Development and Field Application of a New Hydrogen Sulfide Scavenger for Acidizing Sour-Water Injectors

Abstract

Abstract In treating sour, water injectors in carbonate formations in Saudi Arabia, sulfide scavenging, prevention of sulfur and iron sulfide precipitation is a major requirement during acidizing treatments. As the acid spends on the carbonate surfaces, and in the presence of ferric iron in the injected acid, iron sulfide precipitates at pH values less than 1.9. Iron sulfide and elemental sulfur have been implicated in injectivity decline following acid treatments on water injectors under sour conditions. Previous research work has led to the use of a new generation of hydrogen sulfide scavengers (mixture of aldehyes) for use in acidizing treatments.1 However, one of the main drawbacks of this scavenger in acidizing treatments is the formation of oily material, which can adversely affect the performance of water injectors. This paper discusses the main reactions of hydrogen sulfide with various scavengers that can be used during well stimulation. A new scavenger that is based on hydroxyalkyl triaziane was thoroughly examined. Laboratory work included compatibility of the old and new hydrogen sulfide scavenger with live acids. The impact of the new scavenger on corrosion of low-carbon steel was also addressed. Based on encouraging results from the laboratory, field trials were conducted on a number of wells. Post acidizing flowback samples were collected and analyzed to confirm laboratory results. Finally, injectivity results from the field trial were compared with offset well performance to validate the technical benefits of the new hydrogen sulfide scavenger. This paper continues the discussion on the need and importance of using proper sulfide scavengers in well acidizing fluids. It will highlight the fact that there is more science than art involved in carbonate acidizing, especially for sour wells.