To address the three-dimensional (3D) forward modeling problem of transient electromagnetic fields for grounded-wire source, this paper explores a finite element forward modeling method that employs a frequency-time transformation and background-scattered field separation strategy. It utilizes the vector finite element theory, and the 3D model is discretized using structured hexahedral mesh. Subsequently, the frequency-domain numerical response is computed using the MUMPS solver. Ultimately, the time-domain transient electromagnetic response is derived via cosine transformation. On this basis, the reliability of the forward algorithm is validated using both a one-dimensional layered model and an open three-dimensional model, and its computational accuracy is assessed. Theoretical examples show that the calculation results of the 3D transient electromagnetic forward modeling proposed in this paper are accurate and can meet the calculation requirements of 3D inversion research.

The difference in formation wave impedance is one of the important factors affecting the quality of wellbore microseismic monitoring data. Based on Snell's law and the Zoeppritz equation, by studying the influence of wave impedance difference and incident angle on the characteristics of the first arrival wave signals of microseisms, the relationship between the energy of the first arrival waves in wellbore microseismic data, the magnitude of the formation wave impedance difference, and the incident critical angle was revealed and verified through forward modeling. It was concluded that formations with large wave impedance differences have a significant impact on the energy and propagation path of the first arrival waves. Taking Well XX in a coalbed methane field as an example, at Perforation Section 1, some geophones failed to receive the first arrival signals, which affected the three-component rotation positioning of the geophones and the monitoring interpretation. By obtaining the formation velocity information of the target interval from acoustic logging data and combining it with the changes in formation wave impedance, the reasons for the absence of the first arrival waves in the microseismic perforation records of some geophones were analyzed. The deployment depth of the geophones was adjusted in a timely manner to solve the problem that some geophones could not detect the first arrival waves when the wave impedance difference was large and the incident angle was greater than the critical angle. After the depth of the geophones was adjusted upward by 30 meters, good first arrival wave signals were obtained at Perforation Section 2. The positioning results of these signals were used for wellbore microseismic fracturing fracture monitoring. The interpretation results, when comprehensively analyzed with conventional logging and dipole acoustic logging, showed that the microseismic event points were basically consistent in height with the reservoir characteristics and the fracture height indicated by dipole acoustic logging.

The dispersion and attenuation of seismic waves are critical physical properties of hydrate reservoirs, essential for the precise identification and quantitative characterization of hydrate reservoirs. The coupled effects of hydrate saturation and occurrence modes typically exert significant influences on seismic wave velocity dispersion and attenuation characteristics. However, most existing attenuation characterization theories are established based on assumptions of single or limited hydrate morphologies, making it challenging to accurately describe hydrate reservoirs with complex occurrence states. To address this, this study integrates the generalized effective medium model and two-phase media theory to develop an attenuation theoretical model for hydrate reservoirs that simultaneously considers four occurrence modes: contact-cementing, grain-coating, matrix-supporting, and pore-filling. A comparison of P-wave attenuation characteristics modeled using Biot theory (focusing on global fluid flow in porous media) and BISQ theory (Biot-Squirt theory, incorporating both global fluid flow and local squirt mechanisms) under different hydrate morphologies reveals that the attenuation predicted by Biot theory is significantly lower than that of the BISQ model. This discrepancy arises because the BISQ framework accounts for additional energy loss mechanisms, such as microscopic fluid squirt between hydrate-coated grains, which are critical in heterogeneous hydrate-bearing sediments. Based on the BISQ-derived attenuation model, a morphology-constrained attenuation rock physics template is developed, and a crossplot of P-wave velocity, attenuation, and hydrate saturation is constructed to identify hydrate occurrence modes. Furthermore, the developed morphology-constrained attenuation rock physics template is applied to logging data from Sites 1247B and 1250F of the Ocean Drilling Program (ODP) Expedition 204. Field results demonstrate that the constructed crossplot of P-wave velocity and attenuation versus hydrate saturation accurately identifies hydrate occurrence modes, and the attenuation rock physics template aligns well with the distribution characteristics of logging data. These research outcomes provide a new theoretical foundation and technical methodology for utilizing seismic attenuation attributes to identify and evaluate hydrate reservoirs, confirming the capability of attenuation theory to accurately diagnose occurrence states and estimate reservoir physical parameters.

