Induction Logging Research Articles

Mixing laws and causality in high frequency induction log applications

Mixing laws and causality in high frequency induction log applications

Estimation of Reservoir Parameters From Inversion of Triaxial Induction Data Constrained by Mud-Filtrate Invasion Modeling

Mud-filtrate invasion happens commonly during the drilling and has a great effect on the triaxial induction logging data. A good description of the invasion can help achieve a better understanding of the formation. A mud-filtrate invasion constrained inversion approach is thus introduced to simultaneously invert for the sand fraction ( $F_{\text{sand}}$ ), irreducible water saturation ( $S_{\text{wr}}$ ), and average invasion rate ( $q$ ) with the triaxial induction logging data in anisotropic laminated sand–shale formations. In the inversion, the dynamic mud-filtrate invasion is modeled to account for the invasion effect. The invasion modeling provides the profiles of water saturation and salt concentration, which can be used to obtain the conductivity in the sand formation through a saturation-conductivity model (e.g., Archie's law). The anisotropic resistivities $R_h$ and $R_v$ of the laminated sand–shale formation can then be calculated by the anisotropic bimodal system based on the obtained sand conductivity and the shale anisotropic resistivities $R_{\text{shale}{,}h}$ and $R_{\text{shale}{,}v}$ . The triaxial induction logging is finally modeled with $R_h$ and $R_v$ . By matching the calculated logging data with the measured data, the unknowns $F_{\text{sand}}$ , $S_{\text{wr}}$ , and $q$ can be estimated. A quantitative evaluation of the new inversion scheme is performed with the triaxial induction tool Rt Scanner. The synthetic data without noise and with 2% white Gaussian noise are used. From the inversion tests, we observe that the sand fraction and irreducible water saturation can be well estimated by the long-offset measurements, which are less affected by the mud-filtrate invasion in the scenario that the invasion is not deep. In contrast, the short-offset measurements are more sensitive to the average invasion rate, since the detection range of these measurements is in the vicinity of the borehole. In the inversion, the sand fraction, irreducible water saturation, and average invasion rate are estimated simultaneously. The good agreement between the estimated results with their true values demonstrates the effectiveness of the invasion constrained inversion scheme.

Numerical Calculation of Induction Logging Response in Cased Hole

Numerical Calculation of Induction Logging Response in Cased Hole

EVALUATION OF RESERVOIR PERMEABILITY USING ARRAY INDUCTION LOGGING

AbstractDuring drilling, the mud column sustains a slightly higher pressure than the formation to maintain the stability of the well wall, which causes the mud filtrate to penetrate into formation pores and displace in‐situ fluids. The invasion depth is affected by reservoir properties, especially the reservoir permeability. Therefore, it is possible to estimate the reservoir permeability if the invasion depth can be measured.A numerical study was conducted to investigate the feasibility of evaluating reservoir permeability with array induction logging. A mud invasion model was built up by coupling mud cake growth with multiple‐phase fluid flow, and an array induction logging model was established based on the Born geometric factor theory. Joint forward simulations of mud invasion and array induction logging indicated that the responses of array induction logging can reflect the effect of mud invasion on the formation resistivity. Inversion based on the damped least square method revealed that the invasion depth can be acquired from array induction logging data.We investigated the association between reservoir permeability and invasion depth, and found that in a reservoir with a permeability of 1 to 100 mD (1 mD=0.987×10−3 μm2), the reservoir permeability governs the invasion depth, and thus the permeability can be evaluated according to invasion depth. A two‐dimensional numerical simulation showed that the inversed invasion depth curve had a similar fluctuation to the permeability variation. For a layered formation, a series of interpretation charts can be produced to evaluate the permeability of every layer with tolerable errors. The numerical investigation proves the feasibility of estimating reservoir permeability with array induction logging.

Use of Parallel-Seismic and Induction-Logging Tests for Foundation Depth Evaluation Under Difficult Conditions, a Root-Pile Foundation Embedded in Rock

A case study on the application of the parallel-seismic (PS) and induction-logging (IL) tests combined to evaluate the depth of a 25-cm diameter root-pile belonging to the foundations of a telecommunication tower located in Santana de Parnaíba, São Paulo, Brazil, is presented. The foundation element is embedded in a friable and altered meta-sandstone rock. The relatively small diameter of the pile and the presence of rock as surrounding material tend to limit the interpretation of the PS test. Nevertheless, the technique applied in this study showed satisfactory results. On the other hand, the existence of electromagnetic interference from the antenna itself limited the interpretation of the IL test in this case. The estimated depth of the foundation element was evaluated from the PS test as ranging from 6.5 to 7.5 m, which was later verified to be in agreement with the pile as-built documentation. When the possibility to drill boreholes at a site under investigation exists, the methods presented in this paper may become good options for the determination of the unknown depth of foundation elements in altered rock

