The influence of pore fluids and frequency on apparent effective stress behavior of seismic velocities

Geophysics ◽  
2010 ◽  
Vol 75 (1) ◽  
pp. N1-N7 ◽  
Author(s):  
Gary Mavko ◽  
Tiziana Vanorio
Keyword(s):  
Elastic Wave ◽  
Bulk Modulus ◽  
Effective Stress ◽  
High Frequency ◽  
Laboratory Data ◽  
Pore Fluids ◽  
Wave Velocities ◽  
Stress Behavior ◽  
Stress Coefficient ◽  
The Impact

Although poroelastic theory predicts that the effective stress coefficient equals unity for elastic moduli in monomineralic rocks, some rock elastic wave velocities measured at ultrasonic frequencies have effective stress coefficients less than one. Laboratory effective stress behavior for P-waves is often different than S-waves. Furthermore, laboratory ultrasonic velocities almost always reflect high-frequency artifacts associated with pore fluids, including an increase in velocities and flattening of velocity-versus-pressure curves. We have investigated the impact of pore fluids and frequency on the observed effective stress coefficient for elastic wave velocities by developing a model that calculates pore-fluid effects on velocity, including high-frequency squirt dispersion, and we have compared the model’s predictions with laboratory data. We modeled a rock frame with penny-shaped cracks for three situations: vacuum dry, saturated with helium, and saturated with brine. Even if the frame modulus depends only on the differential stress, the saturated-rock effective stress coefficient is predicted to be significantly less than one at ultrasonic frequencies because of two effects: an increase in the fluid bulk modulus with increasing pressure and the contribution of high-frequency squirt dispersion. The latter effect is most significant in soft fluids (helium in this experiment) in which the fluid-bulk modulus is less than or comparable to the thin-crack pore stiffness.

Incorporating mechanisms of fluid pressure relaxation into inclusion‐based models of elastic wave velocities

Geophysics ◽  
2003 ◽  
Vol 68 (4) ◽  
pp. 1173-1181 ◽  
Author(s):  
S. Richard Taylor ◽  
Rosemary J. Knight
Keyword(s):  
Elastic Wave ◽  
Water Saturation ◽  
Laboratory Data ◽  
Fluid Pressure ◽  
P Wave ◽  
Porous Rocks ◽  
Low Frequencies ◽  
Wave Velocities ◽  
Exact Agreement ◽  
Flow Through

Our new method incorporates fluid pressure communication into inclusion‐based models of elastic wave velocities in porous rocks by defining effective elastic moduli for fluid‐filled inclusions. We illustrate this approach with two models: (1) flow between nearest‐neighbor pairs of inclusions and (2) flow through a network of inclusions that communicates fluid pressure throughout a rock sample. In both models, we assume that pore pressure gradients induce laminar flow through narrow ducts, and we give expressions for the effective bulk moduli of inclusions. We compute P‐wave velocities and attenuation in a model sandstone and illustrate that the dependence on frequency and water‐saturation agrees qualitatively with laboratory data. We consider levels of water saturation from 0 to 100% and all wavelengths much larger than the scale of material heterogeneity, obtaining near‐exact agreement with Gassmann theory at low frequencies and exact agreement with inclusion‐based models at high frequencies.

Thermal effective stress in shales

2019 ◽  
Vol 38 (5) ◽  
pp. 374-378
Author(s):  
Jeremy Gallop
Keyword(s):  
Effective Stress ◽  
Reservoir Characterization ◽  
Time Lapse ◽  
Forward Modeling ◽  
Calibration Data ◽  
S Wave ◽  
Wave Velocities ◽  
Proposed Model ◽  
Stress Coefficient ◽  
The Matrix

Calculating velocities in shales in thermal production settings is important to refine time-lapse reservoir characterization from seismic. The effective stress concept is attractive to potentially reduce the amount of expensive core calibration data required. We propose a formulation for thermal effective stress in shales based on the idea of balancing undrained pore pressure increments from thermal expansion with an increase in the matrix stress to minimize pore deformation. This formulation is motivated by a desire to simplify forward modeling, reduce the number of dimensions that must be experimentally calibrated through core testing, and to leverage existing velocity-stress relations for thermal applications. The concept was tested on data from a well-known set of experiments consisting of two North Sea Kimmeridge shale core samples, which displayed a linear dependence of velocity on pressure and temperature. These data were found to be consistent with the proposed thermal effective stress model with a constant effective stress coefficient when considering elastic changes but do not prove that the concept is universally valid. Thermal effective stress coefficients were calculated for P- and S-wave velocities from the data and were found to lie from 0.66 to 1.22, demonstrating reasonable scaling for the proposed model.

