Seismic Profiling Surveys Research Articles

Subaqueous landslides at the distal basin of Lago Nahuel Huapi (Argentina): Towards a tsunami hazard evaluation in Northern Patagonian lakes

The May 22nd, 1960 Valdivia earthquake, Chile (Mw 9.5) triggered a series of subaqueous mass-wasting processes (debris flows and slides) in Lago Nahuel Huapi (Argentina), generating a tsunami-like wave that hit the coasts of San Carlos de Bariloche. Aiming to provide a first preliminary insight into tsunami hazards for the lakeshore communities, in this paper we identify and characterize the subaqueous landslides at the populated distal basin of the lake. Swath bathymetric and seismic profiling surveys were carried out and high-resolution digital elevation models were derived from these data to perform a landslide inventory map. A series of morphometrical parameters (including the landslide area, the volume of displaced materials and the run-out distance, among others) were estimated upon selected events. The results indicated that landslide activity at the distal basin of Lago Nahuel Huapi has been concentrated in the vicinity of Bariloche (massive landslide triggered by the 1960 earthquake) and within steep delta fronts where the slope failures typically initiate at shallow waters (9–11m depth). The sliding mass frequently travels basinward along a great distance (≥1000m). At the delta fronts, the volume of material removed by landslides can reach ~40×104m3, leaving scar areas of up to 13m thick. The periodic occurrence of rotational–translational mass movements initiating at the upper edge of the delta fronts, with vertical displacements of the mobilized materials reaching ~200m, probably represents a potential tsunami hazard for the nearby populated coasts.

Mode‐converted volcanogenic massive sulphide ore lens reflections in vertical seismic profiles from Flin Flon, Manitoba, Canada

ABSTRACTIn October 2006, three‐component zero‐offset vertical seismic profile data were acquired from a deviated well in the Flin Flon mining camp in Manitoba, Canada, using a dynamite source. These vertical seismic profile data were processed to reveal reflections originating from the 85.5 Mt Flin Flon‐Callinan‐777 volcanogenic massive sulphide ore system. From drill records, mine plans, surficial maps, and seismic data, 3D voxel models of the local geology and known ore zones were built, which were then used in 3D finite‐difference modelled simulations of the vertical seismic profile surveys. The number of geological units partitioning the model was incrementally increased to study the effects of the massive sulphide ore and the major rock units on the seismic response. The simulations and field data were jointly visualized, and reflections originating at some of the known ore zones were identified. These reflections were observed in each of the three components in both the real field and the forward modelled data and indicate a strong mode‐converted component of the reflected wavefield.

Traveltime Tomography of qP Reflection Waves in Anisotropic TI Media

AbstractSeismic traveltime tomography is an effective method to invert underground anisotropic parameters. Research about tomography for anisotropic media is, however, relatively a little. And its techniques are still far from mature stage. In real applications, traveltime inversion of qP reflection waves has more extensive practical values, because the cost of surface survey is much cheaper than that of crosshole and vertical seismic profile surveys. The tomographic method suggested in this article combines the anisotropic reflected wave ray tracing, traveltime perturbation equation and nonlinear conjugate gradient method. It can be used to invert anisotropic media with arbitrary anisotropic degree. The main task in this article is to reconstruct the anisotropic parameters for TI media using qP reflection waves. In numerical simulation, traveltime of qP reflections wave was used to invert for the layered and block anomaly model, respectively. The elastic modulus parameters and Thomsen parameters were inverted separately, because the velocity sensitivity functions of them are different. The simulation results show that traveltime of qP reflection waves can be used to invert anisotropic parameters correctly. Iteration reaches a satisfactory convergence level for different anisotropic models. The tomographic method proposed here has a better capability in recovering theoretical models compared than isotropic traveltime tomography.

