Patent ID: 6281172
Filing Date: 2001-08-28
Classification: C09K

Abstract:
A water-based drilling fluid composition which comprises water, at least one viscosity builder and at least one rheological control agent, the rheological control agent being an amphoteric polymer having cationic groups in the form of quaternary ammonium groups, the amphoteric polymer comprising a quaternary ammonium compound of the formula: ##STR5##wherein R.sup.1 is H or OH, R.sup.2, R.sup.3 and R.sup.4 are the same or different and are selected from the group consisting of C.sub.1 -C.sub.2, alkyl, C.sub.6 -C.sub.24 aryl, C.sub.7 -C.sub.24 aralkyl, C.sub.7 -C.sub.24 alkaryl, C.sub.3 -C.sub.24 cycloalkyl, C.sub.2 -C.sub.24 alkoxyalkyl and C.sub.7 -C.sub.24 alkoxyaryl groups, or R.sup.2, R.sup.3, R.sup.4 and the quaternary nitrogen atom form an aliphatic or aromatic heterocyclic ring; n is an integer of 1 to 4, B is O, OC(O), C(O)O, C(O)--NH, NHC(O), S, OSO.sub.3, OPO.sub.3, NH, or NR.sup.5 where R.sup.5 is a C.sub.2 -C.sub.6 acyl, or a C.sub.1 -C.sub.4 alkyl radical, (A).sub.m is an anionic water-soluble polysaccharide or substituted polysaccharide, m is greater than 10 and X.sup.- is an anion.