Resistivity tomography based on multichannel electrodes

With the constantly changing engineering construction sector,the detection accuracy of conventional electrical resistivity tomography(ERT)is no longer suffi cient.A multichannel electrode design(MERT)-based ERT is introduced in this paper to address the growing need for resolution.The imaging accuracy of the ERT method is improved through the collection of apparent resistivity data in various directions by measuring the potential diff erence between diff erent channels.Numerical simulation results of the inclined high-resistivity anomaly model reveal that MERT is a precise representation of the shape,inclined direction,and buried depth of the anomaly,with thoroughfare M2N2 producing the most precise forward and inverse results.Based on the analysis results of the model resolution matrix,when the buried depth of power supply points and the gap between potential acquisition points are 30%-90%and 30%-60%of the electrode distance,respectively,the MERT approach yields superior detection outcomes.The detection eff ect of the MERT method on anomalous bodies with diff erent burial depths under the optimal parameters also indicates that the MERT method can obtain richer potential change information with higher resolution in deep areas compared to the ERT method.With the implementation of the MERT approach,the scope of applications for ERT is expanded,the accuracy of ERT detection is increased,and the progress of near-surface fi ne detection is positively infl uenced.

Prediction of carbonate permeability from multiresolution CT scans and deep learning

The low-resolution CT scan images obtained from drill core generally struggle with problems such as insufficient pore structure information and incomplete image details.Consequently,predicting the permeability of heterogeneous reservoir cores relies heavily on high-resolution CT scanning images.However,this approach requires a considerable amount of data and is associated with high costs.To solve this problem,a method for predicting core permeability based on deep learning using CT scan images with diff erent resolutions is proposed in this work.First,the high-resolution CT scans are preprocessed and then cubic subsets are extracted.The permeability of each subset is estimated using the Lattice Boltzmann Method(LBM)and forms the training set for the convolutional neural network(CNN)model.Subsequently,the highresolution images are downsampled to obtain the low-resolution grayscale images.In the comparative analysis of the porosities of diff erent low-resolution images,the low-resolution image with a resolution of 10%of the original image is considered as the test set in this paper.It is found that the permeabilities predicted from the low-resolution images are in good agreement with the values calculated by the LBM.In addition,the test data are compared with the results of the Kozeny-Carman(KC)model and the measured permeability of the whole sample.The results show that the prediction of the permeability of tight carbonate rock based on deep learning using CT scans with diff erent resolutions is reliable.

Permeability Estimation of Shale Oil Reservoir with Laboratory-derived Data: A Case Study of the Chang 7 Member in Ordos Basin

The shale oil reservoir within the Yanchang Formations of Ordos Basin harbors substantial oil and gas resources and has recently emerged as the primary focus of unconventional oil and gas exploration and development.Due to its complex pore and throat structure,pronounced heterogeneity,and tight reservoir characteristics,the techniques for conventional oil and gas exploration and production face challenges in comprehensive implementation,also indicating that as a vital parameter for evaluating the physical properties of a reservoir,permeability cannot be effectively estimated.This study selects 21 tight sandstone samples from the Q area within the shale oil formations of Ordos Basin.We systematically conduct the experiments to measure porosity,permeability,ultrasonic wave velocities,and resistivity at varying confining pressures.Results reveal that these measurements exhibit nonlinear changes in response to effective pressure.By using these experimental data and effective medium model,empirical relationships between P-and S-wave velocities,permeability and resistivity and effective pressure are established at logging and seismic scales.Furthermore,relationships between P-wave impedance and permeability,and resistivity and permeability are determined.A comparison between the predicted permeability and logging data demonstrates that the impedance–permeability relationship yields better results in contrast to those of resistivity–permeability relationship.These relationships are further applied to the seismic interpretation of shale oil reservoir in the target layer,enabling the permeability profile predictions based on inverse P-wave impedance.The predicted results are evaluated with actual production data,revealing a better agreement between predicted results and logging data and productivity.

Optimizing data for electrical resistivity tomography in hardened sites through the ratio method

To reduce the shielding effect of hardened layers on electrical resistivity tomography,a ratio method based on the distortion correction principle and the isolation coefficient is proposed.The effects of the resistivity and thickness of hardened concrete layers on the detection of target objects are explored.Both numerical simulations and indoor tank tests indicate that when the ratio method is employed to correct the original collected data,the maximum allowable error for the isolation coefficient should not exceed 1%.Notably,when the ratio of hardened layer thickness to electrode spacing does not exceed 1,correction through this method significantly enhances the recognition capability of target objects.However,when the hardened layer thickness is greater than the electrode spacing by a factor of 2 or more,the ratio method cannot achieve satisfactory results.The case study of flood control engineering detection in the Zhangxi section of the Huangpen River in Dongzhi County demonstrates that the detection effect after correction by the ratio method is comparable to that for the adjacent unhardened pavement,and the influence of the hardened layer is obviously weakened,resulting in more reliable results.

