NO20120356A1 - Radiation-induced thickening of sealants for controlled solidification and methods of using the same - Google Patents

Abstract

The present invention includes methods related to solidification of fluids or slurries in a wellbore. An embodiment is related to a method of isolating a portion of a wellbore by preparing a sealing composition comprising a fluid component and a polymer additive. The sealing mixture is placed in a wellbore and exposed to ionizing radiation. The ionizing radiation can cause bonding between the polymer additive and form a polymer matrix in the sealant which increases the mechanical strength of the sealant. The invention also includes compositions related to solidification of fluids or slurries in a wellbore. In one embodiment, the sealing composition has a fluid component and a polymer additive which can be exposed to ionizing radiation. r-H3t. ^

Description

Radiation-induced thickening of sealing compounds for controlled solidification and procedures for using the same.

[0001] The present invention is generally related to test drilling for hydrocarbons and production operations for the same, more specifically mixtures and methods that allow greater control over thickening of fluids or slurry, such as cement during and after underground cementing operations.

Background

[0002] Natural resources such as oil and gas located in an underground formation can be extracted by drilling a well down to the underground formation, typically while circulating drilling fluid in the wellbore. After the wellbore has been drilled, a pipe string, for example casing, is driven into the wellbore. The drilling fluid is then usually circulated downward through the interior of the pipe and upward through the annulus between the outside of the pipe and the walls of the wellbore, although other methodologies are known in the art.

[0003] Fluids and slurries such as hydraulic cement mixtures are in ordinary use in drilling, completion and repair of oil and gas wells. For example, hydraulic cement mixtures are used in primary cementing operations whereby strings of pipe such as casing or extension pipe are cemented into wellbores. When carrying out primary cementing, a hydraulic cement mixture is pumped into the annulus between the walls of a wellbore and the external surfaces of a pipe string are placed in the same. The cement mixture is allowed to solidify in the annulus to thereby form an annular mantle of hardened, substantially impermeable cement. This cement jacket provides physical support for and positions the tubing string relative to the walls of the wellbore and bonds the exterior surfaces of the tubing string to the walls of the wellbore. The cement mantle prevents the unwanted migration of fluids between zones or formations penetrated by the wellbore. Hydraulic cement mixtures are also commonly used to plug lost circulation and other unwanted inflow of fluids in wells, to plug cracks and holes in pipe strings cemented in the same and to perform other required auxiliary operations for the well. After the cement has been placed inside the wellbore, a period of time is required for the cement to harden and achieve sufficient mechanical strength to resume drilling operations. This downtime is often referred to as "waiting-on-cement", or WOC (eng. "waiting-on-cement"). If operations are resumed before the cement achieves sufficient mechanical strength, the structural integrity of the cement may be compromised.

[0004] Two common pumping methods have been used to place the cement mixture in the annulus. The cement mixture can be pumped down the inner diameter of the casing and up through the annulus to the desired location. This is referred to as a conventional circulation method. Alternatively, the cement mixture can be pumped directly down the annulus to thereby displace well fluids present in the annulus by pushing them up and into the inner diameter of the casing. This is referred to as a reverse circulation method. Cement can also be used inside the wellbore in other ways, such as by placing cement inside the wellbore at a desired location and sinking a string of casing into the cement. The latter method can, for example, be used when circulation of well fluids cannot be carried out due to losses into a formation penetrated by the wellbore.

[0005] When carrying out primary cementing operations as well as preventive cementing operations in well holes, the cement mixtures are often exposed to high temperatures, especially when the cementing is carried out in deep underground zones. These high temperatures can reduce the thickening time of the cement mixtures, which means that solidification of the cement occurs before the cement is properly pumped into the annulus. Therefore, it has been required to use solidification-retarding additives in the cement mixtures. These additives extend the setting time for the mixtures so that sufficient pumping time is provided for the placement of the cement in the desired positions.

[0006] While a variety of set retarder additives for cement have been developed and used, known additives such as sugar or sugar acids can produce unpredictable results. Hydroxy carboxylic acids, such as tartaric acid, gluconic acid and glucohectonic acid, are in common use in oil well cementing as cement retarders. If an excess of hydroxycarboxylic acid or any other retarder is used, it can over-retard the solidification of the cement slurry and thereby cause it to remain fluid over a longer period of time. This over-retardation can lead to extended waiting time before drilling can be resumed and can allow gas to invade the slurry thereby causing unwanted gas migration. The extended waiting time leads to delays in subsequent drilling or completion activity.

[0007] In a number of cementing operations, salt solutions have been used as an additive in cement mixtures. The salt, mainly sodium chloride, acts as a dispersant in cement slurry and causes the slurry to expand upon solidification, thereby achieving a good bond between the wellbore and the casing upon solidification of the slurry. However, salt-saturated slurries can cause problems with boundary formations and in certain situations can leak out of the cement slurry, which can cause fracture in the cement. Certain salts, such as calcium salts, can also act as accelerators, which reduce the setting time of the cement mixture. The presence of a setting and strength-accelerating agent, such as calcium salt, in the cement mixture increases the risk that the cement mixture may thicken or solidify before placement. Given the complexity of cement chemistry and the large temperature and pressure gradients that can be present in the wellbore and the problems of predicting the exact downhole temperatures during the deployment and solidification of a cement, it can be difficult to regulate the retarder additive and acceleration to achieve the desired solidification behavior. Systems are generally oversized to have very long setting times (or thickening times) to ensure that the mix remains fluid until all cementitious material is in place.

[0008] There is therefore a need for improved methods to regulate solidification, which entails predictable solidification time for fluid and slurry in underground environments that prevail in wells. There is a particular desire to develop procedures for rapid solidification of such fluids, such as cement-based systems, whereby the timing of fluid solidification is under the control of engineers in the field.

Summary of the invention

[0009] According to one aspect of the present invention, a method for use in a wellbore has been provided which comprises: deploying a mixture comprising a polymer additive in an underground formation after drilling the wellbore therein; and exposing the mixture to ionizing radiation after deployment in the wellbore.

[0010] In another aspect, a mixture has been provided for use in underground formations, which comprises a polymer additive with the ability to solidify the mixture upon exposure to ionizing radiation.

[0011] In yet another aspect, the invention provides a method of isolating a portion of a wellbore comprising: deploying a sealing compound comprising a polymer additive in an underground formation after drilling the wellbore therein; and exposing the sealing compound to ionizing radiation.

[0012] In yet another aspect, the invention provides a method for cementing a wellbore comprising: deploying a cement mixture comprising a polymer additive in an underground formation after drilling the wellbore therein; and exposing the cement mixture to ionizing radiation after deployment in the wellbore.

[0013] In yet another aspect, the invention provides a wellbore sealing compound comprising: a well treatment fluid; and said polymer additive; whereby the sealing compound is capable of solidifying upon exposure to ionizing radiation.

[0014] In yet another aspect, there is provided a cement mixture for use in an underground formation comprising: hydraulic cement; water; and a polymer additive with the ability to solidify the cement mixture upon exposure to ionizing radiation.

[0015] The present invention is generally related to methods for using well fluids and/or slurry mixtures which allow greater control over the solidification of such mixtures in a wellbore.

[0016] A procedure for isolating part of a wellbore is described here by producing a sealing mixture comprising a fluid component and a polymer additive component, placing the sealing mixture into a wellbore and exposing the sealing mixture to ionizing radiation. The ionizing radiation can cause bonding between the polymer additive components and create a polymer matrix within the sealing compound which increases the mechanical strength of the sealing compound. The ionizing radiation can cause the destruction of at least part of the polymer additive molecules, which results in an increase in the mechanical strength of the sealing mixture.

