A case study of stratigraphic interpretation using shear and compressional seismic data

Geophysics ◽  
1984 ◽  
Vol 49 (5) ◽  
pp. 509-520 ◽  
Author(s):  
M. D. McCormack ◽  
J. A. Dunbar ◽  
W. W. Sharp
Keyword(s):  
Physical Properties ◽  
Shear Wave ◽  
Transit Time ◽  
Seismic Data ◽  
Surface Profile ◽  
Compressional Wave ◽  
Horizontal Shear ◽  
Seismic Line ◽  
Transit Times

This paper describes the use of surface recorded compressional and horizontal shear wave seismic data to detect lateral changes in the physical properties of a clastic unit. Shear and compressional wave transit times were measured across a selected interval from CDP stacked sections derived from data collected along coincident shear and compressional seismic lines. At each surface position the ratio of the shear to compressional transit time across the target horizon is calculated. It is shown that lateral variations in this ratio, coupled with the behavior of the individual transit time curves, can be used to infer changes in the physical properties of a formation. The horizon selected for this case study was the lower Pennsylvanian Morrow formation which produces gas from channel sand bodies at the Empire Abo field, New Mexico. A detailed geologic section of the producing horizon was mapped along a seismic line oriented so that it crossed productive and nonproductive regions of the field. Shear and compressional Vibroseis® surveys were conducted along this surface profile using data acquisition parameters designed to produce comparable signal‐to‐noise ratios and resolution in both sets of field data. After processing, the shear and compressional interval transit times through the Morrow formation decreased in going from nonproductive to productive thicknesses of sand. Furthermore there is a proportionately greater decrease in the shear wave transit time than in the compressional transit time resulting in an overall decrease in the ratio of shear to compressional transit times. While several possible physical changes in the lateral properties of the reservoir could explain these observations, it is concluded that the primary mechanism causing these ratio changes is variation in the sand‐shale ratio within the Morrow formation.

Evaluation of direct hydrocarbon indicators through comparison of compressional‐ and shear‐wave seismic data: a case study of the Myrnam gas field, Alberta

Geophysics ◽  
1985 ◽  
Vol 50 (1) ◽  
pp. 37-48 ◽  
Author(s):  
Ross Alan Ensley
Keyword(s):  
Shear Wave ◽  
Seismic Data ◽  
Compressional Wave ◽  
Bright Spot ◽  
Low Velocity ◽  
Gas Reservoir ◽  
Gas Field ◽  
Compressional Waves ◽  
The Relationship

Shear waves differ from compressional waves in that their velocity is not significantly affected by changes in the fluid content of a rock. Because of this relationship, a gas‐related compressional‐wave “bright spot” or direct hydrocarbon indicator will have no comparable shear‐wave anomaly. In contrast, a lithology‐related compressional‐wave anomaly will have a corresponding shear‐wave anomaly. Thus, it is possible to use shear‐wave seismic data to evaluate compressional‐wave direct hydrocarbon indicators. This case study presents data from Myrnam, Alberta which exhibit the relationship between compressional‐ and shear‐wave seismic data over a gas reservoir and a low‐velocity coal.

Comparison of P‐ and S‐wave seismic data: A new method for detecting gas reservoirs

Geophysics ◽  
1984 ◽  
Vol 49 (9) ◽  
pp. 1420-1431 ◽  
Author(s):  
Ross Alan Ensley
Keyword(s):  
Shear Wave ◽  
Seismic Data ◽  
Quantitative Methods ◽  
Qualitative Evaluation ◽  
Compressional Wave ◽  
Bright Spot ◽  
S Wave ◽  
Gas Reservoirs ◽  
Compressional Waves

Compressional waves are sensitive to the type of pore fluid within rocks, but shear waves are only slightly affected by changes in fluid type. This suggests that a comparison of compressional‐ and shear‐wave seismic data recorded over a prospect may allow an interpreter to discriminate between gas‐related anomalies and those related to lithology. This case study documents that where a compressional‐wave “bright spot” or other direct hydrocarbon indicator is present, such a comparison can be used to verify the presence of gas. In practice, the technique can only be used for a qualitative evaluation. However, future improvement of shear‐wave data quality may enable the use of more quantitative methods as well.