Fracture responses of conventional logs in tight-oil sandstones: A case study of the Upper Triassic Yanchang Formation in southwest Ordos Basin, China

Fractures are the main fluid-flow pathways in tight-oil sandstones, and they have a significant influence on tight-oil distribution, exploration, and development. Cores and image logs are commonly unavailable because of their high costs, so employing conventional logs for fracture detection is imperative for tight-oil sandstones. We compared the fracture-response characteristics of conventional logs based on two data sets, one from 8 cored wells with fracture intensities greater than 1 m−1 (3.3 ft−1) and the other from 11 cored wells with fracture intensities less than 0.5 m−1 (1.6 ft−1), with a case study of the Upper Triassic Yanchang Formation in southwest Ordos Basin, China. The results indicate that when tight-oil sandstones are more intensely fractured, the caliper log, acoustic log, compensated neutron log, density log, dual induction logs, and laterolog 8 present fracture responses to some extent. However, it is difficult to make a distinction between fractured and nonfractured zones using conventional logs in sandstones with smaller fracture intensities. The fracture-response intensities of conventional logs are weak, and they are influenced by fracture abundance, fracture occurrence, fracture scale, and mineral-filling degree. Moreover, lithology, fluids, and rock physical properties can cause fracturelike responses. Hence, some ambiguity exists when using conventional logs to directly identify fractures. Accompanying fracture-sensitive conventional logs with some methods to enhance fracture-response intensity and eliminate nonfracture influence could enable fracture identification in tight-oil sandstones.

High-frequency induction logging in deviated and horizontal wells: Geosteering and inversion

The study focuses on processing methods for high-frequency induction data from deviated and horizontal wells. Simulation of electromagnetic fields with analytical algorithms is used to study how the resistivity of rocks above and below the well influences the acquired data. The simulations show that the contribution of under- and overlying layers into the recorded responses is considerable and depends on resistivity contrasts between the layers and on the position of logging arrays relative to the layer boundaries. This fact has to be taken into account when estimating true resistivity of reservoirs and when inverting induction logs from horizontal wells for reservoir characterization. The method is applied to oil- and water-saturated reservoirs in West Siberia, which contain high-resistivity impermeable layers leading to overestimation of apparent resistivity. Due regard for the effect of these layers in inversion of induction logs provides high-quality resistivity estimates.

Calibration response simulation of a triaxial induction tool with a metal mandrel

The calibration of triaxial induction logging tools is commonly performed in large water tanks, which are costly and complicated to use. In contrast, calibration with a metal loop is relatively economical and convenient. A tilted metal loop is introduced to calibrate all the components of a triaxial induction tool simultaneously. We have evaluated and optimized parameters such as radius, resistance, azimuthal angle, and position of the calibration loop with the 3D finite-element method. For validation, the accuracy of the simulation method is verified with analytical solutions with consideration of the metal mandrel effect. A quantitative agreement is found between the simulation results and the measurements of a realistic triaxial induction tool with a metal mandrel. Numerical simulation results demonstrate that the presence of the metal mandrel causes the nine components of the tool to change nonlinearly with the formation conductivities in the double logarithmic coordinate. This nonlinear effect can be reduced by eliminating the background signals from the metal mandrel. After the optimization of the parameters of the calibration loop, the responses of the triaxial induction tool can be calibrated accurately.

Application of fullbore formation microimager logging in the evaluation of anisotropic resistivity in a thin interbed reservoir

Oil and gas reserves in sand-shale thin interbeds are extensive, but it is a challenge to achieve satisfactory precision in the identification of these interbeds using traditional logging data. Phasor induction and three-component induction logging are appropriate tools for the identification of sand-shale interbeds. Unfortunately, phasor induction data are expensive and three-component induction logging is rarely used in major domestic oil fields. As a result, evaluation of sand-shale thin interbeds heavily depends on a traditional logging suite, general image logging, array lateral logging and array induction logging, and so on. In this paper, we investigate the sand-shale thin interbed region in the northern part of the Sulige field. We propose a comprehensive method of anisotropic evaluation which is based on the combination of wellbore microresistivity image logging (fullbore formation microimage (FMI)) and high-resolution array induction logging (HRLA), where HRLA can be used instead of a traditional logging suite or high-resolution array lateral logging. The proposed method works well in the evaluation of thin interbeds in the northern part of the Sulige field. In this paper, the combination of FMI and deep resistivity of HRLA is used. It should be noted that it is possible to use deep resistivity of conventional laterolog or array induction log instead of HRLA.

