Triazine-Based Scavengers: Can They Be a Potential for Formation Damage

Abstract

Hydrogen sulfide (H 2 S) scavengers have been used extensively in different field operations such as drilling and acid stimulation treatments. Typically, H 2 S scavengers are preliminarily designed to react effectively at different in-situ conditions. For example, Triazine-based scavengers are designed for neutral-high pH conditions, while aldehyde-based scavengers are intended for low pH conditions. However, reaction products of these scavengers with H 2 S could lead to potential formation damage.The efficiency of two Triazine-based H 2 S scavengers were investigated over a wide-range of parameters: solution pH value, temperature and exposure time. Additionally, the effects of both scavenger concentration and its ratio to H 2 S gas on the scavenging capacity were explored. In this work, the scavenger concentration varied from 1 to 5 vol%, reaction temperatures up to 50°C.Earlier studies have shown that, at low pH, triazine-based have a very low efficiency in scavenging H 2 S because the hydrolysis rate of triazine is faster than the reaction rate with H 2 S. Nonetheless, in this study, it was found that long exposure time between triazine-based scavengers and H 2 S can result in significant scavenging efficiency even at low pH values. Doubling the exposure time had almost doubled the amount of scavenged H 2 S in acidic solutions. In addition, this work, for the first time, highlights the possibility of calcium sulfide (CaS) precipitation in spent acid containing H 2 S scavengers. This precipitation has been observed when low scavenger concentrations were used in spent hydrochloric (HCl) acid. This paper provides optimum design parameters that allow for much effective use of H 2 S scavengers without causing the formation of calcium sulfide scale.

Formation, Chemical Characterization, and Oxidative Dissolution of Amorphous Polymeric Dithiazine (apDTZ) during the Use of the H2S Scavenger Monoethanolamine-Triazine

“…One prominent misconception is that this solid fouling deposit is the so-called “over-spent” condition of triazines which results in the formation of 1,3,5-trithiane (structure IV, as shown in Figure ). There are many earlier studies that incorrectly assign this species as a reaction product. ,,,, In fact, as this review will show, the reaction of all triazines terminates at dithiazine (the second sulfur molecule substitution), and 1,3,5-trithiane (IV) is not formed in any significant quantity. It is therefore the dithiazine which causes the observed deposits/fouling.…”

“…There are many earlier studies that incorrectly assign this species as a reaction product. 13,16,17,27,28 In fact, as this review will show, the reaction of all triazines terminates at dithiazine (the second sulfur molecule substitution), and 1,3,5-trithiane (IV) is not formed in any significant quantity. It is therefore the dithiazine which causes the observed deposits/fouling.…”

“…The next most prominent H 2 S scavenger is another hexahydrotriazine, 1,3,5-trimethylhexahydro- s -triazine, shown as structure V in Figure . This is commonly known as MMA-triazine and has certain advantages (but also shortcomings) in comparison with MEA-triazine. − …”

The role of biocides and H₂S scavengers in exploitation of hydrocarbon reservoirs and laboratory tests in the field of hydrogen sulfide scavenging

“…It was also found that long exposure time between triazine-based scavengers and H 2 S can result in significant scavenging efficiency even at low pH values. In recent years triazine-based scavengers have been extensively used in stimulation treatments to remove H 2 S from flowed back fluids [8]. Triazine derivatives were also applied as pesticides.…”

Synthesis, Reaction Byproduct Characterization, and Mechanistic Understanding of Hemiformal Hydrogen Sulfide Scavengers: Part 2─Identification of Byproducts, Reaction Mechanisms, and Suppression Thereof

“…The resulting product is the cyclic trimer of thioformaldehyde or 1,3,5-trithiane (structure 2 of Figure ). In fact, 1,3,5-trithiane is often mistakenly thought to be the ultimate reaction product from MEA triazine over-reacted with H 2 S. In fact, the ultimate byproduct in this reaction mechanism is amorphous polymeric dithiazine, a polymer from the 2-sulfur species, dithiazine. ,− …”