The invention concerns a process for producing energy in a hydrocarbon production installation, comprising:

- upward conveying of an hydrocarbon production flow from a reservoir in a production tubing of a production well located in a ground;

- heating a working fluid in an energy production cycle with thermal power transferred from the hydrocarbon production flow to form a heated working fluid;

- expanding the heated working fluid in an expansion machine to produce an expanded working fluid;

- recovering energy from the expansion machine;

- cooling the expanded working fluid in a condenser;

- raising pressure of the cooled expanded working fluid to regenerate the working fluid.

This process applies to onshore or offshore hydrocarbon production installations comprising production wells, in which a warm hydrocarbon production flow is conveyed from a downhole reservoir to the surface through a production tubing.

Hydrocarbon production from a well requires large amounts of energy. Although in some cases, the initial pressure of a reservoir may be high at the beginning of production, the pressure significantly decreases when the reservoir progressively depletes.

Consequently, in many instances, the hydrocarbon production flow has to be artificially lifted from the downhole reservoir to the surface of the well, and then, if the well is offshore, from the surface of the well to the surface of the body of water in which the well is located.

The artificial lift is generally provided by a downhole pump or/and by generating a gas under pressure, conveying it downhole to the production tubing, and injecting it to the production tubing.

Moreover, to enhance oil recovery, it may be necessary to feed pressurized water, pressurized viscosified water, heat (vapor, in situ heating), chemicals (such as surfactants, polymers ...) to the reservoir, via injection wells connected to the reservoir.

These operations require large amounts of energy. Energy is also needed for treating the hydrocarbon production flow at the surface, and for conditioning it before it is transported to the location of its refinery.

In the past, since the hydrocarbon production flow by nature contains a lot of chemical energy, the electrical energy necessary for utilities in wells of a field and around the wells has been produced by combustion of hydrocarbons, which may be derived from the hydrocarbon flow in a generator. However, the production of energy based on hydrocarbon combustion reduces the amount of hydrocarbons which are available for the final client, and hence the overall productivity and efficiency of the field.

Moreover, combustion of hydrocarbons in a generator produces greenhouse gases, whose emissions have to be reduced when possible.

Generally, the hydrocarbon production flow which is extracted from the reservoir is quite warm, since the reservoir is often located deep in the ground.

The hydrocarbon production flow therefore conveys a thermal energy, which is totally lost at the surface of the well.

In order to partially use this energy, FR 2 738 872 discloses an energy production installation located at the bottom of a body of water, the energy production installation using production lines laying on the ground at the bottom of the body of water.

A thermal cycle is carried out to recover heat from the fluid flowing in the production lines, to partially transform the heat into mechanical energy and/or electrical energy.

Such a process partially uses the hydrocarbon production flow thermal energy, but is not very efficient. Moreover, it requires very specific equipment to be placed around each production line, which is not always available on existing fields, or which significantly increases the cost of new production lines to install on the seafloor.

One aim of the invention is therefore to obtain an energy production process in a hydrocarbon production installation, the process optimizing energy recovery from the hydrocarbon production flow and limiting the amount of greenhouse gases which are produced, without disrupting production or requiring substantial modifications of the well architecture.

Another aim of the invention is to use the well as part of the thermal cycle system and reduce the footprint of such installation.

To this aim, the subject matter of the invention is a process for producing energy of the above mentioned type, characterized in that the well defines an annular space in the ground around the production tubing, the process comprising:

- transferring thermal power intended to heat the working fluid, from the hydrocarbon production flow to a fluid located in the annular space; and

- conveying the fluid in the annular space out of the well to form the working fluid circulating in the energy production cycle or to provide heat to the working fluid circulating in the energy production cycle.

The process according to the invention may comprise one or more of the following feature(s), taken alone, or according to any technical feasible combination: - the condenser is placed in heat exchange with a cold source at a surface of the well;

- the process comprises reinjecting in the annular space a fluid cooled with thermal power from the condenser, to regenerate the fluid located in the annular space, the fluid being preferentially reinjected without having its pressure increased in an pump;

- the fluid located at the bottom of the annular space is at least partially liquid, preferentially is totally liquid, and transferring thermal power from the hydrocarbon production flow to the fluid located in the annular space causes evaporation, preferentially via boiling, in the annular space of at least part of the liquid;

- the fluid located at the bottom of the annular space is in a supercritical state wherein transferring thermal power from the hydrocarbon production flow to the fluid located in the annular space causes expansion of the fluid located in the annular space and decrease of its density along the height of the annular space, without undergoing a phase change;

- the process comprises maintaining a liquid height of the fluid in the annular space greater than 1 m, and evaporating gas from the liquid;

- an evaporator preferentially having a boiler or a bubble bath, is formed at the bottom of the annular space at an outer surface of the production tubing;

- the fluid in the annular space is chosen among water, in particular brine, ammonia, at least a hydrocarbon, at least a hydrofluorocarbon, carbon dioxide or a mixture thereof;

- the production tubing defines an inner canal conveying the hydrocarbon production flow, the annular space being totally fluidly isolated from the inner canal;

- the fluid in the annular space is the working fluid circulating in the energy production cycle, the process comprising conveying the regenerated working fluid after compression to the annular space;

