Hydrophilic polymer gel water sealing process

Details Hydrophilic polymer gel water sealing process Hydrophilic polymer gel water sealing process

1991-01-16

1992-09-15

Britts, Ramon S.

Wells

Processes

Distinct, separate injection and producing wells

166295, E21B 4322

Patent

active

051469855

DESCRIPTION:

BRIEF SUMMARY
The present invention relates to a liquid composition for the production of a gel and a process for placing such a gel in a well drilled in the ground for the temporary and selective isolation of the permeable zones in the subsoil crossed by wells. More particularly, the invention applies to oil wells.
It is often necessary to temporarily block or isolate the permeable formations of a well, so that other zones can be treated or stimulated, for example by fracturation or acidification, or when it is necessary to remove or modify well equippment. Similarly, in the course of drilling, it is current practice to carry out isolation of permeable zones, often causing considerable loss of drilling fluid.
Many methods and compositions have been suggested up to the present and are used to provisionally isolate a productive formation. For example, fibrous, flaky or granular plugging agents, cements or viscous gels have been used as plugging agents. The more recent use of aqueous gels, such as those containing crosslinked polysaccharides, dispersed in water in the granular state, as described in U.S. Pat. No. 3,227,212, constitute a great improvement with respect to previous methods. Nonetheless, certain operational difficulties in the use of these gels have been observed, in particular the instability of formulations following abrupt changes in pH values, lack of homogeneity of aqueous dispersions during the placing in wells and, especially, the difficulty in controlling gel setting time so that it swells to the exact size of the formation to be isolated.
Improvements have been sought through the use of hydrogel polymers such as polyacrylamide, cellulose ethers or polysaccharides in a mono- or polyalcohol. Crosslinking of the polymer on contact with water was obtained by the addition of an oxidation-reduction system, particularly sodium bichromate/sodium sulfite. This is the content of U.S. Pat. Nos. 3,881,552 and 3,964,923. The compositions suggested suffer from the instability of oxidizing agents in organic medium and difficulties in controlling the viscosity of the fluid used.
It follows that, despite the many efforts undertaken in this field, there is still a need for a practical composition for the satisfactory production in a well of a waterproof gel.
The present invention provides a suitable and economical solution to this problem. It allows the placing of the gel plug in the required position to be controlled. Contrary to compositions and gel placing according to the prior art, it is not necessary to carry out preliminary laboratory measurements concerning gel setting time as a function of temperature. Hydration of the polymer in solid form is delayed as long as the non aqueous fluid which supports it does not come into contact with water in amounts large enough to cause its gelling.
Another advantage of the technique according to the invention resides in the fact that the risk of filtration of gel constituents into the formation and the risk of irreversible damage to formation injectivity or productivity are reduced. This is particularly important when isolating a fissured or fractured zone, where the rapid setting technique according to the invention provides a solution which is only obtained with difficulty with conventional techniques.
Furthermore, with the technique of the invention, it is possible to considerably increase solid polymer concentration in the gel, and thus the mechanical resistance of the latter, without the pumping difficulties encountered with water-based fluids.
The composition according to the invention, consisting of a suspension or solution of a hydrophilic gel polymer in an organic liquid at least partially miscible with water, is characterized in that it contains a borate of an alkali metal or a complex salt of a polyvalent metallic cation in suspension as a bridging agent.
Contrary to previous practice, which uses aqueous compositions, the alkali borate does not dissolve or dissolves only very slightly in the alcoholic medium of the composition. It was unexpected to find that thes

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