3D Reflection Research Articles

A 3D reflection ray-tracing method based on linear traveltime perturbation interpolation

The linear traveltime interpolation (LTI) method, one of the common methods to calculate the wavefront traveltimes and the raypaths in complex media, is based on the assumption that the traveltime varies linearly along each cell boundary of a discrete model. The linear assumption may result in large calculation errors when the cell size is large. To solve this problem, we have adopted a linear traveltime perturbation interpolation (LTPI) method. In LTPI, the original traveltime is decomposed into two parts: a reference traveltime and a traveltime perturbation. The reference traveltime, being one propagating in the equivalent homogeneous medium, varies nonlinearly. The traveltime perturbation, defined as the difference between the original and reference traveltimes, is assumed to be linear along each cell boundary. The traveltime perturbation is much less than the reference traveltime; therefore, the original traveltime keeps its nonlinearity. We modify LTPI to suit to irregular hexahedral cells for simulating the undulating interfaces more precisely. By combining the modified LTPI with the wavefront group-marching method, we have developed a reflection ray-tracing method in 3D complex media. Numerical experiments indicate that the modified LTPI is more accurate than LTI in computing wavefront traveltimes and raypaths. Besides, the modified LTPI performs more consistently than LTI in different grid spacing. Therefore, under a certain accuracy requirement, the modified LTPI is more efficient than LTI.

Application of extended elastic impedance in seismic geomechanics

We have evaluated an innovative application of extended elastic impedance (EEI) to integrate seismic and geomechanics for geomechanical interpretation of hydrocarbon reservoirs. EEI analysis is used to extract geomechanical parameters. To verify and assess the capabilities of EEI analysis for extracting geomechanical parameters, we selected a jointed, oil-bearing, shale carbonate reservoir in the southwest of Iran, and we used petrophysical data and core analysis to estimate static and dynamic moduli of the reservoir rock. We calculated the corresponding EEI curve to different intercept-gradient coordinate rotation angles (the chi angle, [Formula: see text]), and we selected the angles of the maximum correlation for the corresponding geomechanical parameters. Then, combining the intercept and gradient, we generated 3D reflectivity patterns of EEI at different angles. To obtain a cube of geomechanical parameters, we performed model-based inversion on the EEI reflectivity pattern. A comparison between the modeling results and well data indicated that the geomechanical parameters estimated by our method were well-correlated to the observed data. Accordingly, we extracted the geomechanical and rock-physical parameters from the EEI cube. We further found that EEI analysis was capable of giving a 3D mechanical earth model of the reservoir with the appropriate accuracy. Finally, we verified the proposed methodology on a blind well and compared the results with those of the simultaneous inversion, indicating comparable levels of accuracy. Therefore, application of this method in seismic geomechanics can bring about significant progress in the future.

Cost-Effective Seismic Exploration: 2D Reflection Imaging at the Kylylahti Massive Sulfide Deposit, Finland

We show that by using an advanced pre-stack depth imaging algorithm it is possible to retrieve meaningful and robust seismic images with sparse shot points, using only 3–4 source points per kilometer along a seismic profile. Our results encourage the use of 2D seismic reflection profiling as a reconnaissance tool for mineral exploration in areas with limited access for active seismic surveys. We used the seismic data acquired within the COGITO-MIN project comprising two approximately 6 km long seismic reflection profiles at the polymetallic Kylylahti massive sulfide mine site in eastern Finland. The 2D seismic data acquisition utilized both Vibroseis and dynamite sources with 20 m spacing and wireless receivers spaced every 10 m. For both source types, the recorded data show clear first breaks over all offsets and reflectors in the raw shot gathers. The Kylylahti area is characterized by folded and faulted, steeply dipping geological contacts and structures. We discuss post-stack and pre-stack data processing and compare time and depth imaging techniques in this geologically complex Precambrian hardrock area. The seismic reflection profiles show prominent reflectors at 4.5–8 km depth utilizing different migration routines. In the shallow subsurface, steep reflectors are imaged, and within and underneath the known Kylylahti ultramafic body reflectivity is prominent but discontinuous.

