EA042904B1 - METHOD FOR CONTROL OF OIL WELL PERMEABILITY - Google Patents

Description

This invention relates to a method for controlling the permeability of an oil well. The method of this invention is particularly useful for eliminating lost circulation of drilling fluid during drilling of an oil well in rock formation. The method of the present invention may also be applied to control the permeability of an oil well also during the production and abandonment phases of the well, including its possible shut-in.

Oil well drilling by rotary drilling technology is based on rock drilling using a drilling tool (drill bit) that is rotated and simultaneously pressed against the bottom hole rock by a drill string. The drill string contains a tubular element, usually consisting of a series of hollow pipes screwed together in series, usually made of steel and with a circular cross section, suitable for transmitting rotational motion and forming in its interior a casing suitable for fluid flow. During drilling, rock fragments formed by the drill bit (drill cuttings) are brought to the surface by means of a drilling fluid (so-called drilling mud), usually consisting of a water-based or oil-based fluid. The drilling fluid is made circulating from the surface to the bottom of the well through said hollow tubular element. At the bottom of the well, the drilling fluid is discharged from the pipe, which is a conduit for fluid connection to the underground working area, and from which it returns to the surface, passing the drilling cuttings passing through the gap formed by the annulus, limited on one side by the pipe formed by the sequence rods, and on the other side of the wellbore wall or, more commonly, the wellbore casing. The flowing drilling fluid, after removing the rock fragments, is injected again to the bottom of the well. The circulation of the drilling fluid then takes place in a closed hydraulic circuit, which makes it possible to maintain a constant filling of the wellbore.

The drilling fluid, in addition to delivering rock fragments formed by the drill bit back to the surface, performs other functions such as cooling and lubricating the drill bit, preventing unwanted fluids from entering the well and temporarily containing the destruction of the walls of the wells.

When drilling, drilling fluid can leak into the rock, causing a loss in the circulation system (called loss of circulation). Circulation losses are mainly due to the presence of voids (faults or cracks) in the rock or high permeability of the rock. The rock zone where circulation is lost is also referred to as the lost zone, and the term will be used as such throughout this document and in the claims. This usually serves as an obstacle during the drilling phase near the bottom of the well.

Losses of circulation that occur during drilling of a well can create numerous disturbances. For example, a sudden loss of circulation may cause an undesired entry of a layer of fluids into the wellbore, fractures of the wellbore, or accumulation of debris against the flow of the drill string, creating stratification that may interfere with normal operation or may even compromise the safety of the drilling rig as a whole. In certain cases, circulation losses can be of such magnitude as is required to interrupt drilling operations to allow interventions to restore the circulation system, with consequent negative economic impact on the overall activity.

In the known state of the art, these interventions performed to eliminate circulation losses are based primarily on the injection of plugging fluids into the well, capable of changing the permeability of the thief zone. Plugging fluids are typically prepared by adding fibrous materials (eg, hemp, jute, sawdust), flaked materials (eg, mica sheets, shavings), granular materials (eg, crushed walnut shells), or larger lumpy materials to the drilling fluid. , according to the permeability of the rock. Once they are injected into the well, these fluids form plugs in the lost zone that modify the permeability of the rock, restoring the drilling fluid circulation system.

In case of significant circulation losses, in contrast to the plugging fluids mentioned above, it is also possible to use fluids based on cement slurries or polymerizable compounds. Since the bridging material is formed in these fluids by a chemical reaction (slurry curing reaction or polymerization reaction), they are formulated in such a way as to ensure that the above reaction to form the bridging material only starts when the fluid is located in the thief zone and, in particular, when it has completely flowed out of the sucker rod string used to inject it.

Prior art techniques for eliminating circulation losses have several drawbacks.

The blocking action obtained by means of a stopper, for example, is in many cases only temporary. Since the geological nature of the loss zone to be plugged cannot be known with sufficient accuracy, the plug materials used are often not the most suitable for the purpose.

Plugs made with prior art materials are furthermore not always able to withstand the pressures applied by the drilling fluid when drilling activity on the well is resumed.

An additional disadvantage of the prior art relates to the fact that the injection of plugging fluids often requires the drill string to be pulled out of the well, with a subsequent increase in the time required to perform the intervention, and an increase in the corresponding costs.

In the case of plugging fluids based on cement slurries or polymerizable compounds, in addition, the times for resuming drilling operations are often very long (for example, up to 12 hours). plugging the tubular thus formed, thus endangering the safety of the drilling rig, special additives are added to these fluids to delay the onset of curing or polymerization.However, the presence of these additives inevitably increases the time required for the plugging material to be formed in In addition, these fluids have the additional disadvantage of a limited shelf life, albeit partially extended by the presence of the above additives.The limited shelf life provides operators with a relatively short time to complete the injection of the plugging fluid into the rock after it has been prepared.

Additional disadvantages of the plugging technologies of the prior art are the difficulty of positioning the plugging fluid with sufficient accuracy in the loss zone and the possible contamination of the plugging fluid with the drilling fluid present in the well, which can cause it to dilute, consequently reducing its effectiveness.

Already known in the art is the use of two-component polymerizable systems in oil reservoir operations, however mainly by reference to operations for limited subterranean zones, especially to reduce water coning.

In view of the above state of the art, the Applicant has made it his primary goal to provide a method for controlling, and in particular, reducing or inhibiting the fluid permeability of an oil wellbore, thereby overcoming one or more of the drawbacks of the prior art.

Particularly within the scope of the above main objective, it is an object of the present invention to provide a method for controlling the permeability of an oil well that is efficient and quickly implemented to enable rapid restoration of well activity (eg, in relation to drilling, completion, production, or abandonment).

The second object of this invention is to provide a method for controlling the permeability of an oil well, which can be implemented in a safer manner for plant operators than prior art methods.

