Subsurface Coverage Research Articles

Superior moderate-strength Pd–Pt/Al-based composite tailored for dehydrogenation of perhydroacenaphthene

Pd–Pt-based catalysts are promising for the dehydrogenation of perhydroacenaphthene (PHAN) molecules, yet their effectiveness is hampered by strong adsorption of the product C12H8 and limitations under extreme conditions. Herein, utilizing a relational model involving d-band center, sub-surface coverage, and H atom and C12H8 adsorption energies, the most dehydrogenation-prone crystal facet was identified. Following this, employing Mulliken charge and Sabatier principle, we screened positively charged Pd–Pt/111_O2(Al) surface with moderate interaction strength through the calculation of interaction energy between the chosen Pd–Pt surface and thermally stable MgAl2O4(111) terminal surfaces. Crucially, an extensive examination into reaction mechanisms, microkinetics, and the variation in interaction strength between support and active components at 873.15 K and 3 MPa was conducted. It was observed that the rate-determining step for PHAN molecules on the Pd–Pt/111_O2(Al) surface was C12H19* + * → C12H18* + H*, with a rate of 2.57 × 10-23 s−1. The dehydrogenation of C12H10 to C12H8 proved more favorable than from C12H20 to C12H10, with the latter strengthening support and active components, unlike the weakening effect of the former. This work offers essential foundational support for the development of excellent performance catalysts and the dehydrogenation process of superior heat sink fuels.

Resistivity imaging of river embankments: 3D effects due to varying water levels in tidal rivers

AbstractElectrical resistivity tomography (ERT) has seen increased use in the monitoring the condition of river embankments, due to its spatial subsurface coverage, sensitivity to changes in internal states, such as moisture content, and ability to identify seepage and other erosional process with time‐lapse ERT. Two‐dimensional ERT surveys are commonly used due to time and site constraints, but they are often sensitive to features of anomalous resistivity proximal to the survey line, which can distort the resultant inversion as a three‐dimensional (3D) effect. In a tidal embankment, these 3D effects may result from changing water levels and river water salinities. ERT monitoring data at Hadleigh Marsh, UK, showed potential evidence of 3D effects from local water bodies. Synthetic modelling was used to quantify potential 3D effects on tidal embankments. The modelling shows that a 3D effect in a tidal environment occurs (for the geometries studied) when surveys are undertaken at high water levels and at distances less than 4.5 m from the electrode array with 1 m spacing. The 3D effect in the modelling is enhanced in brackish waters, which are common in tidal environments, and with larger electrode spacing. Different geologies, river water compositions, and proximities to the model parameters are expected to induce a varied 3D effect on the ERT data in terms of magnitude, and these should be considered when surveying to minimize artefacts in the data. This research highlights the importance of appropriate geoelectrical measurement design for tidal embankment characterization, particularly with proximal and saline water bodies.

A new joint reverse time migration method to improve vertical seismic profile image quality

Vertical seismic profile (VSP) data have the advantage of higher data quality than surface seismic data. Using VSP data has become a powerful technology to achieve accurate recognition of fine structures. Conventional VSP seismic migration methods mainly use up-going waves (reflection waves) for imaging and often treat down-going waves (multiple waves) as a kind of noise to be suppressed and eliminated. The up-going waves (reflection waves) only provide a narrow subsurface coverage near the receiver well. However, the down-going waves (multiple waves) also carry underground medium information and can provide much wider subsurface illumination than the up-going waves (reflection waves). The imaging quality can be improved by using reflection and multiple waves simultaneously. Therefore, we developed a new joint reverse time migration (JRTM) method to use both the up-going and down-going waves simultaneously based on the mirror principle. The up- and down-going data can be simultaneously placed at the reflection positions and mirror reflection positions as the boundary conditions and initial conditions for wavefield reverse time extrapolation. Some numerical examples from the graben, the modified Marmousi, and the modified HESS models show that the proposed new JRTM method can jointly use and image multiple and reflection waves simultaneously. In addition, the newly proposed JRTM method also has a higher imaging quality than reflection wave migration and multiple wave migration from VSP data in complex structures. High-quality imaging results from our proposed JRTM can be further used to improve the accuracy of subsequent oil and gas reservoir characterization and seismic inversion of VSP data.

