Abstract
Acrolein can function under a variety of conditions as an effective hydrogen sulfide scavenger in oilfield waterflood systems. The scavenging ability is maximized in waters having a pH range, of 6 through 8, a total dissolved solids level below 1%, and temperatures less than 149 degrees F [65 degrees C]. At least 4 ppm acrolein is necessary to achieve sufficient reaction of each original 1 ppm hydrogen sulfide. This reaction requires about 2 to 20 minutes, depending on the nature of the system. Although sand, garnet, or diatomaceous earth filters do not affect the scavenging ability of acrolein, charcoal filters, large tanks, long pipelines, high-temperature Wemcos, and reboilers can produce diminished effects. Further diminished effects also can be produced when incompatible chemicals are used concurrently with acrolein. Some application techniques that can lessen or eliminate these adverse conditions are presented.
Introduction
Hydrogen sulfide has been both a corrosive and a toxic nuisance to oilfield operations for decades. Although an abundance of literature describing the abatement of hydrogen sulfide in gas and drilling mud systems is available, these techniques and environments do not appear to have significant utility in oilfield waterflood operations. Related industries-such as the geothermal, the pulp and paper, and the wastewater industries-appear to pulp and paper, and the wastewater industries-appear to rely on aeration, bacteria chemical scavengers, metallic salt and oxide beds, and oxidizers. Although some of these methods are applicable to oilfield waterflood operations, the majority appear impractical because of cost and compatibility considerations. Specific oilfield waterflood operations have used mechanical and chemical technologies in an attempt to remove hydrogen sulfide from native waters. Some mechanical methods involve aeration, anion exchange resins, degassing, distillation, steam reforming, and zeolite softeners. Most of these methods are viewed currently as being expensive or impractical. Chemical techniques applied to oilfield waterflood operations involve basically the use of neutralizers, oxidizers, and scavengers. Historically, neutralizers-such as sodium hydroxide, ammonia, and amines-were used first in an attempt to remove hydrogen sulfide from produced fluids. These materials are inexpedient because the produced fluids. These materials are inexpedient because the hydrogen sulfide can be easily regenerated within the oilfield waterflood systems when pH changes. Chemical oxidizers can remove hydrogen sulfide from oilfield waterflood operations but can produce undesirable side effects, such as corrosion and the formation of unwanted solids. Examples of oxidizers include chlorine, chlorine dioxide, hypochlorite, hydrogen peroxide, and thiosulfate. peroxide, and thiosulfate. Some attempts to use metallic salts and oxides as scavengers in oilfield waterfloods have resulted in the formation of undesirable solid, metallic sulfides. Metallic salt coatings on zeolite filter agents have been suggested as an alternative. Both formaldehyde and acrolein are aldehydes and are the most frequently used chemical scavengers in oilfield waterflood operations. The use of acrolein to control hydrogen sulfide in aqueous media was commercially available in the 1960's. The general use of aldehydes as additives in acidic media for the suppression of hydrogen sulfide was patented in 1972. A recent publication has compared the ability of some aldehydes to suppress hydrogen sulfide in 10% aqueous sulfuric acid. Under unspecified conditions, some unidentified aldehydes were observed to provide 86 to 98% removal of hydrogen sulfide. Some authors have proposed that aldehydes form thioaldehyde products when treated with hydrogen sulfide. The formation gem-dithiols and 2-thietanol are also reported. But trivinyl-trithiane, a possible product from acrolein, is not reported prominently in the literature. Although thioaldehydes, gem-dithiols, and thietanols might be formed, a more plausible set of reaction products for acrolein is indicated under the conditions products for acrolein is indicated under the conditions normally found in oilfield waterflood systems.
SPEJ
P. 647
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