Field measurements of fracture characteristics on a wave-cut platform

2021 ◽  
Vol 9 (2) ◽  
pp. T453-T462
Author(s):  
Thomas Loriaux ◽  
James Verdon ◽  
J.-Michael Kendall ◽  
Alan Baird ◽  
James Wookey
Keyword(s):  
High Tide ◽  
Seismic Refraction ◽  
Field Measurements ◽  
Time Lapse ◽  
Natural Fracture ◽  
Effective Density ◽  
Seismic Velocities ◽  
S Wave ◽  
Fracture Characteristics ◽  
The Impact

We have used seismic refraction surveys of a wave-cut platform from a field site in South West England to characterize the impact of natural fracture networks on seismic velocities and anisotropy. Time-lapse surveys were performed as the high tide ebbed to investigate the seismic effects of the water draining from the rock. We also deployed a drone to map the fracture sets from the air. Azimuthal variations in the P- and S-wave velocities reflect the orientation of the main east–west-oriented joint set. Seismic velocities increased as the water drained, an effect attributed to a reduction in the effective density of the medium. The ratio of fracture normal ([Formula: see text]) to tangential ([Formula: see text]) compliance ([Formula: see text]), which can be used as a proxy for fracture saturation and permeability, was observed to increase from [Formula: see text] to [Formula: see text], primarily driven by a drop in [Formula: see text]. These variations are attributed to a decrease in the water content of the main fracture set as the tide retreats.

Surface Seismic Measurements of Near-Surface P- and S-Wave Seismic Velocities at Earthquake Recording Stations, Seattle, Washington

1999 ◽  
Vol 15 (3) ◽  
pp. 565-584 ◽  
Author(s):  
Robert A. Williams ◽  
William J. Stephenson ◽  
Arthur D. Frankel ◽  
Jack K. Odum
Keyword(s):  
Seismic Refraction ◽  
Ground Surface ◽  
Industrial Area ◽  
High Amplitude ◽  
Seismic Velocities ◽  
S Wave ◽  
Near Surface ◽  
Sedimentary Deposits ◽  
Reflection Data ◽  
Seismic Reflections

We measured P- and S-wave seismic velocities to about 40-m depth using seismic-refraction/reflection data on the ground surface at 13 sites in the Seattle, Washington, urban area, where portable digital seismographs recently recorded earthquakes. Sites with the lowest measured Vs correlate with highest ground motion amplification. These sites, such as at Harbor Island and in the Duwamish River industrial area (DRIA) south of the Kingdome, have an average Vs in the upper 30 m (V¯s30) of 150 to 170 m/s. These values of V¯s30 place these sites in soil profile type E (V¯s30 < 180 m/s). A “rock” site, located at Seward Park on Tertiary sedimentary deposits, has a V¯s30 of 433 m/s, which is soil type C (V¯s30: 360 to 760 m/s). The Seward Park site V¯s30 is about equal to, or up to 200 m/s slower than sites that were located on till or glacial outwash. High-amplitude P- and S-wave seismic reflections at several locations appear to correspond to strong resonances observed in earthquake spectra. An S-wave reflector at the Kingdome at about 17 to 22 m depth probably causes strong 2-Hz resonance that is observed in the earthquake data near the Kingdome.

A rock physics strategy for quantifying uncertainty in common hydrocarbon indicators

Geophysics ◽  
1998 ◽  
Vol 63 (6) ◽  
pp. 1997-2008 ◽  
Author(s):  
Gary Mavko ◽  
Tapan Mukerji
Keyword(s):  
Seismic Data ◽  
Rock Physics ◽  
Pore Fluid ◽  
Fluid Substitution ◽  
Seismic Velocities ◽  
S Wave ◽  
Seismic Attribute ◽  
The Impact ◽  
Quantifying Uncertainty ◽  
Range Of Values

