Abstract: Abstract At present, the fault sliding speed functions, or source time functions that used in theoretical seismogram calculation are all theoretical results. That is, the fault speed time functions are the results of the theoretical study, and they are not proved by the measured data. The method that used to calculate fault sliding speed by using Doppler effect has been greatly improved in this paper from the following four perspectives: Firstly, the paper proves theoretically how to confirm the seismic waves that received in some frequency bands by two receivers are emitted by the same source. Secondly, the paper puts forward the method to make sure whether seismic waves received by two receivers in some frequency bands are similar by using relative change of Fourier amplitude standard deviation in some frequency bands of two receivers, and similar seismic waves are emitted by the same frequency bands. Thirdly, to eliminate the interference of reflection and refraction waves, S wave records in fault sliding time are selected for data processing. Finally, long time Fourier transform is replaced by short time Fourier transform (STFT) to enhance fault sliding time positioning accuracy. On the basis of the work above, a general method to calculate the fault sliding speed by using Doppler effect is summarized systematically. The fault sliding speed of Wenchuan earthquake is calculated by the method mentioned above. The calculations show that Wenchuan earthquake fault sliding speeds are basically consistent with the seismic moment changes. It has proved that the sliding speed of Wenchuan earthquake fault has the characteristics of abrupt change, that is, the sliding speed increases suddenly and decreases rapidly. For most of the time, the sliding speed is not large, and sometimes the fault does not slide. There are obvious differences from sliding speed functions that are applied currently, such as Haskell function, Bell shaped functions, Exponential function, Triangle function, etc. To compute fault sliding speed by using Doppler effect, instead of grasping so-far unknown crust parameters, we only need to know the earthquake records, the locations of the epicenter and the receivers. In a word, the calculation method has clear physical meaning and the parameters required are easier to be obtained. PubDate: 2020-01-10

Abstract: Abstract The enhancement of horizontal boundaries of potential field sources is of great significance for the study of geological structures. Most of the existing filters for horizontal edges enhancement are presented based on the derivatives of potential field data, but these filters often show some shortcomings, for example, the output edges are divergent, strong and weak anomalies cannot be balanced, or some extra false edges appear in the results. In this paper, the edges enhancement filter MMA based on mathematical morphology is first defined by the combination of the basic operators of mathematical morphology. In order to make the filter have the ability to balance different amplitude anomalies, MMAZ and MMAT are proposed, and both of them can be used to delineate the horizontal edges of the field sources by their maxima. The experimental results of synthetic data show that MMAZ and MMAT have good equalization and anti-noise performances. Compared with several traditional filters, the horizontal edges of geological bodies obtained by these two filters are clearer and more convergent, and there are no extra edges in the output results for the complex situations that positive and negative anomalies exist simultaneously. Finally, the two new equalization filters are applied to gravity anomaly data in a potash mine area in Vientiane basin of Laos and the aeromagnetic anomaly of a metal mine in northwest China, the obtained positions of the structures are more accurate and clearer, which further illustrates the effectiveness of the two filtering techniques. PubDate: 2020-01-08

Abstract: Abstract In crosswell seismic, imaging section produced by migration employed with wave equation has a serious arc phenomenon at its edge and small effective range due to the restriction of geometry. Another imaging section produced by VSP-CDP stack imaging employed with ray-tracing theory is amplitude-preserved but has difficulty in imaging 3D complex lithological structure accurately. Therefore, the paper proposes inverse Gaussian beam stack imaging in 3D crosswell seismic of deviated well based on the Gaussian beam ray-tracing theory. Through employing Gaussian beam ray-tracing theory into 3D crosswell seismic, the energy relationship between the seismic wave field and its effective rays is analyzed. Then the author converts the single channel seismic wave field data in the common shot point (CSP) gather into multiple effective wave fields in common reflection point (CRP) gather by inverse Gaussian beam when imaging and thus produces more intensive reflection points fold number. Finally, the wave fields of the effective reflection points in the same stack bin, selected from horizontal and vertical direction of the 2D measuring line, are projected onto the 2D measuring line, chosen according to the distribution characteristics of the reflection points, and stacked into an imaging section. The method is applied in X oilfield to identify the internal structure of offshore gas cloud area. The result provides positive support for inverse Gaussian beam stack imaging in producing accurate imaging in 3D complex lithological structure and make it a powerful imaging tool for 3D crosswell seismic data processing. PubDate: 2020-01-08

