Borehole seismic measurements: What can they tell us about S-waves and then reservoir properties?

2017 ◽  
Author(s):  
Robert R. Stewart
Keyword(s):  
Reservoir Properties ◽  
S Waves ◽  
Borehole Seismic ◽  
Seismic Measurements

Collisional Orogeny in the Scandinavian Caledonides (COSC): Some preliminary results from drilling of the 2.276 km deep COSC-2 borehole, central Sweden

2021 ◽  
Author(s):  
Christopher Juhlin ◽  
Bjarne Almqvist ◽  
Mark Anderson ◽  
Mark Dopson ◽  
Iwona Klonowska ◽  
...  
Keyword(s):  
High Amplitude ◽  
Granitic Rocks ◽  
Magnetic Data ◽  
Precambrian Basement ◽  
Tectonic Model ◽  
Core Recovery ◽  
Alum Shale ◽  
Borehole Seismic ◽  
Seismic Reflectors ◽  
Seismic Measurements

<p>COSC investigations and drilling activities are focused in the Åre-Mörsil area (Sweden) of central Scandinavia. COSC-2 was drilled with nearly 100% core recovery in 2020 to 2.276 km depth with drilling ongoing from mid-April to early August. Drilling targets for COSC-2 included (1) the highly conductive Alum shale, (2) the Caledonian décollement, the major detachment that separates the Caledonian allochthons from the autochthonous basement of the Fennoscandian Shield, and (3) the strong seismic reflectors in the Precambrian basement.</p><p>Combined seismic, magnetotelluric (MT) and magnetic data were used to site the COSC-2 borehole about 20 km east-southeast of COSC-1. Based on these data it was predicted that the uppermost, tectonic occurrence of Cambrian Alum shale would be penetrated at about 800 m, the main décollement in Alum shale at its stratigraphic level at about 1200 m and the uppermost high amplitude basement reflector at about 1600 m. Paleozoic turbidites and greywackes were expected to be drilled down to 800 m depth. Below this depth, Ordovician limestone and shale with imbricates of Alum shale were interpreted to be present. Directly below the main décollement, magnetite rich Precambrian basement was expected to be encountered with a composition similar to that of magnetic granitic rocks found east of the Caledonian Front. The actual depths of the main contacts turned out to agree very well with the predictions based on the geophysical data. However, the geology below the uppermost occurrence of Alum shale is quite different from the expected model. Alum shale was only clearly encountered as a highly deformed, about 30 m thick unit, starting at about 790 m. Between about 820 and 1200 m, preliminary interpretations are that the rocks mainly consist of Neo-Proterozoic to Early Cambrian tuffs. Further below, Precambrian porphyries are present. The high amplitude reflections within the Precambrian sequence appear to be generated by dolerite sheets with the uppermost top penetrated at about 1600 m. Several deformed sheets of dolerite may be present down to about 1930 m. Below this depth the rocks are again porphyries.</p><p>A preliminary conclusion concerning the tectonic model is that the main décollement is at about 800 m and not at 1200 m. Also the thickness of the lowermost Cambrian/uppermost Neoproterozoic sediments on top of the basement is much greater than expected (hundreds of meters instead of tens of meters) and likely to have been thickened tectonically. Detailed studies are required to assess the actual importance of the “main décollement” and the degree, type and age of deformation in its footwall. We can also conclude that the Precambrian basement is very similar to the Dala porphyries succession that are typically present farther south.</p><p>An extensive set of downhole logging data was acquired directly after drilling. Borehole seismic measurements in 2021 will help to define and correlate seismic boundaries with lithology and structures in the core. Unfortunately, work for describing the geology of the drill core in detail is still on hold due to Covid-19.</p>

Imaging below a complex overburden with borehole-seismic data

Geophysics ◽  
2020 ◽  
Vol 85 (3) ◽  
pp. S135-S150
Author(s):  
Jakob B. U. Haldorsen ◽  
Leif Jahren
Keyword(s):  
Economic Evaluation ◽  
Seismic Data ◽  
Seismic Profile ◽  
Profile Data ◽  
Vertical Seismic Profile ◽  
S Waves ◽  
Critical Information ◽  
Measured Polarization ◽  
Borehole Seismic