Long-period ground motions in a laterally inhomogeneous large sedimentary basin: observations and model simulations of long-period surface waves in the northern Kanto Basin, Japan

To conduct practical evaluations of the long-period ground motions (period of 4 to 8 s) in a laterally inhomogeneous large sedimentary basin, we constructed a three-dimensional (3D) sedimentary velocity structure model for the northern Kanto Basin in Japan using a simple velocity gradient function, where strong lateral variations of seismic velocities in the sediments were expected. The model construction employs waveform analysis and geophysical data from vertical seismic profiling and microtremor surveys in the target region. To validate the velocity structure model, we conducted large-scale 3D finite-difference method simulations of the long-period ground motions for two shallow moderate earthquakes: the northern Tochigi earthquake and the northern Ibaraki earthquake. The simulation results for both earthquakes accurately reproduced the observed long-period ground motions in terms of arrival times, amplitudes, and durations of surface waves. By detailed comparisons of the seismograms for observational and simulated data, we demonstrated that the lateral variation of the seismic velocities in the sediments determines the characteristics of the surface wave propagation in the northern Kanto Basin. Such analyses can provide a better understanding of the complex propagation characteristics of surface waves in laterally inhomogeneous, large sedimentary basins.

Structural Deformation of Southern Tien Shan Fold-Thrust Belt — Take the North Margin of Kashi for Example

The Structural and deformational features of fold-thrust belt in the north margin of Kashi，southern Tian Shan were disclosed based on various data such as two dimensional seismic profile and field geologic survey. The results show that the fold-thrustbelt can be divided into several rows of anticlines, includingKalaboketuoer-Wenguer, Tuopa-Kangxiweier, Atushi and Kashi on plane,and the development of Atushi anticlines and its north side was controlled by the activity of the thrust system originated along the middle Cambrian Awatage Group from north to south. The fold-thrust belt can be divided into two different spatial levels: the shallow tectonic is a large scale imbricate thrust system, the detachment surface is uplifted from Cambrian system to Neogene system; the deep structure is a buried duplex structure system, the fault in floor and fault in roof are located at gypsic horizon in Cambrian and Neogene systemrespectively. Based on structural deformation analyzing and balanced section technology, the distribution of each anticlinal belt and the structure style of the low and deep thrust systems are confirmed. In this area the distance is shortened by 32.64～49.1km from north to south since Pliocene with the scalage of 40.5%～50.51%，and its average crustal shortening rate is 9.11～13.71mm/a.

Lake-level rise in the late Pleistocene and active subaquatic volcanism since the Holocene in Lake Kivu, East African Rift

The history of Lake Kivu is strongly linked to the activity of the Virunga volcanoes. Subaerial and subaquatic volcanoes, in addition to lake-level changes, shape the subaquatic morphologic and structural features in Lake Kivu's Main Basin. Previous studies revealed that volcanic eruptions blocked the former outlet of the lake to the north in the late Pleistocene, leading to a substantial rise in the lake level and subsequently the present-day thermohaline stratification. Additional studies have speculated that volcanic and seismic activities threaten to trigger a catastrophic release of the large amount of gases dissolved in the lake. The current study presents a bathymetric mapping and seismic profiling survey that covers the volcanically active area of the Main Basin at a resolution that is unprecedented for Lake Kivu. New geomorphologic features identified on the lake floor can accurately describe related lake-floor processes for the first time. The late Pleistocene lowstand is observed at 425m depth, and volcanic cones, tuff rings, and lava flows observed above this level indicate both subaerial and subaquatic volcanic activities during the Holocene. The geomorphologic analysis yields new implications on the geologic processes that have shaped Lake Kivu's basin, and the presence of young volcanic features can be linked to the possibility of a lake overturn.

