBR), which caused any mechanical means of formation isolation to be impractical before workover operations. The formation was in a subhydrostatic condition after a history of acid fracturing operations, so the operator used a high-volume lost circulation material (LCM) pill to isolate the reservoir. After the workover, a high-rate stimulation treatment was necessary to reinstate the well's production potential. Subhydrostatic conditions prevented coiled tubing (CT) pinpoint stimulation, so it was decided to bullhead treatment fluid after wellbore cleanout and perforation washing. A diverter system was required, which works independently from the acid system pH and is solids-free, for uniform treatment of the 75-ft interval. A relative permeability modifier (RPM)-based solids-free acid diverter (SFAD) system was used with 20% diesel-emulsified acid (DEA) and 20% hydrochloric acid (HCl acid) in alternated stages. SFAD changes the effective permeability of the zone, which adheres to the formation and diverts fluid toward untreated zones without reliance on mechanical plugging mechanisms common in typical diverter systems. Elimination of pH-dependent polymers and surfactant-based diverter systems allowed the bullhead treatment of the proposed fluids at a high pump rate. A specific permeability-based criterion defined the required SFAD volume. The treatment sequence included diverter stages with progressively increased volumes to divert stimulation fluid into zones with higher resistance to treatment fluid. The bullhead treatment with 20% diesel-emulsified acid, 20% HCl acid, and SFAD increased gas production by 50% compared to preworkover levels. Relative permeability to water-based fluid decreased, which diverted subsequent stages into previously untreated zones. The low-viscosity system adhered instantaneously onto the rock surface, which helped eliminate any requirement for soak time or pH adjustment and proved suitable for high-rate bullhead treatments. Severe subhydrostatic conditions resulted in heavy losses during stimulation, which revealed new insights into SFAD effectiveness. Typically, chemical diverters used within the industry depend on pH change or a plug-based mechanism. These systems often require tailored soak times, low pump rates, and specific pre- and post-flush or flowback considerations to enable diverter degradation. Moreover, conventional diverters face limitations when used in fractured reservoirs with high permeability contrast. SFAD overcomes these limitations because the system contains no solids, operates without viscosity enhancement for diversion, selectively diverts any water-based system, preserves hydrocarbon zones without damage, and functions effectively in formations up to 6 Darcy permeability.