Applied Geophysics最新文献

3D ground-penetrating radar has been widely used in urban road underground disease detection due to its nondestructive, efficient, and intuitive results. However, the 3D imaging of the underground target body presents the edge plate phenomenon due to the space between the 3D radar array antennas. Consequently, direct 3D imaging using detection results cannot reflect underground spatial distribution characteristics. Due to the wide-beam polarization of the ground-penetrating radar antenna, the emission of electromagnetic waves with a specific width decreases the strong middle energy on both sides gradually. Therefore, a bicubic high-precision 3D target body slice-imaging fitting algorithm with changing trend characteristics is constructed by combining the subsurface target characteristics with the changing spatial morphology trends. Using the wide-angle polarization antenna’s characteristics in the algorithm to build the trend factor between the measurement lines, the target body change trend and the edge detail portrayal achieve a 3D ground-penetrating radar-detection target high-precision fitting. Compared with other traditional fitting techniques, the fitting error is small. This paper conducts experiments and analyses on GpaMax 3D forward modeling and 3D ground-penetrating measured radar data. The experiments show that the improved bicubic fitting algorithm can effectively improve the accuracy of underground target slice imaging and the 3D ground-penetrating radar’s anomaly interpretation.

Fully normalized associated Legendre functions (fnALFs) are a set of orthogonal basis functions that are usually calculated by using the recurrence equation. This paper presented the applicability and universality of the standard forward column/row recurrence equation based on the isolated singular factor method and extended-range arithmetic. Isolating a singular factor is a special normalization method that can improve the universality of the standard forward row recurrence equation to a certain extent, its universality can up to degree hundreds. However, it is invalid for standard forward column recurrence equation. The extended-range arithmetic expands the double-precision number field to the quad-precision number field. The quad-precision number field can retain more significant digits in the operation process and express larger and smaller numbers. The extended-range arithmetic can significantly improve the applicability and universality of the standard forward column/row recurrence equations, its universality can up to degree several thousand. However, the quad-precision number field operation needs to occupy more storage space, which is why its operation speed is slow and undesirable in practical applications. In this paper, the X-number method is introduced in the standard forward row recurrence equation for the first time. With the use of the X-number method, fnALFs can be recursed to 4.2 billion degree by using standard forward column/row recurrence equations.

Presently, the use of sub-bottom profiler sonar signals is limited to inversing the physical parameters of the sediment in the surface layer (first layer). In this study, based on the acoustic theory of porous medium, the acoustic inversion of the physical parameters of the lower layer (second layer) sediment is studied. When acoustic waves propagate in water and sediment media, interlayer reflection and transmission, intralayer attenuation, and other processes change the energy. The reflection and transmission coefficients of acoustic waves incident perpendicularly to the water—sediment and sediment—sediment interfaces are derived, and the effects of the reflection and transmission process of acoustic waves on the amplitude are quantified. The relationship between the frequency shift and relaxation time of the transmitted signal in different particle size sediments is established to estimate the corresponding attenuation coefficient using the frequency shift of each layer signal. On this basis, combined with the diffusion process of acoustic waves, the equation for extracting the acoustic wave reflection and transmission coefficients of each layer at the interface is derived from the measured sonar signal. Further calculations show that the sediment parameters have a greater influence on the reflection coefficient, and the feasibility of calculating the physical parameters of the lower sediment using the reflection coefficient has been proved. Under the premise of obtaining the physical parameters of surface sediment, this study provides specific methods and steps for inverting the physical parameters of the lower sediment. The on-site detection in the Xiaolangdi reservoir area of the Yellow River, combined with the sediment sampling test results, proved that the proposed method of inversion of the lower sediment parameters based on the porous medium acoustic theory is feasible.

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 HDPE film 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 HDPE film leakage areas in a landfill.

