Module for the inline mixing of high viscosity water-soluble polymer solutions and method for hydraulically fracking an oil or gas production well

Abstract

Mixing module comprising - at least one pipe comprising a static mixer (2), - at least one connected to the pipe through at least one injection cannula (4) penetrating laterally within the pipe and extending transversally into the body thereof, the injection cannula being blocked at its free end and having a wall provided, in its part inserted into the body of the pipe, with at least one orifice.

Description

DescriptionTitle of the invention: MODULE FOR THE INLINE MIXING OF HIGH VISCOSITY WATER-SOLUBLE POLYMER SOLUTIONS AND METHOD FOR HYDRAULICALLY FRACKING AN OIL OR GAS PRODUCTION WELLTechnical Field

[0001] . The present invention relates to a module for the inline mixing of high viscosity water-soluble polymer solutions to obtain a homogeneous aqueous solution, ready to be injected in an underground formation.

[0002] It also relates to an installation implementing the mixing module, as well as enhanced oil and / or gas recovery or hydraulic fracking methods implementing said installation.Prior art

[0003] Water-soluble polymers and, in particular, polyacrylamides are commonly used in large quantities in enhanced oil recovery (EOR) or for hydraulic fracking operations.

[0004] Technical solutions have been developed to prepare stock solutions of high viscosity water-soluble polymers (greater than 500 centipoises). As an example, documents WO 2011 / 107683 and WO2016 / 156320 describe devices (PSU - Polymer Slicing Unit) making it possible to both grind and disperse the polymer in powder form in dissolution water. This type of device makes it possible to limit the dissolution time to 30 minutes and to obtain very high polymer concentrations, of around 20g / litre. These high concentrations make it possible to greatly decrease the size of the dissolution tanks positioned downstream from the PSU (also called maturation tanks) and metering pumps, and offer an advantage of a high reduction in the corresponding investments. Indeed, to save space and reduce costs, not only in on-shore application, but also and particular in off-shore application, it is necessary to limit, as much as possible, the implementation of dissolution tanks. Nevertheless, the dissolution of the powders must be as complete as possible in order to prevent injectivity problems in wells.

[0005] Upstream of these water-soluble polymer powder dissolution systems, the water-soluble polymer solutions obtained have high viscosities (beyond 500centipoises). To avoid preparing polymer injection solutions to be stored in tanks (dilution of stock solutions), it is known to inject the stock solution inline (in the pipework) into an injection water flow. The injection water pipework can comprise a static mixer upstream of the injection cannula. However, the water-soluble polymer solution obtained upstream of the static mixer has homogeneity problems, in particular for low flow rates of injection solution or for highly viscous solutions. This induces incorrect viscosity measurements upstream, but also the risk of injecting different solutions in the underground formation, in case of division of the output line to several injection points, and therefore a loss of performance of EOR or hydraulic fracking methods, given that the target viscosity will not be reached.

[0006] Consequently, the problem that propose the invention to resolve is that of developing a device which makes it possible to inject a water-soluble polymer solution S in an underground formation, the viscosity of which is greater than 500 centipoises in a flow of injection water I, which is homogeneous.

[0007] The problem of bulk of the device is all the more significant than the installation (PSU + maturation tanks + injection device) is, in particular, intended to be used for enhanced oil and / or gas recovery operations or for off-shore hydraulic fracking operations.Disclosure of the invention

[0008] Thus, in order to guarantee a homogeneity of the injection solutions containing water-soluble polymer in the underground formation, the Applicant has developed a module for mixing a water-soluble polymer solution, the viscosity of which is greater than 500 centipoises, in an injection water flow circulating within a pipe, by means of one or more polymer solution lines equipped with specific injection cannulas within the pipe, the polymer-concentrated stock solution lines being positioned upstream of a static mixer in the direction of the injection water flow.

[0009] More specifically, the invention aims for a mixing module, comprising:- at least one pipe intended to be supplied with an aqueous injection solution I, and comprising a static mixer,- at least one line intended to be supplied with an aqueous solution S comprising at least one water-soluble polymer with a Brookfield viscosity greater than 500 centipoises (rotational speed: 60rpnr1, 25°C), the line being connected to the pipethrough at least one injection cannula, preferably at least two injection cannulas penetrating laterally within the pipe and extending transversally into the body of it, the injection cannula being blocked at its free end and having a wall provided, in its part inserted into the body of the pipe, with at least one orifice capable of diffusing the aqueous solution S.

