Induction Logging Research Articles

A hybrid inversion algorithm to obtain the resistivity of the uninvaded zone based on the array induction log

This study investigates the impact of the drilling mud invasion on the borehole-measured resistivity. The primary objective is to retrieve the true resistivity of the formation, which helps in identifying different fluids in the reservoir. To achieve this goal, We proposed a hybrid inversion approach integrating the Levenberg-Marquardt and Markov Chain Monte Carlo algorithms with a five-parameter formation resistivity model. Synthetic and real-world data are utilized to assess the method's robustness and reliability. The simulated result indicated that the method is reliable when the data noise level is less than 5%.The method applied to real-world data revealed that the resistivity profile on the water zone showed a slight increase in the inverted resistivity from measured resistivity. Meanwhile, in the oil zone, the calculated resistivity revealed a high deviation from the measured resistivity, indicating the effects of mud invasion. The introduced methods are only applicable when the invasions of mud occur within the range of the logging tool's depth of investigation. Moreover, the method may give no reliable result when the invasion exceeds the tool's investigation depth. It indicates its limitation.

Analysis of the reservoir properties of rocks of the Lower Kura depression (Azerbaijan)

The article analyzes the features characterizing the Lower Kura depression (LKD). A number of hydrocarbon deposits have been discovered in this oil and gas region. The Kalmas underground gas storage facility, which has the largest volume in Azerbaijan, is also located in this area. In the LKD, all PS formations can be traced throughout the entire well section. The reservoir properties of the rocks were considered to study the features of the area. In order to study the reservoir properties in the well section, the field applies data obtained by using a complex of well logging (WL) methods (laterolog, spontaneous potential logging, induction logging, gamma logging, neutron logging, acoustic logging) and analyses of rock samples. The graphs were constructed to evaluate the relationship between petrophysical parameters (porosity, permeability, etc.) determined in the rocks involved in the well sections of the object of research. In the article, maps of porosity distribution, permeability and permeability of sandy siltstone rocks and fractions greater than 0.1 of the Productive Series of the South-Eastern Gobustan and Baku Archipelago, which are part of the Low Kura Depression, are plotted and analysed. Plots showing the porosity distribution of the Low Kura Depression by depth were also constructed and some results were obtained. Based on reservoir properties, the region is divided into 6 groups, and in each group intermediate values of the porosity and permeability coefficient are determined. In general, the porosity coefficient ranges within 5-25%, permeability – 1-250 mD. The reservoir properties of rocks vary over area from worse to better. The capacitance-filtration properties of rocks were studied. The rock samples analysed identified rocks with good and low reservoir characteristics. To study the variation in the determining factors, maps of the distribution of reservoir properties indicators (fractions greater than 0.1 mm; porosity and permeability in sand-siltstone-containing rocks) were compiled by area and their causes were determined by comparison with other oil and gas fields. It was found that with distance from the mouth of the Kura River (towards the right and left banks), the reservoir properties of the rocks deteriorate. This is due to an increase in the amount of clay in rocks. It is also clarified that the change in porosity coefficient does not depend on depth. The content of sand-siltstone composition in the rocks along the section is 20-50%.

3D Controlled‐source electromagnetic modelling in anisotropic media using secondary potentials and a cascadic multigrid solver

AbstractQuantitative interpretation of the data from controlled‐source electromagnetic methods, whether via forward modelling or inversion, requires solving a considerable number of forward problems, and multigrid methods are often employed to accelerate the solving process. In this study, a new extrapolation cascadic multigrid method is employed to solve the large sparse complex linear system arising from the finite element approximation of Maxwell's equations using secondary potentials. The equations using secondary potentials are discretized by the classic nodal finite element method on nonuniform rectilinear grids. The resulting linear systems are solved by the extrapolation cascadic multigrid method with a new prolongation operator and preconditioned Stabilized bi‐conjugate gradient method smoother. High‐order interpolation and global extrapolation formulas are utilized to construct the multigrid prolongation operator. The extrapolation cascadic multigrid method with the new prolongation operator is easier to implement and more flexible in application than the original one. Finally, several synthetic examples including layered models, models with anisotropic anomalous bodies or layers, are used to validate the accuracy and efficiency of the proposed method. Numerical results show that the extrapolation cascadic multigrid method improves the efficiency of 3D controlled‐source electromagnetic forward modelling a lot, compared with traditional iterative solvers and some state‐of‐the‐art methods or software (e.g., preconditioned flexible generalized minimal residual method, emg3d) in the considered models and grid settings. The efficiency benefit is more evident as the number of unknowns increases, and the proposed method is more efficient at low frequencies. The extrapolation cascadic multigrid method can also be used to solve systems of equations arising from related applications, such as induction logging, airborne electromagnetic, etc.

