Background heater for horizontal oil wells

Abstract

The present invention relates to a background heater for horizontal oil wells, the heating cables of which have high electrical insulation, with very high mechanical strength and at the same time are arranged so that their cross-section is minimised, the annular space thus being free for the passage of fluidised oil, which is pulled by the pumping equipment during extraction. Said supply cable is electrically connected to at least one resistive conductor, ideally to three three-phase resistive conductors including their protective sheaths, extending at least over a part of the liner's length.

Description

BOTTOM HEATER FOR HORIZONTAL OIL WELLS

[0001] The present invention relates to a downhole heater for oil extraction in horizontal wells. The heating cables in the heater have high electrical insulation and very high mechanical strength. They are arranged to minimize their cross-section, thus freeing the annular space for the passage of the fluidized oil required for extraction by the pumping equipment. Scope of application of the present invention:

[0002] It is well known that extracting hydrocarbons from horizontal wells requires drilling wells with two distinct sections: a vertical section and a horizontal section. The vertical section is the drilling necessary to reach the formation at a sufficient depth and is generally lined with casing. The horizontal section is the truly productive part.

[0003] The horizontal section is lined with a perforated pipe, called a "liner", which allows the fluid to enter and be pumped and extracted, resulting in a large area of ​​pipe exposed to the entry of oil from the geological formation, and consequently better production is achieved.

[0004] When crude oil is highly viscous, it has difficulty flowing into and along the liner. One solution to this problem, as is known in the industry, is to make the oil more fluid. Of all the solutions that make oil more fluid and that are known in the art, such as the injection of polymers, water vapor, or the use of electric heaters, the present invention focuses on the use of electric resistance heating, and therefore in what follows only this method of heating crude oil will be referred to.

[0005] According to the present invention, to heat the crude oil, a power cable is lowered through the tubing and connected to at least one heating cable attached to the pump rod. However, implementing this second solution is not simple because it requires running the heater to the horizontal section of the well and placing it inside the liner, i.e., the perforated pipe, since installing it externally is impossible given that it is embedded in the rock formation.

[0006] Before beginning installation, the sucker rods are prepared by attaching the heating cable and, optionally, the temperature sensor cable, if required, as this is a common practice. The tubing is removed beforehand if it is in the well. The rods, joined with adapter couplings, are hung below the pump or, if necessary, below the tubing if it is outside the liner and in the casing section. They are then lowered with the production tubing and the heater's power cable attached to them, until the rods are inside the liner. Finally, the wellhead is sealed, and the installation is ready. The heater's power supply is connected, and extraction operations begin. of the crude oil. It should be clarified that the rod in this case is used merely as an element on which to mount the heater and does not have the function of operating the pump. A small-diameter pipe can also be used interchangeably. The term “rod” will be used hereafter, but this term also includes the aforementioned small-diameter pipe, since the only function of this rod according to the invention is to provide support for the heating conductors.

[0007] The problems that the present invention solves are mainly three: a) it allows three resistive conductors to be derived from the power cable, for example, a three-phase cable, that is, conductors physically separated and at a distance from each other, each acting as an electrical resistance arranged along the liner in the required extension or length, delivering the amount of heat uniformly and continuously within the geological formation to decrease the viscosity of the crude oil uniformly.b) It features a cross-section of the resistive or heating conductors distributed in such a way as to leave the cross-section of the annular clearance within the liner with the least possible impediment to the free passage of the oil or crude to be extracted; c) in turn, it introduces a support rod or upright shaft around which the three resistive conductors are arranged, so that by being separated, one is prevented from overheating the other, dissipating the heat energy uniformly.

