Efficient frequency-domain full-waveform inversion (FD-FWI) of wide-aperture data is designed by limiting inversion to a few frequencies and by solving the Helmholtz equation with a direct solver to process multiple sources efficiently. Some variants of FD-FWI, which process the wave equation as a weak constraint, have been proposed to increase the computational efficiency or extend the search space

The presence of noise in towed marine seismic data is a long-standing problem. The various types of noise present in marine seismic records are never truly random. Instead, seismic noise is more complex and often challenging to attenuate in seismic data processing. Therefore, we have examined a wide range of real data examples contaminated by different types of noise including swell noise, seismic

Nonlocal means (NLM) is one of the classic patch-based methods for random noise attenuation. It assumes that a significant amount of redundant information exists in similar patches, which can be used to restore the original data. However, this method is computationally expensive due to a large number of overlapping patches. In addition, because this method uses a weighted average of patches to suppress

We have developed a finite-difference iterative solver of the Helmholtz equation for seismic modeling and inversion in the frequency domain. The iterative solver involves the shifted Laplacian operator and two-level preconditioners. It is based on the application of the preconditioners to the Krylov subspace stabilized biconjugate gradient method. A critical factor for the iterative solver is the introduction

Acquisition of incomplete data, i.e., blended, sparsely sampled, and narrowband data, allows for cost-effective and efficient field seismic operations. This strategy becomes technically acceptable, provided that a satisfactory recovery of the complete data, i.e., deblended, well-sampled, and broadband data, is attainable. Hence, we explore a machine-learning approach that simultaneously performs suppression

We have developed an approach to determine the time-dependent moment tensor and the origin time in addition to commonly derived locations of seismic events using time reverse imaging (TRI). It is crucial to locate and characterize the occurring microseismicity without making a priori assumptions about the sources to fully understand the subsurface processes inducing seismicity. Low signal-to-noise

In microseismic monitoring, obtaining reliable information about event properties, such as the location, origin time, and moment-tensor components, is critical for evaluating the success of fluid-injection programs. Elastic wavefield-based migration approaches can robustly image microseismic sources by extrapolating data through an earth model and evaluating an imaging condition. The success of these

Accurately estimating event locations is of significant importance in microseismic investigations because this information greatly contributes to the overall success of hydraulic-fracturing monitoring programs. Full-wavefield time-reverse imaging (TRI) using one or more wave-equation imaging conditions offers an effective methodology for locating surface-recorded microseismic events. Although, to be

We have developed a case study of geophysical reservoir characterization in which we use elastic inversion and probabilistic prediction to estimate nine carbonate lithofacies and the associated porosity distribution. The study focuses on an isolated carbonate platform of middle Miocene age, offshore Sarawak in Malaysia that has been partly dolomitized — a process that increased the porosity and permeability

Magnetic and gravity data are used in the early stages of exploration for uranium deposits in the Athabasca Basin of Canada, just as for many other mineral exploration scenarios. Uranium mineralization in the Athabasca Basin is located where faults in the basement intersect the unconformity between the basement and the overlying sandstones. The gravity and magnetic data are dominated by signatures

The Marchenko multiple elimination (MME) and transmission compensation schemes retrieve primary reflections in the two-way traveltime domain without model information or using adaptive subtraction. Both schemes are derived from projected Marchenko equations and are similar to each other, but they use different time-domain truncation operators. The MME scheme retrieves a new data set without internal

Real-time open-hole wireline sonic logging data processing becomes a nontrivial task to accurately, automatically, and efficiently evaluate the compressional and shear slowness of a borehole rock formation when human interaction is not possible and the signal processing time is limited to the elapsed time between different transmitter excitations. To address real-time sonic data processing challenges

The reconstruction of seismic data with missing traces has been a long-standing issue in seismic data processing. Deep learning (DL) has emerged as a popular tool for seismic interpolation; it learns priors from training data sets of incomplete/complete data pairs. However, these DL methods are restricted to training data because they are supervised. When the features of the testing and training data

The time-space-domain finite-difference method (FDM) is widely used in forward modeling of wave equations. Conventional explicit FDMs (EFDMs) (with high order in space and the second order in time) would result in apparent temporal and spatial dispersion for high frequencies and large time steps. Moreover, the saturation effect of Taylor expansion seriously restricts the improvement of bandwidth coverage

Lithology identification plays an essential role in geologic exploration and reservoir evaluation. In recent years, machine-learning-based logging lithology identification has received considerable attention due to its ability to fit complex models. Existing work develops machine-learning models under the assumption that the data gathered from different wells are from the same probability distribution