A further object of the present invention is to provide a method for controlling the permeability of an oil well that is easy to perform and economically feasible.

The Applicant has found that these and other objects, which will be better illustrated in the following description, can be achieved by injecting separately into the oil well the two reactive components of the two-component polymerizable system, so that they come into contact and react only after they have reached the mining zone. wellbore rocks whose permeability is to be modified (thief zones); contact between the two reactants activates the polymerization reaction to form in situ a blocking polymer that serves as a fluid impermeable barrier, such as drilling fluid fluids.

The above technical effect can be obtained by injecting into the well one of the two reactive components inside the tubular element, and the other component into the annulus separated by the wall of the tubular element and the well wall, or possibly by the casing associated with them, if present.

A two-component system is formed by a first fluid component (Fluid A) containing at least one polymerizable compound and by a second fluid component (Fluid B) containing at least one polymerization activator to activate the polymerization of the polymerizable compound injected through the first component.

A particularly advantageous aspect of the present invention is that the activation of the polymerization reaction is easily controlled. The reaction starts only after contact of both components inside the well. This makes it possible to control the initiation time with greater precision, thus reducing the period, often of indeterminate length, needed to form a blocking polymer in the wellbore and speed up the recovery of the well, also avoiding, in many cases, the need for the use of polymerization retarders.

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The formation of a blocking polymer by in situ polymerization of two reactive components injected separately downhole through two separate cavities also makes it possible to avoid the formation of plugging material in the hollow tubing string of the inner tubular or in the annulus and subsequently plugging their cavity if, for any reason , fluid containing polymerizable monomers remains in these cavities longer than expected. This significantly reduces the risk of accidents and damage to surface and downhole equipment.

Injection of the two components of the polymerizable system into the wellbore through separate cavities furthermore allows the blocking polymer to be positioned in a precise manner at the desired location in the rock formation in which the wellbore is drilled.

The method of the present invention, in addition to being applicable to control the fluid permeability of the lost circulation zone of an oil well during drilling operations, can also be advantageously applied during the production or decommissioning stages of the well. Also at these stages, problems including the loss of fluids injected into the well may occur due to the presence of thief zones in the rock, or it may become necessary to plug the well in order to be decommissioned to ensure its safety and stability.

The polymerizable two-component system useful for the purposes of the present invention is also not inherently prone to shelf life issues because the two components only begin to form a blocking polymer when they mutually come into contact downhole. In addition, each of the two reactive components alone has a relatively high stability. The two components can then be prepared and stored separately on the surface in a simpler and safer manner than prior art monocomponent polymerizable compositions.

An additional advantage of this invention is that the polymerizable two-component system can be injected into the well using the tubing string present in it (for example, drill rods) without the use of a specialized sucker rod string, with obvious advantages from an economic point of view and from the point of view of organization of the technical installation.

According to a first aspect, the invention further includes a method for controlling the permeability of an oil well, comprising:

at least one hollow tubular element located inside the above well in a direction parallel to its longitudinal axis, optionally at least one tubular casing string on the wall of the above well, and at least one annular space located between the said tubular element and the wall of the above well or said optional tubular casing, said oil well also contains at least one absorption zone, said method includes the following steps:

I) preparation of a polymerizable two-component system containing at least: fluid A, containing:

(a-i) at least one first olefinically unsaturated polymerizable compound;

(a-ii) optionally, at least one radical polymerization initiator IA for polymerizing said polymerizable compound, said initiator IA being thermally activated or in the presence of an accelerating compound;

fluid B containing a radical polymerization activator, said activator selected from:

(bi) a radical polymerization initiator IB for polymerizing said polymerizable compound, said initiator IB having an activation temperature equal to or lower than said absorption zone temperature, (b-ii) an accelerator of said initiator I _A ;

ii) injecting one of said fluid A and said fluid B into said annulus until said loss zone is reached;

iii) injecting the remainder of said fluid A and said fluid B into said hollow tubular until it comes into contact with fluid injected through said annulus to form a blocking polymer in said thief zone.

According to the invention, said steps (II) and (III) can be carried out, in whole or in part, simultaneously with one another, or independently one after the other, or at a suitable time interval of one relative to the other.

For the purposes of this specification and the appended claims, the verb contain and and terms derived from it also include the verb consist of and consist essentially of, as well as terms derived from them.

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The limits and numerical ranges expressed in this specification and in the appended claims also include the stated numerical value or numerical values. In addition, all values or subranges of a limit or numerical range are to be understood as being specifically included as if they were unambiguously stated.

The term oil well, as used herein and in the claims, refers generally to wells for the extraction of both liquid and gaseous hydrocarbon fluids, including also natural gas. An oil well typically contains a borehole within a subterranean or subterranean rock containing hydrocarbon fluids, and it may be at least partially separated by the same rock (well wall), or preferably by a casing, usually made of steel, able to integrate with the borehole wall, possibly through support with a cement material. In certain cases, there may be multiple concentric casing strings. For the purposes of this description, the innermost casing is considered.

In accordance with the present invention, said at least one thief zone is preferably located near the bottom of the well, i.e. in the zone of the well where the tubular element and the annulus are in fluid communication with each other. In this way, the blocking polymer is created in an optimal position to block the loss of circulation.

As indicated, a two-component system is formed by a first fluid A containing at least a polymerizable compound, and by a second fluid B containing at least one polymerization activator.