Three-dimensional gravity inversion is the process of obtaining the location, shape, and physical parameters of underground anomalies using gravity anomaly data observed at the surface. In recent years, the rapid development of data-driven methods has led to widespread interest in applying Deep Learning (DL) techniques to gravity inversion problems, yielding certain results. Research based on the U-Net network that employs an Attention Feature Fusion (AFF) mechanism for three-dimensional gravity inversion enhances the vertical resolution of the inversion results. However, the reconstruction effect for deeper models still needs improvement. Building on this, the use of Global Receptive Convolution (GRC) to replace certain standard convolutions aims to ensure that the convolution process meets the conditions of spatial position and channel indexing. This approach integrates global and local features into a pixel-wise representation, further learning the original features to improve the reconstruction resolution of deeper models. The network's inversion results show enhanced vertical resolution, and experimental results from the San Nicolás deposit in Mexico demonstrate that the inversion network can clearly predict the basic location and approximate shape of the sulfur deposit, aligning well with known geological data.

To utilize wave field characteristics for transient electromagnetic data interpretation, enhance the interpretation accuracy of electromagnetic detection, and overcome the limitations of traditional diffusion field interpretation capabilities. This paper proposes a multi-constrained wavefield transformation algorithm based on integral transform relationships between diffusion and wavefields, with its core being the construction of an objective function that integrates diffusion field data characteristics and wavefield frequency features. First, based on the wavefield transformation theory, this study constructs an objective function framework. Within this framework, filtering process constraints and wavefield characteristic constraints are introduced. The filtering constraints mitigate the loss of wavefield resolution caused by traditional smoothing constraints, while the wavefield characteristic constraints further narrow the solution space based on wavefield propagation features. These two constraint terms are integrated into a unified objective function to enhance the accuracy of inverse transformation. Next, for optimizing the objective function, a quasi-Newton algorithm is employed for iterative optimization. During computation, this approach eliminates the need to compute the complex Hessian matrix required in traditional methods, ensuring both efficiency and robustness. Through iterative calculations, a virtual wavefield that satisfies both data constraints and wavefield characteristics is ultimately obtained. Finally, the proposed algorithm is applied to perform wavefield transformation on Transient Electromagnetic (TEM) forward modeling data from layered and complex geological models, validating its effectiveness and stability in practical applications. During the wavefield transformation process, comparative analysis with forward modeling data is conducted to investigate the algorithm's performance under diverse geological models, ensuring broad applicability and accuracy. Numerical experimental results demonstrate that the transformed wavefields retain the propagation characteristics of the wavefield and align closely with the forward modeling results, fully confirming the validity of the inverse transformation algorithm proposed in this study. This study provides a theoretical foundation for interpreting transient electromagnetic quasi-wave equations and holds application value in deep mineral exploration and complex geological structure identification

With the deepening of exploration and development of unconventional oil and gas reservoirs, especially pore-fracture reservoirs with both pore and fracture reservoir structures have become a research hotspot. Due to the complexity of geological conditions and the band limit of seismic data, these reservoirs often show hidden characteristics on longitudinal seismic data, and it is very necessary to carry out multi-wave seismic response analysis of pore-fracture reservoirs. In this paper, we combine the anisotropic fluid substitution theory of Gassmann equation and Thomsen anisotropic parameter theory to carry out equivalent HTI medium petrophysical modeling; use 2.5-dimensional staggered-grid finite-difference method to carry out highly efficient elastic fluctuation orthotropic simulation; and analyze the characteristics and sensitivity of the multi-wave AVO and AVAz responses in a variety of geological conditions. The model characterization shows that the PP wave near-deviation amplitude and PS wave far-deviation amplitude are more sensitive to the changes of fracture density and porosity, which can better reflect the changes of the two parameters; the amplitudes of different offset distances have similar characteristics of the changes with water saturation, and there is a sudden change near 90%; the PP wave AVAz characteristics show that the amplitude amplitude amplitude is near-deviation and far-deviation, and the PS wave shows the opposite trend, and all of them are periodic changes, which can indicate the The PS wave AVAz characteristics show an opposite trend in amplitude, and both of them change periodically, which can indicate the fracture orientation; the defining equation of the PS wave tuned thickness is deduced, which complements the characterization of the multi-wave tuned thickness. The significance of the pore-fracture type reservoir response characteristics to the actual data interpretation is summarized, which provides an important reference for understanding the fluctuation response characteristics of complex pore-fracture reservoirs, helps to understand the actual seismic data phenomena of complex pore-fracture reservoirs, and can effectively assist the design of the interpretation scheme to improve the accuracy of the interpretation.

