Multi-scale Effective Flow Properties of Heterogeneous Mudstones
Andrew C. Aplin¹, Gary D. Couples², Michael Drews¹, Kuncho D. Kurtev¹, and Jingsheng Ma²
¹School of Civil Engineering and Geosciences, Newcastle University, Newcastle upon Tyne, UK
²Institute of Petroleum Engineering, Heriot Watt University, Edinburgh, UK
Constraining the flow properties of mud-rich sediments is a multi-scale problem which involves the quantification of properties at a sample (10-2m) scale in the laboratory and their use in the determination of effective properties at the log (100m) and seismic/basin modelling grid block (10²m) 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.
Here, we consider how to define the flow properties of Genetic Units (GUs), i.e. seismically definable volumes of sediment which represent the results of deposition in a particular setting, and which could readily be represented by cells within a basin model. Our focus has been on those GUs common within continental slope environments such as hemipelagites, mud turbidites and mass transport deposits. We divide the GUs into background and foreground units, in which background units comprise metre-scale, relatively low permeability, mud-rich sedimentary facies, and foreground units that include the higher permeability flow conduits which could be either depositional in nature (e.g. thin sands within a levee) or which could cross-cut the stratigraphy as a result of sand injection or mechanical deformation. The resulting combination of background and foreground elements defines the effective flow properties of any GU of given character; alternatively the approach allows us to define a small set of pre-determined templates which could be used to generate a look-up database from which one could populate a basin model.
AAPG Search and Discovery Article #120098©2013 AAPG Hedberg Conference Petroleum Systems: Modeling the Past, Planning the Future, Nice, France, October 1-5, 2012