Nano- to Millimeter Scale Morphology of Connected and Isolated Porosity in the Permo-Triassic Khuff Formation of Oman

Abstract

Carbonate reservoirs form important exploration targets for the oil and gas industry in many parts of the world. This study aims to differentiate and quantify pore types and their relation to petrophysical properties in the Permo-Triassic Khuff Formation, a major carbonate reservoir in Oman. For that purpose, we have employed a number of laboratory techniques to test their applicability for the characterization of respective rock types. Consequently, a workflow has been established utilizing a combined analysis of petrographic and petrophysical methods which provide the best results for pore-system characterization. Micro-computed tomography (µCT) analysis allows a representative 3D assessment of total porosity, pore connectivity, and effective porosity of the ooid-shoal facies but it cannot resolve the full pore-size spectrum of the highly microporous mud-/wackestone facies. In order to resolve the smallest pores, combined mercury injection capillary pressure (MICP), nuclear magnetic resonance (NMR), and BIB (broad ion beam)-SEM analyses allow covering a large pore size range from millimeter to nanometer scale. Combining these techniques, three different rock types with clearly discernible pore networks can be defined. Moldic porosity in combination with intercrystalline porosity results in the highest effective porosities and permeabilities in shoal facies. In back-shoal facies, dolomitization leads to low total porosity but well-connected and heterogeneously distributed vuggy and intercrystalline pores which improves permeability. Micro- and nanopores are present in all analyzed samples but their contribution to effective porosity depends on the textural context. Our results confirm that each individual rock type requires the application of appropriate laboratory techniques. Additionally, we observe a strong correlation between the inverse formation resistivity factor and permeability suggesting that pore connectivity is the dominating factor for permeability but not pore size. In the future, this relationship should be further investigated as it could potentially be used to predict permeability from wireline resistivity measured in the flushed zone close to the borehole wall.

Petrophysical characterization, BIB-SEM imaging, and permeability models of tight carbonates from the Upper Jurassic (Malm ß), SE Germany

“…9C) suggests that fluid flow through the matrix primarily depends on pore connectivity and pore throat size distribution rather than on the effective porosity. This is in accordance with results of Smodej et al (2020), showing that the permeability is mostly controlled by the smallest throats. The slightly positive correlation between the argon permeabilities and the r 35 also points to the pore throat size distribution, particularly the r 35 , as the matrix permeability-controlling factor, thereby agreeing with the findings of Saki et al (2020).…”

“…Other models, such as the K-T and the Dastidar Models, which also use pore throat radii at a specific saturation (K-T Model) or capillary pressure (Dastidar Model) correlate significantly worse with measured permeabilities compared to the CT and the Saki Models, suggesting once more that the r 35 parameter is an important matrix permeability-controlling factor, at least in the case of the samples investigated in this study. Although other studies propose that the permeability in tight limestones is primarily controlled by the pore throat radii (Cai et al 2019;Zhao et al 2018) or the smallest pore body sizes (Smodej et al 2020) rather than by the entire effective porosity range, this does not contradict our results. Instead, our results are rather complementary to these findings and specify that one particular pore throat radius, namely, the r 35 , has a particularly strong control on fluid flow in the matrix.…”

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“…For laboratory stuhollow punchs, experimental installations were created that allowed assessing the soil stickiness and strength (bearing capacity), the traction and adhesion properties of Fregat sprinkling machine wheels, and the energy costs of cleaning device operations necessary for removing soil between spade bugs of wheel rims. To study the adhesion conditions for drivers in the soil, an experimental setup was made, which provided a Kachinsky device and made it possible to study the adhesion forces during vertical separation [17,18]. The experimental setup included an electric motor mounted on a rack for the implementation of breakout forces, a strain gauge plate glued on sensors, fixed on a holder, and freely moving on the rack.…”

Reservoir Properties of Low-Permeable Carbonate Rocks: Experimental Features

“…Firstly, published case studies mainly cover only a few methods for characterizing the reservoir properties. The majority of publications present success stories with excellent and reliable results, even in cases of low-and ultra-low permeable reservoir rocks [8,16,17,19]. Therefore, recommended workflows often do not include failure scenarios and do not highlight the limitations of conventional methods.…”