[0017] The sealing compound may contain chemical retarders which are used to inhibit solidification of the sealing compound and the ionizing radiation may cause the destruction of at least part of the chemical retarders, thereby reducing the fluidity of the sealing compound and increasing the mechanical strength of the sealing compound. The sealing mixture may include one or more components selected from the group consisting of sealants, resins, curable drilling muds, structural fluids ("conformance fluid") and combinations thereof. The polymer additive can be a water-soluble crosslinkable polymer, or a branched polymer. The sealing mixture may also include at least one scintillator material capable of emitting secondary ionizing radiation, or non-ionizing radiation, upon exposure to the ionizing radiation.

[0018] The polymer additive can be a homopolymer, copolymer, terpolymer, hyperbranched or dendritic polymer. In one embodiment, the polymer additive may be selected from polyalkylene oxide, poly(vinyl pyrrolidone), poly(vinyl alcohol), polyacrylamide, polyacrylate, poly(vinyl methyl ether) and combinations thereof.

[0019] Embodiments of the present invention are also generally related to well cementing mixtures and methods, which allow greater control over solidification of cement in a wellbore.

[0020] An embodiment of the present invention is a method for cementing a wellbore which includes producing a cement mixture with a polymer additive, deploying the cement mixture into the wellbore and exposing the deployed cement to ionizing radiation. The ionizing radiation may include cross-linking between the polymer chains, thus forming a polymer matrix anchored to two or more particles to increase the mechanical strength of the composite, sufficient to enable resumption of drilling. The ionizing radiation may include neutron radiation, which may be referred to as ionization induction or indirect ionization. The polymer additive can be a monomer, prepolymer or polymer. In one embodiment, at least a portion of the polymer additive contains at least one functional group that can be bound to the surface of the cement particles and at least a portion of the polymer additive contains at least one functional group that is water soluble and that can form cross-links upon exposure to the ionizing radiation.

[0021] The ionizing radiation can cause the destruction of at least part of the polymer additive molecules, which causes an increase in the mechanical strength of the slurry.

[0022] The slurry can also contain chemical retarders that are used to inhibit solidification of the slurry and the ionizing radiation can cause the destruction of at least part of the chemical retarders, thereby reducing fluidity in the cement phase and promoting the increase in mechanical strength in the slurry.

[0023] The slurry can further include bridge formers capable of reacting with the polymer additive. The bridge formers can be selected from the group comprising ethylene glycol, propylene glycol, diethylene glycol, polyvinylpyrrolidone, polyvinyl alcohol, polyvinyl methyl ether, polyacrylamide, polyols (alcohols containing several hydroxy functional groups), polyacrylates and combinations thereof. The slurry can further include at least one scintillator material capable of emitting secondary ionizing radiation, or non-ionizing radiation, upon exposure to the ionizing radiation.

[0024] A cement mixture comprising cement particles, water and a polymer additive is also described here. At least part of the polymer additive may have at least one functional group which can be bound to the surface of the cement particles and at least part of the polymer additive may have at least one functional group which is water soluble and which can form cross-links upon exposure to ionizing radiation. The polymer additive can be a branched polymer which can include polycarboxyl chains (PCA) which are adsorbed on the surface of the cement particles and polyalkylene oxide chains (PAO) which protrude into the water phase of the cement mixture. The polyalkylene oxide chains may be capable of cross-linking upon exposure to the ionizing radiation to form a polymer matrix within the cement mixture to increase the mechanical strength of the composite prior to normal setting of the cement by hydration. The PAO chains can be polyethylene oxide chains. The cement mixture can additionally include at least one scintillator material capable of emitting secondary ionizing, or non-ionizing, radiation upon exposure to the ionizing radiation.

[0025] There is also described here a procedure for cementing a wellbore which includes the production of a cement mixture containing a branched polymer which has cement anchoring groups and protruding ionizable dispersing groups. The method includes deploying the cement mixture in the wellbore and exposing the deployed cement mixture mixed with the branched polymer to ionizing radiation, whereby the ionizing radiation forms cross-links between the polymer chains. The cement anchoring groups can be polycarboxylic acid chains in the branched polymer which are absorbed on the surface of the cement particles. The ionizable dispersing groups may be polyalkylene oxide chains projecting into the water phase of the cement mixture which can ionize and bond with adjacent ionized polyalkylene oxide chains to form a polymer matrix within the cement mixture to increase the mechanical strength of the composite prior to normal hydration setting of the cement. The cement mixture can also include at least one scintillator material capable of emitting secondary radiation upon exposure to the ionizing radiation.

[0026] There is also described here a procedure for cementing a wellbore which includes deploying a cement mixture that includes monomer, prepolymer or polymer into the wellbore and exposing the deployed cement mixture to ionizing radiation. The ionizing radiation initiates polymerization of the monomers or prepolymers and/or crosslinking between the polymer chains of the ionized cement mixture resulting from the ionizing radiation, whereby the emission of the ionizing radiation is subject to the control of technicians in the field. The cement mixture can additionally include at least one scintillator material capable of emitting secondary radiation upon exposure to the ionizing radiation.

[0027] The present invention is also related to well fluids and/or slurry mixtures which allow greater control over the solidification of such mixtures in a wellbore.

[0028] A sealing mixture comprising a well treatment fluid and a polymer additive component which can be placed in a well hole and subjected to ionizing radiation is described here. The polymer additive can be a polymer which is cross-linked by exposure to the ionizing radiation. The ionizing radiation can cause bonding between the polymer additive components and form a polymer matrix within the sealing compound which increases the mechanical strength of the sealing compound. The ionizing radiation can cause the destruction of at least part of the polymer additive molecules, which results in an increase in the mechanical strength of the sealing mixture.

[0029] One embodiment of the invention is a cement mixture with a polymer additive that can be placed in the well and exposed to the ionizing radiation. The ionizing radiation can induce polymerization of at least part of the polymer additive and form cross-links between the polymer chains, thus forming a polymer matrix anchored to two or more particles to increase the mechanical strength of the composite, sufficient to resume drilling. The ionizing radiation can induce neutron radiation, which can be referred to as ionization induction or indirect ionization. The polymer additive can be a monomer, prepolymer or polymer. In one embodiment, at least part of the polymer additive contains at least one functional group that can be bound to the surface of the cement particles and at least part of the polymer additive contains at least one functional group that is water-soluble and that can form cross-links upon exposure to it ionizing radiation.

[0030] A cement mixture is also described here which contains a branched polymer which has cement-anchoring groups and protruding ionizable dispersing groups. The cement mixture can be placed into the wellbore and exposed to ionizing radiation, whereby the ionizing radiation forms cross-links between the polymer chains. The cement anchoring groups can be polycarboxylic acid chains of the branched polymer which are absorbed on the surface of the cement particles. The ionizable dispersing groups can be polyalkylene oxide chains projecting into the water phase of the cement mixture which can ionize and bond with adjacent polyalkylene oxide chains to form a polymer matrix within the cement mixture to increase the mechanical strength of the composite prior to normal hardening of the cement by hydration. The cement mixture may also contain at least one scintillator material capable of emitting secondary ionizing radiation upon exposure to the ionizing radiation.

[0031] There is also described here a cement mixture which includes monomer, prepolymer or polymer which can be placed into the wellbore and exposed to the ionizing radiation. The ionizing radiation initiates polymerization of the monomers or prepolymers and/or cross-linking between the polymer chains of the ionized cement mixture resulting from the ionizing radiation, whereby the emission of the ionizing radiation is subject to the control of technicians in the field. The cement mixture can also include at least one scintillator material capable of emitting secondary ionizing radiation upon exposure to the ionizing radiation.