On the prediction of settlement from high-resolution shear-wave reflection seismic data: The Trondheim harbour case study, mid Norway

2013 ◽  
Vol 167 ◽  
pp. 72-83 ◽  
Author(s):  
J.S. L'Heureux ◽  
M. Long ◽  
M. Vanneste ◽  
G. Sauvin ◽  
L. Hansen ◽  
...  
Keyword(s):  
High Resolution ◽  
Shear Wave ◽  
Seismic Data ◽  
Wave Reflection ◽  
Reflection Seismic

Direct estimation of shear‐wave interval velocities from seismic data

Geophysics ◽  
1985 ◽  
Vol 50 (4) ◽  
pp. 530-538 ◽  
Author(s):  
P. M. Carrion ◽  
S. Hassanzadeh
Keyword(s):  
Shear Wave ◽  
Small Angle ◽  
Seismic Data ◽  
Mode Conversion ◽  
Real Data ◽  
Compressional Wave ◽  
Compressional Waves ◽  
Common Depth Point ◽  
Interval Velocities ◽  
Wave Decomposition

Conventional velocity analysis of seismic data is based on normal moveout of common‐depth‐point (CDP) traveltime curves. Analysis is done in a hyperbolic framework and, therefore, is limited to using the small‐angle reflections only (muted data). Hence, it can estimate the interval velocities of compressional waves only, since mode conversion is negligible when small‐angle arrivals are concerned. We propose a new method which can estimate the interval velocities of compressional and mode‐converted waves separately. The method is based on slant stacking or plane‐wave decomposition (PWD) of the observed data (seismogram), which transforms the data from the conventional T-X domain into the intercept time‐ray parameter domain. Since PWD places most of the compressional energy into the precritical region of the slant‐stacked seismogram, the compressional‐wave interval velocities can be estimated using the “best ellipse” approximation on the assumption that the elliptic array velocity (stacking velocity) is approximately equal to the root‐mean‐square (rms) velocity. Similarly, shear‐wave interval velocities can be estimated by inverting the traveltime curves in the region of the PWD seismogram, where compressional waves decay exponentially (postcritical region). The method is illustrated by examples using synthetic and real data.

scholarly journals Seismic Short-Refraction Studies on the Ross Ice Shelf, Antarctica

1979 ◽  
Vol 24 (90) ◽  
pp. 313-319
Author(s):  
Joseph F. Kirchner ◽  
Charles R. Bentley
Keyword(s):  
Shear Wave ◽  
Transverse Isotropy ◽  
Compressional Wave ◽  
Least Squares Regression ◽  
Horizontal Shear ◽  
Ice Shelf ◽  
Compressional Waves ◽  
Ross Ice Shelf ◽  
Wave Velocities ◽  
Shear Wave Velocities

AbstractSeismic short-refraction studies were carried out at five stations on the Ross Ice Shelf during the 1976–77 summer season as part of the comprehensive Ross Ice Shelf Geophysical and Glaciological Survey. Measurements of the velocities of compressional waves were made at each location. Compressional wave velocities were measured along more than one azimuth at three sites, and shear wave velocities (both components) at two. Travel-time curves were fitted to an exponential expression by means of a non-linear least-squares regression technique. The errors in the apparent velocities are estimated to be about ±50 m s–1 at short distances, diminishing to about ±10 m s–1 near the ends of the profiles. Compressional-wave velocities show only slight variations with azimuth and only over certain depth intervals, showing that constant-velocity surfaces are essentially horizontal. Shear-wave velocities, however, exhibit large variations according to azimuth and polarization, indicating that transverse isotropy is violated at least in the upper 30–40 m of the ice shelf. It is believed that the anisotropy is caused by structural details in the firn perhaps modified by preferred crystal orientation and that it may arise at least partly from anisotropic stresses in the ice shelf.

