Iron Sulfide Inhibition: Field Application of an Innovative Polymeric Chemical

Abstract

Iron sulfide scale is prevalent in the industry and its chemical prevention is an area of recent focus by several research groups. There are very few examples where true inhibitor chemistry has been effective at controlling the scale, rather stoichiometric amounts of chelating agents are required. Partial inhibition has been achieved using classic scale inhibitor species such as phosphonates or maleic acid or sulfonated copolymers. Efficacy of these classic inhibitors against sulfide scale is poor and often uneconomically high concentrations are required. This paper summarizes the work performed to deliver to the industry a true, high-performance sulfide scale inhibitor. This chemistry offers a true step-change in performance from existing technologies. An industry best-in-class rapid screening technique was used to systematically evaluate all current technologies in the market place and from this develop a detailed understanding on the structure-performance relationships of functional groups. By ranking the correlations, a range of novel polymeric chemistries were synthesized which provided significantly superior inhibition. Test methods are presented that mimic formation of these scales in the field and order of magnitude increases in performance over standard species are reported, thus representing a true step-change in the efficacy of sulfide scale inhibition. The paper is largely dedicated to a field trial of this novel chemistry in USA. A severe iron sulfide fouling issue was being experienced in the water handling system. Intense sampling was performed when trialing classic chemistries such as THPS and phosphonate scale inhibitors as well as the novel polymeric product. The results speak for themselves and show that threshold concentrations of the new chemistry controlled sulfide deposition whereas order of magnitude more of standard chemistries are required to achieve the same efficacy.

Review of Iron Sulfide Scale Removal and Inhibition in Oil and Gas Wells: Current Status and Perspectives

“…7 A sample of the scale was obtained from a water injection well revealed that 74% of its composition was iron sulfide. 50 Based on the solubility tests, copolymeric formulation provided the highest dissolving rate for the scale sample which outperformed 47 ppm THPS. In addition to that formulation, new copolymer chemistry containing the acrylamide, phosphonic acid, and sulfonic acid acrylic units has successfully prevented FeS formation when injected as 0.75 ppm active polymer.…”

“…Additionally, several patented works claimed novel structures with different chemistries for the dispersants. An earlier discovery disclosed a free-radical copolymer of olefins and maleic anhydride for the treatment of iron sulfide formed in the petrochemical plants. ,,, A copolymer of acrylate, acrylamide, and methacrylamide or terpolymer of dimethyldiallylammonium salt, 2-hydroxypropyl acrylate, and acrylic acid were also invented for dispersing iron sulfide prior to scales formation…”

“…Downhole squeeze treatment of tetrakis­(hydroxymethyl)­phosphonium sulfate (THPS) was successfully implemented with no operational challenges and with a significant reduction in FeS scales deposition rate . A sample of the scale was obtained from a water injection well revealed that 74% of its composition was iron sulfide . Based on the solubility tests, copolymeric formulation provided the highest dissolving rate for the scale sample which outperformed 47 ppm THPS.…”

“…Based on the solubility tests, copolymeric formulation provided the highest dissolving rate for the scale sample which outperformed 47 ppm THPS. In addition to that formulation, new copolymer chemistry containing the acrylamide, phosphonic acid, and sulfonic acid acrylic units has successfully prevented FeS formation when injected as 0.75 ppm active polymer . Importantly, it is suggested that inhibitors based on dispersion mechanism are more convenient to be employed for FeS inhibition cases in typical sour gas wells rather than nucleation and crystal-growth-based inhibitors …”

“…An earlier discovery disclosed a free-radical copolymer of olefins and maleic anhydride for the treatment of iron sulfide formed in the petrochemical plants. 9,10,49,50 A copolymer of acrylate, acrylamide, and methacrylamide or terpolymer of dimethyldiallylammonium salt, 2-hydroxypropyl acrylate, and acrylic acid were also invented for dispersing iron sulfide prior to scales formation. 51 Polymeric formulations that contain amid group dispersed iron sulfide in water.…”