Mirror reverse time migration using vertical cable seismic data for methane hydrate exploration

Gas hydrates are located in the permafrost and in deepwater shallow sediments, where low temperature and high pressure satisfy the stability conditions of methane clathrates to remain as solid compounds. Hydrates are found in a form of fine-layered or altered-layered structure with hiatuses and necessitate high-resolution surveys, which may not be achieved by conventional marine acquisition using towed streamers. We have developed a recent case study in which the vertical cable seismic (VCS) method has been used for high-resolution subseafloor imaging using a set of buoyed vertical-arrayed receivers that are anchored to the seafloor. The observation close to the target in the deepwater environment provides a higher signal-to-noise ratio and higher resolution. The primary reflections, however, could not achieve reliable depth images in the data processing due to their limited subsurface coverage. We used a reverse time migration (RTM) implementation of mirror imaging to extend the spatial subsurface coverage by using receiver ghost reflections. Because conventional velocity analysis methods are not applicable to the VCS survey due to the asymmetrical reflection path between the source and receiver, we implemented seismic interferometry and generated virtual surface seismic data from VCS data for velocity analysis. To preserve the resolution, amplitudes, and phase characteristics, we applied mirror RTM on the ghost reflections in the original VCS data rather than imaging the virtual data. The introduced case study using a VCS survey for identifying the methane hydrate system of the Umitaka Spur in the Sea of Japan led to high-resolution images, which suggest that a large gas chimney exists beneath a pockmark and is responsible for transferring methane gas from a deep hydrocarbon source to the shallow sediments. A bottom-simulating reflector as the base of the gas hydrate stability zone was also imaged.

Hydrocarbon exploration by optimal cross spread techniques, and permit problems in Nigeria, semblances in Sudan, Ethiopia

One sure method for hydrocarbon exploration is the use of orthogonal geometries, in cross spread techniques. The configuration is based on consistent orthogonal pattern of both receiver lines and source lines. In areas where infrastructural facilities abound and interfere with seismic lines as obstacles, suitable designs of offsets, laminar or lateral types are employed to bypass the obstacles. The angle of excursion of the skirting from the main seismic line should be between17° and 34°. Around the intersection of lines with obstacles a skirting designed about the structure will maintain the source or receiver line spacing in multiples of the original line spacing. Densification of sources are used to recover the near-offset shots and near-mid offsets shots to upgrade the subsurface coverage that will compensate for the gap created by the omission of the obstacles. Compensation source line offsets, are designed as “skirting” around obstacles. This may result in drop in multiplicity or “fold of coverage “due to loss of Nears- and Near-mid CDP bins. Permit problems from host communities to the recording data acquisition is notable in this technique. The severity of the challenges partly varies with the extent of negative impact to the host communities or environment. Certain exploration activities adversely impact on the host communities and their sources of livelihood. The situation was different and in Ethiopia some years ago due to stiff opposition of the Ogaden basin youths in the coastal Somalian Region to Ethiopian Federal Government efforts on hydrocarbon exploration and development.Keywords: Orthogonal lines, skirting, permit problems

