Removal of Hydrogen Sulfide from Waterflood Injection Water

Abstract

To eliminate contamination of the produced gas and to reduce corrosion in the Spraberry Driver unit of West Texas, the injection water is processed through two water treating plants that use flue gas generated by submerged combustion of natural gas to extract the H2S from the water. Six years of experience indicate that the extraction has been successful and that operating costs have been reasonable. Introduction The Spraberry Driver unit of West Texas has evidenced many unusual problems, from both a reservoir and an operational standpoint. A number of these problems have been reported in previous publications. problems have been reported in previous publications. This paper presents the history and results of operating water-treating plants using oxygen-free (less than 0.25 percent) flue gas to extract H2S from sour San Andres water. Selection of San Andres Water for Source Water A number of source waters have been evaluated and used in Spraberry waterfloods. Santa Rosa Sand brackish water with about 15,000 ppm total solids occurring at approximately 1,000 ft was used initially in both the Mobil dump flood and the Midkiff unit. In both areas the water supply proved inadequate. Shallow Trinity Sand fresh water with about 2,000 ppm total solids has been used as a major ppm total solids has been used as a major supplementary source in these two floods and as the only source in seven other units. The third major source is the San Andres dolomite at approximately 4,000 ft, containing salt water with about 92,000 ppm total solids and 300 to 500 ppm H2S. Raw San Andres water was used in the initial Humble pilot waterflood and in the initial nine-section development of the Spraberry Driver unit. Because of its desirable effects on Spraberry permeability, San Andres water was chosen for injection permeability, San Andres water was chosen for injection in the Spraberry Driver unit. Although the raw San Andres water was used in the initial nine-section development of the unit, when oil production response occurred in this initial test enough H2S had been transferred to the oil in the reservoir and thence to the gas at the surface to contaminate the gas beyond marketable limits. This local problem was solved by segregating the affected wells and connecting them to a gasoline plant having gas-sweetening facilities. Use of San Andres water for expansion of the unit would require either that the H2S be removed from the water before injection or that the produced gas be sweetened before sale. The economics relative to this gas problem, coupled with the severe corrosive effects of using problem, coupled with the severe corrosive effects of using raw San Andres water for injection, led to the decision to use sweetened San Andres water for the expansion of the Unit. Two water-treating plants utilizing oxygen-free (0.10 to 0.25 percent oxygen) flue gas generated by submerged combustion of natural gas to remove the H2S from San Andres supply water were designed after the Mobil Pegasus water sweetening plant. plant. Fig. 1 is a flow diagram of the water-sweetening plant. Pertinent design and operating data are plant. Pertinent design and operating data are presented in Table 1. The purpose of submerged presented in Table 1. The purpose of submerged combustion is to reduce the temperature of the flue gas before it enters the stripping tower. The larger plant, Plant 3, has a capacity of 25,000 to 26,000 BWPD, Plant 3, has a capacity of 25,000 to 26,000 BWPD, and can reduce the H2S content of the water from as much as 500 ppm to less than 1 ppm. The treating ratio for Plant 3 ranges from 120 to 130 cu ft of inert gas per barrel of water. The fuel used at Plant 3 has a combustion ratio of 9.62 to 1. JPT P. 913