We present a strategy for quantifying uncertainties in rock physics interpretations by combining statistical techniques with deterministic rock physics relations derived from the laboratory and theory. A simple example combines Gassmann’s deterministic equation for fluid substitution with statistics inferred from log, core, and seismic data to detect hydrocarbons from observed seismic velocities. The formulation identifies the most likely pore fluid modulus corresponding to each observed seismic attribute and the uncertainty that arises because of natural variability in formation properties, in addition to the measurement uncertainties. We quantify the measure of information in terms of entropy and show the impact of additional data about S-wave velocity on the uncertainty of the hydrocarbon indicator. In some cases, noisy S data along with noisy P data can convey more information than perfect P data alone, while in other cases S data do not reduce the uncertainty. We apply the formulation to a well log example for detecting the most likely pore fluid and quantifying the associated uncertainty from observed sonic and density logs. The formulation offers a convenient way to implement deterministic fluid substitution equations in the realistic case when natural geologic variations cause the reference porosity and velocity to span a range of values.

Pressure-dependent seismic velocities based on effective compliance theory and an asperity deformation model

Geophysics ◽  
2012 ◽  
Vol 77 (6) ◽  
pp. D229-D243 ◽  
Author(s):  
Kai Gao ◽  
Richard L. Gibson
Keyword(s):  
Pressure Dependence ◽  
Laboratory Data ◽  
Confining Pressure ◽  
Time Lapse ◽  
Hertzian Contact ◽  
Deformation Model ◽  
Seismic Velocities ◽  
Power Law Distribution ◽  
S Wave ◽  
Effective Compliance

Seismic velocities of rocks depend strongly on confining pressure, which is often explained by the fracture compliances changes within the rocks. It is important to have an accurate model describing the relations between confining pressure and seismic velocities for applications such as time-lapse reservoir characterization. We propose a new model to address this problem by combining the existing effective compliance theory with new solutions for the pressure dependence of fracture compliances. Specifically, we assume the fracture contact surface can be represented by a set of elastic hemispheres with radii following power-law distribution, and the pressure dependence of seismic velocities can be expressed through pressure-dependent normal and tangential fracture compliances that are derived from Hertzian contact theory. Joint data fittings of P- and S-wave velocity laboratory data show that our model is accurate. We also implement fluid substitution using our model to explain the similar stress-induced velocity variations of fluid-saturated fractured rocks.

Seismic Microzonation for Denizli Metropolitan Area, Turkey

2015 ◽  
Vol 802 ◽  
pp. 40-44
Author(s):  
Ali Aydin ◽  
Erdal Akyol ◽  
Mahmud Gungor ◽  
Nuray Soyatik ◽  
Suat Tasdelen
Keyword(s):  
Urban Areas ◽  
Seismic Refraction ◽  
Seismic Microzonation ◽  
Seismic Velocities ◽  
Two Dimensional ◽  
S Wave ◽  
City Center ◽  
Wave Velocities ◽  
Municipal Authority ◽  
Use Studies

This study presents microzonation of the Denizli city center, is about 225 km2. It is mainly rely on t seismic velocities of the tested soil. For seismic microzonation area of has been selected as the study area. Seismic refraction methods have been used to generate two-dimensional profiles at 310 locations. These p and s wave velocities are used to estimate boundaries of the velocities at every 2 and 5 m intervals up to a depth of 60 m. The results are satisfactory for urban planning and it can successfully be used in urban areas. The municipal authority may be considered to use the results for land use studies.

scholarly journals Assessing the impact of sea-level rise on a vulnerable coastal community in Accra, Ghana

2013 ◽  
Vol 5 (1) ◽  
Author(s):  
Kwasi Appeaning Addo ◽  
Michael Adeyemi
Keyword(s):  
Climate Change ◽  
Sea Level Rise ◽  
Sea Level ◽  
High Tide ◽  
Field Measurements ◽  
Marine Turtle ◽  
Intergovernmental Panel ◽  
Adaptation Measures ◽  
Coastal Community ◽  
The Impact

