Field-Scale CO2 Flood Simulations and Their Impact on the Performance of the Wasson Denver Unit
- C-F. Hsu (Shell Western E&P Inc.) | J.I. Morell (Shell Development Co.) | A.H. Falls (Shell Western E&P Inc.)
- Document ID
- Society of Petroleum Engineers
- SPE Reservoir Engineering
- Publication Date
- February 1997
- Document Type
- Journal Paper
- 4 - 11
- 1997. Society of Petroleum Engineers
- 5.1 Reservoir Characterisation, 2.2.2 Perforating, 5.4.1 Waterflooding, 5.4.2 Gas Injection Methods, 5.6.1 Open hole/cased hole log analysis, 5.2.2 Fluid Modeling, Equations of State, 5.5.8 History Matching, 5.4.7 Chemical Flooding Methods (e.g., Polymer, Solvent, Nitrogen, Immiscible CO2, Surfactant, Vapex), 4.3.4 Scale, 5.2.1 Phase Behavior and PVT Measurements, 5.8.7 Carbonate Reservoir, 5.6.9 Production Forecasting, 4.5 Offshore Facilities and Subsea Systems, 1.1 Well Planning, 1.6.6 Directional Drilling, 5.1.1 Exploration, Development, Structural Geology, 5.5 Reservoir Simulation
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Recent advances in software and hardware technology have made possible the development of field-scale, fully compositional CO2 flood simulations capable of capturing areal variations in performance on an individual well basis. This paper first describes the general methodology developed, including key elements used to construct such large models, followed by the validation of this approach. Two modeling studies conducted on the Wasson Denver Unit are then presented to highlight several of the significant outcomes realized so far: high-grading the profitability of new CO2 projects, pinpointing best well candidates to return to production, identifying infill and horizontal drilling locations, and identifying and quantifying injectant losses.
The Denver Unit is located in Yoakum and Gaines County, Texas. The on-going CO2 project in this Unit is one of the world's largest. Each day, more than 500 million SCF of CO2 are injected into, while 39,000 barrels of oil are produced from the 1500 wells within the 21,000-acre project area. Since mid 1984, incremental oil recovery attributable to this tertiary process has exceeded 53 million barrels. Well-planned field operations and careful surveillance have both contributed to the success of this project. As of January 1994, CO2 developments of the Oil Column, the historical producing interval of the San Andres formation. have been relatively complete; the largest untapped reserves within the Unit are the 650 million barrels of paleo residual oil accumulated below the Oil Column.
To profitably operate the on-going floods and to continue expansions of new CO2 developments under current oil prices, a much greater engineering and surveillance effort than ever before is required. As part of this effort, field-scale simulations have been employed to provide well-specific forecasts - a key piece of information which can help uncover flood improvement opportunities and high-grade new CO2 projects. An equation-of-state, compositional simulator has been chosen in the study because it can provide more reliable predictions of CO2-oil phase behavior than a black-oil-type model. Recent advances in simulation technology have made this effort possible. A study by Hill et al. has indicated that the simulator employed in the present study can provide reasonable predictions of the production response of a CO2 pilot in the South Welch Unit.
In this paper, basic building elements of the modeling methodology such as reservoir characterization, phase behavior, relative permeability, and the process of validating the models are described first. Subsequently, key results of two field-scale simulation studies are summarized to highlight the impact of simulations on the field performance. The first case illustrates how we utilized a "TZ model" to design and high-grade CO2 flood expansions to recover residual oil in the Transition Zone. The second case demonstrates the use of a "Battery 1 model" to improve the on-going CO2 developments.
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