Uncertainty Analysis in Capillary Controls Across Faults
Abstract
An important fluid-rock interaction is the capillary control on hydrocarbon flow retardation by fault
rocks formed by the processes of gouge or smear. These capillary controls impact both cross-
fault
flow between juxtaposed reservoirs, and up-
fault
flow for hydrocarbon migration at the reservoir and basin scale. A typical work-flow for evaluating capillary controls on faults cutting siliciclastic rocks is to estimate the clay content from algorithms such as shale gouge ratio or clay smear factor, convert these to capillary threshold pressure, and determine
fault
rock seal capacity. The clay content distribution across the
fault
is determined from the clay in the protolith and the
fault
throw. Uncertainties in this analysis may be introduced by the conversion of the clay content to flow properties, changes in the stratigraphic model, along-
fault
variation in
fault
geometry and throw, and
fault
rock heterogeneity. Introducing these uncertainties into the analysis, however, is often time consuming and tedious to address in 3D models. The stratigraphic distribution is generally modeled from local well data, seismic stratigraphic interpretation, and analogues, but the uncertainty in the clay estimates for the range of possible scenarios remains large. An alternative discussed here is running multiple realizations of base-case models of stratigraphic variation, applying different algorithms for predicting clay content and varying the throw. A range in the fluid properties such as density also defines a range in the predicted free-water level distributions. We define a methodology for the rapid evaluation of these important uncertainties by using multiple realizations based on triangle diagram analysis from single or multiple input wells. The analysis requires only well data and
fault
throw without the constraints of a 3D model. The methodology described results in more efficient calculation of the uncertainties and expected ranges in properties that influence capillary controls on flow.
AAPG Datapages/Search and Discovery Article #90350 © 2019 AAPG Annual Convention and Exhibition, San Antonio, Texas, May 19-22, 2019