Formulae for the moments of the magnetic field response can be derived for simple models which have conductivities that vary suddenly as a function of depth (thin and thick sheets) or not at all (half space). In a companion paper we have derived expressions for the moments of a conductivity-depth profile that varies smoothly, taking the form of a Gaussian function. In this paper we apply the Gaussian

Roadway transient electromagnetic method has been widely used in detecting mine water disaster ahead of roadway excavation face. Due to the strong mutual inductance between transmitting-receiving coils, the early-stage data obtained by this method are seriously distorted and the effective resolving time of transient electromagnetic (TEM) field is greatly lengthened, which leads to the shallow blind

The airborne Time-domain electromagnetic data acquired over the Ilesha Schist Belt in southwestern Nigeria were filtered, enhanced and analysed to generate ground conductivity responses at different time gates and employed to characterise the subsurface in terms of rock distribution, structural framework as well as evaluate the gold and base metal mineralisation potential of the region. The near-surface

In this paper, we present a velocity analysis technique using ground-penetrating radar (GPR) data to estimate near-surface soil-water content affected by topography and solar radiation on a mountain peak, mountain mid-slope, and alluvial plain sites in a semi-arid climate area in central Asia. By making precise measurements of reflected EM wave velocity, the water content in the near-surface soil was

In the early stage of acoustic full-waveform inversion (AFWI), it is important to exploit the long-wavelength features of the gradient and suppress its short-wavelength features to update the background velocity. However, due to strong near-offset PP reflections and multiples within the pressure data, conventional AFWI sometimes primarily reconstructs the short-wavelength features of a given model

Landfill leakage is a concerning source of soil and groundwater pollution. Geophysical methods have been widely used in the exploration of landfill structure and leakage. However, a disadvantage of this method is its inability to delineate the landfill and the leakage area finely. By employing the membership function of fuzzy mathematics, this paper presents a quantitative index of groundwater pollution

To explore crustal structures using seismic records of earthquakes, we proposed a new seismic reflection imaging method based on reverse time migration (RTM) without source information. In the proposed RTM method using multiple reflections between surface and subsurface boundaries, we correlate forward- and backward-extrapolated wavefields of the same observation records from all receivers at once

As the key point of full-waveform inversion (FWI), numerical solution of wave equation is required to simulate the forward propagated and adjoint wavefield. When traditional regular grids are used for forward modelling, scattering artifacts may occur due to the stepped approximation of layer interfaces and rugged topography. Unstructured mesh or irregular grids method can achieve certain geometric

ABSTRACT The severe rugged seabed interfaces bring great difficulties to seismic imaging in the marine environment. To accurately image submarine structures under the rugged seabed interface, an acoustic-elastic coupled curvilinear-coordinated least-squares reverse time migration (AE-CLSRTM) is proposed. This method is based on the coupled equation method, which uses the acoustic wave equations in

The reverse time migration (RTM) aims to image subsurface reflectors by incorporating with the two-way wave equation. RTM has advantages that it does not have dip limitations and can generate subsurface images clearly even in the case of complex geological structures in the near surface. We have proposed a reproduction wavefield reverse time migration (RWRTM) algorithm implemented with backward reproduced

Full waveform inversion (FWI) has the potential to recover high-resolution physical parameters of the Earth from seismic data. Considering the attenuation effects of the subsurface, we develop a new visco-acoustic FWI method in the time domain with a known Q model. The seismic wavefield is modelled by solving a decoupled fractional Laplacian visco-acoustic wave equation, which can better describe amplitude

(2021). Reviewers consulted for Exploration Geophysics during 2020. Exploration Geophysics: Vol. 52, No. 2, pp. 123-124.

Full-waveform inversion (FWI), which is among the most powerful seismic data processing techniques for imaging subsurface geological structures, has a huge computational cost in proportion to the number of sources. To increase the speed of FWI, we explored the use of common-receiver gathers (CRGs) as an alternative to common-shot gathers (CSGs) as observed data. This approach has the potential to reduce

ABSTRACT Airborne electromagnetic (AEM) survey data are typically inverted with one-dimensional (1D) AEM algorithms because 1D approaches are efficient methods for calculating subsurface conductivity and thickness variations. However, 1D AEM inversion algorithms are known to perform poorly in regions where the geology is 2D or 3D. In 2013, a regional-scale (5 km spaced) TEMPEST AEM survey was acquired

Eikonal solvers in the Cartesian coordinates often suffer from source singularity due to the plane-wave assumption for the wavefront near the source point. Traveltime errors induced by the source singularity near the source point will spread to the whole domain and reduce the accuracy of subsequent traveltimes. The source singularity can be avoided if the eikonal equation is formulated and solved in

