| abstract |
A random copolymer comprising four distinct structural units. Methods for producing the random copolymer are also disclosed. The copolymer may be used as a filter loss reducer in a high-calcium drilling fluid. The four structural units, ABC and D are shown below. A is represented by formula 1, B by formula 2, C by formula 3 and D by either formula 4 or formula 5. The random copolymer is formed using free-radical pllymerisation in an alkaline solution in te presence of an initiator (oxidation-reduction or azo) and polymerisation takes place under nitrogen. In an embodiment, the monomers used are acrylamide, 2-acrylamido-2-methyl propanesulfonic acid, N-isopropionyloxy maleamic acid, and acryloxyethyltrimethyl ammonium chloride. In another embodiment, acrylamide, 2-acrylamido-2-methyl propanesulfonic acid,N-glucose hydrochloride maleamic acid, and dimethyldiallyl ammonium chloride are used as monomers. |