WO2022079039A1

WO2022079039A1 - Downhole cooling system

Info

Publication number: WO2022079039A1
Application number: PCT/EP2021/078201
Authority: WO
Inventors: Marek GEBURA; Vladimir SKOKAN; Barbora KALNICKA; Pavol MARCISOVSKY; Tomas ILIT; Fernando Lopez-Parra; Lubomir DUNAJCIK; Tomas CIBULKA
Original assignee: Ga Drilling, A.S
Priority date: 2020-10-12
Filing date: 2021-10-12
Publication date: 2022-04-21
Also published as: GB202016180D0; GB2599733A

Abstract

Described is a system for cooling a component configured to perform an operation at a subterranean location in a wellbore, the system comprising: a reactor at the subterranean location; and first and second conduits in fluid communication with the reactor and configured to deliver a flow of first and second reactants respectively to the reactor at the subterranean location; the reactor being configured to promote intermixing of the first and second reactants so as to encourage a chemical reaction therebetween, wherein at least one of the first and second conduits are configured to supply a flow of at least one of the first and second reactants to the reactor from the surface of the wellbore.

Description

DOWNHOLE COOLING SYSTEM

FIELD OF THE INVENTION

This invention relates to downhole tools and other components, in particular to the cooling of such tools and components.

BACKGROUND

Deep boreholes can have relatively high natural or static temperatures. Such temperatures may, for example, be greater than 175 °C. These temperatures can cause degradation and unreliability of components used downhole. Components such as electronics and polymer parts are especially susceptible to degradation at elevated temperature. These problems are intensified when certain unconventional drilling systems are used downhole. Thermal-based drilling systems such as plasma drilling generate heat. This can increase the borehole temperature significantly above its static temperature.

One approach to managing high borehole temperatures during drilling is to return the drilling tool to the surface to cool down or for repair. This is undesirable because it requires costly tripping of the tool and results in considerable downtime.

Techniques for cooling the borehole have been proposed. One example is to circulate cooling fluid from the surface to the drilling site. However, this can require very high fluid flow rates to achieve adequate levels of cooling. Another example is to use a Peltier unit near the drilling site to absorb heat. However, the Peltier unit itself consumes energy which means that its effect is limited.

The situation is even more complex when drilling for geothermal energy, particularly when temperatures downhole exceed supercritical water conditions (> 374 °C at the required pressures). These temperatures may greatly exceed the design and working conditions of available power electronics. Few electronic parts can work at these temperatures for more than few hours. Moreover, heat dissipation from the rock mass can increase the temperature of fluids flowing downhole, which reduces their cooling ability when they reach the drilling site. There is also a limited number of non-metallic functional materials that can be utilized in drilling systems under such conditions. This means that hardware suitable for operating tools with electronics under such conditions is very limited.

Other previous approaches have used thermal insulation of the drill pipe, as described in US 9,140,077 B2. The endothermic reaction of encapsulated reactants has been used to cool components of downhole tools, as described in US 10,337,300 B2 and WO 2015/034537 A1. However, such systems may provide only a limited cooling effect and may require long trip times, at considerable cost to the operation, to recharge the encapsulated fluids.

It is desirable to develop an improved system for cooling components downhole.

SUMMARY

According to one aspect there is provided a system for cooling a component configured to perform an operation at a subterranean location in a wellbore, the system comprising: a reactor at the subterranean location; and first and second conduits in fluid communication with the reactor and configured to deliver a flow of first and second reactants respectively to the reactor at the subterranean location; the reactor being configured to promote intermixing of the first and second reactants so as to encourage a chemical reaction therebetween. At least one of the first and second conduits may be configured to supply a flow of at least one of the first and second reactants to the reactor from the surface of the wellbore.

The system may comprise a first reactant supply configured to supply a flow of the first reactant to the reactor via the first conduit; and a second reactant supply configured to supply a flow of the second reactant to the reactor via the second conduit; wherein the first and second reactants are capable of reacting together endothermically.

According to another aspect there is provided a system for cooling a component configured to perform an operation at a subterranean location in a wellbore, the system comprising: a reactor at the subterranean location; first and second conduits in fluid communication with the reactor and configured to deliver a flow of first and second reactants respectively to the reactor at the subterranean location; a first reactant supply configured to supply a flow of the first reactant to the reactor via the first conduit; and a second reactant supply configured to supply a flow of the second reactant to the reactor via the second conduit; wherein the first and second reactants are capable of reacting together endothermically.

The reactor may be configured to promote intermixing of the first and second reactants so as to encourage a chemical reaction therebetween. The reactor may be thermally coupled to a heat exchanger for transferring heat from the said component to the reactants and/or a product of their reaction.

The systems described above may have any of the following features.

The first and second conduits may be at least partially situated between the surface of the wellbore and the subterranean location.

The first and second conduits may be configured to supply a flow of the first and second reactants to the reactor from the surface of the wellbore.

The system may further comprise first and second reservoirs configured to store the first and second reactants respectively at the surface of the wellbore, the first and second reservoirs being in fluid communication with the first and second conduits respectively.

The system may be further configured to deliver a cooling medium for cooling the component.

The cooling mixture may be configured to flow through the system so as to extract heat from the cooling medium. The system may further comprise a heat exchanger, wherein the heat exchanger is configured such that the cooling mixture flows through the heat exchanger in a direction opposite to the flow direction of the cooling medium.

The reactor may comprise a reactor body and a reactor filling.

The reactor filling may comprise a plurality of bodies.

The system may further comprise a mixing unit configured to mix the first and second reactants in the reactor.

The system may further comprise a control unit configured to control the mass flow rates and/or concentrations of the first and second reactants.

The system may further comprise a temperature sensor and the control unit may be configured to control the mass flow rates and/or concentrations of the first and second reactants in dependence on the temperature measured by the temperature sensor.

