Abstract
Fluid and mechanical friction (drag) place restrictive limits on many oilfield operations in which either fluid is pumped through pipe or pipe is moved within pipe. Since nearly all oilfield operations require at least one of these dynamics, friction loss due to fluid or mechanical movement is an important consideration. One example operation that involves both frictional forces is provided by coil tubing workovers in which wellbore solids are circulated to the surface using clear brine or viscosified fluids flowing at high rates, typically in turbulence. Energy losses to the walls of the tubing by the flowing fluid and frictional drag between the coil and the casing can prevent a fully successful operation due to excessive pump pressure, limited flow rate, and excessive stress on equipment or failure to reach desired depth. Metal-to-metal lubricants and fluid drag reducers are often used in these and similar operations to reduce the amount of energy lost to friction. During well completions or workovers when tools, pipe and fluids are inside casing or tubing, the frictional forces can be quite different than in the drilling operation where the interfaces are between drillpipe, drilling mud (and filter cake) and formation. Unfortunately, most of the lubricants in use today, outside of the drag reducers developed for production flow lines, were originally developed for drilling. As a consequence, their physical and chemical properties are not always optimized for the different performance criteria required in completions and workovers.
This paper presents a new lubricant that meets many of the challenges presented to the working fluid during complicated completions and workovers. One unique property of the new lubricant is its complete solubility in most completion brines, including the high-density calcium bromides. Unlike many oilfield lubricants that are typically only dispersible in completion brine and in many cases grease, "cheese" or gunk in brine with high hardness (calcium and magnesium), this new lubricant does not increase the turbidity of the working fluid and remains soluble after exposure to high shear and temperature common during circulation. A beneficial outcome of this property is that the lubricant does not add to the oil and grease content of the completion or workover brine, nor does the additive sheen. These properties mean that the lubricant does not negatively impact the ability of the working fluid to be discharged overboard in areas such as the Gulf of Mexico. Its chemistry and solubility further means that in the case of losses to the producing formation, productivity is left undamaged as a result of wettability changes, emulsion formation, precipitation or other incompatibility. Laboratory data provided in this paper demonstrate its solubility and reduction coefficient of friction (CoF) in fresh water, seawater and high salinity and high density brine. Formation damage studies are presented and case histories are discussed in which low concentrations of the lubricant were used to offset frictional forces in the field, both mechanical and fluid related.
