Applied Geophysics最新文献

Acoustic velocity varies in deep-water environments, and the variable-velocity seawater can affect the dispersion characteristics of Scholte wave. To improve the accuracy of inversion, a horizontal layered-seawater and layered-seabed (HLSLS) model is established with continuously varying velocities for seabed S-wave velocity inversion using Scholte wave. First, we deduced the Scholte wave dispersion equation and the amplitude-depth equation of the HLSLS model based on wave theory. Then, with the real acoustic velocity of the seawater and submarine sediments parameters of the Shenhu area in the South China Sea, we analyzed the influence of variable-velocity seawater on the dispersion characteristics of Scholte wave. Finally, we performed two-dimensional (2D) S-wave velocity inversion on the field OBS multi-component data in the South China Sea. The results showed that the variation of seawater acoustic velocity had a certain influence on the dispersion characteristics of Scholte wave in deep water. The accuracy and practicality of our method were verified through numerical and filed data experiments.

Abstract

With the constantly changing engineering construction sector, the detection accuracy of conventional electrical resistivity tomography (ERT) is no longer sufficient. 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 difference between different 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 effect of the MERT method on anomalous bodies with different 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 fine detection is positively influenced.

Abstract

Considering the constraints in the costs and efficiency of seismic exploration acquisition, marine hydrocarbon exploration mainly relies on towed-streamer acquisition. However, the seismic data obtained from streamers have limited azimuthal coverage, posing significant challenges for the prediction of complex fractured reservoirs using azimuthal anisotropy features. To address this issue, we proposed a workflow for conventional offshore narrow-azimuth streamer data, including the local angle domain migration imaging and prestack anisotropy inversion methods based on the Rüger approximation equation. First, the local angle domain full-azimuth migration imaging method is used to perform prestack imaging processing on narrow-azimuth streamer seismic data, thus obtaining prestack gather data with azimuth information. The prestack anisotropy parameter inversion method is then used to predict the fracture intensity distribution. Finally, the method and technical process proposed in this paper are applied to the fractured reservoir description of buried hills reservoirs in the deepwater area of the northern South China Sea. The practical results demonstrate that the proposed workflow, which combines full-azimuth migration imaging processing and prestack azimuthal anisotropy parameter inversion, can accurately predict fractured reservoirs using narrow-azimuth seismic data acquired through marine towed-streamer surveys. This technical workflow is also applicable to fracture predictions and reservoir evaluations in similar seismic survey areas.

The Qilian Orogenic belt is one of the typical orogenic belts globally and a natural laboratory for studying plate tectonics. Many researchers have studied the ophiolite and high pressure and ultra-high pressure metamorphic rocks in the Qilian orogen and obtained valuable achievements. However, a hot debate exists on the basement property, the distribution of ophiolite, and the boundaries of tectonic units. Large-scale high-precision aeromagnetic surveys have recently been conducted in the Qilian Orogenic belt and adjacent areas. In this study, we are trying to analysis the tectonic framework of the Qilian Orogen using 1:500, 000 aeromagnetic data. The results provide geophysical perspectives for studying the structural framework and deformation of this area. According to the aeromagnetic ΔT anomaly map, the central and Southern Qilian have the same magnetic anomaly feature that noticeably differs from the North Qilian Orogenic belt and the Qaidam Block. This result indicates that the central and Southern Qilian have a unified magnetic basement and differ from the North Qilian orogenic belt and Qaidam Block. The map shows the distribution of ophiolite in the North Qilian orogenic belt. Linear magnetic anomalies represent the ophiolites because the mafic–ultramafic rocks usually have high magnetic susceptibility. The ophiolite belts are continuously distributed in the western part of North Qilian orogenic belt and have a large scale. However, the scale of the ophiolite belt and the outcropping of mafic–ultramafic rocks reduces when they pass through Qilian County to the east. The results indicate differences in the evolution process between the eastern and western parts of North Qilian, with Qilian County as the transition zone. This study also systematically defines the geophysical boundaries of the Qaidam Block, Qilian Block, North Qilian Orogenic belt, and Alxa block. It is proposed that the sinistral displacement of the Altun Fault is adjusted and absorbed by the series of NE-trending faults in the Qilian orogen and merge into the Longshoushan–Gushi Fault. The extension of the North Qilian Orogenic belt is strengthened by the neotectonics movement along the shearing direction, which separated the North Qilian Orogenic belt into several segments and formed a series of northeast-trending faults.