The temperature sensor may be configured to measure the temperature of the cooling medium. The control unit may be configured to control the mass flow rates and/or concentrations of the first and second reactants in dependence on the temperature of the cooling medium.

The temperature sensor may be located at a cooling medium outlet of a first submodule of the system.

The system may further comprise a thermal buffer configured to absorb heat from the cooling medium.

The thermal buffer may comprise a temperature controller body and a temperature controller filling contained within the temperature controller body. The temperature controller body may define at least one cooling medium distribution channel. The cooling medium may flow through the at least one cooling medium distribution channel.

The system may comprise at least one cavity between the temperature controller body and the at least one cooling medium distribution channel, wherein the at least one cavity contains the temperature controller filling.

The temperature controller filling may comprise a metallic material.

The temperature controller filling may comprise a eutectic alloy.

The first and second reactants may be one or more of a salt and water, barium hydroxide octahydrate crystals and dry ammonium chloride, ammonium hydroxide and water, ammonium chloride and barium anhydrite, thionyl chloride and cobalt(ll) sulfate heptahydrate, water and ammonium nitrate, water and potassium chloride and ethanoic acid and sodium carbonate, and water with carbon dioxide and chlorophyll.

The component may comprise one or more of a mechanical drill bit, a thermal-based drill bit, a plasma drill bit, a rotary steerable system, a measurement-while-drilling tool, a logging-whilst-drilling tool, a milling tool, a perforation gun, a drill collar, a stabilizer, a reamer, a hole-opener and a bit sub.

According to a further aspect there is provided a method of cooling a downhole component configured to perform an operation at a subterranean location in a wellbore, the method comprising: causing a flow of first and second reactants to a reactor; and mixing the first and second reactants in the reactor to form a cooling mixture for cooling the component; wherein the first and second reactants are capable of reacting together endothermically to form the cooling mixture.

According to a further aspect there is provided a system for cooling a component at a subterranean location in a wellbore, the system comprising: a reactor at the subterranean location; a first source comprising a first reactant, the first source being coupled to the reactor for supplying the first reactant to the reactor; and a second source comprising a second reactant, the second source being coupled to the reactor for supplying the second reactant to the reactor; wherein the first and second reactants are such as to react endothermically with each other for cooling the region of the reactor and the first and second reactants are different and are together selected from the members of a single one of the following groups: a. a salt and water; b. urea and water; c. barium hydroxide octahydrate and ammonium chloride; d. ammonium hydroxide and water; e. ammonium chloride and one or more of barium hydroxide and barium anhydrite; f. thionyl chloride and cobalt(ll) sulfate heptahydrate; g. ammonium nitrate and water; h. water, potassium chloride, ethanoic acid and sodium carbonate; and i. water, carbon dioxide and chlorophyll; j. an acid and sodium carbonate.

According to a further aspect there is provided a method for cooling a component at a subterranean location in a wellbore, the method comprising reacting in a reactor at the subterranean location a first reactant and a second reactant, the first and second reactants being such as to react endothermically with each other for cooling the region of the reactor and the first and second reactants being different and being together selected from the members of a single one of the following groups: a. a salt and water; b. urea and water; c. barium hydroxide octahydrate and ammonium chloride; d. ammonium hydroxide and water; e. ammonium chloride and one or more of barium hydroxide and barium anhydrite; f. thionyl chloride and cobalt(ll) sulfate heptahydrate; g. ammonium nitrate and water; h. water, potassium chloride, ethanoic acid and sodium carbonate; and i. water, carbon dioxide and chlorophyll; j. an acid and sodium carbonate. The acid may be ethanoic acid. The components may be stored locally to the reactor or supplied from the surface. Each reactant may comprise additional components beyond those listed above. The first component may be supplied to the reactor in liquid form either alone or with a carrier (e.g. as a suspension, solution or emulsion). The first component may be supplied to the reactor in gaseous or vapour form. The first component may be supplied to the reactor in solid form. The second component may be supplied to the reactor in liquid form either alone or with a carrier (e.g. as a suspension, solution or emulsion). The second component may be supplied to the reactor in gaseous or vapour form. The second component may be supplied to the reactor in solid form.

One or both of the reactants may comprise an additive such as a stabilising agent.

The cooling mixture may cool the component in one or more of the following ways. The cooling mixture may cool down the tool or component directly (for example, by flowing through or around the component). In other words, the cooling mixture may arrive at the region of the component or tool to be cooled at a temperature lower than that of the component or tool, and as a result of that temperature differential the cooling mixture may absorb heat from the component or tool. In this context, the or each reactant that reacts with the other reactant(s) to form the cooling mixture may arrive at the region of the tool or other component in the same chemical state as that in which it entered the borehole and/or flowed down the borehole. The or each component of the cooling mixture (i.e. the reactant(s)) may arrive at the region of the tool or other component unreacted with any other reactant that produces the cooling mixture. The region of the tool or component may be considered to be the region where effective thermal exchange between the tool or component and the cooling mixture can take place. Effective thermal exchange may be the exchange of between 5 and 500kJs^-1 when the system is in use. The cooling mixture may be in thermal contact with the tool or component. The cooling mixture may cool the component by cooling a cooling medium that cools the component. The cooling medium may be in thermal contact with the component. The cooling medium may be in thermal contact with the cooling mixture. The cooling mixture may flow through the system so as to extract heat from the cooling medium. The cooling mixture may cool the component by extracting heat from the surroundings of the component. The component may be a heat exchanger. The heat exchanger may be thermally coupled to a tool, e.g. by a metal link between the heat exchanger and the tool. The first and second reactants may react endothermically at the region of the tool or component, thereby reducing its temperature below that at which it arrived at the region of the tool or component. As a result of the temperature differential between the reacted mixture and the temperature of the tool or component, the cooling mixture may absorb heat from the tool or component. In this context the or each component (i.e. reactant) of the cooling mixture may arrive at the region of the tool or component in the same chemical state as that in which it entered the borehole and/or flowed down the borehole. One or more of the reactants may then react endothermically in the region of the tool or component.