- the process comprises conveying the regenerated working fluid after compression to a lower region of the annular space by passing the regenerated working fluid through a conveying device arranged in the annular space, the conveying device preferentially being a tube;

- the process comprising continuously conveying the regenerated working fluid after compression to the annular space and continuously conveying the heated working fluid from the annular space to the expansion machine;

- the process comprises adapting the heated working fluid recovered from the annular space in an adaptation device before its introduction in the expansion machine, the adaptation comprising separating the heated working fluid recovered from the annular space into a gaseous working fluid introduced in the expansion machine and into a liquid working fluid, the liquid working fluid being optionally reinjected in the cooled expanded working fluid or being remixed in predetermined proportions with the gaseous working fluid;

- the fluid in the annular space is an intermediate working fluid circulating in an intermediate heat transfer cycle, the intermediate working fluid being separate from the working fluid;

- the process comprises placing in heat exchange relationship the intermediate working fluid and the working fluid in an intermediate heat exchanger, the intermediate working fluid heating the working fluid in the intermediate heat exchanger;

- the process comprises at least partially condensing the intermediate fluid in the intermediate heat exchanger and periodically pumping incondensable gaseous components in the intermediate heat exchanger;

- the process comprises an alternation of phases of:

^* conveying the heated intermediate working fluid out of the annular space to the intermediate heat exchanger, to cool and at least partially condense the intermediate working fluid by heat exchange with the working fluid circulating in the energy production cycle, without conveying the cooled and at least partially condensed intermediate working fluid in the annular space ; and of :

^* conveying the cooled and at least partially condensed intermediate fluid to the annular space without conveying the heated intermediate working fluid out of the annular space to the intermediate heat exchanger;

- the process comprises an alternation of phases of:

^* conveying the heated working fluid out of the annular space to the expansion machine, without conveying the cooled and at least partially condensed working fluid in the annular space; and of :

^* conveying the cooled and at least partially condensed working fluid to the annular space without conveying the heated working fluid out of the annular space to the expansion machine.

The invention also concerns a hydrocarbon production installation comprising:

- a well bored in the ground, the well comprising a production tubing upwardly conveying a hydrocarbon production flow from a reservoir;

- an energy production cycle comprising:

^* a heat transfer surface for heating a working fluid with thermal power transferred from the hydrocarbon production flow to form a heated working fluid;

^* an expansion machine for dynamically expanding the heated working fluid to produce an expanded working fluid;

^* an energy production machine coupled to the expansion machine ; ^* a condenser for cooling the expanded working fluid;

^* a region for raising pressure of the cooled expanded heat transfer to regenerate the working fluid; characterized in that the well defines an annular space in the ground around the production tubing, the production installation comprising:

- in the annular space, a surface for transferring thermal power intended to heat the working fluid, from the hydrocarbon production flow to a fluid located in the annular space, and

- equipment for conveying the fluid located in the annular space out of the well to form the working fluid circulating in the energy production cycle or to provide heat to the working fluid circulating in the energy production cycle.

The hydrocarbon production installation according to the invention may comprise one or more of the following feature(s), taken solely, according to any technical feasible combination:

- it comprises an evaporator preferentially having a boiler or a bubble bath, formed at the bottom of the annular space at the surface for transferring thermal power of the production tubing;

- the fluid in the annular space is the working fluid circulating in the energy production cycle, the installation comprising a device for conveying the regenerated working fluid from the top of the annular space to a lower region of the annular space;

- the installation comprises an adaptation device for adapting the heated working fluid recovered from the annular space before its introduction in the expansion machine, the adaptation device comprising a separating flask for separating the heated working fluid recovered from the annular space into a gaseous working fluid introduced in the expansion machine and into a liquid working fluid, the adaptation device optionally comprising a liquid working fluid expansion turbine to reinject the liquid working fluid in the cooled expanded working fluid or a remixer to remix the liquid working fluid with the gaseous working fluid in predetermined proportions;

- the fluid in the annular space is an intermediate working fluid separate from the working fluid, the installation comprising an intermediate heat transfer cycle in which the intermediate working fluid circulates, the intermediate heat transfer cycle comprising an intermediate heat exchanger to place in heat exchange relationship the intermediate working fluid and the working fluid and to heat the working fluid in the intermediate heat exchanger.

The thermal cycles used in the invention, depending on the working fluid that is chosen can either be classical thermal cycles (the cycle is outside the supercritical region), supercritical cycles (the cycle takes place inside the supercritical region) or transcritical cycles (the cycle takes place in the supercritical region and in the subcritical region).

The invention will be better understood, based on the following description, made in reference to the amended drawings, in which:

- figure 1 is a schematic sectional view of a first hydrocarbon production installation, in which a first process according to the invention is carried out;

- figure 2 is a detailed view of the intermediate heat exchanger of the installation of figure 1 ;

- figure 3 is a view analogous to figure 1 of a second installation for carrying out a second process according to the invention;

- figure 4 is a view analogous to figure 1 of a third installation for carrying out a third process according to the invention;

- figure 5 is a view of a detail of a production tubing used for carrying out a variant of the third process according to the invention ;

- figure 6 is a view analogous to figure 4 of a fourth installation for carrying out a fourth process according to the invention ;

- figure 7 is a view analogous to figure 4 of a fifth installation for carrying out a fifth process according to the invention.