An inclusion‐based model of elastic wave velocities incorporating patch‐scale fluid pressure relaxation

Geophysics ◽  
2003 ◽  
Vol 68 (5) ◽  
pp. 1503-1509 ◽  
Author(s):  
S. Richard Taylor ◽  
Rosemary J. Knight
Keyword(s):  
Elastic Wave ◽  
Elastic Moduli ◽  
Effective Medium Theory ◽  
Fluid Pressure ◽  
P Wave ◽  
Pore Fluids ◽  
Wave Velocities ◽  
Wave Cycle ◽  
Dependent Flow ◽  
Patch Scale

We consider elastic wave velocities in fluid‐saturated porous media with pore fluids distributed in “patches” (i.e., heterogeneity much larger than the typical pore size). We model elastic properties of such materials using inclusion‐based effective medium theory (IBEMT). The standard IBEMT formulation assumes insufficient time during the wave cycle for pore fluids to flow in response to wave‐induced pressure gradients. Our approach accounts for this flow, incorporating wave‐frequency dependent flow effects in the definition of effective elastic moduli for patches. Effective moduli are used in conjunction with IBEMT to estimate elastic moduli of the composite material. In the low‐ and high‐frequency limits, the model reproduces previous theoretical results. At intermediate frequencies, it yields results qualitatively similar to other patch‐scale models. We demonstrate this approach, estimating elastic P‐wave velocities and attenuation in a porous rock that simultaneously contains fluid‐saturated patches of different sizes.

scholarly journals Ultrasonic moduli for fluid-saturated rocks: Mavko-Jizba relations rederived and generalized

Geophysics ◽  
2009 ◽  
Vol 74 (4) ◽  
pp. N25-N30 ◽  
Author(s):  
Boris Gurevich ◽  
Dina Makarynska ◽  
Marina Pervukhina
Keyword(s):  
Elastic Wave ◽  
Bulk Modulus ◽  
Quantitative Model ◽  
Pore Fluid ◽  
Porous Rocks ◽  
Laboratory Measurements ◽  
Shear Moduli ◽  
Wave Velocities

Mavko and Jizba propose a quantitative model for squirt dispersion of elastic-wave velocities between seismic and ultrasonic frequencies in granular rocks. Their central results are the expressions for the so-called unrelaxed frame bulk and shear moduli computed under an assumption that the stiff pores are drained (or dry) but the soft pores are filled with fluid. Mavko-Jizba expressions are limited to liquid-saturated rocks but become inaccurate when the fluid-bulk modulus is small (e.g., for gas-saturated rocks). We have derived new expressions for unrelaxed moduli of fluid-saturated porous rocks using Sayers-Kachanov discontinuity formalism. The derived expressions generalize the established Mavko-Jizba relations to gas-saturated rocks, reduce to Mavko-Jizba results when the pore fluid is liquid, and yield dry moduli when fluid-bulk modulus tends to zero. We tested this by comparing our model and the model of Mavko and Jizba against laboratory measurements on a sample of Westerly granite.

The Impact of Noise Expose on the Hearing Threshold Extended High Frequency

2008 ◽  
Vol 20 (2) ◽  
pp. 81 ◽  
Author(s):  
Nam Jeong Kim ◽  
Joong Keun Kwon ◽  
Ji Ho Lee
Keyword(s):  
High Frequency ◽  
Hearing Threshold ◽  
The Impact

Glucose Levels and Outcome After Primary Intraventricular Hemorrhage

2019 ◽  
Vol 16 (1) ◽  
pp. 40-46
Author(s):  
Rui Guo ◽  
Ruiqi Chen ◽  
Chao You ◽  
Lu Ma ◽  
Hao Li ◽  
...  
Keyword(s):  
Diabetes Mellitus ◽  
Blood Glucose ◽  
Blood Glucose Level ◽  
Incidence Rate ◽  
Glucose Level ◽  
Intraventricular Hemorrhage ◽  
Laboratory Data ◽  
History Of ◽  
Poor Outcomes ◽  
The Impact

