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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, th

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.

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1. A method of degrading a predetermined substrate used for hydrocarbon exploitation comprising:providing a fluid or a solid, or a mixture thereof, containing a substrate-degrading agent inactivated by encapsulation, said inactivated substrate-degrading agent initially being substantially inactive,

1. A method of degrading a predetermined substrate used for hydrocarbon exploitation comprising:providing a fluid or a solid, or a mixture thereof, containing a substrate-degrading agent inactivated by encapsulation, said inactivated substrate-degrading agent initially being substantially inactive, and subsequently becoming active in response to a predetermined triggering signal; andapplying the triggering signal to said fluid or solid or mixture thereof such that said substrate-degrading agent becomes activated, the activated substrate-degrading agent being capable of at least partially degrading the substrate, said triggering signal selected from the group consisting of exposure to a reducing agent, oxidizer, chelating agent, radical initiator, carbonic acid, ozone, chlorine, bromine, peroxide, electric current, ultrasound, change in pH, change in salinity, change in ion concentration, reversal of wellbore pressure-differential, and combinations thereof. 2. The method of claim 1 wherein said step of applying a triggering signal comprises exposing the inactivated substrate-degrading agent to a change in pH environment. 3. The method of claim 2 wherein said step of exposing the inactivated substrate-degrading agent to a change in pH comprises lowering the pH environment. 4. The method of claim 3 wherein said step of lowering the pH environment comprises exposing the inactivated substrate-degrading agent to carbonic acid. 5. The method of claim 1 wherein said step of applying a triggering signal comprises exposing The inactivated substrate-degrading agent to a change in salinity. 6. The method of claim 1 wherein said step of applying a triggering signal comprises exposing the inactivated substrate-degrading agent to a reducing agent. 7. The method of claim 1 wherein said step of applying a triggering signal comprises exposing the inactivated substrate-degrading agent to an oxidizer. 8. The method of claim 1 wherein said step of applying a triggering signal comprises exposing the inactivated substrate-degrading agent to a chelating agent. 9. The method of claim 1 wherein said step of applying a triggering signal comprises exposing the inactivated substrate-degrading agent to a radical initiator. 10. The method of claim 1 wherein said step of applying a triggering signal comprises exposing the inactivated substrate-degrading agent to ozone. 11. The method of claim 1 wherein said step of applying a triggering signal comprises exposing the inactivated substrate-degrading agent to chlorine or bromine. 12. The method of claim 1 wherein said step of applying a triggering signal comprises exposing the inactivated substrate-degrading agent to peroxide. 13. The method of claim 1 wherein said step of applying a triggering signal comprises exposing the inactivated substrate-degrading agent to an electric current. 14. The method of claim 1 wherein said step of applying a triggering signal comprises exposing the inactivated substrate-degrading agent to ultrasound. 15. The method of claim 1 wherein said step of applying a triggering signal comprises exposing the inactivated substrate-degrading agent to a change in ion concentration. 16. The method of claim 1 comprising exposing the inactivated substrate-degrading agent to a reversal of wellbore pressure-differential. 17. The method of claim 1 wherein said substrate-degrading agent comprises at least one agent chosen from the group consisting of enzymes, microorganisms, spores and inorganic chemicals. 18. The method of claim 1 wherein said encapsulation comprises encapsulating said substrate-degrading agent with an encapsulating material that maintains the substrate-degrading agent substantially inactive initially, and is responsive to said triggering signal such that at least a portion of said substrate-degrading agent is released by said encapsulating material upon exposure to said triggering signal. 19. The method of claim 1 wherein said encapsulating material is formed of a co-polymer of (a) an ethylenically unsaturated hydrophobic monomer with (b) a free base monomer of the formula 2 —CR 1 COXR 2 NR 3 R 4 where R is hydrogen or methyl, R 2 is alkylene containing at least two carbon atoms, X is O or NH, R 3 is a hydrocarbon group containing at least 4 carbon atoms and R 4 is hydrogen or a hydrocarbon group. 20. The method of claim 19 wherein R 3 is t-butyl and R 4 is hydrogen. 21. The method of claim 19 wherein R 1 is methyl, R 2 is ethylene and X is O. 22. The method of claim 19 wherein the hydrophobic monomer is a styrene or methylmethacrylate. 23. The method of claim 19 wherein said encapsulating material is a co-polymer of styrene or methyl methacrylate with t-butyl amino ethyl methacrylate. 