Vertical Seismic Profiling Method Research Articles

Results of a walk‐above vertical seismic profiling survey acquired at the Thônex‐01 geothermal well (Switzerland) to delineate fractured carbonate formations for geothermal development

ABSTRACTThis paper deals with the design, acquisition and processing of vertical seismic profiling data collected in 2016 at the directional Thônex‐01 geothermal well, drilled in 1993 in the Geneva Canton (Switzerland). The aim of the study was to obtain additional information from existing‐abandoned well for downhole geophysical characterization of potential geothermal reservoirs in the Geneva area. The main results obtained by this study allowed an improved subsurface image by multi‐offset acquisitions near and around the deviated well. Specifically we were able to (1) improve the velocity model of the Geneva Basin, which, at present, is only constrained by one unique deep exploration well, located at the south‐west of the basin, far away from the study area; (2) image the transition between the Tertiary Molasse siliciclastic sediments and the Mesozoic carbonates; (3) define an acquisition strategy for future vertical seismic profiling surveys in support of the geothermal exploration campaigns in the area. This study has demonstrated the value of vertical seismic profiling method for the refinement of the subsurface geology at local scale, and its usefulness to assist the planning of second well associated with geothermal doublets.

The application of VSP in the Pilbara

The construction of geological and geotechnical models in typical Pilbara iron ore environments is vital to enable an optimized mine design for the life of the asset, while maintaining pit wall integrity and overall mine safety. Geotechnical assessments require the measurement of geomechanical properties, such as the triaxial shear, direct shear and unconfined compressive strength tests and pressure and shear wave velocities on diamond core samples. Ideally, these velocities would be measured in Reverse Circulation (RC) boreholes as their spatial density is far higher than diamond drilled holes. Unfortunately, despite its value, such data is seldom collected as a large proportion of the holes are above the water table, limiting the use of sonic-logging tools. Even if measurements are possible, damage to the borehole caused by drilling biases the resulting velocity measurements. This paper details the results of a trial using the vertical seismic profile method to directly measure in-situ seismic velocities in RC boreholes. The method was successful in determining the velocities of the formations through the entire length of the holes. The data in several boreholes was of sufficient quality for the application of more advanced processing methods, important for geological mapping and the processing and interpretation of surface seismic data. The success of this first trial has implications for future iron-ore developments in the Pilbara. The widespread acquisition of accurate seismic velocity data is likely to enable the creation of more accurate geotechnical models and could improve future development decisions.

Overview and introduction to this special section: 3D VSP

In 1953, Richard Jolly used geophones coupled to the borehole wall to record seismic waves in the subsurface, and he highlighted the interpretive benefits of downhole recording. In the western world, the coupled downhole geophone was a first of its kind and was the ancestor to modern receiver tools (Figure 1) used in the vertical seismic profiling (VSP) method. The translation, by SEG, of Gal'perin's 1974 book on VSP from Russian into English increased awareness of the progress in borehole seismology made in Russia; the case studies outlined in the book gave further prominence to the benefits of the VSP method. Zero-offset VSP (meaning the source is relatively close to the borehole to provide 1D information) or ZVSP is now an essential part of the interpreter's toolkit that gives a seismic time-to-depth relationship, in-situ elastic properties, and multiple-reduced reflectivity. ZVSP continues to provide a key link between surface seismic images and geologic properties. In addition, Q measurement and the identification of multiple-generating and mode-changing horizons from near-offset VSP provide further interpretive insights. In-situ velocities also assist with building velocity models for migration and inversion.

Application of Nonstationary Ray Decomposition to Identifying Deep Seismic Bedrock of the Kanto Sedimentary Basin, Japan

Abstract This study identifies the deep seismic bedrock in the Kanto sedimentary basin of Japan based on the nonstationary ray decomposition method. The reflections of SH waves can be observed from the local maxima of instantaneous power at the intersections of the upcoming and downgoing rays, namely the major boundaries of a multilayer sedimentary bedrock structure. In particular, the depth of the seismic bedrock can be clearly identified because the greatest instantaneous power appears at the top of the seismic bedrock, where the impedance contrast is the highest. Strong-motion data recorded at 12 KiK-net observatory stations in the Kanto area are used to identify the depth of the seismic bedrock. The velocity structures of these 12 sites have previously been investigated by the vertical seismic profiling (VSP) method up to the depth where the observation well could penetrate. The VSP method revealed the velocity structures up to the seismic bedrock at three sites, while for the remaining sites the seismic bedrock was not reachable. The method presented in this paper performs well on identifying deep subsurface structure and gives travel times of the SH wave to the seismic bedrock at the 12 sites, even at sites with extremely deep seismic bedrock, where the VSP method could not reach. Furthermore, assuming that the shear-wave velocity is constant from the bottom of the observation well to the top of the seismic bedrock, the depths of the seismic bedrock at the nine stations are obtained.

Seismic Prediction While Drilling (SPWD): Looking Ahead of the Drill Bit by Application of Phased Array Technology

Abstract. No abstract available. doi:10.2204/iodp.sd.9.06.2010

Investigation of a landslide in the new site of Badong County by integrated geophysical survey

An integrated geophysical survey which combines vertical seismic profile method, shallow reflection seismic method, electric sounding, soil temperature measurement and radioactive gas measurement was used to investigate Zhaoshuling landslide in the new site of Badong County and to assess the stability of the landslide. By rational use of these methods together with borehole geological profile and other geological information, the spatial distribution of the landslide body, the formations and structures within and without the landslide body were determined and the stability of the landslide was also assessed, thus making great contribution to the successful and rational investigation and assessment of the landslide.