Abstract: Abstract The quality factor (or Q value) is an important parameter for characterizing the inelastic properties of rock. Achieving a Q value estimation with high accuracy and stability is still challenging. In this study, a new method for estimating ultrasonic attenuation using a spectral ratio based on an S transform (SR-ST) is presented to improve the stability and accuracy of Q estimation. The variable window of ST is used to solve the time window problem. We add two window factors to the Gaussian window function in the ST. The window factors can adjust the scale of the Gaussian window function to the ultrasonic signal, which reduces the calculation error attributed to the conventional Gaussian window function. Meanwhile, the frequency bandwidth selection rules for the linear regression of the amplitude ratio are given to further improve stability and accuracy. First, the feasibility and influencing factors of the SR-ST method are studied through numerical testing and standard sample experiments. Second, artificial samples with different Q values are used to study the adaptability and stability of the SR-ST method. Finally, a further comparison between the new method and the conventional spectral ratio method (SR) is conducted using rock field samples, again addressing stability and accuracy. The experimental results show that this method will yield an error of approximately 36% using the conventional Gaussian window function. This problem can be solved by adding the time window factors to the Gaussian window function. The frequency bandwidth selection rules and mean slope value of the amplitude ratio used in the SR-ST method can ensure that the maximum error of different Q values estimation (Q > 15) is less than 10%. PubDate: 2019-11-28

Abstract: Abstract To solve problems in small-scale and complex structural traps, the inverse Gaussian-beam stack-imaging method is commonly used to process crosswell seismic wave reflection data. Owing to limited coverage, the imaging quality of conventional ray-based crosswell seismic stack imaging is poor in complex areas; moreover, the imaging range is small and with sever interference because of the arc phenomenon in seismic migration. Thus, we propose the inverse Gaussian-beam stack imaging, in which Gaussian weight functions of rays contributing to the geophones energy are calculated and used to decompose the seismic wavefield. This effectively enlarges the coverage of the reflection points and improves the transverse resolution. Compared with the traditional VSP-CDP stack imaging, the proposed methods extends the imaging range, yields higher horizontal resolution, and is more adaptable to complex geological structures. The method is applied to model a complex structure in the K-area. The results suggest that the wave group of the target layer is clearer, the resolution is higher, and the main frequency of the crosswell seismic section is higher than that in surface seismic exploration The effectiveness and robustness of the method are verified by theoretical model and practical data. PubDate: 2019-11-28

Abstract: Abstract Multiple wave is one of the important factors affecting the signal-to-noise ratio of marine seismic data. The model-driven-method (MDM) can effectively predict and suppress water-related multiple waves, while the quality of the multiple wave contribution gathers (MCG) can affect the prediction accuracy of multiple waves. Based on the compressed sensing framework, this study used the sparse constraint under L0 norm to optimize MCG, which can not only reduce the false in the prediction and improve the image accuracy, but also saves computing time. At the same time, the MDM-type method for multiple wave suppression can be improved. The unified prediction of multiple types of water-related multiple waves weakens the dependence of conventional MDM on the adaptive subtraction process in suppressing water-related multiple waves, improves the stability of the method, and simultaneously, reduces the computational load. Finally, both theoretical model and practical data prove the effectiveness of the present method. PubDate: 2019-11-27