Quantitative imaging of subsurface earth properties in elastic media is performed from distributed acoustic sensing data. A new misfit functional based upon the reciprocity gap is designed, taking crosscorrelations of displacement and strain, and these products further associate an observation with a simulation. In comparison with other misfit functionals, this functional has the advantage of only

We have developed an automated method for velocity picking that allows us to estimate appropriate velocity functions for the normal moveout correction of common-depth-point (CDP) gathers, valid for either hyperbolic or nonhyperbolic trajectories. In the hyperbolic velocity analysis case, the process involves the simultaneous search (picking) of a certain number of time-velocity pairs in which the semblance

The application of reverse time migration (RTM) to land seismic data is still a great challenge due to its low quality, low signal-to-noise ratio, irregular spatial sampling, acquisition gaps, and missing traces. Therefore, prior to the application of this kind of depth migration, the input prestack data must be judiciously preconditioned; that is, it must be interpolated, regularized, and enhanced

I have developed an efficient 3D forward modeling algorithm based on radiation boundary conditions for controlled-source electromagnetic data. The proposed algorithm derives computational efficiency from a stretch-free discretization, air-free computational domain, and a better initial guess for an iterative solver. A technique for estimation of optimum grid stretching for multifrequency modeling of

Multidimensional seismic data reconstruction and denoising can be achieved by assuming noiseless and complete data as low-rank matrices or tensors in the frequency-space domain. We have adopted a simple and effective approach to interpolate prestack seismic data that explores the low-rank property of multidimensional signals. The orientation-dependent tensor decomposition represents an alternative

Land seismic velocity modeling is a difficult task largely related to the description of the near-surface complexities. Full-waveform inversion (FWI) is the method of choice for achieving high-resolution velocity mapping, but its application to land seismic data faces difficulties related to the complex physics, unknown and spatially varying source signatures, and low signal-to-noise ratio (S/N) in

Marchenko focusing and imaging are novel methods for correctly handling multiple scattered energy while processing seismic data. However, strict requirements in the acquisition geometry, specifically the colocation of sources and receivers as well as dense and regular sampling, currently constrain their practical applicability. We have reformulated the Marchenko equations to handle the case in which

We have developed a one-step approach for Bayesian prediction and uncertainty quantification of lithology/fluid classes, petrophysical properties, and elastic attributes conditional on prestack 3D seismic amplitude-variation-with-offset data. A 3D Markov random field prior model is assumed for the lithology/fluid classes to ensure spatially coupled lithology/fluid class predictions in the lateral and

The objective of most seismic time-lapse studies is to detect rock-property changes in a subsurface formation caused by fluid withdrawal or injection, often by comparing seismic reflection images of the subsurface before and after the operation. Because rock-property changes can affect the amplitudes of seismic reflection events associated with the boundaries of the formation, amplitude anomalies are

The effective monitoring of hydraulic fracturing in unconventional oil and gas production requires tools to quantify elastic property variations even in the absence of microseismic activity. To track the subtle time-lapse variations in reservoir properties during such activities, monitoring techniques with high repeatability and high resolution, spatially and temporally, are required. Distributed acoustic

Horizon picking is a fundamental and crucial step for seismic interpretation, but it remains a time-consuming task. Although various automatic methods have been developed to extract horizons in seismic images, most of them may fail to pick horizons across discontinuities such as faults and noise. To obtain more accurate horizons, we have developed a dynamic programming algorithm to efficiently refine

To reduce uncertainties in reconstructed images, geologic information must be introduced in a numerically robust and stable way during the geophysical data inversion procedure. In the context of potential (gravity) data inversion, it is important to bound the physical properties by providing probabilistic information on the number of lithologies and ranges of values of possibly existing related rock

Surface-wave methods are classically used to characterize shear (S-) wave velocities (VS) of the shallow subsurface through the inversion of dispersion curves. When targeting 2D shallow structures with sharp lateral heterogeneity, windowing and stacking techniques can be implemented to provide a better description of VS lateral variations. These techniques, however, suffer from the trade-off between

The acquisition of airborne electromagnetic (AEM) data colocated with water well data provides an essential data set for constructing an accurate rock-physics relationship between resistivity from AEM and lithology from wells. Results from an AEM survey in Butte and Glenn Counties, California, USA, where 41 water wells are located within 100 m of the AEM flight lines, provide a unique opportunity to

Understanding the relationship between dynamic and static mechanical properties of organic-rich shales is crucial for successful in situ stress profile prediction and hydraulic fracturing stimulation in unconventional reservoirs. However, the relationship between dynamic and static properties remains ambiguous, considering the complex rock microstructure and subsurface stress environment. We have reported

