G.D. Sutton, Halliburton Services
The concept of using chemical additives to reduce drag or friction of fluids flowing in turbulence has been a well-known phenomenon for many years. It has been the subject of several papers both in and outside the petroleum industry. There are many stimulation treatments now being performed which would be virtually impossible were it not for friction-reducing chemicals present in the stimulation fluids. Even small-volume acid washes done through small-diameter tubing or coiled tubing units utilize friction-reducing chemicals. Friction reducers, used in small quantities, can provide reduced surface treating pressures, higher injection rates, and lower hydraulic horsepower requirements. Historically, powdered-type friction reducers have been used in the petroleum industry for most aqueous fracturing treatments. The common polymers used to reduce friction on a large scale are guar gum, derivatives of cellulose, and synthetic polymers such as polyethylene oxides and polyacrylamides. Synthetic polymers generally provide higher friction reduction at lower concentrations than do the natural polymers and cellulose materials. Advances in polymerization techniques have made possible the development of polymers in liquid form. Now, synthetic friction-reducing polymers, similar to those previously used as solids, can be obtained in liquid form making handling and mixing less difficult. Liquids do not have a tendency to lump when added to aqueous fluids as do dry powders. When lumps form, they are not easily dispersed and can reduce the material available for lowering friction pressure. Also, the addition of liquid systems to treating fluids can be uniformly controlled. Using proper guidelines, it is possible to select a polymer system which provides good friction reduction, is stable in concentrated acid solutions for extended periods of time, and is compatible with most acid additives. This paper compares the properties of a liquid acid friction-reducing agent with several commonly used powdered materials. Some guidelines for selecting an acid friction reducer and laboratory testing of friction reducers are discussed. Successful field results using a liquid friction reducer in acid are also described.