Zhdanov, Michael (University of Utah) | Endo, Masashi (TechnoImaging) | Burtman, Vladimir (University of Utah) | Cuma, Martin (University of Utah) | Cox, Leif (TechnoImaging) | Sunwall, David (TechnoImaging)
This paper develops a novel method of 3D inversion of induced polarization (IP) survey data, based on a generalized effective-medium model of the IP effect (GEMTIP). The electrical parameters of the new effective-conductivity model are determined by the intrinsic petrophysical and geometrical characteristics of composite media, such as the mineralization and/or fluid content of rocks and the matrix composition, porosity, anisotropy, and polarizability of formations. The GEMTIP model of multiphase conductive media provides a quantitative tool for evaluation of the type of mineralization, and the volume content of different minerals using EM data. The developed method takes into account the nonlinear nature of both electromagnetic induction and IP phenomena and inverts the EM data in the parameters of the GEMTIP model. The goal of the inversion is to determine the electrical conductivity and the intrinsic chargeability distributions, as well as the other parameters of the relaxation model simultaneously. The recovered parameters of the relaxation model can be used for the discrimination of different rocks, and in this way may provide an ability to distinguish between uneconomic mineral deposits and zones of economic mineralization using geophysical remote sensing technology.
Presentation Date: Tuesday, October 18, 2016
Start Time: 2:15:00 PM
Presentation Type: ORAL
One of the major problems in mineral exploration is the inability to reliably distinguish between economic mineral deposits and uneconomic mineralization. While the mining industry uses many geophysical methods to locate mineral deposits, until recently, there was no reliable technology for identification and characterization of mineral resources. The main goal of this paper is an application of the generalized effective-medium theory of induced polarization (GEMTIP) to studying the complex resistivity of typical mineral rocks. We collected representative rock samples from the Cu-Au deposit in Mongolia, and subjected them to the mineralogical analysis using Quantitative Evaluation of Minerals by Scanning Electron Microscopy (QEMSCan) technology. We also conducted an analysis of the electrical properties of the same samples using the laboratory complex resistivity (CR) measurement system. As a result, we have established relationships between the mineral composition of the rocks, determined using QEMSCan analysis, and the parameters of the GEMTIP model defined from the lab measurements of the electrical properties of the rocks. These relationships open the possibility for remote estimation of types of mineralization using spectral IP data.
Presentation Date: Wednesday, October 19, 2016
Start Time: 3:35:00 PM
Location: Lobby D/C
Presentation Type: POSTER
Lin, Wei (University of Utah) | Burtman, Vladimir (University of Utah) | Zhdanov, Michael (University of Utah) | Endo, Masashi (TechnoImaging) | Takakura, Shinichi (National Institute For Rural Engineering)
Summary This paper demonstrates that the generalized effectivemedium theory of induced polarization (GEMTIP) can correctly represent the induced polarization (IP) phenomenon in the artificial rock samples. These samples were manufactured using pyrite and magnetite particles. The results of our study show that the conventional Cole-Cole model cannot adequately describe the IP effect in artificial rocks containing both the pyrite and magnetite. However, the GEMTIP model not only predicted the IP response correctly, but it also opens the possibility of discriminating between rock samples containing pyrite and magnetite, based on complex resistivity (CR) data. Based on the GEMTIP inversion results for a total of 35 artificial rock samples, we demonstrate that the GEMTIP model best represents the CR response of the artificial rock samples.
An ability to understand and control reservoir behavior over the course of production is necessary for optimization of reservoir performance and production strategies. This goal can be achieved by geophysical monitoring of the propagation of the fluids within the reservoir. Electromagnetic (EM) methods represent an important technique of geophysical monitoring of the reservoirs, because they can distinguish between hydrocarbons and saline water based on their differing resistivities. The induced polarization (IP) effect represents another important electrical characteristic of the reservoir saturated by different fluids - the complex resistivity (CR) of the reservoir rocks. This paper considers an application of nanoparticles for reservoir monitoring in order to enhance the electrical conductivity contrast and the IP responses associated with the oil-water interface within the reservoir. We have conducted the measurements of the CR of reservoir rocks in order to examine the effect of adding in water solutions the organic, PEDOT-PSS, and inorganic, Fe3O4, Fe2O3, NiO, and Al2O3, nanoparticles. The results of this study demonstrate that the application of the organic and inorganic nanoparticles may change significantly the resistivity of the reservoir rocks and produce a significant spectral IP effect.
An ability to predict and to control the position and movement of oil-water interface is very important for monitoring the production from the hydrocarbon (HC) reservoirs. The idea of utilizing nanoparticles for monitoring and even for facilitating of the oil production has been developed in a number of publications (e.g., Rahmani et al, 2013, Heagy and Oldenburg, 2013; Hubbard et al., 2014). Several types of nanoparticles were explored in view of possible HC application. For example, magnetic nanoparticles were used by Lesin et al. (2011) to study their effect on the viscosity of liquid suspensions with fractal aggregates in petroleum colloidal structures. The paramagnetic nanoparticles were tested as aqueous dispersions in reservoir rock for enhanced oil recovery and evaluating oil saturation (e.g., Yu et al., 2010, Armani et al., 2013). These studies attempted to utilize the concept of enhancing MRI imaging with the use of paramagnetic nanoparticles for accurate determination of oil saturation and the oil-water interface.