Abstract: Abstract Geophysical inversion under different stabilizers has different descriptions of the target body boundary, especially in complex geological structures. In this paper, we present an extremum boundary inversion algorithm based on different stabilizers for electrical interface recognition. Firstly, we use the smoothest and minimum-support stabilizing functional to study the applicability of adaptive regularization inversion algorithm. Then, an electrical interface recognition method based on different stabilizers is developed by introducing extremum boundary inversion algorithm. The testing shows that the adaptive regularization inversion method does work for different stabilizers and has a low dependence on the initial models. The ratio of the smooth and focusing upper and lower boundaries obtained using the extremum boundary inversion algorithm can clearly demarcate electrical interfaces. We apply the inversion algorithm to the magnetotelluric (MT) data collected from a preselected area of a high-level-waste clay-rock repository site in the Tamusu area. We recognized regional structures with smooth inversion and the local details with focusing inversion and determined the thickness of the target layer combined with the geological and drilling information, which meets the requirement for the site of the high-level waste clay-rock repository. PubDate: 2019-11-27

Abstract: Abstract In this study, the gamma-ray spectrum of single elemental capture spectrum log was simulated. By numerical simulation we obtain a single-element neutron capture gamma spectrum. The neutron and photon transportable processes were simulated using the Monte Carlo N-Particle Transport Code System (MCNP), where an Am-Be neutron source generated the neutrons and thermal neutron capture reactions with the stratigraphic elements. The characteristic gamma rays and the standard gamma spectra were recorded, from analyzing of the characteristic spectra analysis we obtain the ten elements in the stratum, such as Si, Ca, Fe, S, Ti, Al, K, Na, Cl, and Ba. Comparing with single elemental capture gamma spectrum of Schlumberger, the simulated characteristic peak and the spectral change results are in good agreement with Schlumberger. The characteristic peak positions observed also consistent with the data obtained from the National Nuclear Data Center of the International Atomic Energy Agency. The neutron gamma spectrum results calculated using this simple method have practical applications. They also serve as an reference for data processing using other types of element logging tools. PubDate: 2019-11-27

Abstract: Abstract To improve the anti-noise performance of the time-domain Bregman iterative algorithm, an adaptive frequency-domain Bregman sparse-spike deconvolution algorithm is proposed. By solving the Bregman algorithm in the frequency domain, the influence of Gaussian as well as outlier noise on the convergence of the algorithm is effectively avoided. In other words, the proposed algorithm avoids data noise effects by implementing the calculations in the frequency domain. Moreover, the computational efficiency is greatly improved compared with the conventional method. Generalized cross validation is introduced in the solving process to optimize the regularization parameter and thus the algorithm is equipped with strong self-adaptation. Different theoretical models are built and solved using the algorithms in both time and frequency domains. Finally, the proposed and the conventional methods are both used to process actual seismic data. The comparison of the results confirms the superiority of the proposed algorithm due to its noise resistance and self-adaptation capability. PubDate: 2019-11-21

Abstract: Abstract This study aimed to obtain the production profiles of oil-in-water flow under low flow rate and high water-cut conditions in oil wells. A combination production profile logging composed of an arc-type conductance sensor (ATCS) and a cross-correlation flow meter (CFM) with a center body is proposed and experimentally evaluated. The ATCS is designed for water holdup measurement, whereas the CFM with a center body is proposed to obtain the mixture velocity. Then, a drift-flux model based on flow patterns is established to predict the individual-phase superficial velocity of oil-in-water flows. Results show that the ATCS possesses high resolution in water holdup measurement and that flow pattern information can be deduced from its signal through nonlinear time series analysis. The CFM can enhance the correlation of upstream and downstream signals and simplify the relationship between the cross-correlation velocity and mixture velocity. On the basis of the drift-flux model, individual-phase superficial velocities can be predicted with high accuracy for different flow patterns. PubDate: 2019-11-21

Abstract: Abstract With the development of seismic exploration, passive-source seismic data has attracted increasing attention. Ambient noise passive seismic sources exists widely in nature and industrial production. Passive seismic data is important in logging while drilling (LWD), large-scale structural exploration, etc. In this paper, we proposed a passive multiple reverse time migration imaging (PMRTMI) method based on wavefield decomposition and normalized imaging conditions method. This method differs from seismic interferometry in that it can use raw passive seismic data directly in RTM imaging without reconstruction of virtual active gather, and we use the wavefield decomposition method to eliminate the low frequency noise in RTM. Further, the energy normalized imaging condition is used in full wavefield decomposition, which can not only enhance the image quality of both edge and deep information but also overcome the wrong energy problem caused by uneven distribution of passive sources; furthermore, this method exhibits high efficiency. Finally, numerical examples with the Marmousi model show the effectiveness of the method. PubDate: 2019-11-21