[0032] The above has in fairly broad terms provided an overview of the features and technical advantages of the present invention so that the detailed description of the invention can be more easily understood. The features and technical advantages of the present invention will be readily apparent to the person skilled in the art upon study of the detailed description of the embodiments of the invention that follows.

Brief description of the figures

[0033] Figure 1 illustrates a cross-section of a wellbore seen from the side.

[0034] Figure 2 is a diagram with results from a study of radiation doses.

[0035] Figure 3 is a diagram of storage modulus values from a study of radiation doses.

[0036] Figure 4 is a diagram of loss modulus values from a study of radiation doses.

Detailed description

[0037] The present invention is generally related to well operations involving fluids or slurries, and more specifically to fluids or slurries containing polymer or polymer precursors that can be reacted on command to effect thickening of the fluid or slurry. The fluids or slurries referred to herein may be any suitable for well operations, drilling, completion, workover or production operations such as cements, drilling muds, lost circulation fluids, fracturing fluids, conformance fluids, sealants, resins, etc. .

[0038] In embodiments, the fluid or slurry is a cementitious mixture that generally comprises water and a cement component, such as hydraulic cement, which may include calcium, aluminum, silicon, oxygen and/or sulfur, which solidifies and hardens upon reaction with the water.

[0039] With reference to figure 1, an embodiment of a well hole 2 is illustrated in cross-section seen from the side. Surface casing 4 attached to a wellhead 6 is installed in the wellbore 2. Casing 8 hangs from the wellhead 6 to the bottom of the wellbore 2. An annulus 10 is defined between the casing 8 and the wellbore 2. Annular flow line 12 establishes flow-wise contact with the annulus 10 through the wellhead 6 and/or surface casing 4 with an annulus valve 14. Flow line 16 is connected to the wellhead 6 to allow fluid communication with the inner diameter of casing 8 and a casing valve 18. At the lower end of the casing 8 the casing is open to the wellbore 2 or has circulation openings between the annulus 10 and the inner diameter of the casing 8.

[0040] A cement mixture can be pumped down the casing 8 and circulated up the annulus 10 while fluid return is taken from the annulus 10 out of the flow line 12 in a typical circulation direction. Alternatively, the cement mixture can be pumped into the annulus 10 from the annulus flow landing 12 while fluid return is taken from the inner diameter of casing 8 through flow line 16. In this way, fluid flows through the wellbore 2 in a reversed circulation direction.

[0041] In an alternative method, a fluid mixture, such as a cement slurry, can be placed inside the wellbore 2 and a closed or filled pipe, such as casing 8, can be lowered into the wellbore 2 so that the fluid mixture is displaced into the annulus area 10 to thereby place the fluid mixture inside the annulus 10 without pumping the fluid mixture into the annulus 10. The procedure above can be called mud ring cementing ("puddle cementing"). The fluid mixture can be a drilling fluid placed inside the wellbore after drilling operations are complete.

[0042] Any cement suitable for use in underground applications may be suitable for use with the present invention. In certain embodiments, the cement mixtures used in the present invention comprise a hydraulic cement. Examples of hydraulic cements include, but are not limited to, Portland cement (for example, Class A, C, G, and H Portland cement), pozzolan cement, gypsum cement, phosphate cement, high alumina cement, silica cement, high alkalinity cement, and combinations thereof. Cement comprising shale, cement kiln dust or blast furnace slag may also be suitable for use with the present invention. In certain embodiments, the shale may comprise raw shale (for example, unburnt shale) or a mixture of raw shale and vitrified shale.

[0043] The cementitious mixtures used in the present invention generally comprise a base fluid. A wide variety of base fluids may be suitable for use with the present invention including, among other things, a water-based base fluid, a non-aqueous base fluid and mixtures thereof. Where the base fluid is water-based, it may include water which may come from any source provided that the water does not contain any excess of compounds (for example dissolved organic compounds such as tannic acids) which may have a negative effect on other compounds in the cement mixtures. For example, a cement mixture useful with the present invention may comprise fresh water, salt water (for example, water containing one or more salts dissolved therein), salt solution (for example, saturated salt water) or sea water. Where the base fluid is not water-based, the base fluid may comprise any number of organic liquids. Examples of suitable organic liquids include but are not limited to mineral oils, synthetic oils, esters and the like. In certain embodiments of the present invention where primary cementing is performed, a water-based base fluid may be used. The base fluid may be present in an amount sufficient to form a pumpable slurry. In certain embodiments when the base fluid is water, the base fluid may be present in the range of from about 25% by weight to about 150% by weight of the weight of cement ("bwoc"). In certain embodiments where the base fluid is water, the base fluid may be present in the cement mixtures in the range of from about 30% to about 75% bwoc. In other embodiments where the base fluid is water, the base fluid may be present in the cement mixtures in the range of about 40% 3 in I about 60% bwoc. In other embodiments where the base fluid is water, the base fluid may be present in the cement mixtures in the range of from about 35% to about 50% bwoc. The cement mixture may include a sufficient amount of water to form a pumpable cementitious slurry. The water can be fresh water or salt water, for example an unsaturated water-based salt solution or a saturated water-based salt solution such as brine or sea water.

[0044] The cementitious mixtures used in the present invention may additionally comprise a solidification retarder. A wide variety of setting retarders may be suitable for use in the cement compositions used in the present invention. For example, the solidification retarder can include, among other things, phosphonic acid, phosphonic acid derivatives, lignosulfonates, salts, sugars, carbohydrate compounds, organic acids, carboxymethylated hydroxyethylated celluloses, synthetic co- or ter-polymers comprising sulfonate and carboxylic acid groups and/or borate compounds. In certain embodiments, the solidification retarders used in the present invention are phosphonic acid derivatives, such as those described in US Patent 4,676,832. Examples of suitable borate compounds include but are not limited to sodium tetraborate and potassium pentaborate. Examples of suitable organic acids include gluconic acid and tartaric acid. Generally, the setting retarder is present in the cement mixtures used in the present invention in an amount sufficient to delay the setting of the cement mixture in an underground formation for a desired period of time. More specifically, the setting retarder may be present in the cement compositions used in the present invention in an amount ranging from about 0.1% to about 10% bwoc. In certain embodiments, the setting retarder is present in the cement compositions used in the present invention in an amount ranging from about 0.5% to about 4% bwoc. In one embodiment of the present invention, the application of ionizing radiation results in the alteration or destruction of a solidification retarder additive. When the solidification retarder is altered by exposure to the ionizing radiation, the effect of the solidification retarder on the slurry is reduced and the slurry may solidify earlier than it would in the absence of the ionizing radiation.

[0045] The solidification retarders of the present invention may include a sensitizer-containing retarder, such as a boron-containing retarder. The sensitizer can be made of a material with a strong ability to absorb radiation. The sensitizer can also be a scintillator material. The sensitizer can be any material which increases the material's ability to capture ionizing radiation in the slurry. The sensitizer-containing retarder, also referred to as a sensitized retarder, may be a boron-containing retarder, also referred to as a boronated retarder, may include a wide variety of solidification retarders including the solidification retarders described herein, wherein the selected solidification retarder, or combination of solidification retarders, in additionally includes at least one boron atom. As discussed in the section immediately preceding, sugars and/or carbohydrates may be used as a retarder in setting a cement mixture. In one embodiment, the retarder is a sensitized sugar or carbohydrate. In a more specific embodiment, the sensitized retarder is boronated glucose. In an even more specific embodiment, the boronated glucose is represented by 3-O-(o-carboranyl-1-ylmethyl)-D-glucose, as presented in US Patent 5,466,679 (Soloway et al).

