Earth boring – well treating – and oil field chemistry – Earth boring – Contains organic component
Reexamination Certificate
2001-08-07
2004-04-20
Tucker, Philip C. (Department: 1712)
Earth boring, well treating, and oil field chemistry
Earth boring
Contains organic component
C507S212000, C507S902000, C507S090000, C507S920000, C507S921000, C507S927000, C507S930000, C507S931000, C507S939000, C507S110000, C507S118000, C507S211000, C507S221000
Reexamination Certificate
active
06723683
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to biodegradable chemical compositions in which a chemical, particularly at least one oil well chemical, is adsorbed onto particulate starch, particularly granular starch, providing a stable, controlled release formulation suitable for use in oil field applications. The invention further relates to the process of preparing these compositions.
BACKGROUND OF THE INVENTION
The application of coating materials on various substrates is a well known technique for controlling or delaying the release of that substrate when deteriorate. For example, the encapsulation of an oil well chemical intended to be functional in a subterranean oil recovery operation insulates the chemical from immediate contact with the environment into which it is introduced, thereby maintaining the integrity of the chemical and preventing undesirable agglomeration or reaction until the chemical may be released in the desired location.
A variety of chemical compositions are conventionally used as controlled release agents in the food, cosmetic, paint, pharmaceutical, personal care, household, and polymer and oil field industries. Conventional controlled release compositions typically operate as encapsulating agents and include gum arabic, dextrins, low viscosity modified starches, arabinogalactan, gum acacia, casein, gelatin, carboxymethyl cellulose, tragacanth, karaya, sodium alginate, tannin, and celluloses.
Solubilized starches having been disclosed as agents for use in oil field encapsulation technology. U.S. Pat. No. 4,704,214, for example, describes the use of polysaccharides and polyols to form matrices for encapsulating various ingredients, especially oil field chemicals. In this case, a polysaccharide, which may be starch, is solubilized to form an inert film that surrounds an oil absorbent polymer. The film subsequently melts or slowly dissolves, releasing the oil-swelling polymer, which then closes off fractures or large pores without clogging the borehole of the oil well. The encapsulation of a wide range of oil field chemicals is also discussed in U.S. Pat. No. 5,922,652 wherein a complex colloid, which may be a gelatinized starch, forms a coacervate with water-immiscible droplets of the chemical. U.S. Pat. No. 5,546,798 discloses that starch may be used as a water soluble thickening agent in conjunction with a swelling clay and a sealing agent such as calcium carbonate in order to encapsulate and thus preserve oil field core sample integrity. These forms of encapsulation all require the use of solubilized or non-particulate starch in their encapsulation formulation.
The use of particulates, both soft and hard, are also known controlled release ingredients for use in oil field applications. As discussed in U.S. Pat. Nos. 5,560,439 and 5,204,183, typical particulates are calcium carbonate, clays, urea, polyvinyl acetate powder or emulsions. Particulates are often used as fillers or swelling agents in conjunction with water soluble thickening agents such as polyethylene glycols, polyethylene glycol or a sulfonated elastomeric polymer. In particular, U.S. Pat. No. 5,628,813 describes the use of a lignosulfonate coating containing a particulate, such as talc, TiO
2
, silica, clays or gypsum which functions as a filler. The lignosulfonate coating is a secondary encapsulation intended to protect a thin, water permeable polymeric coating for encapsulating pharmaceuticals, agricultural chemical and oil well chemicals. There remains a continuing need for a variety of controlled release agents that may be modified to suit a number of environments, particularly oil field applications.
Accordingly, it has now been discovered that particulate starch desirably adsorbs chemicals, thereby providing stable, controlled release chemical compositions suitable for oil field applications.
SUMMARY OF THE INVENTION
The present invention relates to chemical compositions in which the chemical, particularly at least one oil well chemical, is adsorbed onto particulate starch. The particulate starch of the present invention includes granular starch and, resistant starch made therefrom, particularly granular starch.
The preparation of the present chemical compositions comprises mixing the chemical with the particulate starch. Adjuncts useful in controlled release formulations may optionally be added to the mixture. The mixture may also be optionally subjected to further treatment so that a stable, free-flowing chemical composition is obtained.
The chemical compositions of this invention are advantageously biodegradable and exhibit good controlled release properties, particularly in oil well applications.
DETAILED DESCRIPTION OF THE INVENTION
The present invention relates to controlled release chemical compositions in which the chemical, particularly at least one oil well chemical, is adsorbed onto particulate starch. The invention further relates to the process of obtaining these compositions and their method of use.
Use of starch as a carrier for the oil well chemical offers may advantages over those carriers generally used in the industry. For example, the starch is biodegradable and provides a good environmental profile.
The term starch particulate as used herein is intended to include starches with a highly organized structure, including granular starches and resistant starches made therefrom.
All granular starches and flours (hereinafter “starch”) may be suitable for use herein and may be derived from any native source. A native starch as used herein, is one as it is found in nature. Also suitable are starches derived from a plant obtained by standard breeding techniques including crossbreeding, translocation, inversion, transformation or any other method of gene or chromosome engineering to include variations thereof. In addition, starch derived from a plant grown from artificial mutations and variations of the above genetic composition, which may be produced by known standard methods of mutation breeding, are also suitable herein.
Typical sources for the starches are cereals, tubers, roots, legumes and fruits. The native source can be corn, pea, potato, sweet potato, banana, barley, wheat, rice, sago, amaranth, tapioca, arrowroot, canna, sorghum, and waxy or high amylose varieties thereof. A used herein, the term “waxy” is intended to include a starch containing at least about 95% by weight amylopectin and the term “high amylose” is intended to include a starch containing at least about 40% by weight amylose.
Conversion products which retain their granular structure may be derived from any of the starches, including fluidity or thin-boiling starches prepared by oxidation, enzyme conversion, acid hydrolysis, heat and or acid dextrinization, and or sheared products may also be useful herein.
Particularly useful are granular structures, which have been “pitted” by the action of enzymes or acid, leaving a still organized structure which creates a microporous starch. The enzymatic or acid hydrolysis of the starch granule is carried out using techniques well known in the art. The amount of enzyme used is dependent upon the enzyme, i.e., type, source and activity, as well as enzyme concentration, substrate concentration, pH, temperature, the presence or absence of inhibitors, and the degree and type of modification. Types of modifications are described herein, infra. These parameters may be adjusted to optimize the nature and extent of the “pitting” of the starch granule.
Another particulate starch useful in the controlled release applications of the present invention is resistant starch. Resistant starch is commonly known as a starch not likely to be adsorbed in the small intestine of a healthy individual. Granular or particulate starches, such as of the RS2-type (a starch granule that resists digestion by pancreatic alpha-amylase) and the RS4-type (a chemically modified starch, such as acetylated, hydroxyalkylated, or cross-linked starch) are particularly suitable. However, resistant starches of the RS3-type (retrograded, nongranular starch formed by heat/moisture treatmen
Crossman Martin C.
Rosie James A.
Solarek Daniel B
Kaiser Karen G.
National Starch and Chemical Investment Holding Corporation
Tucker Philip C.
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