Onshore Seismic Data Research Articles

Trends in onshore seismic data acquisition: a case study on cable-free nodal systems

The desire to conduct onshore seismic surveys without cables has been an elusive dream since the dawn of seismic exploration. Since the late 1970s, seismic surveys were conducted with cabled multi-channels acquisition systems. As the number of channels steadily grew, a fundamental restriction appeared with hundreds of kilometres of line cables dragged on the ground. Seismic surveys within rugged terrain—across rivers, steep cliffs, urban areas, and culturally and environmentally sensitive zones—were both challenging and expansive exercises. Modern technology has made different cable-free solutions practical. High-resolution analogue to digital converters are now affordable, as are GPS radios for timing and location. Microprocessors and memory are readily available for autonomous recording systems, along with a battery the size and weight of a field nodal now promising to power an acquisition unit for as long as required for normal seismic crew operations. Many successful 2D and 3D seismic data acquisition using cable-free autonomous nodal systems were attempted in the past few years; however, there remain a number of concerns with these systems. The first concern queries whether the units are working according to manufacturer specifications during the data acquisition window. The second is the limited or no real-time data quality control that inspires sceptics to use the term blind acquisition to nodal operations. The third is the traditional question of geophone array versus point receiver acquisition. Although a string of the geophone can be connected to autonomous nodes, the preference is to deploy a single or internal geophone with the nodes to maintain the proposed flexibility of cable-free recording systems. This case study elaborates on the benefits of the cable-free seismic surveys, with specific examples of 2D and 3D exploration programs conducted in Australia in the past few years. Optimisation of field crew size, field crew resources, cost implications, and footprint to the environment, wildlife and domestic livestock will be discussed. In addition, the study focuses on the data quality/data assurance and the processes implanted during data acquisition to maintain equivalent industry standards to cable recording. Emphases will also include data analysis and test results of the geophone array versus the cable-free point receiver recording.

SAHKE seismic‐scatter imaging of subduction beneath Wellington, North Island, New Zealand

AbstractScattering reflectivity analysis of onshore seismic data (Seismic Array HiKurangi Experiment) images slab geometry and crustal structure at a geodetically locked subduction boundary. A broad seismic scattering zone (BSZ) up to 10 km thick above the subduction interface at depths of 16–30 km has seismic properties (Vp, Vp/Vs, and Q) that imply high fluid pressures, probably associated with underplated sediments. The listric strike‐slip Wairarapa Fault and other splay faults that sole into the BSZ imply long‐term weakness. High rates of intraslab seismicity with low rates above the slab imply stress decoupling across the BSZ. Association of high fluid pressures and long‐term weakness with geodetic locking is in contrast to similar observations at zones of slow slip at the northern Hikurangi margin and suggest that either (1) pore fluid pressure or locking behavior may cycle over times longer than two decades or (2) local material properties play a significant role in determining if slow slip or locking occurs.

Application of the Frequency-Wave Number (F-K) and the Radial Trace Transform (RTT) in the Attenuation of Coherent Noise in Onshore Seismic Data

Application of the Frequency-Wave Number (F-K) and the Radial Trace Transform (RTT) in the Attenuation of Coherent Noise in Onshore Seismic Data

Laplace-Fourier-domain elastic full-waveform inversion using time-domain modeling

To obtain subsurface information from onshore seismic exploration data using full-waveform inversion (FWI) based on the acoustic wave equation, elastic waves, such as ground roll and mode-converted waves, should be suppressed through heavy preprocessing. However, such preprocessing deforms not only the elastic waves but also the acoustic waves. Moreover, it is not easy to separate body waves from surface waves in seismic traces. For these reasons, we need to generate both types of waves in the modeling step to obtain seismic waves that are similar to real seismic waves. Therefore, elastic FWI using the elastic wave equation is necessary to achieve a more accurate FWI. In addition, elastic FWI can provide better geologic information than acoustic FWI because it inverts the P-wave velocity, S-wave velocity, and density. Laplace-Fourier-domain elastic FWI is an effective method because it inverts these multiple parameters and can be applied to real seismic data that lack low-frequency components. However, the conventional Laplace-Fourier-domain FWI requires a matrix solver with a huge memory cost to perform the modeling in the Laplace-Fourier-domain, and memory usage becomes more intensive in the elastic case. In the present study, we combined time-domain wave propagation modeling and Laplace-Fourier-domain elastic FWI to invert multiple parameters with less memory cost. By using time-domain modeling, which does not require a matrix solver, we obtained the forward and adjoint wavefields with less memory cost. The residuals between the recorded and modeled data, the virtual sources, the Hessian matrices, and the gradient directions were calculated in the Laplace-Fourier domain. To validate the proposed algorithm, we performed numerical tests with Model 94 synthetic data and Benjamin Creek real seismic data.

