Subsurface hydraulic storage system and method

Abstract

A subsurface hydraulic energy storage system includes a reservoir configured to store a downhole fluid, a turbine coupled to a generator, and an electrical submersible pump (ESP) installed at a target depth in a wellbore in a geological formation. Geothermal heat from the downhole fluid is configured to drive the turbine and the generator, and the generator is electrically connected to an electrical network. The ESP is electrically connected to a power control system electrically connected to the electrical network. The ESP is in fluid communication with the reservoir, and the ESP is configured in an active mode to utilize electrical power from the electrical network to pump the downhole fluid having the geothermal heat from the geological formation to the reservoir.

Description

SUBSURFACE HYDRAULIC STORAGE SYSTEM AND METHODCROSS-REFERENCE TO RELATED APPLICATION

[0001] The present disclosure claims priority from US Prov. Appl. No. 63 / 592254, filed on October 23, 2023, entitled “Subsurface Hydraulic Storage System and Method,” which is herein incorporated by reference in its entirety.BACKGROUND

[0002] Geothermal plants have recently gained momentum in view of their ability to provide power to an electrical network with minimal carbon dioxide emissions. The variability of electricity demand is rarely aligned with the variability of electricity supply, particularly with electricity supply originating from low carbon dioxide sources. Periods of peak electricity supply may not align with periods of peak electricity demand. Geothermal plants may provide electricity to an electrical network with lower variability than other sources. It is desirable to improve the applicability of geothermal plants to provide electricity to the electrical network.BRIEF SUMMARY

[0003] A subsurface hydraulic energy storage system includes a reservoir configured to store a downhole fluid, a turbine coupled to a generator, and an electrical submersible pump (ESP) installed at a target depth in a wellbore in a geological formation. Geothermal heat from the downhole fluid is configured to drive the turbine and the generator, and the generator is electrically connected to an electrical network. The ESP is electrically connected to a power control system electrically connected to the electrical network. The ESP is in fluid communication with the reservoir, and the ESP is configured in an active mode to utilize electrical power from the electrical network to pump the downhole fluid having the geothermal heat from the geological formation to the reservoir.

[0004] A method of operating a subsurface hydraulic energy storage system in an active mode and a passive mode are described herein. During the active mode of operation, the system lifts a downhole fluid from a target depth in a wellbore in a geological formation into a reservoir using an electrical submersible pump (ESP). Lifting the downhole fluid includes driving the ESP with lifting electricity provided by an electrical network. The downhole fluid has geothermal heat, and the system drives a turbine connected to a generator with the geothermal heat to producegeothermal electricity that is provided to the electrical network. The geothermal electricity is greater than the lifting electricity. During the passive mode of operation, the system directs a return flow of the downhole fluid from the reservoir to the geological formation through the ESP, thereby driving the ESP to produce downhole electricity that is provided to the electrical network.BRIEF DESCRIPTION OF DRAWINGS

[0005] In order to describe the manner in which the above-recited and other features of the disclosure can be obtained, a more particular description will be rendered by reference to specific implementations thereof which are illustrated in the appended drawings. For better understanding, the like elements have been designated by like reference numbers throughout the various accompanying figures. While some of the drawings may be schematic or exaggerated representations of concepts, at least some of the drawings may be drawn to scale. Understanding that the drawings depict some example implementations, the implementations will be described and explained with additional specificity and detail through the use of the accompanying drawings in which:

[0006] FIG. 1 is an embodiment of a subsurface hydraulic energy storage system coupled to an electrical network in an active mode; and

[0007] FIG. 2 is an embodiment of the subsurface hydraulic energy storage system coupled to the electrical network in a passive mode.DETAILED DESCRIPTION

[0008] On FIG. 1, a subsurface hydraulic energy storage system 111 according to the disclosure is shown. As discussed herein the subsurface hydraulic energy storage system 111 includes a geothermal plant that includes a wellbore 102 drilled in the geological formation 100 for extracting a warm fluid (generally brine) from a geological formation 100. The wellbore 102 may be drilled primarily for geothermal purposes or repurposed from another purpose, such as hydrocarbon extraction. In some embodiments, a portion of a wellbore in a depleted, non-producing, or non- profitable hydrocarbon reservoir may be utilized for geothermal energy production. An electric submersible pump (ESP) 104 is located downhole in the wellbore. The ESP 104 includes a pump, i.e., a centrifugal pump, and a motor powered and controlled from the surface 130 by a power control system 106 that is connected to the ESP 104 via downhole electrical lines 108.