We have determined how the measured polarization and traveltime for P- and S-waves can be used directly with vertical seismic profile data for estimating the salt exit points in a salt-proximity survey. As with interferometry, the processes described use only local velocities. For the data analyzed in this paper, our procedures have confirmed the location, inferred from surface-seismic data, of the flank of a steeply dipping salt body near the well. This has provided us more confidence in the estimated reservoir extent moving toward the salt face, which in turn has added critical information for the economic evaluation of a possible new well into the reservoir. We also have found that ray-based vector migration, based on the assumptions of locally plane wavefronts and locally plane formation interfaces, can be used to create 3D reflection images of steeply dipping sediments near the well, again using only local velocities. Our local reflection images have helped confirm the dips of the sediments between the well and the salt flank. Because all parameters used in these processes are local and can be extracted from the data themselves, the processes can be considered to be self-sufficient.

Crosswell seismic imaging in a contaminated basalt aquifer

Geophysics ◽  
2004 ◽  
Vol 69 (1) ◽  
pp. 16-24 ◽  
Author(s):  
Thomas M. Daley ◽  
Ernest L. Majer ◽  
John E. Peterson
Keyword(s):  
Seismic Source ◽  
P Wave ◽  
Low Velocity ◽  
S Waves ◽  
High Attenuation ◽  
Well Spacing ◽  
Simultaneous Acquisition ◽  
Environmental Laboratory ◽  
New Type ◽  
Borehole Seismic

Multiple seismic crosswell surveys have been acquired and analyzed in a fractured basalt aquifer at Idaho National Engineering and Environmental Laboratory. Most of these surveys used a high‐frequency (1000–10,000 Hz) piezoelectric seismic source to obtain P‐wave velocity tomograms. The P‐wave velocities range from less than 3200 m/s to more than 5000 m/s. Additionally, a new type of borehole seismic source was deployed as part of the subsurface characterization program at this contaminated groundwater site. This source, known as an orbital vibrator, allows simultaneous acquisition of P‐ and S‐waves at frequencies of 100 to 400 Hz, and acquisition over larger distances. The velocity tomograms show a relationship to contaminant transport in the groundwater; zones of high contaminant concentration are coincident with zones of low velocity and high attenuation and are interpreted to be fracture zones at the boundaries between basalt flows. The orbital vibrator data show high Vp/Vs values, from 1.8 to 2.8. In spite of the lower resolution of orbital vibrator data, these data were sufficient for constraining hydrologic models at this site while achieving imaging over large interwell distances. The combination of piezoelectric data for closer well spacing and orbital vibrator data for larger well spacings has provided optimal imaging capability and has been instrumental in our understanding of the site aquifer's hydrologic properties and its scale of heterogeneity.

3D slowness time coherence for sonic imaging

Geophysics ◽  
2019 ◽  
Vol 84 (5) ◽  
pp. D179-D189 ◽  
Author(s):  
Nicholas N. Bennett
Keyword(s):  
Feature Extraction ◽  
Modeling And Simulation ◽  
Ray Tracing ◽  
Propagation Direction ◽  
Central Issue ◽  
Imaging Results ◽  
Critical Interpretation ◽  
The Many ◽  
Borehole Seismic ◽  
Seismic Measurements

Although sonic imaging can provide higher resolution images of the near-wellbore region than lower frequency seismic and borehole seismic measurements, many challenges confront its more widespread use. The traditional sonic imaging workflow of first filtering the borehole modes and then migrating the underlying reflected arrival events ignores a critical interpretation step, namely, characterizing these reflected arrivals in terms of their azimuths, raypath types, and other attributes. Furthermore, using sonic imaging results in subsequent modeling and simulation workflows requires determining the 3D coordinates or at least the true dip and azimuth of these near-wellbore reflectors, and feature extraction from noisy 2D sonic imaging migration images cannot provide either of these. To address these interpretation challenges and develop a means of mapping these reflectors without requiring a migration, a central issue that arises is whether we can determine the slowness and propagation direction of a reflected wavefield using a standard array of receiver sensors mounted around the circumference of a tool sonde. To accomplish this task, we have developed 3D slowness time coherence (STC). We combine an automated time pick with a ray-tracing procedure and our 3D STC processing to evaluate the many candidate arrival events that may be present in the filtered waveform measurements, which leads to a 3D map of the reflectors that can be readily integrated into digital models of the surrounding subsurface as well as logs of reflector true dip and azimuth that can be compared with similar logs produced from borehole images.