Mesoarchaean-Palaeoproterozoic crustal-scale tectonics of the central Witwatersrand basin - Interpretation from 2D seismic data and 3D geological modelling

The Witwatersrand Basin represents one of the largest exposures of Meso-Neoarchaean rock on Earth and hosts the Vredefort Dome at its geographic centre. The southern half of the basin is covered by thin Palaeozoic to early Mesozoic marginal sequences of the Karoo Supergroup. However, visualisation and analysis of this unexposed portion of the basin can be achieved in a 3D geomodelling environment through the integration of geophysical (2D reflection seismics) and traditional geological data. In this study, the 3D structural architecture around the Vredefort Dome in the Witwatersrand Basin is evaluated to establish strato-tectonic relationships, first-order scale structures, and a new model for the architecture of basement rocks. From the geological modelling, several strato-structural features have been identified in the seismic sections, including a well-developed listric fault system in the southwest, a prominent fold system observed in the Transvaal Supergroup, and a large listric fault in the east that offsets the aforementioned fold system. Integration of these geophysical and geological data (in 3D space) has provided 3D constraints on the volumes for the Witwatersrand Supergroup, Ventersdorp Supergroup and Transvaal Supergroup to the south, southeast and east of the Vredefort Dome.

Seismic analysis of the gas hydrate system at Pointer Ridge offshore SW Taiwan

Pointer Ridge is a gas hydrate prospect on the South China Sea continental slope offshore SW Taiwan. It is characterized by densely distributed bottom simulating reflections (BSRs), active gas seepage, and potential sandy gas hydrate reservoirs. To understand how the fluids have migrated toward the seafloor, and the role of geological processes in the gas hydrate system, we have collected and analyzed high-quality 2D and 3D reflection seismic data. We first mapped the spatial distribution of the BSRs, and interpreted a major normal fault, Pointer Ridge Fault (PR Fault). The NE-SW trending fault dips to the east, and separates the erosional regime to the west from the depositional regime to the east. One active vent site was identified directly above the PR Fault, while another is located on a topographic high to the west of the fault. On the hanging block of the fault we found at least one major unconformity. The seismic data indicate refilled channels with coarser-grained sediments in the hanging wall of the normal fault. Seismic attribute analysis shows subsurface fluid conduits and potential gas hydrate reservoirs. We propose two types of gas chimneys, which are separated by the fault. Gas plumes derived from hydroacoustic data are mostly from the footwall block of the fault. We infer that fluid flow is more active in the erosional environment compared to the depositional one, and that this is the result of reduced overburden. The methane-bearing fluids migrate upward along the PR Fault and chimneys and form hydrates above the base of the gas hydrate stability zone. Based on seismic interpretation and seismic attribute analysis, we postulate that the channel infill constitutes the most promising hydrate reservoirs in this geological setting. In the surveyed area of Pointer Ridge these channels occur mainly below the gas hydrate stability zone.

3D Imaging of Geothermal Faults from a Vertical DAS Fiber at Brady Hot Spring, NV USA

In March 2016, arguably the most ambitious 4D (3D space + over time) active-source seismic survey for geothermal exploration in the U.S. was acquired at Brady Natural Laboratory, outside Fernley, Nevada. The four-week experiment included 191 vibroseis source locations, and approximately 130 m of distributed acoustic sensing (DAS) in a vertical well, located at the southern end of the survey area. The imaging of the geothermal faults is done with reverse time migration of the DAS data for both P-P and P-S events in order to generate 3D models of reflectivity, which can identify subsurface fault locations. Three scenarios of receiver data are explored to investigate the reliability of the reflectivity models obtained: (1) Migration of synthetic P-P and P-S DAS data, (2) migration of the observed field DAS data and (3) migration of pure random noise to better assess the validity of our results. The comparisons of the 3D reflectivity models from these three scenarios confirm that sections of three known faults at Brady produce reflected energy observed by the DAS. Two faults that are imaged are ~1 km away from the DAS well; one of these faults (middle west-dipping) is well-constructed for over 400 m along the fault’s strike, and 300 m in depth. These results confirm that the DAS data, together with an imaging engine such as reverse time migration, can be used to position important geothermal features such as faults.