[0009] In a first, active, mode of operation shown on FIG. 1, the pump is configured to lift downhole fluid, such as hot brine, from the formation 100 to the surface, for instance from a depleted reservoir 103. The arrows 105 illustrate the flow of downhole fluid into the wellbore 102. The downhole fluid is generally a hot downhole fluid, such as hot brine. Temperatures of the hot brine in the depleted reservoir 103 may be between approximately 80-200°C.

[0010] At surface, the system includes downhole fluid circulation system that includes the wellbore, and a downhole fluid circuit 112 situated at surface 130 and connected to a reservoir 124 (e.g., storage tank). The downhole fluid circuit 112 includes a heat exchanger 114 configured to exchange geothermal heat between the downhole fluid (e.g., hot brine) and a working fluid 115 in a working fluid circuit 116. In some embodiments, the heat exchanger 114 is configured to reduce the temperature of the downhole fluid to ambient surface temperature, such as approximately 5-35 °C. In some embodiments, the reservoir 124 may be insulated.

[0011] The working fluid 115 may include, but is not limited to water, water-glycol mixture, carbon dioxide, ammonia, or another working fluid capable of absorbing heat from the downhole working fluid and operating within the working fluid circuit 116. In some embodiments, the working fluid is a refrigerant. In some embodiments, the working fluid circuit 116 is configured to operate in a thermodynamic cycle (e.g. Rankine cycle, Stirling cycle) transfer geothermal heat from the downhole fluid to electrical energy (e.g., electricity), such as via turbomachinery and a generator.

[0012] In another embodiment, the reservoir 124 may be a second wellbore. The second wellbore may be more shallow than the wellbore 102 (i.e., wherein the fluid is displaced to a depth inferior to the depth of the wellbore 102). For example, wellbore 102 may be to a target depth of approximately 5000 to 10000 ft, and the second wellbore maybe to a target depth of approximately 500 to 3000 ft. The ESP may be positioned at or near the target depth to facilitate pumping the downhole fluid at the target depth to the surface 130. In some embodiments, the second wellbore may include a surface reservoir or near-surface storage reservoir, such as a salt dome or other geological feature. If the formation is over-pressured, the system may work as described in relationship with FIG. 1. The temperature conditions of the second wellbore may be nearer to the ambient surface temperature than the temperature conditions of the wellbore 102. In another embodiment, another ESP may be disposed in the second wellbore and associated to a secondpower control system as discussed in relationship with the ESP that has been already described. Thus, a second ESP may be used to displace the fluid stored in the second wellbore at the surface.

[0013] In the active mode of operation shown on FIG. 1, the hot downhole fluid exits from the wellbore via a well head 110 and enters the downhole fluid circuit 112. The temperature of the hot downhole fluid may be greater than 80 °C, 95 °C, 100 °C, 125 °C, 150 °C, 175 °C, 200 °C or more. Heat is exchanged between the hot downhole fluid extracted from the geological formation and the working fluid. At the exit of the heat exchanger, the downhole fluid circuit is cooled to approximately ambient surface temperature and stored into the reservoir 124. Due to the heat received from the downhole fluid, the working fluid may be heated to approximately the temperature of the hot downhole fluid at the well head 110. In some embodiments, the working fluid vaporizes. For example, the working fluid entering the heat exchanger 114 may be water, and the working fluid exiting the heat exchanger 114 may be steam. In some embodiments, the working fluid circuit 116 is a closed loop circuit independent that only exchanges heat (i.e., geothermal heat) with the downhole fluid 105.

