Hierarchical approach for simulating fluid flow in normal fault zones

Abstract

Two-phase flow in faults is complex and difficult to predict. To analyse the effect of fault zones on fluid flow, this article presents a hierarchical geological/numerical framework aimed at simulating two-phase flow. The starting point is that fault zones consist of structures at several length scales, with each scale represented by suitable techniques within the same numerical model. A series of two-phase flow simulation experiments was conducted on four geological cases: one reference case with undeformed host rock and three cases with increasingly more complexity added to them. All the structures consist of lower permeability fault rocks in a high permeability host rock. The simulations were performed using an in-house flow simulator. The fault core (large scale) was modelled explicitly through local grid refinement, the subsidiary faults (intermediate scale) were represented in a discrete manner, while an upscaling procedure captured the effect of the deformation bands (fine scale). The simulation results show that each scale has a significant effect on the saturation, pressure drop and oil production, and that capillary pressure and anisotropic permeability are important parameters. The results emphasize the importance of the scale-dependent approach for analysing the effect of faults on two-phase flow.

Faults in conventional flow simulation models: a consideration of representational assumptions and geological uncertainties

“…Syversveen et al 2006) or two-phase fault rock properties (e.g. Berg & Øian 2007). Although different groups of workers may apply different geological idealizations of faults to define either the content and structure of the locally refined grids or the input to an upscaling solution, the overriding aim is identical: to represent more accurately the flow implications of fault-related geological heterogeneity.…”

“…Ringrose et al 1993;Manzocchi et al 1998Manzocchi et al , 2002Rivenaes & Dart 2002;Al-Busafi et al 2005;Berg & Øian 2007). The example reservoirs used in this study -although synthetic -contain scales, rates, fluids and pressures representative of real reservoirs (Manzocchi et al 2008a, Matthews et al 2008 and are, therefore, a good test of whether two-phase fault rock properties may, indeed, be of practical significance.…”

Flow processes and pressure evolution in aquifers during the injection of supercritical CO 2 as a greenhouse gas mitigation measure

“…Clearly fault zones with many tens or even hundreds of such deformation bands will have significantly reduced bulk permeability. Upscaling such multiple, millimetre-scale, and perhaps laterally impersistent, features into an equivalent cell permeability for numerical simulation purposes is highly problematical (e.g Walsh et al 1998;Berg & Øian 2007), and beyond the scope of this current paper. Away from the free CO 2 plume, we are mainly interested in single-phase (water) flow through much of the reservoir, so it may be that more empirical information from regional hydrogeological studies (e.g.…”

“…The flow of multi-phase fluids through flow barriers is a subject of considerable current research in the oil industry (e.g. Berg & Øian 2007). In the context of this paper however, we are principally interested in single-phase flow through faults to assess how easily formation water can be displaced laterally through a reservoir as CO 2 is introduced.…”

Laboratory measurements of the relative permeability of cataclastic fault rocks: An important consideration for production simulation modelling

“…The fact that we are assuming the fault to be a single plane, compared to the complex fault zone modelled by Berg and Øian (2007) means that we did not need to perform such an investigation for the present study.…”