Journal of Geophysics and Engineering - Latest Papers

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Latest articles for Journal of Geophysics and Engineering
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The modeling and analysis of frequency-dependent characteristics in fractured porous media

Wed, 06/06/2018 - 7:00pm
At present, most studies have considered partial saturation and aligned fractures separately. However, these two phenomena exist simultaneously in most fractured reservoirs, such as carbonate reservoirs and tight sandstone reservoirs. In this paper, we develop a periodically layered model with alternating fractured layer saturated with gas and water-bearing porous layer to simultaneously model partial saturation and aligned fractures, which is an equivalent viscoelastic vertical transversely isotropic medium. We assume that the two types of attenuation are independent of each other. Firstly, we analyze the phase velocities and attenuation coefficients of quasi-P (P) and quasi-S (S) waves with frequency and incident angle, when the thickness fraction of fractured layer is 0.5. It shows that the attenuation coefficients of P-wave are much greater than the S-wave, when the incident angle is smaller than 30°. Then we analyze the frequency-dependent characteristics of the P-wave with...

Crossline-direction reconstruction of multi-component seismic data with shearlet sparsity constraint

Wed, 06/06/2018 - 7:00pm
In towed-steamer marine seismic acquisition, crossline data are fairly sparse which makes crossline wavefield reconstruction very difficult. Therefore, reconstructing the sparse wavefield becomes a fundamental and crucial step in seismic processing flow. Recently, compressed sensing has provided new insights into the data recovery problem, which combines a sparsifying transform, a sampling strategy, and a sparsity promoting algorithm. Shearlet transform is provided with a fairly good sparse representation of seismic data, and is very robust in the application of seismic wavefield reconstruction. Using multi-component measurement techniques, we propose a multi-component crossline wavefield reconstruction method based on sparse shearlet constraint inversion. By combining the pressure wavefield and its crossline gradient obtained through V y measurements, the proposed method can effectively reduce the multiplicity caused by a limited number of samples. Bo...

Study on coal damage evolution and surface stress field based on infrared radiation temperature

Wed, 06/06/2018 - 7:00pm
To study the evolution of coal damage characteristics based on the infrared radiation temperature (IRT), we analysed the IRT characteristics of coal under uniaxial compression and established a coal damage model according to the relationship between the deformation and maximum IRT (MIRT). In addition, we further deduced a method for imaging the evolution of the surface stress field based on the IRT. The results reveal the following. (1) The MIRT–strain curve corresponds well with the stress–strain curve under loading, and the MIRT can effectively reflect the coal damage. (2) A coal damage evolution model can be established based on the accumulation of the IRT, which can effectively reflect the evolution and development of cracks and the ultimate failure of coal under uniaxial compression. (3) The calculated stresses based on the accumulation of the MIRT can effectively reflect the measured stresses during the destruction of coal. The peak value of the calculated stress–strain cu...

Numerical simulation study of anisotropic velocities in fractured-vuggy carbonate reservoirs

Mon, 06/04/2018 - 7:00pm
The characterization of carbonate reservoirs based on seismic and acoustic log data is difficult due to their anisotropy. Complex pore structures are one of the major factors causing this anisotropy. To solve this issue, a model considering pore structure is proposed. In this model, the differential Kuster–Toksöz model and Hudson’s model are used to add various types of pores in the rock matrix, and Thomsen’s anisotropy theory is used to estimate the anisotropic velocities of carbonate rocks with fractures of arbitrary dips. Based on this model, the effects of pore structure (including porosity, pore aspect ratio, fracture porosity and dip) on elastic wave velocities are discussed. The simulation results show that the pore aspect ratio and porosity are the dominant factors influencing the elastic wave velocities of carbonates. Pores with small aspect ratios (aspect ratios of less than 0.15) have an extremely significant influence on elastic wave velocities. For anisotropic carbo...

