Drilling and/or completion fluids contg. dispersant - comprising polymer with hydroxamic or thio:hydroxamic functions

摘要

The following are claimed: (A) a clay-based aq. drilling and/or completion mud having a viscosity of not more than 20cP (as measured with a Fann viscometer) and the capacity to withstand temps. up to 200 deg.C. (B) a clay-based aq. drilling and/or completion mud contg. a dispersant comprising a (co)polymer (I) which has a molecular wt. of not more than 40,000 and contains 2-95% hydroxamic or thiohydroxamic functions. (C) a method of preparing a polyhydroxamic acid (PHA) by reacting a polyacrylamide with NH2OH.HCl in a soln. or emulsion adjusted to pH 5-7.5 with an alkali(ne earth) metal hydroxide. Dispersants of type (I) are highly effective at temps. up to 200 deg.C, both in fresh water and in brine and in the presence of weighting agents such as CaCO3 and barite, and their ability to control water loss improves after prolonged heating.