Fast electromagnetic modeling in cylindrically layered media excited by eccentred magnetic dipole

AbstractWe developed a fast algorithm to calculate a response of cylindrically layered media excited by the vertical magnetic dipole eccentred with respect to the axis of symmetry. The algorithm calculates response in the range of frequencies typical for induction and dielectric logging. The media conductivity and dielectric constant are described by piecewise‐constant functions. The corresponding boundary value problem is solved by method of separation of variables. Fourier transform is applied to Maxwell equations and boundary conditions to express field components through Fourier transforms of vertical components of an electrical and magnetic field. In addition, an expansion of vertical components into an infinite series with respect to angular harmonics is used to reduce the original problem to a series of 1‐D problems that only depend on the radial coordinate. The solution to each 1‐D radial problem for the angular harmonics is presented as a linear combination of modified Bessel functions. Finally, inverse Fourier transformation is applied to the angular harmonics of vertical components to derive electrical and magnetic field of the original boundary value problem. We provide detailed discussion on the elements that are critical for the numerical implementation of the algorithm: a proper normalization, convergence, and integration. Specifically, we show how to perform integration in the complex plane by avoiding intersection of the integration pass with the cuts located on the Riemann surface. Numerical results show the usefulness of the algorithm for solving inverse problems and for studying the effect of eccentricity in induction and dielectric logging.

Investigating Induction Log response in the presence of natural fractures

Resistivity logging is one of the main types of logging techniques which is used to determine saturation of hydrocarbon. Wrong interpretation of these logs leads to costly risks in determination of pay zones and calculation of hydrocarbon in place. Lithology, fluid types, texture, rock-fluid interaction, shale, anisotropy, bed geometry, borehole shape, mud invasion, and natural fractures (if existed) disturb the reading of resistivity logs.In this regard, the main objectives of this paper is to better understand the effects of fractures on Induction Logs and considering the results in a real dataset. From a highly fractured reservoir. We used a commercial software to model the response of a generic Induction Log in the presence of natural fractures. The effects of different characteristics of fractures including length, aperture, inclination, and distance from borehole wall on the Induction Log were investigated.The present study showed that all characteristics of fractures influence the Induction Log measurements in different degrees. Among them, fracture's conductivity is the most controversial one. For less conductive fractures than matrix, the fracture conductivity has minor impact on the bulk conductivity; however, when fracture to matrix conductivity ratio reaches 10–1000, the bulk conductivity increases to above the actual conductivity of the matrix. In very high conductive fractures, when fracture to matrix conductivity ratio is 10+3 to 10+6, fractures have adverse impact on the bulk conductivity, and the recorded conductivity rapidly decreases below the actual conductivity of matrix. The effect of fracture length and aperture on the Induction Logs is somehow similar. The model showed that fracture inclination has minor impact on the Induction Log's response.

Enhanced real-time determination of resistivity anisotropy and dip using multifrequency and multicomponent induction logging

Multicomponent induction (MCI) logging is able to provide a wealth of measurements at multiple subarrays and frequencies that can be used to evaluate complex subsurface formations. Real-time and postprocessing inversion methods have been introduced by various researchers for determining formation resistivity anisotropy (horizontal and vertical resistivity or conductivity), dip, and dip azimuth/strike using MCI measurements. The majority of these methods are based on single-frequency information. We have developed an enhanced real-time method and relevant workflow for determining formation resistivity anisotropy, dip, and dip azimuth using multifrequency MCI information. This enhanced method can be used to improve accuracy in formation evaluation applications, such as reservoir identification, hydrocarbon/water saturation calculation, and geologic and structural interpretation. Enhancements over the present single-frequency data processing include: (1) optimal harmonization of multiple single-frequency inverted logs, (2) robust determination of dip and dip azimuth angle for low-resistivity anisotropy ratios, (3) practical data-quality evaluation that takes into account the effects of formation resistivity, anisotropy ratio, and dip parameters, and (4) a new integrated workflow that can be used to determine formation anisotropy, true dip, and dip azimuth by integrating processed relative dip and azimuth and borehole directional logging data. Finally, all of these data process enhancements have been validated with synthetic data and field log data.

