Patent Application
20080004188
Surprisingly, it was found that hydroxy- and polyether (PE)-functionalized methacrylate derivatives not only have a very large solubility in the heavy brines that usually are used in the upstream sector of the oil industry, such as, in particular, calcium chloride, calcium bromide or zinc bromide and mixtures thereof, and under conditions of a specific density between 1.20 and 2.50 kg per litre. They also can be polymerized subterraneously. It was not foreseeable that the resulting high molecular weight polymers would not be precipitated from the brine and that homogeneous high-viscosity crosslinked gels which have high thermal stability would form. Moreover, depending on the choice of the crosslinking difunctional methacrylate derivatives and in particular on the length of the polyethylene glycol chains between the two methacrylate functions the gel structure can be broken by of commercial oxidizing agents. These so-called breakers are often encapsulated for retardation. As a result the removal of the brine in a desired process from the well to be explored, for example by pumping away, is facilitated.
Mono- and/or difunctional variants have proved to be particularly suitable methacrylate derivatives. According to the invention, in particular hydroxyethyl methacrylate (HEMA) and hydroxypropyl methacrylate (HPMA) and polyethers (PE) derivatives thereof, preferably end group-protected polyethylene glycol (PEG) derivatives thereof, such as MPEG-200 methacrylate (methacrylate=MA), MPEG-400 MA or MPEG-750 MA, are suitable as monofunctional methacrylate derivatives. For economic reasons the use of HEMA is preferred and, inter alia, in certain cases the longer-chain PE derivatives or nitrogen-containing methacrylate derivatives may be necessary for keeping the resulting polymer in solution. By using PE derivatives, in particular the longer-chain variants, the polymer and hence the gel structure can be readily oxidatively degraded, which is desirable in the process for certain fields of use.
Suitable difunctional methacrylate derivatives (DMA) are in particular such compounds in which the two methacrylate groups are linked via a PE group, such as, in particular, ethylene glycol groups: ethylene glycol-DMA, di-, tri- and tetraethylene glycol-DMA and the longer-chain PEG derivates, PEG-200-DMA, PEG-400-DMA or PEG-600-DMA. Derivatives having longer PEG groups will in particular be chosen if a breaking of the gel structure with oxidizing agents is intended.
Depending on the desired viscosity and structure of the gel, a certain concentration and a certain ratio of mono- and difunctional methacrylates should be chosen, which, however, may vary within wide ranges. The present invention envisages a preferred concentration between 1 and 10% by volume, concentrations between 2 and 6% by volume being particularly suitable. The ratio of mono-functional to difunctional methacrylate derivatives in the salt-containing medium should be 100 to 1:1 and preferably 50 to 5:1.
A feature according to the invention is to be seen in the specific density of the salt-containing media. In preferred cases, they should be between 1.4 and 2.3 kg/l and preferably between 1.7 and 2.3 kg/l.
The present invention likewise envisages adding the methacrylate derivatives to the salt-containing medium in an amount of 0.5 to 15% by volume and preferably in amounts between 1.0 and 10% by volume.
Not least, in order to impart an affinity for certain surfaces (metallic or mineral) to the crosslinked polymers or—as already mentioned above—to protect the resulting polymer from precipitation from the brine, it is also possible, in addition to the mono functional hydroxy- and/or polyether-functionalized methacryl ate derivatives, to add other methacrylate derivatives which are not hydroxy- and/or polyether-functionalized. Methacrylic acid, C1-C10-alkyl-substituted and/or nitrogen-containing methacrylate derivatives, such as 3-trimethylaminopropyl methacrylamide chloride (MAPTAC), 3-dimethylaminopropyl methacrylamide (DMAPMA), 2-trimethylaminoethyl methacrylate chloride (TMAEMC), 2-dimethylaminoethyl methacryl ate (DMAEMA) or N-(2-methacryloyloxyethyl)ethyleneurea (MEEU) are particularly suitable for this purpose. In order to avoid suppressing gel formation too greatly, the amount according to the invention of these other methacrylate derivatives should be not more than 40% by weight and preferably 5 to 25% by weight, based in each case on the sum of the hydroxy- and polyether-functionalized methacrylate derivatives.