Integrated reservoir monitoring at the Illinois Basin – Decatur Project

The Illinois Basin – Decatur Project (IBDP), a United States Department of Energy funded project, is a fully integrated industrial carbon capture and storage (CCS) project where carbon dioxide (CO2) is captured from the Archer Daniels Midland Company (ADM) corn processing plant at the in Decatur, Illinois, USA. The captured CO2 is dehydrated, compressed, and then injected deep into the Mt. Simon Formation. IBDP commenced injection in November 2011 and has a goal of injecting one million metric tonnes of CO2 into the lower Mt. Simon Sandstone over a three-year period. A range of monitoring, verification, and accounting (MVA) tools are being used to monitor the CO2 plume development in the deep subsurface. These monitoring tools include time-lapse RST* reservoir saturation tool logging in the project wells, continuous pressure and temperature measurements from multiple levels above, within, and below the storage formation, deep fluid sampling with associated geochemical analysis, time-lapse three-dimensional (3D) vertical seismic profile (VSP) surveys, and microseismic monitoring. MVA data has been used to quantitatively and qualitatively calibrate the reservoir simulations. As a result, the project now has robust, history-matched reservoir simulations that predict CO2 and pressure plume development over time. MVA data and modelling results indicate that the CO2 plume has spread within a thin, high permeability zone in the lower Mt. Simon Sandstone and that a low permeability zone in the upper part of the lower Mt. Simon Sandstone is currently acting as an effective baffle to CO2 migration and pressure transmission above 2,094 m (6,870 ft). Lessons learned over the course of IBDP are being applied to the adjacent Illinois Industrial CCS Project.

Improving quality and safety through the use of a purposely designed truck-mounted Vibroseis for VSP surveys

SUMMARY Vibrators are the preferred sources for onshore vertical seismic profile (VSP) surveys. Truck-mounted units are especially useful as they are more road mobile than buggy-based units. In particular, they can be driven directly to the wellsite, resulting in improved response times, simplified logistics with fewer vehicles and personnel at the wellsite and improved transport safety. Acquiring broad-bandwidth, high-quality VSP data, using state-of-the art vibrator equipment, however, has generally required the use of the latest buggy-mounted vibrators, compromising well-site logistics and transportation safety for VSP operations. To deliver optimum performance, two new truck vibrator models specifically designed to take advantage of all of the most recent developments in vibrator technology while retaining the logistical advantages of truck-mounted units have been developed. These new truck-mounted vibrators offer greatly improved data quality with tests showing that they can transmit a signal with a frequency bandwidth of 6.6 octaves compared to previous models which can only transmit 2.5 octaves. Being mounted on modern truck chassis these vehicles retain all the mobility and HSE advantages of truck vibrators.

Significant VSP data quality improvements through the use of a broadband source

SUMMARY Seismic vibrators are the preferred sources for land vertical seismic profile (VSP) surveys as they are relatively repeatable, controllable, have high energy, have a low environmental impact, and are cost-effective. Unfortunately, due to the mechanical and hydraulic constraints of the vehicles, the typical swept bandwidth has been quite limited, typically of the order of 3 octaves. In this paper we show that dramatic improvements in seismic data quality can be achieved by extending the bandwidth used for Vibroseis VSPs. These increases are dependent, however, on the use of modern vibrators, specialised low-frequency enhancing sweeps, and downhole sensors with an extended frequency response range.

VSP imaging using free-surface multiples: A case study from the Gulf of Mexico

Vertical seismic profile surveys (VSP) provide a unique opportunity to obtain high-quality seismic images of the subsurface. Placing receivers downhole mitigates many near-surface and overburden challenges associated with surface seismic imaging and results in improved image quality. Unfortunately, these benefits are restricted by the limited area illuminated by the primary P-wave reflection wavefield (typically a relatively narrow cone that underlies the geophone array). The free-surface multiple wavefield recorded in a VSP survey illuminates a significantly larger area, both vertically and laterally, and so can provide an expanded imaging capability (Jiang et al, 2005; Jiang et al, 2007; Lou et al 2007). Subsurface imaging using the multiple wavefield has been demonstrated and is commonly used for imaging deep-water 3D node surveys, which are typically acquired using a sparse distribution of receivers. However, no case studies have been published yet, which present a critical analysis of the images provided by this technology when applied to VSP surveys.