No shale-rock physical model has been established in the observation coordinate system. To this end, this paper carried out anisotropic wave velocity tests on shale rock and compared the Thomsen, Daley, and Berryman solutions to characterize anisotropic acoustic wave velocity. Finally, the Daley solution was selected. Based on basic rock physical models, such as SCA and DEM methods, and combined with the Daley solution, an anisotropic shalerock physical model was established in the observation coordinate system and applied in Well B1 in the Luzhou area, Sichuan Basin. Our research conclusions were as follows: 1. for the samples from the same core, the P-wave velocities in three directions were in the order V_P11 >V_P45 >V_P33, shear-wave velocity V_S11 was the largest, but V_S33 and V_S45 did not follow the law of V_s33 >V_s45 for some samples; 2. the Daley solution, which not only considers the accuracy requirements but also has a complete expression of P-, SV-, and SH-waves, is most suitable for characterization of anisotropic wave velocity in this study area; 3. the rock physical model constructed in the observation coordinate system has high accuracy, in which the absolute value of the relative error of the P-wave slowness was between 0% and 5.05% (0.55% on average), and that of shear-wave slowness was between 0% and 6.05% (0.59% on average); 4. the acoustic waves recorded in Well B1 in the observation coordinate system were very different from those in the constitutive coordinate system. The relative difference of the P-wave was between 6.76% and 30.84% (14.68% on average), and that of the S-wave was between 7.00% and 23.44% (13.99% on average). The acoustic slowness measured in the observation coordinate system, such as in a deviated well or a horizontal well section, must be converted to the constitutive coordinate system before it can be used in subsequent engineering applications; 5. the anisotropic shale-rock physical model built in the observation coordinate system proposed in this paper can provide basic data and guidance for subsequent pore pressure prediction, geomechanical modeling, and fracturing stimulation design for deviated and horizontal wells.

To solve the problems associated with low resolution and high computational effort in finite time, this paper proposes a fast forward modeling method for muon energy loss transmission tomography based on a model voxelization energy loss projection algorithm. First, the energy loss equation for muon transmission tomography is derived from the Bethe—Bloch formula, and the imaging region is then dissected into several units using the model voxelization method. Thereafter, the three-dimensional (3-D) imaging model is discretized into parallel and equally spaced two-dimensional (2-D) slices using the model layering method to realize a dimensional reduction of the 3-D volume data and accelerate the forward calculation speed. Subsequently, the muon energy loss transmission tomography equation is discretized using the ray energy loss projection method to establish a set of energy loss equations for the muon penetration voxel model. Finally, the muon energy loss values at the outgoing point are obtained by solving the projection coefficient matrix of the ray length-weighted model, achieving a significant reduction in the number of muons and improving the computational efficiency. A comparison of our results with the simulation results based on the Monte Carlo method verifies the accuracy and effectiveness of the algorithm proposed in this paper. The metallic mineral identification tests show that the proposed algorithm can quickly identify high-density metallic minerals. The muon energy loss response can accurately identify the boundary of the anomalies and their spatial distribution characteristics.

In this paper, the recurrent neural network structure of a bidirectional long short-term memory network (Bi-LSTM) with special memory cells that store information is used to characterize the deep features of the variation pattern between logging and seismic data. A mapping relationship model between high-frequency logging data and low-frequency seismic data is established via nonlinear mapping. The seismic waveform is infinitely approximated using the logging curve in the low-frequency band to obtain a nonlinear mapping model of this scale, which then stepwise approach the logging curve in the high-frequency band. Finally, a seismic-inversion method of nonlinear mapping multilevel well-seismic matching based on the Bi-LSTM network is developed. The characteristic of this method is that by applying the multilevel well-seismic matching process, the seismic data are stepwise matched to the scale range that is consistent with the logging curve. Further, the matching operator at each level can be stably obtained to effectively overcome the problems that occur in the well-seismic matching process, such as the inconsistency in the scale of two types of data, accuracy in extracting the seismic wavelet of the well-side seismic traces, and multiplicity of solutions. Model test and practical application demonstrate that this method improves the vertical resolution of inversion results, and at the same time, the boundary and the lateral characteristics of the sand body are well maintained to improve the accuracy of thin-layer sand body prediction and achieve an improved practical application effect.

