Abstract

Lower Burgan reservoir is a giant multi layered reservoir in Sabiriyah field of North Kuwait operating under active bottom water drive as well as edge water drive. The reservoir is on production since 1960s and has so far produced about 63% of the original reserves. The effective reservoir management by innovative tracking of water movement, identifying segments with bypassed oil, opportunistic well workovers, prudent selection of infill well targets and continuous reservoir monitoring have made it possible to sustain the reservoir production rate near to the projected plateau and carry it forward for next 4–5 years.

The lower Burgan reservoir comprises predominantly channelised facies, which impact a high degree of heterogeneity to the reservoir. The massive M sand produces through a vertical sweep of aquifer whereas the interbedded L sand experiences largely lateral edge water sweep. The key of the reservoir/production management from this reservoir has been to monitor the water encroachment pattern and track the bypassed oil. The primary tool for tracking water movement &bypassed oil has been thermal neutron decay logs (Schlumberger TDT and Western Atlas PDK logs). These logs have provided excellent data for mapping water movement in lower burgan reservoir due to the high formation salinities and generally high porosities. The data was holistically analyzed in conjunction with time lapsed PLT and well test data. The information on identification of pressure regimes and vertical connectivity available from RFT data from recent penetrations added further confidence to the interpreted results.

A prudent strategy to acquire static bottom hole pressure measurements and PBU tests was developed so as to have the layer wise characterization and optimize the perforation planning. The event based well tests in key wells periodically led to deliverability optimization. The fluid characterization for each flow unit helped to refine the assessment of well performance vis-à-vis the completion. Innovative approach to estimate the sweep/ recovery efficiency and residual oil saturation by analytical methods proved useful to fine-tune the ranges of expectations.

Simulation models were made in 1980s and mid 1995 which are under revision at present. The model is likely to help the field engineers to manage this giant reservoir more effectively and efficiently on long term basis.

Reservoir Description:

Reservoir Structure

The Sabiriyah field, located on the crest of the Kuwait arch in northern Kuwait, is an elongated, north trending, faulted anticline. The structural configuration in Sabiriyah field is a product of Jurassic and late Cretaceous rejuvenated basement structures. North Northwest-South Southeast trending faults dominate over north south and North Northeast-South Southwest trending faults. The fault throws vary from less than 30 feet to more than 100 feet. Integration of recently acquired seismic data with well data shows the faults dip in the range of 45 to 60 degrees but the sealing/ non-sealing natures of faults are yet to be understood. However, some faults, particularly in central and northern part of the field, appear to be non-sealing but the impact on fluid flow is yet to be ascertained. The structural dip at the level of lower Burgan varies from 2 to 2 1/2 degrees on the eastern flank and approximately 1 to 2 degrees on the western flank. Dips are less than 1–1/2 degree on the plunging north and south ends of the structure. At its southern end this structure passes through a saddle to proceed on trend to the north- northwest-trending Bahra structure. At the lower Burgan horizon the Sabiriyah structure has a closure of about 350 feet.

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