Material Compatibility and Systems Considerations in Thermal EOR Environments Containing High-Pressure Oxygen
Authors: Zawierucha R. , Drnevich R.F. , McIlroy K. , Knecht P. 
Published: December 2007

Corrosion is a concern in all thermal EOR projects. In oxygen firefloods, corrosion and the compatibility of metallic and nonmetallic materials with high-pressure oxygen have to be addressed. A materials-selection baseline is evolving from laboratory corrosion and compatibility testing performed to support ongoing oxygen-fireflood projects.

Introduction

Thermal techniques currently account for more than two-thirds of the oil recovered through EOR. Although steam dominates commercial production, air fireflooding also is used commercially. Oxygen fireflooding is relatively new and, depending on reservoir characteristics, can provide cost and process benefits over steam processes or air fireflooding.

Greenwich Oil's Forest Hill project in Texas, which started in Nov. 1985, is the first commercial oxygen fireflood. This project uses an oxygen injection pressure of about 3,000 psi [20.7 MPa], while Canadian fireflooding pilots have used pressures of about 1,000 psi [6.9 MPa]. Higher pressures probably will be required for future applications.

Surface systems to supply steam, air, and oxygen are commercially available, proven, and safe. While there are similarities in materials considerations for well equipment and tubulars for the three EOR techniques, important differences exist. Oxygen firefloods necessitate close attention to the particulars of materials per-formance. Therefore, technical cooperation between the oilfield per-formance. Therefore, technical cooperation between the oilfield operator and oxygen supplier regarding design and operating procedures for the oxygen injection system, injection wells, and procedures for the oxygen injection system, injection wells, and production wells is required to ensure durable and safe fireflood systems. production wells is required to ensure durable and safe fireflood systems.

Corrosion resistance and oxygen compatibility are primary considerations in materials selection and design of systems durable enough for long-term oxygen firefloods. Accordingly, we have developed information on corrosion behavior, oxygen compatibility, and systems considerations to provide a sound basis for materials selection. This long-range activity has focused on the variables that affect these considerations.

Materials

Our ongoing program has included testing of a wide variety of materials for specific fireflood applications. Both downhole and surface systems were considered.

Materials considerations for downhole equipment are site-specific because of such variances as reservoir fluid corrosivity, injection pressure, and oxygen purity. The alloys selected for this pressure, and oxygen purity. The alloys selected for this discussion (Table 1) represent a considerable variation in alloy content and relative cost. Because localized corrosion modes were considered significant in other studies, highly alloyed materials with increased molybdenum levels have been included.

Fireflood systems require nonmetallic materials in such components as wellheads, valves, and packers. The compatibility of these materials with oxygen varies considerably. Table 2 shows the nonmetallics included in this study; hydrocarbon oil was included for comparisons and for demonstration of the effect of oxygen pressure on the autoignition characteristics of a hydrocarbon. pressure on the autoignition characteristics of a hydrocarbon.