The marine exploration environment is generally regarded as a fluid-solid boundary coupling medium. High-precision imaging of the fluid-solid boundary coupling medium can be achieved by using the decoupled elastic wave field for reverse-time migration. Traditional elastic wave decoupling utilizes the Helmholtz principle, but the separated P-waves and S-waves have phase and amplitude issues, which seriously affect the final imaging quality. This paper starts from the first-order velocity-stress elastic medium wave equation, separates the full elastic wave field into pure P-waves and pure S-waves to construct a new coupling equation, avoiding the phase and amplitude problems and crosstalk artifacts caused by the traditional Helmholtz decomposition; analyzes the displacement and stress continuity conditions at the boundary of the fluid-solid boundary coupling medium, and establishes the acoustic-elastic coupling vector separation equation; compares the numerical simulation results with the acoustic wave equation to verify the effectiveness and accuracy of the proposed acoustic-elastic coupling vector separation equation forward modeling method, and compares the results with the conventional reverse-time migration imaging method in a complex seabed model to verify the reliability of the reverse-time migration imaging results.

Dielectric logging technology is limited by its shallow probe depth, and the influence of mud cake cannot be ignored. By measuring the dielectric spectrum of 25 artificial mud cakes with different electrical properties, the electrical characteristics and dielectric dispersion model of mud cakes are revealed in this paper. The mud cake was prepared by mixing barite, bentonite, kaolin, sodium chloride and water, and the effect of salinity, clay mineral content and clay mineral type on the electrical properties of the mud cake was studied and discussed by using the terminal open-circuit coaxial reflection method. The experimental results show that in the low frequency band, the dielectric constant of mud cake increases with the increase of montmorillonite proportion, the increase with the increase of clay mineral content and salinity, and the relationship with salinity is linear positive, and the relationship with clay mineral content is more complex, showing a quadratic function increase. In the high frequency band, the dielectric constant increases with the increase of clay mineral content, and is less affected by clay mineral type and salinity. The modified Shaly Sand model (SHSD) dielectric dispersion model can effectively describe this law. The results of this study provide basic data and theoretical basis for environmental correction and forward and inverse research of sweep frequency dielectric logging data.

The tight oil resources in the Triassic Yanchang Formation in the Ganquan area of the southern Ordos Basin have great potential. However, the research on rock mechanical parameters and in-situ stress analysis of its tight sandstone reservoirs is relatively lagging. In this paper, small cores with angles of 0° (parallel, H), 45° (oblique intersection) and 90° (perpendicular, V) to the bedding plane were drilled, and X-ray diffraction, scanning electron microscopy and triaxial stress experiments were carried out. The research shows that the minerals in the Chang 8 layer samples are mainly quartz (31.8%), plagioclase (22.6%) and clay (26.6%), with a total content of 81.0%. Scanning electron microscopy shows that there are quartz overgrowth, intergranular and grain-surface clay mineral filling in the core, and there are intergranular residual pores. Under different bedding directions, the Kaiser point stress value, peak load value and compressive strength decrease in turn, while the elastic modulus and Poisson's ratio first decrease and then increase. There is a logarithmic function relationship between the pore volume compressibility coefficient and the effective stress. Through the analysis and prediction of logging data and experimental data, the dynamic elastic modulus is higher than the static one, and the dynamic Poisson's ratio is lower than the static one. The prediction results of compressive strength, tensile strength and in-situ stress are consistent with the experimental results. The research results provide new indicators for the prediction of "sweet spots" in the integration of geology and engineering of tight oil reservoirs in the Chang 8 interval of the Ganquan area. They have important guiding value for the identification of comprehensive sweet spots in tight oil reservoirs in the southern part of the Ordos Basin, the optimization of horizontal well trajectories, the design of fracturing stages and clusters, and the optimization of construction parameters.

When numerically simulating the elastic wave field in anisotropic media using the rotated staggered grid finite difference method, numerical dispersion phenomena usually occur. To solve this problem, a time-domain high-order difference coefficient calculation model based on the coupling of Taylor expansion and sampling approximation method is proposed, and an improved space-time domain high-order rotating staggered grid scheme is constructed. To verify the performance of the modified algorithm, the improved algorithm is compared with the general staggered grid and other rotated staggered grids, and the dispersion degree and stability of each algorithm are analyzed. Through the results of numerical experiments, it is found that the algorithm improved by the optimization strategy of the difference operator coefficients based on the Taylor expansion and the sampling approximation method can significantly suppress the dispersion of the elastic wave field in isotropic media, VTI/TTI anisotropic media, and the modified BP model.