The above polymerizable compound is a compound containing at least one ethylenic unsaturation, preferably at least one primary ethylenic unsaturation. Non-limiting classes of polymerizable compounds useful in Fluid A of this invention are acrylates, including methacrylates, cyanoacrylates, acrylonitrile and other substituted acrylates, as well as styrene and substituted styrenes. Acrylic acid and methacrylic acid and the corresponding esters or salts are preferred. Examples of polymerizable compounds useful for the purposes of this invention are: acrylic acid, methacrylic acid, styrene, divinylbenzene, vinyl acetate, acrylamide, acrylates (e.g. methyl methacrylate, ethyl methacrylate, butyl methacrylate, isobutyl methacrylate, 2-ethylhexyl methacrylate, tridecyl acrylate, hexyl acrylate, dodecyl acrylate), polyethylene glycol methacrylates, (e.g. polyethylene glycol methacrylate (PegmaOH, number average molecular weight Mn=500), polyethylene glycol methyl methacrylate (PEGMA, Mn = 200, 300, 400, 600, 1000, 2000), hydroxyalkyl methacrylates (e.g. 2hydroxyethyl methacrylate), diacrylates, chloride solutions [2(methacryloyloxy) ethyl]trimethylammonium (MADQUAT), mono-2-(methacryloyloxy)ethyl succinate (HemaQ), 3-sulfopropyl methacrylate potassium salt (SPMAK) and mixtures thereof.

Preferably, the polymerizable compound is selected from ethyl acrylate, butyl acrylate, hexyl acrylate, methyl methacrylate, ethyl methacrylate, hydroxyethyl acrylate, 2-hydroxyethyl methacrylate, polyethylene glycol methacrylate, and mixtures thereof.

The polymerizable compound may be a monomer, an oligomer, a prepolymer, or a mixture thereof.

Fluid A of the polymerizable system may contain two or more different polymerizable compounds, so as to achieve the formation of a blocking copolymer having the desired properties. As illustrated in more detail below, in some embodiments, the polymerizable compound may be present, at least in part, also in fluid B of the polymerizable two-component system.

For the purposes of this invention, a polymerization activator present in fluid B is an agent capable of initiating the polymerization of a polymerizable compound with which it is in contact when certain thermal or reaction conditions occur, or both.

Depending on the specific composition of fluid A, the polymerization activator present in fluid B may be a radical polymerization initiator that may be activated thermally or by an accelerating agent.

In a first preferred embodiment of the present invention, fluid A contains at least one polymerizable compound and fluid B contains, as an activator, at least one radical polymerization initiator _IB activated thermally to polymerize said polymerizable compound, which has a temperature activation equal to or lower than the temperature of the absorption zone, whose permeability must be controlled. In this first embodiment of the present invention, polymerization activation is initiated by contact between the first fluid A and the second fluid B in the thief zone, following respective injections into the well. Since the activation temperature of the initiator IB is lower than the temperature of the absorption zone, at the moment of contact between two fluids near or within the specified zone, the initiator _IB creates free radicals that promote the polymerization reaction of the polymerizable component contained in fluid A through the formation of a blocking polymer. .

As is well known, the temperature of an oil well varies with its depth. For example, the temperature of the well, and hence the loss zone, can vary from 25°C at the surface to 150°C at a depth of 3000-5000 m.

Preferably, the IB initiator has an activation temperature, as appropriate, in the range of 30 to 150°C.

For the purposes of this specification and the appended claims, the activation temperature of an initiator is the temperature at which the initiator has a half-life of 10 hours (T _1/2 (10I)) in a specified organic solvent, inorganic solvent, or water.

Non-limiting examples of compounds useful as an IB initiator according to this first embodiment of the present invention are diazo compounds such as:

1) 2,2'-azobis[2-(2-imidazolin-2-yl)propane]dihydrochloride (VA-044) - T _1/2 (10 h)=44° C. (solvent = water);

2) 2,2'-azobis[2-(2-imidazolin-2-yl)propane]disulfate dihydrate (VA-046B) - T _1/2 (10 h)=47°C (solvent = water);

3) 2,2'-azobis(2-methylpropionamidine)dihydrochloride (V50) - T _1/2 (10 h)=56° C. (solvent=water);

4) 2,2'-azobis[K-(2-carboxyethyl)-2-methylpropion-amidine]tetrahydrate (VA-057) - T _1/2 (10 h)=57°C (solvent = water);

5) 2,2'-azobis{2-[1-(2-hydroxyethyl)-2-imidazolin-2-yl]propan}dihydrochloride (VA-060) - T _1/2 (10 h)=60°C ( solvent = water);

6) 2,2'-azobis[2-(2-imidazolin-2-yl)propane] (VA-061) - T _1/2 (10 h)=61° C. (solvent=water);

7) 2,2'-azobis(1-imino-1-pyrrolidin-2-ethylpropane) dihydrochloride (VA-067) - T _1/2 (10 h)=67° C. (solvent=water);

8) 2,2'-azobis{2-methyl-K-[1,1-bis(hydroxymethyl)-2-hydroxyethyl]propionamide} (VA080) - T _1/2 (10 h)=80°C (solvent = water);

9) 2,2'-azobis[2-methyl-K-(2-hydroxyethyl)propionamide] (VA086) - T _1/2 (10 h)=87°C (solvent=water);

10) 4,4'-azobis(4-cyanovaleric acid) - T _1/2 (10 h)=50° C. (solvent=water);

11) 2,2'-azobis(2-methylpropionamidine)dihydrochloride, granules - T _1/2 (10 h)=55° C. (solvent=water);

12) azobisisobutyronitrile - T _1/2 (10 h)=65°C (solvent=toluene); peroxides such as

13) ammonium persulfate - T _1/2 (10 h)=65°C (solvent=water);

14) sodium persulfate - T _1/2 (10 h)=65°C (solvent = water);

15) potassium persulfate - T _1/2 (10 h)=65°C (solvent=water);

16) hydroxymethanesulfonic acid monosodium salt dihydrate - T _1/2 (10 h)=60° C. (solvent=water);

17) benzoyl peroxide - T _1/2 (10 h)=70°C (solvent=benzene);

18) tert-butyl peroxide - T _1/2 (10 h)=125° C. (solvent=benzene);

19) cumene hydroperoxide - T _1/2 (10 h)=135°C (solvent = toluene).