24. The method of claim 19 wherein said co-polymer is 55 to 80 weight % styrene, methyl styrene or methyl methacrylate with 20 to 45 weight % t-butylamino-ethyl methacrylate. 25. The method of claim 18 wherein the fluid or solid comprises at least two inactivated substrate-degrading agents, each of which is inactivated by encapsulation, wherein the inactivated substrate-degrading agents are capable of being activated by the same or different triggering signals, such that upon activation the activated substrate-degrading agents are capable of acting upon the same or different substrates independently or in concert. 26. The method of claim 17 wherein said substrate-degrading agent comprises an endo-amylase. 27. The method of claim 17 wherein said substrate-degrading agent is alpha-amylase. 28. The method of claim 17 wherein said substrate-degrading agent comprises at least one enzyme selected from the group consisting of exo-amylases, isoamylases, glucosidases, amylo-glucosidases, malto-hydrolases, maltosidases, isomalto-hydrolases and malto-hexaosidases. 29. The method of claim 17 wherein the released substrate-degrading agent is capable of being deactivated by application of a second triggering signal, wherein the second triggering signal may be the same or a different triggering signal, such that the deactivated substrate-degrading agent no longer acts on the substrate. 30. The method of claim 1 wherein the degradable substrate is selected from the group consisting of celluloses, derivatized celluloses, starches, derivatized starches, xanthans and defivatized xanthans. 31. The method of claim 1 wherein the fluid is chosen from the group consisting of circulating drilling fluid, completion fluid, simulation fluid, gravel packing fluid and workover fluid. 32. The method of claim 1 wherein the fluid is a fracturing fluid. 33. The method of claim 1 wherein said solid comprises a device or particle suitable for use downhole or on the surface for hydrocarbon exploitation. 34. A method of increasing the flow of hydrocarbons from a well, the method comprising:providing a fluid comprising a degradable polymeric substrate and a substrate-degrading agent inactivated by encapsulation, said inactivated substrate-degrading agent being substantially inactive initially, and becoming active in response to a predetermined triggering signal;introducing the fluid into a downhole environment; and,applying the triggering signal, the triggering signal being sufficient to activate the inactivated substrate-degrading agent to give an activated substrate-degrading agent,the activated substrate-degrading agent being capable of selectively degrading the substrate sufficient to alter a physical property of the fluid or a solid formed therefrom such that the flow of hydrocarbons from said well is increased, wherein said triggering signal is chosen from the group consisting of reducing agent, oxidizer, chelating agent, radical initiator, carbonic acid, ozone, chlorine, bromine, peroxide, electric current, ultrasound, change in pH, change in salinity, change in ion concentration, reversal of wellbore pressure-differential, and combinations thereof. 35. The method of claim 34 comprising:carrying out drilling activity wherein said f luid comprises a circulating drilling fluid containing the polymeric substrate and the inactivated substrate-degrading agent, wherein the agent comprises an inactivated enzyme that is capable of withstanding the dynamic environmental conditions generated while drilling; andforming a low-permeability filter cake or fluid invasion zone containing said degradable polymeric substrate and said inactivated enzyme, said low-permeability filter cake or fluid invasion zone retaining low-permeability until receipt of said triggering signal sufficient to activate at least a portion of said enzyme. 36. The method of claim 34 wherein the agent comprises more than one inactivated enzyme, wherein the inactivated enzymes are capable of being activated by the same or different triggering signals, wherein upon activation the activated enzymes are capable of acting upon the same or different substrates. 37. The method of claim 34 wherein the fluid is chosen from the group consisting of a circulating drilling fluid, a completion fluid a workover fluid, a fracturing fluid, a gravel packing fluid and a stimulation fluid. 38. A method of degrading filter cake, the method comprising:providing a fluid comprising a polymeric viscosifier or fluid loss control agent and an enzyme inactivated by sequestration, said inactivated enzyme being responsive to a predetermined triggering signal;introducing the fluid into a downhole environment such that a filter cake containing said polymeric viscosifier or fluid loss control agent and said inactivated enzyme is formed;applying the triggering signal selected from the group consisting reducing agent, oxidizer, chelating agent, radical initiator, carbonic acid, ozone, chlorine, bromine, peroxide, electric current, ultrasound, change in salinity, change in pH, change in ion concentration, reversal of wellbore pressure-differential, and combinations thereof, to activate the inactivated enzyme to give an activated enzyme, the