Assessing the impact of hydrodynamics on capillary seal capacity: application of the Manzocchi & Childs model in trap analysis workflows

Abstract

The evaluation of seal in conventional stratigraphic and structural traps requires the characterisation of the capillary top seal to assess the capacity to hold a hydrocarbon column. Typically, this seal analysis addresses the static seal and does not consider the role that hydrodynamics (the flow of water into or out of the shale seal) may play in influencing the seal capacity. Although possessing extremely low permeability, shale seals are not perfect seals and water can move through them under an imposed hydraulic gradient. Likewise, water can flow through trapped hydrocarbon columns even though relative permeabilities can be very low (Teige et al., 2005). The impact of this flow on the capillary seal capacity can, in theory, be quite profound and should be considered in seal analysis workflows. This paper revisits the Manzocchi & Childs (2013) model for hydrodynamic effects on capillary seals and employs it directly in real-world trap analysis. The implementation of this model is described, and a workflow developed to incorporate the impact of hydrodynamics into column height prediction. The technique is applied to several known over-pressured fields from the Norwegian continental shelf to evaluate its applicability. Preliminary results from Monte Carlo modelling are promising and appear to offer some agreement between the observed column heights and the predicted hydrodynamic seal-controlled columns, dependant on the parameterisation used. Further testing is ongoing, but the methodology should be considered for routine application, particularly in exploration prospect evaluation. The impact of hydrodynamics on seal capacities should not be discounted. Thematic collection: This article is part of the Fault and top seals 2022 collection available at: https://www.lyellcollection.org/topic/collections/fault-and-top-seals-2022