BRIEF DESCRIPTION OF THE FIGURES

The present invention will now be described by way of example with reference to the accompanying drawings.

In the drawings:

Figure 1 shows an example of the cooling system described herein illustrated at a subterranean location in a wellbore during a downhole operation.

Figure 2(a) shows an example of an active cooling submodule of the cooling system viewed along its longitudinal axis.

Figure 2(b) shows a cross-sectional view of the active cooling submodule taken along G-G in Figure 2(a).

Figure 2(c) shows a cross-sectional view of the active cooling submodule taken along H-H in Figure 2(a).

Figure 3(a) shows an example of a passive temperature control submodule of the cooling system viewed along its longitudinal axis. Figure 3(b) shows a cross-sectional view of the passive temperature control submodule shown in Figure 3(a).

Figure 4 shows an example of a method of cooling a downhole component.

DETAILED DESCRIPTION

Figure 1 shows an example of a cooling system for a downhole component, such as a tool or other component, illustrated at a subterranean location in a wellbore. The system comprises a surface-controlled downhole continuous endothermic cooling system. In operation, a rig 101 provides power to drillstring 102, which may comprise coiled tubing, conventional drill pipe or a wireline connection or similar. The wellbore is shown at 103. The wellbore may be at least partially lined with casing 104 and cement 105. The drillstring may provide torque and/or power (for example, rotary, thermal, and/or electrical power) to the bottom hole assembly (BHA), shown generally at 106. The BHA may comprise a tool or other component. The tool may be a drilling tool. It may be a mechanical drilling tool, such as a rotary drilling tool or a reciprocating drilling tool. It may be a thermal drilling tool. It may be a plasma drilling tool. The tool may be a component that dissipates heat during drilling. It may be or comprise an electrical and/or electronic component such as a motor, transformer, electrical switching unit, plasma generator or electrical control unit.

The BHA comprises a cooling module. As will be described in more detail below, the cooling module comprises an active cooling module 107 and a passive temperature control module 108. Further tools or modules may be connected to the passive temperature control module 108 or to other parts of the drillstring or BHA. For example, module 109 in Figure 1 may comprise one or more downhole components such as a mechanical drill bit, a thermal-based drill bit, such as a plasma drill bit, a rotary steerable system (RSS), a measurement-while-drilling (MWD) or logging-whilst- drilling (LWD) tool, a milling tool, or a perforation gun. One or more such devices may constitute the tool or component discussed above. Drilling fluid can be pumped to the component and released into the annulus of the wellbore, as shown at 110. The drilling fluid 110 acts to extract cuttings to the surface.

The BHA can also comprise additional components such as drill collars, stabilizers, reamers, hole-openers and bit subs above or below the cooling module.

Reactants supplied to the cooling module are stored at the surface in a container or reservoir such as tank 111 and pumped to the tool by pump 112 via pipes 113, which connect to the drillstring to supply the reactants to the inlets of the cooling module downhole. There may be separate surface reservoirs and pumps for two or more reactants. The reactants are preferably liquids. One or more of the liquids may contain solid particles. The pipes may deliver specific mass flowrates and/or concentrations of the reactants in dependence on the temperature downhole, as will be described in more detail below.

As will be described in more detail below, the reactants are delivered from the surface to an active cooling module downhole where the reactants react together endothermically to form a cooling mixture. The cooling mixture may cool down the tool or component directly. For example, the cooling mixture may flow through, or around the component (i.e. the cooling mixture may be in thermal contact with the component). The cooling mixture may be a liquid. The cooling mixture may cool the component by cooling a cooling medium that cools the component (i.e. a cooling medium that is in thermal contact with the component). The cooling medium may be a liquid. The cooling mixture may flow through the system so as to extract heat from the cooling medium. The cooling mixture may cool the component by extracting heat from the surroundings of the component. The cooling medium may circulate between a first zone where it is substantially in thermal contact with the cooling mixture (before, during or after reaction thereof) and a second zone where it is in thermal contact with the tool or other component to be cooled. There may be a heat exchanger at the first zone configured for promoting heat exchange between the cooling mixture and the cooling medium. There may be a heat exchanger at the second zone configured for promoting heat exchange between the cooling medium and the tool or other component to be cooled. One example of the active cooling submodule 107 is shown in more detail in Figure 2(a). Cross-sectional views taken along G-G and H-H in Figure 2(a) are shown in Figures 2(b) and 2(c) respectively. The active cooling submodule 107 is mechanically connected to the passive temperature control submodule 108, which is arranged closer to the downhole tool or component to be cooled. As described above, the tool may be further mechanically connected to other module(s) in the direction from the transmission line to which the cooling module is mechanically connected.

The longitudinal axis of the submodule is shown as axis X1 . The longitudinal axis of the submodule is preferably parallel to the longitudinal axis of the drillstring.

As shown in Figure 2(a), in this example the main parts of the active cooling submodule 107 are a heat exchanger body 209 and a reactor body 215, which acts as a chemical mixing reactor.

In the active cooling submodule 107 of the example shown in Figures 2(a) to 2(c), two reactive chemical components are mixed, removing the heat from the surroundings and from a flowing cooling medium via an endothermic reaction. In this example, the active cooling module 107 receives two reactants. In other embodiments, the active cooling module may receive more than two reactants. The first reactant inlet is shown at 203 and the second reactant inlet is shown at 204. The first and second reactants are shown entering the module at E and F respectively. The first and second reactant inlets 203 and 204 are in fluid communication with first and second reactant supplies respectively. The first and second reactant supplies are configured to supply a flow of the first and second reactants to the reactor via the first and second inlets and first and second supply conduits that connect the inlets with surface reservoirs of the reactants as a part of the drill pipe and/or coiled tubing and/or wireline like connection of the tool or component with the surface.

