Stimulation Workflow for an HP/HT High-Anisotropy Carbonate Reservoir in Iraq: Coiled Tubing Wellbore Cleaning with Customized Solvent Blend to Fine-Tune Stimulation Design Using Perforation Sealer Diversion Technique

Abstract The primary objective of this case was to optimize well performance and enhance hydrocarbon recovery from a complex, high- pressure/high-temperature (HP/HT), low-permeability carbonate reservoir. This approach also addressed asphaltene solidification in the wellbore that blocked access to the perforations. Success resulted from the combined application of coiled tubing (CT), a tailored emulsified solvent system (ESS), and subsequent bullhead stimulation. Conventional acid and appropriately sized perforation sealers improved stimulation effectiveness to divert the treatment to low-permeability layers. In response to the complex reservoir characteristics and HP/HT environment, the ESS with a high-dispersant load strategy was deployed for wellbore cleanup using CT and a high differential jetting nozzle. Acid stimulation and diversion design were carefully optimized to ensure maximum coverage in the 52-m interval affected by high anisotropy under extreme HP/HT conditions. Extensive simulations guided the development of a customized diversion solution to enhance stimulation in low-permeability zones. The combined effect of CT and the high-dispersant solvent system enabled thorough wellbore cleanup, effective treatment, and increased hydrocarbon recovery. The integrated workflow led to substantial improvements in hydrocarbon production. The high-dispersant ESS effectively dissolved solidified asphaltenes and restored full access to the perforated interval. Perforation sealers enabled precise diversion and optimized acid penetration into the low-permeability zones. As a result, production rates rose from a completely blocked reservoir to 3,500 BOPD, which confirmed the effectiveness of this synergistic approach. This case study highlights the robustness of the solvent blend, accuracy of the jetting nozzle deployment, and versatility of the diversion technique and establishes a new benchmark for HP/HT carbonate reservoir stimulation. The innovative integration of high-dispersant solvent systems, advanced jetting nozzle deployment, and precise diversion techniques are highlighted in this paper. A repeatable methodology is presented to improve well performance under extreme HP/HT conditions by effectively addressing asphaltene challenges using stimulation optimization in complex, anisotropic reservoirs. The discoveries provide valuable insights into asphaltene remediation, deliver actionable advancements in reservoir management practices, and contribute to more efficient and sustainable hydrocarbon recovery in difficult environments.