Method for controlling the permeability of a petroleum well

Abstract

A method for controlling the permeability of an oil well includes the steps of preparing a polymerizable bicomponent system having at least a fluid with at least an olefinically unsaturated first polymerizable compound; optionally, at least one radical polymerization initiator I.sub.A, the initiator I.sub.A being activated thermally or in the presence of an accelerating compound and a fluid with a radical polymerization activator, the activator being selected from: a radical polymerization initiator I.sub.B for polymerizing the polymerizable compound, the initiator I.sub.B having an activation temperature equal to or lower than the temperature of the thief zone, an accelerator of the initiator I.sub.A, The method further includes injecting one of the fluids into the well annulus until the thief zone is reached, and injecting the remainder into the tubular element, until it comes into contact with the fluid injected through the annulus to form a blocking polymer at the thief zone.

Claims

1. A method for controlling the permeability of an oil well, comprising: at least one hollow tubular element positioned inside said well in a direction parallel to the longitudinal axis of the same, optionally, at least one tubular casing of the wall of said well, and at least one annulus between said tubular element and the wall of said well or of said optional tubular casing, said oil well also comprising at least one thief zone, said method comprising the following steps: I) preparing a polymerizable bicomponent system, comprising, at least: a fluid A comprising: (a-i) at least one first olefinically unsaturated polymerizable compound; (a-ii) optionally, at least one radical polymerization initiator I.sub.A for polymerizing said polymerizable compound, said initiator I.sub.A being activated thermally or in the presence of an accelerating compound; a fluid B comprising a radical polymerization activator, said activator being selected from: (b-i) a radical polymerization initiator I.sub.B for polymerizing said polymerizable compound, said initiator I.sub.B having an activation temperature equal to or lower than the temperature of said thief zone, or, alternatively, (b-ii) an accelerator of said initiator I.sub.A; II) injecting one of said fluid A and said fluid B into said annulus until said thief zone is reached; III) injecting the remainder between said fluid A and said fluid B into said hollow tubular element until it comes into contact with the fluid injected through said annulus to form a blocking polymer at said thief zone.

2. The method according to claim 1, wherein said fluid A comprises said at least one radical polymerization initiator I.sub.A and said fluid B comprises said at least one accelerating compound of said initiator I.sub.A.

3. The method according to claim 1, wherein said fluid A comprises said at least one radical polymerization initiator I.sub.A and said fluid B comprises at least one radical polymerization initiator I.sub.B for polymerizing said polymerizable compound, said initiator Is having an activation temperature equal to or lower than the temperature of said thief zone.

4. The method according to claim 2, wherein said at least one radical polymerization initiator I.sub.A has an activation temperature equal to or higher than the temperature of said thief zone.

5. The method according to claim 2, wherein said at least one radical polymerization initiator I.sub.A has an activation temperature lower than or equal to the temperature of said thief zone and said fluid A comprises at least one polymerization inhibitor for inhibiting the polymerization of said first polymerizable compound.

6. The method according to claim 1, wherein said fluid A comprises said at least one olefinically unsaturated polymerizable compound and said fluid B comprises said at least one radical polymerization initiator I.sub.B having an activation temperature equal to or lower than the temperature of said thief zone.

7. The method according to any of the previous claim 1, wherein said fluid B is injected into said hollow tubular element and said fluid A is injected into said annulus.

8. The method according to claim 1, wherein said fluid A is injected into said hollow tubular element and said fluid B is injected into said annulus.

9. The method according to claim 1, wherein said olefinically unsaturated polymerizable compound is selected from: acrylic acid, methacrylic acid, styrene, divinylbenzene, vinyl acetate, acrylamide, acrylates, methacrylates, polyethylene glycol (meth)acrylates, polyethylene glycol methyl terminal methacrylate, hydroxyalkyl (meth)acrylates, diacrylates, chloride solutions of [2 (methacryloyloxy)ethyl]trimethylammonium (MADQUAT), mono-2-(methacryloyloxy)ethyl succinate (HemaQ), potassium salt of 3-sulfopropyl methacrylate (SPMAK) and mixtures thereof.

