Wells – Processes – Cementing – plugging or consolidating
Patent
1997-08-05
1998-11-17
Schofer, Joseph L.
Wells
Processes
Cementing, plugging or consolidating
166300, 5263077, F21B 3313
Patent
active
058363920
DESCRIPTION:
BRIEF SUMMARY
The present invention relates to polymers and their preparation and their use in oil and gas fields.
Oil and gas fields produce water as well as oil and/or gas, especially when the well is depleted. In addition, secondary recovery techniques such as water flooding to stimulate production of oil involve injection of water under pressure at a distance from a production well to squeeze the oil out. However, in both cases the water moves in the formation along least hindered paths, so that the recovery technique may be inefficient and in the direct recovery increased proportions of water are produced.
To enhance reservoir conformance control, i.e. mobilise the oil that may be present in less permeable areas, blocking agents may be injected to obstruct the high permeability channels thereby encouraging preference for liquid movement via the lower permeability channels. Among known blocking agents are polymer gels, in particular, gels of polyacrylic acid or polyacrylamide/polyacrylic copolymers, cross-linked with chromium ions as disclosed in U.S. Pat. Nos. 4,744,418 and 4,844,168. The copolymer, mixed with cross-linker, is injected into the formation from the production well, often after a flood of cold water to pre-cool the formation rock, to stop premature cross-linking and gelling before the mixture reaches its desired position. Much work has been described to reduce the rate of cross-linking, by reducing the activity of the cross-linking metal ion, e.g. by co-ordinating the chromium with a ligand, e.g. lactate.
An improved cross-linking system has now been discovered which comprises a composition in which the tendency of the polymer to cross-link prematurely has been reduced further by use of a copolymer of a polyacrylamide with a polar monomer.
The present invention provides a water soluble copolymer of:
The invention also comprises compositions comprising the water soluble copolymer and a polyvalent metal ion gelling agent.
The present invention also provides a process for delaying the rate of gelling of an acrylic polymer with a gelling agent, in which the acrylic polymer is said copolymer comprising (i) and (ii).
The invention also provides a method for conformance control of a reservoir, especially one with high formation temperatures, which method comprises: permeability in said formation under increasing temperature conditions,
The copolymer is formed from at least one, e.g. 1-3 polar monomer(s) and at least one, e.g. 1-3 ester(s), and comprises structural units derived from said monomer(s) and ester(s); preferably the copolymer consists essentially of said structural units. The ester is substantially neutral as it is a fully esterified derivative of an acid, i.e. complete ester, rather than a partial ester with free acid group(s).
The ester is usually formed from a hydroxyl compound and an ethylenically unsaturated carboxylic acid. The ethylenically unsaturated group may be in the alpha-beta or beta gamma position relative to the carboxyl group or may be further distant; preferred acids have 3-20 carbons, such as 3-12, e.g. alkenoic and aralkenoic acids with 3-6 or 9-12 carbons respectively. Examples of the acids are acrylic, methacrylic, crotonic and cinnamic acids. The hydroxyl compound is usually an alcohol and may be of formula ROH, where R is a hydrocarbyl group, preferably an alkyl group, e.g. of 1-30 or 2-30 such as 1-6, 2-6, 7-30 or 7-24 carbons, alkenyl groups, e.g. of 2-20 carbons such as 2-6 carbons, cycloalkyl group, e.g. of 5-8 carbons, aryl group, e.g. aromatic hydrocarbyl group such as 6-20 carbons or aralkyl group, e.g. of 7-24 carbons. Examples of such R groups are methyl, ethyl, n- and iso propyl, n, sec, iso and tert butyl, n, sec, iso and tert amyl and hexyl, octyl and 2-ethylhexyl, decyl, allyl, cyclohexyl, palmityl, steryl, phenyl and benzyl. The R group may also be a hydrocarbyl group, substituted by at least one substituent e.g. 1-3 substituents, especially from hydroxyl, ether, and thio ether groups; electron donating groups are preferred. Ether substituents are preferred, e
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Halliburton Energy Service,s Inc.
Sarofim N.
Schofer Joseph L.
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