A first energy production process according to the invention is carried out in a hydrocarbon production installation 10, schematically shown in figures 1 and 2.

The hydrocarbon production installation 10 is located onshore or offshore. In the latter case, the installation 10 is partly located at the bottom of a body of water 12 illustrated in figure 1 .

The hydrocarbon production installation 10 comprises at least a production well 14, and at least an energy production system 16 able to partially recover a thermal energy contained in the hydrocarbon production flow produced in the production well 14.

The production well 14 connects a downhole reservoir 18 located in a ground 20 to the surface 22 of the ground 20.

The surface 22 is located onshore, or at the bottom of the body of water 12, if the well 14 is located offshore.

As schematically represented in figure 1 , the production well 14 comprises a borehole 24 and a wellhead 26 closing the borehole 24 at the surface 22 of the ground 20. It comprises, inside the borehole 24, at least one production tubing 28, defining an annular space 30 around the production tubing 28, outside thereof. The production well 14 further comprises a lower packer 32 downwardly closing the annular space 30 around the production tubing 28. In most cases, the production well 14 comprises a casing 34 delimiting externally the borehole 24, at least in the upper region of the borehole 24.

The borehole 24 is here represented vertical. In variants (not shown), the borehole 24 comprises at least one section which is not vertical, for example inclined or horizontal.

The borehole 24 is upwardly closed by the wellhead 26. It fluidly communicates with the reservoir 18 in a lower region 42 located below the packer 32, advantageously through perforations 36 made in the casing 34, if a casing 34 is present.

In an open bore, it directly communicates with the reservoir 18 to receive a hydrocarbon production flow from the reservoir 18.

The production tubing 28 downwardly extends from the wellhead 26 to an open lower end 38 located below the packer 32, in fluid communication with the reservoir 18.

The production tubing 28 is preferentially made of an end-to-end assembly of metal tubes. The metal tubes of the tubing 28 tightly delimit an inner canal 40 inside the tubing 28 to convey the hydrocarbon production flow extracted from the reservoir 18 to the wellhead 26.

The inner canal 40, and the lower region 42 of the borehole 24 located below the packer 32 are tightly separated from the annular space 30. Therefore, any fluid recovered in the lower region 42 of the borehole 24 is guided to the inner canal 40 and cannot flow through the annular space 30.

Thus, the hydrocarbon production flow produced from the reservoir 18 exclusively flows through the inner canal 40 to the wellhead 26.

The annular space 30 is delimited internally by the production tubing 28 and externally by the casing 34 or by open ground. It is delimited downwardly by the packer 32 and upwardly by the wellhead 26.

The annular space 30 extends longitudinally over a depth that is greater than 10 m, in particular comprised between 10 m and 5000 m.

The annular space has a width, taken between the casing 34 and the tubing 28 generally greater than 1 cm, for example comprised between 2 cm and 5 cm, in particular between 2.4 cm and 2.6 cm.

In the example shown in figures 1 and 2, the energy production system 16 comprises an intermittent intermediate heat transfer cycle 50, intended to recover heat from the hydrocarbon production flow flowing in the inner canal 40 an to convey it to the surface 22. It also comprises an energy production cycle 52 thermally connected to the intermediate transfer cycle 50 to receive heat transferred from the hydrocarbon fluid via the intermediate transfer cycle 50 and to produce energy from the heat received from the intermediate transfer cycle 50.

The intermediate heat transfer cycle 50 comprises an intermediate working fluid 62, a downhole evaporator 60, formed in the annular space 30 of at least a production well 14, in which the intermediate working fluid 62 heats and at least partially evaporates.

The intermediate heat transfer cycle 50 further comprises an intermediate heat exchanger 64 with the energy production cycle 52, forming a condenser of the intermediate heat transfer cycle 50. The intermediate heat exchanger 64 is located out of the borehole 24, at the surface 22.

The intermediate heat transfer cycle 50 also comprises an inlet pipe 66, connecting the annular space 30 to the intermediate heat exchanger 64 to transport the heated and at least partially evaporated intermediate working fluid to the intermediate heat exchanger 64, and an outlet pipe 68 to evacuate a cooled and at least partially condensed intermediate working fluid from the intermediate heat exchanger 64 back to the annular space 30.

In this embodiment, the intermediate heat transfer cycle 50 advantageously comprises at least a pump 70 mounted on the outlet pipe 68, and first and second control valves 72, 74, respectively mounted on the inlet pipe 66, and on the outlet pipe 68.

The evaporator 60 formed in the annular space 30 comprises at least a heat transfer surface 76 formed by at least a lower section of the outside surface of the production tubing 28.

Heat contained in the hydrocarbon production flow flowing through the inner canal 40 is conducted to the heat transfer surface 76 to heat exchange with the intermediate working fluid in the annular space 30, in contact with the heat transfer surface 76.