[0046] The cementitious mixtures used in the present invention may optionally also comprise a fluid loss regulating agent. A variety of fluid sap control agents may be suitable for use with the present invention, including but not limited to fibers, flakes, particles, modified sugars, latexes and acrylamide-methyl-sulfonic acid copolymers such as those described in US Patent 4,015,991; 4,515,635; 4,555,269; 4,676,317; 4,703,801; 5,339,903 and 6,268,406. Generally, the fluid loss control additive is present in the cement mixtures used with the present invention in an amount sufficient to provide a desired degree of fluid loss control. More specifically, the fluid loss control additive may be present in the cement mixtures used in the present invention in an amount ranging from about 0.1% to about 10% bwoc. In certain embodiments, the fluid loss control additive is present in the cement compositions used in the present invention in an amount ranging from about 0.2% to about 3% bwoc.

[0047] Optionally, the cementitious mixtures used in the present invention

also include a modifier for mechanical properties. Examples of suitable modifiers for mechanical properties may include gases that are added at the surface (for example, nitrogen), gas-generating additives that can generate a gas in place at a desired time (for example, aluminum powder or azodicarbonamide), hollow microspheres, elastomers ( for example, elastic particles comprising a styrene/divinylbenzene copolymer), materials with a large length/width ratio (including but not limited to fiber), elastic graphite-containing materials, vapor/fluid-filled spheres, matrix-sorbable materials with time-dependent sorption (initiated by for example degradation), mixtures of these (for example mixtures of microspheres and gases), or equivalent. In certain embodiments of the present invention, the optional mechanical property modifier may include a latex.

[0048] In certain optional embodiments where microspheres are added to the cement compositions useful with the present invention, the microspheres may be present in the cement compositions in an amount ranging from about 5% to about 75% bwoc. In certain embodiments of the present invention, the inclusion of microspheres in the cement compositions useful with the present invention can reduce the density of the cement composition.

[0049] In certain optional embodiments where one or more gas-forming additives are used as a modifier for mechanical properties in the cementitious mixtures used in the present invention, said one or more gas-forming additives can include, among other things, aluminum powder that can generate hydrogen gas on site, or the may include azodicarbonamine which may generate nitrogen gas on site. Other gases and/or gas-generating additives may also be suitable for inclusion in the cementitious mixtures used in the present invention. When included, a gas-generating additive may be present in the cement compositions used in the present invention in an amount ranging from about 0.1% to about 5% bwoc. In certain embodiments where the gas-generating additive is aluminum powder, the aluminum powder may be present in the cement compositions used in the present invention in an amount from about 0.1% to about 1% bwoc. In certain embodiments where the gas-generating additive is an azodicarbonamine, azodicarbonamide may be present in the cement compositions used in the present invention in an amount ranging from about 0.5% to about 5% bwoc.

[0050] The cementitious mixtures used in the present invention may optionally also include additional suitable additives including antifoam agents, dispersants, density-reducing additives, surfactants, weight materials, viscosity-regulating agents, fly ash, silica, agents for regulating free water and the like. Any suitable additive may be incorporated into the cement compositions used in the present invention.

[0051] In one embodiment of the present invention, the fluid or slurry includes a monomer additive. The monomer additive can be a synthetic or natural monomer. Examples of synthetic monomers include hydrocarbons such as ethylene, propylene or styrene monomers. Other synthetic monomers that can be used include the acrylic monomers such as acrylic acid, methyl methacrylate and acrylamide. In one embodiment, the monomer additive is present in amounts from about 0.01% to about 10.0% bwoc, optionally from about 0.05% to about 7.5% bwoc, optionally from about 0.25% to about 2.5% .

[0052] In one embodiment, the fluid or slurry includes a crosslinkable prepolymer additive. The prepolymer additive can be a polymer intermediate or a reactive low molecular weight macromolecule or an oligomer capable of being cross-linked by further polymerisation. An example of a prepolymer is polyurethane prepolymer which is commercially available and well known in the art. Prepolymers can include crosslinkable functional groups attached to an element or compound, such as a crosslinkable prepolymer functional group attached to a polymeric material. In one embodiment, the prepolymer additive is present in amounts from about 0.01% 5 to about 10.0% bwoc, optionally from about 0.05% to about 7.5% bwoc, optionally from about 0.25% to about 2.5 % bwoc.

[0053] In one embodiment, the fluid or slurry includes a polymer additive. Examples of the polymer additive include a monomer, prepolymer or polymer. The polymer additive can be a homopolymer, copolymer, terpolymer, hyperbranched or dendritic polymer. In embodiments, the polymer additive may be selected from polyalkylene oxide, poly(vinyl pyrrolidone), poly(vinyl alcohol), polyacrylamide, polyacrylate, poly(vinyl methyl ether) and combinations thereof.

[0054] The polymer additive can contain at least one functional group which can be bound to the surface of the cement particles and at least one functional group which is water-soluble and which can form cross-links upon exposure to the ionizing radiation. The polymer additive may be a comb polymer. In one embodiment, the polymer additive is present in amounts from about 0.01% to about 10.0% bwoc, optionally from about 0.05% to about 7.5%, optionally from about 0.25% to about 2.5% bwoc .

[0055] In one embodiment, the polymer additive is a polycarboxylate polymer-based superplasticizer (PCS). Superplasticizers can be useful to reduce the amount of water required to liquefy a cement mixture and/or to impart thixotropic properties. PCS may include one or more polymers, copolymers, terpolymers and polymer additive solutions thereof. In one embodiment, PCS is a comb polymer. The comb polymer may have a polycarboxylic acid backbone and side chains of polyalkylene oxide (PAO) chains. Polycarboxylic acid chains, when added to a slurry, can be absorbed on a cement particle surface, while the hydrophilic PAO chains protrude into the water phase. While the polycarboxylic acid chain is absorbed on the cement surface, they are anchored to the cement surface and can resist dissociation forces. The PAO chains can thus be ionized, such as by application of ionizing radiation and can react with ionized PAO chains projecting into the water phase from an adjacent PCS polymer attached to an adjacent cement particle. The ionized PAO chains can be bonded with other ionized PAO chains forming a polymer network structure throughout the cement slurry. The polymer network structure can impart firmness to the cement slurry prior to solidification of the cement slurry through the normal solidification process by hydration.

[0056] In one embodiment, the polymer additive is a polycarboxylate comb polymer-based superplasticizer with a polymer chain that serves as an anchoring group and has appendages in the form of non-ionized dispersing groups. The amount of ionized particle-anchoring groups and non-ionized dispersing groups and their mutual relationship is not limited within the present invention. In one embodiment, the ratio of ionized particle anchoring groups ranges from about 1:100 to about 100:1 with respect to the non-ionized dispersing groups. Alternatively, the ratio of anchoring groups for the ionized particles is about 1:50 to about 50:1, optionally about 1:1 to about 25:1 with respect to the non-ionized dispersing groups. The anchoring groups for the ionized particles may be absorbed on a particle surface while the non-ionized dispersing groups protrude into the water phase. The non-ionized dispersing groups can then be ionized, such as by application of the ionizing radiation, and can react with each other to form a polymer network structure throughout the slurry that thickens the slurry. The polycarboxylate polymer molecules are further available with a range of lengths of pendant polyalkylene oxide groups, where the selection of the correct ratio can regulate both retention of processability and speed of cross-linking upon exposure to the ionizing radiation. Polycarboxylate polymer-based superplasticizers (PCS) suitable for use in the present invention are commercially available from companies such as BASF and W.R. Grace, Sika, Nippon Shokubai, Kao Soap, Nippon Oil and Fats and others.