Design, modelling and imaging of marine seismic swarm surveys

ABSTRACTAutonomous marine vehicles instrumented with seismic sensors allow for new efficient seismic survey designs. One such design is the swarm survey, where a group, or swarm, of slow moving autonomous marine vehicles record seismic data from shots fired by a source vessel sailing around circles within the swarm. The size of the swarm is dictated by the maximum offset requirement of the survey, and it can be shaped to acquire wide‐ and full‐azimuth data. The swarm survey design equation describes the relationship between the source and receiver positions of the survey and the subsurface coverage or fold. It is used to adapt the swarm to the seismic survey requirements and to calculate survey duration time estimates as function of available equipment. It is shown that a survey conducted by a slowly moving swarm requires six times fewer shots than an equivalent seabed node survey conducted over 85.5 km2. Swarm surveys can also be adapted to efficiently conduct infill surveys and replace multi‐vessel undershoots. The efficiency of the survey can further be increased when the autonomous marine vehicles are towing short streamers with multiple receivers. Synthetic tests show that the seismic images for swarm surveys are comparable to those from streamer surveys, while little variation in image quality is found when reducing the number of autonomous marine vehicles but equipping them with a short streamer with multiple receivers.

Hydrostatic pressure effects on the kinetic parameters of hydrogen evolution and permeation in Armco iron

Armco iron samples are exposed to pressures of 0.1–30MPa to study hydrogen permeation during potentiostatic charging. Elecrochemical impedance spectroscopy (EIS) is performed to analyze the electrode/electrolyte interface reaction. According to EIS and first-principles calculations, the hydrostatic pressure decreases the distance between the adsorbed hydrogen atoms and the sample surface, which induces hydrogen atom diffusion into the subsurface by decreasing the diffusion barrier energy. Under high pressure, hydrogen molecules gather at the sample entry side and inhibit the hydrogen recombination reaction. Thus, the amount of adsorbed hydrogen and the hydrogen subsurface coverage increase.

Optimizing Acquisition Geometry in Shallow Gas Cloud Using Particle Swarm Optimization Approach

Many hydrocarbon explorations in mature fields have been severely affected by complex and overburdening issues, such as shallow gas accumulation, gas pockets, and gas seepage. In this work, a new forward modelling technique is proposed in evaluating the potential survey design for fields affected by shallow gas cloud. In recent years, the implementation of innovative acquisition layouts has been producing significantly better seismic images, especially in the low illumination subsurface area. However, the uncertainty of the effectiveness in new acquisition design subsurface coverage always become a major stumbling block. To overcome this constraint, an optimization approach is suggested through the smart source and receiver location arrangement on the surface, with significant alignment to the conventional source and receiver arrangement approach. The particle swarm optimization (PSO) method is used to find the source-receiver configuration with maximum subsurface illumination coverage for the gas affected field situated in Malaysia Basin. Implementation of the PSO algorithm requires both a velocity model building process and wave field extrapolation from a target reflector to the surface level. The wave field data then was used to simulate receiver optimization outputs which eventually determined the subsurface illumination coverage. The results from the new optimization method for both synthetic model and Malaysia Basin data, offer a greater understanding of the consequences of obstacles caused by shallow anomalies with respect to seismic acquisition, data processing, and interpretation.

Experimental Elucidation of the Oxygen Reduction Volcano in Base on a Pt Alloy Single Crystal

It is of fundamental importance to understand the factors controlling trends in activity for electrocatalytic reactions as a function of pH. In the case of the oxygen reduction reaction, numerous reports suggest significant divergences between noble metals surface catalytic performances in acid and base.[1,2] In our earlier studies, we mapped out the experimental Sabatier volcano for the oxygen reduction reaction in 0.1 M HClO4 using the Cu/Pt(111) near-surface alloy system, see Figure 1 for near-surface alloy schematic.[3,4] In this study, as those of [3,4], we found that by changing the subsurface coverage of Cu we could tune the surface binding of the key reaction intermediate, OH; we thus monitored the OH binding energy shift through the observable shifts in the base voltammograms in both acidic and alkaline media. Further, we elucidate the experimental oxygen reduction volcano in 0.1 M KOH for the Cu/Pt(111) near-surface alloy system. Remarkably, we observe that the same trend persists between OH binding shifts and Cu/Pt(111) oxygen reduction activities between acid and alkaline electrolyte, with the optimum catalyst in alkaline exhibiting an 8-fold improvement in activity, relative to Pt(111). However, all surfaces show a ~4 fold improvement in activity in 0.1 M KOH, relative to the same surface in 0.1 M HClO4. At the peak of the volcano the surface exhibits an exceptionally high specific activity of 90 mA/cm2 at 0.9 V with respect to the reversible hydrogen electrode. Thus, our results confirm that OH binding energy is the key descriptor in both alkaline and acid electrolytes. [1] R. Rizo, E. Herrero, J. M. Feliu, Phys. Chem. Chem. Phys. 2013, 15, 15416–25. [2] J. Staszak-Jirkovský, R. Subbaraman, D. Strmcnik, K. L. Harrison, C. E. Diesendruck, R. Assary, O. Frank, L. Kobr, G. K. H. Wiberg, B. Genorio, et al., ACS Catal. 2015, 5, 6600–6607. [3] I. E. L. Stephens, A. S. Bondarenko, F. J. Perez-alonso, F. Calle-vallejo, L. Bech, T. P. Johansson, A. K. Jepsen, R. Frydendal, B. P. Knudsen, J. Rossmeisl, et al., 2011, 5485–5491. [4] A. S. Bondarenko, I. E. L. Stephens, I. Chorkendorff, Electrochem. commun. 2012, 23, 33–36. Figure 1

