Synthetic resins or natural rubbers -- part of the class 520 ser – Synthetic resins – Polymers from only ethylenic monomers or processes of...
Reexamination Certificate
2000-06-08
2002-05-28
Pezzuto, Helen L. (Department: 1713)
Synthetic resins or natural rubbers -- part of the class 520 ser
Synthetic resins
Polymers from only ethylenic monomers or processes of...
C526S274000, C526S287000, C526S303100
Reexamination Certificate
active
06395853
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates to water-soluble copolymers comprising structural units derived from acrylamido-N-methylenepropenylsulfonates (AMPS), vinylphosphonic acid and vinylphosphonic salts (VPS) and cationic allyl or vinyl compounds, such as diallyidimethylammonium chloride (DADMAC), and their use as additives in deep wells, cemented deep wells and completion and clearing-out liquids and for reducing the permeability of the water in the area close to the probe of petroleum or natural gas and water-conveying horizons.
In the area of deep-drilling technology, polymers perform various tasks in water-based drilling muds. Thus, they lead to a reduction of water loss especially when drilling through permeable formations by establishing a thin filter layer which seals the drill hole. In addition, they keep the resulting drillings in suspension by dispersion and thus help, inter alia, to transport the drillings above ground. Moreover, by using polymeric additives, the rheological properties of the drilling muds are changed; in particular, there is an increase in the viscosity and yield point. Especially fluid-loss additives for deep wells should have high thermal stability and little susceptibility to problems under highly saline conditions, in particular with respect to polyvalent cations and should at the same time influence the rheological properties as little as possible since otherwise, when low water loss values are established, there is an undesired increase in the plastic viscosity and yield point.
After a certain section has been drilled, the casing is introduced into the borehole. The casing must then be fixed, i.e. a cement slurry which hardens with high strengths must be pumped into the annular space between the casing and the formation. The hardened cement must be impermeable to gases and liquids so that no gas and/or oil can flow out of the carrier formation into other formations or to the surface. The cement slurry to be pumped must meet very high requirements. It should be readily pumpable, i.e. of the lowest possible viscosity, and nevertheless not separate out. The release of water to the porous formation should be low so that the pumping pressure does not increase excessively as a result of constriction of the annular space by relatively thick filter cakes on the borehole wall, which may lead to disintegration of the formation. If the cement slurry releases too much water, it does not set completely and is permeable to gas and oil. Finally, the resulting cement jacket in the annular space must reach a certain strength as rapidly as possible and shrinkage must not occur during setting, as this would lead to flow channels for gas, oil and water.
An optimal formulation of the cement slurry properties is possible only by means of additives.
A distinction is made between 3 major groups of additives:
1. Retardants which increase the setting time so that the cement slurry remains sufficiently fluid for the entire pumping phase, which lasts for several hours in the case of very deep wells. The most well-known products of this type are lignosulfonates and carboxymethylhydroxyethylcelluloses.
2. Dispersants which homogeneously disperse the cement slurries and reduce the viscosity, which leads to better pumping thereof. As such products, U.S. Pat. No. 3,465,825 describes condensates of mononaphthalenesulfonates and formaldehyde and U.S. Pat. No. 4,053,323 describes N-sulfoalkyl-substituted acrylamides. The lignosulfonates and carboxymethylhydroxyethylcellulose ethers, too, have a dispersing effect on cement slurries in addition to the retarding effect.
3. Water-loss reducers which reduce the release of water by the cement slurries to porous formations during the pumping of the cement slurries into the annular space between casing and borehole wall. The most well-known products of this type are fully synthetic acrylate/acrylamide copolymers according to DE-B-28 30 528 and block copolymers of vinylpyrrolidone and acrylamide according to GB-B-14 73 767 and the semisynthetic carboxymethylhydroxyethyl- and hydroxyethylcellulose ethers.
The water-loss reducers are of particular importance since pumpable cement slurries which consist only of cement and water release large volumes of water when they flow past porous rock layers during cementing of the borehole. The alkaline water causes clays in the formations to swell and, with CO
2
from the natural gas or petroleum, forms precipitates of calcium carbonate. Both effects reduce the permeability of the deposits and decrease the subsequent production rates. The cement optimally formulated above ground for the respective cementing undergoes, as a result of the water release, a viscosity increase which is difficult to calculate and makes pumping more difficult. The release of water to porous formations can lead to an inhomogeneous cement material which does not solidify homogeneously and is permeable to gases, to liquid hydrocarbons and to waters. This can result in the escape of natural gas or petroleum through the annular space filled with porous cement into other formations and, in extreme cases, above ground. Furthermore, aggressive saline waters and gases can act on the casing through the porous cement and corrode said casing.
To ensure a technically satisfactory cementing of boreholes, it is necessary to reduce the water loss of the cement slurries used. The water loss is measured comparatively using a filter press according to API Code 29. The filter area is 45.8±0.7 cm
2
, the superatmospheric pressure is 7±0.7 atm gauge pressure and the filtration time is 30 minutes. Recently, measurements of the water loss have been carried out more and more frequently by means of a high-temperature and high-pressure filter press (Baroid No. 387). Usually, filtration is carried out with a differential pressure of 35 bar, and the temperature is matched to that occurring in practice.
The semisynthetic cellulose ethers of the hydroxyethylcellulose type and partially also carboxymethylhydroxyethylcellulose ethers have been widely used to date for reducing the water loss of cement slurries. Their practical use is limited by the temperatures to which the cement slurries are exposed. The effect declines sharply above 100° C. and can then no longer be compensated by using larger amounts. Fully synthetic copolymers comprising acrylamide and acrylic acid or vinylpyrrolidone have not become established in deeper wells with higher floor temperatures. Particularly when saline waters are used for formulating the cement slurries, said copolymers have a very moderate effect which decreases further at higher temperatures. Saline waters are customary in offshore wells and are necessary when cementing salt layers. These products fail completely if CaCl
2
is used as a setting accelerator. The prior art shows that there is at present a gap in the case of products for reducing the water loss of cement slurries for deep wells, particularly if the cement slurries are exposed to temperatures above 100° C. and are formulated with saline waters.
In some cases, the additives have more than one function. Dispersants, such as lignosulfonates and polymethylenenaphthalenesulfonates, retard setting and slightly reduce water loss. Some water-loss reducers retard setting and dramatically increase viscosity.
The first highly effective water-loss reducers, which are still used today, are hydroxyethyl- and carboxymethylhydroxyethylcellulose. Hydroxyethylcellulose increases viscosity and slightly retards setting. Carboxymethylhydroxyethylcellulose has a greater retardant effect, but this can be compensated by accelerators. The effect declines markedly with increasing temperature. Consequently, many different fully synthetic polymers having higher thermal stability have been proposed and are used.
U.S. Pat. No. 3,994,852 describes, for example, polyvinylpyrrolidone polyacrylamide polymers, U.S. Pat. No. 3,943,996 methacrylamidopropenyltrimethylammonium chloride copolymers, U.S. Pat. No. 4,015,991 hydrolyzed acrylamide-acrylamidomethyl
Heier Karl Heinz
Kayser Christoph
Morschhäuser Roman
Oswald Reinhard J.
Patterson Dan
Clariant GmbH
Pezzuto Helen L.
Silverman Richard P.
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