The Orapa kimberlite field of Botswana is one of the world’s major diamond producing regions. Within this field, there are several small kimberlite pipes that have not been completely explored in terms of their lateral extent, depth, and diamond potential. Two such pipes, BK54 and BK55, were found during a ground gravity and magnetic survey, and subsequent drilling confirmed the presence of kimberlite

Migration techniques are an integral part of seismic imaging workflows. Least-squares reverse time migration (LSRTM) overcomes some of the shortcomings of conventional migration algorithms by compensating for illumination and removing sampling artifacts to increase spatial resolution. However, the computational cost associated with iterative LSRTM is high and convergence can be slow in complex media

The acoustic problem of an eccentric drill collar in a fluid-filled borehole has been of interest in the field of acoustic logging while drilling (ALWD) in recent years. To reduce the effects of tool eccentricity on ALWD measurements, studies on acoustic responses under such conditions are essential. This study therefore has developed an analytical method to investigate borehole wavefields with an

Seismic acoustic impedance inversion plays an important role in reservoir prediction. However, single-trace inversion methods often suffer from spatial discontinuities and instability due to poor-quality seismic records with spatially variable signal-to-noise ratios or missing traces. The specified hyperparameters for seismic inversion cannot be suitable to all seismic traces and subsurface structures

Polarization filters (PFs) are widely used for denoising seismic data. These filters are applied in the fields of seismology, microseismic monitoring, vertical seismic profiling, and subsurface imaging. They are primarily useful to suppress ground roll in seismic reflection data and enhance P- and S-wave arrivals. Traditional implementations of PFs involved the analysis of the covariance matrix or

The physical basis, parameterization, and assumptions involved in root-mean-square (rms) velocity estimation have not significantly changed since they were first developed. However, these three aspects are all good targets for novel application of the recent emergence of machine learning (ML). Therefore, it is useful at this time to provide a tutorial overview of two state-of-the-art ML implementations;

Diffractions are the seismic responses of subsurface small-scale geologic discontinuities or inhomogeneities, whose energy is much weaker than that of reflections. To eliminate the masking effect of strong reflections on weak diffractions, a prestack diffraction separation method is proposed based on the common virtual source gather (CVSG) and the median filter. The reflection generated from a reflector

Knowledge of the S-wave velocity (VS) and density (ρ) is essential for oil and gas reservoir detection and characterization. However, reliable recovery of both parameters, especially density, from the reflected PP-wave data is a difficult issue because this inverse problem is highly ill-conditioned. The reflected SV-SV wave is easier to process than the PS-wave, and it can provide better estimates

Seismic full-waveform inversion (FWI) estimates subsurface velocity structures by reducing data misfit between observed and modeled data. Simultaneous matching of transmitted and reflected waves in seismic FWI causes different updates of different wavenumber components of a given model depending on the diffraction angle between incident and diffracted rays. Motivated by the inverse-scattering imaging

Repeated seismic surveys contain valuable information regarding time-lapse (4D) changes in the subsurface. Full-waveform inversion (FWI) of seismic data can provide high-resolution estimates of 4D change. We have adopted a new time-domain 2D acoustic time-lapse FWI method based on the central-difference scheme with higher order mathematical accuracy and reasonable computational cost. The method is

Suppression of surface-related and internal multiples is an outstanding challenge in seismic data processing. The former is particularly difficult in shallow water, whereas the latter is problematic for targets buried under complex, highly scattering overburdens. We have developed a two-step, amplitude- and phase-preserving, inversion-based workflow that addresses these problems. We apply robust estimation

The full set of transversely isotropic elastic stiffness constants of inorganic shale (mudrock with total organic carbon less than 1.5%) can be successfully modeled and, therefore, predicted based on the mineral composition, mineral stiffnesses, clay platelet orientation distribution function, and microgeometry of the pore space. A fundamentally novel concept drawing from the Maxwell homogenization

Unconsolidated sands provide zones of high porosity and permeability important for freshwater aquifers, hydrocarbon production, and CO2 sequestration. An understanding of the acoustics of unconsolidated sands enables the characterization of such formations using ultrasonics, borehole acoustics, and seismic methods. Inversion of ultrasonic compressional and shear velocities measured for unloading as

Wave-induced fluid flow (WIFF) between cracks and micropores is one of the major mechanisms causing attenuation and dispersion within seismic frequency ranges. Previous non-interaction-approximation (NIA) models often assume that the distribution of cracks is dilute, neglecting the influences of interacting cracks on dispersion and attenuation. To overcome this restriction, we have investigated the

