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<p>Carbonate reservoirs are inherently heterogeneous, making their petrophysical evaluation challenging. Water saturation is a key factor controlling hydrocarbon storage, and its accurate estimation is essential for reservoir evaluation. Accordingly, this study integrates geological and petrophysical analyses to determine Archie’s coefficients and assess how rock-type-dependent parameters affect water saturation estimates in tight carbonate samples. A total of 48 plugs from a Persian Gulf tight-carbonate reservoir were examined for porosity, permeability, and electrical resistivity. Thin section petrography was conducted to assess geological controls on reservoir quality. Rock typing was performed using the FZI* approach and the Lucia rock-fabric classification. Water saturation was calculated with both log and core-derived Archie parameters. Water saturation computed using core porosity and constant Archie parameters, including m, n, and a, was generally lower than values obtained using laboratory-measured core parameters. The mean Sw values were 0.20 versus 0.24 in the FZI* method and 0.13 versus 0.17 in the Lucia classification, implying that gas saturation would be overestimated if constant Archie parameters were imposed. Within the Lucia framework, an inverse relation between porosity and mean water saturation was identified, whereas in the FZI* approach, pore-throat size together with porosity and permeability was shown to govern fluid flow within hydraulic flow units. Water saturation values calculated using laboratory-measured Archie parameters varied systematically with depositional texture and diagenesis: mud-dominated, compacted, and cemented facies yielded higher mean Sw values of about 0.30 (v/v) in the RFN/Lucia framework and 0.35 (v/v) in the HFU/FZI* framework. Grain-dominated shoal facies with preserved interparticle pores yielded lower values of about 0.11 (v/v) and 0.16 (v/v), respectively. It is concluded that determining Archie parameters by considering geological and petrophysical factors produces different water saturation estimates in tight carbonates, generally yielding higher values than those calculated using constant Archie parameters.</p>

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Geological and petrophysical controls on Archie’s coefficients and water saturation in tight carbonates, Permian–Triassic of the Persian Gulf

  • 期刊论文

  • 发表日期：

    2026年7月6日

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  • Marzieh Honarvar Nazari,
  • Vahid Tavakoli

摘要

Carbonate reservoirs are inherently heterogeneous, making their petrophysical evaluation challenging. Water saturation is a key factor controlling hydrocarbon storage, and its accurate estimation is essential for reservoir evaluation. Accordingly, this study integrates geological and petrophysical analyses to determine Archie’s coefficients and assess how rock-type-dependent parameters affect water saturation estimates in tight carbonate samples. A total of 48 plugs from a Persian Gulf tight-carbonate reservoir were examined for porosity, permeability, and electrical resistivity. Thin section petrography was conducted to assess geological controls on reservoir quality. Rock typing was performed using the FZI* approach and the Lucia rock-fabric classification. Water saturation was calculated with both log and core-derived Archie parameters. Water saturation computed using core porosity and constant Archie parameters, including m, n, and a, was generally lower than values obtained using laboratory-measured core parameters. The mean Sw values were 0.20 versus 0.24 in the FZI* method and 0.13 versus 0.17 in the Lucia classification, implying that gas saturation would be overestimated if constant Archie parameters were imposed. Within the Lucia framework, an inverse relation between porosity and mean water saturation was identified, whereas in the FZI* approach, pore-throat size together with porosity and permeability was shown to govern fluid flow within hydraulic flow units. Water saturation values calculated using laboratory-measured Archie parameters varied systematically with depositional texture and diagenesis: mud-dominated, compacted, and cemented facies yielded higher mean Sw values of about 0.30 (v/v) in the RFN/Lucia framework and 0.35 (v/v) in the HFU/FZI* framework. Grain-dominated shoal facies with preserved interparticle pores yielded lower values of about 0.11 (v/v) and 0.16 (v/v), respectively. It is concluded that determining Archie parameters by considering geological and petrophysical factors produces different water saturation estimates in tight carbonates, generally yielding higher values than those calculated using constant Archie parameters.