Materials Performance In Thermal Enhanced Oil Recovery Environments
Authors: Zawierucha R. , Henningson C.J. 
Published: March 2010

Summary
This investigation focused on the performance of materials durable enough for long-term commercial applications in oxygen firefloods. Alloy composition, water quality, temperature, gas composition, pressure and environmental degradation mechanisms were among the experimental variables. Test results showed a complex interaction between these variables. Alloy selection for air or oxygen fire floods is likely to be dependent on variables specific for a site and process. As a consequence, material selection for these applications must be approached on a rigorous basis.

Introduction
Over two-thirds of the oil recovered through EOR has been recovered via thermal techniques(1). Oxygen fire flooding is a new and attractive alternative to other methods such as steam flooding and air fire flooding. Depending upon circumstances it offers improved cost and process benefits in comparison to air fireflooding(2, 3).
It is known that the use of air firefloods can result in extremely corrosive conditions at various stages of the process and some data on corrosion in air fireflood environments are available(4–7). Relatively little data pertinent to operation in oxygen firefloods have been disseminated in the open literature.
Union Carbide has expended a considerable effort on the issues which must be addressed in the design and operation of safe durable systems for long-term commercial use in oxygen firefloods. This paper will focus on a portion of that effort, i.e. the corrosion resistance of various materials in environments associated with oxygen fire floods.

Experimental
To arrive at economical materials selections a variety of alloys has been evaluated. Those which will be discussed in this paper are listed in Table 1. They represent a considerable range in alloy content.
Compatibility tests have been conducted in a number of oilfield fresh and produced waters. Table 2 is a listing of those pertinent to this discussion. All were used in various phases of the corrosion tests to determine the relative performance of materials at both the injection and production wells. A perusal of Table 2 will show they represent a considerable variation in water quality.
Table 3 is a list of the gas mixtures used in the tests. The complex gas mixtures represent estimates of typical produced gas compositions associated with oxygen and air fire floods. The gas compositions are given in weight percentages. Corrosion mechanisms reported in this investigation include general corrosion, pitting and stress corrosion. General corrosion rates were determined electrochemically using a custom designed high-pressure vessel capable of test pressures over 6.9 MPa at operating temperatures over 225 ºC. The method of linear polarization was utilized in the general corrosion tests. A Princeton Model 350–1 System was used for data acquisition. Electrochemical methods were selected for the general corrosion tests because of their ability to rapidly screen materials for operating conditions which were not readily available for coupon tests.
Pitting and stress corrosion experiments were conducted with coupons exposed in an autoclave for 2000 hours. U-bend specimens were used for the stress corrosion experiments. The solutions were not replenished, agitated or pH-controlled during the test.