Faults as Conduit Barrier Systems for Oil and Brine Migration

Yao You¹, Mark Person¹, and Victor Bense^2
1Geological Sciences, Indiana University, Bloomington, IN
²School of Environmental Sciences, University of East Anglia, Norwich, United Kingdom

Faults can act as conduits/barrier systems for brine and petroleum migration in basins provided that significant clay and sand smearing occurs during fault block controlled subsidence. While a great deal of progress has been made during the last decade characterizing the variations in fault permeability due to spatial variations in fault throw and sediment properties, few studies have quantified these effects in a three-dimensional context. Here we present a new three-dimensional finite element model (RIFT3D) to study the effects of faults on subsurface fluid flow within evolving rift basins. Our model uses a novel dynamic remeshing algorithm for representing the geometric and petrophysical evolution of fault zones/blocks in response to subsidence and sedimentation. The conduit/barrier model of Bense and Person (2006, Water Resources Research, 42, W05421, doi:10.1029/2005WR004480) was to calculate hydrogeologic properties of the fault zones. We present results from of idealized compacting basin which included three subsiding fault blocks and two fault zones. Oil migration was represented using Hubbert’s oil potential. We estimated capillary-pressures in confining units based on pore throat radius. Results indicate that for brines, fault act as a conduit in the direction of fault throw and a barrier in the direction perpendicular to the fault plane. For the oil phase, faults act as barrier in both directions. However, when lateral variations in grain size are included, oil migration travels from the lower to upper reservoirs finding the path of least resistance across fault the planes.

AAPG Search and Discover Article #90078©2008 AAPG Annual Convention, San Antonio, Texas