Abstract
The Sabiriyah Mauddud limestone is a super-giant depletion drive oil reservoir in North Kuwait. It is undergoing massive development efforts, with a planned enhancement in oil production through phased water flood development since 2000.
The Phase1 development addresses the crestal area (60 km2) of the structure, which was the focus for development efforts in the past. 14 years of dynamic performance from producers and injectors located in the Ph1 area enhanced the understanding of the reservoir dynamics. Time lapsed monitoring of static reservoir pressures at key wells during the ongoing water flood, coupled with isochronal Pressure surveys during reservoir shut-downs and RFT data from newly drilled wells in the area during the post injection period, helped to confirm the pressure connectivity across the reservoir and the water flood response. As all the wells are on ESP, the live data on Pump-intake Pressures provided insights into response behavior. Production tests gave valuable insights into the well performance, specially water cut build-up and reservoir architecture. Integration of the dynamic data with Production logs & FMIs led to the identification of speed zones with high permeability. One of the limitations of the pattern water flood with a combination of vertical injectors & vertical producers perforated across the whole hydrodynamic unit was a quick water breakthrough via the high perm speed zones and re-circulation of the injected water, as evident from tracer surveys and PLT data. A comprehensive review and updated performance analysis led to the need of re-developing the reservoir with a paradigm shift using a combination of Horizontal injectors drilled & completed at bottom of the hydraulic unit and the horizontal producers drilled/ completed at upper part so that the water breakthrough is delayed and better sweep is achieved. A conformance plan has been taken up so as to switch over to the new strategy.
The Phase2 development consists of all remaining peripheral acreage (250 km2), with immense reservoir rock & fluid uncertainties, leading to the identification of reservoir segments for re-appraisal through drilling & testing of new wells. Re-appraisal work, along with enhanced fluid description, led to the conclusion that a large segment within the Ph2 area, originally considered as a regime of light oil - turned out to be viscous oil with a high pressure ramp. In addition to helping the ongoing Full field dynamic modeling and development planning for this giant reservoir, this also led to the initiation of a peripheral Water flood with vertical wells initially, and switching over to Non-Conventional Wells in the poorer Ph2 area.
This paper documents the case history of Waterflood management in a super-giant carbonate reservoir and the challenges that had to be met with a quick re-adjustment to the development plan as necessitated during the ongoing implementation & evaluation.