Multichannel 3D Ground Penetrating Radar - Advances in Civil Infrastructure Scanning

The scope of this paper is to highlight improvements in Ground Penetrating Radar (GPR) as an infrastructure condition assessment tool, in particular through the use of multichannel 3D GPR. Multichannel 3D GPR is a relatively new and alternative infrastructure scanning tool which can assist geophysicists and engineers in providing 100% sub-surface coverage of an investigation area, where site access is possible. Advantages of an increased level of subsurface coverage using multichannel 3D GPR includes providing the user with improved accuracy in highlighting and quantifying regions that may require further invasive testing for future maintenance programs and also possible long-term monitoring. This paper briefly discusses current applications of standard GPR for infrastructure condition assessments and how multichannel 3D GPR can improve knowledge of the sub-surface in these application areas. Visualisations of multichannel 3D GPR data outputs with interpretations have been presented to illustrate the improved subsurface information made available from this method. The example presented is an approximately 4 m long section of multichannel 3D GPR data acquired along the surface of a reinforced concrete-lined tunnel.

Imaging primaries and high-order multiples for permanent reservoir monitoring: Application to Jubarte field

A superior depth-migration solution that uses all the recorded data, including primaries and all orders of multiples, can be adapted from towed-streamer acquisition to ocean-bottom cable (OBC) or ocean-bottom node (OBN) acquisition. The technology has been validated using the 3D/4D data sets acquired by Petrobras for the deepwater Jubarte PRM pilot in Campos Basin. Images constructed from primaries and all orders of sea-surface reflections shows improved subsurface coverage when compared with images from primaries alone and/or mirror migration. The resulting 4D signal also shows a good match with the well trajectory, validating the use of this novel technology for 4D imaging studies.

Super-Virtual Refraction Interferometric Redatuming: Enhancing the Refracted Energy

onshore seismic data processing. Refraction tomography is becoming a common way to estimate an accurate near surface velocity model. One of the problems with refraction tomography is the low signal to noise ration in far offset data. To improve, we propose using refraction interferometry to enhance the weak energy at far offsets. We use Interferometric Green's functions to redatum sources by cross-correlating two traces recorded at receiver stations, A and B, from a source at location W. The result is a redatumed trace with a source at A and a receiver at B, which can also be obtained by correlating two traces recorded at A and B from different shots. Stacking them would enhance the signal-to-noise ratio of this virtual trace. We next augment redatuming with convolution and stacking. The trace recorded at B from a source at A is convolved with the original trace recorded at A from a source at W. The result is a super-virtual trace at B in the far-offset from a source at W. Stacking N traces gives a vN-improvement. We applied our method to noisy synthetic and field data recorded over a complex near-surface and we could pick more traces at far offsets. It was possible to accommodate more picks resulting in a better subsurface coverage