3D mapping and gravity modelling of Capel and Faust basins

The Capel and Faust basins lie at water depths of 1500- 3000 m, 800 km east of Brisbane. Geoscience Australia began a petroleum prospectivity study of these remote frontier basins with acquisition of reflection and refraction seismic, gravity, magnetic and multi-beam bathymetry data during 2006/07. The approach mapped a complex distribution of sub-basins via traditional 2D reflection seismic interpretation techniques and 3D mapping and gravity modelling. Gravity models were used to inform the seismic interpretation of basement. Gravity models had three sediment layers with average densities inferred from refraction modelling of 1.85, 2.13, 2.31 t/m3 overlying a pre-rift basement of density 2.54 t/m3, itself consisting in part of intruded older basin material. Gravity modelling of the simple density model arising from the initial interpretation of reflection seismic data indicated a first order agreement between observed and calculated data. Second order misfits were accounted for by adjustments to the sediment density values, localised adjustments to basement depths, and heterogeneity in the basement densities. The study concluded that sediment of average velocity 3500 m/s exceeds 6000 m thickness in the northwest of the area, which is sufficient for potential petroleum generation.

Using seismic diffractions for assessment of tectonic overprint and fault interpretation

Assessment of the area of interest on tectonic overprint is a key aspect during various geoscientific exploration endeavors. Conventionally, 3D reflection imaging is used because it provides the highest resolution of the subsurface image. Tectonic features, e.g., faults or fractures, are imaged indirectly by means of discontinuities of the specular reflections. Specular reflections, however, are only a part of the backscattering wavefield. Geologic heterogeneities in the subsurface can act as scattering points or scattering edges, which both evoke diffracted waves. Thus, diffracted waves are a direct seismic response from subsurface heterogeneities, which have a size comparable with the prevailing wavelength or a curvature growing locally to infinity. We investigate a dedicated processing of diffracted waves, which allows direct imaging of such heterogeneities. The method is based on separation of reflections from diffractions with subsequent diffraction focusing. We apply a combination of frequency-wavenumber filtering and an adaptive-subtraction engine to isolate diffractions. Once the reflections are removed from a data set, diffracted waves are focused into their apexes yielding an image of scatter points, which can be interpreted as an indicator for the extent of the degree of inhomogeneities or can be used to map structural elements or fracture density. We use a modified coherence analysis as a focusing tool. Diffractions from the scattering points have a different phase response than diffractions from the edges. These differences can be distinguished and further guide the geologic interpretation.

The use of FWI in coal exploration

Seismic surveys are routinely used for building precise structural images of the coal bearing formations in Australia but coal production related hazards such as weak strata and zones with an increased gas content remain to be fully resolved by seismic measurements. One way of investigating these issues is through the application of Full Waveform Inversion (FWI) methods. To utilise the full power of these methods a high quality seismic dataset is needed. Such conditions are often met by 2D and 3D reflection seismic data acquired over coal seams in Bowen and Sydney basins. FWI can be used for a high resolution estimate of P- and S-wave velocities and the density that can also be translated into geotechnical parameters of interest to mining operations. In this study, we evaluate the applicability of FWI methods for estimating elastic parameters (P and S wave velocities and density) from the inversion of a synthetic seismic dataset that was recorded over the surface of a 2D earth model that represents subsurface geology in Goonyella coal mine in Queensland, Australia. We generated elastic synthetic shot records using finite difference algorithm and inverted these data back for model parameters to assess the potential of the FWI algorithm. Using only a short array of surface receivers (cheaper option), we show that the application of FWI method can still improve the original earth models towards the true solutions. We were also able to reconstruct the elastic boundaries for a major part of the subsurface models within the seismic bandwidth. Interpretation of the estimated parameters for coal mining objectives is then straightforward

The evolution of a Middle Miocene deep-water sedimentary system in northwestern New Zealand (Taranaki Basin): Depositional controls and mechanisms

