Earth boring – well treating – and oil field chemistry – Earth boring – Contains organic component
Reexamination Certificate
2000-03-02
2002-04-30
Tucker, Philip (Department: 1712)
Earth boring, well treating, and oil field chemistry
Earth boring
Contains organic component
C507S123000, C526S263000, C526S264000, C526S240000, C166S295000
Reexamination Certificate
active
06380137
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to novel copolymers and to their use as additives in drilling fluids, for cementation, as completion and workover fluids, and for water shutoff.
DESCRIPTION OF THE RELATED ART
In deep underground wells for recovering oil and natural gas deposits, the use of drilling fluids and cement slurries has been known for some considerable time. The functions of drilling fluids are to carry the drilled rock fragments and the so-called drill dust, to lubricate the bit and the drill pipe, to seal porous rock strata, and to compensate the reservoir pressure by hydrostatic pressure. For the latter purpose, drilling fluids are required to have a high specific weight. This is achieved by adding preferably barite, salts, or clays. Further important features of drilling fluids are temperature stability and appropriate flow properties that are not greatly influenced by changes in electrolyte concentration. The commonest additives for controlling the viscosity and water loss of drilling fluids are polymers such as starch and starch ethers such as carboxymethyl starch, carboxymethylcellulose and carboxymethylhydroxyethylcellulose. However, these additives become ineffective at temperatures above about 120° C. (starch and derivatives) or 140-150° C. (carboxymethylcellulose and carboxymethylhydroxyethylcellulose). Since the 1950s, copolymers of the acrylamide-acrylate type, which are stable even at temperatures of more than 200° C., have been used predominantly in salt-free drilling fluids. The 1970s saw the development of salt-stable copolymers with monomers containing sulfo groups and stable at more than 200° C. (U.S. Pat. Nos. 3,629,101, 4,048,077, 4,309,523).
Cement slurries and completion fluids are used in addition as borehole fluids in the case of deep underground drilling for oil or natural gas. When the borehole has reached a certain depth, iron pipes, known as casing pipes, are introduced into the borehole, the bit for drilling out the next rock strata down being passed through the space inside the pipes. For this purpose, the casing pipes must be secured, i.e., a cement slurry which sets to form a solid stonelike mass must be pumped into the cavity between the rock formation and the outer casing walls, known as the annular space. The hardened cement which forms must be impermeable to gases and liquids in order that no gas and/or oil can flow out of the carrier formation into other formations or as far as the surface. Stringent requirements are placed on the cement slurry to be pumped. It should be readily pumpable, i.e., of extremely low viscosity, and yet should not separate out. The release of water by the cement slurry to the porous rock formation should be low in order to prevent the formation of thick filter cakes at the borehole wall; thick filter cakes would increase the pumping pressure to such an extent, owing to the constriction of the annular space, that the porous rock formation would disintegrate. In addition, if the release of water were excessive, the cement slurry would not set fully and would become permeable to gas and oil. On the other hand, the jacket of cement which forms in the annular space must attain a certain strength as rapidly as possible, and setting must not be accompanied by any shrinkage as this would result in flow channels for gas, oil and water. Establishing the properties of the cement slurry at an optimum is possible only by means of additives.
The most important additives for regulating the setting process are retardants, accelerators, dispersants for liquefaction, and water loss reducers. In some cases, these additives have more than one function. Dispersants such as lignosulfonates and polymethylenenapthalenesulfonates retard setting and also bring about a certain reduction in water loss. Some water loss reducers retard setting and greatly increase viscosity.
Effective water loss reducers used in practice for cement and gypsum slurries include a very wide variety of polymers, copolymers, and combinations thereof.
EP-A-0 483 638 discloses copolymers of acrylamidopropenylmethylenesulfonic acid (AMPS), open-chain and cyclic N-vinylamides, and diolefinically unsaturated ammonium compounds. These monomer combinations produce copolymers which in certain cases are crosslinked and whose thermal stability is inadequate for certain applications.
WO-83/02449 discloses copolymers of acrylic sulfonates such as AMPS, for example, open-chain or cyclic N-vinylamides, amides of acrylic or methacrylic acid, vinylimidazolyl compounds and olefinically unsaturated compounds carrying hydroxyl or alkoxy radicals. The copolymer is crosslinked by using from 5 to 25% by weight of diolefinically unsaturated compounds as further monomers.
DE-A-31 44 770 discloses copolymers of acrylamide or methacrylamide, styrenesulfonates, and N-vinylamides. The latter can be cyclic or open-chain, although the simultaneous use of cyclic and open-chain N-vinylamides is not disclosed.
EP-A-0 141 327 discloses copolymers of (meth)acrylic acid or derivatives thereof, acrylic sulfonates such as, for example, AMPS and N-vinylamides. Here again, the N-vinylamides can be cyclic or open-chain, but not both in the same polymer.
The multiplicity of compounds developed makes it clear that it is always difficult to formulate an optimum cement slurry. In the case of individual parameters predetermined by the type of cementation, the necessary properties must be established at acceptable levels using additives. The large number of compounds developed for reducing water loss indicates just how much of a problem it generally is to establish a required level of water release without substantially increasing the viscosity, to establish the setting time in accordance with the requirement, and to minimize sedimentation. The prior art water-loss-reducing polymers more or less greatly increase the viscosity of the cement slurries, which are usually of high density. In order to be readily pumpable, however, the viscosity of the cement slurries must be kept low. A pumping rate which permits turbulent flow should be possible. Only under such conditions is the drilling fluid completely displaced. This is a prerequisite of effective cementation. In the case of inclined boreholes, the fluid can only be displaced effectively by means of a strong turbulent flow.
High density salt solutions which compensate the reservoir pressure are used for the completion of oil and natural gas wells. The infiltration of such solutions into the reservoir must be kept to a minimum. However, hydroxyethylcelluloses are unsuitable for the prevailing temperatures, which extend to above 200° C., and the high salinities and densities due to CaCl
2
and CaBr
2
.
In the light of the prior art, the object of the present invention was to discover copolymers which are suitable for use in drilling fluids which can in turn be used in an extended temperature range relative to the prior art. The copolymers of the invention should no longer have the thermal instability known from the prior art. A further object was that the copolymers should represent an improvement over the prior art by exhibiting a more uniform flow behavior of the drilling fluid following its preparation and after exposure (aging) within the temperature range in question of from about 130° C. to more than 200° C. The present invention should therefore solve the problem encountered in the prior art of the nonuniform rheological properties of the drilling fluid following its preparation and after exposure (aging), especially in the temperature range from 130° C. to more than 200° C., which problem is manifested in heightened or fluctuating plastic viscosities, yield points and gel strengths.
SUMMARY OF THE INVENTION
It has surprisingly been found that this object is achieved by copolymers which are free from doubly unsaturated ammonium compounds and are composed of structural units derived from AMPS, an open-chain N-vinylamide and a cyclic N-vinylamide. The object is further achieved by copolymers which include certain acrylic derivat
Botthof Gernold
Heier Karl Heinz
Morschhäuser Roman
Tardi Aranka
Weber Susanne
Clariant GmbH
Silverman Richard P.
Tucker Philip
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