Study of electrical resistivity vertical changes in carbonate oil-bearing reservoirs to determine the depth of free water level

Abstract The purpose of the study is to establish the depth of the free water level (FWL), the zone of oxidized oil, the oil-water transition zone, the zone of maximum and decreasing resistivity. Correct understanding of initial oil saturation zonation in carbonate oil-bearing reservoirs is very important for development planning. The article proposes a method for express assessment of the FWL depth and initial oil saturation zonation in carbonate oil-bearing reservoirs based on electrical resistivity study. The values of electrical resistivity determined from induction logging curves in more than 200 wells were used as initial data. The vertical change in the electrical properties is considered using the resistivity values of oil-bearing reservoirs averaged over all wells. The initial oil saturation zonation was analysed using the graphs of electrical resistivity against depth. As a result of the work done, the following conclusions were made regarding the zonation of initial oil saturation and the possible geological characteristics of carbonate oil-bearing reservoirs: 1) based on the graphs of electrical resistivity against depth it is possible to distinguish 3 zones of initial oil saturation: oil-water transition zone above FWL, zone of maximum resistivity in the middle part of the deposit, and zone of decreasing resistivity in the upper part of the deposit; 2) in general, the initial oil saturation in the reservoir (as a function of the electrical resistivity) upward from the initial FWL depth does not grow exponentially, as in the Leverett function, but linearly in each zone. Proposed express method for initial oil saturation zonation in carbonate reservoirs provides novel information for formation testing and perforation planning. In oil-water transition zone it is recommended to use the gentlest methods of perforation and production intensification to preserve the integrity of the oxidized oil zone, since this zone is water confining and can prevent premature water flooding of the product.

An example of the application of neural networks of a simple architecture to unfocused well electrometry probes

An effective method of finding stable solutions of inverse problems of electric and induction logging along the well is proposed, which allows avoiding the influence of the resistance values of the neighboring formations on the determination of the geoelectrical parameters of the object under study. A highly efficient method was proposed for solving such an unstable inverse problem. This method is based on the application of a neural network with inverse error propagation of a simple architecture. Namely three-layer. The mathematical statement of the problem is given, both the topology of the neural network and all its parameters are described in detail. In the course of the numerical experiment, they were selected as optimal. The process of building a base for training a neural network is described in detail. Namely, how each of the examples of the learning base is built by solving a direct problem. With this cut parameter, the training for each example is chosen arbitrarily, which guarantees a comprehensive range for training the neural network. The number of examples in the training base is one hundred thousand examples. As the activation function, the sigmoid is chosen due to the fact that it is differentiable everywhere. The results of testing the written program are given. The learning rate was estimated to obtain the required small error. It is shown that this approach is stably convergent. For testing, the parameters of the layers of the cut, which are inherent to the geophysical parameters of the cuts of the Dnipro-Donetsk depression, were chosen. A complex of lateral logging sounding was chosen as the electrical logging equipment. Four-probe low-frequency induction logging equipment was chosen as induction logging equipment. Examples for induction and electrical logging are given separately. The obtained results are analyzed in detail. Ways of further improvement of the obtained neural network and its use for other problems of geophysics are given.

