Journal of Geophysics and Engineering (J Geophys Eng )

Publisher: Nanjing shi you wu tan yan jiu suo; Institute of Physics (Great Britain)


Published by the Nanjing Institute of Geophysical Prospecting and the Institute of Physics, this major new publication promotes research and developments in geophysics and related areas of engineering. It has predominantly an applied science and engineering focus, but also publishes contributions in all earth-physics disciplines from global geophysics to applied and engineering geophysics.

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Publications in this journal

  • [Show abstract] [Hide abstract]
    ABSTRACT: Imaging conditions can not only affect the computational efficiency and storage cost of reverse time migration (RTM) but determine the quality of the final migrated images. This paper extends the idea of the well amplitude-preserved and highly-efficient excitation amplitude imaging condition from acoustic RTM to elastic RTM. For elastic RTM, the maximum amplitude of the separated P-wave and the corresponding image time of each grid point are saved during the forward modeling of the source wavefield and then PP and PS images are obtained by dividing the separated P- and S-waves of the backward-propagated receiver wavefield by the precomputed P-waves at each grid point that satisfies the image time. However, polarity reversals of the PS image will cause destructive interference when the stacked image is needed. In order to solve this problem, we propose the polarity-consistent excitation amplitude imaging condition by combining the excitation amplitude imaging condition with a shot-domain polarity reversal correction method. Then we provide the detailed realization process of this imaging condition in elastic RTM. By utilizing the relatively stable and well amplitude-preserved source-normalized cross-correlation imaging condition as a comparison, we testify to the feasibility and validity of the proposed imaging condition in the aspects of amplitude preservation property, imaging capability of complex structures, storage cost and computational efficiency. Considering the balance between the efficiency and image quality, the polarity-consistent excitation amplitude imaging condition can be a good choice for elastic RTM.
    Journal of Geophysics and Engineering 02/2015; 12(1).
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    ABSTRACT: The prime objective of this paper is to quantitatively estimate seismic attenuation caused by fractures with different physical parameters. In seismic wave simulation, the fractured media are treated as the anisotropic media and fractures are represented by frequency-dependent elastic constants. Based on numerical experiments with three different parameters, namely viscosity, porosity and the Lamé parameters, this paper has the following observations. First, seismic attenuation is not affected by the viscosity within fractures, although it increases with the increase of porosity and decreases with the increase of the Lamé parameters within fractures. Among the latter two parameters, seismic attenuation is more sensitive to the Lamé parameters than to the porosity. Second, for the attenuation anisotropy, low frequencies have more anisotropic effect than high frequencies. For example, a 50 Hz wavefield has the strongest anisotropy effect if compared to 100 and 150 Hz wavefields. The attenuation anisotropy for low frequency (say 50 Hz) is more sensitive to the viscosity than the porosity and the Lamé parameters have the weakest effect among these three parameters. These observations suggest that low-frequency seismic attenuation, and especially the attenuation anisotropy in low frequency, would have great potential for fluid discrimination within fractured media.
    Journal of Geophysics and Engineering 02/2015; 12(1).
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    ABSTRACT: The precision of displacement monitoring for deformable objects with global positioning system (GPS) is severely affected in highly occluded spaces, such as urban canyons and surface mines. This phenomenon is attributed to the presence of few visible GPS satellites with poor geometric structures, thus leading to ineffective positioning in severely occluded areas. An integrated GPS/pseudolite positioning technique is proposed in this paper as an effective solution for precision deformation monitoring in the abovementioned areas. This technique can effectively increase the number of visible satellites, optimize their geometric structure, and improve their positioning precision and reliability. This technique has been used in monitoring related deformable objects and has yielded favorable results. However, the majority of current studies have focused on static positioning, whereas dynamic positioning has largely been ignored. Furthermore, dynamic positioning requires further research to eliminate or reduce unmodeled systematic errors (particularly the multipath error). This paper explains the necessity and effectiveness of pseudolite introduction on the basis of the derivation of the basic deduction formula for integrated GPS/pseudolite positioning. Thereafter, the importance of pseudolite location selection by simulated test verification and analyses is discussed. Several methods for estimating and reducing the multipath error of pseudolite, which is affected by slow or small ground surface deformation and shows high spatial correlation, are also presented in this paper. A dynamic deformation monitoring model is proposed on the basis of the moving average method to improve the precision of dynamic positioning. The standard deviations of the baseline vectors in the X, Y, and Z directions are calculated at 14.0, 35.3, and 9.0 mm, respectively, thus indicating that the positioning precision is improved to different degrees in the proposed model compared with that of the separate GPS system (33.8, 54.4, and 22.3 mm for the X, Y, and Z directions, respectively), the integrated GPS/pseudolite dynamic positioning model prior to the elimination of the multipath errors of pseudolites (24.9, 56.4, and 13.3 mm for the X, Y, and Z directions, respectively), and the integrated GPS/pseudolite dynamic positioning model on the basis of the estimation of multipath error parameters (29.7, 47.9, and 17.8 mm for the X, Y, and Z directions, respectively).
