In this article, the Editor of Geophysics provides an overview of all technical articles in this issue of the journal.

The magnetotelluric (MT) method is introduced as a geophysical tool to monitor hydraulic fracturing of shale gas reservoirs and to help constrain how injected fluids propagate. The MT method measures the electrical resistivity of earth, which is ...

The coefficients that synthesize seismic data via the hyperbolic Radon transform (HRT) are estimated by solving a linear-inverse problem. In the classical HRT, the computational cost of the inverse problem is proportional to the size of the data ...

We have evaluated the mapping of polarizable material using a Cole-Cole model to fit second-order effects in concentric-loop airborne electromagnetic system responses. At Lewis Ponds in New South Wales, an inverted ground dipole-dipole array data ...

We have analyzed ultrasonic flexural data acquired in a North Sea well using a commercial tool optimized for generating such data, and found how one might separate refractions along successive layers of casings, and from these separated ...

We have developed an efficient approach for picking first-break wavefronts on coarsely sampled time slices of 3D shot gathers. Our objective was to compute a smooth initial velocity model for multiscale full-waveform inversion (FWI). Using ...

Our aim was to confirm the ability of polarizable and superparamagnetic (SPM) thin sheets in the near surface to improve the model fit of airborne electromagnetic data. Our method was to fit induced polarization (IP) effects with Cole-Cole complex ...

With the gradual disappearance of traditional structural reservoirs, widely distributed deep thin lithologic reservoirs developed in continental and transitional sedimentary environments may offer significant petroleum reserves. Reservoir ...

CO2 injection into subsurface reservoirs leads to pressure and saturation changes. Furthermore, CO2-brine-minerals interaction could result in dissolution or reprecipitation of rock frame-forming minerals. Observed time-lapse seismic associated with CO2 ...

The resolution of a multiparameter full-waveform inversion (FWI) is highly influenced by the parameterization used in the inversion algorithm, as well as the data quality and the sensitivity of the data to the elastic parameters because the ...

Quasi-P (qP)-wavefield separation is a crucial step for elastic P-wave imaging in anisotropic media. It is, however, notoriously challenging to quickly and accurately obtain separated qP-wavefields. Based on the concepts of the trace of the stress ...

The P-wave eikonal equation for orthorhombic (ORT) anisotropic media is a highly nonlinear partial differential equation requiring the solution of a sixth-order polynomial to obtain traveltimes, resulting in complex and time-consuming numerical ...

Normal moveout (NMO) velocity is a commonly used tool in the seismic industry nowadays. In 3D surveys, the variation of the NMO velocity in a horizontal plane is elliptic in shape for the anisotropy or heterogeneity of any strength (apart from a ...

The wave equation can be tailored to describe wave propagation in vertical-symmetry axis transversely isotropic (VTI) media. The qP- and qS-wave eikonal equations derived from the VTI wave equation indicate that in the pseudoacoustic approximation,...

We emphasize the existence of stress-dependent microscopic heterogeneities in granular media and their influence on macroscopic property estimation using numerical simulations. Although numerical simulations based on contact mechanics successfully ...

Consider a package of parallel porous layers in which the porosity, the bulk modulus of the pore fluid, and the bulk modulus of the mineral phase are constant within each layer but may vary along the package. We wished to apply Gassmann’s fluid ...

Distributed acoustic sensing (DAS) using fiber optic cables is an emerging seismic acquisition technology for the oil and gas industry, geothermal resource exploration, and underground fluid-storage monitoring. This technology offers the advantage ...

Gassmann’s fluid substitution model is intended for a monomineralic, homogeneous porous rock, in which pore pressures induced by applied loads can equilibrate throughout the pore space. These assumptions are violated when Gassmann’s equations are ...

We have used the wavenumber integration, velocity-time semblance, and dispersion methods to investigate the influence of collar properties including velocities, density, and attenuation on acoustic logging-while-drilling wavefields. We have found ...

The estimation of rock and fluid properties from seismic attributes is an inverse problem. Rock-physics modeling provides physical relations to link elastic and petrophysical variables. Most of these models are nonlinear; therefore, the inversion ...

Low electrical resistivity measurements in organic-rich mudrocks are commonplace in highly mature zones. These low resistivity values are usually difficult to justify and lead to overestimation of water saturation when using conventional ...

The quasi-static theory of poroelasticity presented by Biot and Gassmann provides a relationship between the drained and undrained elastic constants of an isotropic fluid-saturated porous material in terms of the porosity of the material, bulk ...

3D printing techniques (additive manufacturing) using different materials and structures provide opportunities to understand porous or fractured materials and fluid effects on their elastic properties. We used a 3D printer (Stratasys Dimension SST ...

Cased petroleum wells must be logged to determine the bonding and hydraulic isolation properties of the cement. Ultrasonic logging of single casings has been widely studied and is commercially available. However, ultrasonic logging in multiple-...

Multipulse airborne transient electromagnetic (ATEM) systems transmit one high-power pulse and one low-power pulse containing more high-frequency EM signals. Such systems have better near-surface resolutions while maintaining the depth of ...