According to this first embodiment of the present invention, initiator IB is added to fluid B of the polymerizable system in an amount in the range of 0.1-20% by weight based on the weight of the polymerizable compound present in fluid A, more preferably in the range of 0.1-20% by weight. 7%, even more preferably 0.2 to 3% by weight.

For the purposes of this description and the appended claims, unless expressly stated otherwise, when reference is made to the weight of the polymerizable compound, this also includes the weight of any crosslinking agent that may be present.

In accordance with this first embodiment of the present invention, fluid B typically does not contain polymerizable compounds. However, if desired, fluid B may also contain at least a second polymerizable compound identical to or different from the polymerizable compound contained in fluid A, preferably in the presence of an initiator inhibitor compound in fluid B, as described below.

In a second preferred embodiment of the present invention, fluid A contains at least one polymerizable compound and at least one radical polymerization initiator I _A activated thermally or in the presence of an accelerating agent of said initiator.

Initiator I _A may be activated after injection and placement of fluid A in the wellbore, in accordance with one of the following methods: (i) by subjecting it to a temperature higher than its activation temperature; (ii) through the contacting effect of the accelerating agent contained in fluid B.

For the purposes of this specification and the appended claims, an accelerating agent is an agent capable of promoting the activation of a radical polymerization initiator at a temperature lower than the thermal activation temperature of the initiator.

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For the purposes of this invention, when reference is made to a polymerization initiator that can be activated by an accelerating agent at a set temperature T ₁ , it is possible that some initiators can also be thermally activated at a different temperature T ₂ , in particular at a temperature T2 higher than T ₁ .

When initiator IA is used in combination with fluid B containing an accelerating agent, preferably initiator _IA and the associated accelerating agent form a redox initiation system.

Redox initiation systems contain at least two compounds capable of generating free radicals after their reduction-oxidation reaction.

According to this second embodiment, the IA initiator is a radical polymerization initiator whose activation temperature may be lower than or equal to the uptake zone temperature, or preferably the activation temperature is higher than the uptake zone temperature. If the activation temperature of the initiator IA is lower than or equal to the temperature of the absorption zone, said fluid A easily contains a suitable amount of the inhibitor compound.

Preferably, the IA initiator has an activation temperature higher than the absorption zone temperature.

Preferably, the initiator IA has an activation temperature T _1/2 (10 h) in the range of 30-150°C. More preferably, the initiator IA has an activation temperature T _1/2 (10 h) higher than 50°C, even more preferably higher than 80°C.

Generally, the compounds useful as the IA initiator according to this second embodiment of the present invention are the same compounds as originally described for use as IB initiators in Fluid B, provided that the IA initiator preferably has a higher activation temperature than absorption zone temperature.

Preferably, the accelerator IB of initiator IA present in fluid B is a compound containing elements or groups capable of adopting more than one oxidation state and thus capable of providing a reduction-oxidation reaction with initiator _IA . More preferably, said accelerator _IB is selected from aliphatic or aromatic amines, preferably having 2 to 30 carbon atoms and 1 to 5 nitrogen atoms, ferrous salts such as halides, sulfates, phosphates, nitrate salts such as ammonium nitrate, potassium nitrate, silver nitrate, nitro derivatives of organic compounds, quinone compounds, or combinations thereof.

Examples of IA initiator accelerators useful in accordance with this second embodiment of the present invention are paratoluidine; tetramethylenediamine, monoethanolamine, diethanolamine, triethanolamine, ethylenediamine, N,N-dimethylaniline, iron(II) sulfate, silver nitrate.

Non-limiting examples of a redox initiation system that are particularly preferred for the purposes of this invention, containing the following combinations (by reaction and reaction) of compounds:

benzoyl peroxide/paratoluidine;

ammonium persulfate/tetramethylenediamine;

ferrous sulfate (P)/potassium persulfate;

ammonium persulfate/monoethanolamine;

ammonium persulfate/diethanolamine;

ammonium persulfate/triethanolamine;

ammonium persulfate/ethylenediamine;

hydrogen peroxide/iron(II) sulfate;

hydrogen peroxide/silver nitrate;

ammonium peroxide/iron(II) sulfate;

potassium persulfate/iron(II) sulfate.

When the initiator _IA has a higher activation temperature than the absorption zone temperature, it may be advantageous to mix with the polymerizable compound in a homogeneous manner to form polymerizable system fluid A without initiating the polymerization reaction. In fact, the polymerization reaction will only start when, downhole, the accelerator contained in fluid B of the polymerizable system comes into contact with the fluid containing the initiator. Since the polymerization reaction is exothermic, the generated heat of reaction is distributed to the remaining mass of fluid A containing the polymerizable initiator compound IA in the mixture, thermally activating additional initiator IA molecules, which, by generating free radicals, promote the polymerization of the remaining polymerizable compound. Propagation of the thermally initiated polymerization reaction at the site of the reaction mixture to adjacent areas, to the specified site, by propagating the generated heat of reaction, is also known in the art as frontal polymerization.

In the context of this invention, the use of a redox initiator system in order to carry out frontal polymerization of the type described above provides

- 6 042904 a significant advantage in overcoming any difficulties in mixing the polymerizable compound and the initiator, which can occur downhole, when the specified polymerizable compound and the specified initiator are injected separately, in different fluids of the polymerizable two-component system.

When fluid A contains at least a first polymerizable compound and an initiator IA having an activation temperature lower than or equal to the temperature of said absorption zone, said fluid A further comprises at least one polymerization inhibitor to inhibit polymerization of said first polymerizable compound.