3-D Velocity Imaging in the Shallow Subsurface using Multi-well, Multi-offset, VSP Data: A Case Study from the Lawrence Livermore National Laboratory Site

A vertical seismic profiling (VSP) method was developed to produce compressional (p-wave) velocity sections in a 3-D survey volume, down to a maximum depth of [Formula: see text]. The VSP method consisted of a multilevel hydrophone tool deployed down several wells. Multiple offset surface shotpoints were recorded at multiple azimuths around each well head, using an impact source. The VSP data were processed and inverted to produce p-wave interval velocities. These velocity sections were then projected into a model of the survey volume, together with borehole log information and other geologic information, to produce a 3-D visualization which aided the location and interpretation of aquifer boundaries below the water table. The final image displayed several low velocity zones, and these were attributed to partially saturated pore spaces, possibly both natural, or pump induced by air suction. Low velocity layers appeared above several actively pumped aquifers, and it was concluded that the multi-offset, multi-azimuth, VSP method may be suitable for mapping both aquifer channels, and zones of pumping influence.

Assessing Seismic Response of Soft Soil Sites in Hong Kong Using icrotremor Records

Microtremor records have been used to assess seismic ampiification of sou sites in Hong Kong. The method is based on ratios of horizontal and vertical camponents of microtremor (ambient noise) recards, and the ratios are aften referred to as Nakamura’s ratios. The peakfrequency of the Nakamura’s ratio carrelates well with thefundamental modal frequency estimated from the site shear wave velocities which were derived by a vertical seismic profiling method or were converted from SPT data. The amplitudes of the ratios are very stable and the standard deviation of the ratios derived from a series of measurements is reasonably small. Results from rock sites show that the ratios take a value of unity at a wide frequency range when the site has no large topographical effect. The ratios are generally larger than unity if the site has topographical effect but no dominant peak appears in the ratios. Results from sou sites show that a dominant peak appears at the fundamental frequency of the site and the amplitudes ...

Analysis of Shear-Wave Polarization in VSP Data: A Tool for Reservoir Development

Summary This paper presents results of a new method of using vertical seismic profile (VSP) data to deduce information on certain rock properties that are important for reservoir development. These properties are the direction of maximum horizontal stress or the orientation of aligned fractures and the variation of these quantities with depth. Such information can be important for secondary recovery, horizontal drilling, and infill drilling. The VSP method involves a shear-wave (S-wave) source at the surface and a downhole three-component (3-C) geophone to record first-arrival S waves along predominantly vertical ray paths. The data are analyzed to determine particle motion directions (polarizations) and relative travel time of the two S waves. In simple cases, the polarization of the faster S wave is oriented parallel to the direction of maximum horizontal compressive stress orthe predominantfracture alignment.The travel-time differences between the S waves contain information on the effects of unequal horizontal stresses. We recorded a number of VSP's for S-wave analysis in California and Texas oil fields. Results from three VSP's are presented here. In nearly every case, we found measurable travel-time differences and also significant variation of the S-wave polarization azimuths with depth. Polarization azimuths, although typically consistent over depth intervals of several hundred feet, tended to change abruptly at various depths. A simple layer-stripping technique made it possible to follow the polarization changes and determine travel-time differences over successive depth intervals. The variations with depth are particularly interesting because they indicate changes of principal stress direction or fracture orientation.

A multioffset, three‐component VSP study in the Sudbury Basin

A multioffset, three‐component vertical seismic profiling (VSP) experiment was carried out in the Sudbury Basin, Ontario, as a part of the LITHOPROBE Sudbury Transect. The main objectives were determination of the shallow velocity structure in the middle of the Sudbury Basin, development of an effective VSP data processing flow, correlation of the VSP survey results with the surface seismic reflection data, and demonstration of the usefulness of the VSP method in a crystalline rock environment. The VSP data processing steps included rotation of the horizontal component data, traveltime inversion for velocity analysis, Radon transform for wavefield separation, and preliminary analysis of shear‐wave data. After wavefield separation, the flattened upgoing wavefields for both P‐waves and S‐waves display consistent reflection events from three depth levels. The VSP-CDP transformed section and corridor stacked section correlate well with the high‐resolution surface reflection data. In addition to obtaining realistic velocity models for both P‐ and S‐waves through least‐square inversion and synthetic seismic modeling for the Chelmsford area, the VSP experiment provided an independent estimation for the reflector dip using three component hodogram analysis, which indicates that the dip of the contact between the Chelmsford and Onwatin formations, at an approximate depth of 380 m in the Chelmsford borehole, is approximately 10.5° southeast. This study demonstrates that multioffset, three‐component VSP experiments can provide important constraints and auxiliary information for shallow crustal seismic studies in crystalline terrain. Thus, the VSP technique bridges the gap between the surface seismic‐reflection technique and well‐log surveys.

THE USE OF VSP TECHNIQUES IN FIELD EVALUATION

Vertical Seismic Profiling (VSP) techniques have been developed which have found application in the development and production of hydrocarbons as well as in exploration.A VSP is initiated by outlining the objectives of the survey and, using a model of the geology in the vicinity of the borehole, applying inversion techniques to determine the VSP method best suited to provide the required data. Reflection coverage, critical refractions, and mode conversion data (using 3-component geophones) can be used to obtain a structural, lithologic, and petrophysical interpretation.Structural interpretations using recently developed migration techniques based on the scalar wave equation can now provide images of the sub-surface which are superior to those obtained using previous ray-trace schemes.Acoustic impedance estimates from VSP surveys processed with deterministic deconvolution techniques and optimal amplitude recovery to obtain maximum temporal resolution can be more accurate than those obtained from surface seismic data. Offset VSP data can also give an estimate of reservoir porosity variations away from the borehole.