Efficient Removal of Oxygen in a Waterflood By Vacuum Deaeration
Authors: Frank Wallace J. 
Published: December 2007

This paper was prepared for presentation at the 47th Annual Fall Meeting of the Society of Petroleum Engineers held in San Antonio, Tex., Oct. 8–11, 1972. Permission to copy is restricted to an abstract of not more than 300 words. Illustrations may not be copied. The abstract should contain conspicuous acknowledgment of where and by who the paper is presented. Publication elsewhere after publication in the JOURNAL paper is presented. Publication elsewhere after publication in the JOURNAL OF PETROLEUM TECHNOLOGY or the SOCIETY OF PETROLEUM ENGINEERS JOURNAL is usually granted upon request to the Editor of the appropriate journal provided agreement to give proper credit is made. provided agreement to give proper credit is made. Discussion of this paper is invited. Three copies of any discussion should be sent to the Society of Petroleum Engineers office. Such discussion may be presented at the above meeting and, with the paper, may be considered for publication in one of the two SPE magazines.

A one-stage vacuum deaeration process with supplemental gas stripping is being used to reduce the oxygen content of about 40,000 barrels per day of source water to 0.05 ppm or less for per day of source water to 0.05 ppm or less for use in the Robertson Waterflood near Seminole, Texas. The vacuum deaeration process is based on the reduced solubility of oxygen in water at reduced pressure and oxygen content of equilibrium vapors. Addition of an inert gas to the contact tower of a vacuum deaeration process further reduces the concentration of oxygen in equilibrium vapors and thereby the dissolved oxygen in the treated waters. The Robertson plant is mechanically simple and fully automated. plant is mechanically simple and fully automated. The water flows through a packed tower to a treated water surge tank. Water from the surge tank is pumped to waterflood injection wells. A vacuum down to 1.0 inch of mercury absolute is supplied to the contactor by a water sealed pump. The contactor is elevated to provide pump. The contactor is elevated to provide gravity flow into the surge tank. Flow rates are controlled relative to the level in the surge tank to equal the demand of downstream injection pumps.

In operation, the one-stage vacuum deaeration alone reduces the oxygen content of the water to approximately 0.17 ppm. Addition of 0.1 cubic foot of natural gas per barrel of water further reduces the oxygen content to 0.05 ppm or less. The inlet water contains 20 ppm carbon dioxide and some calcium at a pH of 7.4. In this case, partial removal of the carbon dioxide with increase in pH to 7.7 has not caused any carbonate scaling. The corrosivity of the inlet water is being reduced from 14 mils per year (mpy) to 1.6 mpy. The plant has operated essentially maintenance free at a treating cost of 0.17 mils per barrel.

Introduction

Many sources of water used in waterflooding oil formations contain oxygen. Steel or iron corrode several times as fast in contact with water containing even less than one part per million of oxygen as in contact with deaerated water of neutral pH. When carbon dioxide and oxygen are present in equal amounts in a water, corrosion of steel is approximately 10 times as fast as when the same water contains no oxygen.