    Journal of Geophysics and Engineering 02/2015; 12(1).
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    ABSTRACT: Seismic traveltime tomography is an effective method to reconstruct underground anisotropic parameters. Currently, most anisotropic tomographic methods were developed under the assumption of weak anisotropy. The tomographic method proposed here can be implemented for imaging subsurface targets in strongly anisotropic media with a known tilted symmetry axis, since the adopted ray tracing method is suitable for anisotropic media with arbitrary degree. There are three kinds of reflection waves (qP, qSV and qSH waves) that were separately used to invert the blocky abnormal body model. The reflection traveltime tomographiy is developed here because a surface observation system is the most economical and practical way compared with crosswell and VSP. The numerical examples show that the traveltimes of qP reflection wave have inverted parameters &${{c}_{11}},{{c}_{13}},{{c}_{33}}\ \text{and}\ {{c}_{44}}$ ; successfully. Traveltimes of qSV reflection wave have inverted parameters &${{c}_{11}},{{c}_{33}}\ \text{and}\ {{c}_{44}}$ ; successfully, with the exception of the &${{c}_{13}},$ ; since it is less sensitive than other parameters. Traveltimes of qSH reflection wave also have inverted parameters &${{c}_{44}}\ \text{and}\ {{c}_{66}}$ ; successfully. In addition, we find that the velocity sensitivity functions (derivatives of phase velocity with respect to elastic moduli parameters) and raypath illuminating angles have a great influence on the qualities of tomograms according to the inversion of theoretical models. Finally, the numerical examples confirm that the reflection traveltime tomography can be applied to invert strongly anisotropic models.
    Journal of Geophysics and Engineering 12/2014; 11(6).
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    ABSTRACT: Numerical modeling of poroelastic waves by the finite-difference (FD) method is more expensive than that of acoustic or elastic waves. To improve the accuracy and computational efficiency of seismic modeling, variable-grid FD methods have been developed. In this paper, we derived optimal staggered-grid finite difference schemes with variable grid-spacing and time-step for seismic modeling in porous media. FD operators with small grid-spacing and time-step are adopted for low-velocity or small-scale geological bodies, while FD operators with big grid-spacing and time-step are adopted for high-velocity or large-scale regions. The dispersion relations of FD schemes were derived based on the plane wave theory, then the FD coefficients were obtained using the Taylor expansion. Dispersion analysis and modeling results demonstrated that the proposed method has higher accuracy with lower computational cost for poroelastic wave simulation in heterogeneous reservoirs.
    Journal of Geophysics and Engineering 12/2014; 11(6).