The urea derivative N-(2-methacryloyloxyethyl)ethyleneurea (MEEU), commercial product of Degussa GmbH: Mhromer 6852-O and 6844-O), which likewise has a markedly good solubility in the heavy brines described, is suitable as a nitrogen-containing methacrylate derivative which can act as a crosslinking agent.
The polymerization and hence the thickening are effected according to the invention with the aid of free radical polymerization initiators. In particular, azo compounds, such as 2,2′-azobis(2-aminopropane) dihydrochloride, are suitable. In general, temperature ranges >55° C. are recommended for the thickening, a range between 40 and 100° C. being regarded as particularly suitable. The possibility of temperature-induced initiation of the reaction is of particular interest since the solution can be pumped with low viscosity into the formation and can be thickened to give a high-viscosity liquid or to give a crosslinked gel in the formation itself and at the desired point with simultaneously increased temperature in the well. Optionally, oxidizing agents (breakers) can be suspended in the brine for retarded degradation of the thickened liquid before pumping into the formation, peroxides or hypochlorites being particularly suitable for this purpose.
The potential applications of the use according to the present invention in mineral oil and natural gas exploration are the thickening and gel formation of all aqueous media which contain heavy brines, and in particular of completion brines, drilling and drill-in fluids, fracturing fluids, acids, in particular acids weighted with heavy brines, or stimulation fluids.
Of particular interest is the use in acids which are weighted with brines, in particular zinc bromide, calcium bromide or calcium chloride, preferably in association with acidizing of a carbonate-containing ground formation for improving the productivity.
The following examples illustrate the advantages of the present invention.
3.0 g of hydroxyethyl methacrylate (commercial product from Degussa GmbH: Mhoromer BM 903) and 0.6 g of polyethylene glycol-600 dimethacrylate (commercial product from Degussa GmbH: Mhoromer D 1120) as a crosslinking agent were added to 100 ml of zinc bromide/calcium bromide brine having a specific density of 2.06 kg/l (17.2 US pounds per gallon, ppg) and stirred on a magnetic stirrer at ambient temperature until a clear solution had formed. 0.25 g of 2,2′-azobis(2-aminopropane) dihydrochloride (commercial product from Wako Chemicals GmbH: Wako V-50) as initiator was dissolved in 2 ml of tap water and the clear solution was then added to the stirred brine.
The brine containing the components described was then heated with gentle stirring on the magnetic stirrer. The reaction started at a temperature of about 65° C. (140° F.), and a high-viscosity, stable, almost “firm” gel formed.
The gel obtained was placed in a drying oven for 72 hours at 150° C. (300° F.), after which the gel structure was still intact. The thickened brine showed no synthesis.
3.2 g of hydroxyethyl methacrylate (commercial product from Degussa GmbH: Mhoromer BM 903) and 0.5 g of polyethylene glycol-400 dimethacrylate (commercial product from Degussa GmbH: Mhoromer MFM 409) as a crosslinking agent were added to 100 ml of a saturated calcium chloride brine having a specific density of 1.70 kg/l (14.2 US pounds per gallon, ppg) and stirred on a magnetic stirrer at ambient temperature until a clear solution had formed. 0.25 g of 2,2′-azobis(2-aminopropane) dihydrochloride (commercial product from Wako Chemicals GmbH: Wako V-50) as an initiator was dissolved in 2 ml of tap water and the clear solution was then added to the stirred brine.
After heating according to example 1 to about 65° C. (140° F.), the reaction started and a high-viscosity, stable, almost “firm” gel formed, which was stable for 72 h at 150° C. (300° F.).
This example shows how the viscosity of the thickened brine can easily be adjusted by reducing the concentration of crosslinking agent.
The experimental batch was identical to example 2a, but the addition of crosslinking agent, polyethylene glycol-400 dimethacrylate (commercial product from Degussa GmbH: Mhoromer MFM 409), was reduced from 0.5 g to 0.05 g. A greatly thickened brine formed, which, however, was no longer a “firm” gel.
