Electrical Resistivity Monitoring of Saline Tracer Fingering at Pore Scale under Partially Saturated Conditions

2016 ◽  
Author(s):  
D. Jougnot ◽  
J. Jiménez-Martínez ◽  
Y. Méheust ◽  
T. Le Borgne ◽  
N. Linde
Keyword(s):  
Electrical Resistivity ◽  
Pore Scale ◽  
Partially Saturated

Hysteresis in the electrical resistivity of partially saturated sandstones

Geophysics ◽  
1991 ◽  
Vol 56 (12) ◽  
pp. 2139-2147 ◽  
Author(s):  
Rosemary Knight
Keyword(s):  
Electrical Resistivity ◽  
Unsaturated Zone ◽  
Geophysical Data ◽  
Fluid Distribution ◽  
Water Interface ◽  
Pore Scale ◽  
Laboratory Measurements ◽  
Partially Saturated ◽  
Air Water Interface ◽  
Saturation History

Laboratory measurements of the resistivity of three sandstone samples collected during imbibition (increasing Sw) and drainage (decreasing Sw) show pronounced hysteresis in resistivity throughout much of the saturation range. The variation in resistivity can be related to changes in pore‐scale fluid distribution caused by changes in saturation history. The form of the hysteresis is such that resistivity measured during imbibition is consistently less than that measured, at the same saturation, during drainage. This can be attributed to the presence of conduction at the air/water interface in partially saturated samples; an effect that is enhanced by fluid geometries associated with the imbibition process. The results of this study suggest that the dependence of geophysical data on saturation history should be considered when interpreting data from the unsaturated zone.

Characterization of Fluid Drainage Mechanism at Core and Pore Scales: an NMR Capillary Pressure–Based Saturation Exponent Prediction

2021 ◽  
Author(s):  
Abubakar Isah ◽  
Abdulrauf Rasheed Adebayo ◽  
Mohamed Mahmoud ◽  
Lamidi O. Babalola ◽  
Ammar El-Husseiny
Keyword(s):  
Electrical Resistivity ◽  
Capillary Pressure ◽  
Oil Recovery ◽  
Gas Storage ◽  
Pressure Curve ◽  
Pore Scale ◽  
Resistivity Index ◽  
Capillary Pressure Curve ◽  
In Series ◽  
Saturation Exponent

Abstract Capillary pressure (Pc) and electrical resistivity index (RI) curves are used in many reservoir engineering applications. Drainage capillary pressure curve represents a scenario where a non-wetting phase displaces a wetting phase such as (i) during gas injection (ii) gas storage in reservoirs (e.g. aquifer or depleted hydrocarbon reservoirs). The gas used for injection is typically natural gas, N2, or CO2. Gas storage principally used to meet requirement variations, and water injection into oil-wet reservoirs are drainage processes. Resistivity index (RI) curve which is used to evaluate the potential of oil recovery from a reservoir, is also an important tool used in log calibration and reservoir fluid typing. The pore drainage mechanism in a multimodal pore system is important for effective recovery of hydrocarbon reserves; enhance oil recovery (EOR) planning and underground gas storage. The understanding of pore structure and drainage mechanism within a multimodal pore system during petrophysical analysis is of paramount importance to reservoir engineers. Therefore, it becomes inherent to study and establish a way to relate these special core analyses laboratory (SCAL) methods with quick measurements such as the nuclear magnetic resonance (NMR) to reduce the time requirement for analysis. This research employed the use of nuclear magnetic resonance (NMR) to estimate saturation exponent (n) of rocks using nitrogen as the displacing fluid. Different rock types were used in this study that cover carbonates, sandstones, and dolomites. We developed an analytical workflow to separate the capillary pressure curve into capillary pressure curve for macropores and a capillary pressure curve for the micropores, and then used these pore scale Pc curves to estimate an NMR - capillary pressure - based electrical resistivity index - saturation (NMR-RI-Sw) curve for the rocks. We predicted the saturation exponent (n) for the rock samples from the NMR-RI-Sw curve. The NMR-based saturation exponent estimation method requires the transverse (T2) relaxation distribution of the rock - fluid system at various saturations. To verify the reliability of the new workflow, we performed porous plate capillary pressure and electrical resistivity measurements on the rock samples. The reliability of the results for the resistivity index curve and the saturation exponent was verified using the experimental data obtained from the SCAL method. The pore scale Pc curve was used to ascertain the drainage pattern and fluid contribution of the different pore subsystems. For bimodal rock system, the drainage mechanism can be in series, in parallel, or in series - parallel depending on the rock pore structure.

scholarly journals A Mathematical Model for the Electrical Resistivity of Cement Paste at Early Ages Considering the Partially Saturated State