3D seismic imaging over two structurally complex surveys in the foothills of Pakistan

In a tectonically complex area of northwest Pakistan, MOL Pakistan and its partners acquired two 3D seismic surveys. Extreme topography led to irregular shooting geometry. Varied surface access over this terrain required a mix of Vibroseis and dynamite source types to maximize subsurface coverage. With the combination of difficult surface conditions over a structurally complex subsurface, the data processing and merging of these two surveys required close attention to detail throughout the processing sequence, and we had to rely on the most robust algorithms in the data processing toolkit. There was no single technology that stood out in the processing, but by taking care at every stage in the processing sequence we were able to produce a readily interpretable seismic volume.

Everyday misadventures of the everyman of interpretation

To almost every geophysicist CDP means common depth point and calls to mind concepts such as subsurface coverage, fold, move-out and stacking. From that initial thought some geophysicists might go on to contemplate and compare the different meanings of CDP CMP (common midpoint) and CRP (common reflection point)—but at Sam's company, CDP has a much broader and entirely nongeophysical significance, because it stands for Corporate Development Program. This is the fully integrated process through which the company identifies, educates and in general grooms successful candidates for careers in the upper echelons of the organization. It has been said that in Sam's company, no one advances beyond the level of team leader (a management entry-level position) without having scored very highly in the initial testing phase of the CDP.

Chemical Environment Effects on the Atomic Oxygen Absorption into Pt(111) Subsurfaces

Density functional theory is used to study chemical environment effects such as surface coverage of oxygenated species and presence of adsorbed oxygen reduction intermediate OH and water on the atomic oxygen absorption process into Pt(111) subsurfaces. The results show that increasing the on-surface oxygen coverage can energetically and kinetically stabilize subsurface atomic oxygen present at 0.11 and 0.25 monolayer subsurface coverage. At constant subsurface coverage, the absorption energy barrier increases with increasing on-surface coverage. Adsorbed on-surface OH has similar effects on the atomic oxygen absorption process as those caused by on-surface adsorbed atomic oxygen. A monolayer of water over the on-surface oxygen does not significantly alter the thermodynamics and kinetics of the oxygen absorption process.

3D baseline seismics at Ketzin, Germany: The C O2 SINK project

A 3D 25-fold seismic survey with a bin size of 12 by [Formula: see text] and about [Formula: see text] of subsurface coverage was acquired in 2005 near a former natural gas storage site west of Berlin, as part of the five-year EU funded [Formula: see text] project. Main objectives of the seismic survey were to verify earlier geologic interpretations of structure based on vintage 2D seismic and borehole data and to map, if possible, the reservoir pathways in which the [Formula: see text] will be injected at [Formula: see text] depth, as well as providing a baseline for future seismic surveys and planning of drilling operations. The uppermost [Formula: see text] are well imaged and show an anticlinal structure with an east-west striking central graben on its top that extendsdown to the target horizon. About [Formula: see text] of throwis seen on the bounding faults. No faults are imaged near the planned drill sites. Remnant gas, cushion and residual gas, is present near the top of the anticline in the depth interval of about [Formula: see text] and has a clear seismic signature; both higher amplitudes in the reservoir horizons and velocity pulldown are observed. Amplitude mapping of these remnant gas horizons shows that they do not extend as far south as the injection site, which is located on the southern flank of the anticline. Amplitude anomalies, gas chimneys along an east-west striking fault, show that the stored or remnant gas either has been or is presently migrating out of the reservoir formations. Summed amplitude mapping of the planned injection horizon indicates that this lithologically heterogeneous formation may be more porous at the injection site.