10. The method according to claim 9, 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.

11. The method according to claim 1, wherein said initiator I.sub.A and said polymerization initiator I.sub.B are selected from: 2,2′-Azobis[2-(2-imidazolin-2-yl)propane]dihydrochloride; 2,2′-Azobis[2-(2-imidazolin-2-yl)propane]disulfate dihydrate; 2,2′-Azobis(2-methylpropionamidine)dihydrochloride; 2,2′-Azobis[N-(2-carboxyethyl)-2-methylpropion-amidine]tetrahydrate; 2,2′-Azobis{2-[1-(2-hydroxyethyl)-2-imidazolin-2-yl]propane}-dihydrochloride; 2,2′-Azobis[2-(2-imidazolin-2-yl)propane]; 2,2′-Azobis(1-imino-1-pyrrolidine-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.

12. The method according to claim 1, wherein said accelerating compound I.sub.B of said initiator I.sub.A is selected from: amines, nitrate ion salts, ferrous salts, organic nitro-derivatives, quinone compounds or combinations thereof.

13. The method according to claim 12, wherein said accelerating compound is selected from: para-toluidine; tetramethylenediamine, potassium persulfate, monoethanolamine, diethanolamine, triethanolamine, ethylenediamine, ferrous sulfate, silver nitrate.

14. The method according to claim 1, wherein said fluid A comprises at least one cross-linking agent to form a cross-linked blocking polymer.

15. The method according to claim 1, wherein the injection of said fluid A and/or said fluid B is followed by the injection of a displacement fluid.

16. The method according to claim 15, wherein said fluid A and/or said fluid B is substantially immiscible with said displacement fluid.

17. The method according to claim 1, wherein said hollow tubular element in said well is composed of a string of hollow pipes connected in series.

18. The method according to claim 1, wherein said hollow tubular element is in hydraulic communication with said annulus, preferably in the proximity of said thief zone.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) A possible embodiment of the present disclosure is described below with reference to the accompanying FIGS. 1-4. Each of FIGS. 1-4 schematically illustrate an oil well in four successive instants of implementation of the method according to the present disclosure:

(2) FIG. 1 illustrates a circulation loss during the drilling of a well according to an exemplary embodiment;

(3) FIG. 2 illustrates fluid being injected into the well according to an exemplary embodiment;

(4) FIG. 3 illustrates fluid being positioned and additional displacement fluid being injected according to an exemplary embodiment; and

(5) FIG. 4 illustrates a polymerization reaction as a result of the contact between the fluids.

DETAILED DESCRIPTION OF THE DRAWINGS

(6) With reference to FIG. 1, the method according to the present disclosure is applied to remedy a circulation loss during the drilling of a well 10 in a rock formation 15 caused by the presence of a thief zone 20 in proximity to the bottom 70 of the well 10. The well 10 comprises a hole 50, partially cased by a casing 55, and a tubular element comprises a battery of hollow rods 30 (drill string) at the lower end of which a drill bit 40 is connected. The outer surface of the drill string 30 and the wall of the hole 50 and of the casing 55 delimit an annulus 60 that is in hydraulic communication with the inner cavity of the drill string 30.

(7) If the drilling of the hole is carried out using a water-based mud, a polymerizable bicomponent system can be used wherein:

(8) a fluid A 90 comprises a mix formed, for example, by: a polymerizable acrylate monomer (e.g. butyl acrylate), a cross-linking agent (e.g. ethylene glycol dimethacrylate), a radical initiator (e.g. benzoyl peroxide, which is soluble in the acrylate monomer);

(9) a fluid B 74 comprises, for example, a dimethylaniline (accelerator) dissolved in a hydrocarbon solvent.

(10) The fluid A and the fluid A are prepared and stored separately in two distinct tanks positioned on the surface (not shown in the figures) and connected to respective injection pumps.

(11) For the injection of the fluid B 74, the drill string 30 is connected to a pump 80 connected to the storage tank of said fluid.

(12) By means of the pump 80, the fluid B 74 is injected in the drill string 30, which is full of mud, until reaching in proximity to the drill bit 40, but without flowing out of the lower end of the tube formed by the rods. During injection, the fluid B 74 displaces the mud 92 present inside the rods, which escapes towards the bottom of the well flowing mainly towards the thief zone 20 according to the direction indicated by the arrows 24.