Full‐waveform inversion for macro velocity model reconstruction in look‐ahead offset vertical seismic profile: numerical singular value decomposition‐based analysis

ABSTRACTFull‐waveform inversion is currently considered as a potential tool for improving depth‐velocity models for areas with complex geology. It is well‐known that success of the inversion is very sensitive to the available low‐frequency content of the data. In the paper we investigate this issue considering a look‐ahead offset vertical seismic profile survey and applying singular value decomposition analysis of a linearized forward map as the main tool. We demonstrate with this technique the difference between the sequential full‐waveform inversion strategy and the original time‐domain approach proposed in the early 1980s. We emphasize the role of the lowest frequency in the data, which is necessary for reliable velocity model inversion in particular cases. Finally we show the existence of a trade‐off between the lowest frequency and a regularization parameter of the inversion procedure. The presented approach may be adapted to answer general questions regarding the quality of data and acquisition system parameters required for feasible full‐waveform inversion.

Zero-offset vertical seismic profiling survey and estimation of gas hydrate concentration from borehole data from the Ulleung Basin, Korea

Gas hydrate has been receiving much attention in recent years as the demand for energy has increased. Before an economic evaluation of the feasibility of producing gas hydrate can be made, an assessment of reserves must be completed. To evaluate a reserve of gas hydrate, we should accurately know the depth interval of the gas hydrate-bearing region and the concentration of gas hydrate in it. Because vertical seismic profiling (VSP) data can provide higher resolution than surface seismic data, we can improve the reliability of the characterization of the gas hydrate-bearing region using VSP data along with surface seismic data.In this study, we obtained interval velocities and corridor stacked sections from zero-offset VSP data acquired at the UBGH2-6 and UBGH2-10 wells in gas hydrate-bearing zones of the Ulleung Basin, East Sea of Korea. The interval velocities obtained from the zero-offset VSP data agreed well overall with sonic logs and showed a significant decrease at the depth beneath the gas hydrate stability zone. Most reflection events in the corridor stacked section matched well those in the surface migrated seismic section. Additionally, we computed the concentration of the gas hydrate from the log data using a three-phase Biot-type equation, and the result agreed well with the concentration calculated from the resistivity log using Archie's equation.

Tube Wave removal from vertical seismic profiling (VSP) surveys

This paper presents a processing workflow to attenuate the strong tube waves from VSP surveys acquired in Perth, Western Australia. An array of 24 hydrophones spaced at 10 metre intervals is attached to a cable run down the borehole. The hydrophones were unclamped, so they record significant amount of the tube waves which entirely mask the upgoing waves. F-K filtering was used for wavefield decomposition of flattened downgoing waves. Linear moveout correction was applied to flatten the tube waves and removed unusual aliased energy due to shot depth variations and hydrophone positioning errors through the F-K filtering. The flattened data were transformed to tau-pi domain using a very narrow window slowness to produce a model of tube waves. An adaptive wavefield subtraction algorithm was used to subtract the tube wave model using a matching filter from the input data. The result was processed through a F-K filter and moderate tau-pi filter to remove the residual undesired energy. After attenuating the multiple energy and true amplitude recovery, pre stack depth migration, a CDP-VSP mapping and stacking were applied to produce CDP equivalent depth and time images.

Sediment distribution on the inner continental shelf off Khao Lak (Thailand) after the 2004 Indian Ocean tsunami

The coastline of Khao Lak (Thailand) was heavily damaged by the 2004 Indian Ocean tsunami. Onshore tsunami deposits and satellite images, which show large amounts of sediment transported offshore, indicate that the seafloor was impacted by tsunami run-up and backwash. In this study, high-resolution maps of sediment distribution patterns and the geological development of the seafloor are presented. These maps are based on multibeam, side-scan sonar and seismic profiling surveys offshore Khao Lak. Paleoreefs, with associated boulder fields and sandy sediment dominate the inner continental shelf. Patches of fine-grained (silt to fine sand) sediments exist in water depths of less than 15 m. The sediment distribution pattern is stable between 2008 and 2010, apart from small shifts regarding the boundaries of the fine-grained sediment patches. In one sediment core and several grab samples an event layer was documented, situated below a cover of modern sediments which is only a few cm thick. The event-layer is traced down to 18 m water depth. It consists mostly of sand and contains compounds of terrigenous origin. It is interpreted as a 2004 Indian Ocean tsunami deposit. However, over large areas of the study-site, the impact of the tsunami is hardly identifiable by seafloor morphology or sediment distribution.