[0010] In practice, the viscous polymer solution S is distributed in a pipe in the direction of the flow of the injection solution I by means of at least 1 line equipped with at least one injection cannula, preferably at least two injection cannulas the cylindrical part of which immersed in the flow of the injection solution I diffuses the polymer through at least 1 , advantageously 2 through orifices, the injection cannula(s) being located upstream of a static stirrer passed through by the flow of the resulting solution (S+l).

[0011] Advantageously, the orifice(s) through which the polymer solution flows are positioned at least partially facing the mixer. In other words, the orifices are distributed over the wall of the cannula, so as to deliver the polymer solution in the circulation direction of the injection water. In other words, the injection cannula has no orifice positioned opposite the static mixer. No turbulence is thus generated.

[0012] The mixing module according to the invention further advantageously has at least one of the following features:- the injection cannula is cylindrically-shaped and has an inner diameter of between 15 and 200 millimetres, preferably between 15 and 50 millimetres.- the inserted part of the cannula in the pipe has between 1 and 10, advantageously between 3 and 6 circular orifices,- the circular orifices have an identical inner diameter and of between 1 and 50 millimetres, preferably between 4 and 15 millimetres,- the orifices are vertically aligned,- the walls of the injection cannula(s) have a thickness of between 1 and 10 millimetres, preferably between 2 and 5 millimetres.

[0013] As mentioned before, in a preferred embodiment, the line of the mixing module of the invention comprises at least 2 injection cannulas.

[0014] The Applicant has noted that the homogeneity of the mixture has been improved when the distance between the axes of the at least two injection cannulasis between 1 and 10 times the outer diameter of these cannulas, advantageously between 1 and 3 times the outer diameter of these cannulas.

[0015] Likewise, and also according to the invention, the distance between the injection cannula closest to the static mixer and said static mixer is equal to 0.5 to 5 times the diameter of the cannula, preferably equal to 0.5 to 2 times the diameter of the cannula.

[0016] In practice, the axis of the at least one injection cannula, advantageously at least two injection cannulas is positioned perpendicularly to the wall of the pipe.

[0017] In a first embodiment, the at least 2 injection cannulas are aligned along the Pipe.

[0018] In a second embodiment, the at least 2 injection cannulas are offset along the pipe and are inclined against one another.

[0019] In a third embodiment, the line comprises at least 2 first injection cannulas along the pipe and at least 2 second injection cannulas aligned, offset and inclined along the pipe with respect to the first injection cannulas.

[0020] The injection cannulas are, in practice, connected to the line directly or by way of an intermediate part in the form of a flexible or rigid duct. To make it possible to adjust the aqueous polymer solution S flow rate, the at least one injection cannula is provided with a valve capable of blocking it off.

[0021] The polymer solutions prepared by means of the device of the invention can be directly injected in an underground formation for enhanced oil recovery or hydraulic fracking operations, which makes it possible to avoid the installation of tanks for storing said solutions. The footprint of the installation for preparing the injection solution from polymers in powder form (PSU + maturation tanks + device of the invention) is therefore reduced.

[0022] The invention also relates to an installation implementing the mixing module described above.

[0023] More specifically, the installation comprises a so-called “main” pipe intended to be supplied with an aqueous injection solution I, and in which the mixing module according to the invention is inserted, such that the at least one injection cannula,advantageously at least two injection cannulas is positioned upstream of the static mixer in the circulation direction of the aqueous injection solution I.

[0024] Furthermore, the main pipe and the pipe of the mixer preferably have identical internal and external diameters, at least at the insertion of the pipe of the mixer in the main pipe.

[0025] In a particular embodiment, the installation further comprises a silo containing a proppant, the silo being positioned downstream of the mixer in the circulation direction of the aqueous injection solution I.