Abstract: Abstract The April 20, 2013, Ms 7.0 Lushan Earthquake was a major earthquake that followed the Ms 8.0 Wenchuan Earthquake on May 12, 2008. Frequent earthquakes have caused heavy casualties and property loss in Western Sichuan. Earthquake disasters are often closely related to the amplification effect of ground motion. Studying the ground motion characteristics of near-surface geological structures helps to understand the distribution of potential earthquake disasters. In this study, we investigated ground motion amplification in the downtown area of Lushan using numerical simulation and aftershock data from the Lushan Earthquake. Using the Lushan earthquake aftershock data from nine seismic stations distributed in the area, the amplification effect of the sites was determined using the “reference site spectral ratio” method. The results show that the frequency of the ground motion amplification in the area was in the range 5–10 Hz, and the corresponding amplification peak was from 3 to 14. Among the study sites, the amplification (14 times) at L07 was the most prominent. To study further the amplification characteristics, shear-wave velocity models for the structures under these sites were established using passive-source Rayleigh surface-wave exploration. One-dimensional (1D) and two-dimensional (2D) seismic amplification effects were simulated using horizontally propagating shear-wave modeling. Except Site L07, the 1D simulation results of each site well reflected the variation feature of the seismic amplification on the frequency band below the observed peak frequency, although the overall simulated amplification peaks were smaller than the observed results. The 2D simulation of the remarkable amplification phenomenon at L07 was in better agreement with the observation result than was the 1D simulation, indicating that the seismic amplification in the Modong area is influenced by lateral variation of the Quaternary sediments. PubDate: 2019-11-18

Abstract: Abstract Earthquake precursor data have been used as an important basis for earthquake prediction. In this study, a recurrent neural network (RNN) architecture with long short-term memory (LSTM) units is utilized to develop a predictive model for normal data. Furthermore, the prediction errors from the predictive models are used to indicate normal or abnormal behavior. An additional advantage of using the LSTM networks is that the earthquake precursor data can be directly fed into the network without any elaborate preprocessing as required by other approaches. Furthermore, no prior information on abnormal data is needed by these networks as they are trained only using normal data. Experiments using three groups of real data were conducted to compare the anomaly detection results of the proposed method with those of manual recognition. The comparison results indicated that the proposed LSTM network achieves promising results and is viable for detecting anomalies in earthquake precursor data. PubDate: 2019-11-18

Abstract: Abstract Apparent differences in sedimentation and diagenesis exist between carbonate reservoirs in different areas and affect their petrophysical and elastic properties. To elucidate the relevant mechanism, we study and analyze the characteristics of rock microstructure and elastic properties of carbonates and their variation regularity using 89 carbonate samples from the different areas The results show that the overall variation regularities of the physical and elastic properties of the carbonate rocks are controlled by the microtextures of the microcrystalline calcite, whereas the traditional classification of rock- and pore- structures is no longer applicable. The micrite microtextures can be divided, with respect to their morphological features, into porous micrite, compact micrite, and tight micrite. As the micrites evolves from the first to the last type, crystal boundaries are observed with increasingly close coalescence, the micritic intercrystalline porosity and pore-throat radius gradually decrease; meanwhile, the rigidity of the calcite microcrystalline particle boundary and elastic homogeneity are enhanced. As a result, the seismic elastic characteristics, such as permeability and velocity of samples, show a general trend of decreasing with the increase of porosity. For low-porosity rock samples (φ 5%) dominated by tight micrite, the micritic pores have limited contributions to porosity and permeability and the micrite elastic properties are similar to those of the rock matrix. In such cases, the macroscopic physical and elastic properties are more susceptible to the formation of cracks and dissolution pores, but these features are controlled by the pore structure. The pore aspect ratio can be used as a good indication of pore types. The bulk modulus aspect ratio for dissolution pores is greater than 0.2, whereas that of the intergranular pores ranges from 0.1 to 0.2. The porous and compact micrites are observed to have a bulk modulus aspect ratio less than 0.1, whereas the ratio of the tight micrite approaches 0.2. PubDate: 2019-11-18

