Stephan K. Matthai¹, Sebastian Geiger², David J. Campagna³

(1) Imperial College, London, England
(2) Swiss Federal Institute of Technology, CH-8092 Zurich, Switzerland
(3) Fracture Quest, LLC, Williamsburg, VA

ABSTRACT: Drawdown-Dependent Recovery and Water Invasion in Numerical Models of Fractured Hydrocarbon Reservoirs

The efficient extraction of oil from water-diluted, finite-sized hydrocarbon pools in fractured reservoir rock represents a difficult engineering problem. Principally, flow patterns are strongly focused by the fractures but these amount to less than a tenth of a percent of the reservoir's storage. As drawdown spreads faster in the fracture network, larger fractures extending beyond the hydrocarbon pool tap into water-saturated rock and water flow dominates while the hydrocarbons remain trapped in the fracture-bounded blocks. If a large drawdown pressure is applied to the reservoir wells in order to drain it fast, formation water will invade the fracture network and oil production ceases. On the other hand, the slower a reservoir is drained, the longer it takes to recover the exploration and production costs.

It will be shown that a production-rate dependent recovery is partially due to presence of and the nature of capillary barriers existing in the rock bridges among segmented natural fractures. For this purpose we present results from numerical simulations which are aimed at optimizing well placement and the rate of production/injection such that fracture-bounded reservoir blocks are drained, but water invasion from outside of the hydrocarbon pool is minimized. Reservoir geometries for these models are based on natural fracture and deformation band patterns as mapped in sandstones with reservoir properties located at Arches National Park, Utah. These were represented in 2D two-phase flow models the behavior of which shall be illustrated in the presentation.

AAPG Search and Discovery Article #90906©2001 AAPG Annual Convention, Denver, Colorado