Abstract Through the Oligocene and Miocene, New Zealand basins underwent widespread subsidence, related to the evolution of the convergent plate boundary between the Pacific and Australian plates. In Taranaki Basin on the western margin of the North Island, a deep water siliciclastic sedimentary system developed in response to basin subsidence and hinterland uplift. Basinward of the evolving shelf, basin floor sandstones and mudstones were deposited, some of which constitute important petroleum reservoirs and seals. Extensive 3D reflection seismic coverage has enabled us to map the character and distribution of basin floor sedimentary units and to develop a comprehensive sequence stratigraphic model. The stacking patterns of depositional sequences reflect an overall progradation of basin floor sedimentary facies and change in geometries through time, while associated elements such as fan lobes and channel systems increased in dimension. Structural change and southward progressing tectonic uplift most likely controlled increasing sediment input into the basin. In addition, an intensification of bottom current activity led to the development of sediment drifts, which we suggest was related to oceanographic changes at the end of the Middle Miocene Climatic Optimum. While turbidite depositional systems were dominant during lowstands, sediment reworking by shore parallel currents is interpreted to have been a dominant process during highstands. We document a change from sand-dominated to more mud-dominated deposits through the Middle Miocene and propose that this change in sediment character may be related to a higher degree of chemical weathering on land, possibly related to the northward migration and intensification of westerly winds.

Fast-Tracking Gold Exploration Below 300m around a mature mine complex – 3D Seismic Case History of the Darlot – Centenary Gold Mine

The Darlot-Centenary gold deposit is one of the larger known mineralised systems in the southern end of the West Australian Yandal Greenstone Belt, with an estimated 2.7 Moz having been extracted from the Darlot Centenary Mine since 1988. The area is well explored near surface but given the proven endowment there is potential for significant additional mineralisation at depth. With current proven reserves dwindling, Gold Fields recognised the need to identify a technology to fast-track target generation in order to more rapidly evaluate the nearby rock volume.In August 2016 Gold Fields began investigating the potential for 3D reflection seismic to accelerate evaluation of the rock volume accessible via existing workings. In November 2016 a seismic crew was on ground acquiring approximately 150km3 of 3D seismic data (25km2 surface area x 6km depth). The survey coverage was designed to image the local steeply dipping geology and structures. Processing of the seismic dataset was completed in Q1 2017 and Gold Fields has completed preliminary interpretation of the 3D cube.The seismic data has provided a rich 3D picture of the Darlot structural framework to depth, which could not be obtained by any other geophysical method. It has highlighted a number of features with similar characteristics to known mineralisation and has provided a better defined structural framework that has greatly assisted the fundamental geological understanding and further aided ranking of these targets in terms of prospectivity.

Interpretation of a Permian conjugate basin margin preserved on the outer Northwest Shelf of Australia

The Northwest Shelf (NWS) of Australia is characterized as a series of northeast-southwest trending Mesozoic offshore depocenters which both juxtapose and partially overprint a series of onshore, northwest-southeast trending Palaeozoic basins. An integrated interpretation of well bore data, regional seismic data and plate tectonic models suggests that the Palaeozoic section is also present below the Mesozoic depocenter. Referred to as the East Gondwana Interior Rift, the primary rift axis is oriented in a (present day) NE-SW direction, with orthogonal marginal rift basins such as the onshore Canning and Southern Carnarvon basins. While precise age dating for the formation and stratigraphy of the axial rift is speculative, our integrated interpretation suggests that a significant portion of the pre-existing rift was modified by a Mid-Permian extensional event, forming the Northern Carnarvon basin. Interpretation of recently acquired 3D reflection seismic data suggests that the conjugate basin margin from this Permian rifting event is preserved, and is visible below the Mesozoic section. A series of back-stepping, Late Permian carbonate ramps and banks is interpreted to form on a thermally subsiding rift flank. Our interpretation of these carbonate banks is based primarily on seismic geometries, and is supported by area well control and regional paleogeographic models. This interpretation suggests that a deep marine intra-continental basin bisected the NWS in the Late Permian. Shallow marine conditions then persisted across the conjugate margin through the Triassic and into the Jurassic. After Late Jurassic rifting associated with Gondwanan break-up, the region subsided into deep water.