Climate change and its associated sea-level rise are expected to significantly affect vulnerable coastal communities. Although the extent of the impact will be localised, its assessment will adopt a monitoring approach that applies globally. The topography of the beach, the type of geological material and the level of human intervention will determine the extent of the area to be flooded and the rate at which the shoreline will move inland. Gleefe, a coastal community in Ghana, has experienced frequent flooding in recent times due to the increasing occurrence of storm surge and sea-level rise. This study used available geospatial data and field measurements to determine how the beach topography has contributed to the incidence of flooding at Gleefe. The topography is generally low-lying. Sections of the beach have elevations of around 1 m, which allows seawater to move inland during very high tide. Accelerated sea-level rise as predicted by the Intergovernmental Panel on Climate Change (IPCC) will destroy homes of the inhabitants and inundate the Densu wetlands behind the beach. Destruction of infrastructure will render the inhabitants homeless, whilst flooding of the wetlands will destroy the habitats of migratory birds and some endangered wildlife species such as marine turtle. Effective adaptation measures should be adopted to protect this very important coastal environment, the ecology of the wetlands and the livelihoods of the community dwellers.

scholarly journals Measuring and Modeling of P- and S-Wave Velocities on Crustal Rocks: A Key for the Interpretation of Seismic Reflection and Refraction Data

2011 ◽  
Vol 2011 ◽  
pp. 1-9 ◽  
Author(s):  
Hartmut Kern
Keyword(s):  
Seismic Reflection ◽  
Theoretical Calculations ◽  
Seismic Refraction ◽  
Central China ◽  
Seismic Velocities ◽  
S Wave ◽  
Velocity Anisotropy ◽  
Crustal Rocks ◽  
Wave Velocities

Lithologic interpretations of the earth crust from seismic wave velocities are non-unique so that inferences about composition can not be drawn. In order to evaluate how elastic properties of rock materials are controlled by lithology at in situ pressures and temperatures, compressional (Vp), shear wave velocities (Vs) and velocity anisotropy of crustal rocks were measured at conditions of greater depth. The first part deals with the interdependence of elastic wave propagation and the physical and lithological parameters. In the second part data from laboratory seismic measurements and theoretical calculations are used to interpret (1) a shallow seismic reflection line (SE Finland) and (2) a refraction profile of a deep crust (Central China). The comparison of the calculated velocities with the experimentally-derived in situ velocities of the Finnish crustal rocks give hints that microcracks have an important bearing on the in situ seismic velocities, velocity anisotropy and the reflectivity observed at relative shallow depth. The coupling of the experimentally-derived in situ velocities of P- and S-wave and corresponding Poisson's ratios of relevant exhumed high-grade metamorphic crustal rocks from Central China with respective data from seismic refraction profiling provided a key for the lithologic interpretation of a deep seismic crustal structure.

The effect of microstructure and nonlinear stress on anisotropic seismic velocities

Geophysics ◽  
2008 ◽  
Vol 73 (4) ◽  
pp. D41-D51 ◽  
Author(s):  
James P. Verdon ◽  
Doug A. Angus ◽  
J. Michael Kendall ◽  
Stephen A. Hall
Keyword(s):  
Time Lapse ◽  
Data Sets ◽  
Seismic Velocities ◽  
S Wave ◽  
Hydrocarbon Reservoir ◽  
Fluid Saturation ◽  
Nonlinear Stress ◽  
Intrinsic Shape ◽  
Saturation Effects ◽  
Stress Dependent

Recent work in hydrocarbon reservoir monitoring has focused on developing coupled geomechanical/fluid-flow simulations to allow production-related geomechanical effects, such as compaction and subsidence, to be included in reservoir models. To predict realistic time-lapse seismic signatures, generation of appropriate elastic models from geomechanical output is required. These elastic models should include not only the fluid saturation effects of intrinsic, shape-induced, and stress-induced anisotropy, but also should incorporate nonlinear stress-dependent elasticity. To model nonlinear elasticity, we use a microstructural effective-medium approach in which elasticity is considered as a function of mineral stiffness and additional compliance is caused by the presence of low-aspect ratio displacement discontinuities. By jointly inverting observed ultrasonic P- and S-wave velocities to determine the distribution of such discontinuities, we assessed the appropriateness of modeling them as simple, planar, penny-shaped features. By using this approximation, we developed a simple analytical approach to predict how seismic velocities will vary with stress. We tested our approach by analyzing the elasticity of various sandstone samples; from a United Kingdom continental shelf (UKCS) reservoir, some of which display significant anisotropy, as well as two data sets taken from the literature.