Within the module 107, there are separate pipelines for each of the reactants. The first reactant pipeline 213 and the second reactant pipeline 214 are mechanically connected to the first reactant inlet 203 and the second reactant inlet 204 of the active cooling submodule, respectively. The pipelines 213 and 214 connect to the reactor via a first reactant reactor inlet 217 and a second reactant reactor inlet 218, respectively. The pipelines 213 and 214 of the first and second reactants are mechanically connected to and in fluid communication with the reactor body 215. The first and second reactants (and any additional reactants) are kept apart in their own separate pipelines prior to entering the reactor, so as to avoid premature reaction between the reactants.

The pipelines 213 and 214 act as supply conduits that are configured to substantially continuously supply the first and second reactants respectively to the reactor during a downhole operation. The supply of the reactants may not be a continuous flow but may instead be an intermittent flow, i.e. the supply may have short breaks or may supply the reactants in bursts having a certain frequency. However, the supply of the first and second reactants should be so as to be capable of providing continuous cooling to the downhole tool by supplying the reactants at the subterranean location on demand, as opposed to only a predefined amount of the reactants being available in the BHA, for example in an encapsulated chamber in the BHA.

At least one of the first and second reactants may be supplied to the reactor from the surface via at least one of the first and second conduits. The first reactant may be supplied from the surface, via either or both the first or second conduit, and the second reactant may be supplied from an encapsulated chamber in the BHA. Alternatively, the second reactant may be supplied from the surface, via either or both the first or second conduit, and the first reactant may be supplied from an encapsulated chamber in the BHA. It is also possible for both the first and second reactant to be supplied from the surface via the conduits.

The surface reservoirs of the reactants may be larger than an encapsulated chamber in the BHA. There may be less limitation on space for the surface reservoir compared to the space available for an encapsulated chamber in the BHA. Hence, providing a supply of the first and second reactants from the surface of the wellbore, instead of from an encapsulated chamber in the BHA, can enable a greater supply before the first and second reactants run out. This may enable the BHA to operate for longer without stoppages. This may enable the BHA to be smaller. This may enable the BHA to contain other components in place of an encapsulated chamber. Storing the first and second reactants at the surface may also be easier for controlling the conditions for the respective chemicals. At the BHA the conditions may constantly vary during operation. For example, an increase in temperature at the BHA may make it unsuitable for storing the first and second reactants for extended periods of time. Storing the reactants in the surface reservoirs may provide more suitable conditions for storing the reactants.

The first and second reactants may be supplied via the first and second supply conduits via fluid flow. The first and second reactants may be in contact with the inner wall(s) of the supply conduits during supply of the first and second reactants via the conduits. The first and second conduits may be designed in such a way so as to reduce the fluid friction caused by the first and second reactants interacting with the inner wall(s) of the supply conduits. In other words, the inner wall(s) of the conduits may comprise a low skin friction material.

Each of the first and second conduits may extend from a respective reservoir to the reactor body. The respective reservoir may be located at the surface or otherwise substantially proximally of the reactor body. Each of the first and second conduits may take the form of a pipe or a plurality of pipes running in parallel. Each of the first and second conduits may be capable of carrying a continuous flow of the respective reactant to the reactor body. The flow may suitably be of gaseous or liquid reactant or of a gaseous or liquid medium carrying the reactant (e.g. in suspension or solution). When each reactant is being conveyed in such a flow it may conveniently be in contact with an interior wall of the respective conduit. The apparatus may comprise one or more pumps communicating with the or each conduit for causing a continuous flow of the respective reactant(s).

Reaction of the reactants at the reactor body may occur at the same time as reactants are being conveyed to the reactor body. In this way, a continued cooling process may be implemented. The process may comprise delivering a continuous flow of the reactants to the reactor body via the first and second conduits. The continuous flow may be delivered over an extended period of time. The extended period of time may be greater than 10s, greater than 30s, greater than 60s, greater than 5 minutes or greater than 10 minutes. The process may comprise pressurising a column of one or both reactants for urging the column to flow to the reactor body. The column may be pressurised by a pump or by other means such as a stored volume of compressed gas. The pressurisation may result in an increased pressure and/or flow of the or each reactant than would result from gravity alone.

As reactants are being delivered to the reactor body they may be consumed and replenished with further reactant delivered via the conduits. In at least part of the process reactant may be continually consumed such that reactant consumed towards the end of that part of the process was not present in the borehole at the start of that part of the process. By cooling the drilling region using a flow of reactants from proximally in the drillstring, reactive cooling may be sustained over an extended period of time. This can increase the rate of drilling.

The drilling fluid and the cooling medium are shown entering the module 107 at A and D respectively. The active cooling module 107 comprises a drilling fluid inlet and outlet, shown at 201 and 202 respectively. The cooling medium inlet is shown at 205. The cooling medium supply channel is shown at 207, and the cooling medium outlet with temperature sensor is shown at 208.

The drilling fluid, otherwise known as drilling mud, may be a water-based fluid containing a clay, such as bentonite, to give it sufficient viscosity to carry rock cuttings to the surface. The drilling fluid may also contain a mineral such as barite to increase the weight of the column of drilling fluid in the borehole enough to stabilise the borehole. The drilling fluid may flow continuously through the system during the operation.

The cooling medium may be water or another suitable coolant. The cooling medium may flow continuously through the system during the operation. The cooling medium is in thermal contact with the component to be cooled. The cooling medium may, for example, flow through or around the component to cool the component.

As will be described in more detail below, the reactor is configured to promote intermixing of the first and second reactants so as to encourage a chemical reaction therebetween. The system may comprise a static mixing unit configured to mix the continuously delivered two or more reactants. The static mixing unit is preferably located in the reactor.