Integration of 3D reflection seismics and magnetic data for deep platinum mine planning and risk mitigation: a case study from Bushveld Complex, South Africa

Loss-of-ground due to slumping, faulting or replacement of mineral horizons are common problems during mining in the Bushveld Complex, South Africa. Integrating high-resolution aeromagnetic and 3D reflection seismic data to delineate geological features allows for efficient mine planning and risk reduction. We use high-resolution seismic data from the western Bushveld Complex to image slump structures, iron-rich ultramafic pegmatoids (IRUPs), faults, dykes and diapirs that impact the economic horizons (UG-2). The seismic data are able to resolve faults with throws as small as ~10 m. These data reveal a slump structure in the north of the survey area, extending ~5 km along strike and causing up to 1 km of vertical displacement. This region is characterised by strong magnetic anomalies that are interpreted to be associated with IRUPs, as there were no boreholes drilled in this region. The structure is bounded on several sides by faults and IRUPs. Another feature that is better imaged using seismic data is a large-scale fault mapped on surface (locally known as the Chaneng structure). On seismic data, this structure is imaged as a complex fault network in the west of the study area and a region of material flow in the east. Seismic data also show good mapping resolution of dykes due to their close association with faults, which cause displacements on economic horizons. The seismic data are also characterised by disrupted seismic amplitude zones associated with a diapir (~6 km in diameter), which is linked with the upwelling of basement rocks during the emplacement of the complex. This diapir displaces the economic UG-2 horizon at the mining levels by ~0.05 s two-way traveltime or 175 m. This information could be used for future mining planning and design to assess and mitigate the risks posed by these features during mining activities.

A compact multi-plane broadband (0.5-17 keV) spectrometer using a single acid phthalate crystal.

Acid phthalate crystals such as KAP crystals are a method of choice to record x-ray spectra in the soft x-ray regime (E ∼ 1 keV) using the large (001) 2d = 26.63 Å spacing. Reflection from many other planes is possible, and knowledge of the 2d spacing, reflectivity, and resolution for these reflections is necessary to evaluate whether they hinder or help the measurements. Burkhalter et al. [J. Appl. Phys., 52, 4379 (1981)] showed that the (013) reflection has efficiency comparable to the 2nd order reflection (002), and it can overlap the main first order reflection when the crystal bending axis ( b -axis) is contained in the dispersion plane, thus contaminating the main (001) measurement in a convex crystal geometry. We present a novel spectrograph concept that makes these asymmetric reflections helpful by setting the crystal b -axis perpendicular to the dispersion plane. In such a case, asymmetric reflections do not overlap with the main (001) reflection and each reflection can be used as an independent spectrograph. Here we demonstrate an achieved spectral range of 0.8-13 keV with a prototype setup. The detector measurements were reproduced with a 3D ray-tracing code.

Dual mode grating sensor using microring conjugate mirror and plasmonic island

AbstractIn this study, we propose a model for the dual mode gold grating sensor using a microring conjugate mirror (MCM) and the plasmonic island. The sensor measurement of derived quantity is the change in the Bragg wavelength and electron mobility that can be related to the optical phase‐shift or gold grating mobility changes. The plasmonic island consists of the stacked layers of silicon‐graphene‐gold materials. At the resonant condition, the gold electron mobility is driven by the whispering gallery mode generated by the nonlinear microring resonator. Additionally, the 3D reflection power profile of the grating sensor and target source interaction can be formed by the MCM. By selecting the suitable parameters, it can be arranged to have the four‐wave mixing output, which is the criterion of the 3D output of the MRC. The calculation results have shown that there is a relationship between the change in the electron mobility and Bragg wavelength of ~1.5 × 10−21 cm2 V−1 s−1 (mW)−1 at the λ Bragg of 1.55 μm, where the separation of 1 nm is obtained. The related mathematical formulas are re‐arranged for suitable applications.

Efficient Ice-Bath Texturing Route for Multi-Crystalline Silicon Solar Cell Application

To minimize reflection from the flat surface, the multicrystalline silicon (mc-silicon) wafers were textured by low-temperature acid etching technique, which was optimized etching parameters (e.g. temperature and time) in HF-HNO3-H2O system. The textured surfaces and the light trapping property of wafers were analyzed by 3D microscope and reflection spectrum, respectively. It is found the low temperature etching process is more effective in controlling the reaction speed and obtaining favorable textured structure compared with the room temperature etching process. Moreover, the large difference exists for reaction rate affected by temperature with different etching environments. It shows the ice-bath etched wafers give rise to many deep pit textures in a short time, and was good at light trapping. The reflectance is 31% lower than that obtained from the RT etching environment. By ice-bath etching step, we achieved conversion efficiency, open circuit voltage, short circuit and fill factor as high as 17.24%, 0.617V, 8.529A and 0.81, respectively. This work establishes that it is possible to fabricate the multicrystal silicon solar cells of low cost and high efficiency using low-temperature acid etching technique.