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    ABSTRACT: There are many outcropping masses on the Kıratlı travertine fields where a new or open quarry is planned to be exploited. In this study, ground penetrating radar (GPR) and vertical electrical sounding (VES) have been applied on these fields in order to identify massive or weathered blocks and fracture–cracked systems in a short time and at low cost. GPR data were acquired on two areas, named Ocakustu (Ocakustu 1, Ocakustu 2) and Alarduc (Alarduc 1, Alarduc 2), using a 100 MHz unshielded and 250 MHz shielded antennas on 35 profiles. Generally, radargrams obtained from GPR profiles revealed massive or weathered blocks and fracture–cracked systems of these fields. The quarry operation was stopped in Ocakustu 1 due to the intensely fracture–cracked and weathered structures of the travertine field imaged by GPR. Detailed information was not obtained under the topping layer of 4 m from GPR sections on Ocakustu 2 area. Therefore, VES was also performed along four profiles which made it possible to define the areal extension and thickness of the lithotype in this site. Electrical resistivity tomography (ERT) sections have been generated by the inversion of the VES data. The subsurface geometries with resistivity values in the area were determined from these sections. Massive blocks with high resistivity could be seen at depths of 2–10 m and 10–20 m below the surface on these results and it was suggested that the quarry should be extended these parts. In addition, according to the GPR data, fracture–cracked blocks were present in Alarduc where a travertine quarry is thought to be operated. The places that will be started and orientated to quarry can be determined with respect to radargrams on Alarduc 1. Ultimately, the exploitation of a quarry was not recommended due to the extremely fracture–cracked systems found in Alarduc 2.
    Journal of Geophysics and Engineering 11/2014; 11(6):065009.
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    ABSTRACT: Subsurface fractures within many carbonates and unconventional resources play an important role in the storage and movement of fluid. The more reliably the detection of fractures could be performed, the more finely the reservoir description could be made. In this paper, we aim to propose a method which uses two important tools, a fractured anisotropic rock physics effective model and AVAZ (amplitude versus incident and azimuthal angle) inversion, to predict fractures from azimuthal seismic data. We assume that the rock, which contains one or more sets of vertical or sub-vertical fractures, shows transverse isotropy with a horizontal axis of symmetry (HTI). Firstly, we develop one improved fractured anisotropic rock physics effective model. Using this model, we estimate P-wave velocity, S-wave velocity and fracture weaknesses from well-logging data. Then the method is proposed to predict fractures from azimuthal seismic data based on AVAZ inversion, and well A is used to verify the reliability of the improved rock physics effective model. Results show that the estimated results are consistent with the real log value, and the variation of fracture weaknesses may detect the locations of fractures. The damped least squares method, which uses the estimated results as initial constraints during the inversion, is more stable. Tests on synthetic data show that fracture weaknesses parameters are still estimated reasonably with moderate noise. A test on real data shows that the estimated results are in good agreement with the drilling.
    Journal of Geophysics and Engineering 11/2014; 11(6):065007.
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    ABSTRACT: The deep geothermal reservoirs in the Larderello-Travale field (southern Tuscany) are found in intensively fractured portions of intrusive/metamorphic rocks. Therefore, the geothermal exploration has been in search of possible fracture signatures that could be retrieved from the analysis of geophysical data. In the present work we assess the feasibility of finding seismic markers in the pre-stack domain which may pinpoint fractured levels. Thanks to the availability of data from boreholes that ENEL GreenPower drilled in the deep intrusive basement of this geothermal field, we derived the expected amplitude versus angle (AVA) responses of the vapour reservoirs found in some intensely, but very localized, fractured volumes within the massive rocks. The information we have available limit us to build 1D elastic and isotropic models only and thus anisotropy effects related to the presence of fractures cannot be properly modelled. We analysed the velocities and the density logs pertaining to three wells which reached five deep fractured zones in the basement. The AVA response of the fractured intervals is modelled downscaling the log data to seismic scale and comparing the analytical AVA response (computed with the Aki and Richards approximation) and the AVA extracted from a synthetic common mid point (calculated making use of a reflectivity algorithm). The results show that the amplitude of the reflections from the fractured level is characterized by negative values at vertical incidence and by decreasing absolute amplitudes with the increase of the source to receiver offset. This contrasts with many observations from hydrocarbon exploration in clastic reservoirs where gas-sand reflections often exhibit negative amplitudes at short offsets but increasing absolute amplitudes for increasing source to receiver offsets. Thereby, some common AVA attributes considered in silicoclastic lithologies would lead to erroneous fracture localization. For this reason we propose a modified AVA indicator which may highlight fracture locations in this peculiar rock type.
