Redeveloping Mature Fractured Carbonate Reservoirs

Abstract

Naturally fractured carbonate reservoirs (NFCRs) comprise the majority of the oil and gas reservoirs around the Persian Gulf. Many of these reservoirs have a long history of exploitation, but vast amounts of oil remain in place. A major redevelopment process for light oil based NFRs will likely be the use of horizontal wells combined with gravity drainage at constant pressure based on voidage replacement with natural gas (top-down) and natural bottom water drive or deliberate bottom water injection (bottom up), or controlled flank water invasion for reservoirs with adequate dip. The excellent recovery factors achieved in Alberta NFCRs depends on appropriate well placement, careful voidage replacement management, and continuous monitoring of pressures, rates and fluid ratios.<br /> Geomechanical aspects of such a redevelopment approach may involve the placing of horizontal wells in orientations conducive to small-scale well stimulation activities revolving around hydraulic fracturing. Such fracturing helps guarantee that sufficient aperture vertical channels are available so that stable gravity drainage can develop and give adequate production rates per well.<br /> The proposed approach and information needs for the proper placement of wells and appropriate stimulation practices are outlined. In particular, good understanding of reservoir permeability distribution, water/oil interfaces, lithology data, and <em>in situ</em> stress field data are needed, and this is more challenging in reservoirs that have already gone through some amount of pressure depletion.