Channel waves in cross‐borehole data

Geophysics ◽  
1992 ◽  
Vol 57 (2) ◽  
pp. 334-342 ◽  
Author(s):  
Larry R. Lines ◽  
Kenneth R. Kelly ◽  
John Queen
Keyword(s):  
Seismic Velocity ◽  
Test Facility ◽  
Equation Modeling ◽  
Borehole Data ◽  
Geological Information ◽  
Channel Wave ◽  
First Arrival ◽  
Borehole Seismic ◽  
Seismic Velocity Contrasts ◽  
Ray Bending

Layered geological formations with large seismic velocity contrasts can effectively create channel waves in cross‐borehole seismic data. The existence of channel waves for such waveguides can be confirmed by ray tracing, wave equation modeling, and modal analysis. Channel wave arrivals are identified in cross‐borehole data recorded at Conoco’s Newkirk test facility. For these data, where velocity contrasts are about 2 to 1, tomography based on first arrival traveltimes, is limited due to problems with extreme ray bending and seismic shadow zones. However, it may be possible to extract geological information using channel wave information. The seismometer differencing method appears to be a promising approach for detecting waveguide boundaries by use of cross‐borehole data.

A study of methods for tomographic velocity estimation in the presence of low‐velocity zones

Geophysics ◽  
1985 ◽  
Vol 50 (6) ◽  
pp. 969-988 ◽  
Author(s):  
Sven Ivansson
Keyword(s):  
Seismic Velocity ◽  
Synthetic Data ◽  
Velocity Estimation ◽  
Low Velocity ◽  
Hole Area ◽  
First Arrival ◽  
Interpretation Process ◽  
Iterative Procedures ◽  
Ray Bending ◽  
Made In

This paper deals with the problem of seismic velocity estimation from first‐arrival traveltimes in a two‐dimensional (2-D) cross‐hole geometry where explosions are detonated in one borehole while recordings are made in another borehole and on the surface. Standard tomographic procedures are based on decomposition of the cross‐hole area into a number of cells and a simplifying assumption of straight raypaths. In the presence of significant low‐velocity zones, the resulting images may be contaminated. Different ways of performing tomographic inversion are tested on a number of synthetic examples. Images obtained by direct, unrestricted least‐squares inversion are often seriously distorted. However, methods using more cells and some kind of damping often give more satisfactory results. Because the risk of distorted images is always present in inversion procedures, comparison with synthetic data (forward modeling) is a valuable tool in the interpretation process. With a reasonably good initial solution, improvements can often be achieved by using iterative procedures to take account of ray‐bending affects as proposed in Bois et al.(1971). An alternative way of performing these calculations is described.

Remote monitoring of the steam‐flood enhanced oil recovery process

Geophysics ◽  
1987 ◽  
Vol 52 (11) ◽  
pp. 1457-1465 ◽  
Author(s):  
E. F. Laine
Keyword(s):  
Oil Recovery ◽  
Heavy Oil ◽  
High Frequency ◽  
Oil Sands ◽  
Seismic Velocity ◽  
Color Image ◽  
Vertical Plane ◽  
Recovery Process ◽  
Steam Flood ◽  
Borehole Seismic

Cross‐borehole seismic velocity and high‐frequency electromagnetic (EM) attenuation data were obtained to construct tomographic images of heavy oil sands in a steam‐flood environment. First‐arrival seismic data were used to construct a tomographic color image of a 10 m by 8 m vertical plane between the two boreholes. Two high‐frequency (17 and 15 MHz) EM transmission tomographs were constructed of a 20 m by 8 m vertical plane. The velocity tomograph clearly shows a shale layer with oil sands above it and below it. The EM tomographs show a more complex geology of oil sands with shale inclusions. The deepest EM tomograph shows the upper part of an active steam zone and suggests steam chanelling just below the shale layer. These results show the detailed structure of the entire plane between boreholes and may provide a better means to understand the process for in situ heavy oil recovery in a steam‐flood environment.