    Journal of Geophysics and Engineering 11/2014; 11.
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    ABSTRACT: The rock physics model is an important tool for the characterization of shale reservoirs. We propose an improved anisotropic rock physics model of shale by introducing clay lamination (CL) index as a modeling parameter in effective medium theories. The parameter CL describes the degree of preferred orientation in distributions of clay particles, which depends on deposition and diagenesis history and determines intrinsic anisotropy of shales. Those complicated parameters of sophisticated methods that are difficult to quantify are substituted by CL. The applications of the proposed rock physics method include the inversion for anisotropy parameters using log data and the construction of a rock physics template for the evaluation of the Barnett Shale reservoir. Results show reasonable agreement between the P-wave anisotropy parameter ε inverted by the proposed method and those measured from core samples. The constructed rock physics templates are calibrated on well log data, and can be used for the evaluation of porosity, lithology, and brittleness index defined in terms of mineralogy and geomechanical properties of the Barnett Shale. The templates predict that the increase in clay content leads to the increase in Poisson's ratio and the decrease in Young's modulus on each line of constant porosity, which confirms the consistent and reveals quantitative relations of the two ways of defining the brittleness index. Different scenarios of mineralogy substitutions present the varied layout of constant lines on the templates.
    Journal of Geophysics and Engineering 11/2014; 11(6):065006.
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    ABSTRACT: In facies analysis, seismic data are clustered in different groups. Each group represents subsurface points with similar physical properties. Different groups can be related to differences in lithology, physical properties of rocks and fluid changes in the rocks. The supervised and unsupervised data clustering are known as two types of clustering architecture. In supervised clustering, the number of clusters is predefined, while in unsupervised clustering, a collection of patterns partitions into groups without predefined clusters.
    Journal of Geophysics and Engineering 11/2014; 11(6):065005.
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    ABSTRACT: The spatial aliasing of seismic data is usually serious because of the sub-sampling rate of the acquisition system. It induces amplitude artifacts or blurs the migration result when the spatial aliasing is not removed before migration. The compressed sensing (CS) method has been proven to be an effective tool to restore a sub-sampled signal which is compressible in another domain. Since the wave-fronts of seismic data are sparse and linear in a local spatiotemporal window, they can be significantly compressed by linear Radon transform or Fourier transform. Therefore, seismic data interpolation can be considered as a CS problem. The approximate solution of a CS problem using L0-norm can be achieved by matching pursuit (MP) algorithm. MP becomes intractable due to the high computing cost induced by the increasing dimension of the problem. In order to tackle this issue, a variant of MP—weighted matching pursuit (WMP)—is presented in this paper. Since there is little spatial aliasing in the data of low frequency and the events are supposed to be linear, the linear Radon spectrogram of the interpolated data of low frequency can be used to predict the energy distribution of data of high frequency in a frequency-wavenumber (FK) domain. The predicted energy distribution is then utilized to form the weighted factor of WMP. With this factor, WMP possesses the ability to distinguish the linear events from the spatial aliasing in the FK domain. WMP is also proven to be an efficient algorithm. Since projection onto convex sets (POCS) is another common sparsity-based method, we use Fourier POCS and WMP to realize high-dimension interpolation in numerical examples. The numerical examples show that the interpolation result of WMP significantly improves the quality of seismic data, and the quality of the migration result is also improved by the interpolation.
    Journal of Geophysics and Engineering 10/2014; 11(6):065003.
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    ABSTRACT: To determine the void spaces of rock joints under different normal stresses and shear displacements, we mainly introduce a numerical method which was developed based on equivalent void space derived from composite topography. The new method requires the 3D surface data of rock joints, and the normal closure data of the compression test under different shear displacements, while in conventional methods, some disparate materials are inserted between the joint surfaces or special equipments are needed for the measurement of the void space of rock joints without shearing occurs. To apply the technique, a modified 3D box counting method that considers the self-affine fractal property of void spaces was employed to calculate the 3D fractal dimension of the void space. Specially designed experiment was conducted on a cylindrical specimen of artificial joints to explore aperture distribution, and the correlations between void space characteristics, 3D fractal dimension and mean aperture, and normal stress under different shear displacements. The present study focuses on the introduction of the new method for estimating void spaces of rock joints, while the void spaces model obtained contains the combined surfaces roughness and aperture information of rock joints under different normal loads and shear displacements is promising in investigating the mechanical and hydraulic properties during the loading process.
