Seismic Imaging Technology Research Articles

Long-term monitoring of microseismic emissions: Earth tides, fracture distribution, and fluid content

Monitoring of microseismic emissions for periods of 10–30 days has established a clear relationship between solid earth tides and microseismic activity. In addition, an event magnitude versus recurrence relationship has been established that can be used to predict oil, gas, or water content of open fractures in imaged rock volumes. Originally developed to explore for oil and gas, the detection technology used has been applied in Eurasia, the Middle East, and Texas. When visualized in three dimensions at scales of several kilometers on a side, including depth, the observations shows systems of subvertical fracture volumes distributed as clusters in the subsurface. When visualized in sequential time windows, microseismic activity can be seen to respond in detail to lunar-solar gravitational changes. The seismic imaging technology used to detect the location and temporal changes within these fracture systems is based on deploying geophone receiver arrays using array patterns and processing algorithms similar to those used in phased array radar in the electromagnetic spectrum. This passive listening technology has been termed seismic location of emission centers (SLEC). Examples of applied SLEC monitoring are presented for surveys performed in Russia and Texas.

Improving the greater K2 area subsalt imaging with advanced seismic acquisition, model building, and imaging technologies — A Gulf of Mexico case study

Subsalt imaging has proven challenging in part because of the complex geometries of the salt canopies, which can yield highly variable illumination on subsalt reflectors. The resulting complexity of the seismic wavefields has also challenged traditional velocity-model-building tools and migration algorithms. A case study for the K2 field illustrates how improved seismic data in the form of long-offset, full-azimuth acquisition and more advanced model building and imaging tools have substantially enhanced the imaging quality of this major subsalt field. The higher fold and more complete azimuthal coverage afforded by the full-azimuth coil data improved the effectiveness of the combined tomographic and full-waveform inversion approach for velocity-model building. Utilization of TTI RTM migration algorithms provided further benefits not only for better delineation of the salt geometry during model building but also in delivering superior final image volumes relative to that which could be provided by less robust algorithms, such as Kirchhoff, beam, and one-way wave equation.

Case studies of geophysical imaging for road foundation design on soft soils and embankment risk assessment

Population growth along the coast of eastern Australia has increased demand for new and upgraded transport infrastructure within intervening coastal floodplains and steeper hinterland areas. This has created additional challenges for road foundation design.The floodplain areas in this region are underlain by considerable thicknesses of recently deposited alluvial and clayey marine sediments. If characterisation of these deposits is inadequate they can increase road construction costs and affect long-term road stability and serviceability. Case studies from a major coastal highway upgrade demonstrate how combining surface wave seismic and electrical geophysical imaging with conventional geotechnical testing enhances characterisation of these very soft and soft soils. The geophysical results also provide initial foundation design parameters such as void ratio and pre-consolidation pressure.A further significant risk issue for roads is potential embankment instability. This can occur during new road construction or when upgrades of existing embankments are required. Assessing the causes of instability of existing steeper embankments with drilling and probing is often difficult and costly due to access and safety problems. In these situations combinations of electrical, ground penetrating radar and P-wave seismic imaging technologies can rapidly provide information on the likely conditions below both the roadway and embankment. Case studies show the application of these technologies on two unstable road embankments.It is concluded that the application of both geophysical imaging and geotechnical testing is a cost-effective enhancement for site characterisation of soft soils and for risk assessment of potentially unstable embankments. This approach overcomes many of the current limitations of conventional methods of site investigation that provide point location data only. The incorporation of geophysics into a well crafted site investigation allows concentration on fewer but higher quality soil probings and geotechnical boreholes.