Response characteristics and novel understandings of dual induction logging of horizontal wells in fractured reservoirs

Previous studies commonly used dual laterolog or induction logging in vertical wells to study fractured reservoirs. However, there are few studies about the response characteristics of dual induction logging of horizontal wells in fractured reservoirs, which interferes with the evaluation of horizontal wells in fractured reservoirs. In this study, firstly, the finite element method is used to establish the fractured reservoir model and the dual induction instrument of horizontal well. Then, the response characteristics of dual induction logging in fractured reservoirs with different fracture conductivity, fracture dip angle, fracture width and fracture length are simulated and analyzed. The results show the response characteristics as follows: (1) The apparent conductivity of dual induction logging increases first and then decreases along with the increase of fracture conductivity, when the fracture conductivity is lower than formation conductivity, the apparent conductivity is similar to formation conductivity; (2) The fracture dip angle has little effect on the apparent conductivity of induction logging, when the fracture conductivity is high, the apparent conductivity decreases with the increase of the fracture dip angle; (3) The effect of fracture width and fracture length on apparent conductivity is similar. The larger the fracture width or length, the greater their influence on the apparent conductivity, which is different from the response characteristics of laterologs. In applications, these characteristics can be demonstrated by two wells in the southwest Ordos Basin, China. Finally, advantages and disadvantages of the simulation method, applications, logging responses discussed in detail, as well as the response characteristics and the shielding effect of fractures on electromagnetic waves of dual induction instrument are discussed in detail. The applications and discussions show that this study can provide response characteristics and novel understandings for the evaluations of horizontal wells in fractured reservoirs, especially in areas where dual induction logging is widely used.

Результаты определения коэффициента пористости в нефтенасыщенных глинистых породах

The article studies the wells that opened clayey reservoirs of Paleogene age. When predicting the trajectory of a crack during hydraulic fracturing (HF), it is necessary to take into account the percentage of minerals in the rock, since cracks during hydraulic fracturing are formed at the contacts between mineral grains. This conclusion is indisputable, but obtaining complete information about the percentage of minerals in a rock is an expensive and not always feasible task. At the same time, the physical and mechanical characteristics of clayey rocks are no less significantly influenced by their porosity. Therefore, it is important to note that a reliable determination of the porosity coefficient from the exposed geological section will undoubtedly have a primary positive impact on the reliability of hydraulic fracturing modeling. Based on this, in wells that opened clayey reservoirs, the values of porosity coefficients determined by various methods were analyzed, including the direct one – analysis of core, cuttings and the indirect one – geophysical methods. During the work, a coincidence of the porosity coefficient in the core, cuttings and electrical logging was discovered. Based on the results of the study, it can be concluded that the porosity coefficient determined from acoustic logging (AL) significantly exceeds the values of the porosity coefficient determined from core, cuttings and induction logging. This is due both to the influence of clay content on the acoustic logging readings, and due to the low quality of AC materials induced by erosion of the wellbore. It should be noted that the calculations of porosity coefficients in the above-reference part – in the Batalpashinsky formation based on core and induction logging – coincide almost completely. However, in the sub-reference part of the formation the readings differ slightly. The porosity coefficient calculated is a maximum of 2% lower than the porosity coefficient determined from the core, which is quite acceptable.

Study of vertical electrical resistance changes in reservoir beds of Tournaisian oil deposits

The article proposes a method for rapid assessment of the initial position of oil-water contacts, oxidized oil zones, transition zones, zones of high and decreasing resistance in the Lower Carboniferous Tournaisian oil deposits at one of the oilfields of the Republic of Tatarstan. As initial data, the values of electrical resistivity of effective interlayers from the catalog of geological and geophysical data, determined from induction logging curves, were used. Well log data for more than 200 wells drilled in elevation areas were used in analysis. The change in the electrical properties of deposits vertically is considered using the average resistivity values of effective interlayers averaged over all wells. Conclusions are based on the results of the done work: according to the resistivity values in massive carbonate deposits of the Tournaisian age, it is possible to distinguish various zones of oil saturation along the vertical; initial oil saturation does not grow exponentially, as in the Leverett function, but linearly in each zone.