[0057] In one embodiment, the polymer additive is a polymer selected from a group comprising polyalkylene oxide (PAO), polyvinyl pyrrolidone (PVP), polyvinyl alcohol (PVA), polyvinyl methyl ether (PVME), polyacrylamide (PAAm). The polymer chains may be dispersed in the water phase of the fluid or slurry and may be ionized, such as by application of the ionizing radiation, to react with adjacent ionized polymer chains. The interlinking of adjacent ionized polymer chains forms a polymer network structure throughout the fluid that imparts thickening to the water phase. The polymer network structure can impart thickening to the cement slurry prior to solidification of the cement slurry through the normal hydrating solidification process. In alternative embodiments, the polymer network structure may impart thickening to other fluids such as a malleable fluid used to seal a water-bearing zone or to a solidifiable drilling fluid. The polymer additive can be a water-soluble polymer which can be cross-linked by exposure to the ionizing radiation. The polymer additive can also be a comb polymer with at least two functional groups, one which can be anchored, such as to a cement grain, and another which can be cross-linked by exposure to the ionizing radiation.

[0058] In one embodiment of the present invention, application of the ionizing radiation leads to a change or destruction of the polymer additive. While the polymer additive changes upon exposure to the ionizing radiation, the resulting altered polymer additive can result in a thickening of the slurry. In embodiments, the slurry may solidify faster than it would in the absence of the ionizing radiation.

[0059] The fluid or slurry mixtures used in the present invention may additionally include a scintillator material. The scintillator material can serve to increase the capture effect of the ionizing radiation and/or emit radiation upon exposure to the ionizing radiation. A scintillator material with fluorescence properties can emit radiation, which can be termed secondary radiation, as a result of absorption of radiation from another source. For example, a scintillator material can emit gamma radiation, X-ray radiation or UV radiation when exposed to neutrons or gamma rays. This secondary radiation can be used to impart radiation to promote the degradation of polymers and/or the release of accelerator into the fluid or slurry. If the secondary radiation includes photons or particles with the same wavelength as the absorbed radiation, it can be described as resonant radiation.

[0060] There are a number of known neutron scintillators, a non-limiting list includes LiF/ZnS:Ag, Li-glass and LihEu. LiF/ZnS:Ag has been shown to produce a very large neutron multiplier factor and has been measured at 160,000 photons per neutron absorbed where the bulk of the radiation occurs below about 450 nm. Li-glass typically has an emission maximum below approximately 400 nm.

[0061] There are a number of known gamma scintillators, and a non-limiting list includes Nal:TI+, Bi4Ge3Oi2(GSO), Gd2SiO5:Ce3+, ZnS:Ag. Alkali halides include Csl and Nal. Typical emission spectra observed for some scintillators are: Csl - about 300 nm; BaF2 - about 190 to about 305 nm; CaF2:Eu - about 410 nm; GSO:Ce - about 420 nm; YAI:CaTi03:Ce - about 350 nm.

[0062] The scintillator can be used in the form of a powder or crystal or with a coating such as a polymer. Advantages of including scintillators in the fluid or slurry herein

the invention can include local formation of secondary radiation which can minimize the impact from the well casing or other environmental impacts. Potentially large multiplier factors can occur, for example some scintillators will emit more than 10,000 photons for each ionizing radiation particle/photon absorbed. The photons produced by scintillators can be in X-ray and UV spectral regions that can be largely absorbed by the polymer component of the slurry. Since these photons are generated locally by the scintillation, their emission can increase the efficiency of the polymer shell degradation. More photons above the limit for radical formation from the polymer can increase the rate of either cross-linking or polymer degradation via chain scission or both simultaneously, depending on the polymer chemistry. This process can accelerate the rate of thickening of the cement slurry and promote the setting initiation behavior.

[0063] The scintillator material can be added to the fluid or slurry. The scintillator material may be incorporated into a polymer additive or component.

[0064] The term polymer-based additive or polymer additive as used herein may include one or more polymers or one or more polymer precursors such as a monomer or prepolymer intermediate, or combinations thereof.

[0065] In one embodiment, the polymer additive is added to a cement mixture before water is added to the mixture. In another embodiment, the polymer additive is added to a cement mixture after water has been added to the mixture. In yet another embodiment, the polymer additive is added to water to be added to a cement mixture. In yet another embodiment, the polymer additive is added during the mixing of a cement and water. In another embodiment, different polymer additives are added at any of the separate times as described above during the preparation of the cement mixture.

[0066] In one embodiment, as soon as the cementitious mixture containing the polymer additive has been obtained, the mixture is then placed in the wellbore, such as in an annulus between the wellbore and the casing. When deploying the cement mixture containing the polymer-based component in the wellbore, the cement particles will be in intimate contact with each other and the absorbed polymer chains of adjacent particles will be mixed together.

[0067] According to embodiments of the invention, after the mixed mixture is placed in the wellbore, ionizing radiation is applied. Ionizing radiation contains subatomic particles or electromagnetic waves that are sufficiently energetic to release electrons from atoms or molecules and thereby ionize them. The occurrence of ionization depends on the energy of the penetrating individual particles or electromagnetic waves, which must have energy above the ionization limit (ie photoelectric effect). In one embodiment, the amount of ionizing radiation supplied to the wellbore is determined by the amount of ionizing radiation required to ionize the monomer, prepolymer or polymer chains in the polymer additive. The ionizing radiation can be emitted from or in the form of charged particles.

[0068] In one embodiment, the charged particles include alpha particles, beta particles, or gamma particles, or combinations thereof. In an optional embodiment, the amount of ionizing radiation required to ionize a polymer additive is between about 1 KiloGray to about 500 KiloGray, optionally between about 1 KiloGray to 100 KiloGray, optionally between about 4 KiloGray to about 40 KiloGray. The amount of ionizing radiation emitted is determined by the level of cross-linking desired and the type of polymer added to the cement mixture. The fluid or slurry may also include at least one scintillator material capable of emitting secondary radiation upon exposure to the ionizing radiation. In embodiments, scintillator material is capable of reducing the ionizing radiation required. In one embodiment, the scintillator material is capable of reducing the ionizing radiation required to less than half of that required without the scintillator material.

[0069] In one embodiment, the ionizing radiation is supplied by an emitter of ionizing radiation located at a point inside the well. In another embodiment, an ionizing radiation emitter located at the surface supplies ionizing radiation directed down into the well. In another embodiment, a radiation source is lowered into the well, such as on a cable, and the ionizing radiation is emitted. The radiation source may be shielded so as not to emit radiation other than when the shielding is removed. For example, a radiation source can be shielded at the surface when personnel could otherwise be exposed. As soon as the radiation source is placed in the well and the ionizing radiation can be safely started, the shielding can be removed or opened, such as by an electronically activated signal transmitted from the surface down the wire to the shielding. In one embodiment, the radiation emitter may emit ionizing radiation while being lowered down the well and while being pulled up the length of the well. In yet another embodiment, two or more radiation emitters are lowered separately to two or more depths, so that two or more depths of the wellbore can be exposed to the ionizing radiation at the same time.