In the example shown in Figures 2(a) to 2(c), the reactor body 215 comprises a reactor filling 216 for promoting thorough homogenization of the reactants of the endothermic chemical reaction. The preferred aim is quantitative course of the endothermic chemical reaction (i.e., reaction to the maximum possible extent). The reactor filling 216 preferably comprises a plurality of bodies, preferably having a substantially spherical shape. The material of the bodies is heat-resistant, sufficiently chemically resistant, and inert; i.e. it cannot react chemically with the reactants or with the final product of the chemical reaction, or otherwise influence the course of the endothermic reaction. For example, the reactor filling may comprise an aluminium alloy, glass, or ceramic material.

The reactor body 215 is mechanically connected to and in fluid communication with the heat exchanger body 209. The heat exchanger body 209 comprises cooling mixture channels 211 that run parallel to the longitudinal axis of the device and end by cooling mixture outlet in a drilling fluid. The cooling mixture channels are preferably cylindrical and are preferably formed by drilling the channels into the heat exchanger body. The cooling mixture channels are preferably elongated in a direction parallel to the longitudinal axis of the module and are preferably distributed uniformly about the longitudinal axis of the module X1 .

The material of the heat exchanger body preferably has a high thermal conductivity, for example in excess of 20 W/mK at temperatures above 120 °C.

The cooling medium channel 212 runs parallel to the longitudinal axis of the active cooling module, through the heat exchanger and subsequently through the reactor. The cooling medium channel 212 is connected to the heat exchanger at the side of the cooling medium inlet 205 (at a border with a transmission line) by the cooling medium supply channel 207, wherein behind the supply channel, this channel branches within the heat exchanger body into at least two cooling medium distribution channels 210 running parallel to the axis of the device through the heat exchanger. Preferably, the cooling medium distribution channels 210 run generally parallel to the longitudinal axis of the device through the heat exchanger body and are preferably elongated in a direction parallel to the longitudinal axis of the module.

At the outlet of the heat exchanger, the cooling medium distribution channels 210 are preferably combined into one cooling medium channel 212, which runs parallel to a longitudinal axis of the device through the reactor, and out of the active cooling module. The active cooling module 107 is mechanically connected to the cooling medium supply channel 304 of the passive temperature control module 108 at the cooling medium outlet 208.

The first and second reactants of the endothermic chemical reaction enter the active cooling submodule from the transmission line via the first reactant inlet and the second reactant inlet, 203 and 204 respectively.

The reactants of the endothermic chemical reaction are transported in separate pipelines from the inlets 203, 204 of the first and second reactants to the rector body 215. The first reactant of the endothermic chemical reaction enters the reactor through the first reactant reactor inlet 217. The second reactant of the endothermic chemical reaction enters the reactor through the second reactant reactor inlet 218.

The components of the chemical reaction are mixed in the reactor, endothermically reacting with each other and forming a cooling mixture. The cooling mixture formed in the reactor removes heat from the surroundings and at the same time flows further into the heat exchanger. The cooling mixture removes the heat from the surrounding environment, i.e. from the reactor body and particularly from the heat exchanger body and the cooling medium, due to the reaction effect and its subsequent flow through the system.

The cooling mixture generally flows through the heat exchanger in a direction opposite to the flow direction of the cooling medium. The counter flow heat exchanger is therefore configured to allow the product of the two reacting components (the cooling mixture) to flow against the fluid that is being cooled by the reactants (the cooling medium). The heat exchanger may comprise temperature sensors for measuring the temperature of the different fluids in the system.

The cooling mixture flows through the cooling mixture channels 211 of the heat exchanger to the cooling mixture outlet 206, where it is released into the drilling fluid (A), where it is subsequently mixed with the drilling fluid flowing through the active cooling submodule from the inlet 201 to the outlet 202 of the drilling fluid.

Under normal operating conditions, the drilling fluid is in significant volume excess relative to the cooling mixture. Thus, the cooling mixture has minimal effect on the physical properties and function of the resulting fluid mixture. Therefore, the resulting mixture will be called drilling fluid hereafter. The cooling medium enters the active cooling submodule 108 via the cooling medium inlet and flows further to the heat exchanger. It transfers heat to the walls of the heat exchanger as it flows through the distribution channels of the heat exchanger, while the cooling medium itself cools down.

Released heat from components of the tool is continuously absorbed by the cooling mixture flowing through the heat exchanger in the direction opposite to the flow direction/flow of the cooling medium. This counter-current cooling arrangement, with the cooling mixture flowing through the heat exchanger in the direction opposite to the flow direction/flow of the cooling medium, may enable continuous heat removal from the cooling medium (via the heat exchanger body) thus maximizing the cooling effect over time.

After leaving the cooling medium distribution channels 210, the cooling medium enters the cooling medium channel 212, where it continues to transfer its heat to the refrigerated walls of the cooling medium channel, thereby lowering its temperature. The cooling medium temperature is lower at the outlet of the active cooling module than at the inlet of the active cooling module. Subsequently, the cooling medium enters the passive temperature control module 108 via the cooling medium inlet 303.

The flow of reactants may be supplied to the tool continuously during the operation.

This has the advantage of cooling during the whole operation, without the need to trip to the surface to replenish the reactants, with continuous heat extraction and cooling downhole.

Advantageously, a control system can control the mass flow rates and concentration of the first and second (and any additional) reactants based on the temperature measured downhole inside the tool.

The cooling medium outlet temperature (at outlet 208, the outlet from the active cooling submodule) may be controlled by controlling or regulating the flowrates and/or concentration of the reactants. This regulation can be performed via a control system at the surface and/or by a downhole control unit equipped with valves. The system may be configured to adjust the flowrates and/or concentrations of the first and second (and any additional) reactants in dependence on the temperature of the component to be cooled.

The cooling system may therefore comprise a control system configured to control the mass flowrates and/or concentrations of the reactants based on the temperature measured inside the tool.