For the purposes of this invention, a polymerization inhibitor is an agent that can stabilize a polymerizable compound present in fluid B, preventing it from premature polymerization. Typically, polymerization inhibitors are compounds that trap free radicals present in the reaction medium, preventing polymerization from starting. Examples of compounds useful as polymerization inhibitors for the purposes of this invention are: hydroquinone, methoxyphenol, acetanilide.

According to this second embodiment, preferably initiator IA is added to fluid A of the system to be polymerized in an amount in the range of 0.1-10% by weight based on the weight of the compound to be polymerized, more preferably in the range of 1.1-6%.

The inhibitor is dosed in such a way that the amount that affects the inhibition of polymerization is maintained at least as long as fluid A comes into contact with fluid B, which contains an accelerating agent, downhole.

Preferably, the inhibitor is added to Fluid A of the polymerizable system in an amount in the range of 0.1-8% by weight based on the weight of the polymerizable compound, more preferably in the range of 1.5-4%.

According to a third preferred embodiment of the method of this invention, the frontal polymerization mechanism can be advantageously applied when using a polymerizable two-component system in which the first fluid (fluid A) contains at least one polymerizable compound mixed with a first polymerization initiator, which can be thermally activated in situ after injection, and the second fluid (fluid B) contains at least a second polymerization initiator _IB to polymerize said polymerizable compound, said initiator _IB has an activation temperature equal to or lower than the absorption zone temperature.

According to this third embodiment, upon contact between fluid A and fluid B downhole, initiator IB initiates a polymerization reaction. By spreading the progressively generated heat of reaction, the polymerization reaction propagates from the point of contact between the two fluids and the remaining mass of fluid A. The presence of the first initiator uniformly distributed in fluid A promotes more rapid and homogeneous formation of the blocking polymer.

In all embodiments of this invention, adjusting the concentration ratio between the polymerization initiator and the polymerizable compound in the two-component system is possible to change the degree of formation of the blocking polymer.

The first and second components of the polymerizable system are typically in liquid form at ambient temperature and can therefore be easily injected downhole. The liquid form may be due to the liquid nature of the ingredients of the two components of the polymerizable system, eg the polymerizable compound and the initiator, or it may be obtained by dissolving or dispersing the ingredients of Fluids A and B in a solvent.

Preferably, Fluid A and Fluid B of the polymerizable system are in the form of solutions.

Because Fluid A and Fluid B of the polymerizable system are injected into a well that is typically filled or partially filled with drilling fluids, preferably these fluids are substantially immiscible with the drilling fluid.

The immiscibility of the fluid of the polymerizable system with respect to the drilling fluid can be controlled, for example, by adding water to the fluid in the case of an oil-based drilling fluid, or adding hydrocarbon solvents in the case of a water-based drilling fluid. Examples of suitable hydrocarbon solvents are mixtures commercially available under the trade name Lamix® (a mixture of Sc-C14 hydrocarbons containing n-alkanes, isoalkanes and cyclic hydrocarbons, an aromatic hydrocarbon content of less than 2% by mass) and Versalis E-solv G® (a mixture solvents in the form of aliphatic and aromatic hydrocarbons).

Preferably, water and hydrocarbon solvents are added to the fluid in an amount of up to 50% by weight based on the polymerizable compound, more preferably in the range of 10-30%.

The use of fluids A and B of the polymerizable system in dilute form after the addition of water or hydrocarbon solvents also has the advantage of providing

- 7 042904 improved heat dissipation, which is created during the polymerization reaction, and in avoiding excessively intense heat generation, which can occur, for example, if pure polymerizable compounds are used.

Optionally, the polymerizable system may also contain at least one crosslinker to form a crosslinked blocking polymer or copolymer.

Examples of cross-linking agents that can be used for the purposes of this invention are: ethylene glycol dimethacrylate, 1,4-butanediol diacrylate, glycerol dimethacrylate, N,N'-methylenebis-acrylamide, divinylbenzene, poly(tylene glycol) diacrylate, trimethyl propane triacrylate, 1,4 -bis(4vinylphenoxy)butane, bis(2-methacryloyl)oxyethyl disulfide.

The degree of crosslinking of the blocking polymer can be varied by adjusting the concentration of the crosslinking agent in the polymerizable system. As a rule, by increasing the relative concentration of the crosslinking agent relative to the concentration of the polymerizable compound, stiffer polymers with higher mechanical strength are obtained.

Preferably, the crosslinker is added to the component that contains the polymerizable compound in an amount in the range of 10-50% by weight based on the weight of the polymerizable compound (including said crosslinker), more preferably in the range of 15-30% by weight.

Optionally, one or both components of the polymerizable system may contain at least one thickening agent to control the rheological characteristics of the component. Examples of thickening agents useful for the purposes of this invention are: methylcellulose, ethylcellulose, synthetic oils (eg Lucant®), carboxymethylcellulose, glycerin, quantan gum, starch, lipophilic bentonites.

Preferably, the thickening agent is added to the component in a total amount of up to 50% by weight relative to the weight of the polymerizable compound, more preferably in the range of 0.1-15% by weight.

The thickening agent may be present in one or both components of the polymerizable system.

Optionally, one or both components of the polymerizable system may contain at least one weighting agent to control the rheological characteristics of the component. Examples of a weighting agent useful for the purposes of this invention are: barite (barium sulfate), siderite, hematite, galena or soluble salts (eg alkali or alkaline earth metal chlorides).

Preferably, the weighting agent is added to the component in a total amount of up to 100% by weight relative to the weight of the polymerizable compound, more preferably in the range of 5-60% by weight.

