Earth boring – well treating – and oil field chemistry – Earth boring – Contains organic component
Patent
1993-11-12
1996-04-02
Tucker, Philip
Earth boring, well treating, and oil field chemistry
Earth boring
Contains organic component
507111, 507113, C09K 702
Patent
active
055040616
DESCRIPTION:
BRIEF SUMMARY
This application is a 371 of PCT/EP 92/02920 filed Dec. 16, 1992.
So-called drilling fluids (drilling fluid compositions) which can be constructed either on a water basis or on an oil basis are used in boring oil wells and gas wells. A clay mineral is usually added to the so-called water based fluids as a viscosifying agent. Clay minerals which are frequently used for this are bentonite or attapulgite. A disadvantage of such clay-water fluids is that the so-called plastic viscosity of the drilling fluid is very high at the clay concentration required to achieve an adequate lifting capability of the drill cuttings. It is known that a high plastic viscosity slows down the drilling progress and thus has to be regarded as unfavourable.
An additive based on a mixed metal hydroxide is known from the U.S. Pat. No. 4,664,843 which eliminates the aforementioned disadvantages of aqueous bentonite suspensions. There is still a problem with drilling fluids treated with the mixed metal hydroxide in that this fluid exhibits an unusual behaviour with the anionic filtrate reducers which are usually used in drilling fluids. This means that depending on the respective dosage, anionic filtrate reducers either substantially thin the drilling fluid (i.e. the viscosity breaks down) or lead to an undesired increase in the plastic viscosity. Similar effects occur, although not to the same extent, when common non-ionic filtrate reducers are used such as e.g. starch or guar gum. Since control over the filtrate properties of a drilling fluid is an essential prerequisite for its successful use, this therefore leads to a major limitation in the use of a drilling fluid based on mixed metal hydroxides.
The object of the present invention is therefore to develop a drilling fluid composition and a process for drilling fluid compositions containing mixed metal hydroxides which does not have the said disadvantages of the state of the art but rather has good filtrate-reducing properties and at the same time does not substantially change the special rheological properties of this fluid composition.
This object is achieved according to the present invention in that a polysaccharide that is partially etherified with hydroxyethyl and/or hydroxypropyl groups is used as a filtrate reducing agent. It surprisingly turned out that the non-ionic filtrate-reducing agents used according to the present invention do not have a major effect on the viscosity of fluids admixed with mixed metal hydroxides although the usual non-ionic additives have this undesired property.
In the process of the invention, drilling fluid compositions based on mixed metal hydroxides such as those known from U.S. Pat. No. 4,664,843 are used. An essential feature of the present invention is that a polysaccharide that is partially etherified with hydroxyethyl and/or hydroxypropyl groups is used as a filtrate reducing agent in which in particular starch, locust bean gum, guar gum or cellulose come into consideration as the polysaccharide. The polysaccharide can be used for the etherification in an unsubstituted or substituted form in which OH groups which are still free must be present for the etherification. Derivatives with carboxymethyl groups and a degree of substitution of <0.2 are used as preferred substituted basic polysaccharides into which the hydroxyethyl or/and hydroxypropylether groups are introduced.
It has proven to be particularly advantageous when the partially etherified polysaccharides have a degree of etherification of 0.02 to 2.5, preferably 0.1 to 1.2 because then the advantages achieved according to the present invention are particularly pronounced. In this connection the degree of etherification is understood as the average number of hydroxyethyl or hydroxypropyl groups bound to a glucose unit. The filtrate-reducing agents used according to the present invention and their production are known from the literature. Thus in particular hydroxypropyl starch is described in U.S. Pat. No. 4,003,838, hydroxypropyl guar in U.S. Pat. No. 4,025,443, hydroxyethyl and
REFERENCES:
patent: 4652384 (1987-03-01), Francis et al.
patent: 4990268 (1991-02-01), Burba, III et al.
Gray et al, "Composition and Properties of Oil Well Drilling Fluids" 4th ed., Houston, Gulf Publishing, 1980, pp. 548-552.
SKW Trostberg Aktiengesellschaft
Tucker Philip
LandOfFree
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