Scale Control with Aminomethylenephosphonates
Authors: Ralston P.H. 
Published: December 2007

Profits are reduced when water-formed scales calcium sulfate, Profits are reduced when water-formed scales calcium sulfate, barium sulfate, calcium carbonate interfere with primary and secondary oil recovery. Laboratory and field experience confirms that aminomethylenephosphonate inhibitors are an economical and effective solution to the problem.

Introduction

Water as connate brine or injection fluid coexists with oil in primary and secondary recovery processes. This unhappy marriage of water and oil reduces oil production rate and fosters water-related problems production rate and fosters water-related problems of scale, corrosion and microbiological growths.

These water-formed deposits result when the solubility concentrations of scale-forming anions and cations are exceeded. Temperature, pressure and pH changes often reduce these concentration levels. Extended equilibrium periods and the presence of scale-forming "seed" crystallites also presence of scale-forming "seed" crystallites also favor incompatibility and objectionable deposits and scale. The result is a syndrome of trouble clogged capillaries in the formation and wellbore area, scaled pumps, inefficient heater-treaters, ineffective filters and choked transmission and disposal lines. In short, water-formed deposits are responsible for wasted time, reduced production and lower profits.

These expensive scale problems are markedly reduced or eliminated in many industrial applications by removal of the scale-forming ions. There are several approaches to this solution. Precipitants or ion exchange resins can be used to reduce or eliminate the objectionable anion or cation; however, this is seldom practical in the oil field. Water volumes are large; capital expenditures would be high; and produced water cannot be segregated down hole for ion removal. Chemical treatment of these waters for scale control, however, can be both economical and effective.

Polyphosphates Polyphosphates More than 30 years ago, Rosenstein observed that small concentrations of molecularly dehydrated phosphates (polyphosphates) were particularly phosphates (polyphosphates) were particularly effective in retarding calcium carbonate precipitation when bicarbonate irrigation waters precipitation when bicarbonate irrigation waters were treated with ammonia. In 1939, Hatch and Rice reported that small amounts of the same polyphosphates would stabilize bicarbonate waters polyphosphates would stabilize bicarbonate waters on conversion to the objectionable carbonate by heating. Moreover, Hatch and Rice recognized this scale stabilization property as a surface reaction in which the scale-forming nuclei were inactivated in the threshold of precipitation from solution. Reitemeier and Buehrer, in 1940, confirmed that extremely low concentrations of glassy polyphosphate in the milligram-per-liter range would effectively retard calcium carbonate precipitation. Buehrer and Reitemeier also concluded that this inhibition process involved adsorption. The polyphosphate was process involved adsorption. The polyphosphate was attracted to potential scale-forming crystal faces with resulting restricted and deranged crystallization.

During the past 10 years, control of oilfield scale with inorganic polyphosphates has been very successful. Such compositions with controlled solubility rates have been described by Sloat.

JPT

P. 1029