Special Issue on Challenges of Earthquake Forecast Research Illuminated by the 2011 Tohoku-Oki Earthquake

The 2011 off the Pacific coast of Tohoku Earthquake, hereafter referred to as Tohoku-Oki earthquake, occurring off northeastern Japan’s Pacific coast on March 11, 2011 had a moment magnitude of 9.0 and generated a tsunami responsible for most of the deaths of the event’s 19,000 victims. Identifying scientifically what happened before, on, and after March 11 is one starting point for a discussion on how to reduce casualties and mitigate the impact of such natural disasters. The 14 papers in this special issue cover incidents related to pre-, co- and post-seismic phenomena, including volcanoes. Three papers discuss why and how such a large quake occurred. Three more papers go into the implications of short- and long-term crustal deformations seen in northeastern Japan. Four papers detail short- and long-term phenomena leading to the Tohoku-Oki quake. Two papers discuss real-time tsunami forecasting based on off-shore and on-shore geodetic, seismic and tsunami observation data. The last two papers explore the effects of the 2011 temblor on volcanic phenomena. The magnitude 9.0 produced in the 2011 event is the largest historically recorded in Japan and may not necessarily have been anticipated beforehand, and the generation mechanism behind such a gigantic occurrence is not yet completely understood. Even so, preparations should be made for such earthquakes in other parts of Japan and in other countries. The Nankai trough is an example of areas that require our attention. A national project for observation and study for earthquake prediction is now being integrated into a new program, Earthquake and Volcano Hazards Observation and Research Program (2014-2019). Studies presented in this special issue are also being supported in part by this program. We are certain that readers will find that this special issue will contribute much to our understanding of gigantic earthquakes and at least some of the measure to be taken in preparation for such natural phenomena. Finally, we extend our sincere thanks to all of the contributors and reviewers involved with these articles.

Maximising safety and environmental performance during onshore seismic acquisition using cable-less technology

Recent advances in the acquisition of onshore seismic data without cables have greatly reduced impacts on environmental and heritage values and increased recording efficiency. Onshore oil and gas exploration has expanded significantly across Australia. As a result, the need to gather quality data while reducing the environmental, social, and safety impacts of the activities has driven innovation in exploration technologies. In WA, exploration permits are granted for areas that include privately held farm land, pastoral leases or unallocated crown land. This can result in tensions between exploration companies, their contractors, and land holders. Cable-less seismic data acquisition systems provide significant opportunities to reduce the environmental, community, and safety impacts. Cable-less systems typically require significantly fewer trips along the acquisition line, considerably reducing the likelihood of negative impacts on plants, animals, and soils in the area. Other benefits include reducing fuel consumption, vehicle and traffic movement and the risk of injury to the seismic crew associated with the deployment of cables. This extended abstract reviews the recent use of a cable-less system for Fleet Resources’ seismic acquisition conducted by Terrex Seismic in the Carnarvon Basin, WA, demonstrating the environmental, social, and safety benefits compared with traditional cabled systems for both 3D and 2D seismic programs. This extended abstract also draws on the experiences of Terrex’s use of the technology on behalf of UIL Energy and it explores the opportunities for capturing these benefits during the preparation of environmental and safety plans for regulatory approval.

MODELING WORKFLOW FOR DISTRIBUTION OF SEISMIC WAVES VELOCITIES IN THE CENTRAL PART OF DNIEPER-DONETS BASIN

In order to provide more detailed understanding for distribution of seismic velocities in central, most prospective for petroleum exploration, part of Dnieper-Donets Basin (DDB) a velocity model incorporating well VSP and onshore seismic data was built.

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

Seismic investigations of buried tunnel valleys on- and offshore Denmark

Abstract Tunnel valleys on- and offshore Denmark have been investigated based on a database of 1000 km two-dimensional (2D) onshore seismic data, 5600 km 2D offshore seismic data and 1200 km 2 three-dimensional (3D) offshore seismic data. From the 2D data we identified 216 onshore and 674 offshore seismic tunnel valley intersections, and 55 individual valleys were identified from three 3D surveys. The majority of the valleys have depths ranging from 50 to 200 m and widths between 500 and 1500 m. Up to seven generations of tunnel valleys were identified, indicating repeated erosion and deposition within the study area. The valleys were most likely formed by subglacial meltwater erosion during the last three glaciations. Statistical analyses conducted on the data show that there are no significant differences between the onshore and offshore valleys with respect to their depth and shape; they share morphological and structural characteristics. The onshore seismic data have been analysed in conjunction with lithological information from boreholes. The analyses show that tunnel valley bottoms terminate equally commonly in substrates dominated by clay and sand, and that the valley shapes are similar for the two substrates.

