Towards a Petrophysically Consistent Implementation of Archie’s Equation For
            Heterogeneous Carbonate Rocks

Ramamoorthy, Raghu; Ramakrishnan, T.S.; Dasgupta, Sagnik; Raina, Ishan

doi:10.30632/t60als-2019_p

Cited by 6 publications

(4 citation statements)

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“…Both our analysis and Ramamoorthy et al. 's (2019) work suggest that the effective medium model is adequate when the pore size distribution is not unimodal and the microporosity is randomly distributed. Depending on the spatial distribution of microporosity, water in micropores could contribute significantly to electrical conductivity or could only contribute to saturation.…”

Section: Discussionsupporting

confidence: 68%

“…To properly simulate the resistivity index curve, the models also need to consider the electrical properties of each pore system and the saturation changes in each pore system during drainage or imbibition. We assume that (a) the electrical resistivity of both macropore and micropore systems (represented by subscripts M and m , respectively) can be described by Archie's equation with the same saturation exponent, n (Isah et al., 2021; Ramamoorthy et al., 2019; Swanson, 1985), namely,

{RI}_{i}={S}_{i}^{-n},\,i=m,\,M,

and (b) linear superposition applies for the capillary pressure‐saturation relationship of the bimodal system (Costa & Cavalcante, 2021; Romano et al., 2011; Swanson, 1985), that is, the non‐wetting phase invades pores following the threshold capillary pressure, and the water saturation of the medium is given by

{S}_{w}={f}_{m}{S}_{m}+\left(\mathit{1}-{f}_{m}\right){S}_{M}.

…”

Section: Discussionmentioning

confidence: 99%

“…While various analytical and empirical models have been proposed to explain and model the electrical behavior of rocks exhibiting bimodal pore‐size distributions, these models have different assumptions about the connectivity between fluids present in macropores and micropores (Dong et al., 2017; Fleury, 2002; Padhy et al., 2006; Petricola & Watfa, 1995; Ramamoorthy et al., 2019; Sen, 1997; Swanson, 1985). Such a glaring contradiction in modeling assumptions is due to poor understanding of the effects of pore‐structure on fluid displacement and electrical properties (Isah et al., 2021).…”

Section: Introductionmentioning

confidence: 99%

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The Role of Pore‐Shape and Pore‐Space Heterogeneity in Non‐Archie Behavior of Resistivity Index Curves

Sun

Torres‐Verdín

2022

JGR Solid Earth

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Resistivity index curves describe the relationship between electrical resistivity and water saturation of porous media and are critical in formation evaluation and for the geophysical monitoring of subsurface processes. Archie's second equation enforces a linear relationship between resistivity index and water saturation in log‐log plots which has been widely used for the assessment of in situ hydrocarbon saturation. However, resistivity index curves that deviate from Archie's equation are ubiquitous in subsurface reservoirs, especially complex carbonates exhibiting bimodal pore‐size distributions, where the effects of pore‐scale controlling factors on rock resistivity remain unclear. We implement pore‐network models built under controlled conditions of pore shapes, bimodal pore‐size distributions, pore connectivity, micropore fractions, and anisotropy to investigate the effects of pore shapes and pore‐space heterogeneity on resistivity index curves. Results indicate that percolating wetting films associated with pore shapes decrease the resistivity index at low values of water saturation and cause a decrease in saturation exponent. In cases of bimodal pore‐size distributions, micropore fractions control the connectivity between macropores, thus affecting water drainage and resistivity index curves. At low fractions of micropores, the resistivity index curve is governed by the connected macropore system at high values of water saturation and is then determined by micropores, thereby resulting in non‐Archie behavior. Pore‐size distributions and spatial anisotropy also affect the resistivity index curves. We summarize the observed pore‐space heterogeneity effects on resistivity index curves and compare model predictions to numerical simulations; both the geometric mean model and effective medium theory provide acceptable estimates of the electrical properties of bimodal porous media.

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Section: Discussionsupporting

confidence: 68%

{RI}_{i}={S}_{i}^{-n},\,i=m,\,M,

{S}_{w}={f}_{m}{S}_{m}+\left(\mathit{1}-{f}_{m}\right){S}_{M}.