Successful sidetracking of a well onshore Germany by integration of 3D vertical seismic profiling technology – a case study

ABSTRACTThe exploration for and exploitation of deep Lower Rotliegend gasfields onshore in North Germany often suffers from poor surface seismic imaging. This is owing to the depth of the reservoirs and a thick and complex Zechstein salt overburden. RWE Dea conducted a 3D vertical seismic profile (VSP) survey in a low‐performing production well after the borehole was plugged near total depth. Our main objective was to improve the seismic image of the reservoir zone in the vicinity of the well to determine a new landing point for a planned sidetrack. Because acquisition was in a densely populated and also partially environmentally protected area, there were surface restrictions concerning source deployment. Additionally, due to the complex geological setting, we conducted two 2D VSP field tests and thorough pre‐survey modelling to achieve the best results in terms of seismic imaging, environmental impact and reasonable cost. Deformation bands in the drill core suggest that the initial well was drilled close to a major fault, which was regarded as the main reason for the disappointing production rate. Therefore, we put special emphasis on fault detection in our processing and interpretation. Our interpretation approach used an enhanced structural mapping workflow that helped to design a sidetrack. When the sidetrack was drilled two years later, it ended up being one of the most productive wells in the field.

Performance of low-fold scalar migration for downhole seismic imaging of massive sulfide ore deposits at Norman West, Sudbury, Canada

The Downhole Seismic Imaging consortium conducted two consecutive vertical seismic profiling surveys in the Norman West mining camp (Sudbury, Canada) in 1998 and 1999. These were aimed toward imaging a massive sulfide ore deposit situated within the footwall of the Sudbury Igneous Complex (SIC). Three-component seismic data were acquired in four boreholes with variable signal-to-noise ratio and poor polarization quality. Consequently, the images suffered from strong azimuthal ambiguity. A strike filter, passing only reflections originating from within the SIC, was applied during migration to enhance interpretability of the images obtained. Migrated images showed structures correlating with the known position of an ore deposit located 1800 m away from one borehole (N40). Diffraction coherency migration enhanced the image of the deposit, and suggested strong seismic scattering from within the footwall of the SIC.

Optimal designs of time-lapse seismic surveys for monitoring CO2 leakage through fault zones

Cost-effective time-lapse seismic surveys are crucial for long-term monitoring of geologic carbon sequestration. In this paper, we numerically model time-lapse seismic surveys for monitoring CO2 leakage through fault zones, and design optimal surveys for time-lapse seismic data acquisition using elastic-wave sensitivity analysis. Two stages of CO2 leakage through fault zones are simulated. In the early stage of leakage, when CO2 is confined in a relatively deep region, and our results show that the most desired location for receivers at the surface is at the hanging-wall side of the fault zone, of normal faults (with large dip angles) or reverse faults. The most sensitive places at the surface to the change of different elastic parameters (e.g. P- and S-wave velocity and density) are similar to one another, and are often not sensitive to the source location. In a late stage of leakage, in which CO2 migrates close to the surface, our modeling demonstrates that the best region at the surface for time-lapse seismic surveys is very sensitive to the source location and the elastic parameter to be monitored. For time-lapse vertical seismic profiling (VSP) surveys, our modeling suggests that it is important to account for the effect of free-surface reflections, especially for large offset VSP surveys.

Application of 3D vertical seismic profile multi‐component data to tight gas sands‡

