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US 5,851,959 AGranted
High temperature stable modified starch polymers and well drilling fluids employing same
AssigneeChemstar Products Company
InventorCory J. Bernu
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AssigneeChemstar Products Company
InventorCory J. Bernu
Estimating the term…
A modified starch polymer derived from an unmodified starch having an amylopectin content of at least 80% by weight. The starch is modified by crosslinking with epichlorohydrin, the amount of epichlorohydrin crosslinking being equivalent to that which is obtained when a crosslinking reaction is subjected to a Brabender viscosity which reaches a maximum value and then is reduced with further crosslinking from its maximum to a value which is no more than 50% of the maximum value, and is carboxymethylated with a degree of substitution of at least 0.1 carboxymethyl groups per anhydroglucose unit. Fermentation stability is obtained when the degree of carboxymethyl substitution is about 0.4 or more. The modified starch polymer may also be hydroxypropylated. The modified starch polymers provide improved high temperature fluid loss performance when incorporated into well drilling fluids. They may also be used in other applications for which cellulosic polymers have heretofore been employed because of their better high temperature tolerance compared to conventional starch polymers.
A modified starch polymer, obtained from an unmodified starch or blend of starches having a content of amylopectin of at least 80% by weight, the starch polymer being crosslinked with epichlorohydrin and carboxymethylated, the amount of epichlorohydrin crosslinking being equivalent to that which is obtained when a crosslinking reaction is subjected to a Brabender viscosity which reaches a maximum value and then is reduced with further crosslinking from its maximum to a value which is no more than 50% of the maximum value, and the degree of carboxymethyl substitution being at least 0.1 carboxymethyl groups per anhydroglucose unit, and the starch polymer being further modified by hydroxypropylation of the polymer.
A well treating fluid formulation comprising a mixture of starch and at least one of brine and clay wherein the starch is a modified starch polymer obtained from an unmodified starch or blend of starches having a content of amylopectin of at least 80% by weight, the starch polymer being crosslinked with epichlorohydrin and carboxymethylated, the amount of epichlorohydrin crosslinking being equivalent to that which is obtained when a crosslinking reaction is subjected to a Brabender viscosity which reaches a maximum value and then is reduced with further crosslinking from its maximum to a value which is no more than 50% of the maximum value, and the degree of carboxymethyl substitution being at least 0.1 carboxymethyl groups per anhydroglucose unit.
In a well treating process comprising the step of providing a treating fluid comprising a mixture of brine, clay and a fluid loss polymer to a bore hole, the improvement that at least a portion of the fluid loss polymer is a modified starch polymer obtained from an unmodified starch or blend of starches having a content of amylopectin of at least 80% by weight, the starch polymer being crosslinked with epichlorohydrin and carboxymethylated, the amount of epichlorohydrin crosslinking being equivalent to that which is obtained when a crosslinking reaction is subjected to a Brabender viscosity which reaches a maximum value and then is reduced with further crosslinking from its maximum to a value which is no more than 50% of the maximum value, and the degree of carboxymethyl substitution being at least 0.1 carboxymethyl groups per anhydroglucose unit.
A method of preparing a modified starch for well drilling comprising the steps of:
Dependencies are inferred from the claim text.