activated enzyme being capable of selectively degrading said polymeric viscosifier or fluid loss control agent such that said filter cake containing said viscosifier or fluid loss control agent at least partially disintegrates, anddislodging a piece of drilling equipment from said at least partially disintegrated filter cake. 39. A wellbore treatment method comprising:providing a fluid or a solid, or mixture thereof, containing a substrate-degrading agent inactivated by sequestration, said inactivated substrate-degrading agent being responsive to a predetermined triggering signal such that said substrate-degrading agent becomes activated upon exposure to said triggering signal, the activated substrate-degrading agent being capable of degrading a previously existing downhole substrate;introducing said fluid or solid, or mixture thereof, into a downhole environment that contains said substrate; providing said triggering signal selected from the group consisting of exposure to a reducing agent, oxidizer, chelating agent, radical initiator, carbonic acid, ozone, chlorine, bromine, peroxide, electric current, ultrasound, change in salinity, change in pH, change in ion concentration, reversal of wellbore pressure-differential, and combinations thereof, to activate the substrate-degrading agent; andallowing the substrate-degrading agent to at least partially degrade the substrate. 40. The method of claim 1 comprising allowing said substrate to at least partially degrade. 41. The method of claim 1 comprising initial conditions of use of said fluid or solid or mixture thereof, and subsequent conditions of use of said fluid or solid or mixture thereof resulting from said applying said triggering signal. 42. The method of claim 1 wherein said fluid or solid or mixture thereof contains said degradable substrate. 43. The method of claim 42 wherein said solid comprises a filter cake or a bridging particle. 44. The method of claim 42 comprising allowing said substrate to degrade whereby a physical property of s aid fluid or solid is altered, said triggering signal being incapable of effecting said alteration if applied in the absence of said inactivated substrate-degrading agent. 45. The method of claim 3 wherein said step of lowering the pH environment comprises reducing the pressure within an excavation so that naturally-occurring carbonic acid, hydrosulfuric acid, or other naturally occurring acid or precursor thereof, previously excluded from said excavation by application of higher pressure, enter into said excavation to lower the pH environment of the inactivated substrate-degrading agent. 46. The method of claim 1 wherein said inactivated substrate-degrading agent is separate from said substrate and said method comprises:supplying said triggering signal to said fluid or solid or mixture thereof containing said inactivated substrate-degrading agent such that said substrate-degrading agent becomes activated; andexposing said activated substrate-degrading agent to said substrate. 47. The method of claim 1 wherein said inactivated substrate-degrading agent comprises particles up to about 74 microns in diameter. 48. The method of claim 1 wherein said inactivated substrate-degrading agent is capable of withstanding shear forces generated during drilling. 49. The method of claim 1 wherein said inactivated substrate-degrading agent is capable of withstanding dynamic exposure to drilling temperatures. 50. The method of claim 49 wherein said inactivated substrate-degrading agent is capable of withstanding dynamic exposure to temperatures up to 200° F. 51. The method of claim 2 wherein said inactivated substrate-degrading agent comprises an encapsulating material that becomes permeable to said substrate-degrading agent after exposure to said pH change, and said method comprises applying said pH change whereby said substrate-degrading agent passes through said encapsulating material. 52. A method of increasing the permeability of filter cake in a wellbore, the method comprising:obtaining a polymeric viscosifier or fluid loss control agent and a breaking agent capable of degrading said polymeric viscosifier or fluid loss control agent;encapsulating said breaking agent in an ionophoric encapsulating material to obtain an encapsulated breaking agent, said ionophoric encapsulating material being impermeable to said breaking agent at a defined first pH and permeable to said breaking agent at a defined second pH;carrying out drilling activity whereby a filter cake is formed comprising said polymeric viscosifier or fluid loss control agent and said encapsulated breaking agent, said filter cake having a firs permeability to a defined wellbore fluid;changing the pH of the filter cake from said first pH to said second pH, whereby permeability of said encapsulating material to said breaking agent changes such that said breaking agent becomes unencapsulated;allowing said unencapsulated breaking agent to at least partially degrade said polymeric viscosifer or fluid loss control agent such that the permeability of said filter cake changes from said first permeability to a second permeability that is greater than said first permeability. 