scholarly journals India’s Commitments to Increase Tree and Forest Cover: Consequences for Water Supply and Agriculture Production within the Central Indian Highlands

Water ◽  
2021 ◽  
Vol 13 (7) ◽  
pp. 959
Author(s):  
Benjamin Clark ◽  
Ruth DeFries ◽  
Jagdish Krishnaswamy
Keyword(s):  
Groundwater Recharge ◽  
Forest Cover ◽  
Hydrological Modeling ◽  
Monsoon Season ◽  
Forest Policy ◽  
Central India ◽  
Field Measurements ◽  
Tree Cover ◽  
Policy Goals ◽  
The Impact

As part of its nationally determined contributions as well as national forest policy goals, India plans to boost tree cover to 33% of its land area. Land currently under other uses will require tree-plantations or reforestation to achieve this goal. This paper examines the effects of converting cropland to tree or forest cover in the Central India Highlands (CIH). The paper examines the impact of increased forest cover on groundwater infiltration and recharge, which are essential for sustainable Rabi (winter, non-monsoon) season irrigation and agricultural production. Field measurements of saturated hydraulic conductivity (Kfs) linked to hydrological modeling estimate increased forest cover impact on the CIH hydrology. Kfs tests in 118 sites demonstrate a significant land cover effect, with forest cover having a higher Kfs of 20.2 mm hr−1 than croplands (6.7mm hr−1). The spatial processes in hydrology (SPHY) model simulated forest cover from 2% to 75% and showed that each basin reacts differently, depending on the amount of agriculture under paddy. Paddy agriculture can compensate for low infiltration through increased depression storage, allowing for continuous infiltration and groundwater recharge. Expanding forest cover to 33% in the CIH would reduce groundwater recharge by 7.94 mm (−1%) when converting the average cropland and increase it by 15.38 mm (3%) if reforestation is conducted on non-paddy agriculture. Intermediate forest cover shows however shows potential for increase in net benefits.

Application of geophysical methods for the investigation of the large gravitational mass movement of Séchilienne, France

2005 ◽  
Vol 42 (4) ◽  
pp. 1105-1115 ◽  
Author(s):  
O Meric ◽  
S Garambois ◽  
D Jongmans ◽  
M Wathelet ◽  
J L Chatelain ◽  
...  
Keyword(s):  
Rock Mass ◽  
Mass Movement ◽  
Seismic Refraction ◽  
Geophysical Methods ◽  
Time Lapse ◽  
Gravitational Mass ◽  
Electrical Tomography ◽  
Refraction Tomography ◽  
Geophysical Surveys ◽  
Geophysical Techniques

Several geophysical techniques (electromagnetic profiling, electrical tomography, seismic refraction tomography, and spontaneous potential and seismic noise measurement) were applied in the investigation of the large gravitational mass movement of Séchilienne. France. The aim of this study was to test the ability of these methods to characterize and delineate the rock mass affected by this complex movement in mica schists, whose lateral and vertical limits are still uncertain. A major observation of this study is that all the zones strongly deformed (previously and at present) by the movement are characterized by high electrical resistivity values (>3 kΩ·m), in contrast to the undisturbed mass, which exhibits resistivity values between a few hundred and 1 kΩ·m. As shown by the surface observations and the seismic results, this resistivity increase is due to a high degree of fracturing associated with the creation of air-filled voids inside the mass. Other geophysical techniques were tested along a horizontal transect through the movement, and an outstanding coherency appeared between the geophysical anomalies and the displacement rate curve. These preliminary results illustrate the benefits of combined geophysical techniques for characterizing the rock mass involved in the movement. Results also suggest that monitoring the evolution of the rock mass movement with time-lapse geophysical surveys could be beneficial.Key words: gravitational movement, geophysical methods, Séchilienne.

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