There is a growing awareness among petroleum engineers of the value of rock mechanics based analytical approaches to wellbore stability and sand production problems. It is readily accepted that the key to successful engineering lies in the acquisition of reliable data. Geomechanical properties testing is often perceived, however, as being expensive. All to often only limited numbers of samples are tested. This paper demonstrates how porosity can be employed as a geomechanical index to enable rock mechanics materials properties to be estimated using general and field specific correlations. Such an approach can be used to extend the application of a limited number of calibration samples.

General correlations exist between porosity and the uniaxial compressive strength and Young's modulus of sandstones and carbonates. Most of the work reported in the literature has concentrated on correlating porosity with absolute values of mechanical properties. Strength is, however, a stress sensitive property, increasing as confining stress increases. It is shown that porosity correlates with the constants required to construct theoretical and empirical failure criteria which describe such behaviour. Porosity also reflects other geomechanical characteristics of sedimentary rocks including failure mode, fracture intensity, drilling rate and perforation penetration.

The utility of porosity as a geomechanical index enables existing core and log data to be utilised to extend the use of limited core material.

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