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Journal of Applied Geophysics
Elsevier
Journal of Applied Geophysics

Elsevier

0926-9851

Journal of Applied Geophysics/Journal Journal of Applied GeophysicsAHCIISTPSCIEI
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    Resistivity anisotropy analysis of Longmaxi shale by resistivity measurements, scanning electron microscope, and resistivity simulation

    Wu, FengDai, JinYao, CongShi, Xiangchao...
    15页
    查看更多>>摘要：The resistivity anisotropy of shale has a non-negligible effect on resistivity logs. Many studies have shown that the macroscale factors of shale anisotropy are depositional environment, compaction process, and diagenesis process, and the microscale factors mainly include lamination, orientation of clay minerals, and microfractures. However, the mechanism of laminations, pores, organic matters, pyrite and clay minerals driving resistivity anisotropy remains unclear. In this research, experiments and simulations were performed to investigate the characteristics and mechanism of the resistivity anisotropy of shale. Two sets of shale samples were collected at different inclination angles from the Lower Silurian Longmaxi Formation in the Pengshui area, southeastern Sichuan Basin, China. Core sample resistivities were measured in several water saturation states established using imbibition, pressurized saturation and centrifuge methods. Scanning electron microscopy, thin sections, X-ray diffraction, the mercury injection capillary method, and N-2 adsorption were also performed. Resistivity simulations were applied to three-dimensional models derived from the microimages. The results of the experiments and simulations show that Longmaxi shale has strong resistivity anisotropy. The resistivity anisotropy coefficient (lambda) of Longmaxi shale ranged from 1.3699 to 2.1623. Longmaxi shale has a strong lamination structure. In the submillimeter scale, strawberry-like pyrite (3.8%-10.2%, v/v) aggregates in elongated strips with an extension direction consistent with the horizontal direction. Due to the differential compaction, the clay minerals (21.1%- 26.4%, v/v) also tend to be parallel to the formation bedding. The most obvious directional distribution of pores occured in the organic pores. Most interparticle pores between detrital minerals did not exhibit anisotropic characteristics. Because of the horizontal distribution of lamination, pyrite, clay minerals and organic pores, a higher resistivity is measured in the vertical direction than in the horizontal direction.
      原文链接:
    • NSTL
    • Elsevier

    Hybrid boundary full-wave-equation depth migration based on dual-sensor acquisition system and its application

    Li, AnyuLiu, XueweiZhao, QingweiYou, Jiachun...
    11页
    查看更多>>摘要：The dual-sensor acquisition system arranges two-layer geophones on the surface and their corresponding underground positions, and receives the wavefield simultaneously for accurately solving the full-wave equation. Theoretically, using the two-layer wavefield data obtained by the acquisition system, the two-way wavefield extrapolation can be realized in the depth domain without approximate processing of the wave equation, and the migration algorithm based on the dual-sensor framework has better amplitude preservation. However, limited to the acquisition expenses and difficulties, the spacing of the two-layer sensors is hard to match the actual migration step in real data acquisition. Meanwhile, poor geophone coupling and nonstandard data processing procedures would also lead to unsatisfied imaging results. Thus, some schemes suitable to dual-sensor data, including hybrid boundary wavefield extrapolation strategy, data processing, quality monitor, are proposed to handle these issues, using the delay time difference as a main analyzing object. The numerical simulation and actual data verify the feasibility and effectiveness of the proposed method.
      原文链接:
    • NSTL
    • Elsevier

    Seismic acoustic full waveform inversion based on the steepest descent method and simple linear regression analysis

    Ren, Qianci
    18页
    查看更多>>摘要：Full waveform inversion (FWI) is a high-resolution imaging tool in seismic exploration. The steepest descent (SD) method is the simplest local optimization algorithm to update the P-wave velocity model in acoustic FWI, but it takes more iterations than other algorithms due to its inefficient search direction. In this study, we provide a SDSLR method, which can significantly shorten the convergence process of the SD method by using the simple linear regression (SLR) analysis. The SLR analysis has two important effects in this method: compute a SLR model to approximately estimate the recent variation trend of P-wave velocity model and directly predict the inversion result of the SD method of the next iteration. Based on the prediction of the SLR analysis, the SDSLR method can obtain the final inversion result of the traditional SD method with fewer iterations. Three numerical examples have tested the performance of the SDSLR method. Results show that the SDSLR method has great potential in constructing high-velocity anomalies. The computational efficiency of the SDSLR method is similar to that of the SD and L-BFGS methods, while the convergence rate and accuracy of the SDSLR method are clearly better than those of the SD and L-BFGS methods.
      原文链接:
    • NSTL
    • Elsevier

