Physics-Driven Interface Modeling for Drainage and Imbibition in Fractures

Authors: Prodanovic, Masa, and Bryant, Steven L., University of Texas at Austin.

Venue: Society of Petroleum Engineers’ Annual Technical Conference & Exhibition in Anaheim, CA, November 11–14, 2007 (http://www.spe.org/atce/2007/ [external site].

Abstract: The geometric distribution of immiscible fluid phases in fractures is not readily accessible experimentally, so aperture-scale simulations of drainage and imbibition in realistic fractures can provide valuable insight. The project researchers implemented a level set method for computing location within a fracture of the interface between two fluids controlled by capillary forces. The movement of the interface in response to changes in capillary pressure is approximated as quasi-static displacement. Fluid interfaces are thus constant mean curvature surfaces, satisfying the Young-Laplace equation. Researchers applied a progressive-quasistatic (PQS) algorithm to determine when spontaneous pore-level events occur during fluid displacement. The algorithm captures reversible and irreversible behavior. The researchers illustrated the approach with two types of rough-walled fractures: a 3-D crack between irregular, impermeable surfaces; and a gap between irregular 2-D and 3-D grain packs. Researchers focused on the disconnected (defending) fluid volumes and (advancing) fluid main pathway, as the geometric properties of the fracture are varied—notably aperture and the number of contact points between the upper and lower fracture surfaces. The curvature of the fluid-fluid interface in the plane of the fracture is often ignored by invasion percolation simulation techniques, yet it is known to influence strongly the fluid cluster properties. The researchers’ simulations established the exact position and shape of the interface in realistic fracture geometries, from which fluid volumes, contact areas, and interface curvatures can be obtained. This establishes a new, mechanistic basis for predicting relative permeabilities in fractures and for evaluating transfer functions in dual-porosity flow models.

Related NETL Project
The goal of the related NETL project DE-FC26-06NT43067, “Mechanisms Leading to Co-existence of Gas and Hydrate in Ocean Sediments,” is to quantitatively describe and understand the manner in which methane is transported within the HSZ and, consequently, the growth behavior of methane hydrates at both the grain scale and bed scale.

NETL Project Contacts
NETL - Robert Vagnetti (Robert.Vagnetti@netl.doe.gov or 304-285-1334)
UT-Austin – Steven Bryant (steven_bryant@mail.utexas.edu or 512-471-3250)