Lamellipod Reconstruction by Three-Dimensional Reflection Interference Contrast Nanoscopy (3D-RICN).

There are very few techniques to reconstruct the shape of a cell at nanometric resolution, and those that exist are almost exclusively based on fluorescence, implying limitations due to staining constraints and artifacts. Reflection interference contrast microscopy (RICM), a label-free technique, permits the measurement of nanometric distances between refractive objects. However, its quantitative application to cells has been largely limited due to the complex interferometric pattern caused by multiple reflections on internal or thin structures like lamellipodia. Here we introduce 3D reflection interference contrast nanoscopy, 3D-RICN, which combines information from multiple illumination wavelengths and aperture angles to characterize the lamellipodial region of an adherent cell in terms of its distance from the surface and its thickness. We validate this new method by comparing data obtained on fixed cells imaged with atomic force microscopy and quantitative phase imaging. We show that as expected, cells adhering to micropatterns exhibit a radial symmetry for the lamellipodial thickness. We demonstrate that the substrate-lamellipod distance may be as high as 100 nm. We also show how the method applies to living cells, opening the way for label-free dynamical study of cell structures with nanometric resolution.

Three-dimensional sparse seismic deconvolution based on earth Q model

Abstract We propose a multichannel efficient method for recovery of three-dimensional (3D) reflectivity signal from 3D seismic data. The algorithm consists of solving convex constrained optimization problems that promote the sparsity of the solution. It is formulated so that it fits the earth Q model that describes the attenuation and dispersion propagation effects of reflected waves. At the same time, the method also takes into account the relations between spatially-neighboring traces. These three features together with low computational cost make the proposed method a reliable solution for the emerging need to accurately estimate reflectivity from large volumes of 3D seismic data. We also derive a theoretical bound on the recovery error in the case of horizontal layered sub-terrain. We show that the recovery error is inversely proportional to the number of traces taken into account in the estimation process. Synthetic and real data examples demonstrate the robustness of the proposed technique compared to single-channel recovery.

Post-rift stratigraphic evolution of the Atlantic margin of Namibia and South Africa: Implications for the vertical movements of the margin and the uplift history of the South African Plateau

Abstract The aim of this study is to constrain the post-rift deformations of the Atlantic passive margin of Namibia and South Africa using an extensive industrial 2D reflection seismic dataset calibrated by wells and onshore outcrops that have been revaluated in age (biostratigraphy) in order to discuss the evolution of the South African Plateau uplift. The first-order evolution of the margin is tectonically driven and can be divided into three principal phases. The first (131–93.5 Ma) comprises an overall retrogradational trend that results from a rate of accommodation, created by the thermal flexure of the margin, that is higher than the sediment supply. The second (93.5–66 Ma) comprises an overall aggradational-progradational trend that results from a relative increase in sediment supply due to an uplift and subsequent erosion of the margin and the inland domain. The third (66–0 Ma) is retrogradational again in response to a decrease in sediment supply induced by a relative stability of the margin and climate conditions. This study demonstrates that the present-day configuration of the margin is acquired during the Late Cretaceous (from 81 to 66 Ma) with a strike, long-wavelength and seaward tilt of the margin which could be related to the growth of the onshore main escarpment. We also characterize a regional Oligocene unconformity marked by a significant downward shift of the shoreline which suggests a moderate uplift of the inland domain and could be associated with a reactivation of the relic late Cretaceous relief.

One world. One diverse, evolving geophysical community

In our geophysical community, you might find a technician from a small geophysical company located in a small Oklahoma town who is working in a remote area of China. At the same time, you might find a geophysicist trained in China and Canada who is working on redeveloping an oil field not far from that same small Oklahoma town. In our community, you will see geophysicists around the world who have spent their careers interpreting 3D reflection data and who are now learning to use new technologies, such as machine learning and passive seismology, to improve and guide field development in unconventional plays.