Study on the effect of fractures on conventional induction log based on physical and numerical simulation

Fractures are important storage area and migration pathway in fractured reservoir. Abnormal conventional induction logging response has been found in fracture zone of reservoir, but few scholars have studied the conventional induction log response of fractured reservoirs. In this paper, the effect of fractures on conventional induction log has been studied based on physical and numerical simulation. Firstly, a physical model has been built to simulate the influence of fractures on conventional log. Secondly, the geometric factor theory has been used to find the minimum fracture width that the conventional induction log could identify, and the minimum interval between two adjacent fractures that the conventional induction log could distinguish. Thirdly, a fracture evaluation method based on numerical simulation was proposed, and a complex model containing surrounding rock and fractures was established to test the possibility of evaluating the fracture parameters using this method. Finally field data were used to test this method. From the results in this paper, we conclude that fractures influence conventional induction log significantly and fractures could be detected and evaluated by the conventional induction log.

Time-lapse downhole electrical resistivity monitoring of subsurface CO2 storage at the Maguelone shallow experimental site (Languedoc, France)

A shallow field experimental site for CO2 injection was established at Maguelone (Languedoc, France), in order to test in an integrated manner a suite of surface and downhole hydrogeophysical monitoring methods. The objective is to improve monitoring of gas transport in the shallow subsurface and to determine the sensitivity of CO2 monitoring systems for leakage detection. The site offers a natural laboratory to study the processes associated with CO2 injection in a clastic and clay-rich context saturated with saline fluids. Prior to CO2 injection, three nitrogen (N2) injections were undertaken in 2012 to measure the site response to neutral gas injection. In 2013, a volume of 111m3 (mass of 220kg) of CO2 was injected during 3.5h at 15m depth. During each experiment, the gas plumes were successfully detected from pressure monitoring, time-lapse induction logging and downhole resistivity monitoring with dipole–dipole array. Increases in resistivity are attributed to free gas propagation (either N2 or CO2) whereas decreases in resistivity correlate with CO2 dissolution in the pore fluid. Chemical analyses confirm this hypothesis with a decrease in pH and an increase in the concentration of dissolved species in the latter case.

Geophysical characteristics and structural composition of clay rocks in the terrigenous complex of the southeastern part of the West Siberian oil and gas bearing province

The basic attributes identifying the clay rock composition in the terrigenous complex of the southeastern part of the West-Siberian platform have been determined, based on the correlation of structural composition and geophysical data, including induced potential logging, apparent resistivity, induction logging, radioactive and caliper logging. According to the obtained results it is possible to identify above-mentioned rocks in well logs, even under conditions of limited core samples, their application in well log correlation and back stripping. Key words: geophysical well logging, the West-Siberian oil and gas bearing province, terrigenous complex, clay rocks, back stripping.

Improving the accuracy of determining the character saturation reservoirs on the results of log interpretation in the oil field ”K”(Tomsk region)

Log interpretation has revealed a number of factors that have a significant impact on the determination of reservoir fluid content (oil saturation factor). The presented research paper is focused on the analysis of petrophysical properties of reservoir fluids considering laboratory studies of core samples. Based on core sample analysis, data of laboratory studies have been correlated to estimates of radioactive logging and high-frequency induction logging. To determine the oil saturation factor a method which considers the effect of mixed clay on reservoir fluid saturation has been proposed.

A fast algorithm to forward model the triaxial induction logging response in layered transversely isotropic dipping formations

We have developed a new analytic method to compute the response of triaxial induction logging tools in layered transverse isotropic (TI) dipping formations without borehole and invasion zones. A triaxial induction tool is composed of one or more sets of three orthogonal transmitter coils and three orthogonal receiver coils arranged along the tool axis. The tool axis may intercept a formation with dip, azimuthal, and rotation angles. Based on the electromagnetic (EM) field in planarly layered media, formulations of the EM fields generated by these three transmitting coils are derived. A fast-forward-modeling algorithm to compute the responses of an induction tool was developed. Compared with the algorithm using the coefficient propagator method previously developed, the proposed algorithm calculates the generalized reflection and transmission coefficients only once for each layer regardless of the position of the transmitters, and therefore, it greatly speeds up the computation. The simulation code solves for all nine components of the magnetic field in a TI layered medium. Results of this new method were developed for several formation models, which agreed very well with the published data. For a dipping or nondipping case in a 28-layer formation, the proposed method was about 37 times faster, which was more appropriate to be used in an inversion algorithm.