[0008] For the purposes of the present invention, and without this being mandatory or limiting its scope, it is advisable to use the teachings of Publication AR116183 A1, from the same applicant. According to the construction offered in said patent application, the support rod incorporates centralizers, defined by sets of radial fins linked to the rod's periphery, which allow it to be centered within the liner, or also potentially within an additional protective tube that can be housed inside the liner depending on the design, leaving a substantially uniform annular clearance that allows the housing, within the liner or the additional tube, as applicable, of the heating conductors, possibly associated with the temperature sensors, without risk of jamming or stresses that could cause the cables to break. According to this construction method, the resistive conductors are placed individually between each pair of centralizing fins, which act as separators for said conductors.

[0009] The inner diameter of the liner will dictate the limits of the material that can be used, since there must be sufficient space for the heater, the temperature sensor(s), and, as already mentioned, a clearly open cross-section for the fluid to circulate without restriction. Objectives of the present invention:

[0010] The object of the present invention is a downhole heater for horizontal oil wells consisting of at least one electrical conductor arranged along a rod substantially coaxial to the liner in the horizontal portion of the wellbore for extracting crude oil from the formation. geological, with said conductor having the necessary and variable length for the reduction of the viscosity of the crude oil to be extracted.

[0011] The objective of the invention is that said at least one resistive conductor be a monofilament conductor made of an electrically conductive material, such as for example conductive polymers or metal alloys.

[0012] The objective of the invention is to provide three conductors powered by a three-phase source, physically separated from each other by a sufficient distance to prevent one conductor from overheating the adjacent one, thus distributing heat evenly. Single-phase power is possible, as this is technically feasible, but consideration must be given to phase balance in installations requiring higher power, such as those described below.

[0013] The objective of the invention is to maximize the cross-section of each resistive conductor, allowing the circulation of a greater current intensity, with a larger heat exchange area without obstructing the interior of the liner, allowing the transfer of crude oil under the demand of the pumping equipment.

[0014] The objective of the invention is for the power cable to run down, linked to the tubing, to the vicinity of the bend where the horizontal liner coupling begins, where said power cable branches off into at least one resistive conductor, and ideally into three resistive conductors in parallel (three-phase power supply).

[0015] The objective of the invention is that each resistive conductor be coated with at least one PEEK sheath, which has the dual function of dielectric insulation and is inert to the action of HC

[0016] The objective of the invention is for the PEEK sheath to have an outer over-coating of ETFE or PFA (PerFluoroAlkoxy).

[0017] The objective of the invention is that, if necessary, an aluminum foil can be placed between the PEEK sheath and the over-cover sheath, defining a barrier against the gases present in the crude oil under extraction.

[0018] The objective of the invention is to provide a three-phase heating device capable of operating in an environment of up to 250ºC and pressures of 10,000 psi, with a maximum power of 300Kw and a maximum of 5,000V.

[0019] The objective of the invention is that each resistive conductor is located, separated from the other two conductors, between two centralizing fins, according to the constructions of publication AR116183A1, linked to the periphery of the coaxial support rod to the liner, preventing a resistive conductor from increasing the temperature of a second resistive conductor by proximity or direct contact of one on the other.

[0020] The objective of the invention is to house, preferably coaxially, a second auxiliary pipe for the protection of the heating conductors within the liner, this additional pipe also being provided with passages or perforations along at least part of its length. Description of the invention:

[0021] A DOWNHOLE HEATER FOR HORIZONTAL OIL WELLS, comprising a vertical borehole within which at least the tubing, with the wellhead and pumping devices and seals, is installed, the vertical borehole extending to a certain depth, from which the borehole has a curve that gives rise to a substantially horizontal section of borehole and penetrates the geological formation that contains the crude oil to be extracted, said horizontal section comprising at least one liner with perforations for the entry of the crude oil, the vertical section having the drop of an electrical power cable characterized in that in the vicinity of the curve in which the aforementioned vertical section of the borehole becomes a substantially horizontal section, said power cable is electrically connected to at least one resistive conductor which extends at least part of the length of the liner;Inside the liner, a longitudinal rod with a smaller inner diameter than the liner is arranged, defining an annular space between the inner surface of the liner and said rod. This rod constitutes a support axis on which at least one resistive conductor rests for retention. The cross-section of said resistive conductor is smaller than the cross-section of the annular gap, leaving free passage for the crude oil to be extracted. Said resistive conductor is surrounded by at least one PEEK electrical insulation sheath, which in turn is coated with a sheath of a fluoropolymer with high chemical resistance. List of representative figures of a construction of the present invention:

[0022] Figure 1 represents in a very schematic and simplified way, without any complementary accessories known in the art, a cross-section of a borehole with a vertical section, the bend and the horizontal section that penetrates the geological substrate for the extraction of crude oil, also schematically showing a preferred construction of the present invention using the separators or centralizing fins of the rod with respect to the inside of the liner;

[0023] Figure 2 illustrates in diametral section a construction of a resistive conductor of the invention in one of its possible constructions in which it can be seen that the conductor is coated by a PEEK sheath which in turn is coated by a second sheath of ETFE or PFA (PerFluoroAlkoxy) or some other equivalent fluoropolymer of high chemical resistance;

[0024] Figure 3 illustrates in cross-section another construction of a resistive conductor incorporating an aluminum foil barrier sheet against the gases present in the crude oil under extraction, arranged between the PEEK sheath and that of the ETFE or PFA.

[0025] Figure 4 shows section AA of Fig. 1, in a preferred construction of the invention, with three three-phase powered conductors, separated from each other and arranged on the centralized support rod using the teachings of publication AR116183A1.

[0026] Figure 5 shows another cross-section of a heating cable construction, coated only with a PEEK sheath.

[0027] Figure 6 shows the cross-sectional construction in which the second additional pipe is located, within which the rod, conductors, and separator fins are arranged, also employing the teachings of publication AR116183A1. Detailed description of preferred constructions of the invention:

[0028] To illustrate the preferred embodiments of the present invention, the following drawings are attached, along with the descriptions provided below. These examples should be interpreted as one of the many possible embodiments of the invention and should not be considered limiting. The scope of protection of the invention includes any means equivalent to those illustrated. The full extent of the present invention is defined by the first claim in the corresponding section of Claims. Furthermore, in these figures, the same references identify identical and / or equivalent means.

[0029] In Figure 1, (1) indicates a portion of the tubing that lines the vertical perforation of an oil well, the wellhead and all pumping accessories already known in the art having been omitted for the sake of simplicity in the aforementioned Figure 1.

[0030] According to the invention, at least one power cable (2), preferably a three-phase cable, is passed inside the tubing (1), even though the The present invention also achieves results with single-phase power. In what follows, the option of a three-phase cable is chosen. This three-phase power cable runs down to the bend (3) where, by means of a connector, it branches into three resistive conductors (4a, 4b and 4c) (See Fig. 4), of which in Fig. 1, to avoid obstructing the figure, one of them is generically represented with the reference (4).

[0031] El formato del cable de alimentación (2) preferiblemente es un conductor deThe copper conductor has a smaller cross-section than the resistive conductors (4). The power cable (2) is shielded, making it a single three-phase cable.

[0032] Resistive conductors (4) can be made of various materials / alloys depending on the power required (voltage and current), such as conductive polymers or metal alloys, this being indicated as a mere example.

[0033] As previously stated, conventionally, after the bend (3), a longitudinal and substantially horizontal section of a liner (5) is attached. This liner, as is known, is a conduit with a plurality of perforations (13) communicating with its interior, through which the crude oil being extracted passes. Within this liner (5), and according to the invention, a rod (6) is placed, or alternatively, an additional intermediate pipe (12) (See Fig. 6) can be used as protection if required by the design, without modifying the structure of the invention. This additional pipe is, in turn, slotted or has passages (14) communicating with its interior. This additional protective pipe (12) has as Its further function is to increase the weight of the assembly once the rod (6) is installed inside (12), along with the electrical conductors, if necessary to ensure that the pipe is lowered by its greater weight. It is generally preferred that (12) consist of a simple 2-inch tubing. 3 / 8 "or of 2 7 / 8 “.