[0026] Finally, two other last aspects of the invention relate to an enhanced oil and / or gas recovery method and a method for hydraulically fracking an oil or gas reservoir, implementing the installation described above, these two methods comprising a step of preparing a water-soluble polymer injection solution with the mixing module of the invention.

[0027] More specifically, the invention relates to a mixing module to mix an aqueous solution S comprising at least one water-soluble polymer with a Brookfield viscosity greater than 500 centipoises (rotational speed: 60rpnr1, 25°C) in a pipe travelled by a flow of an aqueous injection solution I, in particular for enhanced oil and / or gas recovery operations or for hydraulic fracking operations, said device comprising:- a pipe travelled by a flow of solution I, said pipe comprising a static mixer;- at least one line travelled by a flow of solution S, connected to the pipe transversally by means of a cylindrically-shaped and transversally perforated injection cannula, advantageously at least two injection cannulas in its part immersed in the fluid I, by at least 1 circular orifice to diffuse the solution S in the direction of the flow of solution I, the injection cannula being located upstream of the static mixer.

[0028] Preferably, the solution S has a Brookfield viscosity of between 500 and 10000 centipoises (rotational speed: 60rpnr1, 25°C), more preferably between 1000 and 3000 centipoises. The viscosity of the solution S is determined with a Brookfield viscosimeter. A person skilled in the art knows how to choose the module of the viscosimeter to measure the targeted viscosity range (advantageously, modules LV1 or LV2).

[0029] The solution S is an aqueous solution, advantageously the solution S comprises at least one water-soluble polymer dissolved in water or dissolved in a brine containing alkaline and / or alkaline earth salts. Alkaline salts are preferably monovalent and / or divalent.

[0030] The water-soluble polymer has a molecular weight greater than or equal to 1 million daltons, preferably between 1 and 40 million daltons, more preferably between 3 and 30 million daltons. Molecular weight is defined as weight-average molecular weight.

[0031] The molecular weight is determined by the intrinsic viscosity of the polymer. The intrinsic viscosity can be measured by methods known to a person skilled in the art and can be calculated from the reduced viscosity values for different polymer concentrations by a graphical method consisting in plotting the reduced viscosity values (y-axis) against the concentration (x-axis) and extrapolating the curve to zero concentration. The intrinsic viscosity value is plotted on the y-axis or using the leastsquares method. The molecular weight can then be determined using the Mark- Houwink equation:[q] = K.Ma[q] represents the intrinsic viscosity of the polymer as determined by the solution viscosity method.K represents an empirical constant.M represents the molecular weight of the polymer. a represents the Mark-Houwink coefficient.K and a depend on the particular polymer-solvent system.

[0032] The term “water-soluble polymer”, means a polymer which gives an aqueous solution without insoluble particles when it is dissolved under stirring at 25°C and with a concentration of 10g. L'1in deionised water.

[0033] Advantageously, the solution S is prepared from at least one water-soluble polymer in powder form by using a device such as the PSU (Polymer Slicing Unit) described in documents WO2011 / 107683 and WO2016 / 156320. This device makes it possible to both grind and to disperse the polymer in powder form in the aqueous dissolution solution. At the output of this device, the solution S obtained residessuccessively in one or more maturation tanks (tanks equipped with stirring blades to ensure the complete dissolution of the polymer).

[0034] The injection fluid I circulating in the pipe is an aqueous solution such that the water or a brine containing alkaline metal and / or alkaline earth salts. This aqueous solution can be seawater drawn directly over the operating field of the underground formation, in particular when the field is an off-shore field.

[0035] A person skilled in the art knows how to adapt the materials constituting the pipe of the mixing module according to the injection fluid I. As an example, the material can be chosen to avoid corrosion. The pipe of the mixing module is preferably cylindrical and rigid.

[0036] The invention also relates to an enhanced oil and / or gas recovery method and a method for hydraulically fracking an oil or gas reservoir, implementing the installation described above.

[0037] These methods comprise, in particular, the following steps:- preparing a polymer solution S comprising at least one water-soluble polymer, the solution S having a Brookfield viscosity greater than 500 centipoises,- supplying the line with polymer solution S,- supplying the main pipe with solution I composed of water or brine,- adjusting the flow rate of polymer solution S with the flow of solution I circulating in the pipe of the mixer, the solution thus obtained constituting an injection fluid.