The intermediate working fluid 62 is for example water, in particular brine. In a variant, the intermediate working fluid 62 comprises ammonia, at least a hydrocarbon, at least a hydrofluorocarbon, carbon dioxide or a mixture thereof. Examples of hydrocarbons are benzene, i-butane, n-butane, ethane, n-pentane, propane. Examples of hydrofluorocarbons are 1 ,1 ,1 ,2-tetrafluoroethane (R134a) or difluoromethane (R32). In a favorable choice, the heat transfer fluid has a boiling point comprised between 30°C and 100°C, in a most favorable choice between 40°C and 90°C.

In an embodiment, the intermediate working fluid 62 is in subcritical conditions in the annular space 30. At least part of the intermediate working fluid 62 in the annular space 30 is in a liquid phase.

Along the liquid height, the hydrocarbon production flow in the inner canal 40 transfers heat to the intermediate working fluid 62 to at least partially evaporate the liquid contained in the bottom part of the annular space 30. This produces a heated gaseous or at least partially gaseous intermediate working fluid, which is removed from the annular space 30 at the top of the annular space 30.

The height of liquid intermediate working fluid 62 in the annular space 30 is generally greater than 1 m, and advantageously ranges from 10 m to 1500 m. It can be up to the height of the annular space 30.

In a preferred embodiment, the intermediate working fluid 62 is able to form a boiling bath or “boiler” in the evaporator 60 at the bottom of the annular space 30 when receiving heat form the hydrocarbon production flow.

The position and height of the boiling bath are able to self-adjust according to the power needs extracted from the surface.

The intermediate working fluid 62 then undergoes boiling, which leads to a phase change from liquid to gas, with a significant decrease in density. The boiling generates gas bubbles which produce a natural agitation within the liquid. This is highly favorable to heat transfer and allows a significant decrease of the area of the heat transfer surface 76 needed to heat the fluid (for example from 100 to 1000 times less than without boiling).

In a variant, the intermediate working fluid 62 is in supercritical conditions in the annular space 30. The intermediate working fluid 62 merely expands in the annular space 30, significantly decreasing its density along the height of the annular space 30, without undergoing a phase change.

In the annular space 30, the intermediate working fluid 62 lifts in the gravity field, which leads to a decrease in hydrostatic pressure. The decrease is however limited by the low density of fluid.

This decrease is also accompanied by a pressure loss due to friction and in case of a subcritical fluid, by slip due to gas hold up.

At the top of the annular space 30, the intermediate working fluid 62 is either purely gaseous, diphasic, or supercritical. The phase composition of the intermediate working fluid 62 may also change along time, due to changing well conditions along time, as will be described below.

The inlet pipe 66 connects the annular space 30 to the intermediate heat exchanger 64. It is equipped with the first control valve 72.

The first control valve 72 is operable between an open position in which the intermediate working fluid flows from the annular space 30 to the intermediate heat exchanger 64 and a closed position which stops the flow of intermediate working fluid through the inlet pipe 66. As shown in figure 2, the intermediate heat exchanger 64 located out of the borehole 24 comprises a transfer vessel 80, an inner tubing 82 defining a heat exchange surface with the energy production cycle 52, and preferentially a purging system 83.

The vessel 80 has an upper inlet 84 in which the inlet pipe 66 emerges. In subcritical conditions, the heated working fluid 62 is introduced in the vessel 80 in a gaseous or biphasic form through the inlet 84.

The inner tubing 82 protrudes in the inner volume vessel 80 to allow contactless heat exchange between a fluid circulating in the inner tube 82 and the heated intermediate working fluid 62.

The heated intermediate working fluid is therefore able to provide heat to the fluid circulating in the inner tubing 82. It therefore cools down and advantageously condenses in the inner volume of the vessel 80.

The outlet 86 is located in a lower region of the vessel 80. It is connected to the outlet pipe 68. The outlet 86 is able to collect the fluid located at the bottom of the vessel 80, in particular the liquid collected at the bottom of the vessel 80. The outlet pipe 68 connects the outlet 86 to the top of the annular space 30. It is equipped with the second control valve 74 and with the pump 70 to pump the cooled and at least partly condensed intermediate working fluid to the annular space 30.

When the intermediate working fluid is reintroduced in the annular space 30, it undergoes a hydrostatic compression due to its fall in the gravity field. This compression is all the more strong as the density of the fluid has been previously increased, in particular by a phase change to liquid when subcritical, and when necessary, by recompression in the pump 70 (the pump 70 may be optional).

This increase is also accompanied by a pressure loss due to friction and in case of a subcritical fluid, by slip due to gas hold up.

The second control valve 72 is operable between an open position in which the intermediate working fluid flows from the intermediate heat exchanger 64 to the annular space 30 and a closed position which stops the flow of intermediate working fluid through the outlet pipe 68.

The control valves 72, 74 are able to be maneuvered between an alternation of condensation phases of the intermediate working fluid and regeneration phases of the intermediate working fluid. This allows a control of working fluid 62 height in the well 14.

In each condensation phase, the first control valve 72 is open and the second control valve 74 is closed. The heated intermediate working fluid is conveyed from the annular space 30 to the vessel 80, in which it cools down and at least partly condensates. When the level of liquid in the vessel 80 is beyond a predefined limit, a regeneration phase starts. In each regeneration phase, the first control valve 72 closes and the second control valve 74 opens to refill the annular space 30 with cooled and at least partially condensed intermediate fluid.