THE SELECTION OF COMPLEX RESERVOIRS OF HYDROCARBONS OPENED ON SALINE FLUSH DRILLING FLUIDS IN DEEP EXPLORATORY WELLS

We have investigated the usefulness of GIS methods (geophysical investigations in boreholes) and GTI (mud logging) in distinguishing low-power numerous collectors HC (hydrocarbons) in deep exploratory wells, complicated by the high caverns and drilled for saline drilling fluid. Limitations of techniques emisions and determine their characteristics leads to skipping of productive intervals and their erroneous selection. Data electrical methods (BKZ (lateral sounding), MKZ (microcerotermes sensing), IR (induction logging), PS (logging potentials spontaneous polarization)) in terms of the mineralized mud and cavernous wellbore distorted, poorly reflect the incision and therefore uninformative. There are no direct characteristics collector - positive increment on the microprobes (MHS (micro-gradient probe), MPZ (micro-potential probe) and clay crust against the collector by DS (inspection), at the substation are not marked minimum values of the net (Neglinnaya) terrigenous formations. Saturated and reservoirs on IR also not differentiated. Readings radioactive methods (COG (neutron gamma logging) and GGC-p (gamma-gamma density logs)) are distorted by the presence of large cavities in the wellbore. For successful execution of exploration drilling designed research methodology perspective on HC intervals. The method is based on an integrated use of all possible methods of GIS, the GTI and direct methods for the steady reservoir and determine their characteristics. Proposed rational complex GIS detailed geophysical studies in Sandstone reservoirs, exploration and appraisal wells drilled in saline solutions.

Development prospects for Bazhenov formation bituminous claystones in the southeast of the West Siberian Plate (Tomsk Region)

The article considers the use of time-tested bituminous shale development technologies in the southeast of the West Siberian Plate (Tomsk Region). A research target is the bituminous claystones of the Bazhenov formation. The Bazhenov formation was divided into stratigraphic units, and the sequence of forming these units within the territory under study was restored on the basis of the peculiarities of the Bazhenov formation section structure with gamma-ray logging data. The joint analysis of logs (gamma-ray logging, resistivity logging, SP logging, neutron gamma-ray logging, induction logging) and core data revealed the wide development of carbonatization processes in the lower stratigraphic units of the Bazhenov formation, whereas the upper, most bituminous units do not have the signs of carbonatization. It is a favorable factor for using the existing technologies of producing hydrocarbons from analogous sedimentary deposits. Considering the degree of lithological disconnection of an oilbearing object from adjacent reservoir formations allows making a conclusion that the application of the existing technologies for developing bituminous claystones can be implemented only in the insignificant territory of the area under study where the Bazhenov formation overlies Georgiev formation claystones being over 8 meters thick. To develop the oil and gas potential of the Bazhenov formation in other territories, there will be a need for new technologies that allow forming a fracture-cavernous matrix in a carbonate rock.

Three dimensional Born geometrical factor of multi-component induction logging in anisotropic media

Geometrical factor has been widely used in the design of induction tool and analysis of complex logging responses, as well as the high resolution processing of logging data. Works in this area are usually limited to two-dimensional isotropic medium and are only available to cases of coaxial transmitter and coaxial receiver coupling. For a more thorough understanding of multicomponent induction logging in the presence of transverse anisotropy, a knowledge of anisotropic geometrical factor is often necessary. In this paper, the two-dimensional and isotropic geometrical factors are extended to the anisotropic media using Born approximation, and the expressions of 3D Born geometrical factors for multicomponent induction logging are derived. Then the sensitivity and detectability of coaxial, coplanar and cross-coupling measurements are investigated. Numerical results show that with increasing coefficients of conductivity anisotropy, the spatial distribution of geometrical factors becomes increasingly complicated, and more sensitivity information can be detected by multicomponent induction tools. The multicomponent induction tool is sensitive to conductivity anisotropy at arbitrary dipping angles. In vertical wells, coplanar measurements are significantly affected by the conductivity anisotropy. Compared with coaxial and coplanar measurements, cross-coupling component offers superior sensitivity information to the conductivity anisotropy with the dipping angle being 40～ 60°. In horizontal wells, coaxial measurements are the most sensitive to the conductivity anisotropy. The extended 3D Born geometrical factor directly exhibits the anisotropy sensitivity in terms of spatial contribution, and has made up for the shortage of previous geometrical factors. The new geometrical factor will create favorable conditions for the development of new multicomponent induction tool and the interpretation of anisotropic formations.