High-resolution seismic attenuation imaging from wide-aperture onshore data by visco-acoustic frequency-domain full-waveform inversion

SUMMARY Here we assess the potential of the visco-acoustic frequency domain full-waveform inversion (FWI) to reconstruct P-wave velocity (VP) and P-wave attenuation factor (Q) from surface onshore seismic data. First, we perform a sensitivity analysis of the FWI based upon a grid search analysis of the misfit function and several synthetic FWI examples using velocity and Q models of increasing complexity. Subsequently, we applied both the acoustic and viscoacousticFWItorealsurfacewide-apertureonshoreseismicdatafromthePolishBasin,wherea strongattenuationoftheseismicdataisobserved.Thesensitivityanalysisofthevisco-acoustic FWI suggests that the FWI can jointly reconstruct the velocity and the attenuation factor if the signatureoftheattenuationissufficientlystronginthedata.Asyntheticexamplecorresponding to a homogeneous background model with an inclusion shows a reliable reconstruction of VP and Q in the inclusion, when Q is as small as 90 and 50 in the background model and in the inclusion, respectively. A first application of acoustic FWI to real data shows that a heuristic normalization of the data with offset allows us to compensate for the effect of the attenuation in the data and reconstruct a reliable velocity model. Alternatively, we show that visco-acoustic FWI allows us to reconstruct jointly both a reliable velocity model and a Q model from the true-amplitude data. We propose a pragmatical approach based upon seismic modelling and source wavelet estimation to infer the best starting homogeneous Q model for visco-acoustic FWI. We find the source wavelet estimation quite sensitive to the quality of the velocity and attenuation models used for the estimation. For example, source-to-source wavelets are significantly more consistent when computed in the final FWI model than in the initial one. A good kinematic and amplitude match between the early-arriving phases of the real and time-domain synthetic seismograms computed in the final FWI model provides an additional evidence of the reliability of the final FWI model. We find the recovered velocity and attenuation models consistent with the expected lithology and stratigraphy in the study area. We link high-attenuation zones with the increased clay content and the presence of the mineralized fluids.

The use of seismic interpretation for delineating the characteristic features of Messinian channels in the north Nile Delta, Egypt

Abu Madi Messinian Formation occupied a prominent issue as the most exploratory target in the search for natural gas in the Nile Delta. Interpretation of the available onshore seismic reflection data of the northeastern part of the Nile Delta reveals that there is a series of troughs, depressions, and mounded structures within the Abu Madi Formation (Messinian time). Onlap, downlap, and truncation relationship of reflections were observed very close to fault locations in the Miocene time. Many channels have been imaged clearly and described on the seismic reflection data of the onshore Nile Delta. The depths to these channels range between 2.5 s in the southeast to 3.1 s (t.w.t.) while their width ranges from 1 km to more than 5 km. These channels were formed by two factors: (1) submarine erosion and redeposition, during the relative sea level falls and (2) tectonic effect. Many of these channels followed more or less the trends of the historic branches of the ancient Nile Delta. The classification of these channels is based on some factors: (1) channel morphology (depth and width), (2) channel shape, and (3) tectonic effect.

Near-surface P-velocity modelling by integrated seismic, EM, and gravity data: examples from the Middle East

Onshore seismic data from the Middle East and around the world are adversely affected by near-surface velocity anomalies. Shallow-section velocity characterization represents a key issue for land data processing in both time and depth domains. In the Middle East, near-surface complexity can be attributed to sand dunes, wadies, sabkha environment, shallow high-velocity layers (carbonate outcrops), karsting, and fractured layers. The correct estimate of the near-surface velocity field is fundamental to obtain reliable seismic images. Conventional workflows for near-surface model building often involve interpreting and inverting refracted arrival information. These methods may fail to appropriately reconstruct the shallow velocity complexities in the presence of large velocity inversions, rapid lateral velocity changes, and noisy refracted arrival data. The combination of additional geophysical measurements (i.e., non-seismic), not influenced by the problems affecting seismic propagation, are needed to address the shallow velocity modelling problem. This paper describes three different approaches recently applied in distinctly different environments around the Middle East to solve near-surface modelling problems. The first example from the United Arab Emirates (UAE) demonstrates the integration of seismic and time-domain electromagnetics (TDEM) for sand dune statics application. The second example from Saudi Arabia also addresses sand dune statics, but this time by simultaneous joint inversion (JI) of seismic and gravity measurements. The final example applies the simultaneous JI technique for the near-surface velocity component of a depth migration model.