[0034] As an example, each resistive conductor (4) is covered by a sheath of at least one inert material, preferably PEEK (see Fig. 5), specially adapted for extrusion over the conductor. The maximum permissible operating temperature is 250°C, with a maximum power of 300 kW. The maximum length of the heater is 2,500 meters, operating at a maximum voltage of 5,000 V. The maximum continuous operating temperature is 250°C. The tubing (1) can be 178 mm (7") conduit, and the power cable can have a total cross-section of 20 mm (7 / 8"). The tubing can be of any type. The casing can also be of any type, as standard combinations allow for the installation of the power cable. The liner cannot be smaller than 4.5" because otherwise, the equipment of the present invention cannot be housed within it.[0035} The diameter of the resistive conductors (4) totals up to 11 mm, making them suitable for installation in wells with limited space within the liner. The rod (6) is an elastically deformable component, with a diameter ranging (for this use) from 5 / 8" to 1" (16.1 mm to 25.4 mm) measured from its inner diameter. It is selected to leave a minimum clearance between the outer face of the heater and the inner surface of the liner (or auxiliary tubing) of 0.8 to 3 mm, preferably 1 mm, considering that the critical diameter occurs not in the rod itself but in its couplings, which are of a larger diameter. This rod (6). It accommodates the horizontal deviations of the liner (5) without fracturing, and can have, for example, up to 90º and in some cases, even greater deviations from the horizontal due to pressures in the geological layer.

[0036] Resistive conductors (4) are insulated heating wires that act as an electrical resistance that can take different values ​​depending on the application.

[0037] Figure 2 shows a cross-section of one of these conductors according to a construction of the invention. The figure shows the monofilament core (4) surrounded by a PEEK sheath (7). PEEK is the primary insulation. Its high chemical resistance and mechanical strength make it ideal for a demanding application such as this. Exposure temperatures can reach approximately 250°C, and the medium is petroleum. Furthermore, pressures at the formation level can be as high as 10,000 psi. This sheath (7) is in turn coated with a second sheath (8) of ETFE or PFA (PerfluoroAlkoxy) or some other equivalent fluoropolymer with high chemical resistance, which helps to create a first protective barrier against both the medium and dielectric properties, in addition to the PEEK. The PEEK sheath has a thickness ranging from 1 to 4 mm, which in turn is coated by the aforementioned sheath of high chemical resistance fluoropolymer, with a thickness ranging from 0.3 to 3 mm.

[0038] In Fig. 3, we observe another construction of the resistive conductor, in which an aluminum foil (9) is installed between the PEEK sheath (7) and the outer layer or sheath (8). This Al foil is helically wound like an aluminum Mylar film. Its sole function is to provide a barrier against gases that eventually find themselves in the well, preventing them from migrating to the interior of the resistance (4).

[0039] In summary, the downhole heater of the present invention has a much more robust structure and is based on PEEK insulation with a possible ETFE over-coating and the option of placing an aluminum foil in between if gas is present. The main feature is the use of PEEK as an insulator due to its chemical and, primarily, mechanical properties. PEEK is a polymer that, in this application, has the dual function of being a good dielectric (i.e., it prevents short-circuiting of the conductor (4) by contact with the metal parts (rod and liner)) and, at the same time, offers high mechanical strength, high hardness, and is inert to the corrosive action of hydrocarbons.

[0040] As previously mentioned, according to the invention, the function of the rod (6) is to provide an axially aligned support shaft with the liner (5), which is equipped with perforations or passages (13) and on which the conductors (4) are individually arranged. Ideally, though not exclusively, it is preferable to employ the principles of publication AR116183A1 of the same inventor and applicant, whereby (see Fig. 4) the rod (6) has a series of radial, centralizing fins (10) at regular intervals. Between each pair of fins (10) is arranged one of the structural conductors (4, 7) or (4, 7, 8) or (4, 7, 8 and 9), i.e., complete with its sheathing, preventing excessive proximity of the conductors from causing one to overheat due to direct heat transfer. The conductors (4) of the invention are installed individually and separately, one from the another around the shaft or rod (6), possibly with the centralizers (10). The optional temperature sensor(s) are indicated by (11).