(13) Advantageously, the fluid B 74 it pushed towards the bottom of the drill string 30 by means of a displacement fluid 94, immiscible with the fluid B 74. The displacement fluid 94 can be, for example, the same drilling mud used for drilling the well or another fluid having lower density than that of the fluid B 74. The displacement of the fluid B 74 is achieved in such a way as to leave a certain quantity of drilling mud 92 inside the drill string 30 so as to form a plug (for example, with height equal to 20 m) that prevents the fluid B 74 from escaping from the drill string 30.

(14) The fluid A 90 is injected into the annulus 60 of the well 10 by means of a pump 82 (FIG. 2) connected to the tank for the preparation and storage of said fluid A (not shown in the figures). By effect of the injection of the fluid A, the mud present in the annulus 60 is pushed towards the thief zone 20, where it disperses in the rock formation 15, leaving space to the fluid A 90 in the annulus 60 (FIG. 2).

(15) The quantity of fluid A 90 injected is a function of the dimensions of the thief zone 22 to be blocked. After the injection, the fluid A 90 is further pushed towards the thief zone 22 using a displacement fluid 76.

(16) With reference to FIG. 3, once the fluid A 90 is positioned, in the drill string 30 is injected additional displacement fluid 94 until causing the fluid B 74 to escape from the drill string. The fluid B 74 thus comes in contact with the fluid A 90 starting the polymerization reaction. After displacing all of the fluid B 74 from the interior of the drill string 30, the latter is preferably raised to a safe level not involved in the formation of the blocking polymer.

(17) With reference to FIG. 4, once the polymerization reaction starts as a result of the contact between the fluids A and B, it continuous in the remaining mass of the fluid A 90 by effect of the diffusion of the reaction heat (frontal polymerization), leading to the formation of a blocking polymer 97 at the thief zone 20, which is then made impermeable to drilling mud.

(18) At the end of the formation of the blocking polymer 97, the well drilling activity can resume, proceeding first of all with drilling of the excess of blocking polymer 97 which may be present in the hole.

(19) The following examples are provided to further illustrate the present disclosure and should not be construed in a sense that would limit the scope of protection defined by the enclosed claims.

EXAMPLE 1

Preparation of a Polymerizable Bicomponent System Suitable for Use in Combination with a Water-Based Mud

(20) The first component of the polymerizable system (fluid A) was prepared using 20 g of a mix of monomers containing butyl acrylate (BA) and methyl methacrylate (MMA) in a BA/MMA weight ratio of 20/80. To the mix of monomers were added 30% by weight of ethylene glycol dimethacrylate (EGDMA) (cross-linking agent) and 1.4% by weight of benzoyl peroxide (BPO) (radical initiator, half-life temperature of 70° C., using benzene as a solvent), the aforesaid weight percentages being referred to the weight of the mix of BA and MMA monomers.

(21) The viscosity of the fluid A was then adjusted adding 9% by weight of ethylcellulose (EC) and 50% by weight of barium sulfate (percentages referred to the weight of the mix of BA and MMA monomers of the fluid A).

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

(23) The viscosity of the fluid B was then adjusted adding 0.7% by weight of ethylcellulose (EC) and 50% by weight of barium sulfate (percentages referred to the weight of the mix of BA and MMA monomers of the fluid A).

(24) The first component and the second component were found to be immiscible in a water-based mud with density of 1.44 kg/L having the following composition: Water: 825 L/m3 Viscosifier: 3 kg/m3 Filtrate reducer: 6 kg/m3 Barite: 625 kg/m3 Sodium hydroxide: 1.5 kg/m3 Sodium carbonate: 1.5 kg/m3 Sodium or Potassium Chloride (optional): 285/m3.

(25) The fluids A and B, in the aforesaid quantities, were mixed and made to react introducing the fluid B in the fluid A. The mix of the two fluids was then conditioned in a stove at 60° C., observing after a few minutes the formation of a solid polymeric material.

(26) The fluids A and B were also conditioned separately at 60° C. to prove their stability over prolonged times. The fluids were found to be stable at the aforesaid temperature for at least 24 hours.

EXAMPLE 2

Polymerization of a Bicomponent System Suitable for Use in Combination with a Water-Based Mud in Frontal Polymerization Mode

(27) A bicomponent system was prepared with the same procedures and the same reactants in the same proportions used in the previous example 1 for the preparation of the fluids A and B respectively. 50 gr of mix of BA and MMA, 20/80 by weight, were used.

