Field Experience Shows That New Lubricant Reduces Friction and Improves Formation Compatibility and Environmental Impact

Abstract

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. Introduction Completion operations can minimize torque and drag through properly designed completion brine. Traditionally, attempts have been made to utilize conventional drilling fluid or brine-dispersible lubricants in completion fluids. The success of these types of lubricants has been very limited due to incompatibilities with the brines, especially those containing high concentrations of calcium and magnesium. The lighter completion fluids such as seawater, potassium chloride, sodium chloride and diluted calcium chloride are less lubricious than their higher density counterparts, thus, they often require friction reducing agents to provide lubricity. These types of brines are also generally discharged if prevailing environmental requirements allow. Cheesing (so called because the resulting emulsion resembles loose cheese), greasing and/or gunking of the lubricant can render it not only ineffective, but environmental restrictions later may disallow discharge of the treated brine. Furthermore, insoluble or dispersible additives that grease out in surface tanks and lines will cause troublesome surface cleaning that adds time and cost to the operation. Moreover, these types of additives generally result in damage to the formation. Thus, the need for a soluble, non-greasing, non-oily lubricant is evident.