Flexible, Linear, and Systematically Expanded Tetraphosphonate Bolaamphiphiles and Their Inhibition Performance against Calcite and Barite Scale Formation

Oilfield scaling is one of the mostprevalent water-based oilfieldproduction problems. Chemical inhibitors are often used to combatand prevent scale deposition. The phosphonate functional group iscommonly used in many scale inhibitors. A series of bolaamphiphilicalkyldiamine tetrakis(methylenephosphonic acid)s have been synthesizedfrom 1,X-diamines, where X in thepolymethylene spacer groups has an even number of 2-12 carbonatoms. These inhibitors were coined CX-T (X is the number of C atoms between the N atoms on the inhibitorbackbone, and T stands for tetraphosphonates). All tetraphosphonatesshowed excellent compatibility with calcium ions at 100 ppm or less,i.e., normal scale inhibitor dosage levels. At higher dosages, thecalcium concentration and length of the alkylene spacer chain betweenthe nitrogen atoms also determine the compatibility. Crystal structureswere determined for the calcium complexes with thetetraphosphonates C2-T, C4-T, C6-T, and C8-T. All tetraphosphonateswere investigated for calcite and barite scale inhibition under dynamicconditions using oilfield produced waters based on the Heidrun fieldwater composition, offshore Norway. For calcite scaling, tetraphosphonateswith ethylene (2 carbons) and hexamethylene (6 carbons) spacer groupsgave the best inhibition performance. For barite scaling, the bestinhibition was observed for the tetraphosphonates with ethylene andtetramethylene spacer groups, which relates to the ability of bothdisphosphonate moieties to interact with a single barium ion.

Automated summary

Oilfield scaling is a common problem in water-based oilfield production. Chemical inhibitors, such as phosphonate functional group, are used to combat and prevent scale deposition. A series of tetrakis(methylenephosphonic acid)s, named CX-T, showed excellent compatibility with calcium ions at normal scale inhibitor dosage levels. Crystal structures of calcium complexes with four tetrakis(methylenephosphonic acid)s were determined. The tetraphosphonates with ethylene and hexamethylene spacer groups performed best for calcite scaling, while those with ethylene and tetramethylene spacer groups were most effective for barite scaling.