Accurate inversion of time-lapse amplitude variation with offset (AVO) to reservoir pressure change requires knowledge of strain/stress changes in the reservoir and overburden. These geomechanical effects have not been taken into account in previous studies. We have determined that there are three contributions of importance that must be included in the AVO equations: a density term in the reservoir

Through the study of microseismic focal mechanisms, information such as fracture orientation, event magnitude, and in situ stress status can be quantitatively obtained, thus providing a reliable basis for unconventional oil and gas exploration. Most source inversion methods assume that the medium is isotropic. However, hydraulic fracturing is usually conducted in sedimentary rocks, which often exhibit

Nuclear magnetic resonance (NMR) relaxometry typically involves the analysis of a relaxation time distribution. The surface relaxivity (ρ) is the key parameter that relates the relaxation time to the pore radius. Only a good estimate of the surface relaxivity enables a reliable determination of the pore radius distribution in a rock or sediment sample. A wide variety of approaches for the estimation

I have developed an approximate inversion scheme for surface-borehole electromagnetic data. The method aims at reducing the computational burden arising by the fine discretization required to accurately solve for the field distribution in the full complexity of the borehole system together with the reservoir medium. I first analyze numerical simulations of the surface-borehole response performed for

Quantitative interpretation of waveform attenuation for determining petrophysical properties remains one of the most challenging problems associated with rock physics. In this study, two effective methods are proposed to compute gas saturation in organic-rich shale and tight gas formations from full-waveform sonic attenuations. We first extract compressional (P)- and shear (S)-wave attenuations from

Water injection is one of the most common methods used to enhance the oil recovery of reservoirs with low permeability and strong heterogeneity. However, with the injection of water in the production process, the formation water salinity, oil saturation, and the distribution of the residual oil in the reservoir are altered, causing difficulties in the evaluation of the flooded layers. Consequently

The Lebedev grid finite-difference (FD) method allows modeling of anisotropic elastic-wave propagation. On Lebedev grids, erroneous point-source excitations can create spurious (nonphysical) waves. The only known remedy for such artifacts in the literature is the Lisitsa-Vishnevsky method. This method uses a distributed array to create point sources and point receivers on the FD grid. However, the

Several recent studies have advanced the use of time-lapse distributed acoustic sensing vertical seismic profile data in horizontal wells for determining hydraulically stimulated fracture properties. Hydraulic fracturing in a horizontal well typically generates vertical fractures in the rock medium around each stage. We have modeled the hydraulically stimulated formation with vertical fracture sets

We have developed a new approach for acoustic wave modeling in transversely isotropic media with a vertical axis of symmetry. This approach is based on using a pure acoustic wave equation derived from the basic physical laws — Hooke’s law and the equation of motion. We find that the conventional equation noted as a pure quasi-P-wave equation computes only one stress component. In our approach, there

Time migration, as opposed to depth migration, suffers from two well-known shortcomings: (1) approximate equations are used for computing Green’s functions inside the imaging operator and (2) in case of lateral velocity variations, the transformation between the image-ray coordinates and the Cartesian coordinates is undefined in places where the image rays cross. We have found that the first limitation

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

The eastern Adirondack Highlands of northern New York host dozens of iron oxide-apatite (IOA) deposits containing magnetite and rare earth element (REE)-bearing apatite. We use new aeromagnetic, aeroradiometric, ground gravity, and sample petrophysical and geochemical data to image and understand these deposits and their geologic framework. Aeromagnetic total field data reflect highly magnetic leucogranite

Seismic interferometry is a method used to calculate wavefields for sources and receivers that are located where only sources or only receivers are available. There are correlation- or deconvolution-based interferometric methods that can be used to reposition the seismic array from the earth’s surface to an arbitrary datum at depth. Based on the one-way reciprocity theorems of convolution and correlation

Hydrocarbon generation in a source rock is a complex, irreversible phase change that occurs when a source rock is heated during burial to change the phase to a fluid. The fluid density is less than the kerogen density; therefore, in a closed or partially closed system, the volume of the pore space occupied by fluids increases. Burial also increases the effective stress, which leads to compaction and

Determining saturation and pore pressure is relevant for hydrocarbon production as well as natural gas and CO2 storage. In this context, seismic methods provide spatially distributed data used to determine gas and fluid migration. A method is developed that allows the determination of saturation and reservoir pressure from seismic data, more accurately from the rock-physics attributes of velocity,

We have developed a new method for simultaneous denoising and reconstruction of 5D seismic data corrupted by random noise and missing traces. Several algorithms have been developed for seismic data restoration based on rank-reduction (RR) methods. More recently, a damping operator has been introduced into the conventional truncated singular-value decomposition (TSVD) formula to further remove residual