…”

Section: Discussionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

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The Role of Pore‐Shape and Pore‐Space Heterogeneity in Non‐Archie Behavior of Resistivity Index Curves

Sun

Torres‐Verdín

2022

JGR Solid Earth

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“…Previous studies have applied effective medium theory to calculate conducting properties of heterogeneous media (Ramakrishnan et al., 2001; Ramamoorthy et al., 2019). We apply effective medium theory to our networks with bimodal pore‐size distributions (David et al., 1990; Kirkpatrick, 1973), that is,

{f}_{\mathrm{L}}\frac{{\sigma }_{\mathrm{m}}-{\sigma }_{\mathrm{L}}}{{\sigma }_{\mathrm{m}}+{\sigma }_{\mathrm{L}}}+(1-{f}_{\mathrm{L}})\frac{{\sigma }_{\mathrm{m}}-{\sigma }_{\mathrm{S}}}{{\sigma }_{\mathrm{m}}+{\sigma }_{\mathrm{S}}}=0

where σ m is the electrical conductivity of the medium, σ L is the conductivity when f L = 1, and σ S is the conductivity when f L = 0.…”

Section: Resultsmentioning

confidence: 99%

Pore‐Scale Investigation of the Electrical Resistivity of Saturated Porous Media: Flow Patterns and Porosity Efficiency

2021

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The electrical resistivity‐porosity relationship of porous media is critical for reliable formation evaluation. Archie's equation is empirical, and uses only porosity as pore‐space property, neglecting the spatial variability of the pore space; its fitting parameters may have unclear physical meaning and be nonconstant over a wider porosity range or in spatially complex rocks. We use microfluidics augmented with pore‐network modeling to investigate the effects of pore‐space properties and their evolution processes on electrical resistivity‐porosity relationships. Both a flow‐pattern parameter and a measure of porosity efficiency are implemented to quantify the spatial variability of the flow field and the conduction efficiency of porous media. Results indicate that both pore‐size distribution and pore‐space evolution impact the electrical behavior considerably. In cases of unimodal pore‐size distributions, a larger pore‐size variation or a higher porosity reduction in small pores results in higher values of Archie's porosity exponent, m; the flow pattern becomes more heterogeneous, and the efficiency of porosity to conduct electricity decreases. For cases of bimodal pore‐size distributions, the formation factor‐porosity relationship is nonlinear in log–log plots; the flow behavior is primarily affected by the fraction and connectivity of large pores. Results suggest that using porosity alone as pore‐space characteristic is inadequate to describe the electrical behavior of complex porous media. Petrophysical classification based on flow patterns and porosity efficiency is an effective alternative to differentiate the results. We introduce the electrical quality index as an effective parameter for petrophysical classification, which is verified with core data for both Fontainebleau sandstones and carbonates.

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Modified Archie’s parameters for estimating water saturation for carbonate reservoir in north of Iraq

Jumaah

2021

J Petrol Explor Prod Technol

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Archie’s parameters, cementation factor (m), saturation exponent (n) and tortuosity factor (a), are general factor that have effects on water saturation magnitude, due to their sensitivity to pores distribution, lithofacies properties and wettability, particularly in carbonate reservoirs. Water saturation magnitude has a direct effect in estimating initial oil-in-place values, and inaccuracy in its values will lead to huge impact errors in initial oil-in-place values, so it would affect the economics of field management and development plans. In this paper, the main objective was to investigate the impact of using conventional and modified Archie’s parameters in the determination of water saturation from well log interpretation for Tertiary reservoir in Khabaz oil field, a heterogenous carbonite reservoir in the north of Iraq which was affected by different digenesis processes that impacted the reservoir quality. Tertiary reservoir of Khabaz field consists of five geological units (A, B, C, D and E), and the selected well penetrated the top of the reservoir at 2200.5 m RTKB and passed through five geological units and reached total depth at 2348 m RTKB. The geothermal gradient of the field was 1.12 ℉ per 100 ft, and formation water resistivity (Rw) was about 0.029 Ω m. Water saturation was at first estimated from resistivity logs by Archie model with conventional known values of parameters (a, m and n) (1, 2 and 2), respectively, and then Archie’s parameters were modified and determined by graphical technique of Pickett plot for each geological unit to estimate water saturation. Finally, the results show the water saturation value was more sensitive for Archie’s parameter in low-porosity and high-clay-volume zone, but less sensitive in clean high-porosity zone, and water saturation values determined by modified Archie model were less about 18.5% at mean than their value by using conventional Archie’s parameters.

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Towards a Petrophysically Consistent Implementation of Archie’s Equation For Heterogeneous Carbonate Rocks

Cited by 6 publications

References 0 publications

The Role of Pore‐Shape and Pore‐Space Heterogeneity in Non‐Archie Behavior of Resistivity Index Curves

The Role of Pore‐Shape and Pore‐Space Heterogeneity in Non‐Archie Behavior of Resistivity Index Curves

Pore‐Scale Investigation of the Electrical Resistivity of Saturated Porous Media: Flow Patterns and Porosity Efficiency

Modified Archie’s parameters for estimating water saturation for carbonate reservoir in north of Iraq

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