Assessment and compensation of inconsistent coupling conditions in point‐receiver land seismic data

ABSTRACTWe introduce a method to detect and compensate for inconsistent coupling conditions that arise during onshore seismic data acquisitions. The reflected seismic signals, the surface waves, or the ambient‐noise records can be used for the evaluation of the different coupling conditions of closely spaced geophones. We derive frequency‐dependent correction operators using a parametric approach based upon a simple model of the interaction between geophone and soil. The redundancy of the measurements available permits verification of the assumptions made on the input signals in order to derive the method and to assess the validity of the model used. The method requires point‐receiver data in which the signals recorded by the individual geophones are digitized.We have verified the accuracy of the method by applying it to multicomponent ambient‐noise records acquired during a field experiment in which the coupling conditions were controlled and modified during different phases of the experiment. We also applied the method to field data, which were acquired without the coupling conditions being controlled, and found that only a few geophones showed an anomalous behaviour. It was also found that the length of the noise records routinely acquired during commercial surveys is too short to provide enough statistics for the application of our method.

Mapping the Moho beneath the Southern Alps continent‐continent collision, New Zealand, using wide‐angle reflections

A wide‐angle stack using all onshore‐offshore, and onshore seismic data from the SIGHT'96 experiment provides a direct three‐dimensional (3‐D) image of the Moho below the continental collision zone through the South Island of New Zealand. A bright reflector sequence (up to 4 s thick), the base of which coincides with the PmP modeled Moho, extends throughout most of the lower crust and bends downward asymmetrically beneath the Southern Alps. The crustal root reaches a maximum depth at ∼15 s (45 km), beneath the regional (−80 mGal) Bouguer gravity low and is flanked east and west by shallower Moho where the average crustal thickness is ∼20 km. The 3‐D structure of the crustal root in the central South island is moderately well resolved by the SIGHT'96 experiment.

ABSTRACT: Seismic Visualization of Subtle Fault/Fracture Zones in Carbonate Reservoirs: Two Case Studies (Fahud - Oman and Waterton - Canada)

One of the key elements in unravelling the structural geometry of carbonate reservoirs is the analysis of seismic data. This poster is compiled primarily to give an insight in the visualization techniques used to highlight fault/fracture patterns. Secondly a work around is given to solve the problems encountered with data management between the different software packages used in the studies. The two case studies discussed are both part of separate multi-disciplinary asset studies carried out in the Shell International Carbonate Development team in Rijswijk. The first study (carried out in the first half 2000) focussed on the Upper Cretaceous Natih E reservoir of the Fahud oil field in Oman. The shallow onshore seismic data suffered from severe noise and quality loss due to amongst others soft overburden. The second study, which is still under evaluation, is carried out on the pre-stacked imaged seismic data in the foothills of the Rocky Mountains in Alberta. The North Waterton gas reservoirs are situated in the thrusted Lower Carboniferous to Devonian sequence. Due to the large terrain effects the seismic acquisition and processing is a tedious job with results that are difficult to interpret.

Evolution of a seismic acquisition methodology through integrated testing - onshore Abu Dhabi, United Arab Emirates, 1996-2000

Summary For onshore seismic data the resolution at the exploration target level depends on the complex interaction of many factors. These include the survey environment, geology, acquisition configuration and data processing procedures. When designing seismic surveys we wish to achieve the required target level resolution while minimising both cost and risk. For Vibroseis surveys, the time expended recording each source point, called the sweep effort/VP, can be a key cost factor. Uncertainty about the impact of differing options for the acquisition geometry and source point sweep effort on the target level resolution represents a risk factor. A 3D seismic exploration methodology driven by the resolution at the target level has been implemented for onshore Abu Dhabi, United Arab Emirates, by the Abu Dhabi Company for Onshore Operations (ADCO), in co-operation with Western Geophysical. Techniques originally developed for the on-crew processing of 2D acquisition parameter tests have been extended to 3D. Integrated data acquisition and processing tests provide fully processed, 3D migrated data volumes. Test analysis is based on the interpreted resolution at the target level, allowing direct judgements on key parameters affecting data cost and quality. The spatial distribution of source energy, improving the trace offset distribution and increasing the CMP fold is seen as significantly more important than the sweep effort/VP. Close co-operation between ADCO and Western's Geophysical Abu Dhabi data acquisition and processing staff ensure that complex data manipulation issues are handled in a timely manner, allowing the results of the testing to influence an ongoing 3D project. Use of this methodology has so far provided both improvements in data quality to levels not seen before for Abu Dhabi onshore data while simultaneously reducing the cost and risk of data acquisition. This paper summarises results from some of the key events in the development of the acquisition testing methodology: (A) 1996 – 2D testing for 2D acquisition. (B) 1997 – 2D testing for 3D acquisition. (C) 1998 – Simultaneous downhole acquisition. (D) 1999 – 3D testing for 3D acquisition.

