Abstract
Production of sour crude oil releases hydrogen sulfide (H2S) into production tubing and surface equipment, causing corrosion, flow assurance issues, i.e., iron sulfide deposition, safety, and environmental concerns for the producer. As a result, increased costs related to metallurgical upgrades, gas sweetening equipment (i.e., towers), increased manpower costs for monitoring, and liability from the potential release of H2S can become significant parts of the total operation cost. These issues can be alleviated if the H2S is reliably removed downhole and prevented from reaching the surface.
Conventional hydrogen H2S scavengers such as triazines or glyoxal are commonly applied by direct injection topside to mitigate H2S in oil and gas production facilities. However, when applied in direct-injection applications, these scavengers exhibit slow kinetics that reduce their effectiveness in short residence-time systems, resulting in a much greater amount required than theoretical efficiency would predict. Neither triazines nor glyoxal are suitable for downhole application because of their low thermal stability and, in the case of triazine, its high scaling tendency.
To achieve reliable and cost-effective removal of H2S downhole, the development of a new scavenger and a new delivery system was required. As a result, a new non-triazine, organic acid metal complex-based H2S scavenger (OAC) with high-temperature stability, fast kinetics and quantitative H2S removal was developed. The new delivery equipment comprises an injection skid, H2S monitoring equipment and an automated chemical dosing system to assure delivery of the precise dosage required to remove H2S downhole.
Field test results for the new OAC scavenger and delivery system will be presented for mixed production applications, demonstrating the ability of this approach to reliably remove H2S downhole.
