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.