Integrating the Fluid Quality and Rock Description in Sabiriyah Mauddud Limestone in North Kuwait To Rationalize the Waterflood Development Strategy—A Case History
Authors: Chetri H. B. , Najeh H. , Al-Janaie D. , Al-Mutawa M. , Chandran T. P. , Al-Anzi E. , Wells J. , Cig K. 
Published: December 2007

The Sabiriyah Mauddud limestone of North Kuwait is a super giant depletion drive oil reservoir. Massive development efforts are underway, with a planned enhancement in oil production through phased pattern water flood. The Phase 1 development addresses the crestal area (50 km2) of the structure, which was the focus for development efforts in the past. The Phase 2 development consists of all remaining peripheral acreage (200 km2), with immense reservoir rock & fluid uncertainties, leading to the identification of reservoir segments for re-appraisal through drilling & testing of new wells.

The fluid description had been a challenge for the reservoir, especially in the mid flank and down flank areas with poor rock / fluid quality. The past data on fluid quality had been the average for the whole of the Mauddud unit perforated together. A serious data gap existed with respect to the vertical variation of the reservoir oil quality. Sampling of formation fluids has been historically not possible in the formation due to low permeability and sharp viscosity variation with depth, to fully develop and discover the potential of the formation. The permeability and viscosity combination of the formation has not allowed fluids to be sampled with a probe formation tester tool. The slick line sampling operation has been also attempted with nitrogen lifting without any result. In early 2002, in order to match the field development plan, formation tester with an inflatable dual packer module was utilized to achieve sampling. The operation was completed successfully in the 9 5/8" cased hole environment. Second half of the year, sampling was also achieved in 8.5" open hole conditions. Late 2002 and onwards, the sampling operation became part of the open hole logging program and the versatility of the wireline tester tool also allowed performing mini-DST and vertical interference applications in required wells. Re-appraisal & testing work, along with enhanced fluid description, led to the conclusion that a large segment within the Phase 2 area, originally considered as a regime of light oil - turned out to be viscous oil.

Prior to progressing on the water flood development in Phase 2 area, significant amount of data was acquired through a rational placement of new wells so as to reduce the uncertainty on rock quality. Numerous injectivity tests / step rate tests were conducted, the results of which were suggestive of the concept of injecting above the formation parting pressure in down flank areas with poorer rock & fluid quality and design the facilities accordingly to meet the subsurface requirements.

The earlier estimates of the water flood recovery were discovered to be quite optimistic as reflected by the latest full field reservoir simulation model runs. The above realizations changed the past outlook of development plan and led to the fine-tuning of the way forward.

The paper proposes to share the unique experience & benefits of progressing through a phase development approach for this giant & challenging carbonate reservoir in North Kuwait.