Solid anti-friction devices – materials therefor – lubricant or se – Lubricants or separants for moving solid surfaces and... – Protein – carbohydrate – lignin – plant matter of indeterminate...
Reexamination Certificate
2001-03-28
2002-10-08
McAvoy, Ellen M. (Department: 1764)
Solid anti-friction devices, materials therefor, lubricant or se
Lubricants or separants for moving solid surfaces and...
Protein, carbohydrate, lignin, plant matter of indeterminate...
C508S472000, C508S591000, C507S111000
Reexamination Certificate
active
06461999
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates to the use of compositions comprised of starch and semi-solid, highly viscous and/or high molecular weight lubricants having a pour-point within the range. of about 20° C. to about −25° C. as additives in drilling fluids. Compositions are prepared by a continuous steam jet cooking process that is carried out in the complete absence of surfactants or emulsifiers. Starch is dissolved in water during the jet cooking process; and a water-immiscible (oil-based; oleaginous-based) lubricant is reduced to micron-sized droplets that remain suspended in the starch-water matrix and do not separate or coalesce, even after the dispersion is dried. Dried compositions are easily dispersed in water and impart improved lubricity to drilling fluid compositions. Uncooked, granular special functional starches, e.g. high-temperature fluid-loss starches, may also be blended into these compositions before drum drying to enhance fluid loss properties.
2. Description of the Prior Art
Starch is a high molecular weight natural polymer composed of repeating 1,4-alpha-D-glucopyranosyl units (anhydroglucose units or AGU) and is typically a mixture of linear and branched components. The linear component (amylose) has a molecular weight of several hundred thousand, while the molecular weight of branched amylopectin is on the order of several million. Although normal dent cornstarch contains about 25% amylose, commercial cornstarch varieties are available that range in amylose content from 0% (waxy cornstarch) to about 70% (high amylose cornstarch).
Starch occurs in living plants as discrete granules ranging from about 5 to 40 micrometers in diameter, depending upon the plant source. Starch, as isolated in its native state, is insoluble in water at room temperature because of hydrogen bonding between polysaccharide macromolecules and areas of crystallinity within the starch granule. When a water solution of starch is heated, granules initially take up water with limited swelling. Then, at a definite temperature (typically about 70° C.), granules swell rapidly and irreversibly; therefore, areas of crystallinity within the granule are lost. The temperature at which this occurs is referred to as the gelatinization temperature.
Near the gelatinization temperature, a measurable percentage of the starch, in particular the amylose component, becomes soluble and diffuses out of the granule matrix. As the temperature is increased beyond about 70° C., a greater percentage of the starch becomes soluble. Granules become highly swollen, until, at a temperature of about 90-100° C., a viscous dispersion of starch in water is obtained. However, despite the outward appearance of solubility, starch is only partially water soluble and exists largely as highly swollen granules and granule fragments that may be easily separated from starch solution by centrifugation.
True solutions of starch in water are difficult to prepare using conventional cooking techniques and require the application of specialized techniques, such as autoclaving at elevated temperatures and steam pressures. Steam jet cooking is another technique for preparing starch solutions, which is simpler and more economical than autoclaving, and is suitable for continuous processing. Because of these processing advantages, jet cooking has been used for decades to prepare starch solutions for commercial applications. The method of steam jet cooking involves pumping a water slurry of starch through an orifice located in a heating chamber (i.e., hydroheater), where the starch slurry contacts a jet of high-temperature, high-pressure steam. There are two basic steam jet cooker designs used commercially, and these are discussed in an article by R. E. Klem and D. A. Brogly in
Pulp & Paper, Vol
. 55, 1981, pages 98-103. In the first of these designs (which is referred to as thermal jet cooking) the amount of steam is carefully controlled to achieve complete steam condensation during the cooking process (i.e., little or no excess steam passes through the cooker). In the second of these designs (which is referred to as excess steam jet cooking), the steam entering the hydroheater exceeds the amount required to achieve the required cooking temperature and pressure, thus allowing considerable amounts of excess steam to pass through the cooker along with the cooked starch solution. The intense turbulence caused by the passage of this excess steam through the hydroheater promotes mechanical shearing and degradation of starch molecules, especially those having the highest molecular weight, and it also produces starch solutions with reduced viscosity (see Dintzis & Fanta,
Journal of Applied Polymer Science
, Vol. 62, 1996, pages 749-753). The high degree of turbulence and mechanical shear of the excess steam jet cooking process also converts the water-immiscible lubricant phase to a homogeneous aqueous dispersion of micrometer-sized oleaginous droplets. These unique aqueous starch-oil dispersions form the basis for the lubricant compositions of this invention.
An inherent property of starch pastes and solutions is their tendency to form gels on cooling, and this property is commonly referred to as retrogradation. Retrogradation is caused by aggregation of starch molecules through hydrogen bonding and crystallization. The tendency of starch solutions to retrograde and form gels increases with the amylose content of the starch, because amylose is a straight chain polymer with little or no branching. Although retrogradation has also been observed in amylopectin solutions, retrogradation is much slower with amylopectin, and is generally observed only after solutions have been allowed to stand for prolonged periods of time.
U.S. Pat. Nos. 5,676,994 and 5,882,713, which are herein incorporated by reference, describe the preparation of starch-oil compositions by mixing starch, water and oil at room temperature and then passing this mixture through an excess steam jet cooker. The resulting jet cooked compositions are stable with respect to separation and coagulation of oil droplets and are comprised of microscopic droplets of oil, about 1-10 micrometers in diameter, uniformly distributed in the starch-water phase. No emulsifying agents, dispersing agents or surface-active agents are used in the process. The amount of oil in these formulations normally does not exceed about 50% of the total product, and preferred compositions are comprised of about 20-40 parts of oil per 100 parts of starch (17-29% oil, by weight). If the oil content is held within this preferred range, jet cooked compositions are easily dried, using techniques such as drum drying, to yield outwardly dry, flake-like products that can be easily reduced in size by milling, and that exhibit no separation of oil from the dried starch matrix. The dried, jet cooked compositions hydrate rapidly and are easily dispersed in water to form smooth, stable, lump-free dispersions that are similar in properties and appearance to undried dispersions freshly collected from the jet cooker. Water dispersions do not phase separate into their oil and aqueous components on prolonged standing because of a thin layer or shell of starch that spontaneously forms around each oil droplet during the jet cooking process. Scanning electron micrographs of these thin starch shells and possible reasons for their formation are discussed in an article by Fanta et al. in
Carbohydrate Polymers
, Vol. 39, 1999, pages 25-35.
When oil and gas wells are drilled, fluid formulations with a multitude of properties, including lubricity, are pumped down the well through the drill string and out through nozzles in the drill bit, so that the drilling fluid circulates upward through the annular space between the rotating drill string and the rock formation. The functions of these drilling fluids or “muds” are to cool and lubricate the bit and drill string, to carry the cuttings from the drilling process to the surface, to control and reduce fluid loss into the rock formations, and to supp
Erhan Selim M.
Eskins Kenneth
Eskins Sandra
Fanta George F.
Felker Frederick C.
Eskins Sandra
Fado John D.
McAvoy Ellen M.
Ribando Curtis P.
Silverstein M. Howard
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