[0070] In one embodiment, ionizing radiation is applied under the control of a technician in the field. The technician, engineer, or other personnel in the field can control the release of ionizing radiation by providing a signal that causes a release of ionizing radiation from an emitter. In this embodiment, the ionizing radiation is released at the command of the technician in the field. The ionizing radiation can be released from a control system with parameters such as timers, flow meters, temperature sensors or the like. In another embodiment, the lowering and/or release of the ionizing radiation source is initiated by a timer mechanism. In yet another embodiment, the lowering and/or release of the ionizing radiation source is initiated by a flow meter which detects the amount of mixture delivered into the well.

[0071] Upon application of the ionizing radiation, a network of cross-links can be formed between the polymer chains. This can result from the ionizing radiation on the polymer chain and from the effects of ionizing radiation on other compounds present such as water and solvents. Radiation, such as alpha radiation, can also initiate the splitting of molecules, which can be termed radiolysis. In one embodiment, the radiolysis of water can generate hydroxide radicals, which can extract hydrogen from the polymer chains and thereby form a polymer radical. The polymer radicals can combine through intermolecular and/or intramolecular cross-linking and produce a gel state. The radiolysis of other compounds such as solvents (solvent radiolysis) can generate intermediates that can also react with the polymer chain. Such a network of cross-links increases the mechanical strength of the mixture, for example a cement composite, before the typical cement hardening by hydration.

[0072] The modification of mechanical strength in the fluid, slurry or composite depends on the level of cross-linking. Cross-linking at low density can increase the mixture's viscosity to a rubber-like consistency and cross-linking at high density can cause the mixture to set. In one embodiment, the ionizing radiation is introduced so that a low cross-linking is achieved followed by another introduction of the ionizing radiation so that finally a greater degree of cross-linking is achieved. The increase in the mechanical strength of a cement composite prior to the typical cement hardening by hydration may allow activities to be resumed at an earlier time compared to having to wait for the cement to set by hydration.

[0073] The fluid or slurry mixtures used in the present invention may additionally include a scintillator material. The scintillator material can serve to increase the ability to capture the ionizing radiation and/or emit radiation upon exposure to ionizing radiation.

[0074] In an embodiment where the polymer is a polycarboxylate-based superplasticizer, the ionizing radiation can be used to cross-link adjacent polymer chains in the water phase. In this embodiment, particles are separated by the steric hindrance caused by anchored polymer chains, which means that very few cross-links are required to form a continuous cross-linked network resulting in increased strength. This effect can be further enhanced by adding agents in the water phase that can increase the density of potential reactants in the presence of the particles and improve the kinetics of the radiation-promoted solidification process of the present invention without affecting the properties of the fluid, slurry or composite, such as a cement mixture , in another way.

[0075] The ionizing radiation of the present invention can destroy molecules in addition to causing cross-linking. For example, the destruction of polymer chains and the chemical retarders used to inhibit solidification also serve to reduce the fluidity of the cement phase and in this way promote the increase of the mechanical strength in the process. Rather than being problematic, this result of the invention may serve to improve the performance of "solidification on command" according to the present invention.

[0076] In one embodiment, the cementitious mixtures described here may also contain a water-soluble cross-linking agent to promote the reaction between two polymer chains. In one embodiment, the water-soluble crosslinking agent is a low molecular weight compound with good mobility in the water phase and high reactivity against the free radicals formed by the ionizing radiation of the polymer additive. In one embodiment, the water-soluble cross-linker is a water-soluble polymer. In another embodiment, the water-soluble crosslinker is a high molecular weight water-soluble polysaccharide. In one embodiment, the water-soluble crosslinker is selected from the group consisting of ethylene glycol, diethylene glycol, propylene glycol, polyalkylene oxides such as polyethylene oxide, polyvinyl alcohol and polycarboxylic acids such as polyacrylic acid, citric acid, butanetetracarboxylic acid and the like.

[0077] As mentioned above, the ionizing radiation according to the present invention can be under the control of technicians in the field. In one embodiment, the ionizing radiation may induce an initial increase in mechanical strength in the cement mixture prior to hardening of the cement by hydration. Therefore, the increase in mechanical strength of the concrete mixture according to the invention under the control of technicians in the field. Such control can lead to a reduction in the time required to wait for cement (WOC) during drilling and completion of a wellbore. In one embodiment, the WOC time for the cement mixture according to the invention that contains a polymer additive reactive to ionizing radiation is shorter than the WOC time for a substantially similar cement mixture that does not contain the polymer additive. In embodiments, the cement compositions of the invention reduce the WOC time by at least one hour, at least two hours, at least five hours, or at least 10 hours compared to a substantially similar cement composition that does not contain the polymer additive.

Examples

[0078] Example 1

[0079] Cement class H was mixed in an amount of 800 grams with 320 ml of water (to give a ratio of water to cement, w/c, of 0.40) and 0.5% bowc of a 900,000 MW PEO (polyethylene oxide) to form a slurry. The slurry also contained 0.50% bowc maltodextrin, a setting retarder for cement. The slurry was mixed for 45 seconds in a Waring blade mixer at high shear. The slurry was divided into two samples. One sample was exposed to 4.3 Mrad of gamma radiation from a Co-60 source while the other was kept as a control. The control sample, which was not irradiated, was still fluid (yield strength at 3.5 Pa) while the gamma irradiated sample was cross-linked and completely solid.

[0080] Example 2

[0081] Several slurries were made using a cement class H, water (to give a ratio of water to cement, w/c, of 0.40) with two different PEOs (100,000 MW and 900,000 MW) . Other components in the slurries were a polycarboxylate ether (dispersant), Diutane gum (viscosity modifier) and maltodextrin (retarder). The compositions of the mixture are shown in table 1.

[0083] All slurries were exposed to 4.3 Mrad of gamma radiation from a Co-60 source and were found to crosslink and gel upon exposure to gamma radiation while non-irradiated controls were still fluid. The yield strength of the controls was determined using a FANN 35 viscometer and is shown in Table 2. No such measurements were possible for the gelled samples.

[0085] Example 3

[0086] Cement class H in an amount of 800 grams was mixed with 320 ml of water (w/c=0.40) and 0.5% bowc of a 360,000 MW poly(vinylpyrrolidone) to form a slurry. The slurry also contained 0.50% bwoc maltodextrin, a cement retarder. The slurry was bladed for 45 seconds in a Waring high shear blade mixer. The slurry was divided into two samples. One sample was exposed to 4.3 Mrad of gamma radiation from a Co-60 source while the other was kept as a control. The non-irradiated control sample was still fluid with a yield point measured at 150 Pa while the gamma-irradiated sample had cross-linked and was completely solid.

[0087] Example 4

[0088] Cement class H was mixed in an amount of 800 grams with 320 ml of water (w/c=0.40) and 0.5% bowc of a 900,000 MW PEO (polyethylene oxide) to form a slurry. The slurry also contained 0.50% bwoc maltodextrin, a cement retarder. The slurry was mixed for 45 seconds in a high shear Waring blade mixer. The slurries were exposed to 0.4-2.5 Mrad of gamma radiation. All the gamma-irradiated samples resulted in gelation of the samples while the control samples remained fluid with a yield strength of 36 Pa.

[0089] Figure 2 illustrates the results of the dose/response study in PEO with varying exposure to radiation. Figures 3 and 4 illustrate the results from the dose/response study in PEO with varying exposure to radiation and the resulting effect on storage modulus and loss modulus. The modulus values increased with the radiation dose.

[0090] Example 5

[0091] Aqueous solutions of PEO and polycarboxylates were irradiated with 4.3 Mrad gamma radiation. The observations were as shown in table 3.