[0014] Downstream of the heat exchanger 114, the working fluid circuit 116 includes a turbine 118 that is driven by the vaporized working fluid. The turbine 118 is configured to drive a generator 120, such as via a common shaft. In the active mode of operation shown in FIG. 1, the turbine 118, and therefore generator 120 (in particular a rotor of the generator 120), are driven in rotation by the vaporized working fluid, and the generator 120 produces electricity (e.g., geothermal electricity). The electricity may be supplied to an electrical network 122, or a local electrical energy storage system 123. The working fluid circuit 116 may also include a condenser 117 to condense the working fluid downstream of the turbine 118. In some embodiments, the condenser 117 condenses and cools the working fluid by air cooling, evaporative cooling, or heat exchange with a cold reservoir. In some embodiments, a cooled portion of the downhole fluid from the reservoir 124 may be used to condense the working fluid. The same working fluid may be reused to vaporize and drive the turbine 116 again. It may for instance be pumped from the condenser using a pump 119.

[0015] The generator 120 is connected to the electrical network 122, such as the electrical network. The generator 120 sends electricity (e.g., geothermal electricity) to the electrical network 122 for consumption by loads connected to such network 122. In an embodiment, the generator 120 may be connected to a supply power control system 107 to condition and provide electricitysuitable for the electrical network 122. The supply power control system 107 may include a variable speed drive (VSD) to control properties of the electricity (e.g., frequency, current, voltage) supplied into the electrical network 122.

[0016] In some embodiments, the electrical network 122 is connected to a geothermal plant power control system 106 that powers the ESP 104 so that the ESP operation is a load to the electrical network 122. The geothermal plant power control system 106 may include a VSD to efficiently control power (e.g., lifting electricity) supplied to the ESP 104. The geothermal electricity harvested from the subsurface hydraulic energy storage system 111 may partially or completely offset the lifting electricity used by the ESP 104 to pump the downhole fluid 105. In some embodiments, the generator 120 or a local electrical energy storage system 123 (e.g., battery) may be configured to power the ESP 104, thereby reducing or eliminating any loading by the subsurface hydraulic energy storage system 111 on the electrical network 122.

[0017] FIG. 1 therefore describes an active mode of operation of the subsurface hydraulic energy storage system 111 where lifting electricity is utilized to lift the hot downhole fluid 105 from the formation 102, and geothermal electricity is generated through heat exchange of the hot downhole fluid with a working fluid in a thermodynamic cycle. Such mode of operation that may utilize power input from the electrical network 122 may for instance be used during night / low power need periods. In some embodiments of the active mode, the subsurface hydraulic energy storage system 111 provides 50%, 75%, 100%, 150%, or 200% or more power to the electrical network 122 than is utilized to lift the hot downhole fluid 105.

[0018] FIG. 2 describes a second, passive, mode of operation of the subsurface hydraulic energy storage system 111. In the passive mode of operation, the cold downhole fluid stored into the reservoir 124 is directed back into the geological formation 100 via the downhole fluid circuit 112 and wellbore 102. Such operation may be controlled through the geothermal plant power control system 106. After the ESP 104 stops pumping the downhole fluid 105 to the surface, the downhole fluid 105 will drop due to gravity, requiring no additional power. That is, the downhole fluid 105 may return to the geological formation 100 from the reservoir 124 due at least in part to a siphon. However, in other embodiments, such operation may be controlled using additional flow control elements (such as additional pumps and / or valves) depending on the configuration at the wellsite. The cold downhole fluid 125 is then directed back into the primary circuit 112, the wellhead 110, and the ESP 104 to return to the geological formation 100. The cold downhole fluid 125 isaccelerated through the wellbore 102 due to gravity. The ESP centrifugal pump 104 and motor are reversible and operate as a turbine connected to a generator. Thus, the ESP 104 and motor may generate electricity (e.g., downhole electricity) that is injected to the electrical network via the downhole electrical lines 108 and geothermal plant power control system 106. Furthermore, the downhole fluid 125 returned into the geological formation 100 will warm and increase the availability of hot downhole fluid 105 during subsequent operation in the active mode of operation.