[0038] In the case of the enhanced oil and / or gas recovery method, said method further comprises the following steps:- injecting the injection fluid in an underground formation,- sweeping the underground formation using the injected fluid,- recovering the aqueous and hydrocarbon mixture.

[0039] In the case of the hydraulic fracking method, said method further comprises the following steps:- injecting the injection fluid in a silo containing a proppant to obtain a fracking fluid,- injecting the fracking fluid under pressure to create fractures distributed perpendicularly to the production well,- recovering an aqueous and hydrocarbon mixture.

[0040] In a known manner, the proppant is preferably sand. The fracking fluid is an aqueous suspension containing at least the proppant and the polymer.

[0041] In particular embodiments, the 2 methods further have at least one of the following features:- the cumulated flow rate of the solution S within the injection cannulas is between 0.5 and 2.5m.S'1,- the flow rate of the solution I in the pipe of the mixing module is between 5 and 10 times greater than the cumulated flow rate of the solution S in the injection cannulas.

[0042] Example of an embodiment

[0043] The invention and the resulting advantages will become apparent from the following description, made in support of the accompanying figures.

[0044] Figure 1 is a schematic representation of the mixing module according to a first embodiment of the invention.

[0045] Figure 2 is a schematic representation of the installation according to the invention integrating a mixing module according to a second embodiment.

[0046] As represented in figure 1 , the mixing module according to the invention comprises a pipe (1 ) itself comprising a static mixer (2). A person skilled in the art knows how to choose the geometry of the elements of the static mixer. This static mixer is advantageously composed of spacers which cross one another (SMX type from Sulzer). According to the embodiments, either the elements of the static mixer are integrated directly in the pipe (1 ) as represented in figure 1 , or the static mixer integrating the elements is added directly at the end of the pipe (1 ) as represented in figure 2.

[0047] The module further comprises a line (3) intended to be travelled by a polymeric solution S, the line being constituted of materials that a person skilled in the art knows how to choose, according, in particular, to the nature of the solution S. This line is advantageously a cylindrical pipe. In practice, the line 3 is intended to be connected to a reservoir of solution S, not represented in the figures, located upstream of said line. As an example, this reservoir can be a maturation tank.

[0048] Also according to figure 1 , the line (3) is connected to the pipe (1 ) in which the injection solution I circulates by means of 3 injection cannulas (4), aligned longitudinally with respect to the axis of the pipe (1 ). A person skilled in the art knows how to choose the material composing the injection cannulas (4). In practice, the injection cannulas (4) are connected to the line (3) permanently (for example, crimping, welding) or temporarily (screw thread / threading). The connection can be made directly on the line (3) as represented in figure 1 or through an intermediate duct (8) as represented in figure 2.

[0049] The injection cannulas (4) are connected to the pipe (1 ) transversally, i.e. that they are positioned perpendicularly to the wall of the pipe (1 ). The cannulas are fixed to the pipe (1 ) permanently (for example, crimping, welding) or temporarily (for example, screw thread / threading).

[0050] The injection cannulas (4) penetrate into the pipe (1 ) up to the proximity of its opposite wall. In practice, the injection cannulas penetrate into the pipe (1 ) perpendicularly to the wall thereof and sink into the body of the pipe over a distance equivalent to 50 to 90% of its diameter.

[0051] As figure 1 shows, the injection cannulas (4), in this specific embodiment, penetrate into the pipe (1 ) over a distance equivalent to 60% of its diameter.

[0052] Also according to the embodiment of figure 1 , the injection cannulas (4) are cylindrically-shaped and perforated, in their part immersed in the fluid I, through 3 circular orifices (5) distributed along a vertical axis. The orifices thus diffuse the solution S in the direction of the flow of solution I. The injection cannulas are positioned longitudinally, upstream of the static mixer (2). In an embodiment not represented, the cannulas can comprise several series of orifices distributed along a vertical axis, each series being distributed over half the circumference of the injection cannula facing the static mixer.

