Wells – Processes – Cementing – plugging or consolidating
Reexamination Certificate
1999-02-18
2001-02-27
Bagnell, David (Department: 3672)
Wells
Processes
Cementing, plugging or consolidating
C166S305100
Reexamination Certificate
active
06192986
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to polymeric compositions and their use for blocking subterranean formations in oil and gas fields.
2. Discussion of Realted Art
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. to 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, for example, 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. Other cross-linking agents which have been used are metals such as zirconium and other transition metals.
Whilst the use of metal cross-linking agents is reasonably satisfactory in practice, there are certain disadvantages. For example, there can be environmental effects with the use of metal ions, particularly with chromium. For some rocks, such as carbonate rocks, the metals used as cross-linking agents are absorbed by the rocks and are hydraulically unstable at temperatures above 70° C. and so cannot function properly, thus reducing the effectiveness of the blocking polymers.
U.S. Pat. No. 4,773,481 describes a process for reducing the permeability of a subterranean formation by the gelation of water-soluble polymers of polyalkyleneimines and polyalkylenepolyamines with certain polymeis which are anionic or hydrolysable to form anionic polymers and which are cross-linked by the water-soluble polymers. Examples of the anionic or non-ionic polymers are polyacrylamide and alkylpolvacrylamides, copolymers of polyacrylamide and alkylpolyacrylamides with ethylene, propylene and styrene, polymaleic anhydride and polymethacrylate and hydrolysis products thereof. As described in the patent, when the water-soluble polymer and the anionic polymer are mixed, a viscous gel is quickly formed. In use, a solution of the water-soluble polymer is pumped into the subterranean formation first, followed by water to cleanse the bore of the water-soluble polymer to prevent premature gelling upon introduction of the anionic polymer. and finally the anionic polymer is introduced.
This three step procedure has a number of disadvantages in practice but it is necessary because the water-soluble polyalkyleneimine or polyalkylenepolyamine reacts very quickly with the anionic polymer and hence cannot be premixed before injection without substantial risk of premature gelation. To some extent, this problem can be reduced by using a non-ionic polymer which is hydrolysable to an anionic polymer at a relatively slow rate, but this limits the choice of materials and is not generally satisfactory. So far as we are aware, the process of U.S. Pat. No. 4,773,481 has either not been commercially utilised, or has only been used to a small extent, presumably because of the substantial practical difficulties involved.
SUMMARY OF THE INVENTION
We have now found a way of avoiding the use of metal ion cross-linking agents and of controlling the gelling rate of polymers whereby premixes of polymer and gelling agent can be made and safely injected into a downhole formation without serious risk of premature gelation.
In one aspect, the invention provides a composition for use in a subterranean formation, which composition comprises a water-soluble copolymer comprising
(i) at least one non-acidic ethylenically unsaturated polar monomer and
(ii) at least one copolymerisable ethylenically unsaturated ester;
and at least one organic gelling agent, characterized in that the organic gelling agent is a polyalkyleneimine, polyfunctional aliphatic amine, an aralkylamine or a heteroaralkylamine.
The organic gelling agents are free from metal ions, and are preferably water-soluble polymers capable of cross-linking the copolymers. Among the preferred water-soluble polymers for use as gelling agents are polyalkyleneimines, polyalkylenepolyamines and mixtures thereof. Additional details concerning these polymers and their preparation are disclosed in U.S. Pat. No. 3,491,049. The preferred polyalkylenepolyamines are the polymeric condensates of lower molecular weight polyalkvlenepolyamines and a vicinal dihaloalkane. The polyalkyleneimines are best illustrated by polymerized ethyleneimines or propyleneimine. The polyalkylenepolyamines are exemplified by polyethylene and polypropylenepolyamines.
Other gelling agents which can be used include water-soluble polyfunctional aliphatic amines, aralkylamines and heteroaralkylamines optionally containing other hetero atoms.
In a second aspect. the invention provides a method of conformance control of a subterranean reservoir, which comprises:
(a) injecting into a formation an aqueous solution of a composition of the invention;
(b) allowing the solution to flow through at least one permeable zone in said formation; and
(c) allowing the composition to gel.
In the method of the invention. it is generally unnecessary to have any pre-cool step, especially in wells with bottom hole temperatures up to about 120° C. As the solution is pumped downhole and permeates into the zone, it heats up and eventually reaches the downhole temperature after which gelling occurs. The permeability of the zone is preferably high but it can be down to about 60 mD.
REFERENCES:
patent: 4757862 (1988-07-01), Naiman et al.
patent: 4776398 (1988-10-01), Chu et al.
patent: 4909324 (1990-03-01), Shu
patent: 5003006 (1991-03-01), Chu et al.
patent: 5346013 (1994-09-01), Pusch et al.
patent: 5836392 (1998-11-01), Urlwin-Smith
patent: 0 005 835 (1979-12-01), None
patent: 07 011 211 (1995-01-01), None
Bagnell David
Dougherty Jennifer R.
Halliburton Energy Service,s Inc.
Kent Robert A.
LandOfFree
Blocking composition for use in subterranean formation does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Blocking composition for use in subterranean formation, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Blocking composition for use in subterranean formation will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-2559541