Accurate estimation of the hydrological properties of near-surface aquifers is important because these properties strongly influence groundwater flow and solute transport. Laboratory-based investigations have indicated that induced polarization (...

The depressurization of coal seam gas formations causes in situ fluids to migrate through pores and fractures in the earth. The removal or discharge of large volumes of water from coal measures reduces in situ fluid pressure allowing natural gas ...

The primary aim of my research is to improve the characterization of induced polarization (IP) responses in airborne electromagnetic (AEM) survey data. The principal objectives are to test alternative methodologies for quantitative modeling and ...

When exploring subsurface environments using electromagnetic (EM) induction (EMI) tools, approximate forward-modeling methods based on a homogeneous half-space kernel have been extensively evaluated in the past. For large-scale exploration methods,...

Many types of classical models of the induced polarization (IP) effects of rock ore have been introduced in previous studies. Our focus is on determining the most effective model for describing the rock ore IP effects based on a numerical ...

We have first analyzed the ability of polarizable and superparamagnetic thin sheets in the near surface to fit airborne electromagnetic (AEM) data using data from western Tasmania. Then we analyzed the results of such fitting in the context of ...

Electromagnetic surveys using a vertical transmitter loop are common in land, marine, and airborne geophysical exploration. Most of these horizontal magnetic dipole (HMD) systems operate in the frequency domain, measuring the time derivative of ...

The knowledge of the distribution of leachate and gas in a municipal landfill is of vital importance to the landfill operators performing improved landfill treatments and for environmental protection and efficient biogas extraction. We have ...

We have conducted proton nuclear magnetic resonance (NMR) measurements of relaxation times T1 and T2 as well as the diffusion coefficient D to detect and quantify gasoline, diesel, crude oil, and trichloroethylene (TCE) in sediment samples containing ...

We have developed a new level-set-based structural parameterization for joint inversion of gravity and traveltime data, so that density contrast and seismic slowness are simultaneously recovered in the inverse problem. Because density contrast and ...

Salt body interpretation is important for building subsurface models and interpreting seismic horizons and faults that might be truncated by the salt. Salt interpretation often includes two steps: highlighting salt boundaries with a salt attribute ...

Many of the transforms and attributes used in gravity and magnetic interpretation can be expressed as a 2D or 3D vector. The horizontal gradient and the 2D analytic signal are 2D vectors. The gravity or magnetic field, the 3D analytic signal, and ...

The forecasting and risk assessment of induced seismicity associated with fluid injection have considerable importance for subsurface energy development. We have developed a seismic evaluation method called the possible seismic moment (PoSeMo) ...

We have determined source mechanisms for nine high-quality microseismic events induced during hydraulic fracturing of the Montney Shale in Canada. Seismic data were recorded using a dense regularly spaced grid of sensors at the surface. The design ...

Microseismic data acquired in a single observation well parallel to the axis of rotational symmetry of surrounding rocks — typically, in a vertical well drilled through a horizontally layered isotropic or vertically transversely isotropic ...

We have investigated the use of ambient-noise data to extract phase and group velocities from surface-noise sources in a microseismic monitoring context. The data were continuously recorded on 44 patch arrays with an interpatch distance on the ...

In today’s industry, automatic detection of geologic features such as faults and channels is a challenging problem when the quality of data is not good. Edge detection filters are generally applied for the purpose of locating such features. Until ...

Survey design for converted-wave (PS) reflection is more complicated than for standard P-wave surveys, due to raypath asymmetry and increased possibility of phase distortion. Coal-scale PS surveys (depth <300  m) require particular consideration, partly ...

The theory of seismic interferometry predicts that crosscorrelations of recorded seismic responses at two receivers yield an estimate of the interreceiver seismic response. The interferometric process applied to surface-reflection data involves ...

The availability of low-frequency data is an important factor in the success of full-waveform inversion (FWI) in the acoustic regime. The low frequencies help determine the kinematically relevant, low-wavenumber components of the velocity model, ...

Three-dimensional implementations of reverse time migration (RTM) and full-waveform inversion (FWI) require efficient schemes to access the incident field to apply the imaging condition of RTM or build the gradient of FWI. Wavefield reconstruction ...

Wide-azimuth long-offset ocean bottom cable (OBC)/ocean bottom node surveys provide a suitable framework to perform computationally efficient frequency-domain full-waveform inversion (FWI) with a few discrete frequencies. Frequency-domain seismic ...

Adjoint methods are a key ingredient of gradient-based full-waveform inversion schemes. While being conceptually elegant, they face the challenge of massive memory requirements caused by the opposite time directions of forward and adjoint ...

Density is known to be difficult to reconstruct in multiparameter full-waveform inversion (FWI). This difficulty results from the similarity of the diffraction patterns of velocity and density at small scattering angles. In addition, the ...

A successful full-waveform inversion implementation updates the low-wavenumber model components first for a proper description of the wavefield propagation and slowly adds the high wavenumber potentially scattering parts of the model. The low-...

Conventional full-waveform seismic inversion attempts to find a model of the subsurface that is able to predict observed seismic waveforms exactly; it proceeds by minimizing the difference between the observed and predicted data directly, ...