[0019] Preferably the power control system 106 includes a variable speed drive (VSD) to control the flow of electricity injected (a) into the electrical network in the passive mode of operation, and (b) into to the ESP 104 in the active mode of operation.

[0020] The passive mode of operation may be used during the day / peak power need periods of the electrical network 122, thereby enabling the subsurface hydraulic energy storage system 111 to generate electricity on demand without CO2 emissions or power consumption. While operating in the passive mode of operation, the working fluid circuit 116 may be idled. In some embodiments while operating in the passive mode, the subsurface hydraulic energy storage system may provide electricity (e.g., downhole electricity) to the electrical network via the ESP without drawing any electricity (e.g., lifting electricity) to actively drive any fluid systems (e.g., pumps).

[0021] The subsurface hydraulic energy storage system 111 may include a control device including one or more processors for switching the subsurface hydraulic energy storage system 111 between the two modes of operations that have been described, for instance based on an electrical load of the network that is measured by sensors of the control device 128 and / or communicated to the control device. The control device 128 is configured to provide instructions to the geothermal plant power control system 106 and the supply power control system 107 based at least in part on an electrical load on the electrical network 122. The control device 128 may utilize one or more thresholds to control operation of the subsurface hydraulic energy storage system in the active mode or the passive mode. For example, a first threshold may be based on one or more of a peak loading of the electrical network, a time of day, an availability of other electricity providers to the electrical network, or any combination thereof. In some embodiments, the first threshold may be 75%, 50%, 25% or less of a peak loading of the electrical network 122. For example, the control device 128 may switch to the active mode of operation when the load on the electrical network 122 is less than 50% of the peak loading of the electrical network 122, thereby avoiding increasing the load on the electrical network 122 with lifting electricity foroperation of the ESP 104. In some embodiments, the first threshold may be the peak loading hours of the day, such as noon until 8 pm. Thus, the control device 128 may switch to the active mode of operation during off-peak loading hours, and switch to the passive mode of operation during peak loading hours. In some embodiments, the first threshold may be the availability of wind, solar, or battery storage to provide lifting electricity for operation of the ESP 104. Thus, the control device 128 may switch to the active mode of operation when additionally available low-emission power generation on the electrical network 122 is sufficient to provide the lifting electricity for operation of the ESP 104. The control device may be situated on site or remotely, and control the ESP - via the geothermal plant power control system 106, valves, and other pumps of the system to operate the subsurface hydraulic energy storage system in the desired mode of operation.

[0022] Overall cycle efficiency is a function of losses (fluid friction losses, electrical joule losses in the reservoir, well, ESP and binary plant) and the thermal to electrical conversion efficiency.

[0023] Assuming flowing 100,000 barrels per day (bpd) in a wellbore where the water table (and ESP) is 1km below surface, and conventional pump, motor and cable / drive efficiencies, such a system may generate about 1.4MW.

[0024] In the case where the reservoir 124 is a second wellbore including an ESP (i.e., second ESP), in the first mode of operation, the fluid is stored in the second wellbore. The second ESP operates as a turbine and downhole electricity may be recovered from the second ESP as described hereinabove. That is, gravity on the fluid flowing into the second wellbore may accelerate the fluid through the second ESP, thereby driving the ESP and the connected motor to generate downhole electricity. As may be appreciated, the downhole electricity generated from fluid flow into the second wellbore at a more shallow depth may be less than downhole electricity that is generated from fluid flow into the first wellbore at a greater depth. Such downhole electricity from the second ESP may be reinjected to the electrical network 122 via the geothermal plant power control system associated to such second ESP. In the second mode of operation, the fluid stored in the second wellbore may be pumped to the surface 130 using lifting electricity to the second ESP. The lifting electricity utilized to operate the second ESP in the second mode of operation is lower than the lifting electricity to the first ESP in the first mode of operation as the second wellbore is shallower than the first wellbore. Once at the surface, the fluid drops into the first wellbore as explained hereinabove.