Seismic data typically contain random missing traces because of obstacles and economic restrictions, influencing subsequent processing and interpretation. Seismic data recovery can be expressed as a low-rank matrix approximation problem by assuming a low-rank structure for the complete seismic data in the frequency-space (f-x) domain. The nuclear norm minimization (NNM) (sum of singular values) approach treats singular values equally, yielding a solution deviating from the optimal. Further, the log-sum majorization-minimization (LSMM) approach uses the nonconvex log-sum function as a rank substitution for seismic data interpolation, which is highly accurate but time-consuming. Therefore, this study proposes an efficient nonconvex reconstruction model based on the nonconvex Geman function (the nonconvex Geman low-rank (NCGL) model), involving a tighter approximation of the original rank function. Without introducing additional parameters, the nonconvex problem is solved using the Karush-Kuhn-Tucker condition theory. Experiments using synthetic and field data demonstrate that the proposed NCGL approach achieves a higher signal-to-noise ratio than the singular value thresholding method based on NNM and the projection onto convex sets method based on the data-driven threshold model. The proposed approach achieves higher reconstruction efficiency than the singular value thresholding and LSMM methods.

The objective function of full waveform inversion is a strong nonlinear function, the inversion process is not unique, and it is easy to fall into local minimum. Firstly, in the process of wavefield reconstruction, the wave equation is introduced into the construction of objective function as a penalty term to broaden the search space of solution and reduce the risk of falling into local minimum. In addition, there is no need to calculate the adjoint wavefield in the inversion process, which can significantly improve the calculation efficiency; Secondly, considering that the total variation constraint can effectively reconstruct the discontinuous interface in the velocity model, this paper introduces the weak total variation constraint to avoid the excessive smooth estimation of the model under the strong total variation constraint. The disadvantage of this strategy is that it is highly dependent on the initial model. In view of this, this paper takes the long wavelength initial model obtained by first arrival traveltime tomography as a prior model constraint, and proposes a weak total variation constrained wavefield reconstruction inversion method based on first arrival traveltime tomography. Numerical experimental results show that the new method reduces the dependence on the initial model, the interface description is more accurate, the error is reduced, and the iterative convergence efficiency is significantly improved.

In this paper, we use high-precision airborne gravity and magnetic data to study the geophysical characteristics of the western slope of the Songliao Basin and its adjacent areas and evaluate the resource potential. We performed an in-depth analysis of three aspects of the basin characteristics: the characteristics of residual strata, the development characteristics of faults, and the distribution characteristics of magmatic rocks. Next, we analyzed the forming background of organic (oil and gas) resources and inorganic (uranium ore and hot dry rock) resources. The results showed that the new Upper Paleozoic strata have significant differences in different regions of the study area (with a thickness of 0–8000 m), mainly distributed in the eastern and northern regions but absent in the middle eastern and western regions. Furthermore, the thickness and depth of the Mesozoic layer varied between the eastern and western regions; it was thicker and deeper in the middle eastern region but thinner and shallower in the western region, and it is absent in most western regions. The main faults in the region are in the north-northeast (NNE) direction. Faults in the NE-NNE and NW directions jointly controlled the morphology of the secondary structural units. Magmatic rocks are relatively developed in the middle and eastern parts of the region. Most magmatic rocks are distributed along the faults and their sides, clearly reflecting the control of the faults on magmatic activities. The western slope of the Songliao basin and its surroundings have a favorable geological setting for the accumulation (mineralization) of oil, gas, shale oil, hot dry rock, and uranium ore. It is conducive to oil and gas exploration of deep new strata and collaborative exploration of multiple resources.