Brittleness computation from rock moduli without density

Abstract

Brittleness is a key property for horizontal well placement, fracture development, and production sustainability assessments of unconventional shale and gas plays. Conventionally, brittleness is estimated from Young’s modulus and Poisson’s ratio, and averaged. As Young’s modulus is a function of density, field wide brittleness estimation from Young’s modulus after seismic inversion may be compromised because density is the least accurate estimate compared to acoustic impedance and shear impedance. A simple quantitatively equivalent brittleness computation can be made from using Young’s modulus × density rather than directly from Young’s modulus. Further, it is preferable to use the average brittleness estimation from Young’s modulus × density and shear modulus × density rather than the conventional average, because Poisson’s ratio is an indicator of lithology rather than brittleness. Examples of brittleness and total organic carbon estimation first from well logs, then from rock parameters inverted from 3D land seismic data successfully mapped a brittle shale zone in a Silurian hot shale, a known source rock onshore Turkey and now targeted as oil shale play. The estimated brittleness and total organic carbon showed agreement with the core analysis made at another well on the same prospect.