The height of liquid intermediate heat transfer in the annular space is hence controlled by the opening and closing of the valves 72, 74.

The purging system 83 is able to collect incondensable gases present in the upper gaseous atmosphere of the vessel 80, in particular during regeneration phases. It comprises a control valve 88, and a vacuum pump 91 able to evacuate the incondensable gases out of the vessel 80.

Moreover, the purging system 83 is able to manage pressure drop in the vessel 80. A chromatograph may be connected at the output of purging system 83 to characterize the compound collected and determine potential leaks.

The energy production cycle 52 comprises an evaporator formed by the intermediate heat exchanger 64 comprising the inner tubing 82. It further comprises an expansion machine 90 coupled to an energy production machine 92, a condenser 94 and when necessary, a pump 96.

It contains a working fluid. The working fluid is for example similar to the intermediate working fluid described above.

The working fluid is able to be heated in the inner tubing 82. It is then able to be expanded in the expansion machine 90 to produce mechanical work by rotation of the expansion machine 90.

The expansion machine 90 is for example a dynamic expansion turbine, when the working fluid fed to the turbine is monophasic, i.e. gaseous, supercritical. The expansion machine 90 is for example a multiphasic volumetric turbine such as a cavity or “Moineau” turbine when the working fluid fed to the expansion machine 90 is biphasic.

The expansion machine 90 is preferentially connected to an energy production machine 92. Typically, the machine 92 is able to produce electrical power from the rotation of a rotor of the expansion machine 90. It for example comprises an alternator mechanically coupled to a rotor of the expansion machine 90.

The condenser 94 is for example located in the ground 20 or at the surface of the ground 20 in the body of water 12 when the installation 10 is offshore. It is able to at least partially condense the expanded working fluid arising from the expansion machine 90.

The pump 96 is able to compress the cooled expanded working fluid to regenerate working fluid to be introduced in the inner tubing 82.

A first energy production process according to the invention will now be described. The process is carried out when the hydrocarbon production installation produces a hydrocarbon production flow. The hydrocarbon production flow circulates from the downhole reservoir 18 through the inner canal 40 of the production tubing 28, in the production well 14.

The hydrocarbon production flow is a warm source. When entering the inner canal 40, the hydrocarbon production flow has a temperature generally greater than 30°C and comprised between 40°C and 350°C.

In the production tubing 28, it heats the outer surface 76 and therefore transfers heat to the at least partially liquid intermediate working fluid 62 located in the bottom part of the annular space 30.

When in subcritical conditions, the intermediate working fluid 62 advantageously boils at the bottom of the annular space 30 and at least partially evaporates, leading to a significant density decrease. It lifts along the annular space and forms a pressurized gaseous intermediate working fluid in the upper part of the annular space 30.

In each condensation phase of the intermediate heat transfer cycle 50, the first control valve 72 located in the inlet pipe 66 is opened and the control valve 68 located in the outlet pipe 68 is closed.

The heated intermediate working fluid flows from the top of the annular space 30 through the inlet pipe 66 to the top of the intermediate heat exchanger 64.

In the intermediate heat exchanger, 64, the intermediate working fluid is placed in heat transfer with the fluid contained in the inner tubing 82 and cools by contact with the inner tubing 82. Preferentially, the intermediate working fluid at least partially condensates and forms a liquid which accumulates at the bottom of the vessel 80.

When the liquid level at the bottom of the vessel 80 increases beyond a predetermined height, a regeneration phase of the heat transfer cycle 50 is triggered.

The first control valve 72 in the inlet pipe 66 is closed. The second control valve 74 in the outlet pipe 68 is opened and the pump 70, if present, is activated to draw liquid contained at the bottom of the vessel 80 to the annular space and restore the level of liquid in the annular space 30.

As described above, in the annular space 30, the intermediate working fluid it undergoes a hydrostatic compression due to its fall in the gravity field.

When present, the purging system 83 is activated to evacuate the incondensable gases out of the vessel 80.

Another condensation phase is then carried out. At the same time, the working fluid circulating in the inner tubing 82 is heated by the heat transferred from the hydrocarbon production flow, via the intermediate working fluid 62.

The temperature of the working fluid at the inlet of the expansion machine 90 is for example greater than 10°C and comprised between 10°C and 80 °C.

The heated working fluid is expanded in the dynamic expansion machine 90 and releases energy to produce work.

The work produces movement of a rotor of the expansion machine 90 which is directly used as mechanical energy, or preferentially, which is transformed in electrical power by the energy production machine 92.

Then, the expanded working fluid is transferred to the condenser 94, in which it is cooled down by heat transfer with the cold ground 20 and/or with water of the body of water 12. It is then transferred to the pump 96 to be compressed and to regenerate working fluid.

The process according to the invention is therefore extremely efficient. It is able to collect thermal energy in the hydrocarbon production flow over a significant height of the production tubing 28 in the annular space 30.

