In mature carbonate reservoirs, the potential for bypassed or under-stimulated pays need to be addressed in order to enhance the productivity of the wells. Reservoir restimulation is one of the viable option to do this. However, due to issues with completion, perforation and other associated issues that given wells may have, restimulation should be designed and implemented such that well productivity is enhanced while simultaneously maintaining the requirements for well completion integrity. Proper design for restimulation in thick carbonate reservoirs could eliminate any negative issues that may occur during completion and prevent integrity failure during the process. In thick carbonate reservoirs, like those found in the Middle East, the aforementioned criteria contain both petrophysical properties and current production profile obtained by production logging, establishing good foundation for implementing restimulation. Petrophysical properties help define the stimulation strategy necessary based on log potential, while the current production profile identifies the best location to stimulate over the existing completed perforated interval. In thick carbonate stimulation, uneven reservoir recovery is often observed and considerable parameters must be set during the stimulation design. Major changes to consider during the candidate evaluation for the restimulation in thick carbonate reservoir are: non-uniform pressure depletion across the formation, various pressure drawdowns, and change in PVT properties. In addition, wormholes which formed during the initial reservoir stimulation are major factor for consideration. These wormholes may act as thief zones during restimulation work and could lead to improper zonal coverage. This paper describes restimulation design strategy which has been tailored for well preparation based on mature well conditions while also considering factors of completion and well-integrity issues. The well preparation includes focus on the reperforation selection, post-reperforation production log evaluation and production profile matching. Within the stimulation strategy, fluid selection and placement strategy will be discussed, taking into considering all aspects of a mature well.

After more than a decade of production years, the thick heterogeneous carbonate reservoir in the middle-east region would need to be rejuvenated to unlock more potential from the hidden layers that were not properly stimulated on the initial completion phase resulting deficient recovery distribution. The giant carbonate reservoir constitutes a tremendous thick pay zone with multiple heterogeneities that increase the uncertainty level. The reservoirs were completed using various completion and stimulation design initially. These various completion designs implement the effort to overcome the initial uncertainties due to formation thickness and complexity. As the reservoirs are being recovered, the degree of uncertainty is also increase by having production dynamics. Despite the well-known reservoir characteristics, the well production dynamic also affect the reservoir heterogeneity such as uneven pressure depletion due to wormholes from previous stimulation. On the mature carbonate formation that had stimulation treatment, existing wormholes from the previous stimulation may still exist and normally they are on the high conductivity layers due to improper diversion. As the degree of uncertainty is increased, restimulation treatment becomes more challenging as more uncertainties need to be taken into account on the design. Additional data to initial completion phase would have to be analyzed in order to minimize the uncertainties from the production dynamics. To overcome these uncertainties, proper stimulation treatment has to be designed and diverter utilization would take an important role of the treatment. Preliminary validation to the design is required in order to achieve optimum and efficient treatment. This paper will present the single-stage restimulation design methodology based on the field case history. It consists of an exceptional design, execution, and evaluation cycle for fine tuning the details covering the major uncertainties available on these mature wells. The cycle is started from collecting the additional information to the initial ones, analyzing the production dynamics, and eventually designing and fine tunes the diverter design to optimize the stimulation fluid placement. The restimulation treatment is proposed in such an efficient way to deal with the additional uncertainties from the production dynamic. The output from this is fluid selection, treatment schedule (sequence and pumping rate), diversion design, and treatment conveyance. The design will have more than one scenario as a result of potential uncertainties during the execution. The cycle was then completed with the evaluation of the treatment and the lesson learnt was applied. Production profile after restimulation treatment shows that the stimulation target has been achieved efficiently in order to drain unstimulated layers. A combination of bottomhole pressure data and production log results more accurate on fluid placement estimation and as basic for the future design. Optimizing treatment fluid through all layers can be achieved for maximizing the well potential.