Impact ground pressure events occur frequently in coal mining processes, significantly affecting the personal safety of construction workers. Real-time microseismic monitoring of coal rock body rupture information can provide early warnings, and the seismic source location method is an essential indicator for evaluating a microseismic monitoring system. This paper proposes a nonlinear hybrid optimal particle swarm optimisation (PSO) microseismic positioning method based on this technique. The method first improves the PSO algorithm by using the global search performance of this method to quickly find a feasible solution and provide a better initial solution for the subsequent solution of the nonlinear optimal microseismic positioning method. This approach effectively prevents the problem of the microseismic positioning method falling into a local optimum because of an over-reliance on the initial value. In addition, the nonlinear optimal microseismic positioning method further narrows the localisation error based on the PSO algorithm. A simulation test demonstrates that the new method has a good positioning effect, and engineering application examples also show that the proposed method has high accuracy and strong positioning stability. The new method is better than the separate positioning method, both overall and in three directions, making it more suitable for solving the microseismic positioning problem.

Shallow geothermal heat has the characteristics of wide distribution and huge reserves. However, for northern rural buildings, the heating load in winter is much greater than the cooling load in summer, and thermal imbalance of the soil is prone to occur. This paper takes rural residences in southern Hebei as an example and designs a solar-assisted shallow geothermal energy system. Compared with the original shallow ground-source heat pump system, the indoor and outdoor temperature differences of the target building were first analyzed. Second, the changes in the soil temperature field and the differences in the supply and return water temperature were monitored. Finally, the initial investment and operating costs of the assisted system are analyzed. The results show that the average ground temperature field increases significantly in winter. Through the alternate operation of solar energy and ground-source heat pumps, heat extraction from the ground is reduced, and the imbalance cycle of heat extraction in winter and heat removal in summer is shortened. It alleviates the imbalance of the cold and heat loads for soil throughout the year. The inlet and outlet water temperature and heat exchange efficiency of the buried pipes have been significantly improved. The energy efficiency ratio of the system using the assisted system has increased from 3.40 in 2020 to 4.17, an increase of 0.77. The optimal ratio of the solar- assisted shallow geothermal energy system is a 12.80 m² solar heat-collection area and one buried hole. The winter heating operating cost of the solar-assisted shallow geothermal energy system is 18.86 CNY/m². It can save 37% of the annual operating costs of heating, cooling, and hot water compared to a single ground-source heat pump system and 40%–45% compared to traditional heating and cooling modes.

According to a comprehensive analysis of regional geology–geophysics, this article focuses on structural conditions for dry hot rocks in the middle section of the northern margin of the North China Block and adjacent areas, revealing the controlling effect of the structure of dry hot rock reservoirs. Based on processing the latest high-precision data from an aeromagnetic survey, studying the characteristics of aeromagnetic anomalies such as geophysical field boundaries, anomaly zones, and anomaly dislocation lines, and quantitative calculation results of wavelet analysis and other methods, this study discusses the characteristics, scales, and cutting relationships and further clarifies the levels, active periods, and relative strengths of the faults in the middle section of the northern margin of the North China Block and its adjacent areas. According to their aeromagnetic data and aeromagnetic identification mark, faults in the studying region are determined in detail. The study region mainly develops four groups of regional faults. The main faults in this region are in the near-EW, NE, SN, and NW directions. Their interlacing and overlapping constitute the complex structural features of the study area and control regional magmatic activity. The deep faults are important channels for upwelling deep heat sources and the eruption or intrusion of magma. The control degree of regional faults in different directions on magmatic activity differs. Next, we discuss the fault system and its mutual control and propose that the faults in the near-NW direction also have great importance in tectonic evolution in the northern part of the North China Block and merit more attention.