The tubes/pipes can deliver specific mass flowrates and concentrations of the two or more reactants as a part of the drill pipe and/or coiled tubing and/or wireline like connection of the tool with the surface.

The flow rate and/or concentration of the reactants may be dependent on the temperature of the tool. The temperature may be measured by a temperature sensor at the cooling medium outlet of the system, or at another suitable location within the system, or at the tool or component.

As described above, the cooling system described herein uses flows of two or more reactants that can be continuously pumped downhole during operation and undergo an endothermic reaction when mixed together. Some examples of reactants that may be used will now be described. In one example, the first reactant is urea and the second reactant is water. The urea may be further mixed with oil. This may prevent the urea from reacting prematurely. This combination of reactants is advantageous because water is being pumped into the wellbore anyway during normal operation, and using water as part of the reaction can therefore be economical,

Another example of the reactants is ammonium chloride and barium hydroxide octahydrate. Under ambient conditions, these reactants are powders. The powders can be dissolved in water or another solvent in order to pump them downhole.

The products of this reaction are barium chloride dihydrate (in the solid state), ammonia (in the gaseous state) and water (in the liquid state). The stoichiometry may be 1 :2mol => 1 :2:8mol. The endothermic reaction between these reactants is as shown below:

2NH₄ Cl(s) + Ba(OH)₂.8H₂O(s -► BaCl₂.2H₂O(s) + 2NH₃(aq) + 8H₂O(l)

Considering a power level of 100kW and a reaction time at room temperature of approximately 40s, the energy required is approximately 4000kJ. The molar enthalpy at room temperature is approximately 130kJ/mol. The maximum expected mass required for 100 kW cooling is approximately 0.5 kg/min ammonium chloride and 1.5 kg/min barium hydroxide octahydrate (both in solution in water). The approximate costs are 0.1 -0.2 EUR/min for ammonium chloride and 0.3-0.6 EUR/min barium hydroxide octahydrate.

Using these reactants, in laboratory experiments, an average temperature drop (A T) was measured to be approximately 44°C.

More generally, the first reactant may be NH4X where X is one Fl, Cl and Br. The second reactant may be Y(OH)_m.nH2O where Y is one of of Be, Mg, Ca, Sr, Ba. m is typically 2 but may be another number if Y is other than divalent, n may be any suitable value depending on the hydration state of the second component. If a product of the reaction is water, as in the example above, that can be advantageous since water is liquid, allowing it to contribute to the removal of other products of the reaction from the well bottom, and has a relatively high specific heat capacity.

Other examples of materials comprising the first and second reactants may include a salt, such as NaCI, and water, barium hydroxide octahydrate crystals and dry ammonium chloride, ammonium hydroxide and water, ammonium chloride and barium anhydrite, thionyl chloride (SOCI2) and cobalt(ll) sulfate heptahydrate, water and ammonium nitrate, water and potassium chloride and ethanoic acid and sodium carbonate, and water with carbon dioxide and chlorophyll. Generally, any two or more suitable reactants may be used that result in an endothermic reaction when mixed.

The passive temperature control module 108 is shown in Figures 3(a) and 3(b). The presence of this module in the BHA is optional. The incorporation of this additional module may be advantageous where the component is at least partially cooled by a cooling medium in thermal contact with the component. The addition of this module may help to provide an even and continuous reduction in the temperature of a continuously flowing cooling medium during the process. The additional advantage of the passive temperature control provided by the submodule is temperature stabilization at a safe level in the event of an unexpected cooling medium temperature increase above a critical value, thus gaining the time necessary for completing the work process and removing the equipment from a borehole without damaging it.

The main parts of the passive temperature control submodule 108 are a passive temperature controller body 307 wrapped in insulation 309 to suppress heat exchange between the controller body and the drilling fluid and passive temperature controller filling 306 contained in the body. As shown in the cross-sectional view of Figure 3(b), the passive temperature controller body 307 is placed centrally (in the radial direction, along the longitudinal axis X1 ) of the device. The passive temperature controller body 307 has an inlet 303 into the cooling medium supply channel 304, which is mechanically connected to the active cooling submodule 107, and an outlet, which is mechanically connected to a control module (not shown). The drilling fluid A flows from the drilling fluid inlet 301 to the drilling fluid outlet 302, through the passive temperature control submodule, around the passive temperature controller body 307.

Within the passive temperature controller body 307 at least one cooling medium distribution channel 305 runs in parallel with the axes of the device through the passive temperature controller body 307. In this example, the passive temperature controller has a plurality of cooling medium distribution channels 305. The at least one distribution channel is preferably formed by a pipe.

The passive temperature control submodule 108 is configured to extract the heat from the flowing cooling medium as a result of the change of state of the passive temperature controller filling 306 from the solid state to the liquid state, which prevents a further increase in the temperature of the cooling medium for some time period.

At least one cavity is formed between the wall of the passive temperature controller body 307 and at least one cooling medium distribution channel 305 within the passive temperature controller body 307. The or each cavity contains the passive temperature controller filling 306. The or each cavity is preferably hermetically and pressure-sealed in order to prevent leakage of the filling or mutual contact between the passive temperature controller filling and the cooling medium.

Preferably, the passive temperature controller filling 306 is made of a metallic alloy with a low melting point. The metallic alloy is preferably a eutectic alloy due to the very precise melting temperature of such alloys. It is beneficial to have an alloy with the highest possible latent heat of fusion. Suitably, the melting point of the passive temperature controller filling is lower than the design temperature of the components which require active cooling. For example, the low melting point metallic alloy may be Sn42Bi58, ln52Sn48, Sn90Bi9.5Cu0.5, Sn63Pb37, ln97AgO3, ln52Sn48, or Sn51 ,2Pb30.6Cd18.2. Preferably, the alloy has a melting temperature in the range from 90 to 240 °C.