Three different approaches to provide urban geological information from a geological survey perspective: the Catalan case study

2020 ◽  
Author(s):  
Guillem Subiela ◽  
Miquel Vilà ◽  
Roser Pi ◽  
Elena Sánchez
Keyword(s):  
Urban Areas ◽  
Geological Survey ◽  
Anthropogenic Activity ◽  
Geological Environment ◽  
Borehole Data ◽  
Geological Information ◽  
Geological Factors ◽  
Geological Map ◽  
The Government

<p>Studying urban geology is a key way to identify municipal issues involved with urban development and sustainability, land resources and hazard awareness in highly populated areas. In the last decade, one of the lines of work of the Catalan Geological Survey (Institut Cartogràfic i Geològic de Catalunya) has been the development of (i) 1:5.000 scale Urban Geological Map of Catalonia project. Besides, two pilot projects have recently been started: (ii) the system of layers of geological information and (iii) the fundamental geological guides of municipalities. This communication focuses on the presentation of these projects and their utility, with the aim of finding effective ways of transferring geological knowledge and information of a territory, from a geological survey perspective.</p><p>The 1:5.000 urban geological maps of Catalonia (i) have been a great ambitious project focused on providing detailed, consistent and accurate geological, geotechnical and anthropogenic activity information of the main urban areas of Catalonia. Nevertheless, it must be taken into account that the compilation and elaboration of a large volume of geological information and also the high level of detail require a lot of time for data completeness.</p><p>In order to optimize a greater distribution of information, a system of layers of geological information (ii) covering urban areas is being developed. This pilot project consists of providing specific layers of Bedrock materials, Quaternary deposits, anthropogenic grounds, structural measures, geochemical compositions, borehole data and so on. However, as information layers are treated individually, it may not be clear the coherence between data from different layers of information and its use is currently limited to Earth-science professionals working with geological data.</p><p>Hence, as a strategy to reach a wider range of users and also provide a homogeneous and varied geological information, the development of fundamental geological guides for municipalities is also being carried out (iii). These documents include the general geological characterization of the municipality, the description of the main geological factors (related to geotechnical properties, hydrogeology, environmental concerns and geological hazards and resources) and the list of the sources of geological information to be considered. Moreover, each guide contains a 1:50.000 geological map that has cartographic continuity with the neighbouring municipalities. The municipal guides allow a synthesis of the geological environment of the different Catalan municipalities and give fundamental recommendations for the characterization of the geological environment of the municipality.</p><p>In conclusion, the three projects facilitate the characterization of geological environment of urban areas, the evaluation of geological factors in ground studies and also, in general, the management of the environment. These products differ depending on the degree of detail, the coherence of the geological information, the necessary knowledge for their execution or their purpose of use. This set of projects defines a geological urban framework, which is adjusted depending on the government’s requirements, the society’s needs and the geological survey’s available resources.</p>

Seismic mapping of on-shore sediments at Andøya, Norway, deposited prior to the North Atlantic rifting

2020 ◽  
Vol 8 (4) ◽  
pp. SQ105-SQ114
Author(s):  
Tor Arne Johansen ◽  
Bent Ole Ruud ◽  
Tormod Henningsen ◽  
Marco Brönner
Keyword(s):  
North Atlantic ◽  
Seismic Velocity ◽  
Traffic Noise ◽  
Seismic Exploration ◽  
Small Scale ◽  
Near Surface ◽  
The North ◽  
Seismic Surveying ◽  
The North Atlantic ◽  
Seismic Velocity Contrasts

Andøya is an island in the north of Norway. On its eastern side, it contains a local downfaulted basin of Mesozoic sediments sheltered from erosion during subsequent periods of Pleistocene glaciation. The sediments were deposited before the North Atlantic rifting and partly overlie weathered basement. We have recently carried out seismic surveying to better understand the geometry and seismic responses of the basin system. Extensive civil infrastructure and wet mire made the study area challenging for seismic exploration. We shot the survey lines at wet mire with detonating cord during winter when the mire was frozen. In the summer, we conducted seismic surveying along road shoulders with a small-scale vibrator. The seismic processing was particularly challenging due to the influence of traffic noise, heterogeneous near-surface conditions, and large seismic velocity contrasts. We interpreted the seismic lines in integration with other geophysical data and well logs to obtain a consistent and best possible seismic model of the basin. Our interpretation indicates a reorganization of the regional paleostress regime that took place during the continental breakup in the Eocene. In spite of severe obstacles for seismic surveying of the area, our results honor the robustness of the seismic method for subsurface imaging.

