Improved Displacement and Sweep Efficiency in Gas Flooding

Public Abstract

Oil recovery from miscible gas flooding is the fastest growing improved oil recovery technique in the US. The contribution of miscible and immiscible gas flooding to US production is currently about 330,000 barrels of oil per day. As oil fields in the US mature, gas flooding will play a significant and growing role in meeting the energy demands of our domestic economy. Unfortunately, the recover efficiency from CO2 injection or other gases remains low. Thus, any technology that maximizes the efficiency of miscible gas flooding and reduces the volume and costs of the injected fluids would have a significant impact on US oil production.

Recovery by gas flooding can be extremely high when miscibility is achieved between gas and oil. There are two factors, however, that can lead to reduced gas-flood oil recovery. First miscibility may not be achieved because of limits on reservoir pressure, especially, in shallow oil reservoirs. Miscibility can still be achieved in lower-pressure oil reservoirs if the injected gas is enriched with components miscible with the oil. In such cases, miscibility between gas and oil depends on mass transfer between injected gas and resident oil; however, the effective concentration of the gas that contacts the oil is degraded by dispersive processes, crossflow, and mixing between injected slugs of water and gas. The degradation process reduces displacement efficiency. Second, sweep efficiency is often low with gas flooding, so that only a small portion of the reservoir is contacted by gas. Poor sweep efficiency increases the volume of gas required to recovery one barrel of oil, which significantly increases project costs. Sweep efficiency can be greatly improved with foam, but field application of foam is limited by a lack of connection between experimental studies of CO2 foam and knowledge of foam mechanisms. Furthermore, foam simulations to date have been limited either to purely empirical models, lacking a firm basis for prediction, or schematic, unrealistic reservoir geometries. Sweep efficiency can also be improved to a lesser extent by alternate water and gas injection (WAG), but the industry's current understanding of this complex process is limited.

The proposed research will address these needs. Fine-grid simulation studies of dispersive processes, applying a compositional simulator, will for the first time examine the combined effects of foam, dispersion and crossflow, and injection and enrichment strategies for miscibility in field application. Studies will examine optimal WAG ratios for both oil displacement and the limited improvements in sweep efficiency possible with conventional WAG processes. Mechanistic experimental and simulation studies will provide the physical data needed for predictive process simulation of gas flooding with either WAG or foam.

The proposed research will improve the recovery efficiency for miscible gas flooding of oil reservoirs, especially shallow reservoirs, through the application of foam, WAG processes, and CO2 enriched-gas injection. The specific objectives of the proposed research are to

  1. Quantify and predict the displacement efficiency that results from the interaction of phase behavior and dispersive mixing of injected gas with a variety of resident oils.
  2. Investigate the tradeoff between displacement efficiency and sweep efficiency that occurs during WAG injection in heterogeneous reservoirs.
  3. Measure laboratory data for CO2 foam needed for mechanistic foam modeling.
  4. Simulate foam floods using these laboratory data in realistically heterogeneous formations.
  5. Combine analytical and simulation models for microscopic displacement, dispersion, foam processes, and WAG to model for the firs time the interaction between compositional displacement waves and the advance of foam into the reservoir.

This research would be sponsored by the Department of Energy.

Contact:

Russell T. Johns
Center for Petroleum and Geosystems Engineering
1 University Station C0304
The University of Texas at Austin
Austin, Texas 78712-0228
Phone: (512) 471-1267 FAX: (512) 471-9605
Email: rjohns@mail.utexas.edu

See the Reservoir Engineering page for information on related research.