Through-casing Resistivity Research Articles

Design of conditioning circuit for weak signal in through-casing resistivity logging

Design of conditioning circuit for weak signal in through-casing resistivity logging

Convolution effect on TCR log response curve and the correction method for it

Through-casing resistivity (TCR) logging has been successfully used in production wells for the dynamic monitoring of oil pools and the distribution of the residual oil, but its vertical resolution has limited its efficiency in identification of thin beds. The vertical resolution is limited by the distortion phenomenon of vertical response of TCR logging. The distortion phenomenon was studied in this work. It was found that the vertical response curve of TCR logging is the convolution of the true formation resistivity and the convolution function of TCR logging tool. Due to the effect of convolution, the measurement error at thin beds can reach 30% or even bigger. Thus the information of thin bed might be covered up very likely. The convolution function of TCR logging tool was obtained in both continuous and discrete way in this work. Through modified Lyle-Kalman deconvolution method, the true formation resistivity can be optimally estimated, so this inverse algorithm can correct the error caused by the convolution effect. Thus it can improve the vertical resolution of TCR logging tool for identification of thin beds.

The Research of Through-casing Resistivity Logging Logging Calibration System Leakage Current Measurement Method

This paper introduces the logging principle of through-casing resistivity logging technology, finds a phenomenon that the leakage current measurements are susceptible to sufferring interferences. The through-casing resistivity logging technology in Russia and that of Schlumberger are studied, and the system of through-casing resistivity logging is established to improve the accuracy of calibrating, testing and measuring of the instrument. In this paper, distribution parameters of the form is replaced by the lumped parameter, and precision resistor array simulation in formation leakage current and scale pool simulation in different resistivity of formation are conducted, which make the dynamic range of the simulation in formation resistivity of the medium increase to 1- 300 Ω·m and meet the requirement of through-casing resistivity logging technology measurement range, 1 Ω·m ~ 100 Ω·m. Since the measuring signals of calibration acquisition and processing systems are extremely weak and calculation signals need to tell the nV (nanovolts) level, the high accurate data acquisition system of 24 digits is applied. DOI: http://dx.doi.org/10.11591/telkomnika.v11i12.3671

Through-Casing Resistivity Logging Signal Acquisition and Processing Techniques

Weak signal detection is the key technique in developing through-casing resistivity logging tool. In this paper, ultra-low-noise preamplifier, oversampling method, sampling integration and sampling average method, digital phase-sensitive detection technique are applied in detecting logging signals and 30nV is achieved. The indoor calibration test and field experiment of through-casing resistivity logging model machine with those weak signal detection techniques were carried out. The result showed that the measurement range of formation resistivity is 0~200 Ω.m.

New post-processing method for interpretation of through casing resistivity (TCR) measurements

We propose a new iterative method for post-processing through casing resistivity (TCR) measurements. This method can be seen as a correction or extension of Kaufman's theory to more complex scenarios, in which the casing is no longer assumed to be uniform along the axis of the borehole. It can also be seen as a simplified inversion method based on the main physical principles of TCR measurements. To derive our post-processing method, we first use the method of images, which enables us to introduce all key factors involved on TCR measurements, including casing length, casing radius, casing thickness, formation resistivity, location of injected current, and resistivity distribution of formation layers. Then, we design our iterative post-processing method by simplifying the complex formulation resulting from using the method of images. This post-processing method can also be derived as a particular inversion algorithm. Numerical results using goal-oriented hp-FEM simulations show that our post-processing method provides a more accurate approximation to the actual formation resistivity than that predicted by Kaufman's theory. In addition, the new method is proven to be very efficient and suitable for problems with spatial resistivity variations in the formation.

Arithmetic Method of Double-Injection-Electrode Model for Resistivity Measurement Through Metal Casing

Through-casing resistivity (TCR) measurement instruments such as Cased Hole Formation Resistivity are extensively used for the dynamic monitoring of oil reservoirs during the production phase in oil wells to evaluate the residual oil distribution. However, two shortcomings still exist in the common TCR model based on single-injection electrodes: The real value of steel-casing resistance is difficult to acquire, and the effect from mechanical tolerances of electrode scale is unpredictable. This paper proposes an innovative model based on double-injection electrodes. In this new model, all the required variables can be measured simultaneously; furthermore, a compensating arithmetic method is employed to obtain the real casing resistance. Self-adaptive goal-oriented <i xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">hp</i> -finite-element simulations have been performed to prove that the influence of mechanical tolerances of electrode scale can be reduced effectively. Therefore, the TCR measurement accuracy is highly improved.

Study on forward modeling of through-casing resistivity logging

Through-casing resistivity logging (TCRL) is a new kind of logging method for formation evaluation, reservoir monitoring and saturation changes tracking. In this paper, the basic principle of TCRL is detailed, and the modified transmission line equation method (MTLEM) is first proposed in China. The MTLEM has been employed to simulate the responses of TCRL, on the basis of which, the effects of formation resistivity, cement and casing on the responses of TCRL are analyzed, and the signals induced in different formations are also calculated, which can help the design of TCRL tool and data processing and interpretation in China.