Abstract: Abstract In this study, on the basis of absolute first-arrival times of 84756 P- and S-waves from 6085 earthquakes recorded at 56 fixed stations in Yibin and surrounding areas in China from January 2009 to January 2019, focal parameters and three-dimensional (3D) body-wave high-resolution velocity structures at depths of 0–30 km were retrieved by double-difference tomography. Results show that there is a good correspondence between the spatial distribution of the relocated earthquakes and velocity structures, which were concentrated mainly in the high-velocity-anomaly region or edge of high-velocity region. Velocity structure of P- and S-waves in the Yibin area clearly shows lateral inhomogeneity. The distribution characteristics of the P- and S-waves near the surface are closely related to the geomorphology and geologic structure. The low-velocity anomaly appears at the depth of 15–25 km, which is affected by the lower crust current. The Junlian-Gongxian and Gongxian-Changning earthquake areas, which are the two most earthquake-prone areas in the Yibin region, clearly differ in earthquake distribution and tectonic characteristics. We analyzed the structural characteristics of the Junlian-Gongxian and Gongxian-Changning earthquake areas on the basis of the 3D body-wave velocity structures in the Yibin region. We found that although most seismicity in the Yibin area is caused by fluid injection, the spatial position of seismicity is controlled by the velocity structures of the middle and upper crust and local geologic structure. Fine-scale 3D velocity structures in the Yibin area provide important local reference information for further understanding the crustal medium, seismogenic structure, and seismicity. PubDate: 2019-11-18

Abstract: Abstract Acoustic reflection imaging in deep water wells is a new application scope for offshore hydrocarbon exploration. Two-dimensional (2D) geological structure images can be obtained away from a one-dimensional (1D) borehole using single-well acoustic reflection imaging. Based on the directivity of dipole source and four-component dipole data, one can achieve the azimuth detection and the three-dimensional (3D) structural information around the wellbore can be obtained. We first perform matrix rotation on the field four-component data. Then, a series of processing steps are applied to the rotated dipole data to obtain the reflector image. According to the above dipole shear-wave imaging principle, we used four-component cross-dipole logging data from a deviated well in the South China Sea to image geological structures within 50 m of a deviated well, which can delineate the structural configuration and determine its orientation. The configuration of near-borehole bedding boundaries and fault structures from shear-wave imaging results agrees with those from the Inline and Xline seismic profiles of the study area. In addition, the configuration and orientation of the fault structure images are consistent with regional stress maps and the results of the borehole stress anisotropy analysis. Furthermore, the dip azimuth of the bedding boundary images was determined using borehole wall resistivity data. Results of this study indicate that integrating borehole acoustic reflection with seismic imaging not only fi lls the gap between the two measurement scales but also accurately delineates geological structures in the borehole vicinity. PubDate: 2019-11-16

Abstract: Abstract Acoustic and electrical methods are commonly used to evaluate hydrate saturation based on the P-wave velocity and resistivity, respectively. In this paper, petrophysical parameters, which are directly related to the presence of hydrates, are used to evaluate hydrate saturation. First, five petrophysical parameters sensitive to hydrate saturation are analyzed using the equivalent medium rock physical model (MBGL), logging intersection plots and petrophysical parameter inversion. Then, the simulated annealing global optimization method is used to estimate the hydrate saturation profile in the Shenhu area. The petrophysical parameters Vp, λρ and λμ, which are associated with the rock modulus (both the elastic modulus and shear modulus), are highly sensitive to hydrate saturation, with an estimated saturation range of 0.1-0.44. This range is highly consistent with that based on the original well diameter curves. However, the parameters Vs and μρ, which are only related to the shear modulus of the rock, yield high hydrate saturation estimates of 0.22-0.43 and exhibit some deviations from real data. Due to its sensitivity, Poisson's ratio (σ) is least desirable for hydrate evaluation among the studied parameters. The sensitivity of hydrate saturation depends on the petrophysical model used in studies of the physical properties of hydrate and analyses of hydrate storage. PubDate: 2019-11-08

