Method and composition for the triggered release of polymer-degrading agents for oil field use

Abstract

Disclosed are methods and related compositions for altering the physical and chemical properties of a substrate used in hydrocarbon exploitation, such as in downhole drilling operations. In a preferred embodiment a method involves formulating a fluid, tailored to the specific drilling conditions, that contains one or more inactivated enzymes. Preferably the enzyme is inactivated by encapsulation in a pH responsive material. After the fluid has been introduced into the well bore, one or more triggering signals, such as a change in pH, is applied to the fluid that will activate or reactivate the inactivated enzyme, preferably by causing it to be released by the encapsulation material. The reactivated enzyme is capable of selectively acting upon a substrate located downhole to bring about the desired change in the chemical or physical properties of the substrate.

Description

CROSS-REFERENCE TO RELATED APPLICATIONS [0001] This application claims the benefit of U.S. Provisional Patent Application No. 60 / 165,393 filed Nov. 12, 1999.BACKGROUND OF THE INVENTION [0002] 1. Field of the Invention [0003] The present invention generally relates to compositions and methods used for hydrocarbon exploitation such as in the drilling of and production from wells, especially oil and gas wells. More particularly, the invention relates to such compositions and methods which alter the physical or chemical properties of a polymeric component of an oil field fluid or residue, such as decomposing a polymeric viscosifier or fluid loss control agent contained in such fluid or residue in response to a defined chemical or physical signal. [0004] 2. Description of Related Art [0005] The selection of materials for well construction is essential to the successful completion of an oil or gas well. Among the most important is the selection of a drilling fluid. A drilling fluid having...

AI Technical Summary

Benefits of technology

[0076] Also provided in accordance with the present invention is a wellbore servicing composition comprising a fluid or a solid device containing at least one degradable substrate, said substrate contributing to the structural integrity of said device or to the structural integrity of a residue of said fluid, and an inactivated substrate-degrading agent. The substrate-degrading agent is capable of responding to a triggering signal such that the agent becomes at least partially reactivated sufficient to degrade said substrate under degradation promoting conditions in a downhole environment such that a physical or chemical property of the composition is altered. The utility of the invention in destroying solid filter cake formed in the wellbore and containing the inactivated agent can be extended to pre-formed solid materials. An example would be to make solid particles from starch and starch-containing synthetic polymers to serve a rigid bridging particles, for example, for use in low density fluids where the density of calcium carbonate cannot be tolerated, and strong chemicals cannot be used to clean up the filter cake, or where cleanup chemicals may not be able to be applied. Another application could be to cash sheets of degradable polymer containing the inactivated agent for use as cover for premium screens such as prepacked sand screens. The covers could prevent damage of the screens whilst being placed into the wellbore, and then destroyed by application of the trigger or exposure to CO2 from the well.

[0077] Still flurther provided in accordance with the invention is a wellbore treatment method comprising formulating a fluid comprising an encapsulated substrate-degrading agent; introducing the fluid into a downhole environment containing a predetermined substrate capable of being degraded by the agent under degradation promoting conditions; and providing for generation of the trigger upon reaching the desire point. One example would be the use of encapsulation to preserve the activity of the agent that would normally be lost during the trip to the site of use, say by thermal degradation of enzymes in a brine pumped to the producing zone at the bottom of a deep, hot well. Including materials that generate a trigger as they thermally degrade would provide for the preserved agent to be released where it could immediately act.

Problems solved by technology

The formation of a filter cake seal is fostered by an imbalance of pressure of the mud column over the pressure exerted by fluids within the formation.

Although filter cake formation is essential to drilling operations, the filter cake can be a significant impediment to the production of hydrocarbon or other fluids from the well.

Since filter cake is compacted and often adheres strongly to the formation, it may not be readily or completely flushed out of the formation by fluid action alone.

As the '995 patent disclosed, however, oxidants are ineffective at low temperature ranges, from ambient temperature to 130° F, As reported, in this temperature range the oxidants are stable and do not readily undergo homolytic cleavage to initiate the degradation of the filter cake.

High oxidizer concentrations are frequently poorly soluble under the treatment conditions.

Reactions involving common oxidants are also often difficult to control.

For example, oxidants can react with iron found in the formation, producing iron oxides that precipitate and damage the formation, decreasing permeability.

Acid treatments, however, corrode steel and equipment used in the operation.

Acid treatments may also be incompatible with the formation and / or its fluids.

Residues, such as filter cakes, can also present difficulties during drilling operations.

Further, poor filter cakes may cause the drill pipe to become stuck, known as “differential sticking.” Helmick and Longley, “Pressure-Differential Sticking of Drill Pipe and How it Can Be Avoided or Relieved,”API Drill. Prod. Prac. (1957). pp.55-60; Outmans, H. D., “Mechanics of Differential-Pressure Sticking of Drill Collars,”Trans.

This occurs when part of the drill string bears against the side of the hole while drilling, and erodes away part of the filter cake.

Sometimes, the pipe can be freed by spotting oil around the stuck section, but if this procedure fails, more expensive and time consuming methods are entailed (H. C. H. DARLEY & GEORGE R. GRAY, COMPOSITION AND PROPERTIES OF DRILLING AND COMPLETION FLUIDS 405-11 (5th ed.

In addition, drilling fluid residues remaining in the well tend to interfere with other phases of drilling and completion operations such as cementing the casing to the wall of the bore.

Unfortunately, this procedure, often referred to as a “spacer” flush, is inadequate in many applications.

Conventional flushing fluids are not always capable of sufficiently decreasing the gel strength, viscosity and other rheological properties of the mud caused by polymeric additives therein.

As a result, the mud cannot be flushed out of the well.

Instead, expensive squeeze cementing operations are carried out to fill in the gaps in the cement caused by the mud.

However, as nature's catalysts, enzymes are usually only active within the range of conditions, particularly pH, temperature, and aqueous solvents, found within the cells from which they are isolated.

This reaction continues on and on again, causing the degradation of the polymer chain.

The cellulose backbone, however, can only be broken after treating the xanthan to degrade the trisaccharide side chains with another enzyme such as a mannosidase.

Simply adding a breaker to the fluid, however, is problematic; results are often unreliable, and can lead to premature breaking of the fluid before the fracturing process is complete, resulting in a decrease in the number or length of fractures, and well productivity.

The most serious problem associated with this system is that the breaker tends to be released over a significant period of time due to differences in the thickness of the protective coating and in variations of length of time and temperature exposure of the individual pellets.

When the fracturing fluid passes or leaks off into the formation, or the fluid is removed by back flowing, the resulting fractures in the subterranean formation close and crush the beads.

For instance, premature release of the enzyme payload sometimes occurs due to product manufacturing defects, imperfections, or coating damage experienced in pumping the particles through surface equipment tubular and perforations.

Although the literature reflects a great deal of effort directed at controlling the activity of fracturing fluid breakers, most of those methods are limited in their usefulness by unfavorable downhole conditions or by economic factors.

Particularly lacking in the field are adequate ways of avoiding the problems associated with drilling fluids, which must undergo high shear while drilling, cycling of temperature between bottom-hole and surface, and remain useable for weeks.

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