[0093] The fluid or slurry mixture used in the present invention may additionally include a sensitizer material. The sensitizer can be made of a material with a strong ability to absorb radiation. The sensitizer can also be a scintillator material. The sensitizer can be any material which increases the ability to capture the ionizing radiation in the slurry.

[0094] Various elements can be used as a sensitizer. In general, elements with a larger absorption cross-section than the wellbore treatment fluid mixture can be used to increase the trapping effect of the ionizing radiation in the mixture. Many well treatment fluids may include calcium, which has an absorption cross section for 2200 m/s neutrons of approximately 0.43 ren. A non-limiting listing of elements with an absorption cross-section of 2200 m/s neutrons of 10 children or more is shown below in Table 4. A child is defined as IO"<28>m<2>, and is roughly equivalent to the cross-sectional area of a uranium nucleus .

[0096] The term "comb polymer" as used herein refers to those polymers which have a backbone and linear side chains as pendant groups.

[0097] The term "polycarboxylate-based comb superplasticizers" refers to the cement dispersants and copolymers which have a polycarboxylate chain and polyalkylene oxide groups hanging from the same, such as polyethylene oxide, polypropylene oxide, etc. and mixtures thereof. Polymers of these general types can be produced in any suitable manner such as by copolymerization of unsaturated (alkoxy)polyalkylene glycol-mono(meth)acrylic acid or ester type monomers with (meth)acrylic acid type monomers as described in US Patent 6,139,623.

[0098] The term "cementitious mixture" as used herein includes pastes (or slurries), mortars and slurries, such as an oil well cementing slurry, shotcrete and concrete mixtures comprising a hydraulic cement binder. The terms "paste", "mortar" and "concrete" are terms from the field: pastes are mixtures made of a hydratable (or hydraulic) cement binder (usually but not exclusively Portland cement, Masonry cement, Mortar cement and/or gypsum, and may also include limestone, hydrated limestone, fly ash, granulated burnt furnace slag and silica fume or other materials commonly included in such cements) and water; "Mortar" is paste that also includes fine aggregate (for example, sand), and "concrete" is mortar that also includes coarse aggregate (for example, crushed stone or gravel). The cement mixtures described in this invention are formed by mixing required amounts of certain materials, for example a hydraulic cement, water and fine and/or coarse aggregate, which may be required to make a specific cementitious mixture.

[0099] The term "ionizing radiation" as used herein may refer to ionization-inducing or indirect ionization, which is capable of releasing electrons from atoms or molecules, and may include alpha radiation, beta radiation, gamma radiation, proton radiation, neutron radiation, UV and X-ray radiation .

[0100] The term "polymer additive" as used herein may include one or more of: a polymer or polymer precursor, such as a monomer or a prepolymer intermediate, which is exposed to ionizing radiation.

[0101] The term "solidifying" as used herein refers to an increase in mechanical strength in a fluid or slurry sufficient to effect a desired result, such as restricting movement of an object or preventing fluid flow or pressure transfer through a fluid . A cement can be said to be set when it can restrict the movement of a pipe, or prevent fluid flow or pressure transfer, regardless of whether the cement has hardened to a completely solid mixture or not. A fluid or slurry can be said to be solidified when it has thickened to a sufficient level so that it achieves the desired result, such as isolating a specific zone or limiting fluid flow or pressure transfer, regardless of whether it has reached its final consistency.

[0102] Depending on the context, all references to the "invention" herein may in some cases refer only to certain specific embodiments. In other cases, reference may be made to subjects reproduced in one or more of the requirements, but not necessarily all. While the above is directed to embodiments, versions and examples of the present invention, which are included to enable a person of ordinary skill in the art to practice the invention when the information in this document is combined with available information and technology, the invention is not limited to only these specific embodiments, versions and examples. Other and further embodiments, versions and examples of the invention can be provided without deviating from the basic idea thereof and the scope is determined by the subsequent patent claims.

[0103] While compositions and methods are described as "comprising", "containing" or "including" various components or steps, the compositions and methods may also "consist essentially of" or "consist of" the various components and steps. All numbers and intervals described above may vary to a certain extent. When a numerical interval with lower and upper bounds is described, any number and any included interval is considered to lie within the interval specifically described. In particular, any interval of values (in the form "from about a to about b" or equivalently "from about a to b", "from about a-b") described here shall be interpreted as illustrating any number and interval that falls within the wider interval of values. Designations in the requirements also have their clear and ordinary meaning, unless otherwise expressly and clearly stated.

Claims (57)

