PHPA as a Frictional Pressure Loss Reducer and its Pressure Loss Estimation

Abstract

Abstract Significant circulating system pressure losses occur between mud and extreme long drill pipes during deep or ultra deep offshore drilling operations with the available fluid circulation technology. Therefore high pump horsepower is required to circulate the mud. Addition of a small amount of frictional drag reducer can decrease these circulating system pressure losses significantly. As a result, pipe flow capacity can be increased with lower horsepower requirements. Frictional drag reducing polymers are often composed of high molecular weight linear molecules and can be used with water or hydrocarbon based solvents. The performance of a liquid polymer emulsion which contains partially hydrolyzed polyacrylamide/polyacrylate (PHPA) co-polymer was studied in this paper. Straight cylindrical pipe flow experiments were performed at different concentrations of solutions for measuring frictional pressure losses. Measured and theoretical frictional pressure loss values shows that as the "PHPA" concentration increases, considerable drag reduction (as high as 60 %) can be obtained. The optimum concentration for drag reduction purposes was estimated as 0.0020 (v/v). A new friction factor is proposed as a function of "PHPA" concentration and Reynolds number, and the results showed that the pressure losses can be estimated with an error less than 15 % by using the developed friction factor. Introduction There are several studies about frictional pressure loss reducers in the literature but the mechanism behind is not fully understood yet. The first study was published by B. A. Toms (1948) and he has shown that addition of very small amount of certain linear polymer can result in a lower pressure drop at high Reynolds numbers compared to the flow of solvent alone. Since then this phenomenon is called as "Toms Effect". Polymers, surfactants and fibers are the main drag reducers used in the literature. Majority of the studies include experimental analysis of drag reduction with polymers at turbulent flow conditions. Most of them are also used in drilling operations to reduce the circulating system frictional pressure losses between mud and drill pipe. They are also used in oil transportation by pipeline to increase the pipe flow capacity. Moreover, during hydraulic fracturing jobs, drag reducers lower the pressure losses especially for deep wells. Three main mechanisms were proposed for drag reduction (Savins, 1964); boundary layer thickening, viscosity gradient and viscoelasticity. Those proposed mechanisms are being investigated with the latest methods such as Direct Numerical Simulations (Toonder et al, 1997). Although the mechanism is not fully understood yet the effect of these agents is lower friction factors at turbulent flow, compared to the solvent alone. This paper presents drag reduction characteristics of PHPA solutions at straight turbulent pipe flow conditions.