Abstract
Sonic log data and core measurements are often used to develop models of in-situ stress profiles and rock elastic properties for use in hydraulic fracture design treatments in unconventional reservoirs. "Unconventional?? reservoirs, for the purposes of this paper, include shale-gas, coalbed methane, and tight-gas projects. In unconventional reservoirs, many of the assumptions underlying rock property estimation and stress profiling in conventional reservoirs may not apply. In fact, the result of using conventional approaches may be an incorrect and often misleading stress profile. Fracture geometry predicted using conventionally derived rock properties and stresses might also be inaccurate.
Methods of deriving rock properties from log and core measurements and the effect of various parameters on resulting moduli and stress estimates are examined. The paper also discusses the effects of rock anisotropy and inhomogeneity on static and dynamic properties. The impact of organic materials and trapped gas on sonic logs and conventional mechanical properties interpretation and the use of synthetic sonic logs are also presented. For static and dynamic measurements on core samples, the effects of the condition of recovered core and applied laboratory procedures on measurement results are also considered.
Potential errors resulting from the use of inappropriate mechanical properties for stress profiling and fracture geometry prediction can be significant. The paper identifies common pitfalls in core and log interpretation. A recommended procedure to determine useful and accurate rock mechanical properties for stress profile prediction and fracture design is presented.