(28) 20 ml of the fluid A thus prepared were transferred to a glass vial with diameter of 15 mm and length of approximately 300 mm. Maintaining the vial inclined by approximately 45°, approximately 3 ml of fluid B were poured along the inner wall, letting it slowly flow towards the surface of the fluid A. The two fluids were not mixed except for a thickness of approximately 5 mm in the zone of mutual contact. The remaining fluid B formed a layer of approximately 2 cm above the fluid A.

(29) After approximately half a minute, browning was observed at the interface of the two fluids, while the wall of the vial became warm to the touch. The browning and the temperature increase were rapidly propagated towards the bottom of the vial. After approximately 3 minutes the fluid A was completely polymerized, as it was possible to ascertain after breaking the vial.

(30) The ability of the bicomponent system according to the present disclosure to block the permeability of an underground loss is thus evident, triggering polymerization in a relatively distant point from the thief zone, after introducing the fluid A in the porosities of the zone. In this way it is possible to modify the permeability of a thief zone in an oil well, until it is completely blocked for a sufficient segment to assure its seal, with not need to use potentially unstable and uncontrollable systems like mono-component systems.

EXAMPLE 3

(31) In a vial with length of 300 mm and diameter of 15 mm, similar to the one used in the previous example 2, CaCO.sub.3 in granules was introduced (mean particle size 500 μm) for a height of approximately 100 mm. In the vial held inclined by 45° was then slowly introduced the fluid A prepared as described above, until complete imbibition, thus obtaining a layer of approximately 100 mm of impregnated calcium carbonate similar to a layer of porous rock into which fluid A was introduced according to stage (II) of the process according to the present disclosure.

(32) Similarly to the example 2, approximately 1 ml of fluid B prepared as in the example 2 was then made to flow, which formed a layer with a height of approximately 1 cm above the mixed phase of saturated carbonate of fluid A. The walls became warm to the touch, indicating the start and the propagation of the frontal polymerization. The coloration of the mixed phase turned pale yellow. After approximately 10 minutes, the vial was cooled and its glass wall was fractured. The material contained was found to be completely solidified retaining all carbonate.

EXAMPLE 4

Preparation of a Polymerizable Bicomponent System Suitable for Use in Combination with an Oil-Based Mud

(33) The first component (fluid A) of the polymerizable system was prepared using a mix of monomers containing 2-hydroxyethyl methacrylate (HEMA) and hydroxyethyl acrylate (HEA) in a weight ratio HEMA/HEA of 75:25. To 20 g of the mix of monomers were added 20% by weight (2 g) of ethylene glycol dimethacrylate (EGDMA) (cross-linking agent), 7% by weight of hydrogen peroxide and 35% by weight of water, the aforesaid percentages by weight being referred to the weight of the mix of HEMA/HEA monomers of the fluid A.

(34) The viscosity of the fluid A was adjusted adding 4.5% by weight of methylcellulose (MC) and 68% by weight of barium sulfate (percentages referred to the weight of the mix of HEMA and HEA monomers of the fluid A).

(35) The second component of the polymerizable system (Fluid B) was prepared dissolving in water 0.48 g of ferrous sulfate (FeO) (2.4% by weight relative to the weight of the mix of HEMA and HEA monomers in the fluid A), until reaching an iron sulfate concentration equal to 7.2% by weight relative to the weight of the solution.

(36) The fluid A and the fluid B were found to be immiscible in an oil-based mud with density of 1.30 kg/L having the following composition: Base oil: 650 L/m3 Water: 170 L/m3 Calcium Chloride: 42 kg/m3 Primary emulsifier: 22 L/m3 Wetting Agent: 10 L/m3 Organophilic clay: 20 kg/m3 Calcium hydroxide: 22 kg/m3 Barite: 495 kg/m3.

(37) The fluids A and B, in the aforesaid quantities, were mixed and made to react at 60° C. as described in the example 1, observing, in this case too, the formation of a solid polymeric material after a few minutes.

(38) The fluids A and B were also conditioned separately at 60° C. and found to be stable at the aforesaid temperature for at least 24 hours.

(39) It is finally understood that the disclosure described and illustrated herein can be made additional modifications and variants without thereby departing from the scope of protection as defined by the attached claims.