Background and Purpose: Hyperglycemia is reported to be associated with poor outcome in patients with spontaneous Intracerebral Hemorrhage (ICH), but the association between blood glucose level and outcomes in Primary Intraventricular Hemorrhage (PIVH) remains unclear. We sought to identify the parameters associated with admission hyperglycemia and analyze the impact of hyperglycemia on clinical outcome in patients with PIVH. Methods: Patients admitted to Department of Neurosurgery, West China Hospital with PIVH between 2010 and 2016 were retrospectively included in our study. Clinical, radiographic, and laboratory data were collected. Univariate and multivariate logistic regression analyses were used to identify independent predictors of poor outcomes. Results: One hundred and seventy patients were included in the analysis. Mean admission blood glucose level was 7.78±2.73 mmol/L and 10 patients (5.9%) had a history of diabetes mellitus. History of diabetes mellitus (P = 0.01; Odds Ratio [OR], 9.10; 95% Confidence Interval [CI], 1.64 to 50.54) was independent predictor of admission critical hyperglycemia defined at 8.17 mmol/L. Patients with admission critical hyperglycemia poorer outcome at discharge (P < 0.001) and 90 days (P < 0.001). After adjustment, admission blood glucose was significantly associated with discharge (P = 0.01; OR, 1.30; 95% CI, 1.06 to 1.59) and 90-day poor outcomes (P = 0.03; OR, 1.27; 95% CI, 1.03 to 1.58), as well as mortality at 90 days (P = 0.005; OR, 1.41; 95% CI, 1.11 to 1.78). In addition, admission critical hyperglycemia showed significantly increased the incidence rate of pneumonia in PIVH (P = 0.02; OR, 6.04; 95% CI 1.27 to 28.80) even after adjusting for the confounders. Conclusion: Admission blood glucose after PIVH is associated with discharge and 90-day poor outcomes, as well as mortality at 90 days. Admission hyperglycemia significantly increases the incidence rate of pneumonia in PIVH.

Global Algorithmic Capital Markets

2018 ◽  
Keyword(s):  
Public Policy ◽  
Capital Markets ◽  
Systemic Risk ◽  
High Frequency ◽  
Investor Protection ◽  
High Frequency Trading ◽  
Market Making ◽  
Market Governance ◽  
Policy Objectives ◽  
The Impact

This book illustrates and assesses the dramatic recent transformations in capital markets worldwide and the impact of those transformations. ‘Market making’ by humans in centralized markets has been replaced by supercomputers and algorithmic high frequency trading operating in often highly fragmented markets. How do recent market changes impact on core public policy objectives such as investor protection, reduction of systemic risk, fairness, efficiency, and transparency in markets? The operation and health of capital markets affect all of us and have profound implications for equality and justice in society. This unique set of chapters by leading scholars, industry insiders, and regulators sheds light on these and related questions and discusses ways to strengthen market governance for the benefit of society at large.

scholarly journals Crisis Management in Higher Education in the Time of Covid-19: The Case of Actor Training

2021 ◽  
Vol 11 (3) ◽  
pp. 132
Author(s):  
Anna McNamara
Keyword(s):  
Higher Education ◽  
Crisis Management ◽  
High Frequency ◽  
High Reliability ◽  
Actor Training ◽  
Management Actions ◽  
The Usa ◽  
The Uk ◽  
The Impact ◽  
High Frequency Words

The impact of Covid-19 placed Higher Education leadership in a state of crisis management, where decision making had to be swift and impactful. This research draws on ethea of mindfulness, actor training techniques, referencing high-reliability organisations (HRO). Interviews conducted by the author with three leaders of actor training conservatoires in Higher Education institutions in Australia, the UK and the USA reflect on crisis management actions taken in response to the impact of Covid-19 on their sector, from which high-frequency words are identified and grouped thematically. Reflecting on these high-frequency words and the thematic grouping, a model of mindful leadership is proposed as a positive tool that may enable those in leadership to recognise and respond efficiently to wider structural frailties within Higher Education, with reference to the capacity of leaders to operate with increased mindfulness, enabling a more resilient organisation that unlocks the locus of control.

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