The cooling medium enters the passive temperature control submodule 108 through the cooling medium inlet 303 and via the cooling medium supply channel 304 enters the passive temperature controller body 307, flows through the cooling medium distribution channels 305 in the passive temperature controller body and exits through the cooling medium outlet channel 308, which preferably incorporates a temperature sensor. Via the cooling medium outlet 308, the cooling medium exits the passive temperature control module 108 and enters the rest of the downhole tool or component.

The passive temperature controller body may be equipped with temperature sensors to measure the temperature of the fluids at various locations.

The cooling medium may have a different temperature at entering the body 306, and depending on its value, one of the following situations may occur:

If the cooling medium temperature is lower than the established critical temperature, the cooling medium can flow through the passive temperature control submodule without changing its temperature.

If the cooling medium temperature is equal to or higher than the critical temperature, the following processes can take place after the cooling medium enters the cooling medium distribution channels: the cooling medium having critical temperature transfers its heat to the colder passive temperature controller body at the contact

- subsequently, the passive temperature controller body transfers the heat to the passive temperature controller filling

- the heat received from the passive temperature controller body and from the cooling medium flowing through the passive temperature controller filling is used to change the state of the filling by consuming the latent heat of fusion.

Thus, the filling does not change its temperature unless all of the heat of fusion is consumed. Thanks to this effect, the cooling medium temperature increase can be slowed down, or even stopped, so as not to overcome the melting temperature of the filler. The filling based on a metallic and/or eutectic alloy is therefore configured to decrease, or even prevent, the temperature increase of the cooling medium through consuming the heat up to the latent heat of fusion.

The passive temperature control submodule therefore acts as a thermal buffer (or thermal battery) and may help to achieve a greater level of heat absorption per unit mass when used in addition to the active cooling submodule.

Figure 4 summarizes an example of a method of cooling a downhole component configured to perform an operation at a subterranean location in a wellbore. At step 401 , the method comprises causing a flow of first and second reactants to a reactor. At step 402, the method comprises mixing the first and second reactants in the reactor to form a cooling mixture for cooling the component. The first and second reactants are capable of reacting together endothermically to form the cooling mixture and may comprise any of the examples given above or other suitable reactants.

The cooling mixture may cool the component in one or more of the following ways. The cooling mixture may cool down the tool or component directly (for example, by flowing through or around the component) or may cool down a cooling medium that cools the tool or component. The cooling mixture may flow through the system so as to extract heat from the cooling medium. The cooling mixture may also cool the tool or component by extracting heat from the surroundings of the tool or component (to feed the endothermic reaction or via general heat flow from hot to cold).

The system described herein may allow for regulated during the whole drilling operation, resulting in continuous heat extraction and cooling effect downhole for tens up to hundreds of hours, with negligible or even without any waste heat incorporated.

Based on the temperature of the cooling medium entering and leaving cooling module downhole, the system or the operator (in this case manually) can increase/decrease the mass flow rate and/or concentration of the reactants and thus control the cooling power and temperature of the tool. This can be controlled in such a way that the temperature of the drilling tool does not exceed maximum defined temperature of the tool or BHA. The system may therefore provide continuous active cooling of critical downhole components during drilling of high-temperature-high-pressure (HTHP) wells. The system can provide localized heat extraction and cooling of one or more tools or components.

The heat extraction capability (cooling power) of the system may, in some implementations, be from 1 to 500 kW, with a temperature decrease ability (per specific mass flow) of approximately 1 to 40 degrees.

In the system described above with reference to Figure 1 , the operation is a drilling operation, preferably using a thermal-based drilling technique such as plasma drilling. In this case, the tool is a plasma drill bit. However, the cooling system described herein may be utilized in any other operation or situation where cooling of a tool or component is desirable. For example, in one embodiment, the cooling system may be used in a plug and abandonment operation, where at least a section of the steel casing lining the wellbore is removed, before plugging the well with a cement plug. In this case, the tool to be cooled may be a milling tool, such as a junk mill, section mill or taper mill.

The system may also be used to cool multiple tools in the BHA. For example, the BHA may comprise a drill bit, a RSS and a reamer. The cooling system described herein may be configured to provide active cooling to multiple ones of the plurality of tools in the BHA.

The system may be implemented in oil and gas drilling operations, geothermal drilling operations, plug and abandonment operations, or any other operation where cooling of a tool is desirable. The operation need not be subterranean.

The applicant hereby discloses in isolation each individual feature described herein and any combination of two or more such features, to the extent that such features or combinations are capable of being carried out based on the present specification as a whole in the light of the common general knowledge of a person skilled in the art, irrespective of whether such features or combinations of features solve any problems disclosed herein, and without limitation to the scope of the claims. The applicant indicates that aspects of the present invention may consist of any such individual feature or combination of features. In view of the foregoing description it will be evident to a person skilled in the art that various modifications may be made within the scope of the invention.

Claims

1. A system for cooling a component configured to perform an operation at a subterranean location in a wellbore, the system comprising: a reactor at the subterranean location; and a first conduit in fluid communication with the reactor and configured to deliver a flow of a first reactant to the reactor at the subterranean location; the reactor being configured to promote intermixing of the first reactant and a second reactant so as to encourage a chemical reaction therebetween; wherein the first conduits is configured to supply a flow of the first reactant to the reactor from the surface of the wellbore.

2. A system as claimed in claim 1 , comprising: a first reactant supply configured to supply a flow of the first reactant to the reactor via the first conduit; and a second reactant supply configured to supply a flow of the second reactant to the reactor via the second conduit; wherein the first and second reactants are capable of reacting together endothermically.

3. A system for cooling a component configured to perform an operation at a subterranean location in a wellbore, the system comprising: a reactor at the subterranean location; first and second conduits in fluid communication with the reactor and configured to deliver a flow of first and second reactants respectively to the reactor at the subterranean location; a first reactant supply configured to supply a flow of the first reactant to the reactor via the first conduit; and a second reactant supply configured to supply a flow of the second reactant to the reactor via the second conduit; wherein the first and second reactants are capable of reacting together endothermically;

26 wherein at least one of the first and second conduits are configured to supply a flow of at least one of the first and second reactants to the reactor from the surface of the wellbore.