The components of the polymerizable system may also contain additional additives, such as, for example, additives used in the preparation of drilling fluids, such as plasticizers, emulsifiers, antifoam agents, etc.

The components of the polymerizable system can be prepared in accordance with the technologies and devices commonly used for the preparation of drilling fluids.

In accordance with the present invention, fluid A and fluid B of the polymerizable system may be injected into the wellbore, indifferently, through the hollow tubular or through the annulus.

Preferably, fluid A containing the polymerizable compound is injected into the annulus while fluid B containing the activator is injected into the hollow tubular.

The ratio between the amounts of injected fluid A and fluid B varies mainly in accordance with the composition of the individual fluids and with the location of the loss zone of the well to be waterproofed. Generally, the volume ratio between the amount of fluid A and the amount of fluid B injected is in the range of 1 to 40, preferably in the range of 3 to 20.

In order to facilitate the injection of fluids A and B of the polymerizable system and their location downhole, a replacement fluid may be used, for example, a drilling fluid that is injected after the respective fluids A and B. Preferably, the replacement fluid and the fluid to be replaced are essentially incompatible with each other.

In another embodiment of the present invention, the method may also be applied to modify the well's permeability upon shutdown and/or completion of a step. In this case, for example, blocking polymer formation can be directed to the desired zone by using the production string as the tubular to move fluid B, and the wellbore annulus to move fluid A.

An exemplary embodiment of the present invention is described below with reference to the corresponding FIGS. 1-4 which schematically illustrate an oil well in four successive embodiments of the method of the present invention.

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With reference to FIG. 1, the method of this invention is applied to eliminate the loss of circulation during drilling of a well 10 in rock 15 due to the presence of a lost zone 20 near the bottom 70 of the well 10. a row of hollow rods 30 (drill string), with the end of which the drill bit 40 is connected. The outer surface of the drill string 30 and the wall of the wellbore 50 and casing string 55 limit the annulus 60, which is in hydrodynamic relationship with the internal cavity of the drill string 30.

If the wellbore is drilled with water-based drilling fluid, a polymerizable two-component system can be applied in it:

fluid A 90, consisting of a mixture formed, for example, by: a polymerizable acrylate monomer (eg, butyl acrylate), a cross-linking agent (eg, ethylene glycol dimethacrylate), a radical polymerization initiator (eg, benzoyl peroxide, which is soluble in the acrylate monomer); fluid B 74 consisting, for example, of dimethylaniline (accelerator) dissolved in a hydrocarbon solvent.

Fluid A and Fluid A are prepared and stored separately in two separate tanks located on the surface (not shown in the figures) and connected to their respective injection pumps.

To inject fluid B 74, the drill string 30 is connected to a pump 80 connected to a reservoir for storing said fluid.

Through the pump 80, fluid B 74 is injected into the drill string 30, which is filled with drilling fluid, until it reaches a location near the drill bit 40, but without flowing out of the bottom of the pipe formed by the drill rods. During injection, fluid B 74 replaces the drilling fluid 92 present in the pipes, which flows towards the bottom of the well, flowing generally towards the loss zone 20 in accordance with the direction indicated by arrows 24.

Advantageously, fluid B 74 is pushed to the bottom of the drill string 30 by a replacement fluid 94 immiscible with fluid B 74. The replacement fluid 94 may be, for example, the same drilling fluid that is used to drill the well, or another fluid having a lower density than the density of fluid B 74. The displacement of fluid B 74 thus achieves the retention of a certain amount of drilling fluid 92 within the drill string 30 in order to form a plug (for example, with a height of 20 m) that prevents fluid B 74 from escaping from the drill string. columns 30.

Fluid A 90 is injected into the annulus 60 of well 10 by means of a pump 82 (FIG. 2) connected to a reservoir for preparing and storing said fluid A (not shown in the figures). Through the effect of fluid A injection, the drilling fluid present in the annulus 60 is pushed to the lost zone 20 where it is distributed in the rock formation 15 leaving room for fluid A 90 in the annulus 60 (FIG. 2).

The amount of injected fluid A 90 is a function of the size of the absorption zone 22 to be blocked. After injection, fluid A 90 is further pushed to the loss zone 22 by the application of replacement fluid 76.

With reference to FIG. 3, once fluid A 90 has been placed, additional replacement fluid 94 is injected into drill string 30 until fluid B 74 is caused to flow out of the drill string. Fluid B 74 thus comes into contact with fluid A 90 causing the polymerization reaction to start. After the displacement of all fluid

At 74 from the interior of the drill string 30, it preferably rises to a safe level that does not involve the formation of a blocking polymer.

With reference to FIG. 4, when the polymerization reaction begins as a result of contact between fluids A and B, it continues in the remaining mass of fluid A 90 through the effect of spreading the created heat of reaction (frontal polymerization), leading to the formation of blocking polymer 97 in the absorption zone 20, which then becomes impermeable. for drilling mud.

At the end of blocking polymer 97 formation, activity in the wellbore may be resumed by continuing to drill at first with an excess of blocking polymer 97 that may be present in the wellbore.

The following examples are provided to further illustrate the invention and should not be construed in a way that limits the scope of legal protection that is defined by the appended claims.

Example 1 Preparation of a polymerizable two-component system suitable for use in combination with a water-based drilling fluid.

The first component of the polymerizable system (fluid A) was prepared using 20 g of a monomer mixture containing butyl acrylate (BA) and methyl methacrylate (MMA) at a BA/MMA weight ratio of 20/80. To the monomer mixture were added 30% by weight of ethylene glycol dimethacrylate (EGDMA) (crosslinking agent) and 1.4% by weight of benzoyl peroxide (BPO) (radical polymerization initiator, half-life temperature 70°C, using benzene as solvent ), the above mass percentages refer to the mass of the mixture of the indicated monomers VA and MMA.

