Water injection is being used extensively in the North Oregon Basin, Wyoming Tensleep formation to improve oil recovery. This paper describes the development of a discrete fracture network (DFN) model of the reservoir, and the use of that model to simulate the effect of water injection. In the fractured, heterogeneous Tensleep formation, discrete fractures and eolian sandstones provide discrete pathways both for oil production and for water migration. The DFN approach addresses the geometry and occurrence of these pathways directly by explicitly modeling fractures, dolomite barriers, and conductive eolian bedding planes. In addition, the DFN approach is used to address the geometry of hydraulic compartments formed by networks of discrete features
The Oregon Basin in Wyoming contains major oil and gas reservoirs, with production from two domes separated by a small saddle. Production from the 500 meter thick Paleozoic oil column in the Phosphoria carbonate, Tensleep sandstone, and the Madison limestone has been over 350 MMBO since the discovery of oil in 1927 (Stone, 1984).
Water injection started in the 1960's and until 1968, increased water brought increased oil production. At the peak, 50,000 BPD of water were injected and 9,000 BPD of oil was produced (Cordinet & Livingston, 1977). In 1968 production dropped when water breakthroughs occurred in wells near the water-oil contact. Since 1968, improved production has depended upon strategic completion, horizontal wells, and gel treatments to maintain production while minimizing water breakthrough.
This paper describes the use of the discrete fracture network (DFN) approach to optimize water injection for improved oil recovery (IOR) in the Tensleep Formation of the Oregon Basin North Dome (Figure 1). In the discrete fracture network approach, we build a 3D model of the hydraulic features that control water and oil movement within the reservoir. This information makes it possible to better understand both the compartmentalization which controls oil delivery to wells and the hydraulic pathways which result in water breakthrough from underlying aquifers.