Hence, a significant amount of thermal energy contained in the hydrocarbon production flow can be collected and used for producing mechanical energy or/and electrical power, which decreases the needs for electrical supply of the utilities around the installation 10.

The produced energy is directly recovered from the hydrocarbon production fluid. This reduces combustion of hydrocarbons due to production, hence reducing greenhouse gases produced by the installation 10.

The process according to the invention can be carried out in an existing production well 14, without having to significantly modifying the structure of the production well 14. The setting in place of the energy production system 16 only requires connecting the energy production system 16 to the annular space 30 of the production well 14. Therefore, the investment costs and the operation costs are small for the installation 10.

In a variant shown in figure 3, the energy production system 16 does not comprise an intermediate heat transfer cycle or an intermediate working fluid. The energy production cycle 52 is directly connected to the annular space 30 forming the evaporator of the energy production cycle 52. The working fluid circulating in the energy production cycle 52 is directly sampled from the annular space 30 and is directed to an expansion machine 90. The working fluid is as defined above. Depending on the phase composition of the working fluid at the inlet of the expansion machine 90, the expansion machine 90 is a dynamic expansion turbine when the working fluid is monophasic or supercritical or is a multiphasic volumetric turbine when the working fluid is biphasic.

The inlet pipe 66 equipped with the first control valve 72 is connected to the inlet or the expansion machine 90. The outlet pipe 68 equipped with the second control valve 74 connects the outlet of the pump 96 to the annular space 30.

The operation of the second process according to the invention comprises an alternation of condensation phases of the working fluid and of regeneration phases of the working fluid.

In each condensation phase, the first control valve 72 is open, and the second control valve 74 is closed. The pump 96 is inactive.

The working fluid is heated and at least partially evaporated preferentially through boiling in the annular space 30 by heat exchange with the hydrocarbon production flow along the heat transfer surface 76 of the production tubing 28. It is then directly sampled from the annular space 30 through the inlet pipe 66.

The working fluid is subsequently expanded in the expansion machine 90 to produce work which is converted in electrical power by the energy production machine 92. The expanded working fluid is cooled and at least partially condensed in the condenser 94, and collected in liquid form in the condenser 94.

The second control valve 74 being closed, and the pump 96 being inactive, liquid is prevented from being reintroduced in the annular space 30.

In each regeneration phase, when the liquid level in the condenser 94 increases above a predetermined level, the first control valve 72 closes, and the second control valve 74 is opens.

The pump 96 is activated to pump the liquid contained in the condenser 94 to the annular space 30. As described above, in the annular space 30, the intermediate working fluid falls in the gravity field and hence undergoes a hydrostatic compression.

The height of liquid working fluid in the annular space 30 is restored.

In a variant of the installation of figure 3, shown in figure 4, the energy production system 16 also only has an energy production cycle 52 without intermediate heat transfer cycle and without intermediate working fluid.

The working fluid which circulates in the energy production cycle 52 is provided from the annular space 30, as in the process of figure 3.

Contrary to the process of figure 3, the well further comprises a device 100 for conveying the regenerated working fluid from the pump 96 to a lower region 102 of the annular space 30. The conveying device 100 is here a tube connected at its upper end to the outlet pipe 68. The tube opens at its lower end in the lower region 102 of the annular space 30.

The tube is for example a coiled tubing pushed in place in the annular space 30.

In a variant, shown in figure 5, the conveying device 100 is a tube which is attached to the production tubing 28. The tube is then put in place when the production tubing 28 is lowered in the borehole 24, or when a replacement of the production tubing 28 is carried out. The setting up of the tube can then be done in the normal course of well maintenance, without affecting the structure of the well 14.

Contrary to the process of figure 3, the energy production cycle 52 continuously operates, thanks to the conveying device 100.

In operation, as described previously, the working fluid is heated and at least partially evaporated in the annular space 30 by heat exchange with the hydrocarbon production flow along the heat transfer surface 76 of the production tubing 28. It is also heated by thermal contact with the working fluid contained in the conveying device 100.

As described before, the working fluid is preferably able to form a boiling bath at the bottom of the annular space 30 when receiving heat form the hydrocarbon production flow.

The working fluid undergoes boiling, which leads to a phase change from liquid to gas, with a significant decrease in density. The boiling generates a natural agitation within the liquid.

In a variant, the working fluid is in supercritical conditions in the annular space 30. The working fluid merely expands in the annular space 30, significantly decreasing its density along the height of the annular space 30, without undergoing a phase change.

In the annular space 30, the working fluid lifts in the gravity field, which leads to a decrease in hydrostatic pressure.

The heated working fluid is extracted from the annular space 30. It is then conveyed to the expansion machine 90 where it is expanded to produce work.

The expanded working fluid is then directed to the condenser 94 to be cooled and at least partially condensed. The liquid working fluid collected in the condenser 94 is continuously pumped by the pump 96 to the conveying device 100. It travels in the conveying device 100 through the annular space 30 down to the lower region 102,

When the working fluid is reintroduced in the annular space 30, it undergoes a hydrostatic compression due to its fall in the gravity field, as described above.

The recycled liquid working fluid undergoes a liquid expansion at the bottom outlet of the conveying device 100. The expansion occurs inside the annular space 30 as the recycled liquid working fluid is injected in the liquid working fluid present at the bottom of the annular space 30.

