Integrating Fault Seal Techniques – Explaining The Duality in Fault Behaviour

Dee, Stephen J.¹, Graham Yielding², Herald Ligtenberg³, Steven Losh⁴, Amanda Pouwel³, Brett Freeman², Peter Bretan² (1) Badley Geoscience Limited, Hundleby, Lincolnshire, United Kingdom (2) Badley Geoscience Ltd, Lincolnshire, United Kingdom (3) dGB Earth Sciences, Enschede, Netherlands (4) Cornell University, Ithaca, NY

Analysis of the sealing behaviour of faults re quires an understanding of the impact of faults on lateral and vertical fluid movement. Faults act both as migration and accumulation barriers, and as potential migration pathways vertically in the reservoir section. This duality in fault behaviour, as both barrier and conduit, is often overlooked in studies of migration and fault seal.

Fault bounded traps in siliciclastic rocks often depend on capillary seal to retain hydrocarbons. Estimates of properties such as SGR (shale gouge ratio) made from a static deterministic model of the reservoir structure and stratigraphy can be used in turn to estimate the capillary entry pressure of the fault zone and thus be used in modelling the fill and spill history.

Fluid migration pathway analysis on seismic data illustrates that this static understanding of reservoir juxtapositions and fault rock properties is an incomplete model to describe the hydraulic properties of faults. Faults may act as conduits to fluids, as evidenced by breached traps, gas chimneys, shallow charged reservoirs and seabed features.

A number of techniques exist for analysing leak potential of faults, including static deterministic models, stochastic models of stratigraphy, geomechanical reactivation models, seismic attribute analysis and neural network processing to reveal fluid movements.

In this paper we compare methodologies on the well-studied and constrained dataset from South Eugene Island Block 330 Field offshore Louisiana and illustrate how the conceptual models of fault behaviour can be used to make predictions of the hydraulic properties of subsurface faults.