Multi-level parallel computing of reverse time migration for seismic imaging on blue Gene/Q

Blue Gene/Q (BG/Q) is an early representative of increasing scale and thread count that will characterize future HPC systems: large counts of nodes, cores, and threads; and a rich programming environment with many degrees of freedom in parallel computing optimization. So it is both a challenge and an opportunity to it to accelerate the seismic imaging applications to the unprecedented levels that will significantly advance the technologies for the oil and gas industry. In this work we aim to address two important questions: how HPC systems with high levels of scale and thread count will perform in real applications; and how systems with many degrees of freedom in parallel programming can be calibrated to achieve optimal performance. Based on BG/Q's architecture features and RTM workload characteristics, we developed massive domain partition, MPI , and SIMD Our detailed deep analyses in various aspects of optimization also provide valuable experience and insights into how can be utilized to facilitate the advance of seismic imaging technologies. Our BG/Q RTM solution achieved a 14.93x speedup over the BG/P implementation. Our multi-level parallelism strategies for Reverse Time Migration (RTM) seismic imaging computing on BG/Q provides an example of how HPC systems like BG/Q can accelerate applications to a new level.

Technologies from foothills seismic imaging: replacements or complements?

Rob Vestrum and Jon Gittins challenge the assumption that the latest seismic imaging technology is always superior to older tried and tested methods, taking exploration in the Canadian foothills as an example.

Seismic Imaging of Unstable Ground

Unstable ground conditions caused by unexpected collapse of existing buried infrastructure or incidents during tunnelling represent major geotechnical risks.Specially developed crosshole, SUBS and SEWREEL seismic imaging technologies that operate from boreholes and underground openings can be applied to define the subsurface extent of the unstable ground and to monitor the effectiveness of remedial works. These technologies use below ground hydrophone arrays and surface seismic sources.A case study of a shallow sewer collapse that followed a rainfall event in a beach suburb of Sydney, demonstrates the application of these imaging technologies, showing their ability to define the resulting unstable ground hazard and to assist with geotechnical risk reduction.

On The Issue of Strike or Dip Streamer Shooting for 3D Multi-Streamer Acquisition

Any decision to pursue 3D multi-streamer acquisition in a certain shooting direction requires a consideration of several seismic phenomena, including subsurface illumination, spatial sampling, wave propagation, and the idiosyncrasies of seismic imaging technology. We provide both theoretical and synthetic modelling examples to provide a framework for objective discussion, so that the significance of each issue can be understood.The 2D dip-shooting requirement becomes largely irrelevant in 3D seismic acquisition. In any 3D survey location, a series of arguments may arise that supports each possible shooting direction. The key issue is that both the subsurface model and the surface acquisition geometry are intimately linked, and each must be given specific consideration during processing.Both shooting direction and shooting method (single-source vs. dual-source, parallel vs. anti-parallel, no sail line overlap vs. sail line overlap, etc.) have a direct influence upon the nature of both severe and subtle imaging artefacts arising during processing. We use synthetic and real examples to demonstrate the need for proper 3D survey planning and evaluation on a case-by-case basis, prior to any new survey.

3D strike vs. dip streamer shooting direction comparison

A decision to pursue 3D streamer acquisition in a certain shooting direction requires a consideration of seismic phenomena including subsurface illumination, spatial sampling, wave propagation, and the idiosyncrasies of seismic imaging technology. We provide both theoretical and synthetic modeling examples to provide a framework for objective discussion. The important aspect is that the 2D dip-shooting requirement becomes irrelevant in 3D. In any 3D survey location, a series of arguments will arise that support each possible shooting direction. The key issue is that both the subsurface model and the surface acquisition geometry are intimately linked, and each must be given specific consideration during processing. Consideration is also given to new streamer acquisition technologies that are helping to blur the distinctions between dip and strike shooting results.