Abstract: Abstract Coal seam is thin compared to the wavelength of seismic wave and usually shows strong anisotropy. It may form special geological bodies such as goaf and collapse in coal mining. The existence of these phenomena may lead to instability in numerical simulation of goaf area in coal seam. And the calculation speed of simulation is always a factor that restricting the development of simulation technique. To improve the accuracy and efficiency of seismic numerical simulation of goaf area, an improved vacuum method has been imported in a rotated staggered grid scheme and the calculation is implemented by combining parallel computing and task parallelism. It makes sure that the numerical simulation method can be utilized in a geological model with large differences in elastic parameters among layers and improve the performance of a parallel application by enabling full use of processor resources to expedite calculation speed. We set up anisotropic coal seam models, and then analyze the characteristics of synthetic seismograms and snapshots of different goaf areas with or without collapse by modeling. Results show that the proposed method can accurately simulate the goaf area and the calculation method can run with high speedup ration and parallel efficiency. The research will further advance the technology of anisotropic seismic exploration in coal fields, provide data for seismic inversion and give a theoretical support for coal mine disaster prediction. PubDate: 2019-10-23

Abstract: Abstract Wave field extrapolation is critical in reverse time migration (RTM). At present, wavefield extrapolation in RTM imaging for tunnels is mostly carried out via the finite difference method. However, complex tunnel models, such as those for karst and fault fracture zones, are constructed using regular grids with straight curves which can easily cause numerical dispersion and reduce imaging accuracy. In this study, the wavefield extrapolation for tunnel RTM was conducted using the finite element method, where an unstructured mesh is employed as the body-fitted partition in a complex model. The Poynting vector calculation equation suitable for the unstructured mesh finite element method was established to suppress low-frequency noise interference. The tunnel space was considered during the wavefield extrapolation to suppress mirror artefacts by using the flexibility of mesh generation. Finally, the influence of the survey layouts (one-sidewall and two-sidewall) on the tunnel imaging results was explored. The RTM results for a simple tunnel model with an inclined interface show that the method based on unstructured meshes can effectively suppress low-frequency noise and mirror artefacts, thus obtaining clearer imaging results. Also, the two-sidewall tunnel survey layout more accurately obtains the real position of the inclined interface ahead of the tunnel face. Complex tunnel numerical modelling and actual data migration results further illustrate the effectiveness of the finite element unstructured mesh method. PubDate: 2019-07-16

Abstract: Abstract The development of the Tongchuan city, Shaanxi, located in northwestern region of China is restricted by water resources. The application of direct current resistivity method and induced polarization (IP) sounding method are usually used to find urban groundwater. These methods, however, are not effective due to its complicated topography and geological conditions. The application practice shows that the audio magnetotelluric method (AMT) is of large depth of exploration, high work efficiency and high lateral resolution. To investigate the distribution of groundwater resources, we deployed three audio-frequency magnetotelluric profiles in the city area. The impedance tensor information of AMT data is obtained using SSMT2000. AMT data dimension analysis reveals that the two-dimensional structure features of the observation area are obvious. The main structure of the observation area is about 45° northeast by structural trend analysis. A shallow two-dimensional electrical profile of 1 km in Tongchuan City is obtained by a two-dimensional nonlinear conjugate gradient inversion.. Finally, combined with regional geological information, the geological structure characteristics reflected by the electrical profile were obtained with detailed the characteristics of water-rich structures in the area. The influence of the structure on the distribution of groundwater was analyzed and the water-rich areas were trapped. That contributes prospective development of Tongchuan city. PubDate: 2019-07-15