Enhanced Oil Recovery Through Oxygen-Enriched In-Situ Combustion: Test Results From the Forest Hill Field in Texas
Authors: Hvizdos Leonard J. , Howard John V. , Roberts George W. 
Published: December 2007

Summary
This paper presents selected results from the first known field test in which oxygen-enriched air was successfully used in an in-situ combustion process for the enhanced recovery of crude oil. The literature contains process for the enhanced recovery of crude oil. The literature contains several articles on laboratory experiments and computer modeling of in-situ combustion with oxygen concentrations of more than 21 vol%. However, no reference to previous field testing with oxygen-enriched air could be found.
The advantages of using pure oxygen instead of air for in-situ combustion are discussed, and a comparison of the relative economics of oxygen and air injection is presented. Safety issues, which mainly concern the increased flammability of metals in oxygen and the oxygen compatibility of oil-field materials, are also discussed.
Oxygen-enriched air was injected into a single well in the Forest Hill field in Wood County, TX. Over the course of the 2-year test, the injection rate varied from 200 to 300 Mscf/D (5.7 × 10(3) to 8.6 × 10(3) std ml/d), the injection pressure varied from 1,750 to 2,500 psig (12.1 to 17.2 MPa), and the oxygen concentration in the injected gas ranged from 21 to 90 vol%. Air also was injected into four other wells in the field during the time that oxygen-enriched air injection took place.
Some data are presented on the heat-energy content of the produced gases from wells influenced by oxygen injection.
Oil-production rates are presented for the oxygen and air patterns. Although rigorous comparisons are difficult, there are indications that the use of oxygen-enriched air permits production rate advantages.
The results of the Forest Hill field test show that essentially pure oxygen can be handled and injected safely in a typical oil-producing field, and that oxygen-enriched air can be used to advantage in oil recovery by means of in situ combustion.

Introduction
The use of in-situ combustion with air for increasing oil recovery from an oil reservoir has been studied and used since the late 1940's and early 1950's. In 1954, Grant and Szasz published a concise history of the early work on in-situ combustion and presented the results of their field tests, which were operated from 1948 to 1953. Their primary goal was to "…recover substantially all of the oil left in the reservoir …" which we now call enhanced oil recovery (EOR). In their tests, the concentration of oxygen in the injected gas was varied by dilution of air with produced gas or natural gas. There is no indication that oxygen enrichment of air was tried.
In his discussion of the Grant and Szasz paper, Ramey presented several ideas for improvement of the in-situ combustion process. One of these ideas was the concept of oxygen enrichment of the injected gas stream. Ramey recognized that there would be a lower total gas injection rate at a lower injection pressure if the concentration of the oxygen in the injected gas was above the level in atmospheric air. He also stated that the economics of EOR by means of oxygen enrichment would depend to a great extent on the cost of oxygen.
JPT
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