The tight oil/gas reservoirs in China have showed the great exploration prospects and high production potential, with the characteristics of low porosity, low permeability, and significant heterogeneity in formation rocks. It remains a challenge to sort out the relations between reservoir wave responses and rock physical properties, and the further studies on the wave response patterns of tight reservoirs are in an urgent demand. The shear modulus and S- (shear) wave attenuation of rocks are affected by the properties of pore fluid and confining pressure. The ultrasonic wave experiments are performed on eight partially-saturated tight sandstone samples at different confining pressures, and we estimate S-wave attenuation with the spectral-ratio method. Results show that S-wave attenuation decreases with increasing confining pressure, and the water saturation case shows more loss compared to the oil saturation case, while the gas saturation case gives the lowest attenuation. We observe the S-wave relaxation peak at an intermediate water saturation for the gas-water partial-saturation case in general. S-wave attenuation increases with increasing porosity or permeability. Based on the measured rock physical properties, and combined with the Voigt–Reuss–Hill (VRH) average, differential effective medium (DEM) model and squirt-flow model, a tight rock attenuation model is proposed for analyzing the attenuation characteristics of fluid-saturated rocks at different confining pressures. The model reasonably describes the S-wave attenuation characteristics. The model predictions of S-wave attenuation show apparent pressure- and fluid-sensitivity at full saturation and partial saturation conditions. For sample TS1-19 at full saturation with different confining pressures, the S-wave peak attenuation predicted by the model ranges from 11.6 to 69.5, and decreases with confining pressure, while the relaxation frequency shifts to high frequency end. For the partial saturation condition of the sample, the predicted S-wave peak attenuation ranges from 15.5 to 39.8 at a confining pressure of 30 MPa and increases with water saturation, while the relaxation frequency shifts to low frequency end. For all the samples at 30MPa confining pressure, the predicted S-wave attenuation ranges from 5.6 to 38.6. At the full-saturation case, the predicted S-wave attenuation increases with porosity and decreases with confining pressure. For the partial saturation case, the S-wave attenuation predicted with the model and the Voigt and Reuss bounds generally increases with water saturation, whereas the experimentally-measured attenuation exhibits the peak attenuation at an intermediate saturation.

Seismic stochastic inversion method has received much attention because of its considerable advantage of having higher vertical resolution than deterministic inversions. However, due to the lack of cross-well data, the inversion results typically exhibit poor lateral continuity. Furthermore, the inversion efficiency is low, and the inversion result is highly random. Therefore, this study proposes a geostatistical seismic inversion method constrained by a seismic waveform. The correlation coefficient of seismic data is used to measure the similarity of the seismic waveforms, replacing the traditional variogram for sequential Gaussian simulation. Under the Bayesian framework, the Monte Carlo-Markov Chain (MCMC) algorithm is combined with the constraints of seismic data to randomly perturb and optimize the simulation results for obtaining the optimized parameter inversion results. The model data tests show that the initial model based on seismic waveform constraints can accurately describe the spatial structure of the subsurface reservoir. In addition, perturbing and optimizing initial model can increase the convergence speed of the Markov chain and effectively improve the accuracy of the inversion results. In this paper, the proposed geostatistical inversion method is applied to the actual seismic data of an oil field. Under the constraints of the stochastic simulation process and objective function, the geological information contained in the seismic waveforms is fully mined, and a theoretical foundation is provided for realizing the multidata joint-constrained seismic inversion.

Most existing seismic data frequency enhancement methods have limitations. Given the advantages and disadvantages of these methods, this study attempts to apply deep learning technology to improve seismic data resolution. First, on the basis of the UNet deep learning method, which combines well-logging and seismic data, a synthetic seismic record is established with logging acoustic data and density, the borehole synthetic seismic record is labeled, and the borehole seismic trace data are taken as the input data. The training model of the borehole seismic trace data and the borehole synthetic seismic record is established to improve the medium- and high-frequency information in the seismic data. Second, the gate recurrent unit (GRU) is used to retain the low-frequency trend in the original seismic record, and the UNet and GRU results are combined to improve the medium- and high-frequency information while preserving the low-frequency information in the seismic data. Then, model training is performed, the model is applied to the three-dimensional seismic data volume for calculation, and the seismic data resolution is improved. The information extracted using our method is more abundant than that extracted using previous methods. The application of a theoretical model and actual field data shows that our method is effective in improving the resolution of poststack seismic data.