Deriving rock moduli from acoustic velocities is the most common method for evaluating formation mechanical strength in the petroleum industry. While common, the accuracy of the method is hindered by the difficulty correcting the moduli, as measured by the acoustic logging tool to values representative of the actual moduli of the rock.
Analysts generally rely on simple empirical equations to provide the estimates for the corrections that must be made. These empirical equations are usually derived from wireline logs or from core analysis of samples taken from the formation of interest. The usefulness and accuracy of this method of modulus correction is hampered by the fact that the dynamic-to-static conversions are strongly non-linear. The method is also hampered by the rather narrow range of values available in a particular empirical function.
This paper presents an empirical method featuring a simple, single equation that provides estimates of static Young's modulus across the whole-range stresses and rock strengths that might be encountered in a reservoir.