This is due to two different pressure regimes present at the bottom outlet. A first pressure regime resulting from the liquid working fluid weight column in the conveying device 100. The second pressure regime results from the pressure reduction which the liquid working fluid undergoes in the annular space 30 resulting from evaporation in the subcritical state or from expansion in the supercritical space.

A variant of the installation of figure 4 is shown in figure 6. The installation 10 of figure 6 is adapted to the potentially changing phase content of the working fluid recovered at the top of the annular space 30. The working fluid can indeed be fully gaseous, in the supercritical state, or in a biphasic liquid-gas state.

The working fluid recovered from the annular space 30 may change over time during transient when starting the installation 10, during a change in the well production plan, or consecutively the progressive evolution of production conditions, for example, due to reservoir depletion and maturity of the field.

In addition, implementing the method according to the invention with effluent production wells from a reservoir underground induces a degree of uncertainty and variability (e.g. 20-30%) of the pressure conditions, flow and temperature of the system, particularly at the heat exchange surface 76 along the production tubing 28.

In addition, the hydrocarbon production wells often produce a multiphase effluent, which has an unstable flow regime, comprising successive plugs of vapor and liquid. The unstable flow regime may appear and settle over extended periods.

These successive plugs are progressively formed in the flow of effluent production from the well bottom to the surface. They are the result of sliding between the vapor and liquid phases induced in the effluent by gravity forces that generate accumulations, called "liquid hold-up" in the dynamic map of the flow.

The same phase-slip phenomena and liquid accumulation may occur in the working fluid raising in the annular space 30 in certain operating conditions of the well 14, and the working fluid many not be maintained monophasic when rising along the annular space 30.

As a difference to the installation of figure 4, the installation 10 of figure 6 further comprises an adaptation stage 120 interposed between the outlet of the annular space 30 and the expansion machine 90 to adapt the phase composition of the working fluid recovered from the annular space 30. It optionally comprises a working fluid heater 122 located between the annular space 30 outlet and the adaptation stage 120. The optional fluid heater 122 is configured to heat the working fluid before entering the adaptation stage 120 to dry it or even to overheat it. The working fluid hence moves away from its saturation curve to prevent any liquid condensation during its expansion in the expansion machine 90. This is in particular the case if the working fluid is water and ammonia. In variant, the use of organic working fluid reduces this tendency.

The optional fluid heater 122 advantageously comprises a heat exchanger and a heat source.

The adaptation stage 120 shown in figure 6 is adapted to an expansion machine 90 able to receive only a monophasic working fluid, such as a dynamic expansion turbine.

It comprises a separation flask 124 able to separate the working fluid in a gaseous working fluid 126 to be introduced in the expansion machine 90 and in a liquid recycle working fluid 128.

The adaptation stage 120 further comprises a liquid expansion turbine 130 able to expand the liquid recycle working fluid 128 and to redirect it to the pump 96, without passing through the expansion machine 90. Advantageously, the liquid expansion turbine 130 is coupled to the pump 96, to use the mechanical energy generated during the liquid expansion in the liquid expansion turbine 130 to at least partially power the pump 96.

Thanks to the adaptation device 120, the expansion machine 90 only receives the gaseous working fluid 126 at any time. The expansion machine 90 then expands the working fluid and directs it to the condenser 94.

In a supercritical regime, the whole working fluid is directed to the expansion machine 90, without separation in the separation flask 124.

The condenser 94 is able to let the working fluid release the heat remaining from the heat received at the bottom of the annular space 30.

In this example, the condenser 94 receives cooling thermal power from a cold source. The cold source is for example ambient air and the installation comprises an aero- coolant (not shown) which cools a cooling fluid circulating in a coil 132 inside the condenser 94.

Alternatively, the cold source is for example, the water current of a river, a lake or a body of water (sea, ocean, river, lake) in the case of offshore installations.

In subcritical conditions, de-superheating of the working fluid advantageously occurs if the working fluid leaves the expansion machine 90 dry and superheated, before the working fluid condensation begins in the condenser 94. During condensation in the condenser 94, the working fluid gives its latent heat to the coolant circulating in the coil 132. The condensed working fluid may be sub-cooled to acquire a lower temperature than at the end of the condensation. A lower temperature allows the working fluid to capture more heat in the boiler at the bottom of the annular space 30 in heat transfer with the production fluid stream.

In the case of a supercritical regime, no phase change occurs in the condenser 94. The condenser 94 is a mere heat exchanger and the working fluid only transfers its sensible heat to the coolant circulating in the coil 132. The density of the working fluid increases in the condenser 94.

When out of the condenser 94, the working fluid is totally in the liquid or supercritical state.

The working fluid out of the condenser 94 is then mixed with the expanded liquid working fluid arising from the liquid expansion turbine 130, before being pumped in the annular space 30 via the pump 96.

Figure 7 depicts a variant of the installation of figure 6. The expansion machine 90 of the installation 10 of figure 7 is a multiphase expansion machine, such as a volumetric or multiphase turbine, in particular a progressive cavity (or “Moineau”) turbine.