基于全局灵敏度分析的大坝温度场影响因子探讨

运行期大坝温度场与渗流场耦合数学模型包含诸多参数,采用灵敏度分析方法能确定大坝温度场的主要影响因子,从而减小模型校正的工作量,为相关研究提供借鉴。基于大坝热-流耦合稳态模型,对大坝温度场分别做了局部灵敏度分析和全局灵敏度分析。分析结果表明,大坝温度场对上游水库库底温度和下游坝面温度较灵敏,其余参数的灵敏度顺序依次为水力梯度、渗透率、岩石热导系数、孔隙率和介质比热。实例分析结果也证实全局灵敏度分析能用来定量研究参数间共同作用对数值模型的影响。

A patchy-saturated rock physics model for tight sandstone based on microscopic pore structures

The wave-induced local fluid flow mechanism is relevant to the complex heterogeneity of pore structures in rocks.The analysis of the local fluid flow mechanism is useful for accurately describing the wave propagation characteristics in reservoir rocks.In the exploration and production of hydrocarbon reservoirs,the real stratum may be partially saturated with a multi-phase fluid mixture in general.Therefore,it is of great significance to investigate the wave velocity dispersion and attenuation features in relation to pore structures and fluids.In this work,the characteristics of fabric microstructures are obtained on the basis of pressure dependency of dry rock moduli using the effective medium theory.A novel anelasticity theoretical model for the wave propagation in a partially-saturated medium is presented by combining the extended Gurevich squirt-flow model and White patchysaturation theory.Numerical simulations are used to analyze wave propagation characteristics that depend on water saturation,external patchy diameter,and viscosity.We consider a tight sandstone from the Qingyang area of the Ordos Basin in west China and perform ultrasonic measurements under partial saturation states and different confining pressures,where the basic properties of the rock are obtained at the full gas saturation.The comparison of experimental data and theoretical modeling results shows a fairly good agreement,indicating that the new theory is effective.

Seismic wavefield modeling based on time-domain symplectic and Fourier finite-difference method

Seismic wavefield modeling is important for improving seismic data processing and interpretation. Calculations of wavefield propagation are sometimes not stable when forward modeling of seismic wave uses large time steps for long times. Based on the Hamiltonian expression of the acoustic wave equation, we propose a structure-preserving method for seismic wavefield modeling by applying the symplectic finite-difference method on time grids and the Fourier finite-difference method on space grids to solve the acoustic wave equation. The proposed method is called the symplectic Fourier finite-difference （symplectic FFD） method, and offers high computational accuracy and improves the computational stability. Using acoustic approximation, we extend the method to anisotropic media. We discuss the calculations in the symplectic FFD method for seismic wavefield modeling of isotropic and anisotropic media, and use the BP salt model and BP TTI model to test the proposed method. The numerical examples suggest that the proposed method can be used in seismic modeling of strongly variable velocities, offering high computational accuracy and low numerical dispersion. The symplectic FFD method overcomes the residual qSV wave of seismic modeling in anisotropic media and maintains the stability of the wavefield propagation for large time steps.

Acoustic-electrical properties and rock physics models for shale-oil formations:prediction of reservoir properties of interbedded sandstone and shale layers

In recent years,the Yanchang shale-oil formations of the Ordos Basin are rich in reserves with complex lithology and structure characteristics,low porosity and low permeability,and weak anomalies for oil and water discriminations,have been the key targets of unconventional oil/gas resource exploration and development in the relevant areas.The joint acoustic-electrical(AE)properties can be used to interpret reservoir lithology,mineralogy,pore structure,and fluid saturation.To conduct tests of thin section analysis,X-ray diff raction,and ultrasonic and electrical experiments at diff erent pressures and saturation degrees,cores from the shale-oil formations in the Q area of the basin are collected.The variations in AE properties with respect to clay content,porosity,pressure(microfracture),and saturation are analyzed.The experimental results indicate that the rock physics behaviors of sandstones with diff erent clay contents vary significantly.The AE properties of clean sandstones are basically dependent on the microfractures(pressure),while for muddy sandstones,the clay content is an important factor affecting the responses.The target reservoir consists of interbedded sandstone and shale layers.The AE equivalent medium equations and the Gurevich theory are applied to establish the joint models for the diff erent lithologies and simulate the variations in AE properties with respect to fluid type,pore structure,and mineral components.The three-dimensional joint templates of clean and muddy sandstones,as well as shale,are developed based on the elastic and electrical attributes and then calibrated using the experimental and well-log data.The reservoir properties are estimated with the templates and validated by the log data.The results indicate that the joint templates based on lithology characteristics can eff ectively characterize the properties of interbedded sandstone and shale layers.Furthermore,the combined application of AE data provides more beneficial information for the assessment of rock properties,leading to precise estimates that conform with the actual formation conditions.

Accurate detection method of high-density polyethylene fi lm leakage location based on secondary electric potential difference

High-density polyethylene(HDPE)film leakage location detection is frequently accomplished using the double-electrode technique.The electric potential and potential difference are the main physical parameters in the double-electrode approach.Due to the impact of the complex geoelectric environment,the electric potential and the electric potential difference are not sensitive enough to respond to minimal leakage.The tiny leaking area cannot be precisely located using the electric potential and electric potential difference.Using the COMSOL Multiphysics software,this study created a standard geoelectric model of the double-electrode method.We calculated a new parameter—the G parameter through secondary electric potential difference—based on the response characteristics of the electric potential and the electric potential difference while the HDPEfilm is leaking.The experiment demonstrates that the G parameter is more sensitive than the electric potential and electric potential difference for detecting the leaking area of HDPE film.The G parameter is more effective at detecting leakage than the electric potential and electric potential difference.The results of this study can be used to locate HDPEfilm leakage areas in a landfill.