53. The method of claim 39 comprising removing drilling fluid from said downhole environment before applying said triggering signal. 54. The method of claim 1 further comprising exposing the inactivated substrate-degrading agent to a change in pressure and/or temperature. 55. The method of claim 33 wherein the solid comprises a perforation gun holder or a film sheath for a sand screen assembly. 56. The method of claim 34 further comprising exposing said inactivated substrate-degrading agent to a change in pressure and/or temperature. 57. The method of claim 34 wherein applying said triggering signal comprises exposing said inactivated substrate-degrading agent to a downhole reversal of wellbore pressure-differential. 58. The method of claim 34 wherein said substrate-degrading agent comprises at least one enzyme. 59 . The method of claim 34 wherein said fluid comprises a drilling fluid. 60. The method of claim 39 further comprising exposing said inactivated degrading agent to a change in pressure. 61. The method of claim 39 further comprising exposing said inactivated degrading agent to a change in temperature. 62. The method of claim 39 wherein said sequestration comprises encapsulation of said degrading agent. 63. The method of claim 39 wherein said degrading agent comprises at least one enzyme. 64. The method of claim 39 wherein said fluid comprises a drilling fluid. 65. The method of claim 52 wherein said breaking agent comprises at least one enzyme. 66. The method of claim 19 wherein the fluid is chosen from the group consisting of a circulating drilling fluid, a completion fluid, a workover fluid, a fracturing fluid, a gravel packing fluid and a stimulation fluid. 67. The method of claim 19 wherein said solid comprises a device or particle suitable for use downhole or on the surface for hydrocarbon exploitation. 68. The method of claim 67 wherein said solid comprises a filter cake or a bridging particle. 69. The method of claim 57 wherein said downhole reversal of wellbore pressure-differential causes the release of CO 2 in the downhole environment which causes a change in pH. 70. The method of claim 1 wherein said encapsulated substrate-degrading agent is capable of responding to said triggering signal such that said agent becomes sufficiently unencapsulated to allow said agent to degrade the substrate. 71. A method of degrading a predetermined substrate used for hydrocarbon exploitation comprising:providing a fluid or a solid, or a mixture thereof, containing a substrate-degrading agent inactivated by sequestration, said inactivated substrate-degrading agent initially being substantially inactive, and subsequently becoming active in response to a predetermined triggering signal; andapplying said triggering signal to said fluid or solid or mixture thereof such that said substrate-degrading agent becomes activated, the activated substrate-degrading agent being capable of at least partially degrading the substrate, wherein said triggering signal is select the group consisting of exposure to a reducing agent oxidizer, chelating agent, radical initiator, carbonic acid, ozone, chlorine, bromine, peroxide, electric current, ultrasound, change in salinity, change in pH, change in ion concentration, reversal of wellbore pressure-differential, and combinations thereof, andexposing the inactivated substrate-degrading agent to a change in pH environment, and wherein exposing the inactivated substrate-degrading agent to a change in pH comprises lowering the pH environment, andwherein lowering the pH environment comprises exposing the inactivated substrate-degrading agent to carbonic acid. 72. The method of claim 52 wherein said encapsulating material is formed of a co-polymer of (a) an ethylenically unsaturated hydrophobic monomer with (b) a free base monomer of the formula 2 ═CR 1 COXR 2 NR 3 R 4 where R is hydrogen or methyl, R 2 is alkylene containing at least two carbon atoms, X is O or NH, R 3 is a hydrocarbon group containing at least 4 carbon atoms and R 4 is hydrogen or a hydrocarbon group. 73. The method of claim 72 wherein R 3 is t-butyl and R 4 is hydrogen. 74. The method of claim 72 wherein R 1 is methyl, R 2 is ethylene and X is O. 75. The method of claim 72 wherein the hydrophobic monomer is a styrene or methylmethacrylate. 76. The method of claim 72 wherein said encapsulating material is a co-polymer of styrene or methyl methacrylate with t-butyl amino ethyl methacrylate. 77. The method of claim 72 wherein said co-polymer is 55 to 80 weight % styrene, methyl styrene or methyl methacrylate with 20 to 45 weight % t-butylamino-ethyl methacrylate. 78. The method of claim 1 wherein said substrate-degrading agent inactivated by encapsulation is prepared prior to containment in said fluid, solid or mixture thereof. 79. The method of claim 34 wherein said substrate-degrading agent inactivate by encapsulation is prepared prior to containment in said fluid. 80. The method of claim 39 wherein said substrate-degrading agent inactivated by encapsulation is prepared prior to containment in said fluid, solid or mixture thereof. 81. The method of claim 52 comprising combining said encapsulated breaking agent and said polymeric viscosifier or fluid loss control agent in a drilling fluid.