Anisotropic velocity tomography: A case study in a near‐surface rock mass

Geophysics ◽  
1993 ◽  
Vol 58 (12) ◽  
pp. 1748-1763 ◽  
Author(s):  
R. G. Pratt ◽  
W. J. McGaughey ◽  
C. H. Chapman
Keyword(s):  
Rock Mass ◽  
Fault Zone ◽  
Seismic Velocity ◽  
Anisotropic Media ◽  
Rock Properties ◽  
Initial Assessment ◽  
Borehole Data ◽  
Near Surface ◽  
Crown Pillar ◽  
Velocity Tomography

Cross‐borehole data were acquired in the surface crown pillar of a massive sulfide ore mine. The data consist of five, two‐dimensional (2-D), cross‐borehole panels, each with approximately 900 source‐receiver pairs. The panels were located within the crown pillar at either side of and within a major subvertical fault zone that intersects the orebody. An initial analysis of the data indicates that the bedrock containing the orebody is seismically anisotropic. A rigorous analysis of the traveltimes using anisotropic velocity tomography confirms the initial assessment that anisotropy exists within the crown pillar rock mass. Anisotropic velocity tomography is the generalization of tomographic methods to anisotropic media. As in any geophysical problem, the data are insufficient to completely resolve the distributions of the rock properties at all scale lengths; we use external constraints on the roughness of the final solution to ensure an algebraically well‐posed problem. Plots of the data residuals (the “traveltime surfaces”) are an essential tool in determining an optimal level of constraint. Of equal importance are plots of the relationship between the solution roughness and the rms level of the residuals. The final results of anisotropic velocity tomography are a set of images (tomograms) of the velocity and selected anisotropy parameters for the five panels. Our images do not contain the distortions typically exhibited when using isotropic tomography in anisotropic media. The velocity tomograms clearly show the geometry of the overburden contact at the top of the bedrock. The anisotropy tomograms show a decrease in anisotropy with depth on two of the panels. They also show a decrease in anisotropy with proximity to the fault zone. These features of the seismic velocity anisotropy are consistent with observations of fracture orientation and distribution. The results of the crosshole data interpretation contribute to the overall site investigation and provide a reliable interrogation of the bulk properties of the rock mass.

Downhole seismic logging for high‐resolution reflection surveying in unconsolidated overburden

Geophysics ◽  
1998 ◽  
Vol 63 (4) ◽  
pp. 1371-1384 ◽  
Author(s):  
J. A. Hunter ◽  
S. E. Pullan ◽  
R. A. Burns ◽  
R. L. Good ◽  
J. B. Harris ◽  
...  
Keyword(s):  
High Resolution ◽  
Seismic Velocity ◽  
P Wave ◽  
Unconsolidated Sediments ◽  
Dynamic Shear Modulus ◽  
S Wave ◽  
Interface Shear ◽  
Similar Frequency ◽  
Surface Reflection ◽  
First Arrival

Downhole seismic velocity logging techniques have been developed and applied in support of high‐resolution reflection seismic surveys. For shallow high‐resolution reflection surveying within unconsolidated overburden, velocity‐depth control can sometimes be difficult to achieve; as well, unambiguous correlation of reflections with overburden stratigraphy is often problematic. Data obtained from downhole seismic logging can provide accurate velocity‐depth functions and directly correlate seismic reflections to depth. The methodologies described in this paper are designed for slimhole applications in plastic‐cased boreholes (minimum ID of 50 mm) and with source and detector arrays that yield similar frequency ranges and vertical depth resolutions as the surface reflection surveys. Compressional- (P-) wave logging uses a multichannel hydrophone array with 0.5-m detector spacings in a fluid‐filled borehole and a high‐frequency, in‐hole shotgun source at the surface. Overlapping array positions downhole results in redundant first‐arrival data (picked using interactive computer techniques), which can be processed to provide accurate interval velocities. The data also can be displayed as a record suite, showing reflections and directly correlating reflection events with depths. Example applications include identification of gas zones, lithological boundaries within unconsolidated sediments, and the overburden‐bedrock interface. Shear- (S-) wave logging uses a slimhole, well‐locked, three‐component (3-C) geophone pod and a horizontally polarized, hammer‐and‐loaded‐plate source at ground surface. The pod is moved in successive 0.5- or 1-m intervals downhole with no redundancy of overlapping data as in the P-wave method. First‐arrival data can be obtained by picking the crossover onset of polarized energy or by closely examining particle‐motion plots using all three components of motion. In unconsolidated sediments, shear‐wave velocity contrasts can be associated with changes in material density or dynamic shear modulus, which in turn can be related to consolidation. Example applications include identification of a lithological boundary for earthquake hazard applications and mapping massive ice within permafrost materials.

scholarly journals A Rapid Method for Information Extraction from Borehole Log Images

2020 ◽  
Vol 10 (16) ◽  
pp. 5520
Author(s):  
Junqiang Zhang ◽  
Yi Zhang ◽  
Yiping Tian ◽  
Gang Liu ◽  
Lirui Xu ◽  
...  
Keyword(s):  
Information Extraction ◽  
Current Method ◽  
Borehole Data ◽  
Information Platform ◽  
Geological Information ◽  
Structured Information ◽  
Borehole Logs ◽  
Recognition Efficiency ◽  
Borehole Log ◽  
Image Format

