Fast Barite Scale Dissolution with an 18-Membered Macrocyclic Tetraacetate Ligand─18-py₂N₄Ac₄

Deposits of inorganic salts during the production of oil and gas are known as scales. Scale can cause blockages in wells and lines, reducing the flow of hydrocarbons with a concomitant economic loss. The most notorious scale and hardest to manage is barium sulfate, which is known as Barite. Barite deposits can be removed mechanically by drilling or jetting or by the use of chemical dissolvers. The commonest industrial dissolvers for Barite are based on salts of diethylenetriamine-N′,N′,N″,N‴,N‴-pentaacetic acid (DTPA) at high pH. However, dissolution can be slow even at elevated temperatures. Here, we present results on a new Barite dissolver based on the macrocyclic polyamino-poly(carboxylic acid) (3,6,14,17,23,24-hexaazatricyclo[17.3.1.1(8.12)]tetracosa-1(23),8,10,12(24),19,21-hexaene-3,6,14,17-tetraacetic acid = PYTA). A 20.8 wt % aqueous solution of K4PYTA was able to dissolve field samples of Barite scale at a greater rate than 20.8 wt % K5DTPA solution and with almost the same dissolver capacity. For example, the dissolution rate was approximately double in the first hour. We propose that the reason for the enhanced dissolution rate of K4PYTA compared to K5DTA originates from the solution structure of H4PYTA where all acetate pendant arms are located on the same side of the macrocycle and are able to simultaneously interact with surface-exposed Ba(II) ions. This would allow for enhanced initial sorption of the PYTA ligand onto the Barite surface. In addition, these acetate groups also help to place the metal ion into the PYTA ligand cavity, which is preorganized for large metal ions. This leads to fast Barite scale dissolution.