3-D induction log modelling with integral equation method and domain decomposition pre-conditioning

SUMMARY The deployment of electromagnetic (EM) induction tools while drilling is one of the standard routines for assisting the geosteering decision-making process. The conductivity distribution obtained through the inversion of the EM induction log can provide important information about the geological structure around the borehole. To image the 3-D geological structure in the subsurface, 3-D inversion of the EM induction log is required. Because the inversion process is mainly dependent on forward modelling, the use of a fast and accurate forward modelling tool is essential. In this paper, we present an improved version of the integral equation (IE) based modelling technique for general anisotropic media with domain decomposition pre-conditioning. The discretized IE after domain decomposition equals a fixed-point equation that is solved iteratively with either the block Gauss–Seidel or Jacobi pre-conditioning. Within each iteration, the inverse of the block matrix is computed using a Krylov subspace method instead of a direct solver. An additional reduction in computational time is obtained by using an adaptive relative residual stopping criterion in the iterative solver. Using this domain decomposition scheme, numerical experiments show computation time reductions by factors of 1.97–2.84 compared to solving the full-domain IE with a GMRES solver and a contraction IE pre-conditioner. Additionally, the reduction of memory requirement for covering a large area of the induction tool sensitivity enables acceleration with limited GPU memory. Hence, we conclude that the domain decomposition method is improving the efficiency of the IE method by reducing the computation time and memory requirement.

METHODOLOGY FOR SUBSTANTIATING THE CALCULATION PARAMETERS OF COMPLEXLY CONSTRUCTED TERRIGENOUS RESERVOIRS IN WESTERN SIBERIA, INCLUDING THOSE WITH TRIZ, ACCORDING TO THE CORE AND GIS STUDY

The article presents an analytical solution to the direct problem of the method of spontaneous polarization of rocks in a well crossing an electrically inhomogeneous reservoir of limited thickness with a drilling mud penetration zone. The analytical solution of the problem by the employees of Schlumberger-Doll Research (M.R. Taherian, at all) for an impermeable reservoir in the absence of a penetration zone is a special case of the analytical solution of the direct problem of the spontaneous polarization (PS). The accuracy of the interpretation of the analytical and numerical solution of the inverse PS problem does not exceed the permissible accuracy of measuring the PS potential. The static potential of the ESP calculated on the basis of the analytical solution of the direct and inverse PS problem is used to construct the correlation dependence of the «core-GIS» static potential of the ESP on the volumetric humidity W, equal to the product of the porosity coefficient KP by the coefficient of residual water saturation KOV. An example of the interpretation of low-permeable, low-resistance oilsaturated reservoirs of Jurassic sediments for the operational assessment of reserves of the Yegansky, Martovsky and Zaozerny deposits of Western Siberia is given. The algorithm proposed in the article can be used for automated interpretation of the PS method and multi-probe induction logging in the corporate software of PJSC OC Rosneft.

An information theoretic Bayesian uncertainty analysis of AEM systems over Menindee Lake, Australia

SUMMARY Long-range, active-source airborne electromagnetic (AEM) systems for near-surface conductivity imaging fall into two categories: helicopter (rotary-wing) borne or fixed-wing aircraft borne. A multitude of factors such as flying height, transmitter loop area and current, source waveforms, aerodynamic stability and data stacking times contribute to the geological resolvability of the subsurface. A comprehensive comparison of the relative merits of each system considering all such factors is difficult, but test flights over well-constrained subsurface geology with downhole induction logs are extremely useful for resolution studies. However, given the non-linear nature of the electromagnetic inverse problem, handling transmitter–receiver geometries in fixed-wing aircraft is especially challenging. As a consequence of this non-linearity, inspecting the closeness of downhole conductivities to deterministic inversion results is not sufficient for studying resolvability. A more comprehensive picture is provided by examining the variation in probability mass of the depth-wise Bayesian posterior conductivity distributions for each kind of AEM system within an information theoretic framework. For this purpose, probabilistic inversions of data must be carried out. Each acquiring system should fly over the same geology, survey noise levels must be measured and the same prior probabilities on conductivity must be used. With both synthetic models as well as real data from over the Menindee calibration range in New South Wales, Australia, we shed new light on the matter of AEM inverse model uncertainty. We do this using two information theoretic attributes derived from different Kullback–Leibler divergences—Bayesian information gain, and a strictly proper scoring rule, to assess posterior probabilities estimated by a novel Bayesian inversion scheme. The inversion marginalizes fixed-wing geometry attributes as generic nuisance parameters during Markov chain sampling. This is the first time-domain AEM study we know of, that compares nuisance marginalized subsurface posterior conductivities from a fixed-wing system, with rotary-wing derived posterior conductivities. We also compare field results with induction log data where available. Finally, we estimate the information gain in each case via a covariate shift adaptation technique that has not been used before in geophysical work. Our findings have useful implications in AEM system selection, as well as in the design of better deterministic AEM inversion algorithms.