Data-domain elastic wavefield tomography is an effective method for updating multiparameter elastic models that exploits much of the information provided by observed multicomponent data. However, poor illumination of the subsurface by P- and S-...

Full-waveform inversion (FWI) is a technique for determining the optimal model parameters by minimizing the seismic data misfit between observed and modeled data. The objective function may be highly nonlinear if the model is complex and low-...

Strong subsurface attenuation leads to distortion of amplitudes and phases of seismic waves propagating inside the earth. The amplitude and the dispersion losses from attenuation are often compensated for during prestack depth migration. However, ...

Compaction in the reservoir overburden can impact production facilities and lead to a significant risk of well-bore failures. Prevalent practices of time-lapse seismic processing of 4D data above compacting reservoirs rely on picking time ...

Clarifying and locating small-scale discontinuities or inhomogeneities in the subsurface, such as faults and collapsed columns, plays a vital role in safe coal mining because these discontinuities or inhomogeneities may destroy the continuity of ...

Seismic imaging techniques often require an input velocity model. Velocity analysis is one of the most critical stages in seismic data processing. Standard ways to find the velocity model from seismic data in the time domain are constant velocity ...

We have developed a 3D reverse time migration (RTM) implementation, with an extended imaging condition, in the presence of tilted transverse isotropy (TTI), using finite-difference time-domain solvers on the rotated staggered grid (RSG) and the ...

I have developed two high-resolution imaging methods that do not require a priori information on the structural dip. The dip information is often necessary to image complex structures using Kirchhoff migration by selecting only the constructively ...

Illumination and resolution analysis provides vital information regarding the response of an imaging system to subsurface structures. However, generating the resolution function is often computationally intensive, which prevents it from being ...

We have developed a fast and practical wave-equation-based migration method to image subsurface diffractors. The method is composed of three steps in our implementation. First, it decomposes extrapolated receiver wavefields at every imaging point ...

The objective of prestack depth migration is to position reflectors at their correct subsurface locations. However, migration methods often also generate artifacts along with physical reflectors, which hamper interpretation. These spurious ...

Common-image gathers in the dip-angle domain may be computed in relation to wave-equation migration methods, extended by the subsurface offset. They involve the application of a postmigration local Radon transform on the subsurface-offset extended ...

Least-squares migration (LSM) is commonly regarded as an amplitude-preserving or true amplitude migration algorithm that, compared with conventional migration, can provide migrated images with reduced migration artifacts, balanced amplitudes, and ...

Angle-domain common-image gathers provide much useful data about the subsurface, such as seismic velocities and amplitude-versus-angle (AVA) information, and they can be manipulated to provide high-quality stacked images. However, the computation ...

Krauklis waves are of major interest because they can lead to resonance effects in fluid-filled fractures. This resonance is marked by seismic signals with a dominant signature frequency, which may reveal fracture-related rock properties. In our ...

We have developed efficient splitting algorithms for high-order compact finite-difference methods to approximate second-order space derivatives. In general, the methods’ high-order compact finite-difference schemes require the inversion of a ...

Wavefield injection in finite-difference (FD) grids can be described by the method of multiple point sources. The method teaches how synthetically generated wavefields and wavefield constituents can be reconstructed from surface recordings using a ...

To accurately simulate seismic wave propagation for the purpose of developing modern land data processing tools, especially full-waveform inversion (FWI), we have developed an efficient high-order finite-difference forward-modeling algorithm with ...

Noninvasive geophysical techniques based on the dispersion of surface waves in layered media are commonly used approaches for measuring shear-wave velocity profiles of the subsoil. Acquiring surface waves is a simple task, but the interpretation ...

Based on an average-derivative method, we developed a new nine-point numerical scheme for a frequency-domain elastic-wave equation. Compared with the classic nine-point scheme, this scheme reduces the required number of grid points per wavelength ...

The conventional energy flux density vector indicates the propagation direction of mixed P- and S-wave wavefields, which means when a wavefront of P-wave encounters a wavefront of S-wave with different propagation directions, the vectors cannot ...

Normal moveout (NMO) correction is routinely applied to traces of each common-midpoint (CMP) gather before forming a stack section. Conventional NMO correction has the drawback of producing stretching as a natural result of convergence of the NMO ...

We developed a new and simple method for denoising seismic data, which was inspired by data-driven empirical mode decomposition (EMD) algorithms. The method, which can be applied either as a trace-by-trace process or in the f-x domain, replaces the ...

Air-gun arrays can be encoded by firing individual air guns sequentially over a range of time. This marine source encoding is shown to be particularly beneficial for simultaneous source separation, which can exploit the orthogonality of the ...

An asymmetric chirplet transform, also called the asymmetric Gaussian chirplet model (AGCM), was recently introduced for fast and accurate extraction of important information from seismic signals. Unlike Fourier or wavelet transforms with fixed ...

Geophysics publishes abstracts of dissertations and titles of master’s theses both in print and online. Recent graduates are invited to submit their abstracts or titles by completing and submitting the appropriate form found at http://seg.org/...

This article lists contributors to this issue and provides brief biographies of them.