Orbital vibrator seismic source for simultaneous P‐ and S‐wave crosswell acquisition

Geophysics ◽  
2001 ◽  
Vol 66 (5) ◽  
pp. 1471-1480 ◽  
Author(s):  
Thomas M. Daley ◽  
Dale Cox
Keyword(s):  
Seismic Energy ◽  
Seismic Source ◽  
P Wave ◽  
S Wave ◽  
Circularly Polarized ◽  
S Waves ◽  
Polarized Waves ◽  
Coordinate Rotation ◽  
Processing Algorithms ◽  
Borehole Seismic

A recently developed borehole seismic source, the orbital vibrator, was successfully deployed in a crosswell survey in a fractured basalt aquifer. This seismic source uses a rotating eccentric mass to generate seismic energy. Source sweeps with clockwise and counter‐clockwise rotations are recorded at each source location. Because this source generates circularly polarized waves, unique processing algorithms are used to decompose the recordings into two equivalent linearly oscillating, orthogonally oriented seismic sources. The orbital vibrator therefore generates P‐ and S‐waves simultaneously for all azimuths. A coordinate rotation based on P‐wave particle motion is used to align the source components from various depths. In a field experiment, both P‐ and S‐wave arrivals were recorded using fluid‐coupled hydrophone sensors. The processed field data show clear separation of P‐ and S‐wave arrivals for in‐line and crossline source components, respectively. A tensor convolutional description of the decomposition process allows for extension to multicomponent sensors.

Tunnel signature prediction for a cross‐borehole seismic survey

Geophysics ◽  
1995 ◽  
Vol 60 (1) ◽  
pp. 76-86 ◽  
Author(s):  
Richard D. Rechtien ◽  
Roy J. Greenfield ◽  
Robert F. Ballard
Keyword(s):  
Cross Section ◽  
Field Data ◽  
Rectangular Cross Section ◽  
Circular Cross Section ◽  
Data Interpretation ◽  
P Wave ◽  
Seismic Survey ◽  
S Waves ◽  
Borehole Seismic ◽  
Tunnel Size

Seismic location of tunnels or voids with a cross‐borehole survey is examined with field data and theory. The field data were taken at a site with a 2.2-m high by 2.7-m wide, roughly rectangular cross‐section tunnel, using a newly developed 1 to 5 kHz system employing a P‐wave sparker source. The synthetic records were obtained using a 2.5-D boundary‐valued solution for an explosive point source near a cylindrical void, and the solution was evaluated with the method of steepest descent. The synthetic waveforms compared well to the field data; both showed a maximum reduction of amplitude in the tunnel shadow of 8 dB and a maximum first arrival delay of 0.1 ms. Additional theoretical modeling was used to examine the variations of the received signals with tunnel size and frequency and showed amplitude reduction increased with frequency and tunnel size. Calculations showed that S‐waves scattered from the tunnel are more than 20 dB smaller than the primary P‐wave on hydrophones and more than 12 dB smaller on particle velocity sensors and so could be difficult to see in field data. The close comparison of synthetic waveforms to the field data indicate that the cylindrical model can be used to model data for roughly square cross‐section tunnels or voids, as well as for circular cross‐section tunnels, and thus is useful for data interpretation and survey planning.

A plane‐wave decomposition for elastic wave fields applied to the separation of P‐waves and S‐waves in vector seismic data

Geophysics ◽  
1986 ◽  
Vol 51 (2) ◽  
pp. 419-423 ◽  
Author(s):  
A. J. Devaney ◽  
M. L. Oristaglio
Keyword(s):  
Plane Wave ◽  
Elastic Wave ◽  
Seismic Data ◽  
Seismic Profile ◽  
P Waves ◽  
Wave Fields ◽  
S Waves ◽  
Plane Wave Decomposition ◽  
Wave Decomposition ◽  
Seismic Measurements

We describe a method to decompose a two‐dimensional (2-D) elastic wave field recorded along a line into its longitudinal and transverse parts, that is, into compressional (P) waves and shear (S) waves. Separation of the data into P-waves and S-waves is useful when analyzing vector seismic measurements along surface lines or in boreholes. The method described is based on a plane‐wave expansion for elastic wave fields and is illustrated with a synthetic example of an offset vertical seismic profile (VSP) in a layered elastic medium.

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