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AuthorAhmed, Musa
AuthorOnawole, Abdulmujeeb
AuthorHussien, Ibnelwaleed
AuthorSaad, Mohammed
AuthorMahmoud, Mohammed
AuthorNimir, Hassan
Available date2020-08-12T09:32:59Z
Publication Date2019
Publication NameProceedings - SPE International Symposium on Oilfield Chemistry
ResourceScopus
URIhttp://dx.doi.org/10.2118/193573-MS
URIhttp://hdl.handle.net/10576/15509
AbstractIron Sulfides scale has been a critical problem for oil and gas wells for several decades. One of the best candidates to remove these scales is tetrakis(hydroxymethyl)phosphonium sulfate (THPS). Most studies on the dissolution of iron sulfide scale using THPS have been done at neutral or acidic medium. Such conditions lead to a high corrosion rate when THPS is used in tubular wells. However, this work aims to give a holistic view on the pH effect, especially in alkaline medium, on the ability of THPS to dissolving iron sulfides. A combined approach of experimental and computational methods is used to get a better understanding of the pH effect on THPS ability to dissolve pyrite. Both experimental and theoretical techniques suggest that the pyrite dissolution ability of THPS decreases as pH increases. Conversely, combing THPS with EDTA (Ethylenediaminetetraacetic acid) proved effective in dissolving a mixture of different iron sulfide field scales. EDTA is a basic chelating agent which gave a pH of 8 when combined with THPS giving a slightly alkaline solution. For the field scale the combined formulation of THPS and EDTA yielded more than 70 % scale solubility however, for pure pyrite it was less than 10%. This implies that THPS and EDTA combination is effective in dissolving other iron sulfide scales, such as pyrrhotite (Fe7S8) and troilite (FeS) which are more soluble in comparison with pyrite. Also, THPS with Di-ethyline Tri-amine Penta Acitic acid (DTPA) formulation was tested and resulted in slightly lower solubility compared to THPS/ EDTA formulation. Moreover, oilfield scales are usually a mix of a variety of minerals and not only pyrite. Hence, using THPS in combination with EDTA to attain a basic pH would reduce the corrosion rate and subsequently reduce or eliminate the need for corrosion inhibitors.
SponsorThis publication supported by NPRP Grant # 9-084-2-041 from Qatar National Research Fund (a member of Qatar Foundation). Qatar University and the Gas Processing Center are accredited for their support. The findings attained herein are only the responsibility of the authors.
Languageen
PublisherSociety of Petroleum Engineers (SPE)
SubjectpH
iron sulfide scales
THPS
TitleEffect of pH on dissolution of iron sulfide scales using THPS
TypeConference Paper
Volume Number2019
dc.accessType Abstract Only


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