Materials ◽  
2020 ◽  
Vol 13 (15) ◽  
pp. 3306 ◽  
Author(s):  
Ye Tian ◽  
Xin Xu ◽  
Haodong Ji ◽  
Zushi Tian ◽  
Xianyu Jin ◽  
...  
Keyword(s):  
Mathematical Model ◽  
Electrical Resistivity ◽  
Cement Paste ◽  
Isothermal Calorimetry ◽  
Setting Time ◽  
Degree Of Saturation ◽  
Early Age ◽  
Saturation State ◽  
Partially Saturated ◽  
Saturated State

For cementitious materials, electrical resistivity is often used in the study of the cement hydration process at early age, as one of the few indicators that can be continuously and non-destructively monitored. Variation characteristics of resistivity are widely reported to interact with the early-age performance of cement paste, such as hydration kinetics parameters and setting time. However, there is no reasonable mathematical model to predict the resistivity at early ages, especially within the first 24 h, due to significant changes in the porosity and degree of saturation. In this work, a mathematical model was developed by considering the partially saturated state and density change of C-S-H (calcium silicate hydrate). To verify the model, two experimental methods were chosen, including the non-contact electrical resistivity test and isothermal calorimetry test. The hydration heat and resistivity of cement paste with a water–cement ratio of 0.35 and 0.45 were continuously monitored for 3 days. In the resistivity test, embedded temperature sensors were used to monitor the internal temperature and temperature correction was treated carefully in order to obtain accurate data. The test results prove that the mathematical model can accurately predict electrical resistivity and describe the saturation state of early-age cement pastes under sealed curing.

Pore-Scale Joint Evaluation of Dielectric Permittivity and Electrical Resistivity for Assessment of Hydrocarbon Saturation Using Numerical Simulations

SPE Journal ◽  
2016 ◽  
Vol 21 (06) ◽  
pp. 1930-1942 ◽  
Author(s):  
Huangye Chen ◽  
Zoya Heidari
Keyword(s):  
Electrical Resistivity ◽  
Spatial Distribution ◽  
Dielectric Permittivity ◽  
Pore Structure ◽  
Maximum Error ◽  
New Method ◽  
Pore Scale ◽  
Resistivity Measurements ◽  
Hydrocarbon Saturation ◽  
Permittivity Measurements

Summary Complex pore geometry and composition, as well as anisotropic behavior and heterogeneity, can affect physical properties of rocks such as electrical resistivity and dielectric permittivity. The aforementioned physical properties are used to estimate in-situ petrophysical properties of the formation such as hydrocarbon saturation. In the application of conventional methods for interpretation of electrical-resistivity (e.g., Archie's equation and the dual-water model) and dielectric-permittivity measurements [e.g., complex refractive index model (CRIM)], the impacts of complex pore structure (e.g., kerogen porosity and intergranular pores), pyrite, and conductive mature kerogen have not been taken into account. These limitations cause significant uncertainty in estimates of water saturation. In this paper, we introduce a new method that combines interpretation of dielectric-permittivity and electrical-resistivity measurements to improve assessment of hydrocarbon saturation. The combined interpretation of dielectric-permittivity and electrical-resistivity measurements enables assimilating spatial distribution of rock components (e.g., pore, kerogen, and pyrite networks) in conventional models. We start with pore-scale numerical simulations of electrical resistivity and dielectric permittivity of fluid-bearing porous media to investigate the structure of pore and matrix constituents in these measurements. The inputs to these simulators are 3D pore-scale images. We then introduce an analytical model that combines resistivity and permittivity measurements to assess water-filled porosity and hydrocarbon saturation. We apply the new method to actual digital sandstones and synthetic digital organic-rich mudrock samples. The relative errors (compared with actual values estimated from image processing) in the estimate of water-filled porosity through our new method are all within the 10% range. In the case of digital sandstone samples, CRIM provided reasonable estimates of water-filled porosity, with only four out of twenty-one estimates beyond 10% relative error, with the maximum error of 30%. However, in the case of synthetic digital organic-rich mudrocks, six out of ten estimates for water-filled porosity were beyond 10% with CRIM, with the maximum error of 40%. Therefore, the improvement was more significant in the case of organic-rich mudrocks with complex pore structure. In the case of synthetic digital organic-rich mudrock samples, our simulation results confirm that not only the pore structure but also spatial distribution and tortuosity of water, kerogen, and pyrite networks affect the measurements of dielectric permittivity and electrical resistivity. Taking into account these parameters through the joint interpretation of dielectric-permittivity and electrical-resistivity measurements significantly improves assessment of hydrocarbon saturation.

scholarly journals Numerical estimation of electrical resistivity in digital rocks using GPUs

2020 ◽  
pp. 306-318
Author(s):  
Т.С. Хачкова ◽  
В.В. Лисица ◽  
Г.В. Решетова ◽  
В.А. Чеверда
Keyword(s):  
Electrical Resistivity ◽  
Electric Field ◽  
Electric Current ◽  
Spectral Method ◽  
Numerical Estimation ◽  
Thomas Algorithm ◽  
Rock Samples ◽  
Partially Saturated ◽  
Heterogeneous Models ◽  
Homogeneous Media