Significance and behaviour of the homogeneous and inhomogeneous components of linearized viscoelastic reflection coefficients

Mon, 06/04/2018 - 7:00pm
In a recent paper, seismic amplitude-variation-with-offset (AVO) equations describing P-to-P and P-to-S reflections from boundaries separating low-loss viscoelastic media, taking into account variations in the attenuation angle, have been derived. We find that opportunities now present themselves to use these equations to expose a range of relationships between measured amplitudes and subsurface elastic and anelastic properties. This has significant applicability in the quantitative interpretation of seismic data in, for instance, reservoir characterization. To facilitate the analysis, we decompose the equations into three parts: elastic, homogeneous and inhomogeneous. We show that, for PP modes, the elastic part is sensitive to changes across a reflecting boundary in density and P- and S-wave velocities; the homogeneous part is sensitive to changes in density, S-wave velocity and the P- and S-wave quality factors; and the inhomogeneous part is sensitive to changes in density, a...

Estimation of dispersion attributes at seismic frequency—a case study from the Frigg-Delta reservoir, North sea

Mon, 06/04/2018 - 7:00pm
Estimation of the reservoir physical parameters in hydrocarbon zones is important for seismic exploration. Frequency analysis has proven to provide useful information on the velocity dispersion and attenuation of seismic wave-fields propagating through porous media. In this study we have carried out a velocity and reflectivity dispersion analysis using borehole and post-stack angle dependent seismic datasets from the Frigg-Delta reservoir in the North Sea. Rock physics analysis using borehole datasets indicate that in the seismic frequency range (1–100 Hz) dispersion maxima appear at ∼5 Hz frequency, assuming an oil saturation associated with the reservoir ranging between 40% and 60%, porosity as 30% and permeability as 1 Darcy. Moreover, the P-wave velocity ( V p ) dispersion is estimated ∼5 times less for the high oil saturation in the upper part of the reservoir compared to that for low oil saturation in the deeper part of the reservoir. Dispersion analysis on...

A method for production data analysis considering significant discontinuities in unconventional reservoirs

Mon, 06/04/2018 - 7:00pm
Significant discontinuities exist in the production data of many unconventional reservoirs, which always causes difficulties in production data analysis (PDA). This paper proposes a PDA method to address the problem caused by the significant discontinuities based on the virtual equivalent time, which is calculated by using the average formation pressure. With the virtual equivalent time, production data with significant discontinuities are converted into several interconnected segments, and new type curves are then generated and applied to PDA, which improves the fitting precision of the production data. With the improved fitting results, accurate productivity forecasting can be achieved. A field case study is carried out, comparing the new method with commercial software. The results show that the new method has better fitting results, and that the errors caused by significant discontinuities are effectively eliminated. The effectiveness of the proposed method is further verifi...

A new approach to predict local site effects related to blast-induced ground vibrations

Mon, 06/04/2018 - 7:00pm
Wave peak particle velocity (PPV) is an index often used internationally to determine the structural damage caused by mining blasts. Since detailed spatial variations due to local soil effects are ignored in empirical PPV equations, new artificial intelligence (AI) methods have become a proper tool for describing the local effect of wave propagation in complex areas. An artificial neural network (ANN) has been developed in this work to overcome traditional empirical method limitations. Data collected from several seismic stations strategically located within a pilot study area, where two controlled explosions were designed and detonated exclusively for this research, were used to train an ANN model and a non-linear regression (NLR) model. The goodness of fit of the two methods applied in this research, as well as the spatial variation of the site effects, were analyzed. Results showed that the ANN model has a high capacity to adapt to the local soil effects, overcoming the probl...

Study on energy band characteristic of microseismic signals in water inrush channel

Mon, 06/04/2018 - 7:00pm
In this paper the mechanism of water inrush disaster is analyzed, and the correlation between the evolution law of water inrush channel and microseismic (MS) monitoring in prevention structure is established. The main MS events include water and rock mass impact, filling and rock impact in the water inrush channel. The idea of positioning the water inrush channel is presented by analyzing the filling and rock impact MS signal. A large model test restores the environment of various water inrush channels. The MS technique is used to monitor the water inrush channels in the test. Wavelet packet theory is used to decompose the MS signals of water inrush channel. The result indicates that the background noise frequency is 0–1 kHz and the effective signal frequency range is above 1250 Hz. The paper statistically analyzes the MS energy in the different water inrush channels. The result indicates that the shape of water inrush channel has little influence on the energy. It is concluded ...