The seismic expression of synsedimentary channel features within the Chalk of southern England

Onshore seismic reflection data to the north of Bournemouth, reveal a series of troughs or depressions (concave-up) and mounded (concave-down) structures within the Upper Chalk. Onlap, downlap and truncation of reflections is observed and the structures lie in close proximity to faults in the underlying Jurassic strata. It is probably the first time that such prominent and significant erosive channel structures have been imaged so clearly and described on seismic reflection data from onshore UK. Similar stratal geometries observed in the Chalk at crop are interpreted as channels formed by submarine erosion and redeposition, during relative sea-level falls. We interpret the structures described here as of primary syndepositional submarine erosion of the Chalk, producing channels, the infill to which may be slumped. Eustatic global sea-level changes are often cited as the cause of anomalous Chalk thicknesses and structures. Increasingly, however, such features are being linked to syndepositional tectonics which were clearly affecting Chalk deposition in surrounding basins. The structures described here may provide important information in the debate about whether late Cretaceous tectonics locally contributed to sea-level changes which affected Chalk sedimentation in the Anglo-Pads Basin, and that considering just one external control (such as eustasy) is oversimplified.

地震波シミュレーションが地下構造探査に果たす役割

Seismic simulation technology has been developed for many years. Recent trend that targets of exploration have become deeper and more complicated recalls demand of the seismic simulation technology. However, it has been only used for limited study due to various technical reasons. In recent years, the seismic simulation technology is rapidly advanced with new simulation methods and parallel computers. We have developed the wave propagation methods and applied to various exploration problems. We will show some results of seismic simulation in this paper.The first example is related to the Marmousi model. This simulation result shows that the wave propagation is very complicated and is beyond our image. The second example is a virtual seismic survey related to the sub-salt play. The virtual exploration shows the problems and solutions for sub-salt seismic imaging. The third example is the difference between acoustic and elastic modeling. This result shows the problem in onshore seismic data and the future direction.Using a seismic simulation, we can recognize various pitfalls and limitation in seismic processing and seismic interpretation. Seismic simulation can be used as potential tools for virtual explorations. We can gain the knowledge and the virtual experience through the virtual explorations.

Evolution and Structuring of the Joseph Bonaparte Gulf as Delineated by Aeromagnetic Data

A large portion of the southern Joseph Bonaparte Gulf area, northwestern Australia, was originally underlain by extensive contiguous Proterozoic sills and volcanic rocks. Subsequent extension and basin formation in this area during the Palaeozoic fractured this horizontal basic magnetic sheet. Evidence of this fracture patten and the extensional movements are obvious in images of the magnetic field over the basin. A series of transfer fault accommodation zones trending at 035 degrees and an associated series of perpendicular normal faults have been mapped. Onshore geology, gravity and seismic data support the transfer fault model. An underexplored graben, 75 kilometres long and 50 kilometres wide, which formed as a result of the extension process, has been mapped on the western edge of the Joseph Bonaparte Gulf adjacent to the Proterozoic Kimberley Basin.

COMPUTING FIELD STATICS WITH THE HELP OF SEISMIC TOMOGRAPHY*

ABSTRACTField static corrections in general need be applied to all onshore seismic reflection data to eliminate the disturbing effects a weathering layer or near‐surface low velocity zone has on the continuity of deep seismic reflections. The traveltimes of waves refracted at the bottom of the low velocity zone (or intermediate refracting interfaces) can often be observed as first breaks on shot records and used to develop a laterally inhomogeneous velocity model for this layer, from which the field static corrections can then be obtained. A simple method is described for computing accurate field statics from first breaks. It is based on a linearization principal for traveltimes and leads to the algorithms that are widely and successfully applied within the framework of seismic tomography. We refine an initial model for the low velocity layer (estimated by a standard traveltime inversion technique) by minimizing the errors between the observed first arrivals on field records and those computed by ray theory through an initial model of the low velocity layer. Thus, one can include more lateral velocity variations within the low velocity layers, which are important to obtain good field static corrections. Traditional first break traveltime inversion methods cannot, in general, provide such refined velocity values. The technique is successfully applied to seismic data from the Amazon Basin. It is based on a simple model for the low velocity layer that consists of an undulating earth surface and one planar horizontal refractor overlain by a laterally changing velocity field.