Absorption of Atomic Oxygen into Subsurfaces of Pt(100) and Pt(111): Density Functional Theory Study

Density functional theory is used to examine binding energies and the most stable sites of atomic oxygen adsorbed on Pt(111) and Pt(100) surfaces as a function of surface coverage, as well as to evaluate the absorption energies and the energetically most favorable sites of atomic oxygen located in the subsurface, as a function of subsurface coverage. Based on the absorption energies, it is found that the tetrahedral site underneath the hcp hollow site is energetically the most favorable site to absorb atomic oxygen in the subsurface of Pt(111), and the tetrahedral site underneath the bridge site is the corresponding energetically most favorable subsurface site in Pt(100) cells. Minimum energy paths identified for the diffusion of low-coverage adsorbed atomic oxygen into the subsurface sites for Pt(111) and Pt(100) cells indicate the existence of high kinetic barriers to such diffusion.

Migration methods for imaging different‐order multiples

ABSTRACTMultiples contain valuable information about the subsurface, and if properly migrated can provide a wider illumination of the subsurface compared to imaging with VSP primary reflections. In this paper we review three different methods for migrating multiples. The first method is model‐based, and it is more sensitive to velocity errors than primary migration; the second method uses a semi‐natural Green's function for migrating multiples, where part of the traveltimes are computed from the velocity model, and part of the traveltimes (i.e., natural traveltimes) are picked from the data to construct the imaging condition for multiples; the third method uses cross‐correlation of traces. The last two methods are preferred in the sense that they are significantly less sensitive to velocity errors and statics because they use “natural data” to construct part of the migration imaging conditions. Compared with the interferometric (i.e., crosscorrelation) imaging method the semi‐natural Green's function method is more computationally efficient and is sometimes less prone to migration artifacts.Numerical tests with 2‐D and 3‐D VSP data show that a wider subsurface coverage, higher‐fold and more balanced illumination of the subsurface can be achieved with multiple migration compared with migration of primary reflections only. However, there can be strong interference from multiples with different orders or primaries when multiples of high order are migrated. One possible solution is to filter primaries and different orders of multiples before migration, and another possible solution is least squares migration of all events. A limitation of multiple migration is encountered for subsalt imaging. Here, the multiples must pass through the salt body more than twice, which amplifies the distortion of the image.

Using dual-azimuth data to image below salt domes

In complex geological areas, subsurface illumination is largely determined by the acquisition geometry. More recently, multi-azimuth and wide-azimuth surveys are increasingly being used to maximize subsurface coverage, but these can present new challenges; for example, how to combine the images from different azimuths into a single migrated image for use by the interpreter. Traditionally, the common practice is to ignore potential azimuthal velocity variations and build a single vertical velocity model, in some cases incorporating VTI anisotropy. Data from different azimuths are pre-stack migrated separately, but with a single velocity model usually derived from one azimuth, and then combined into a single image after application of residual move-out corrections. We present a case history of building a single velocity model for pre-stack depth migration of dual-azimuth data in the southern North Sea. The dual-azimuth data gave us enhanced illumination of the target zone, but somewhat to our surprise, it also showed strong azimuthal velocity variations in the overburden. We devised a methodology and built a single velocity model that incorporated these azimuthal velocity variations so that all events are migrated to their correct position. When the data sets are combined, primary events are reinforced while noise cancels out to give one optimal data set.

Portable dense geophone array for shallow and very shallow 3D seismic reflection surveying: Part 2—3D imaging tests

In part I of this paper we demonstrate how the use of a portable dense geophone array increases S/N ratio and the ability to record faint near‐surface reflections. The dense array can also be used as an approximate acoustical lens with appropriate prestack imaging techniques, similar to those used in medical imaging and nondestructive testing. Such use of the array provides flexibility when imaging with sparse shot distributions and improves the overall resolution of the array. We show how, with prestack focusing, one can extend the subsurface coverage beyond conventional common‐midpoint (CMP) coverage. We study optimal imaging configurations and show that although the effective aperture of the array is reduced when focusing off‐center targets, we can still image small targets adequately. Maximum aperture and therefore best target definition occur when the source and geophone arrays are on top of the target. Both synthetic and field results show that the limited‐aperture array can image very small targets with resolution of 0.25 m in three dimensions. We also demonstrate that different acquisition geometries should be used when imaging continuous geological targets versus small point diffractors.