[0053] Such as represented, the injection cannulas (4) have an inner diameter of between 15 and 200 millimetres.

[0054] The circular orifices (5) of one same injection cannula (4) have an identical inner diameter and of between 1 and 50 millimetres.

[0055] The walls of the injection cannula(s) have a thickness of between 1 and 10 millimetres.

[0056] According to this embodiment, the injection cannulas (4) are identical.

[0057] Advantageously, the distance between the axes of the three injection cannulas (4) is between 1 to 10 times the outer diameter of these cannulas.

[0058] Also in this embodiment, the distance between the cannula (4) closest to the static mixer and the static mixer (2) is equal to 0.5 to 5 times the diameter of the cannula (4).

[0059] The flow rate of the polymer solution P in each injection cannula is controlled by means of a valve (9).

[0060] Figure 2 is a representation of an installation according to the invention integrating a mixing module according to a second embodiment.

[0061] The installation thus comprises a so-called “main” pipe (6) intended to be supplied with aqueous injection solution I in the direction of the arrow (7). The mixing module according to the invention is inserted in the main pipe (6) through the pipe (1 ). The diameter of the pipe (1 ) is identical to that of the main pipe. The pipe (1 ) further comprises a static mixer (2) positioned downstream of the pipe (1 ) in the direction of the injection solution flow represented by the arrow (7). As represented in figure 2, the static mixer (2) is added to the pipe (1 ). The elements of the static mixer cannot be seen in figure 2, but correspond to those represented in figure 1.

[0062] In this embodiment, the module has 2 series of 2 injection cannulas, respectively a first series of aligned injection cannulas (4.1 , 4.2) and a second series of injection cannulas (4.3, 4.4) offset longitudinally and transversally with respect to the first series. The distance between the axes of the 4 injection cannulas (4) is identical, equal in practice to twice the outer diameter of these cannulas.

[0063] The 4 injection cannulas are connected to one single line (3), which is supplied with polymer solution S.

[0064] The invention also relates to an enhanced oil and / or gas recovery method and a method for hydraulically fracking an oil or gas reservoir, implementing the installation described above.

[0065] The installation such as represented in figure 2 can be used in the two types of method and implements the following common steps of preparing the injection fluid:- preparing a polymer solution S comprising at least one water-soluble polymer, the solution S having a Brookfield viscosity greater than 500 centipoises,- supplying the line with polymer solution S,- supplying the main pipe with solution I composed of water or brine,- adjusting the flow rate of polymer solution S with the flow of solution I circulating in the pipe of the mixer, the solution thus obtained constituting an injection fluid.

[0066] In the case of the enhanced oil and / or gas recovery method, said method further comprises the following steps:- injecting the injection fluid in an underground formation,- scanning the underground formation using the injected fluid,- recovering the aqueous and hydrocarbon mixture.

[0067] In the case of the hydraulic fracking method, said method further comprises the following steps:- injecting the injection fluid in a silo not represented in figure 2, containing a proppant to obtain a fracking fluid,- injecting the fracking fluid under pressure to create fractures distributed perpendicularly to the production well,- recovering an aqueous and hydrocarbon mixture.

[0068] In both cases, the cumulated flow rate of the solution S within the injection cannulas (4) is preferably between 0.5 and 2.5m.s'1, even more preferably between 1 .5 and 2m. s-1. This flow rate is controlled by means of valves (9).

[0069] The flow rate of the solution I in the pipe (1 ) is between 2 and 20 times greater than the cumulated flow rate of the solution S in the injection cannulas (4), more advantageously between 5 and 10 times greater.

[0070] The invention and the advantages resulting therefrom are highlighted in the description. The capacity of the mixing module to produce a homogeneous injection fluid which can be used directly and inline in an oil / gas enhanced recovery or hydraulic fracking method with a limited ground impact is noted, in particular.