Machine-Learning-Based Convolution Method for Fast Forward Modeling of Induction Log

We built a convolution model using machine learning (ML) to calculate induction log responses for one-dimensional (1D) earth models. Compared to analytical forward modeling, the convolution model is extremely fast. ML-based convolution finds accurate induction tool responses from an earth model with layer resistivity and layer boundaries. For a unit induction tool 2C40, the 101-point, 50-ft window convolution model works satisfactorily for a well deviation angle of 60.

Machine-Learning-Based Deconvolution Method Provides High-Resolution Fast Inversion of Induction Log Data

We built a deconvolution model for induction log data using machine learning (ML). Unlike iterative forward modeling inversion methods, the deconvolution model is extremely fast. Unlike linear deconvolution models in the past, ML-based deconvolution finds accurate layer resistivity and layer boundaries. For a unit induction tool 2C40, the 21-point, 10-ft window deconvolution model works satisfactorily.

Multi-component induction logging detection characteristics of the fracture azimuth and dip angles and the fast extraction methods of fracture distribution parameters

In the field of log interpretation of tight sandstone and shale reservoirs, it is difficult to quantitatively evaluate the fracture distribution parameters (fracture azimuth angle and fracture dip angle) near the borehole. Multi-component induction logging can measure the apparent resistivities of the reservoir in different directions by an orthogonal coil system, which lays a foundation for the quantitative evaluation of the fracture distribution parameters near the borehole. First, we derive the finite element equations for numerical calculation from the Maxwell equations for the time-harmonic field and construct a three-dimensional (3D) vector finite element numerical algorithm for the fractured formation. Second, we quantitatively analyze the multi-component induction logging detection characteristics of the fracture azimuth and dip angles. Third, we establish a fast extraction method of the fracture azimuth angle based on coordinate system rotation and an analytical calculation method of the fracture dip angle using the combination of cross components and coplanar components of multi-component induction logging. Finally, we use field data to test the fracture distribution parameter extraction method, and the fracture dip and azimuth angles calculated by multi-component induction logging are consistent with those calculated by borehole imaging logging, which realizes the fast extraction of the distribution parameters of fractures in tight sandstone and shale reservoirs.

Signal processing methods for crosswell electromagnetic imaging system

The principle of crosswell electromagnetic (EM) imaging is similar to that of induction logging. The difference between them is that conventional induction logging can only measure the formation conductivity within a few meters around the well. However, crosswell EM imaging can be used in two wells with a separation distance of up to 1000 m. Several novel signal processing methods for crosswell EM imaging systems are developed for calibration, casing correction, and hybrid Jacobian matrix calculation. To conveniently perform calibration on the ground, the EM field formula in a vertical layered media is derived based on Maxwell equations, and the relationships between the received signal and frequency, formation conductivity, and transceiver spacing are subsequently derived. Furthermore, a new calibration method is developed. The EM field formula for a radial layered media is derived, and the analytical expressions describing the relationship between the receiving signal and borehole parameters, metal casing parameters, formation parameters, and receiver location are obtained. The effects of mud resistivity, metal casing position, metal casing resistivity, permeability, cement ring resistivity, transmitting frequency, and receiver location on the crosswell EM receiving signal are simulated. It is determined that only the casing required a correction. The influence of the metal casing is corrected by establishing a database. The difference between the corrected data and data obtained without a metal casing is less than 1%. There is a large error in the calculation of the Jacobian matrix in some regions when Green’s function was used. A hybrid Jacobian matrix calculation method combining local perturbation and a global Green’s function is developed, which significantly reduced the error and improved the inversion accuracy.

