Determination of lithology and brittleness of rocks with a new attribute

Abstract

The discrimination of fluid content and lithology in a reservoir is an important characterization that has a bearing on reservoir development and its management. For unconventional reservoirs such as shale-gas formations, it is vital that reservoir zones are brittle, besides other favorable considerations that are expected of them. Brittle zones fracture better, and fracturing of shale-gas reservoirs is required for their production. Among the different physical parameters that characterize the rocks, Young's modulus (E) is a measure of brittleness. Attempts usually are made to determine this physical constant from well-log data, but such measurements are localized over a small area. For studying lateral variation of brittleness in an area, 3D seismic data need to be used. Computation of Young's modulus from seismic data requires the availability of density (ρ). The computation of density in turn requires long-offset seismic data, which usually are not available. A new attribute (Eρ) is in the form of a product of Young's modulus and density. For a brittle rock, both Young's modulus and density are expected to be high, and so the Eρ attribute would exhibit a high value and serve as a brittleness indicator. This new attribute is useful for lithofluid detection, when it is used in conjunction with the product of bulk modulus and density.