Success of Rigless Multi-Stage Selective Stimulation in Super-Giant Tight Reservoirs - Case History from UAE

Abstract

Enhancing hydrocarbon recovery is the ultimate goal in the oil and gas business; nowadays there are many technologies that can be applied effectively to reach that goal; Maximum reservoir contact (MRC) wells, Under-balanced drilling (UBD), Multi-laterals (ML), fishbone. etc. However, still the preferable, economical option is to improve the well production by stimulation which is applied easily and riglessly in existing or newly drilled wells. In many horizontal or long pay zone wells; the optimum results cannot be achieved through conventional stimulation techniques because it is difficult to ensure even stimulation fluid distribution (i.e. acid in the case of carbonate stimulation) across the entire lateral hole unless some sort of selective stimulation can be performed. This is a prerequisite for successful result. It becomes more challenging in heterogeneous open hole completions which have natural fractures. Even more challenging is trying to achieve selective stimulation in such complex geological environment when specific reservoir compartments need to be treated specifically. A tight gas carbonate reservoir with no oil rim in a super-giant onshore gas field in Abu Dhabi was particularly targeted for stimulation during a field review to increase field production. Conventional stimulation treatments performed to restore well productivity resulted in rapid performance decline as a result of undesired worm-holing throughout the existing bore hole and uneven flow contributions. PLTs’ were run in three wells to understand the well productivity. The results showed that most of the gas production (approximately 95%) was from upper zones while the remaining production came from the lower zones which were of poor reservoir quality. It became necessary to look at selective fracturing stimulation techniques that could be applied riglessly and allow contribution from the non-producing zones. This paper describes a unique engineering approach, the Hydrajet Fracturing (HJF) technique that was successfully executed for this purpose. The objective was to apply an economically feasible, rigless, selective fracturing technique with efficient placement approach that would lead to proper reservoir drainage. Pin-point stimulation at selected points was considered an important factor for the development of this field. After the unique stimulation treatment, a new technology based on spectral noise logging and temperature distribution survey was used to evaluate the contribution of the targeted fractured zones in conjunction with pressure buildup well test analysis. Several lessons were learnt from the first use of this technology and some interesting conclusions were reached from these investigations.