Borehole logs are very important for geological analysis and application. Extracting structured information from borehole logs in the image format is the key to any analysis and application based on borehole data. The current method has defects in solving the beard phenomenon of the borehole log and the identification of special geological symbols. This paper proposes an automatic extraction method for borehole log information by combining the structural analysis based on the corner mark, as well as the structural understanding based on deep learning. The principles and key technologies of the method are described in detail. The performance of the method was tested by specific examples. This method is implemented on a geological information platform called QuantyView. The information extraction of 100 borehole logs with the same specification is used to verify the effectiveness of the proposed method. The results show that the method can not only effectively solve the inconsistency between the thickness and the description information in the borehole log but it can also address the low recognition efficiency of professional vocabulary, which can improve the extraction efficiency and accuracy of the borehole log information.

scholarly journals A Seismic Reconnaissance in the Mcmurdo Sound Region, Antarctica

1966 ◽  
Vol 6 (44) ◽  
pp. 209-221 ◽  
Author(s):  
Robin A. I. Bell
Keyword(s):  
Seismic Velocity ◽  
Seismic Refraction ◽  
P Wave ◽  
Velocity Measurements ◽  
Frozen Ground ◽  
Mcmurdo Sound ◽  
Wave Velocities ◽  
Taylor Valley ◽  
Minimum Age ◽  
First Arrival

AbstractA portable first-arrival seismic refraction instrument was used to measure seismic P-wave velocities in ice, frozen ground, till and shattered rock at various places in the McMurdo Sound region, Antarctica. It was found that some frozen ground exhibits the same seismic velocity as ice, so that buried ice cannot be idengified by seismic velocity measurements.The depth of exfoliation of a granite outcrop in Taylor Valley was successfully measured, as was the depth of an ice-free moraine in Wright Valley. From this latter depth, and from reasonable assumptions about the diffusion of water vapour through till, a minimum age of 75,000 yr. has been deduced for the moraine. This age implies that no through-glacier occupied Wright Valley during the last Northern Hemisphere glaciation.

Passive monitoring and 3D imaging of the bedrock response to the 2018 Espoo/Helsinki geothermal stimulation

2020 ◽  
Author(s):  
George Taylor ◽  
Gregor Hillers
Keyword(s):  
Seismic Velocity ◽  
Imaging Techniques ◽  
Body Wave ◽  
Coda Wave ◽  
Geothermal System ◽  
Enhanced Geothermal Systems ◽  
Induced Earthquakes ◽  
Borehole Data ◽  
Passive Monitoring ◽  
Short Period

<p>In recent years several deep geothermal energy projects have been forced to close following the occurrence of large seismic events associated with the stimulation of the surrounding bedrock. In 2018, an enhanced geothermal system (EGS) experiment performed in Helsinki, Finland concluded with no seismicity exceeding the threshold magnitude and thus provides an intriguing showcase for future stimulation experiments in similar environments. During the 49 days of the experiment, the five-stage injection of ~18,000 cubic meters water stimulated many thousands of earthquakes. Like in all previous stimulation cases the earthquake data constitute the primary source for the assessment of the scientific and operational aspects of the reservoir response. Here we apply ambient noise based monitoring and imaging techniques to data collected by 100 short period three-component stations that were organized in three large arrays consisting of nominally 25 stations, in addition to three small four-station arrays, and 10 single stations, during a 100 day period. We compute daily nine-component noise correlations between all stations pairs except for the intra-array pairs in a frequency range between 0.5 and 10 Hz. We measure waveform delays within our correlation functions as a function of frequency and lag time using the Continuous Wavelet Transform. We then invert these observations using a Markov chain Monte Carlo method to obtain the temporal variation in seismic velocity dv/v during the injection. By exploiting the variable spatial sensitivities of the surface- and body-wave components at different coda-wave lapse times and frequencies, we are able to image the medium response to the stimulation in both time and space. We compare the estimated seismic velocity variations to other observations such as H<sup>2</sup>/V<sup>2</sup>, as well as dv/v observations obtained from collocated borehole data. Importantly, we also compare the observed medium response to seismicity and pumping parameters. Our results suggest that we are able to resolve medium changes that are not solely associated with the induced earthquakes, but also potential signatures of fluid content or pressure changes in the bedrock. The combined observations of seismicity, pumping parameters and dv/v changes collected in this experiment can further advance passive monitoring techniques in the context of enhanced geothermal systems, and facilitate a more comprehensive analysis of fluid-rock interactions that may occur aseismically.</p>

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