The viscosity of Fluid A was then adjusted by adding 9% by weight of ethyl cellulose (EC) and 50% by weight of barium sulfate (percentages refer to the weight of fluid A's mixture of BA and MMA monomers).

The second component of the polymerizable system (fluid B) was prepared by mixing 1/1 by volume of commercially available hydrocarbon solvent Lamix® with 1.4 g of dimethylaniline (DMA) (equal to 7% by weight of the mixture of BA and MMA monomers used in the preparation fluid A).

The viscosity of Fluid B was then adjusted by adding 0.7% by weight of ethyl cellulose (EC) and 50% by weight of barium sulfate (percentages refer to the weight of fluid A's mixture of BA and MMA monomers).

The first component and the second component were found to be immiscible with a 1.44 kg/L water-based drilling fluid having the following composition:

water: 825 l/m ³ ;

thickener: 3 kg/m ³ ;

filtration reducer: 6 kg/m ³ ;

barite: 625 kg/ ^m3 ;

sodium hydroxide: 1.5 kg/m ³ ;

sodium carbonate: 1.5 kg/m ³ ;

sodium or potassium chloride (optional): 285/m ³ .

Fluids A and B, in the above amounts, were mixed and brought to a reaction by introducing fluid B into fluid A. The mixture of the two fluids was then conditioned in a heater at 60° C., observing after several minutes the formation of a solid polymeric material.

Fluids A and B were also conditioned separately at 60°C to test their stability over long periods of time. The fluids have been found to be stable at the above temperature for at least 24 hours.

Example 2 Polymerization of a two-component system suitable for use in combination with a water-based drilling fluid in frontal polymerization mode.

A two-component system was prepared by the same procedures and the same reagents in the same proportions that were used in the previous example 1 for the preparation of fluids A and B, respectively. 50 g of a mixture of butyl acrylate (BA) and methyl methacrylate (MMA), 20/80 by weight, was used. 20 ml of fluid A thus prepared was transferred into a glass tube with a diameter of 15 mm and a length of approximately 300 mm. While maintaining the tube in an inclined position at an angle of about 45°, about 3 ml of fluid B was poured along the inner wall, allowing it to slowly flow to the surface of fluid A. The two fluids were not mixed, except for a thickness of about 5 mm in the zone of mutual contact. The rest of fluid B formed a layer about 2 cm above fluid A.

After about half a minute, brown coloration was observed at the interface between the two fluids, along with the tube wall becoming warm to the touch. The brown coloration and temperature increase rapidly spread towards the bottom of the tube. After about 3 minutes, Fluid A was completely polymerized, as could be determined after opening the tube.

The ability of the two-component system according to the present invention to block subterranean permeability is thus evident by initiating polymerization at a relatively remote location from the loss zone, after fluid A has been introduced into the porous structure of the zone. Thus, it is possible to modify the permeability of a thief zone in an oil well, as long as it is completely blocked for a sufficient part to make it impermeable, without the need for potentially unstable and uncontrollable systems like monocomponent systems.

Example 3

In a test tube 300 mm long and 15 mm in diameter, similar to that used in the previous example 2, CaCO ₃ was introduced in the form of granules (average particle size 500 μm) for a height of about 100 mm. The tube, held at an angle of 45°, was then slowly injected with fluid A, prepared as described above, until completely absorbed, thus obtaining a layer of approximately 100 mm of impregnated calcium carbonate, similar to the layer of porous rock into which fluid A was introduced in accordance with step (II) the method according to the present invention.

Similar to example 2, about 1 ml of fluid B, prepared as in example 2, was then allowed to flow, which formed a layer about 1 cm high above the mixed carbonate phase saturated with fluid A. The walls became warm to the touch, indicating the beginning and spread of frontal polymerization. The color at this stage of mixing became pale yellow. After about 10 minutes, the tube was cooled and its glass wall was cracked. The contained material was found to be fully solidified while retaining all carbonates.

Example 4 Preparation of a polymerizable two-component system suitable for use

Claims (14)