Induction logging as a method of monitoring the movement of technological solutions during in-situ leaching of hydrogenic uranium deposits

Induction logging as a method of monitoring the movement of technological solutions during in-situ leaching of hydrogenic uranium deposits

Multi-probe low-frequency induction log and high-frequency induction log if the reservoir contains the low resistivity annulus zone

A low resistivity annulus appearing near the well due to reservoir fluid displacement by mud filtrate is a reliable indicator of movable oil presence in the reservoir. In practical cases estimation of low resistivity annulus parameters is possible based on high-frequency induction logging data analysis. When interpreting practical data of other resistivity logging methods its influence on signals is usually not taken into account. The paper discusses the results of the 5IK and VIKIZ logs numerical simulation which substantiate the possibility of identifying low resistivity annulus according to multi-probe low-frequency induction logging in geoelectric conditions typical for the Cretaceous mixed-saturation reservoirs of the Imilorskoye oilfield.

Reconstruction of a 2D geoelectric model by numerical inversion of galvanic and induction logging signals

The practice of two-dimensional inversion of electrolog signals leads to the conclusion that the results obtained to a large extent depend on the set of devices. Russian geophysical companies mainly use lateral logging (measuring by a set of gradient sondes), focusing lateral logging, high-frequency electromagnetic sounding and low-frequency induction logging, including multi-sonde tool. The article considers the possibilities of determining the parameters of permeable formations by two-dimensional inversion of synthetic signals for these tools, on the example of a geoelectric model of the Lower Cretaceous deposits in Western Siberia. The model includes permeable formations with mud filtrate invasion zones. The different starting value of the invasion depth determines the accuracy of estimating the parameters of the invaded zone by inverting the data of various sets of sonde signals.

Borehole Effects on Coaxial and Coplanar Logs of Triaxial Tools in Laminated Formations with Anisotropic Shale Host

This paper studies the borehole effect in the triaxial induction logs within sand-shale laminated models with isotropic and anisotropic shale laminae with transverse isotropy. This study compares results from a 3D Vector Finite Element program (with borehole) and a 1D-Analytic code (no borehole). In comparison with the coaxial configuration, the vertical coplanar logs show a stronger horning effect in front of the laminated pack boundaries; a more intense skin effect to the conductivity media; and a more prominent oscillation within the laminated formation. In addition, feature changes (angular or smooth shapes) occur on the coaxial and coplanar responses as the dipping angle varies. The sensitivities of the logs to the anisotropy and borehole are opposite, i.e., for small angles where the coaxial is least sensitive, the coplanar is most sensitive, and for large angles where the coaxial is most sensitive, the coplanar is least sensitive. The main physical cause of these opposite behaviors to the anisotropy and borehole effect is the same: the weight of the horizontal magnetic component of the horizontal dipole contribution on the coaxial and coplanar dipping logs since it is the only one of the four magnetic field components that has anisotropy sensitivity and strongest skin effect.

Using the multi-component induction logging data to evaluate the geometric parameters of the hydraulic fracture

Abstract Hydraulic fracturing technology can effectively improve the seepage capacity of low-porosity and -permeability reservoirs. Geometric parameters evaluation (height, aperture and length) of hydraulic fracture is essential at different stages of fracturing. This paper presents a new method to evaluate the three parameters of small-scale fractures by multi-component induction logging based on numerical simulations. First, the model of calculation of the induced electric field with vertical hydraulic fractures is established using a three-dimensional finite element method (3D FEM), and the algorithm is verified correctly by comparing it with the analytical solution. Five coil systems of xx, xz, yy, yz and zz that are sensitive to the geometric parameters of the fracture are determined. The relationships between the geometric parameters of the fracture and the measurement signals of five coils are then investigated. The results show that the length and aperture of the fracture have a power exponent relationship with the measurement voltage, while the height parameter is closely related to the logging curves. Based on the relationships, the calculation models of the geometric parameters are established and the applicable range of it is analyzed. It is demonstrated that the complete characterization of fracture geometric can be realized by combining multi-spacing and multi-coil systems. Finally, the influence of the borehole and surrounding formation on the measurements is also considered, and the results indicate that the resistivity of the formation has less influence on the signals than the resistivity of the mud. Compared to the current instrument, the new method can evaluate all three geometric parameters of the hydraulic fracture.