Method aids calculation of PHPA depletion rates

A series of tests comparing partially hydrolyzed polyacrylamide (PHPA) concentration amounts has helped determine a new method for monitoring the depletion rate of the inhibitor in drilling fluids. Being able to monitor actual excess inhibitor levels helps in the evaluation of drilling fluid performance and overall mud cost. Cost and performance relate to the rate at which the inhibitors are spent, regardless of the mechanism for formation control (e.g., chemical inhibition, physical encapsulation, or a combination of mechanisms). The depletion rate of inhibitive agents in drilling fluids can, in many cases, present serious problems to a drilling operation. As the formation type varies with depth, the depletion rate varies; thus, the inhibitor level should be adjusted to correspond with the formation reactivity. For the most part, the drilling industry uses qualitative methods to determine the inhibition level of a mud (e.g., determining the level of inhibition from a subjective analysis of the cuttings passing over the shaker screens). Many quantitative analysis methods fail to present correct values of excess inhibitor level, particularly for muds which depend on PHPA for inhibition. Excess polymer can increase the mud cost and may cause operating inefficiencies. This paper reports on an inhibitive index experimentmore » that was designed to further the understanding of PHPA depletion rates and to develop a method of quantitatively identifying these rates.« less