4. A system as claimed in claim 3, wherein the reactor is configured to promote intermixing of the first and second reactants so as to encourage a chemical reaction therebetween.

5. The system as claimed in any preceding claim, wherein the first and second conduits are configured to supply a flow of the first and second reactants to the reactor from the surface of the wellbore.

6. The system as claimed in any preceding claim, wherein the system further comprises first and second reservoirs configured to store the first and second reactants respectively at the surface of the wellbore, the first and second reservoirs being in fluid communication with the first and second conduits respectively.

7. The system as claimed in any preceding claim, wherein the system is further configured to deliver a cooling medium for cooling the component.

8. The system as claimed in claim 7, wherein the cooling mixture is configured to flow through the system so as to extract heat from the cooling medium.

9. The system as claimed in claim 7 or claim 8, wherein the system further comprises a heat exchanger, wherein the heat exchanger is configured such that the cooling mixture flows through the heat exchanger in a direction opposite to the flow direction of the cooling medium.

10. The system as claimed in any preceding claim, wherein the reactor comprises a reactor body and a reactor filling.

11 . The system as claimed in claim 10, wherein the reactor filling comprises a plurality of bodies.

12. The system as claimed in any preceding claim, wherein the system further comprises a mixing unit configured to mix the first and second reactants in the reactor.

13. The system as claimed in any preceding claim, wherein the system further comprises a control unit configured to control the mass flow rates and/or concentrations of the first and second reactants.

14. The system as claimed in claim 13, wherein the system further comprises a temperature sensor and the control unit is configured to control the mass flow rates and/or concentrations of the first and second reactants in dependence on the temperature measured by the temperature sensor.

15. The system as claimed in claim 14 as dependent on claim 7, wherein the temperature sensor is configured to measure the temperature of the cooling medium and the control unit is configured to control the mass flow rates and/or concentrations of the first and second reactants in dependence on the temperature of the cooling medium.

16. The system as claimed in claim 15, wherein the temperature sensor is located at a cooling medium outlet of a first submodule of the system.

17. The system as claimed in any of claims 7 to 9 or any of claims 10 to 16 as dependent on claim 7, wherein the system further comprises a thermal buffer configured to absorb heat from the cooling medium.

18. The system as claimed in claim 17, wherein the thermal buffer comprises a temperature controller body and a temperature controller filling contained within the temperature controller body.

19. The system as claimed in claim 18, wherein the temperature controller body defines at least one cooling medium distribution channel.

20. The system as claimed in claim 19, wherein the system comprises at least one cavity between the temperature controller body and the at least one cooling medium distribution channel, wherein the at least one cavity contains the temperature controller filling.

21. The system as claimed in any of claims 18 to 20, wherein the temperature controller filling comprises a metallic material.

22. The system as claimed in any of claims 18 to 21 , wherein the temperature controller filling comprises a eutectic alloy.

23. The system as claimed in any preceding claim, wherein the first and second reactants are one or more of: a salt and water; urea and water; barium hydroxide octahydrate crystals and dry ammonium chloride; ammonium hydroxide and water; ammonium chloride and barium anhydrite; thionyl chloride and cobalt(ll) sulfate heptahydrate; water and ammonium nitrate; water and potassium chloride and ethanoic acid and sodium carbonate; and water with carbon dioxide and chlorophyll.

24. The system as claimed in any preceding claim, wherein the component comprises one or more of a mechanical drill bit, a thermal-based drill bit, a plasma drill bit, a rotary steerable system, a measurement-while-drilling tool, a logging-whilst-drilling tool, a milling tool, a perforation gun, a drill collar, a stabilizer, a reamer, a hole-opener and a bit sub.

25. A method of cooling a downhole component configured to perform an operation at a subterranean location in a wellbore, the method comprising: causing a flow of first and second reactants to a reactor; and mixing the first and second reactants in the reactor to form a cooling mixture for cooling the component; wherein the first and second reactants are capable of reacting together endothermically to form the cooling mixture.

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26. A system for cooling a component at a subterranean location in a wellbore, the system comprising: a reactor at the subterranean location; a first source comprising a first reactant, the first source being coupled to the reactor for supplying the first reactant to the reactor; and a second source comprising a second reactant, the second source being coupled to the reactor for supplying the second reactant to the reactor; wherein the first and second reactants are such as to react endothermically with each other for cooling the region of the reactor and the first and second reactants are different and are together selected from the members of a single one of the following groups: a. a salt and water; b. urea and water; c. barium hydroxide octahydrate and ammonium chloride; d. ammonium hydroxide and water; e. ammonium chloride and one or more of barium hydroxide and barium anhydrite; f. thionyl chloride and cobalt(ll) sulfate heptahydrate; g. ammonium nitrate and water; h. water, potassium chloride, ethanoic acid and sodium carbonate; and i. water, carbon dioxide and chlorophyll; j. an acid and sodium carbonate.

27. A method for cooling a component at a subterranean location in a wellbore, the method comprising reacting in a reactor at the subterranean location a first reactant and a second reactant, the first and second reactants being such as to react endothermically with each other for cooling the region of the reactor and the first and second reactants being different and being together selected from the members of a single one of the following groups: a. a salt and water; b. urea and water; c. barium hydroxide octahydrate and ammonium chloride; d. ammonium hydroxide and water;

30 e. ammonium chloride and one or more of barium hydroxide and barium anhydrite; f. thionyl chloride and cobalt(ll) sulfate heptahydrate; g. ammonium nitrate and water; h. water, potassium chloride, ethanoic acid and sodium carbonate; and i. water, carbon dioxide and chlorophyll; j. an acid and sodium carbonate.

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