Abstract: A method for inhibiting oilfield scale formation including calcite in a high brine environment comprises introducing an effective amount of a scale inhibiting composition to a high brine environment susceptible to calcite scale formation. The environment has a total dissolved solids content of at least about 150 g/l, and the scale inhibiting composition comprises an aminomethylene posphonate of the formula ##STR1## wherein x is 2 or 3, each Z is independently selected from among H and CH.sub.3, and R.sup.1, R.sup.2, R.sup.3, and R.sup.4 are independently selected from among hydrogen and --CH.sub.2 PO.sub.3 M.sub.2 wherein the M's are independently selected from among the hydrogen and cations associated with Lewis bases, such that at least about 80% of the R.sup.1, R.sup.2, R.sup.3, and R.sup.4 in the composition is --CH.sub.2 PO.sub.3 M.sub.2.

Abstract: A method for preparation of an aminomethylene phosphonate useful as a scale inhibitor in high brine environments. The method comprises phosphonomethylating an amine of the formula ##STR1## wherein x is an integer from 1 to 6 and the Z's are selected from the group consisting of hydrogen and --CH.sub.3, to produce an aminomethylene phosphonate of the formula ##STR2## wherein x and the Z's are defined as above and R.sup.1, R.sup.2, R.sup.3 and R.sup.4 are indepenedently selected from the group consisting of hydrogen and --CH.sub.2 PO.sub.3 H.sub.2, such that at least about 80% of the R.sup.1, R.sup.2, R.sup.3 and R.sup.4 in a mixture of the aminomethylene phosphonate is --CH.sub.2 PO.sub.3 H.sub.2. Related methods and compositions are also disclosed.

Abstract: A method for inhibition of scale formation using a composition comprising an N-phosphonomethylated amino-2-hydroxypropylene polymer having a molecular weight of between about 300 and about 5000 and having the structural formula ##STR1## wherein (i) R.sub.1, R.sub.2, R.sub.3, R.sub.4, R.sub.5 and R.sub.6 are independently selected from the group consisting of hydrogen, phosphonomethyl radical corresponding to the formula --CH.sub.2 PO(OH).sub.2, and water treating acceptable salts of such phosphonomethyl radical, with the proviso that the percentage of R.sub.1, R.sub.2, R.sub.3, R.sub.4, R.sub.5 and R.sub.