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...

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Benefits of technology

[0067] Accordingly, certain embodiments of the invention are directed to methods and related compositions for altering the physical and / or chemical properties of substrates used in hydrocarbon exploitation, in both downhole and in surface applications. These compositions and methods will find use in a variety of drilling, completion, workover, production, reclamation and disposal operations. The more preferred embodiments include the triggered release of agents, such as enzymes and chemicals that specifically act on defined substrates, such as polymeric viscosifiers, fluid loss control agents and.chemical contaminants like H2S. Creating a new drilling fluid formulation, including an enzyme within the circulating fluid system could provide for easy decomposition of the drilling fluid at the end of drilling operations, both in the fluid returned to tanks on the surface and the fluid lost to the formation or discharged whole or on cuttings into the environment. In certain of the new reservoir drilling fluid compositions, the encapsulated enzyme retains the enzyme during drilling operations and releases the enzyme or enzymes upon receipt of a chemical trigger such as pH or salinity change, or the enzyme is released over a defined period of time. An important trigger has been found to be CO2, which is present in many reservoirs.

[0072] According to another embodiment, a method of increasing the flow of production fluid from a well is provided that comprises formulating a fluid comprising a degradable polymeric substrate and an inactivated enzyme. This method also includes introducing the fluid into a downhole environment and applying a triggering signal to the fluid. The triggering signal is sufficient to reactivate the inactivated enzyme to give a reactivated enzyme, and the reactivated enzyme is capable of selectively degrading the substrate sufficient to alter a physical property of the fluid such that the flow of production fluid is increased. In some embodiments the step of introducing the fluid into a downhole environment comprises forming a filter cake containing said degradable substrate and said inactivated enzyme. In some embodiments the fluid comprises more than one inactivated enzyme, wherein the inactivated enzymes are capable of being reactivated by the same or different triggering signals, wherein upon reactivation the reactivated enzymes are capable of acting upon the same or different substrates. In some embodiments the fluid is a circulating drilling fluid, a completion fluid, a workover fluid or a stimulation fluid. According to another embodiment, a method of increasing the flow of production fluid from a well is provided that comprises formulating a fluid comprising a degradable polymeric substrate and an inactivated enzyme. This method also includes introducing the fluid into a downhole environment, where the fluid is present as whole fluid, such as drilling fluid lost to natural fractures and other open features. The direct application of a physical, triggering signal, such as a change in pH with weak acids, is sufficient to reactivate the inactivated agent, such as an enzyme, to give a reactivated enzyme, and the reactivated enzyme is capable of selectively degrading the substrate sufficient to alter a physical property of the fluid as viscosity or particle suspending ability or pore-plugging ability such that the flow of production fluid is increased. Cementing and other activities that indirectly increase fluid production can also benefit by, for example, liquefaction and sloughing of drilling fluids left behind by imperfect cleaning of the well bore.

[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.

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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