scholarly journals High-resolution shear wave reflection seismics as tool to image near-surface subrosion structures – a case study in Bad Frankenhausen, Germany

2016 ◽  
Author(s):  
Sonja Wadas ◽  
Ulrich Polom ◽  
Charlotte Krawczyk
Keyword(s):  
High Resolution ◽  
Shear Wave ◽  
Wave Reflection ◽  
Horizontal Shear ◽  
Seismic Profiles ◽  
Near Surface ◽  
Reflection Seismics ◽  
Seismic Sections ◽  
The Church

Abstract. Subrosion is the subsurface leaching of soluble rocks that results in the formation of depression and collapse structures.This global phenomenon is a geohazard in urban areas. To study near-surface subrosion structures four shear-wave reflection seismic profiles with a total length of ca. 332 m were carried out around the famous leaning church tower of Bad Frankenhausen in northern Thuringia, Germany, which shows an inclination of 4.93° from the vertical. Most of the geological underground of Thuringia is characterized by soluble Permian deposits, and the Kyffhäuser-Southern-Margin Fault is assumed to be a main pathway for water to leach the evaporite. The seismic profiles were acquired with the horizontal micro-vibrator ELVIS developed at LIAG and a 72 m long landstreamer equipped with 72 horizontal geophones. The high-resolution seismic sections show subrosion-induced structures to a depth of ca. 100 m and reveal five features associated with the leaching of Permian deposits: (1) lateral and vertical varying reflection patterns caused by strongly heterogeneous strata, (2) discontinuous reflectors, small offsets and faults, which show the underground is strongly fractured, (3) formation of depression structures in the near-surface, (4) diffractions in the unmigrated seismic sections that indicate an increased scattering of the seismic waves, (5) varying seismic velocities and low-velocity zones that were presumably caused by fractures and upward-migrating cavities. A previously undiscovered southward-dipping, listric normal fault was also found, located northward of the church. It probably serves as a pathway for water to leach the Zechstein formations below the church and causes the tilting of the tower. This case study shows the potential of horizontal shear-wave reflection seismics in imaging near-surface subrosion structures in an urban environment with a horizontal resolution of less than 1m in the uppermost 10–15 m.

scholarly journals High-resolution shear-wave seismic reflection as a tool to image near-surface subrosion structures – a case study in Bad Frankenhausen, Germany

Solid Earth ◽  
2016 ◽  
Vol 7 (5) ◽  
pp. 1491-1508 ◽  
Author(s):  
Sonja H. Wadas ◽  
Ulrich Polom ◽  
Charlotte M. Krawczyk
Keyword(s):  
High Resolution ◽  
Shear Wave ◽  
Urban Areas ◽  
Seismic Reflection ◽  
Seismic Velocities ◽  
Horizontal Shear ◽  
Near Surface ◽  
Seismic Sections ◽  
The Church

Abstract. Subrosion is the subsurface leaching of soluble rocks that results in the formation of depression and collapse structures. This global phenomenon is a geohazard in urban areas. To study near-surface subrosion structures, four shear-wave seismic reflection profiles, with a total length of ca. 332 m, were carried out around the famous leaning church tower of Bad Frankenhausen in northern Thuringia, Germany, which shows an inclination of 4.93° from the vertical. Most of the geological underground of Thuringia is characterized by soluble Permian deposits, and the Kyffhäuser Southern Margin Fault is assumed to be a main pathway for water to leach the evaporite. The seismic profiles were acquired with the horizontal micro-vibrator ELVIS, developed at Leibniz Institute for Applied Geophysics (LIAG), and a 72 m long landstreamer equipped with 72 horizontal geophones. The high-resolution seismic sections show subrosion-induced structures to a depth of ca. 100 m and reveal five features associated with the leaching of Permian deposits: (1) lateral and vertical varying reflection patterns caused by strongly heterogeneous strata, (2) discontinuous reflectors, small offsets, and faults, which show the underground is heavily fractured, (3) formation of depression structures in the near-surface, (4) diffractions in the unmigrated seismic sections that indicate increased scattering of the seismic waves, and (5) varying seismic velocities and low-velocity zones that are presumably caused by fractures and upward-migrating cavities. A previously undiscovered southward-dipping listric normal fault was also found, to the north of the church. It probably serves as a pathway for water to leach the Permian formations below the church and causes the tilting of the church tower. This case study shows the potential of horizontal shear-wave seismic reflection to image near-surface subrosion structures in an urban environment with a horizontal resolution of less than 1 m in the uppermost 10–15 m.