Full waveform inversion (FWI) plays a major role in the oil and gas industry as a state-of-the-art technique that produces quantitative subsurface structures with high-fidelity images. Various FWI studies have been conducted, and these suggest that FWI is a promising inversion method. Recently, many attempts have been made toward three-dimensional (3D) and four-dimensional FWI applications (which were

Gas hydrate exploration was conducted using logging-while-drilling (LWD) and wireline logging (WLL) at two sites (UBGH2-6 and UBGH2-10) in the Ulleung Basin, East Sea (Sea of Japan). Coring for gas hydrate sampling was also conducted. Seismic profiles revealed that the upper layers at the logged sites (∼180 m at UBGH2-6 and ∼150 m at UBGH2-10) are dominated by turbidite/hemipelagic sediments, whereas

Low-frequency signal and noise are the main components of seismic data in Northwest China desert area. To remove noise and preserve data details, we introduce a method of nonlinear autoregressive with external input neural network (NARX) which is based on recent developments in nonlinear time series prediction and improve its performance according to signal detection theory. The input of NARX is a

The present work demonstrates a case study in the Mahanadi offshore basin in the eastern margin of India, where gas hydrates have been delineated by seismic experiment, mainly by identifying a bottom simulating reflector or BSR on seismic section, based on its characteristic features. The BSR represents an acoustic impedance contrast between the high-velocity gas hydrates bearing sediments above and

The presence of noise degrades the quality of seismic data and makes the subsequent processing tasks and interpretation more challenging. Therefore, seismic noise attenuation is a key step in the processing of seismic data. We propose a novel convolutional neural network (CNN) framework with learning noise prior. Unlike conventional CNN-based seismic denoising methods, this new network is composed

Zone A in Nanpu Sag of Bohai Bay has the characteristics of multiple provenances, multiple sedimentary systems, fast phase transition, many faults, a short fault distance, thin reservoirs and rapid lateral changes. At present, due to the low resolution of seismic data and thin sand layer of the target formation, it is difficult to depict the channel sand body, and it is also difficult to meet the requirements

When the fracture normal forms an angle relative to the borehole axis, the induction logging response to the fractured formation consists of two contributions: one is the volume contribution caused by the eddy current, and the other is the charge contribution caused by the cumulative charges on the upper and lower boundaries of the fracture; both contributions are nonlinear. Researching the distribution

The selection of the most appropriate method(s) for a specific engineering geophysical site characterisation can be challenging due to the complexity and potential ambiguity of the factors influencing the utility and cost-effectiveness of the methods. This paper, using matter-element analysis techniques with analytic hierarchy process (AHP), proposes a demonstration matter-element model for selecting

Migration velocity analysis (MVA) has been widely used for large scale model construction. To make full use of the wavefield information and obtain stable inversion results, wave-equation-based methods, such as differential semblance optimisation (DSO) or travel-time tomography, become popular in recent years. Compared with traditional ray-based methods, wave-equation-based methods are intrinsically

The recording of raw or streamed airborne electromagnetic (AEM) data, as done by CGG during MEGATEM surveys, allows for the extraction of passive EM signals also present, but not normally processed. These include (1) powerline responses, (2) responses in the very low frequency (VLF) range due to radio transmissions and (3) natural-source audio-frequency magnetic (AFMAG) and VLF responses in the frequency

This paper reports the results of a case study of the application of the microtremor exploration method in western Turkey. We have conducted microtremor surveys at strong motion stations in Aydin and Denizli provinces to derive shallow S-wave velocity profiles. Array records of vertical microtremor motion were acquired at 12 and 15 stations in Aydin and Denizli provinces, respectively. A spatial autocorrelation

The selection of the most appropriate method(s) for a specific engineering geophysical site characterisation can be challenging due to the complexity and potential ambiguity of the factors influencing the utility and cost-effectiveness of the methods. This paper, using matter-element analysis techniques with analytic hierarchy process (AHP), proposes a demonstration matter-element model for selecting

Migration velocity analysis (MVA) has been widely used for large scale model construction. To make full use of the wavefield information and obtain stable inversion results, wave-equation-based methods, such as differential semblance optimisation (DSO) or travel-time tomography, become popular in recent years. Compared with traditional ray-based methods, wave-equation-based methods are intrinsically

The recording of raw or streamed airborne electromagnetic (AEM) data, as done by CGG during MEGATEM surveys, allows for the extraction of passive EM signals also present, but not normally processed. These include (1) powerline responses, (2) responses in the very low frequency (VLF) range due to radio transmissions and (3) natural-source audio-frequency magnetic (AFMAG) and VLF responses in the frequency

This paper reports the results of a case study of the application of the microtremor exploration method in western Turkey. We have conducted microtremor surveys at strong motion stations in Aydin and Denizli provinces to derive shallow S-wave velocity profiles. Array records of vertical microtremor motion were acquired at 12 and 15 stations in Aydin and Denizli provinces, respectively. A spatial autocorrelation