Seismic methods for deep mineral exploration: Mature technologies adapted to new targets

Nonseismic methods—such as electromagnetic, induced-polarization, and potential-field surveying techniques—have been the geophysical backbone of mineral exploration for decades. These methods exploit anomalous physical properties of ore deposits (e.g., enhanced conductivity, chargeability, or magnetization) to locate potential targets for drilling. Although well suited to many shallow (< 500 m) exploration problems, the underlying physical principles of these methods impose inescapable limitations on their sensitivity and resolving power at depth. Recent declines in base metal reserves caused by the depletion of known shallow deposits and declining rates of discovery for new deposits underscore the need for geophysical exploration methods that can locate economically viable deposits at depths of up to several km. Seismic methods offer one possible solution. The need to develop efficient and robust seismic imaging techniques for mineral exploration has long been recognized. In the 1980s two key case histories established the potential of seismics as a mapping tool in the hardrock environment. Green and Mair (1983) presented seismic images of complex fracture systems at a radioactive waste disposal site in the Canadian Shield. Subsequently, Pretorius et al. (1989) demonstrated the usefulness of an integrated seismic and petrophysical approach to image key geologic structures for mineral exploration in Witwatersrand Basin, South Africa. These initial studies served as catalysts for a number of largely independent research efforts over the following decade—in North America, southern Africa, Scandinavia, and Australia—aimed at developing useful and cost-effective seismic technology for deep mineral exploration and mine planning. A number of fundamental aspects of seismic exploration for minerals, including the acoustic properties of ores and the scattering characteristics of orebodies, were poorly known until recently. Moreover, significant advances have been made in seismic imaging technology for mineral exploration, from downhole seismic techniques to large-scale 3D surveys over known deposits. This article reviews some advances in applying seismic …

Synergies in geophysical, medical, and space imaging: Overview and introductory session

The workshop's first session reviewed seismic, medical, and space imaging technology with two presentations from each field—one to introduce basic concepts and demystify the jargon, and one to describe the state of the art. Bob Stolt's introductory seismic overview presented the basic concepts of 2- and 3D, pre- and poststack, time and depth migration, and gave simplified tutorials on different integral- and difference-equation migration techniques. “Seismic depth imaging of complex geological structures” by Larry Lines emphasized the complexity of the earth as a propagating medium, and the need for sophisticated processing to produce accurate structural images. Complex geologic structures (which often involve steeply dipping beds, folded structures, and anisotropic velocities) usually invalidate many conventional processing methods. However, according to Lines, Kirchhoff, f-x , and reverse-time prestack depth imaging perform adequately (at a minimum) when a reasonable velocity model and data with coherent signals are available. Figure 1 shows the final interpretation for a prestack depth migration of a triangle zone feature in the Alberta Foothills. A complete description of the data and imaging can be found in “Seismic imaging and velocity analysis for an Alberta Foothills seismic survey” by Yan and Lines (Geophysics, 2001). Figure 1. The final interpretation for a prestack depth migration of a triangle zone …

A review of high-resolution seismic profiling across the Sudbury, Selbaie, Noranda, and Matagami mining camps

Lithoprobe high-resolution seismic surveys have provided the first systematic images of the deep stratigraphy in four major Canadian mining camps (Noranda, Matagami, Sudbury, and Selbaie). Systematic compressional wave velocity and density measurements in deep boreholes have established that lithological contacts were the main impedance contrast imaged, although reflections from faults and deformation zones have also been observed. The strongest reflections are attributed to mafic intrusions and some sulphides and oxides. Integrating seismic, physical rock property measurements, and geological data has resulted in the revision of several geological models with direct impact on local strategies for deep mineral exploration. Mining companies have shown an interest in seismic reflection methods and this has led to several follow-up studies. The application of seismic methods to the direct detection of massive sulphides, based on physical rock property measurements, has been studied through two-dimensional and three-dimensional (3D) seismic imaging and vertical seismic profiling technologies. The challenge will now be to optimize 3D seismic imaging for mineral exploration and to improve seismic data processing by enhancing the seismic response from deep, lenticular orebodies.

