Applying the Manzocchi & Childs Model for Hydrodynamic Seal to Column Height Prediction in Traps

Abstract

Summary The role of hydrodynamics in capillary trapping has often been ignored in exploring for hydrocarbons in over-pressured basins. Conventional seal evaluation regards a top seal as static with seal capacity largely a function of the threshold capillary entry pressure, governed by the shale composition and its grain size distribution, and the relative fluid densities. Although possessing very low permeability, shale seals are not perfect seals and water can flow through them under an imposed hydraulic gradient. Likewise, water can also flow through hydrocarbon columns even though, because of the high hydrocarbon saturation, relative permeabilities may also be very low. The impact that this flow can have on the capillary seal capacity can, in theory, be quite profound and ideally should be considered in seal analysis workflows. This talk revisits the Manzocchi & Childs (2013) model for hydrodynamic seal as a means of evaluating the effect of excess pressure on seal capacity. How to implement the Manzocchi & Childs modelling approach in trap analysis is described and the technique then applied to several known over-pressured fields from the Norwegian continental shelf to assess its applicability. Results are shown to offer agreement between predicted and observed columns, potentially supporting the modelling approach.