scholarly journals Seismic Short-Refraction Studies on the Ross Ice Shelf, Antarctica

1979 ◽  
Vol 24 (90) ◽  
pp. 313-319 ◽  
Author(s):  
Joseph F. Kirchner ◽  
Charles R. Bentley
Keyword(s):  
Shear Wave ◽  
Transverse Isotropy ◽  
Compressional Wave ◽  
Least Squares Regression ◽  
Horizontal Shear ◽  
Ice Shelf ◽  
Compressional Waves ◽  
Ross Ice Shelf ◽  
Wave Velocities ◽  
Shear Wave Velocities

AbstractSeismic short-refraction studies were carried out at five stations on the Ross Ice Shelf during the 1976–77 summer season as part of the comprehensive Ross Ice Shelf Geophysical and Glaciological Survey. Measurements of the velocities of compressional waves were made at each location. Compressional wave velocities were measured along more than one azimuth at three sites, and shear wave velocities (both components) at two. Travel-time curves were fitted to an exponential expression by means of a non-linear least-squares regression technique. The errors in the apparent velocities are estimated to be about ±50 m s–1at short distances, diminishing to about ±10 m s–1near the ends of the profiles. Compressional-wave velocities show only slight variations with azimuth and only over certain depth intervals, showing that constant-velocity surfaces are essentially horizontal. Shear-wave velocities, however, exhibit large variations according to azimuth and polarization, indicating that transverse isotropy is violated at least in the upper 30–40 m of the ice shelf. It is believed that the anisotropy is caused by structural details in the firn perhaps modified by preferred crystal orientation and that it may arise at least partly from anisotropic stresses in the ice shelf.

scholarly journals The Wavelets show it – the transit time of water varies in time

2018 ◽  
Vol 66 (3) ◽  
pp. 295-302 ◽  
Author(s):  
Milan Onderka ◽  
Vladimír Chudoba
Keyword(s):  
Transit Time ◽  
Time Distribution ◽  
Conceptual Modeling ◽  
Flow Paths ◽  
Transit Times ◽  
The Mean ◽  
Transit Time Distribution ◽  
Mathematical Techniques ◽  
Time Invariant

Abstract The ways how water from rain or melting snow flows over and beneath the Earth‘s surface affects the timing and intensity at which the same water leaves a catchment. Several mathematical techniques have been proposed to quantify the transit times of water by e.g. convolving the input-output tracer signals, or constructing frequency response functions. The primary assumption of these techniques is that the transit time is regarded time-invariant, i.e. it does not vary with temporarily changing e.g. soil saturation, evaporation, storage volume, climate or land use. This raises questions about how the variability of water transit time can be detected, visualized and analyzed. In this paper we present a case study to show that the transit time is a temporarily dynamic variable. Using a real-world example from the Lower Hafren catchment, Wales, UK, and applying the Continuous Wavelet Transform we show that the transit time distributions are time-variant and change with streamflow. We define the Instantaneous Transit Time Distributions as a basis for the Master Transit Time Distribution. We show that during periods of elevated runoff the transit times are exponentially distributed. A bell-shaped distribution of travel times was observed during times of lower runoff. This finding is consistent with previous investigations based on mechanistic and conceptual modeling in the study area according to which the diversity of water flow-paths during wet periods is attributable to contributing areas that shrink and expand depending on the duration of rainfall. The presented approach makes no assumptions about the shape of the transit time distribution. The mean travel time estimated from the Master Transit Time Distribution was ~54.3 weeks.

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