To improve reservoir management and field recovery, Karachaganak Petroleum Operating b.v. (KPO), the operator of the giant Karachaganak gas-condensate field in Kazakhstan, drills long horizontal wells and then stimulates them with acid. A variety of different acid stimulation techniques have been used, progressing from simple acid washes to high rate matrix acid treatments and hydraulic fracturing with gelled acid. With the advent of mechanical downhole diversion equipment, KPO now performs multistage selective acid stimulation treatments using Swell Packers for isolation and Ball Activated Multistage Selective Valves for selection stimulation and effective reservoir management.

To date, KPO has drilled several long horizontal wells, completed them with multistage selective completions and stimulated the wells using acid. Analysis of both pre- and post-stimulation pressure build-up tests from these wells has shown the benefit of using this completion technique with improvements in both productivity index (PI) and flow capacity (Kh). There is also a significant improvement in the flow profile along the wellbore which is a direct result of being able to control where the acid enters the formation rather than it treating a limited interval. Future reservoir fluid management will also be enhanced with this completion technique as it will be easier to isolate zones should they start producing water. KPO’s use of swelling packers for selective stimulation has been extended to restoring or enhancing production from existing wells

This paper summarises the on-going Multistage Selective Acid Stimulation (MSSAS) treatments, with emphasis on the treatment definition process for each stage, and presents initial quantitative conclusions from the analysis of the pre-post-stimulation well tests, production behaviour and fluids production profile with available PLT.

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