Such a multiphase expansion machine requires, in order to preserve its performance and its longevity, that the working fluid which enters the machine 90 contains a minimal fraction of liquid, for example at least 5% by volume.

Contrary to the installation of figure 6, the adaptation device 120 comprises a remixer 140 to remix a determined amount of liquid working fluid 128 recovered at the bottom of the separation flask 124 in the gaseous working fluid 126 recovered at the top of the separation flask 124.

The remixer 140 for example comprises a suction nozzle having a Venturi to accelerate the gaseous working fluid and to suck the liquid working fluid in the gaseous working fluid. The working fluid generated in the remixer 140 then has liquid and gas phases in the required proportions to enter the expansion machine 90.

The adaptation device 120 also comprises a liquid level controller 142 to control liquid level in the separation flask 124. The liquid level controller 142 comprises a liquid level sensor 144 and a level control valve 146 able to control liquid flow to the remixer 140.

The separation flask 124 is able to absorb and capture any liquid plugs coming out from the working fluid recovered from the annular space 30. The liquid level controller 142 is able to form a buffer reserve of liquid, whose interface level is regulated by the level control valve 146. In case of a temporary or non-temporary supercritical regime of the working fluid exiting the annular space 30, the expansion machine 90 is also suited to receive the working fluid. The adaptation device 120 becomes inactive and is ready to operate as soon as a biphasic subcritical regime reappears

The processes of figures 4 to 7 are particularly efficient, since they do not comprise an intermediate heat recovery cycle 50 and they are able to continuously operate.

The installations 10 to carry out these processes also have a very simple structure, and only require a single working fluid.

The installations 10 are able to co-produce chemical energy (resulting from hydrocarbons) and mechanical energy via a di-thermal cycle (Rankine or equivalent).

The expansion of the working fluid is advantageously valued in an expansion machine 90 (e.g. expansion turbine for monophasic flows or progressive cavity turbine for diphasic flows), without necessarily controlling the temperature and phase composition of the working fluid, which can depend on the effluents produced in the well 14.

The installation 10 takes advantage of the length of the production tubing 28 to capture excess thermal power from the fluid circulating in the production tubing 28 when an annular space 30 exists between the production tubing 28 and the casing 24.

Therefore, no heat exchanger is needed at the surface of the well 14 for capturing the thermal energy.

In addition, the depth of the well 14 inherently generates a conversion of thermal power transferred to the working fluid into mechanical power by a two-phase or supercritical thermosiphon effect applying on the working fluid while it lifts to the surface of the well 14.

Similarly, the recompression of the cooled working fluid essentially takes place through its fall in the annular space 20, hence reducing, even sometimes canceling the need for pumping.

Furthermore, the thermal power is captured deep in the annular space 30, as close as possible to the production reservoir, which constitutes a hot source for the installation 10.

The installation 10 is able to be implemented in existing wells 16 without requiring significant and/or expensive modification.

As a result, it is a viable solution for recovering excess thermal energy from producing wells 14 by co-producing carbon-free electrical or mechanical energy (exergy) from the production fluid circulating in the wells 14. It also allows high temperature wells 14 to be refrigerated, in order to reduce the constraints and design costs of downhole systems. In practice, the structure of the well 14 is affected only by the presence of the conveying device 100, which can be introduced as a coiled tubing or in connection with the production tubing 28 as shown in figure 5.

In a variant (not shown), at least part of the energy necessary to run the pump 70, 96 is taken from the expansion machine 90.

In another variant (not shown), the installation 10 is without a recirculation pump 70, 96. The hydrostatic pressure developed by the fall of the working fluid in the liquid state (condensed state) in the annular space 30 in the conveying device 100 is then greater than or equal to the hydrostatic pressure required for lifting of the expanded working fluid in the annular space 30.

The recirculation pump 70, 96 can be omitted thanks to a combination of an appropriate choice of the working fluid and of the outlet pressure so that the latter is sufficiently dense due to its cooling to allow gravity to achieve the pressure required at the bottom of the well. The working fluid is dense enough for gravity to carry out sufficient compression it as it descends to the bottom of the well without the need for a pump 70, 96 at the surface before it is re-injected into the well.

The choice may be constrained by temperature at the outlet of the condenser and therefore by the available cold source and the pressure at which the condenser operates.

In an additional variant (not shown), the liquid expansion which the compressed working fluid undergoes at the bottom outlet of the conveying device 100 is used to power a bottom generator for producing electrical power, or a bottom pump for pumping a production fluid in the production tubing 28.

More generally, the process and installation according to the invention is able to withdraw heat from a fluid vein of a producing well, at the bottom of the well. This allows recovering the excess heat from the fluid vein, while cooling the fluid vein. An evaporator 60, preferentially having a boiler or bubble bath is formed in the well 16 at the external wall of the tubing 76 in a conventional and simple completion design, including in transcritic conditions. The position and amplitude of the bubble bath in this active process step is self-adjustable at any time, without significant performance degradation as a function of the power need extracted from the surface.

As such, the process and installation according to the invention allow recovery of thermal energy from producing wells to be profitable and thus contribute to reduction of green house gases emissions and zero carbon energy production.