| Low-resistivity pay (LRP) is a major formation-evaluation challenge because hydrocarbon-bearing intervals may display low formation resistivity and consequently high calculated water saturation, leading to underestimation of potential pay. This study investigates the Abu Roash (G) Dolomite reservoir in the northern Western Desert, Egypt, using an integrated field-to-pore-scale workflow. The dataset covers twelve wells, with detailed emphasis on five cored wells and three principal petrophysical and dynamic case wells: W-60, W-66, and W-93. Integrated data include open-hole logs, raw petrophysical outputs, conventional and special core analysis (SCAL), sedimentology, petrography, formation-resistivity-factor and resistivity-index measurements, mercury-injection capillary pressure (MICP), NMR, water-oil relative permeability, X-ray fluorescence (XRF), organic geochemistry, mud-log evidence, formation pressure, completion/testing records, and production history.
Results show that the Abu Roash (G) succession is laterally continuous but internally heterogeneous, comprising reefal dolostone, inner-ramp limestone/dolomitic limestone, and mud-rich facies. Reservoir-quality indicated the the dolostone retains substantial storage and flow capacity, with core porosity commonly around 30-38% and permeability ranging from several millidarcies to locally more than 100 mD. MICP and petrography demonstrate a multiscale pore system dominated by mesopore throats with local macro-, moldic-, and vuggy porosity with R35 of approximately 0.81-2.44 micrometres. SCAL electrical measurements reveal non-generic Archie behavior, with cementation exponents (m) of approximately 2.26-2.83 and saturation exponents (n) of approximately 2.29-2.51. Relative-permeability measurements indicate irreducible-water saturations of approximately 16-27% of the pore volume and confirmed continued oil mobility at intermediate water saturations. Petrographic analysis identified ferroan dolomite/calcite and local pyrite, while W-60 XRF confirms Fe-bearing components; these are interpreted as supporting, rather than sole, conductivity mechanisms. W-60 and W-66 produced oil for extended periods, whereas W-93, despite historical classification as essentially non-pay or only marginal pay because of high calculated water saturation, produced movable oil from 5914-5930 ft with high water cut and limited commercial performance. The present study concludes that electrical conductivity, water saturation, and fluid mobility are related but not interchangeable. Abu Rawash (G) low-resistivity pay is best explained by a coupled geological-electrical-hydraulic mechanism in which favorable dolomitized storage and flow pores coexist with smaller connected brine-filled pores and wetting films, while non-generic electrical exponents and Fe-bearing mineralogy add further complexity. An evidence-based screening workflow is proposed in which conventional petrophysics remains the baseline but is calibrated with SCAL, pore-system and mineralogical data and finally validated using hydrocarbon shows, pressure, well testing, and production whenever conventional saturation criteria conflict with geological or dynamic evidence. This workflow proved efficient in identifying low resistivity pay zones in Abu Rawash-D member.
| Abstract |