The need for a reliable, quantitative analytical method for the determination of the partially hydrolyzed Polyacrylamide (PHPA) polymer content, of drilling mud and other water-base fluids has been evident for some time. Previous methods have been based on either the precipitation of the anionic PHPA molecule or alkaline hydrolysis of the amide nitrogen to form ammonia. All these methods are semiquantitative determinations and are subject to a wide variety of interferences. Another severe limitation, in the case of drilling fluids, is that a portion of the mud filtrate is used for analysis. The free polymer content of the filtrate is rarely, if ever, the same as the unfiltered liquid phase of the whole mud.
The method described in this paper is truly quantitative and is an absolute rather then an empirical method. It is based on the total oxidation of all organic material in a sample of the liquid phase of a water-base drilling fluid. The amide nitrogen in the polymer molecule forms ammonium ions during the digestion and oxidation process. These ammonium ions are then measured with an ammonia gas-sensing electrode after conversion to ammonia by means of a simple pH adjustment.
In addition, a sampling technique has been developed which enables the analyst to obtain a solids-free portion of the liquid phase of a drilling mud sample without filtering the liquid through the mud filter cake. Thus, the method assures measurement of the available free polymer content of the fluid phase of the whole mud.
The method described is ideally suited to the determination of the PHPA content of any aqueous solutions including those encountered in wastewater treatment and sludge dewatering operations. The results of both laboratory and field evaluations of the method are presented.