Safety Considerations for High-Pressure Air Injection Into Light-Oil Reservoirs and Performance of the Holt Sand Unit Project

Abstract

Summary The presence of oxygen and carbon dioxide in the injection and production streams of any high-pressure-air-injection (HPAI) project or the high oxygen partial pressures associated with enriched-air-/oxygen-injection projects may create serious safety concerns such as the potential for explosion or corrosion. Compilation of field problems and reported solutions from such projects indicate that no insurmountable problems exist in the implementation of HPAI projects. Generally, the operators have implemented safe operations successfully when injecting at pressures as high as 6,000 psi. The long-term successes of the HPAI projects in the Williston basin, which were initiated in 1978 by Koch Industries and continue to be operated today by Continental Resources, have confirmed that HPAI is a viable and safe process for recovering light oils. A number of oilfield oxygen-injection projects have also been undertaken since the early 1980s, when Greenwich Oil operated the first oxygen-injection project at Forest Hills, Texas. In Canada during the 1980s, oxygen was injected by BP/AOSTRA at Marguerite Lake, by Dome Petroleum at Lindberg, by Husky Energy at Golden Lake, by Mobil Oil at Fosterton, and by Gulf Canada at Pelican. In the US, oxygen-injection pilots were operated by Arco in the Holt Sand Unit (HSU), Texas, and more recently by NiMin Energy at Pleito Creek, California. With increased oxygen partial pressure, there is a greater chance of safety or corrosion problems. In fact, the high oxygen content associated with the HSU project in west Texas caused a severe energy release that resulted in test termination. The reported data on this field are scarce, and the nature of the energy release has not been discussed in detail. This paper will first review the operational aspects of some key air-injection field tests. Then, some important details on the HSU oxygen-injection pilot test will be discussed as a case study. The reasons behind the energy release in the HSU project will be discussed by use of the surveillance data, as well as combustion-tube-test and numerical-modeling results. Finally, best practices for future operation of HPAI tests will be reviewed. This paper is intended to provide a better understanding of the safety aspects of air/oxygen handling and proper practices in such operations.