Представлен алгоритм расчета потенциального электрического поля в образцах горных пород и предложены оценки их удельного электрического сопротивления (проводимости). Алгоритм ориентирован на расчет поля в существенно неоднородных моделях среды с частично насыщенными и полиминеральными образцами горных пород. В основе алгоритма – итерационные методы крыловского типа, в качестве предобусловливателя используется оператор, обратный к оператору Лапласа для однородной среды. Для вычисления предобусловливателя используется спектральный метод в направлениях, нормальных к основному направлению электрического тока, а серия одномерных задач решается методом прогонки. Решатель реализован с использованием графических процессоров (GPU) и позволяет обрабатывать образцы размером до 4003 вокселей на одном GPU. We present a numerical algorithm for computing the electric field in digital rock samples and estimating their electrical resistivity (conductivity). The main peculiarity of the algorithm is its applicability tostrongly heterogeneous models including partially saturated and multi-mineral rock samples. The algorithm is based on the iterative Krylov-type solver preconditioned by the inverse Laplace operator for homogeneous media. The preconditioner is computed using the spectral method in directions orthogonal to the direction of the main electric current, whereas the series of 1D problems are solved by the Thomas algorithm. We implement the algorithm using GPUs, which allows us to use a single GPU to solve the problems for samples whose size is up to 4003 voxels.

Pore-scale fluid distributions determined by nuclear magnetic resonance spectra of partially saturated sandstones

Geophysics ◽  
2019 ◽  
Vol 84 (3) ◽  
pp. MR107-MR114 ◽  
Author(s):  
Chunhui Fang ◽  
Baozhi Pan ◽  
Yanghua Wang ◽  
Ying Rao ◽  
Yuhang Guo ◽  
...  
Keyword(s):  
Nuclear Magnetic Resonance ◽  
Water Saturation ◽  
Acoustic Property ◽  
P Wave ◽  
Distribution Model ◽  
Fluid Distribution ◽  
Pore Scale ◽  
Saturation Model ◽  
Partially Saturated ◽  
P Wave Velocity

The acoustic property and the P-wave velocity of partially saturated rocks depend not only on the water saturation but also on the pore-scale fluid distribution. Here, we analyzed the pore-scale fluid distribution using nuclear magnetic resonance (NMR) [Formula: see text] spectra, which present the variation of porosity components associated with NMR transverse relaxation time [Formula: see text]. Based on the [Formula: see text] spectra, we classified the pore-scale fluid distribution during water imbibition and drainage into three models: a low-saturation model, a patchy distribution model, and a uniform distribution model. We specifically assigned the low-saturation model to deal with the acoustic property of the rocks at the imbibition starting stage and the drainage final stage because cement softening has a nonnegligible effect. We studied the acoustic properties of sandstone rocks with various pore-scale fluid distributions, at the imbibition process and the drainage process. We confirmed that, once the variations in water saturation and pore-scale fluid distribution are taken into account, the P-wave velocity prediction matches well with the laboratory measurement of samples, representing nearly tight sandstone rocks that are partially saturated with distilled water.

Estimating seismic velocities at ultrasonic frequencies in partially saturated rocks

Geophysics ◽  
1994 ◽  
Vol 59 (2) ◽  
pp. 252-258 ◽  
Author(s):  
Gary Mavko ◽  
Richard Nolen‐Hoeksema
Keyword(s):  
Large Scale ◽  
Scale Effects ◽  
Pore Space ◽  
Degree Of Saturation ◽  
Velocity Versus ◽  
Seismic Velocities ◽  
Pressure Gradients ◽  
Pore Scale ◽  
S Wave ◽  
Partially Saturated

Seismic velocities in rocks at ultrasonic frequencies depend not only on the degree of saturation but also on the distribution of the fluid phase at various scales within the pore space. Two scales of saturation heterogeneity are important: (1) saturation differences between thin compliant pores and larger stiffer pores, and (2) differences between saturated patches and undersaturated patches at a scale much larger than any pore. We propose a formalism for predicting the range of velocities in partially saturated rocks that avoids assuming idealized pore shapes by using measured dry rock velocity versus pressure and dry rock porosity versus pressure. The pressure dependence contains all of the necessary information about the distribution of pore compliances for estimating effects of saturation at the finest scales where small amounts of fluid in the thinnest, most compliant parts of the pore space stiffen the rock in both compression and shear (increasing both P‐ and S‐wave velocities) in approximately the same way that confining pressure stiffens the rock by closing the compliant pores. Large‐scale saturation patches tend to increase only the high‐frequency bulk modulus by amounts roughly proportional to the saturation. The pore‐scale effects will be most important at laboratory and logging frequencies when pore‐scale pore pressure gradients are unrelaxed. The patchy‐saturation effects can persist even at seismic field frequencies if the patch sizes are sufficiently large and the diffusivities are sufficiently low for the larger‐scale pressure gradients to be unrelaxed.

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