Prediction of seismic-wave velocities in rock at various confining pressures based on unconfined data

Abstract

Laboratory measurement of P- and S-wave velocities ([Formula: see text] and [Formula: see text], respectively) under confining pressure indicates that with an increase in confining pressure, [Formula: see text] and [Formula: see text] will increase. The trend is exponential at low pressures, transitioning to linear above a critical pressure. However, the trend of the velocity-pressure curve for each rock specimen may be determined knowing the coefficients of this curve. We first studied how the coefficients of the velocity-pressure curve were expected to be functions of elastic moduli. Then, four empirical equations were used to estimate four coefficients of the velocity-pressure curve, using the rock density and [Formula: see text] and [Formula: see text] at atmospheric pressure (unconfined conditions). This analysis was carried out based on laboratory experiments on 285 rock specimens of different lithology from around the world, namely the United States, China, Germany, Iran, and deep-sea-drilling projects. For each rock specimen, [Formula: see text] and [Formula: see text] were measured at different confining stress levels, rendering more than 4000 data points. The accuracy of the estimated wave velocities was on the order of 2%–3% of the measured values on average. This methodology is especially valuable for prediction and analysis of the rock behavior at deep well conditions. This is applicable for predicting geophysical properties of the earth’s crust at depth, geomechanical study of hydrocarbon and geothermal reservoirs, wellbore stability analysis, and in situ stress determination.

Seismicity and the State of Stress in the Dezful Embayment, Zagros Fold and Thrust Belt

“…The study carried out by Najibi, et al [59] shows that the uniaxial compressive rock strength (UCS) of limestone in the Sarvak and Asmari Formations varies considerably between 30 to 180 MPa, with the most-frequent value being 80 MPa (Figure S4). The same results have been reported by other studies [59][60][61][62][63][64][65][66]. Note that the Asmari and Sarvak Formations, as described above, also contain sandstone and shale of lower strength than the carbonate parts.…”

Method for weak zones location at the coal-bed – host rock joint relative to the problem of sudden outbursts: theory and laboratory experiment

“…The velocity of elastic waves in rocks depends on stresses [45,46]. Weak zones at the coal-bed-host rock interface perturb the stress field (Figs.…”

Optimization of neural-network model using a meta-heuristic algorithm for the estimation of dynamic Poisson’s ratio of selected rock types

“…In addition, several attempts have been made to develop predictive relationships for different physic-mechanical parameters of rocks such as compressive strength, tensile strength, shear strength, elastic moduli, porosity, permeability, acoustic wave velocities, etc. 16 , 29 – 32 . There is limited literature available that focuses on the predictive modeling of dynamic Poisson’s ratio.…”