PML Enhanced with a Self-Adaptive Goal-Oriented $hp$-Finite Element Method: Simulation of Through-Casing Borehole Resistivity Measurements

We describe the application of a perfectly matched layer (PML) combined with a self-adaptive goal-oriented $hp$-finite element (FE) method to the simulation of borehole resistivity measurements. The adaptive refinements and fast convergence of the self-adaptive $hp$-FE method enhance the performance of the PML, thereby enabling the accurate and efficient truncation of the computational domain in open-domain problems. We apply this method to the simulation of axisymmetric through-casing resistivity measurements acquired in a borehole environment that are typically used for the assessment of rock formation properties. Our numerical results confirm the accuracy and efficiency of our method and provide evidence of highly accurate and reliable simulations of borehole logging measurements in the presence of a conductive steel casing and material contrast of fourteen orders of magnitude in electrical conductivity. Moreover, the combination of adaptivity and PML enables us to significantly reduce the size of the computational domain with substantial savings in computer time and memory.

Fourier series expansion in a non-orthogonal system of coordinates for the simulation of 3D-DC borehole resistivity measurements

We describe a new method to simulate 3D borehole resistivity measurements at zero frequency (DC). The method combines the use of a Fourier series expansion in a non-orthogonal system of coordinates with an existing 2D goal-oriented higher-order self-adaptive hp-finite element algorithm. The new method is suitable for simulating measurements acquired with borehole logging instruments in deviated wells. It delivers high-accuracy simulations and it enables a considerable reduction of the computational complexity with respect to available 3D simulators, since the number of Fourier modes (basis functions) needed to solve practical applications is limited (typically, below 10). Furthermore, numerical results indicate that the optimal 2D grid based on the 0th Fourier mode (also called central Fourier mode) can be employed to efficiently solve the final 3D problem, thereby, avoiding the expensive construction of optimal 3D grids. Specifically, for a challenging through-casing resistivity application, we reduce the computational time from several days (using a 3D simulator) to just 2 h (with the new method), while gaining accuracy. The new simulation method can be easily extended to different physical phenomena with similar geometries, as those arising in the simulation of 3D borehole electrodynamics and sonic (acoustics coupled with elasticity) measurements. In addition, the method is especially suited for inversion, since we demonstrate that the number of Fourier modes needed for the exact representation of the materials is limited to only one (the central mode) for the case of borehole measurements acquired in deviated wells.

Simulations of 3D DC borehole resistivity measurements with a goal-oriented hp finite-element method. Part II: through-casing resistivity instruments

We simulate direct current (DC) borehole resistivity measurements acquired in steel-cased deviated wells for the assessment of rock formation properties. The assumed data acquisition configuration considers one current (emitter) and three voltage (collector) electrodes that are utilized to measure the second difference of the electric potential along the well trajectory. We assume a homogeneous, 1.27-cm-thick steel casing with resistivity equal to 10 − 5 Ω· m. Simulations are performed with two different numerical methodologies. The first one is based on transferring two-dimensional (2D) axisymmetric optimal grids to a three-dimensional (3D) simulation software. The second one automatically produces optimal 3D grids yielded by a 3D self-adaptive goal-oriented algorithm. Both methodologies utilize high-order finite elements (FE) that are specially well-suited for problems with high-contrast coefficients and rapid spatial variations of the electric field, as it occurs in simulations that involve steel-cased wells. The method based on transferring 2D-optimal grids is efficient in terms of CPU time (few seconds per logging position). Unfortunately, it may produce inaccurate 3D simulations in deviated wells, even though the error remains below 1% for the axisymmetric (vertical) well. The method based on optimal 3D grids, although less efficient in terms of CPU time (few hours per logging position), produces more accurate results that are validated by a built-in a posteriori error estimator. This paper provides the first existing simulations of through-casing resistivity measurements in deviated wells. Simulated resistivity measurements indicate that, for a 30° deviated well, measurements in conductive layers 0.01 Ω· m) are similar to those obtained in vertical wells. However, in resistive layers (10,000 Ω· m), we observe 100% larger readings in the 30° deviated well. This difference becomes 3,000% for the case of a 60° deviated well. For this highly-deviated well, readings corresponding to the conductive formation layer are about 30% smaller in magnitude than those in a vertical well. Shoulder effects significantly vary in deviated wells.