5.0 g of hydroxyethyl methacrylate (commercial product from Degussa GmbH: Mhoromer BM 903) and 0.8 g of polyethylene glycol-200 dimethacrylate (commercial product from Degussa GmbH: Mhoromer D 1133) as a crosslinking agent were added to 100 ml of a saturated zinc bromide brine having a specific density of 2.30 kg/l (19.2 US pounds per gallon, ppg) and stirred on a magnetic stirrer at ambient temperature until a clear solution had formed. 0.25 g of 2,2′-azobis(2-aminopropane) dihydrochloride (commercial product from Wako Chemicals GmbH: Wako V-50) as an initiator was dissolved in 2 ml of tap water and the clear solution was then added to the stirred brine.
After heating according to example 1 to about 65° C. (140° F.), the reaction started and a high-viscosity, stable, “firm” gel formed. The thermal stability was comparable with that of examples 1 and 2.
3.0 g of hydroxyethyl methacrylate (commercial product from Degussa GmbH: Mhoromer BM 903) and 0.8 g of polyethylene glycol-400 dimethacrylate (commercial product from Degussa GmbH: Mhoromer MFM 409) as a crosslinking agent were added to 100 ml of saturated calcium bromide brine having a specific density of 1.39 kg/l (11.6 US pounds per gallon, ppg) and stirred on a magnetic stirrer at ambient temperature. 0.25 g of 2,2′-azobis(2-aminopropane) dihydrochloride (commercial product from Wako Chemicals GmbH: Wako V-50) as an initiator was dissolved in 2 ml of tap water and the clear solution was then added to the stirred brine.
After heating according to example 1 to about 65° C. (140° F.), the reaction started. Instead of forming a gel, the brine became turbid and a white precipitate formed which did not have a thickening or a gel-forming effect. Rather, the resulting polymer was precipitated from the brine.
The following examples show the prevention of the precipitation can be prevented for the purposes of the invention by the addition of PE- or nitrogen-containing methacrylate derivatives.
1.0 g of hydroxyethyl methacrylate (commercial product from Degussa GmbH: Mhoromer BM 903), 4.0 g of a 50% strength aqueous solution of MPEG-750 methacrylate (commercial product from Degussa GmbH: Rohamere 6850-O) and 0.8 g of polyethylene glycol-600 dimethacrylate (commercial product from Degussa GmbH: Mhoromer D 1120) as a crosslinking agent were added to 100 ml of saturated calcium chloride brine having a specific density of 1.39 kg/l (11.6 US pounds per gallon, ppg) and stirred on a magnetic stirrer at ambient temperature. 0.25 g of 2,2′-azobis(2-aminopropane) dihydrochloride (commercial product from Wako Chemicals GmbH: Wako V-50) as an initiator was dissolved in 2 ml of tap water and the clear solution was then added to the stirred brine.
After heating according to example 1 to about 65° C. (140° F.), the reaction started and, in contrast to example 4a, a high-viscosity, stable, “firm” gel formed which had a milky turbidity. The thermal stability was comparable with that of examples 1 to 3.
2.5 g of hydroxyethyl methacrylate (commercial product from Degussa GmbH: Mhoromer BM 903), 0.65 g of 2-dimethylaminoethyl methacrylate (DMAEMA, commercial product from Degussa GmbH: Mhoromer BM 601) and 0.5 g of polyethylene glycol-400 dimethacrylate (commercial product from Degussa GmbH: Mhoromer MFM 409) as a crosslinking agent were added to 100 ml of a saturated calcium chloride brine having a specific density of 1.39 kg/l (11.6 US pounds per gallon, ppg) and stirred on a magnetic stirrer at ambient temperature. 0.25 g of 2,2′-azobis(2-aminopropane) dihydrochloride (commercial product from Wako Chemicals GmbH: Wako V-50) as an initiator was dissolved in 2 ml of tap water and the clear solution was then added to the stirred brine.
After heating according to example 1 to about 65° C. (140° F.), the reaction started and, in contrast to comparative example 4a, a high-viscosity, stable, “firm” gel formed which had a milky turbidity. The thermal stability was comparable with that of examples 1 to 3.
| Number | Date | Country | Kind |
|---|---|---|---|
| 10 2006 029 752.0 | Jun 2006 | DE | national |