The industry has widely accepted that AEM data are more frequently affected by induced polarisation (IP) effects than previously acknowledged. However, we still lack a clear understanding of how much, where, and when IP is present. Full modelling of airborne IP (AIP) is time and computationally intensive. As an alternative, we derive a novel tool, the “AIP scanner”, based on a combination of extensive

Time migration is an important tool to provide a subsurface image because it is faster and less sensitive to velocity errors than depth migration. However, a reliable and focused time migration image is achievable only with well-determined time-migration velocities. As an alternative of prestack time migration, equivalent offset migration (EOM) provides intermediate common scatterpoint (CSP) gathers

L0-norm constrained sparse seismic inversion is an effective way to invert reflectivity series of underground rocks. A blocky impedance model with sharp formation boundaries can be estimated from sparse reflectivity series. At present, the most two common used methods to solve L0-norm constrained sparse seismic inversion problem are iterative hard thresholding (IHT) and matching pursuit (MP). IHT has

ABSTRACT In this paper, we introduce a fast iterative adaptive approach for the reconstruction of 3D seismic data with randomly missing traces. Our method starts by transforming 3D seismic volume to 2D harmonic signal for each frequency slice, and then the power spectrum of the frequency slice is iteratively estimated by a weighted least square fitting criterion. The missing data can be recovered with

The dynamic and static Young’s moduli of a number of reservoir sandstones were measured using ultrasonic P- and S-waves velocities in a standard uniaxial set-up. We developed and modified an experimental method to simultaneously measure the stress–strain and stress–velocity (P- and S-waves) while the samples are subjected to stress. The static and dynamic Young’s modulus and Poisson’s ratio were calculated

Ground-penetrating radar (GPR) mapping provides a three-dimensional analysis of archaeological features within the context of landscape studies. The method’s ability to measure the intensity of radar reflections from deep in the ground can produce images and maps of buried features not visible on the surface. A study was conducted in some areas near the Domus Romana in Rabat (Malta) in order to investigate

Local shear wave (S-wave) velocity structure and sedimentary cover thickness are essential parameters that control local amplification of ground motion and associated seismic hazard during earthquakes. Recently, analysis of environmental background noise from individual stations has been used to estimate horizontal-to-vertical spectral ratio (H/V) curves. In the present study, we inverted H/V curves

ABSTRACT To improve the computational efficiency of reverse-time migration (RTM) for vertically transverse isotropic (VTI) media, various acoustic approximations of the elastic wave equations have been presented. Among these, the pseudo-acoustic wave equation, which combines differential and scalar operators, has the advantage that it does not produce shear wave artefacts. In this study, we investigate

Geomagnetic measurements detect the superposition of both regional and residual anomalies. Regional anomalies are caused by deep geological structures, while the residual ones are due to shallow sources. The presence of regional anomalies complicates the interpretation of magnetic data; to this end, a variety of techniques have been proposed for regional-residual anomaly separation. Most of them are

Frequency-dependent anisotropy can be used for detection and evaluation of fractured reservoirs. In this study, three numerical models of fractured reservoirs are designed to study the frequency dependence of amplitude variation with azimuth (AVAZ). Here, two factors, which can make the AVAZ responses frequency dependent, are taken into consideration, the fluid flow and the tuning effect. Model I is

Pre-stack Q migration can eliminate the absorption effect and accurately image underground structures, which is conducive to subsequent reservoir interpretation and hydrocarbon prediction. However, the instability of Q migration amplifies high-frequency noise, which seriously reduces the imaging quality. To solve the instability problem, this paper studies the stability conditions for Q migration in

A novel method for Q (quality factor Q) estimation is proposed based on crosscorrelation function and S-transform (CRST). We use the S-transform to analyse the time–frequency spectra of the crosscorrelation coefficients and extract the amplitude spectra corresponding to the maximum energy time in time–frequency spectra. The Q can be estimated using the spectra ratio based on the linear relationship

Staggered-grid finite-difference (SFD) method has higher accuracy and stability than conventional method, so it is widely used in reverse time migration and full waveform inversion. However, due to the high dominant frequency and large grid interval, numerical dispersion is an inevitable problem. To suppress numerical dispersion, we first propose a weighted convolution combination window function for

Cracks and pores coexist in carbonate reservoirs, and this complex pore structure has a significant impact on acoustic and resistivity logging. Making full use of acoustic and electrical well logging data can help to identify carbonate gas reservoirs. First, this paper studies the controlling effects of different lithologies on the acoustic velocity according to the elastic theory of porous and fractured

An unmanned airship was used to overcome the limitations of conventional aeromagnetic exploration systems. The airship was fabricated from non-magnetic fibre-reinforced plastic and urethane cloth, and filled with helium. The maximum payload is 10 kg and the flight time (with all equipment installed) is approximately 1 h. The airship is simple to move and store prior to gas injection, and easy to handle