Feasibility study for 2D frequency-dependent electromagnetic sensing through casing

We perform a numerical-sensitivity study of various physical phenomena of interest for borehole resistivity logging applications in steel-cased wells. Specifically, we analyze the sensitivity of through-casing measurements for detecting water invasion, shale-laminated sands, and electrical anisotropy in the formation. In addition, we study the influence of the frequency of operation on through-casing resistivity measurements. The sensitivity analysis is performed using a highly accurate and reliable numerical method based on a 2D self-adaptive, goal-oriented, high-order, finite-element method (FEM). This method can be applied to simulate all types of resistivity logging measurements, including normal/laterolog, induction, and through-casing resistivity measurements. Results quantify the effects of several physical phenomena that can be sensed through casing and that can be measured with accurate sensors. We find that water invasion and shale-laminated sands behind casing can be detected and accurately quantified at frequencies below [Formula: see text]. On the other hand, measurements are almost insensitive to electrical anisotropy behind casing, but otherwise highly sensitive to frequency variations. Our simulations indicate that a frequency in the range of [Formula: see text] is the most adequate for maximizing the sensitivity of through-casing measurements with respect to spatial variations of electrical conductivity within the formation.

Simulation of multifrequency borehole resistivity measurements through metal casing using a goal-oriented hp finite-element method

The authors simulate multifrequency through-casing resistivity tool measurements operating at different frequencies in a borehole environment for the assessment of rock-formation properties. Rock formations are assumed to exhibit axial symmetry around the axis of a vertical borehole. The simulations are performed with a goal-oriented hp-adaptive finite-element method that delivers exponential convergence rates in terms of the quantity of interest (for example, the second vertical difference of the electric potential) against the CPU time. Numerical results confirm the efficiency and accuracy of the method, allowing for high-accuracy and reliable simulations of borehole logging measurements in the presence of highly conductive steel casing. The study of different tool configurations shows the advantages of using calibrated instruments with toroid antennas located on the borehole wall. The agreement between the numerical and analytical results, when the latter is available, is quantified. Errors on the simulations are consistently below 0.1%.

Integral equation approach based on contraction operators and krylov subspace optimisation

SUMMARY We report development of a new code for modelling electromagnetic fields in complicated 3D environments and provide examples of the code application to a number of typical borehole as well as some non-borehole problems. The code is based on an integral equation for the scattered electromagnetic field presented in the form used by the Modified Iterative Dissipative Method (MIDM). Such integral equation possesses contraction properties that allow the equation to be solved iteratively. The iterative sequence of approximations converges to the equation solution at any frequency, for an arbitrary earth model, and any source of the electromagnetic field. The approach can also be applied to media with anisotropy of electrical properties and displacement currents. The system of linear equations that represents a finite -dimensional counterpart of the continuous integral equation is derived using a projection definition of the system matrix. In this definition, the matrix is calculated by integrating the Green’s function over the “source” and “receiver” cells of the numerical grid. The system of linear equations preserves contraction properties of the continuous equation and can be solved using the same iterative technique. The condition number of the system matrix and, therefore, the convergence rate depend only on the physical properties of the model under consideration. These parameters remain independent of the numerical grid used for numerical simulation. Applied to the system of linear equations, the iterative perturbation approach generates a sequence of approximations converging to the equation solution. The number of iterations necessary to reach the specified accuracy of the numerical solution is significantly reduced by finding the best possible approximant inside the Krylov subspace, which spans the iterates accumulated in the preceding steps. The effect of the optimisation grows with the complexity of the model under consideration. 3D codes based on the above principles have been applied to a number of problems of subsurface and borehole geophysics. The applications include such problems as global electromagnetic induction, regional and local magnetotelluric and magneto-variational soundings with natural and controlled sources, through-casing resistivity, etc. We compare our results for a number of models with independent results obtained using different approaches. The robustness of the algorithm is demonstrated by running the same model with different numerical grids. Models used for the code demonstration include a vertical borehole in a stratified formation excited by co-axial induction and coplanar tools. We also consider tilted boreholes and decentralized tools.

Well-bore reservoir evaluation technologies to optimize field revitalization

The economic success of field revitalization projects depends upon draining reservoir compartments that frequently contain smaller reserves volumes than those targeted by the initial field development, in a cost-effective manner. Well-bore measurements can contribute to risk management of redevelopment by identifying and monitoring the drainage of remaining hydrocarbons. Applications of cased-hole and open-hole measurements to optimizing field redevelopment are illustrated using case studies from the Brent Field, UK; Block IV, Venezuela and the T&amp;J Ashworth Lease, USA. Cased-hole logging using nuclear tools has evolved from time-lapse monitoring to detect changes in saturation to also include through-casing formation evaluation. Where deep invasion prevents the use of these nuclear methods, through-casing resistivity tools can successfully detect hydrocarbons. Open-hole formation pressures can significantly impact redevelopment strategies, as can evaluation of filtrate invasion using open-hole array resistivity tools. Emerging permanent sensor technologies enable continuous monitoring of both water saturation and formation pressure, thereby offering the potential to improve the performance of future field revitalization projects.

Through-Casing Resistivity Technology Improves Recovery

Technology Update - No abstract available.