Fast Barite\nScale Dissolution with an 18-Membered\nMacrocyclic Tetraacetate Ligand18-py<sub>2</sub>N<sub>4</sub>Ac<sub>4</sub>

Deposits of inorganic salts during the production of\noil and gas\nare known as scales. Scale can cause blockages in wells and lines,\nreducing the flow of hydrocarbons with a concomitant economic loss.\nThe most notorious scale and hardest to manage is barium sulfate,\nwhich is known as Barite. Barite deposits can be removed mechanically\nby drilling or jetting or by the use of chemical dissolvers. The commonest\nindustrial dissolvers for Barite are based on salts of diethylenetriamine-<i>N</i>′,<i>N</i>′,<i>N</i>″,<i>N</i>‴,<i>N</i>‴-pentaacetic acid (DTPA)\nat high pH. However, dissolution can be slow even at elevated temperatures.\nHere, we present results on a new Barite dissolver based on the macrocyclic\npolyamino-poly(carboxylic acid) (3,6,14,17,23,24-hexaazatricyclo[17.3.1.1<sup>(8.12)]</sup>tetracosa-1(23),8,10,12(24),19,21-hexaene-3,6,14,17-tetraacetic\nacid = PYTA). A 20.8 wt % aqueous solution of K<sub>4</sub>PYTA was\nable to dissolve field samples of Barite scale at a greater rate than\n20.8 wt % K<sub>5</sub>DTPA solution and with almost the same dissolver\ncapacity. For example, the dissolution rate was approximately double\nin the first hour. We propose that the reason for the enhanced dissolution\nrate of K<sub>4</sub>PYTA compared to K<sub>5</sub>DTA originates\nfrom the solution structure of H<sub>4</sub>PYTA where all acetate\npendant arms are located on the same side of the macrocycle and are\nable to simultaneously interact with surface-exposed Ba(II) ions.\nThis would allow for enhanced initial sorption of the PYTA ligand\nonto the Barite surface. In addition, these acetate groups also help\nto place the metal ion into the PYTA ligand cavity, which is preorganized\nfor large metal ions. This leads to fast Barite scale dissolution.