Multi-scale effective flow properties of heterogeneous mudstones

Constraining the flow properties of mud-rich sediments is a multi-scale problem which involves the quantification of properties at a sample (10-2 m) scale in the laboratory and their use in the determination of effective properties at the log (100 m) and seismic/basin modelling grid block (102 m) scale. At the sample scale, we generally assume that samples are homogeneous and have compressibilities, permeabilities and threshold capillary pressures which are controlled mainly by lithology, defined, for example, by the proportions of clay, silt and sand. At larger scales, mud-rich sediments cannot be assumed to be homogeneous, so it is necessary to: (1) recognise the geometric arrangements at appropriate length scales; (2) construct models that capture these arrangements; (3) populate them with appropriate small-scale properties; and (4) run flow simulations from which it is possible to determine the effective properties at the target scale. This approach can be repeated at increasing length scales to derive upscaled properties at any scale that is needed in a simulation setting, such as in basin modelling. In the process of determining upscaled properties, knowledge is derived concerning which parts of the sedimentary and mechanical architecture exert critical controls on fluid flow up to and including that length scale.