Claims

Claims1. Mixing module comprising- at least one pipe intended to be supplied with an aqueous injection solution I, and comprising a static mixer (2),- at least one line intended to be supplied with an aqueous solution S comprising at least one water-soluble polymer of Brookfield viscosity greater than 500 centipoises (rotational speed: 60rpnr1, 25°C), characterised in that the line is connected to the pipe through at least two injection cannulas (4) penetrating laterally within the pipe and extending transversally into the body of it, the injection cannulas being blocked at their free ends and having a wall provided, in their parts inserted into the body of the pipe, with at least one orifice capable of diffusing the aqueous solution S and in that the distance between the axes of at least two injection cannulas (4) is between 1 and 10 times the outer diameter of the cannulas.

2. Mixing module according to claim 1 , characterised in that the injection cannulas are cylindrically-shaped and have an inner diameter of between 15 and 200 millimetres.

3. Mixing module according to one of claims 1 or 2, characterised in that the inserted part of the cannulas in the pipe has 3 to 6 circular orifices (5).

4. Mixing module according to claim 3, characterised in that the circular orifices (5) have an identical inner diameter, and of between 1 and 50 millimetres.

5. Mixing module according to any one of the preceding claims, characterised in that the orifices are vertically aligned.

6. Mixing module according to any one of the preceding claims, characterised in that the at least one orifice is positioned at least partially facing the static mixer.

7. Mixing module according to any one of the preceding claims,, characterised in that the distance between the axes of the at least two injection cannulas (4) is between 1 and 3 times the outer diameter of these cannulas.

8. Mixing module according to any one of the preceding claims,, characterised in that the at least 2 injection cannulas are aligned along the pipe.

9. Mixing module according to one of claims 1 to 7 , characterised in that the at least 2 injection cannulas are offset along the pipe and are inclined against one another.

10. Mixing module according to one of the claims 1 to 7, characterised in that the line (3) comprises at least two first injection cannulas aligned along the pipe and at least two second injection cannulas aligned, offset and inclined along the pipe compared to the first injection cannulas.11 . Mixing module according to any one of the preceding claims, characterised in that the at least two injection cannulas (4) are provided with a valve.

12. Installation comprising a so-called “main” pipe intended to be supplied with an aqueous injection solution I, characterised in that it further comprises a mixing module according to one of claims 1 to 11 , inserted in the main pipe, such that the at least two injection cannulas are positioned upstream of the static mixer in the circulation direction of the aqueous injection solution I.

13. Installation according to claim 12, characterised in that it further comprises a silo containing a proppant, the silo being positioned downstream of the mixing module in the circulation direction of the aqueous injection solution I.

14. Enhanced oil and / or gas recovery method implementing the installation which is the subject matter of claim 12, comprising the following steps:- preparing a polymer solution S comprising at least one water-soluble polymer, the solution S having a Brookfield viscosity greater than 500 centipoises,- supplying the line (3) with polymer solution S,- supplying the main pipe with solution I composed of water or brine,- adjusting the flow rate of polymer solution S with the flow of solution I circulating in the pipe of the mixer, the solution thus obtained constituting an injection fluid,- injecting the injection fluid in an underground formation,- scanning the underground formation using the injected fluid,- recovering the aqueous and hydrocarbon mixture.

15. Method for hydraulically fracking an oil or gas production well implementing the installation which is the subject matter of claim 13, comprising the following steps:- preparing a polymer solution S comprising at least one water-soluble polymer, thesolution S having a Brookfield viscosity greater than 500 centipoises,- supplying the line (3) with polymer solution S,- supplying the main pipe with solution I composed of water or brine,- adjusting the flow rate of polymer solution S with the flow of solution I circulating in the pipe of the mixer, the solution thus obtained constituting an injection fluid, injecting the injection fluid in a silo containing a proppant to obtain a fracking fluid,- injecting the fracking fluid under pressure to create fractures distributed perpendicularly to the production well,- recovering an aqueous and hydrocarbon mixture.

16. Enhanced oil and / or gas recovery or hydraulic fracking method according to one of claims 14 or 15, characterised in that the cumulated flow rate of the solution within the injection cannulas (4) is between 0.5 and 2.5m.s-1.

17. Enhanced oil and / or gas recovery or hydraulic fracking method according to one of claims 14 to 16, characterised in that the flow rate of the solution I in the pipe (1 ) is between 5 and 10 times greater than the cumulated flow rate of the solution in the injection cannulas (4).

Images