    Journal of Geophysics and Engineering 10/2014; 11(6):065004.
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    ABSTRACT: Facies models try to explain facies architectures which have a primary control on the subsurface heterogeneities and the fluid flow characteristics of a given reservoir. In the process of facies modeling, geostatistical methods are implemented to integrate different sources of data into a consistent model. The facies models should describe facies interactions; the shape and geometry of the geobodies as they occur in reality. Two distinct categories of geostatistical techniques are two-point and multiple-point (geo) statistics (MPS). In this study, both of the aforementioned categories were applied to generate facies models. A sequential indicator simulation (SIS) and a truncated Gaussian simulation (TGS) represented two-point geostatistical methods, and a single normal equation?simulation (SNESIM) selected as an MPS simulation representative. The dataset from an extremely channelized carbonate reservoir located in southwest Iran was applied to these algorithms to analyze their performance in reproducing complex curvilinear geobodies. The SNESIM algorithm needs consistent training images (TI) in which all possible facies architectures that are present in the area are included. The TI model was founded on the data acquired from modern occurrences. These analogies delivered vital information about the possible channel geometries and facies classes that are typically present in those similar environments. The MPS results were conditioned to both soft and hard data. Soft facies probabilities were acquired from a neural network workflow. In this workflow, seismic-derived attributes were implemented as the input data. Furthermore, MPS realizations were conditioned to hard data to guarantee the exact positioning and continuity of the channel bodies. A geobody extraction workflow was implemented to extract the most certain parts of the channel bodies from the seismic data. These extracted parts of the channel bodies were applied to the simulation workflow as hard data. This study showed how different sources of data can be employed in a multiple-point simulation algorithm to get reliable facies models. In addition, concerning the reproduction of curvilinear channel bodies, the modeling results revealed the strength of MPS algorithms (SNESIM in this study) in comparison with two-point geostatistical methods (including the SIS and TGS).
    Journal of Geophysics and Engineering 10/2014; 11(6):065002.
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    ABSTRACT: We investigated the electrical properties of laminated rock consist of macro-porous layers and micro-porous layers based on digital rock technology. Due to the bedding effect and anisotropy, traditional Archie equations cannot well describe the electrical behavior of laminated rock. The RI-Sw curve of laminated rock shows a nonlinear relationship. The RI-Sw curve can be divided into two linear segments with different saturation exponent. Laminated sand-shale sequences and laminated sands of different porosity or grain size will yield macroscopic electrical anisotropy. Numerical simulation and theoretical analysis lead to the conclusion that electrical anisotropy coefficient of laminated rock is a strong function of water saturation. The function curve can be divided into three segments by the turning point. Therefore, the electrical behavior of laminated rock should be considered in oil exploration and development.
    Journal of Geophysics and Engineering 09/2014; 11(5):055008.
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    ABSTRACT: We have developed a mixed-grid finite element method (MGFEM) to simulate seismic wave propagation in 2D structurally complex media. This method divides the physical domain into two subdomains. One subdomain covering the major part of the physical domain is divided by regular quadrilateral elements, while the other subdomain uses triangular elements to correctly fit a rugged free surface topography. The local stiffness matrix of any quadrilateral element is identical and matrix-vector production is calculated using an element-by-element technique, which avoids assembling a huge global stiffness matrix. As only a few triangular elements exist in the subdomain containing the rugged free surface topography, the memory requirements for storing the assembled subdomain global stiffness matrix are significantly reduced. To eliminate artificial boundary reflections, the MGFEM is also implemented to solve the system equations of PML absorbing boundary conditions (PML ABC). The accuracy and efficiency of the MGFEM is tested in numerical experiments by comparing it with conventional methods, and numerical comparisons also indicate its tremendous ability to describe rugged surfaces.
    Journal of Geophysics and Engineering 09/2014; 11(5):055009.