Reduction of Friction Loss in Fracturing Operations

Abstract In modern fracturing treatments, friction loss in pipe often has been the limiting factor in obtaining high injection rates desired for maximum effectiveness. Additives now available can reduce the friction loss of water by 70 per cent, permitting horsepower savings or higher injection rates, and completion of wells with smaller-size casing. The additives are used at very low concentrations for reducing friction loss. Higher concentrations give even lower friction loss, even though these fluids are viscous enough to give effective viscosity control of fracture leak-off. The friction-loss reduction is attributed to viscoelasticity of the solutions, which partially suppresses turbulence. Introduction The major trends in hydraulic fracturing during recent years have been the use ofhigher injection rates,more efficient fluids andengineering methods in designing the treatments. These trends focus attention On the friction pressure-drop in pipe as a major factor in the operation. The cost of power used in overcoming friction does not contribute to increasing the fracture area achieved. A surface pressure limit, set by the strength of the pipe, often determines the maximum attainable injection rate. This rate may not be high enough to give the most efficient treatment in terms of fracture area per dollar spent. The use of chemical additives to reduce friction loss in pipe significantly improves efficiency in fracturing treatments. It is known that the soap-gelled crude oils used in fracturing have lower friction losses than the same crude oils without gelling agents. In fracturing with brine or fresh water, still larger reductions of friction losses have been attained by two types of materials: a natural gum polymer and, more recently, a synthetic water-soluble polymer. Besides reducing friction loss, both additives are used to thicken fresh water, and the natural polymer thickens brine. Such "gelled water" has a low sand-falling rate and good viscous control of leak-off from the fracture.