Smith International, Inc. (Houston, TX) received U.S. Patent 7,749,947 for high performance rock bit grease using carbon nanotubes, nanocopper and nanosilver as well as nanodiamonds. Lubricants for a drill bit that include from about 0.1 to about 10 weight percent of nanomaterial, from about 5 to 40 weight percent of a thickener, and a basestock are disclosed by inventors Anthony Griffo and Madapusi K. Keshavan
Rock bits are employed for drilling wells in subterranean formations. Such bits have a body connected to a drill string and a single roller cone or a plurality (typically two or three) of roller cones mounted on the body for drilling rock formations. The roller cones are mounted on journals or pins integral with the bit body at its lower end. In use, the drill string and bit body are rotated in the bore hole, and each cone rotates on its respective journal as the cone contacts the bottom of the bore hole being drilled.
Drill bits are used in hard, often tough formations and, therefore, high pressures and temperatures are encountered. The total useful life of a drill bit is typically on the order of 20 to 200 hours for bits in sizes of about 6 to 28 inch diameter at depths of about 5,000 to 20,000 feet. Useful lifetimes of about 65 to 150 hours are typical. When a drill bit wears out or fails as a bore hole is being drilled, it is necessary to withdraw the drill string to replace the bit which is a very expensive and time consuming process. Prolonging the lives of drill bits minimizes the lost time in "round tripping" the drill string for replacing bits.
Replacement of a drill bit can be required for a number of reasons, including wearing out or breakage of the structure contacting the rock formation. One reason for replacing the rock bits includes failure or wear of the journal bearings on which the roller cones are mounted. The journal bearings are subjected to very high drilling loads, high hydrostatic pressures in the hole being drilled, and high temperatures due to drilling, as well as elevated temperatures in the formation being drilled. The operating temperature of the grease in the drill bit can exceed 300.degree. F. Considerable work has been conducted over the years to produce bearing structures and employ lubricants between the bearing surfaces that reduce friction, minimize wear and failure of such bearings.
Drill bits are used in hard, often tough formations and, therefore, high pressures and temperatures are encountered. The total useful life of a drill bit is typically on the order of 20 to 200 hours for bits in sizes of about 6 to 28 inch diameter at depths of about 5,000 to 20,000 feet. Useful lifetimes of about 65 to 150 hours are typical. When a drill bit wears out or fails as a bore hole is being drilled, it is necessary to withdraw the drill string to replace the bit which is a very expensive and time consuming process. Prolonging the lives of drill bits minimizes the lost time in "round tripping" the drill string for replacing bits.
Replacement of a drill bit can be required for a number of reasons, including wearing out or breakage of the structure contacting the rock formation. One reason for replacing the rock bits includes failure or wear of the journal bearings on which the roller cones are mounted. The journal bearings are subjected to very high drilling loads, high hydrostatic pressures in the hole being drilled, and high temperatures due to drilling, as well as elevated temperatures in the formation being drilled. The operating temperature of the grease in the drill bit can exceed 300.degree. F. Considerable work has been conducted over the years to produce bearing structures and employ lubricants between the bearing surfaces that reduce friction, minimize wear and failure of such bearings.
The nanolubricants are intended to prolong the life of rock drill bits. Lubricious solids that may be incorporated in the rock bit lubricants disclosed may include, for example, molybdenum disulfide, graphite, polarized graphite, carbon black, metals, such as lead, copper, and silver, metal oxide particles, such as lead oxide, zinc oxide, aluminum oxide, copper oxide, bismuth oxide, and antimony trioxide, carbon nanostructures, and diamond particles.
The incorporation of nanomaterials may improve thermal performance including thermal breakdown and conductivity. Increases in the load bearing capacity may also be achieved which may also lead to increases in rate of penetration and the life of the bearing. Various additives may also add corrosion resistance to a metal surface to which the lubricant may be applied. The lubricants may also aid in reducing the hub wear and improve seal appearance with low leakage rates. The range of applicability for the nanomaterials may also allow them to be used with a variety of existing grease compositions to improve lubrication properties and broaden the applicable uses of the greases to otherwise non-applicable uses, such as drilling.
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