ABSTRACTDue to the complicated geophysical character of tight gas sands in the Sulige gasfield of China, conventional surface seismic has faced great challenges in reservoir delineation. In order to improve this situation, a large‐scale 3D‐3C vertical seismic profiling (VSP) survey (more than 15 000 shots) was conducted simultaneously with 3D‐3C surface seismic data acquisition in this area in 2005. This paper presents a case study on the delineation of tight gas sands by use of multi‐component 3D VSP technology. Two imaging volumes (PP compressional wave; PSv converted wave) were generated with 3D‐3C VSP data processing. By comparison, the dominant frequencies of the 3D VSP images were 10–15 Hz higher than that of surface seismic images. Delineation of the tight gas sands is achieved by using the multi‐component information in the VSP data leading to reduce uncertainties in data interpretation. We performed a routine data interpretation on these images and developed a new attribute titled ‘Centroid Frequency Ratio of PSv and PP Waves’ for indication of the tight gas sands. The results demonstrated that the new attribute was sensitive to this type of reservoir. By combining geologic, drilling and log data, a comprehensive evaluation based on the 3D VSP data was conducted and a new well location for drilling was proposed. The major results in this paper tell us that successful application of 3D‐3C VSP technologies are only accomplished through a synthesis of many disciplines. We need detailed analysis to evaluate each step in planning, acquisition, processing and interpretation to achieve our objectives. High resolution, successful processing of multi‐component information, combination of PP and PSv volumes to extract useful attributes, receiver depth information and offset/ azimuth‐dependent anisotropy in the 3D VSP data are the major accomplishments derived from our attention to detail in the above steps.

北上低地西縁断層帯・南昌山断層群の変動地形と地下構造

The Kitakami Lowland fault zone (KLFZ) is an active reverse fault zone that extends about 70 km eastward along the Quaternary volcanic front of the northeast Japan arc. The activity of this fault zone in the Quaternary is mostly recognized as a fault reactivation of Miocene normal faults in the area. We conducted a high-resolution seismic reflection profile survey, Nanshozan 09, to define the geological structure of the Nanshozan fault group, northern portion of the KLFZ. The Nanshozan fault group is composed by three reverse faults, F1, F2, and F3 faults, and deforms late Quaternary fluvial terraces and alluvial fans in the Kitakami Lowland. Several isolated andesite hills such as Jonaisan and Kitayachi-yama, line the eastern edge of the hanging-wall of the F3 fault. The high-resolution seismic reflection profile shows that the fault scarps and tilted fluvial terraces are traced down to a depth of 2 km along the Nanshozan fault group, formed by an west-dipping high-angle reverse fault (F1 fault) and along two of the thrusts that have a flat-ramp geometry (F2 and F3 faults). Furthermore, the results of K-Ar dating and field observations show that the Jonaisan hill is certainly composed of Pliocene andesitic rocks, not Quaternary intrusives. Cross-section restoring across the Nanshozan fault group implies that F2 fault activity occurred after the initiation of F3 fault activity. Hence, isolated hills near F3 fault, such as Jonaisan and Kitayachi-yama, are recognized as volcanic blocks that survived long periods of erosion while being deformed by F3 fault thrusting.

3D VSP migration by image point transform

The common characteristic of the seismic methods involving downhole measurements is the difficulty of designing surveys able to image the subsurface space evenly. Migration schemes for these layouts are sensitive to reconstruction artifacts. The defining property of the image point (IP) transform is its ability to accumulate amplitudes of curved reflection events appearing in time-distance profiles into approximately discoidal (or spherical in three dimensions) vicinities in the IP domain. Due to the reflected wavefields collapsing into such vicinities in the IP domain, the emphasizing of the reflectors consists of enhancing regions with higher amounts of accumulated amplitude. True-dip filtering can also easily be performed, even for reflectors appearing in the time-distance profiles as curved events due to their dip, source offset or variable velocity field. Reflecting interfaces aredefined as sets of linked piecewise planar-reflector elements rather than as collections of point diffractors. True reflectors fitting this description are enhanced by the IP transform while diffraction patterns, events produced by other wave types, multiples, and noise of any kind, tend to be suppressed. The inverse transform leads to filtered versions of time-distance profiles. An alternative to performing the inverse transform back to the original time-distance representation is computing 2D/3D migrated images directly from the transformed IP space. Although the 3D migration by IP transform is applicable to any seismic survey geometry, we focused on procedures for enhancing prestack migrated images obtained by sparse multioffset, multiazimuth vertical seismic profiling (VSP) surveys as typically performed for mining site characterization and mineral exploration. The real data used were collected within an extensive mining seismic investigation program performed in Canada.