This paper demonstrates that an ellipsoidal model of the generalized effective-medium theory of induced polarization (GEMTIP) can be used to effectively invert complex resistivity (CR) data into petrophysical parameters of rocks, including matrix resistivity, volume fraction, etc. The inversion of the CR data has proven to be very challenging due to the nonuniqueness and instability of this problem. This paper introduces a new hybrid method based on a genetic algorithm with simulated annealing and regularized conjugate gradient minimization (SAAGARCG). This fast and effective approach combines the advantages of both the SAAGA and RCG methods and converges into the global minimum. The case study presents the results of inversion of the observed CR data and their comparison with a QEMSCAN analysis for representative mineral rock samples.
The induced polarization (IP) effect has been used in mineral exploration (e.g., Pelton et al., 1978; Nelson, 1997) and in oil and gas prospecting for a long time (e.g., Zonge and Wynn, 1975; Pelton et al., 1978; Vanhala, 1997). Zhdanov (2008) introduced the generalized effectivemedium theory of induced polarization (GEMTIP) using a rigorously formulated complex resistivity (CR) model to describe the relationships between the resistivity of the multiphase heterogeneous rocks and their petrophysical and structural properties.
The GEMTIP model can be used to study the petrophysical properties of rocks by inverting the CR data for the GEMTIP parameters. The inversion of CR data is a very challenging task because of the nonuniqueness and instability of this inverse problem. In this paper, we introduce a hybrid approach to inversion of the CR data for GEMTIP model parameters by combining the genetic algorithm with simulated annealing -- SAAGA -- at the initial phase of the iterative inversion with the regularized conjugate gradient (RCG) method at the final stage for rapid convergence to the global minimum. We demonstrate that the novel hybrid inversion algorithm is faster and more effective than the original SAAGA method, and it converges rapidly into the global minimum. We present a case study of inverting the observed CR data and a comparison of the results of the inversion with the QEMSCAN analysis of representative mineral rock samples.
Unconventional hydrocarbon (HC) reserves, e.g., heavy oils, bituminous sands, and oil- and gas-shale substantially surpass those of conventional resources and therefore are extremely economically attractive; however, exploration and production of unconventional reserves is challenging. This paper demonstrates that one can observe significant induced polarization (IP) effects in shale reservoir rocks, which can be used in exploration for unconventional reserves. This study is based on application of the generalized effective-medium theory of induced polarization (GEMTIP) for analysis of the complex resistivity (CR) of oil- and gas-shale rocks. GEMTIP modeling provides a basis for remote petrophysical analysis of shale rocks, which we compared with an actual structural analysis of shale rocks using Quantitative Evaluation of Minerals by Scanning Electron Microscopy (QEMSCAN) and core analysis. We demonstrate that GEMTIP modeling provides an evaluation of mineral composition and volume fractions in rock samples. Spectral induced polarization (SIP) measurements were conducted for different types of shale rocks to test the feasibility of the SIP method and GEMTIP modeling for studying unconventional HC reserves. The results of this study provide a basis for future application of the SIP method for exploration and monitoring of unconventional reserves.
In this paper, we study the anisotropy effect in IP data in the context of the generalized effective-medium theory of induced polarization (GEMTIP). The effective-medium conductivity defined by the GEMTIP model, in a general case, is represented by a tensor function. This tensorial property of the effective-medium conductivity provides a new insight on the anisotropy phenomenon in the IP effect. As an example, we consider a multiphase composite polarized model of a rock formation with ellipsoidal inclusions. We demonstrate that the effective conductivity of this formation may be anisotropic, even if the host rock and all the grains are electrically isotropic.
It is well known that the effective conductivity of rocks is not necessarily a constant and real number but may vary with frequency and be complex. There are several explanations for these properties of effective conductivity. Most often they are explained by the physical-chemical polarization effects of mineralized particles of the rock material and/or by the electrokinetic effects in the poroses of reservoirs (Wait, 1959; Marshall and Madden, 1959; Luo and Zhang, 1998). This phenomenon is called the induced polarization (IP) effect. It was demonstrated in Zhdanov (2006a,b, 2008), that the IP phenomenon can be mathematically explained by a new composite geoelectrical model of rock formations. This model is based on the effective-medium approach, which takes into account both the volume polarization and the surface polarization of the grains. This new generalized effective-medium theory of the IP effect (GEMTIP) can be used for examining the IP effect in complex rock formations with different mineral structures and electrical properties.
The effective-medium conductivity defined by the GEMTIP model, in a general case, is represented by a tensor function. This tensorial property of the effective-medium conductivity shines a new light on the anisotropy phenomenon in the IP effect. The study of the IP anisotropy is the major subject of this paper. In order to develop a quantitative characterization of the IP anisotropy, we use as an example a medium with ellipsoidal inclusions, which allows us to calculate the analytical solutions for the effective-conductivity tensor of the model with the IP effect.
BASIC FORMULAS OF THE EFFECTIVE-MEDIUM THEORY OF INDUCED POLARIZATION
The last formula provides a general solution of the effective conductivity problem for an arbitrary multiphase composite polarized medium. This formula allows us to find the effective conductivity for inclusions with arbitrary shape and electrical properties. That is why the new composite geoelectrical model of the IP effect may be used to construct the effective conductivity for realistic rock formations typical for mineralization zones and/or petroleum reservoirs.
EFFECTIVE CONDUCTIVITY OF THE MULTIPHASE COMPOSITE POLARIZED MEDIUM WITH ELLIPSOIDAL INCLUSIONS
We assume now, that all grains have an ellipsoidal shape, and their axes are parallel to one another. It is clear that in this situation, similar to the case of the conventional effective-medium theory without IP effects (Sihvola, 2000), the effective medium becomes anisotropic.