Rock physics aims to link geological and reservoir properties to the elastic and seismic parameters. By analysing well logs and seismic data in a rock physics framework, reservoir conditions and key reservoir properties such as lithology and fluid saturations could be understood and/or predicted more precisely. In this study, we have conducted a detailed rock physics study on a heterogeneous sandstone

Desert seismic data pose a particular problem due to its low signal-to-noise ratio and severe spectral overlapping. Most of the existing denoising methods have negative suppression effect on the desert mixed seismic noise, which mainly includes random noise and surface waves. The convolutional neural network (CNN) is a classical supervised deep-learning method that has proven to be an effective tool

The finite-difference (FD) scheme is extensively applied in seismic modelling, imaging and inversion due to its advantages of large-scale parallel computing and programming. However, numerical dispersion caused by using a difference operator in substitution for the differential operator is non-negligible, which reduces the accuracy of the modelling and can lead to some misinterpretations. In addition

Euler deconvolution is a widely used semiautomatic method for potential field data, but it produces sprays of solutions which complicate interpretation. It is demonstrated here that the accuracy of the solution locations can be improved if the method is applied iteratively. Euler deconvolution uses a window of datapoints to solve for the horizontal and vertical distances from the centre of the window

Steeply dipping structures bring huge challenges in high-resolution imaging. The imaging of the steeply dipping structures can be improved by incorporating the prismatic waves, which has some steeply dipping structure information where primaries cannot contain. In this paper, an elastic reverse time migration of prismatic waves (ERTM-P) is proposed to produce high-resolution multi-component images

The West Delta Deep Marine (WDDM) concession is one of the abundant natural gas resources in the world characterised by the presence of several active gas chimneys conduit feeding pockmarks. The detection of shallow gas accumulations has been gaining importance in hazard assessments before and during offshore drilling operations, whereas there is no way to estimate the exact pressure of the gas content

We propose a new interpretation procedure based on Gassmann’s theory, to estimate rock properties from seismic P-wave velocity (Vp ) and S-wave velocity (Vs ) data, mainly for near-surface applications. Rock properties estimated in the procedure are porosity, water saturation, and clay content of rock. Water saturation is first estimated by an analysis of a cross-plot of Vp/Vs and S-wave velocity,

The recovery of 3D volume of density from gravity field data is a key feature of geophysical and geological interpretations. Gravity field data inversion involves solving an underdetermined problem; therefore, large-scale data inversion is costly in time and memory consumption. Calculation efficiency is a primary concern for gravity field data inversion; therefore, multiple methods are considered and

Seismic inversion methods are routinely used to estimate attributes such as P-impedance, S-impedance, density, P-wave and S-wave velocity, and elastic impedances from seismic and well log data. These attributes help to understand subsurface lithology and fluid content. There are several types of seismic inversion methods available in which model-based inversion has got more attention. In the present

2D electrical resistivity tomography (ERT) coupled with electrical resistivity profiling, induced polarisation, and self-potential (ER-IP-SP) measurements and pumping-test data has been used to acquire subsurface electrical properties for the assessment of groundwater reserves in weathered terrains of Huidong County, China. In this investigation, ERT was performed using a pole-dipole array with 305

The use of non-invasive investigation methods is becoming frequent as a support for the monitoring of water reservoirs and for the management of dam safety. In this context, geophysical techniques are much less invasive than geotechnical tests and allow to obtain two-dimensional or three-dimensional representations of the mechanical parameters of an engineering structure. A case of application of constrained

In conventional vibroseis data processing, the recorded sweep is correlated with the recorded trace, assuming that the estimated groundforce is equal to the sweep, but it is demonstrated that due to the non-linearity associated with the vibrator system, the true groundforce and the recorded sweep are not the same. Further, while processing, it is assumed that the zero phase Klauder wavelet is convolved

Using orthogonal-octahedron finite-difference (FD) stencils, even-order accuracy for temporal and spatial derivatives can be reached for 3D acoustic wave equation modelling. However, the required length of FD operator is still long for high accuracy modelling. To tackle this issue, we have developed an optimization method using a combination of Taylor-series expansion plus Remez exchange methods. The

The advantage of the finite element method (FEM) lies in its flexibility in addressing rugged interfaces in complex geological models. However, the efficiency of the FEM is relatively low for large-scale seismic wave modelling. Here, we introduce an order-corrected symplectic FEM (OCSFEM) with structure-preserving properties and parsimonious memory requirements for the elastic wave equation. In this

Deconvolution is essential for high-resolution seismic data processing. Conventional deconvolution methods are either based on a stationary convolution model or under the assumption that Q factor and the source wavelet are known. However, in reality, seismic wavelet is usually unknown and time-varying during propagation due to attenuation. Thus, we propose a blind nonstationary deconvolution (BND)