[0041] Figure 5 shows a cross-section of a heating electrical conductor (4) with a single PEEK sheath (7).

[0042] In Figure 6, at an enlarged scale, we observe the liner (5), with the additional pipe (12) preferably coaxial arranged inside, with its passages (14) the rod (6), separators (10) and conductors (4) inside (12).

Claims

1 / 3 CLAIMS 1- BOTTOM HEATER FOR HORIZONTAL OIL WELLS, comprising a vertical borehole within which at least the tubing is installed, with the wellhead and pumping devices and seals; the vertical borehole extending to a certain depth, from which the borehole has a curve giving rise to a substantially horizontal section of borehole and penetrating the geological formation containing the crude oil to be extracted, said horizontal section comprising at least one liner with perforations for the entry of the crude oil, the vertical section having the drop of at least one electrical power cable characterized in that in the vicinity of the curve in which the said vertical section of the borehole becomes a substantially horizontal section, said power cable is electrically connected to at least one resistive conductor which extends at least part of the length of the liner;Inside the liner, a longitudinal rod with a diameter smaller than the inner diameter of the liner is arranged, defining an annular space between the inner surface of the liner and the said rod, said rod constituting a vertical axis on which the resistive conductor rests for retention and support, the cross-section of said resistive conductor being smaller than the cross-section of the annular gap, leaving free passage of the crude oil to be extracted; said resistive conductor is surrounded by at least one sheath of; 2 / 3 PEEK electrical insulation with a layer thickness ranging from 1 to 4 mm. 2- BOTTOM HEATER, as claimed in 1, characterized in that the electrical supply is three-phase, with three resistive conductors arranged on the support rod, each physically separated and spaced apart from the other on the periphery of said rod. 3- BOTTOM HEATER, as claimed in 1 and 2, characterized in that the diameter of the resistive conductors totals up to 11 mm, said rod constituting an elastically deformable component, with a diameter ranging from 5 / 8" to 1" (16.1 mm to 25.4 mm), measured from its internal diameter, determining an annular clearance between the external face of the rod and the inner surface of the liner with a diameter ranging from 0.8 to 3 mm.4- A BACKGROUND HEATER, as claimed in claims 1 to 3, characterized in that the material comprising each resistive conductor is chosen from conductive polymers or metal alloys, depending on the required power (voltage and current), the diameter of the resistive conductors being a total of 11 mm; the maximum permissible working temperature is 250°C, with a maximum power of 300 kW; the maximum length of the resistive conductors is up to 2,500 meters operating with a maximum potential difference of 5,000 V and a maximum continuous operating temperature of 250°C. 5- A BACKGROUND HEATER, as claimed in claims 1 to 4, characterized in that the support rod has separating fins arranged between the... 3 / 3 periphery thereof, the resistive conductors being placed individually between each pair of separating fins. 6- BOTTOM HEATER, as claimed in claims 1 to 4, characterized in that a second sheath of a chemically resistant fluoropolymer, with a thickness ranging from 0.3 to 3 mm, is coated over the PEEK sheath. 7- BOTTOM HEATER, as claimed in claims 1 to 6, characterized in that a gas barrier, including an aluminum foil wound between said two sheaths, is interposed between the PEEK sheath and the fluoropolymer sheath. 8- BOTTOM HEATER, as claimed in claims 1 to 7, characterized in that a second perforated conduit is arranged between the liner and the rod, within which the resistive heating conductors are accommodated, surrounding said rod.9- BOTTOM HEATER, as claimed in 8, characterized in that between the liner and the rod there is a second screened conduit, within which the separating fins are arranged with the resistive heating conductors surrounding the said rod and arranged separately between each pair of fins.

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