in combination with oil-based drilling fluid. The first component (fluid A) of the polymerizable system was prepared using a mixture of monomers containing 2-hydroxyethyl methacrylate (HEMA) and hydroxyethyl acrylate (HEA) in a HEMA/HEA weight ratio of 75:25. To 20 g of the monomer mixture was added 20 wt.% (2 g) of ethylene glycol dimethacrylate (EGDMA) (crosslinking agent), 7 wt. A. The viscosity of Fluid A was then adjusted by adding 4.5% by weight of methylcellulose (MC) and 68% by weight of barium sulfate (percentages refer to the weight of fluid A's mixture of HEMA and HEA monomers). The second component of the polymerizable system (fluid B) was prepared by dissolving 0.48 g of iron (II) sulfate (FeO) (2.4% by weight in relation to the mass of the mixture of HEMA and HEA monomers in fluid A) in water, until the sulfate concentration was reached iron, equal to 7.2% by weight relative to the mass of the solution. Fluid A and Fluid B were found to be immiscible in a 1.30 kg/L oil-based drilling fluid having the following composition: crude oil: 650 l/m ³ ; water: 170 l/m ³ ; calcium chloride: 42 kg/m ³ ; primary emulsifier: 22 l/m ³ ; wetting agent: 10 l/m ³ ; organophilic clay: 20 kg/m ³ ; calcium hydroxide: 22 kg/m ³ ; barite: 495 kg/ ^m3 . Fluids A and B, in the above quantities, were mixed and reacted at 60° C. as described in Example 1, observing in this case also the formation of a solid polymeric material after a few minutes. Fluids A and B were also conditioned separately at 60°C and were found to be stable at the above temperature for at least 24 hours. In conclusion, it should be understood that further modifications and variations may be made to the invention described and illustrated herein without deviating from the scope of legal protection defined by the appended claims. CLAIM 1. A method for regulating the permeability of an oil well, comprising: at least one hollow tubular element located inside said well in a direction parallel to its longitudinal axis, at least one annulus between said tubular element and the wall of said well, said oil well also contains at least one absorption zone, said method includes the following stages: I) preparation of a polymerizable two-component system containing at least: fluid A, containing: (a-i) at least one first olefinically unsaturated polymerizable compound; fluid B containing a radical polymerization activator, ii) injecting one of said fluid A and said fluid B into said annulus until said loss zone is reached; iii) injecting the remainder of said fluid A and said fluid B into said hollow tubular until it comes into contact with fluid injected through said annulus to form a blocking polymer in said thief zone, where the radical polymerization initiator in fluid B is a radical polymerization initiator IB for polymerizing said polymerizable compound, said initiator IB has an activation temperature equal to or lower than the temperature of said absorption zone, or alternatively said fluid A further comprises said at least one radical polymerization initiator I _A , and said fluid B contains at least one accelerating compound of said initiator I _A as a polymerization activator, or alternatively, said fluid A further comprises said at least one radical polymerization initiator I _A , and said fluid B contains at least at least one radical polymerization initiator _IB as a polymerization activator, for the polymerization of said polymerizable compound, said initiator _IB has an activation temperature equal to or lower than that - 11 042904 the temperature of the specified absorption zone, wherein one of the two specified reactive components A and B is injected into the tubular element, and the remaining component is injected into the gap bounded by the wall of the tubular element and the wall of the wellbore or, more commonly, the casing string of the well, when present, said tubular member and gap being hydraulically connected to each other in a loss zone near the bottom of the well. 2. The method of claim 1, wherein said at least one radical polymerization initiator IA has an activation temperature equal to or higher than said uptake zone temperature. 3. The method of claim 1, wherein said at least one radical polymerization initiator IA has an activation temperature lower than or equal to the temperature of said uptake zone, and said fluid A contains at least one polymerization inhibitor to inhibit polymerization of said first polymerizable compound. 4. The method of claim 1, wherein said fluid A contains said at least one olefinically unsaturated polymerizable compound, and said fluid B contains said at least one radical polymerization initiator _IB having an activation temperature equal to or lower than the temperature of said zone absorption. 5. A method according to any one of the preceding claims, wherein said fluid B is injected into said hollow tubular and said fluid A is injected into said annulus. 6. A method according to any of the preceding claims 1 to 4, wherein said fluid A is injected into said hollow tubular and said fluid B is injected into said annulus. 7. Process according to any one of the preceding claims, wherein said olefinically unsaturated polymerizable compound is selected from acrylic acid, methacrylic acid, styrene, divinylbenzene, vinyl acetate, acrylamide, acrylates, methacrylates, polyethylene glycol methacrylates, polyethylene glycol methyl methacrylate, hydroxyalkyl methacrylates, diacrylates, chloride solutions [2(methacryloyloxy)ethyl ]trimethylammonium (MADQUAT), mono-2-(methacryloyloxy)ethyl succinate (HemaQ), 3-sulfopropyl methacrylate potassium salt (SPMAK) and mixtures thereof. 8. The method of the preceding claim, wherein said olefinically unsaturated polymerizable compound is selected from ethyl acrylate, butyl acrylate, hexyl acrylate, methyl methacrylate, ethyl methacrylate, hydroxyethyl acrylate, 2-hydroxyethyl methacrylate, polyethylene glycol methacrylate, and mixtures thereof. 9. The method according to any one of the preceding claims, wherein said initiator IA and said polymerization initiator _IB are selected from: 2,2'-azobis[2-(2-imidazolin-2-yl)propan]dihydrochloride; 2,2'-azobis[2-(2-imidazolin-2-yl)propane]disulfate dihydrate; 2,2'-azobis(2-methylpropionamidine)dihydrochloride; 2,2'-azobis[K-(2-carboxyethyl)-2-methylpropionamidine]tetrahydrate; 2,2'-azobis{2-[1-(2-hydroxyethyl)-2-imidazolin-2-yl]propan}dihydrochloride; 2,2'-azobis[2-(2-imidazolin-2-yl)propane]; 2,2'-azobis(1-imino-1-pyrrolidin-2-ethylpropane) dihydrochloride; 2,2'-azobis'2-methyl-N-[1,1-bis(hydroxymethyl)-2-hydroxyethyl]propionamide}; 2,2'-azobis[2-methyl-N-(2-hydroxyethyl)propionamide]; ammonium persulfate; sodium persulfate; potassium persulfate; hydroxymethanesulfonic acid monosodium salt dihydrate; 4,4'-azobis(4-cyanovaleric acid); 2,2'-azobis(2-methylpropionamidine)dihydrochloride; azobisisobutyronitrile; benzoyl peroxide; tert-butyl peroxide; cumene hydroperoxide. 10. The method of claim 1 wherein said accelerating compound of said initiator IA is selected from amines, nitrate salts, ferrous salts, organic nitro derivatives, quinone compounds, or combinations thereof. 11. The method according to the preceding claim, wherein said accelerating compound is selected from paratoluidine, tetramethylenediamine, potassium persulfate, monoethanolamine, diethanolamine, triethanolamine, ethylenediamine, N,N-dimethylaniline, iron (II) sulfate, silver nitrate. 12. The method of any one of the preceding claims, wherein said fluid A contains at least one crosslinker to form a crosslinked blocking polymer. 13. A method according to any one of the preceding claims, wherein injection of said fluid A and/or said fluid B is followed by injection of a replacement fluid. 14. The method of the preceding claim, wherein said fluid A and/or said fluid B are substantially immiscible with said replacement fluid. -