    Estimation of shallow subsurface structures on granitic hillslopes based on electrical resistivity distribution

    Yoshihara, NaoyukiHattanji, Tsuyoshi
    9页
    查看更多>>摘要：Electrical resistivity (ER) survey is an efficient method for investigating subsurface structure without destruction. However, this has not been used for estimating shallow subsurface zones of hillslopes that is related to the occurrence of shallow landslides. If the ER survey can alter conventional methods such as cone penetration test and boring to investigate soil thickness, an effective method for detecting landslide-prone area would be developed. In this study, ER survey was conducted on two granite hillslopes in Japan with low soil-moisture conditions to verify the usefulness of the ER survey to estimate the shallow subsurface structures. To compare the subsurface structure and the ER distribution, sounding by using a boring stick and a cone penetrometer were conducted along each ER survey line. Two soil pits were also referred near the survey lines. The subsurface structures were composed of topsoil, saprolite, and bedrock in our study sites. Results of ER survey with the unit electrode spacing of 0.5 m demonstrated that the ER increases with depth at the depths of the bottom of the topsoil layers, but the ER values were unconstrained. Below the bedrock surface, the ER generally decreased with depth, showing low ER less than 12800 omega center dot m excepting an exposed bedrock indicating more than 20000 omega center dot m. These spatial changes in ER are consistent with changes in grain size distribution and electrical conductivity of soil of each subsurface layer measured in this study and literature on ER of granite. ER distribution can visualize shallow subsurface structures and potential sliding surfaces for shallow landslides because the bottom of topsoil layer that was successfully estimated exhibits a discontinuity of shear strength, which generally corresponds to sliding surfaces for shallow landslides. Therefore, ER survey is applicable as an alternative to conventional methods for estimating shallow subsurface structures on granite hillslopes. Furthermore, ER survey can be a useful tool to estimate where shallow landslides will occur and how we should assess the risks of landslide hazards if a targeted subsurface zone has a distinct contrast in physical properties between each layer.
      原文链接:
    • NSTL
    • Elsevier

    Low-frequency seismic random noise attenuation based on EPLL-TV under double prior constraints

    Liang, ChaoLin, HongBoMa, HaiTao
    16页
    查看更多>>摘要：The expected patch log likelihood (EPLL) method utilizes the learned Gaussian mixture model (GMM) as a prior for white Gaussian noise removal, so that every patch from noisy data is likely under the prior and the global morphology is remained along with denoising. For suppressing the low-frequency seismic random noise having similar waveforms to the signals, we propose an Expected Patch Log Likelihood-Total Variation (EPLL-TV) algorithm, which is constrained by the EPLL prior and the total variation (TV) prior. In the denoising process, the TV prior introduces the structural features of the current data and restrains the random noise by enhancing the gradient sparsity of seismic data. Hence, the EPLL-TV algorithm is able to choose the Gaussian component which is closest to the features of signals from pre-learned general prior of EPLL, although the features in the patch are severely disturbed by the low-frequency noise. Then the seismic events with complex structures can be accurately restored by the chosen Gaussian component, which provides more reliable structures for denoising via the TV prior. We use the alternating direction method of multipliers (ADMM) to solve the proposed optimization model with double constraints and reconstruct the data in Fourier domain to reduce computational complexity. The results of the synthetic and field seismic data demonstrate that the proposed EPLL-TV method is superior to the other methods mentioned in our paper in terms of recovering the seismic events with complex structures and suppressing the low-frequency seismic random noise which has similar waveforms to the signals.
      原文链接:
    • NSTL
    • Elsevier