Seismic monitoring of a CO2 flood in a carbonate reservoir: A rock physics study

A carbon dioxide (CO2) injection pilot project is underway in Section 205 of the McElroy field, West Texas. High‐resolution crosswell seismic imaging surveys were conducted before and after CO2 flooding to monitor the CO2 flood process and map the flooded zones. The velocity changes observed by these time‐lapse surveys are typically on the order of −6%, with maximum values on the order of −10% in the vicinity of the injection well. These values generally agree with laboratory measurements if the effects of changing pore pressure are included. The observed dramatic compressional ([Formula: see text]) and shear ([Formula: see text]) velocity changes are considerably greater than we had initially predicted using the Gassmann (1951) fluid substitution analysis (Nolen‐Hoeksema et al., 1995) because we had assumed reservoir pressure would not change from survey to survey. However, the post‐CO2 reservoir pore fluid pressure was substantially higher than the original pore pressure. In addition, our original petrophysical data for dry and brine‐saturated reservoir rocks did not cover the range of pressures actually seen in the field. Therefore, we undertook a rock physics study of CO2 flooding in the laboratory, under the simulated McElroy pressures and temperature. Our results show that the combined effects of pore pressure buildup and fluid substitution caused by CO2 flooding make it petrophysically feasible to monitor the CO2 flood process and to map the flooded zones seismically. The measured data show that [Formula: see text] decreases from a minimum 3.0% to as high as 10.9%, while [Formula: see text] decreases from 3.3% to 9.5% as the reservoir rocks are flooded with CO2 under in‐situ conditions. Such [Formula: see text] and [Formula: see text] decreases, even if averaged over all the samples measured, are probably detectable by either crosswell or high‐resolution surface seismic imaging technologies. Our results show [Formula: see text] is sensitive to both the CO2 saturation and the pore pressure increase, but [Formula: see text] is particularly sensitive to the pore pressure increase. As a result, the combined [Formula: see text] and [Formula: see text] changes caused by the CO2 injection may be used, at least semiquantitatively, to separate CO2‐flooded zones with pore pressure buildup from those regions without pore pressure buildup or to separate CO2 zones from pressured‐up, non‐CO2 zones. Our laboratory results show that the largest [Formula: see text] and [Formula: see text] changes caused by CO2 injection are associated with high‐porosity, high‐permeability rocks. In other words, CO2 flooding and pore pressure buildup decrease [Formula: see text] and [Formula: see text] more in high‐porosity, high‐permeability samples. Therefore, it may be possible to delineate such high‐porosity, high‐permeability streaks seismically in situ. If the streaks are thick enough compared to seismic resolution, they can be identified by the larger [Formula: see text] or [Formula: see text] changes.

Can we image beneath salt?

A decade has passed since petroleum geologists first recognized that Jurassic salt in the extensional Gulf of Mexico often appeared to be thrust between layers of younger sediments. Since then, many teams of geoscientists have been faced with the problems of either (1) improving subsalt quality through better data collection or (2) making subsalt interpretations from data of very poor quality. These problems aren’t new; in fact, they have faced the seismic industry from the beginning. In the Gulf of Mexico, however, the cause of the problem — salt — is obvious. In particular, high‐velocity, structurally contoured salt bodies act as sonic lenses that disperse or concentrate seismic signals in haphazard ways. Many advances in seismic imaging technology have been in response to these salt‐related problems of velocity and structure.

Multichannel impulse responses for outdoor sound propagation

A new visualization method is introduced to present simulated and measured impulse responses for outdoor sound propagation. The method stems from seismic imaging technology and provides significantly improved insight in the complexity of outdoor sound. The proposed transmission images are multichannel and unambiguously show the characteristic multiarrival effect in outdoor sound measurements. Caustics and ground reflections are clearly visible and the related wavefront directions can be easily estimated. The new visualization method is explained and illustrated with a number of practical examples. In addition, it is shown that the method is very effective for comparing different numerical simulation techniques. The examples demonstrate that the images reveal the strong and weak points of different algorithms in a transparent and detailed way. Transmission images should thus play an important role in the refinement of numerical simulation methods for outdoor sound propagation.