1. Method for use in a wellbore comprises: deploying a mixture comprising a polymer additive in an underground formation after drilling the wellbore, and exposing the mixture to ionizing radiation after placement in the wellbore. 2. Method according to claim 1, whereby the method comprises a cementing method and that the mixture comprises a cement mixture. 3. Method according to claim 1, whereby the method comprises a method of isolating a part of a wellbore and that the mixture comprises a sealing mixture. 4. Method according to one of claims 1 to 3, whereby the step of exposing the mixture to ionizing radiation initiates thickening of the mixture. 5. Method according to claim 3 or 4, comprises: production of a sealing mixture comprising the polymer additive, whereby the step of exposing the sealing mixture to the ionizing radiation changes the polymer additive. 6. Method according to one of claims 1 to 5, whereby the sealing mixture contains at least one sensitivity material to increase the sealing mixture's ability to capture the ionizing radiation. 7. Method according to one of claims 3 to 6, whereby the step of exposing the sealing mixture to the ionizing radiation enables the polymer additive to react with compounds in the sealing mixture. 8. Method according to one of claims 3 to 7, whereby the ionizing radiation causes bonding between the polymer additive and forms a polymer matrix in the sealing mixture. 9. Method according to one of claims 3 to 8, whereby the sealing mixture comprises a chemical retarder which is used to inhibit solidification of the sealing mixture and the ionizing radiation causes destruction of at least part of the chemical retarder to thereby increase the mechanical strength of the sealing mixture. 10. Method according to one of claims 3 to 9, whereby the sealing mixture comprises one or more components selected from the group consisting of a resin, a cement, a solidifiable drilling mud, a loss circulation fluid, a forming fluid and combinations thereof. 11. Method according to one of claims 1 to 10, whereby the polymer additive is a homopolymer, a copolymer, a terpolymer, a hyperbranched or dendritic polymer. 12. Method according to one of claims 1 to 11, whereby the polymer additive is a comb polymer. 13. Method according to claim 12, whereby the comb polymer contains two or more connected polyalkylene oxide groups with varying chain lengths, with a ratio between mutual chain lengths of at least 1.3. 14. Method according to one of claims 1 to 13, whereby the polymer additive is a water-soluble crosslinkable polymer selected from the group consisting of poly(alkenoxd), poly(vinyl pyrrolidone), poly(vinyl alcohol), polyacrylamide, poly(vinyl methyl ether) and combinations thereof. 15. Method according to one of claims 1 to 14, whereby the ionizing radiation is selected from the group consisting of alpha radiation, beta radiation, gamma radiation, neutron radiation, proton radiation, UV radiation, X-ray radiation and combinations thereof. 16. Method according to one of claims 3 to 15, whereby the sealing mixture additionally comprises at least one scintillator material capable of emitting secondary radiation upon exposure to the ionizing radiation. 17. Method according to claim 16, whereby the scintillator material is selected from the group consisting of LiF/ZnS:Ag, Li-glass, Lil:Eu, Nal:TI<+>, Bi4Ge3012(GSO), Gd2Si05:Ce<3+>, ZnS :Ag, Csl, Nal; BaF2, CaF2:Eu, GSO:Ce, YAI:CaTi03;Ce and combinations thereof. 18. Method according to claim 2, or one of claims 11 to 15, whereby the polymer additive contains at least one functional group that can be bound to the surface of the cement particles, and a second functional group that is water-soluble and can form cross-links upon exposure to the ionizing radiation . 19. Method according to one of claims 1 to 18, whereby the polymer additive is a comb polymer with cement anchoring groups and attached ionizable dispersible groups. 20. Method according to claim 19, whereby the comb polymer contains two or more connected polyalkylene oxide groups with varying chain length, with a ratio between mutual chain lengths of at least 1.3. 21. Method according to one of claims 1 to 20, whereby the polymer additive is a polycarboxylate-based superplasticizer comprising a stem of polycarboxylic acid and polyalkylene oxide chains attached to the polycarboxylic acid stem. 22. Method according to one of claims 1 to 21, whereby the polymer additive is selected from a group consisting of polyalkylene oxide, poly(vinyl pyrrolidone), poly(vinyl alcohol), polyacrylamide, poly(vinyl methyl ether), polyacrylate and combinations thereof. 23. Method according to claim 2 or one of claims 11 to 15 or 18 to 22, whereby the ionizing radiation causes a polymer matrix to form in the cement mixture which increases the mechanical strength of the cement mixture. 24. Method according to claim 2 or one of claims 11 to 15 or 18 to 23, whereby the ionizing radiation causes the destruction of at least part of the polymer additive, which results in an increase in the mechanical strength of the cement mixture. 25. Method according to claim 2 or one of claims 11 to 15 or 18 to 24, whereby the cement mixture comprises a chemical retarder which is used to inhibit solidification of the slurry and the ionizing radiation causes destruction of at least part of the chemical retarder. 26. Method according to claim 2 or one of claims 11 to 15 or 18 to 25, whereby the amount of polymer additive is in an amount in the range from approximately 0.01% to approximately 25% of the weight of the cement mixture. 27. Method according to claim 2 or one of claims 11 to 15 or 18 to 26, whereby the cement mixture comprises a sensitivity material to increase the ability of the cement mixture to capture ionizing radiation. 28. Method according to claim 27, whereby the sensitivity material is a boronated retarder. 29. Method according to one of claims 1 to 28, whereby it additionally comprises locating an emitter in the wellbore and releasing the ionizing radiation from the emitter. 30. Method according to one of claims 1 to 29, in that a bridging agent is added to react with the polymer additive. 31. Method according to claim 30, whereby the bridging agent is a water-soluble polymer or polymer precursor with the ability to ionize upon exposure to the ionizing radiation to form a polymer radical. 32. Method according to claim 30, whereby the bridging agent is selected from the group consisting of ethylene glycol, propylene glycol, diethylene glycol, polyalkylene oxide and polyols (alcohols containing several functional hydroxy groups) and combinations thereof. 33. Method according to claim 2 or one of claims 11 to 15 or 18 to 32, whereby the cement mixture additionally comprises a scintillator material capable of emitting secondary radiation upon exposure to the ionizing radiation. 34. Method according to claim 33, whereby the scintillator material is selected from the group consisting of LiF/ZnS:Ag, Li-glass, LikEu, Nal:TI<+>, Bi4Ge3Oi2(GSO), Gd2Si05:Ce<3+>, ZnS:Ag , Csl, Nal; BaF2, CaF2:Eu, GSO:Ce, YAI:CaTi03;Ce and combinations thereof. 35. Mixture for use in an underground formation comprises a polymer additive capable of solidifying the mixture upon exposure to ionizing radiation. 36. A mixture according to claim 35, whereby the mixture is a sealing mixture for well holes and comprises a well treatment agent and the polymer additive. 37. Mixture according to claim 35 or 36, whereby the polymer additive is a polymer which crosslinks upon exposure to ionizing radiation. 38. Mixture according to one of claims 35 to 37, whereby the polymer additive is a comb polymer with anchoring groups and ionizable dispersing groups. 39. Mixture according to claim 38, whereby the comb polymer contains two or more attached polyalkylene oxide groups with varying chain length, with a ratio between mutual chain lengths of at least 1.3. 40. Mixture according to one of claims 35 to 39, whereby the polymer additive is selected from a group consisting of polyalkylene oxide, poly(vinyl pyrrolidone), poly(vinyl alcohol), polyacrylamide, poly(vinyl methyl ether) and combinations thereof. 41. Mixture according to one of claims 35 to 40, whereby the polymer additive is a homopolymer, a copolymer, a terpolymer, a hyperbranched or dendritic polymer. 42. Mixture according to claim 41, whereby the polymer additive is selected from a group consisting of polyalkylene oxide, poly(vinyl pyrrolidone), poly(vinyl alcohol), polyacrylamide, polyacrylate, poly(vinyl methyl ether) and combinations thereof. 43. A mixture according to one of claims 36 to 42, whereby the sealing mixture comprises cement and that the polymer additive is present in an amount in the range from about 0.01% to about 25% of the weight of the cement. 44. Mixture according to one of claims 35 to 43, whereby it comprises a bridging agent capable of reacting with the polymer additive. 45. Mixture according to claim 44, whereby the bridging agent is selected from the group consisting of ethylene glycol, propylene glycol, diethylene glycol, polyalkylene oxide and polyols (alcohols containing several functional hydroxy groups) and combinations thereof. 46. Mixture according to one of claims 35 to 45, whereby it comprises a scintillator material capable of emitting secondary radiation upon exposure to the ionizing radiation. 47. Mixture according to claim 46, whereby the scintillator material is selected from the group consisting of LiF/ZnS:Ag, Li-glass, LikEu, Nal:TI<+>, Bi4Ge3Oi2(GSO), Gd2Si05:Ce<3+>, ZnS:Ag , Csl, Nal; BaF2, CaF2:Eu, GSO:Ce, YAI:CaTi03;Ce and combinations thereof. 48. Mixture according to claim 35 or one of claims 37 to 42 or 44 to 47, whereby the mixture is a cement mixture comprising a hydraulic cement, water and the polymer additive. 49. Cement mixture according to claim 48, whereby the polymer additive contains at least one functional group which can be bound to the surface of cement particles, and a second functional group which is water-soluble and which can form cross-links upon exposure to the ionizing radiation. 50. Mixture according to claim 48 or 49, whereby the polymer additive is a comb polymer with cement anchoring groups and attached ionizable dispersing groups. 51. Mixture according to claim 50, whereby the comb polymer contains two or more attached polyalkylene oxide groups with varying chain length, with a ratio between mutual chain lengths of at least 1.3. 52. Mixture according to one of claims 48 to 51, wherein the polymer additive is a polycarboxylate-based superplasticizer. 53. Mixture according to claim 52, whereby the polycarboxylate-based superplasticizer comprises a strain of polycarboxylic acid and polyalkylene oxide chains attached to the polycarboxylic acid strain. 54. Mixture according to one of claims 48 to 53, wherein the polymer additive is present in an amount in the range from about 0.01% to about 25% of the weight of the cement. 55. A mixture according to one of claims 48 to 54, whereby it comprises a chemical retarder used to inhibit solidification of the cement mixture, which is at least partially destroyed by the ionizing radiation. 56. Mixture according to one of claims 48 to 55, whereby it comprises a sensitivity material to increase the ability of the cement mixture to capture the ionizing radiation. 57. Mixture according to claim 56, whereby the sensitivity material is a boronated retarder.