[0025] The examples hereinabove have been provided for a binary-cycle power plant. The turbine 116 may be fluidly connected to the working fluid circuit and fluidly isolated from the downhole fluid. However, a plant working in the two modes of operations outlined above may be designed for other types of power plants, such as dry steam or flash power plant. In such scenarios, the downhole fluid is the working fluid, the turbine therefore if fluidly connected in the downhole fluid circuit, and the reservoir is situated at the exit of the turbine 118. In such embodiments, the downhole fluid exiting the turbine 118 may be directed to the reservoir 124 by a first conduit, and a second conduit may connect the reservoir 124 to the wellhead 110 for return of the cold downhole fluid.

[0026] The present disclosure relates to systems and methods for planning a well according to any of the following:

[0027] Clause 1 : A subsurface hydraulic energy storage system including an electrical submersible pump (ESP) installed at a target depth in a wellbore drilled into a geological formation, and electrically connected through electrical lines extending in the wellbore to a power and control system, wherein the power and control system is electrically connected to an electrical network, a space for storing downhole fluid, wherein the storing space is situated at the surface or downhole; a downhole fluid circulation system, configured so that the ESP and the storage tank are in fluid communication, and allowing the downhole fluid to flow from the ESP to the storage space and from the storage space to the ESP; and a turbine and a generator, wherein the turbine is configured to drive the generator, and wherein the generator is electrically connected to the grid.

[0028] Clause 2: The subsurface hydraulic energy storage system from clause 1, configured so that, in an active mode of operation, the electrical submersible pump is powered by the power and control system to lift a downhole fluid to the storage space.

[0029] Clause 3: The subsurface hydraulic energy storage system from clause 2, wherein the turbine is situated in the downhole fluid circulation system so that the turbine is driven by the downhole fluid.

[0030] Clause 4: The subsurface hydraulic energy storage system from clause 2, wherein the turbine is situated in a working fluid circulation system containing a working fluid so that the turbine is driven by the working fluid.

[0031] Clause 5: The subsurface hydraulic energy storage system from clause 4, wherein the working fluid circulation system and the downhole fluid circulation system circulate through a heat exchanger allowing heat exchange between the downhole and working fluids.

[0032] Clause 6: The subsurface hydraulic energy storage system from clause 5, wherein the heat exchanger is configured so that the working fluid vaporizes in the heat exchanger.

[0033] Clause 7: The subsurface hydraulic energy storage system from clauses 1-6, wherein, in a passive mode of operation, the fluid circulation system is operated to flow the downhole fluid from the storage space to the ESP so that the ESP is driven in rotation by the downhole fluid.

[0034] Clause 8: The subsurface hydraulic energy storage system from clauses 1-7, wherein the power and control system of the ESP comprises a variable speed drive (VSD).

[0035] Clause 9: The subsurface hydraulic energy storage system from clauses 1-8, wherein the generator is connected to a variable speed drive (VSD) and the VSD is connected to the electrical network.

[0036] Clause 10: The subsurface hydraulic energy storage system from clauses 1-9, wherein the fluid circulation system includes a first flow path for flowing the downhole fluid from the ESP to the storage space and a second flow path for flowing the downhole fluid from the storage space to the ESP.

[0037] Clause 11 : The subsurface hydraulic energy storage system from clauses 1-10, wherein the storage space includes a storage tank situated at surface.

[0038] Clause 12 The subsurface hydraulic energy storage system from clauses 1-10, wherein wellbore is a first wellbore and the storage space includes a second wellbore.

[0039] Clause 13: The subsurface hydraulic storage system from clause 12, wherein the ESP is a first ESP and the power and control system is a first power and control system and wherein the second wellbore includes a second ESP associated to a second power and control system.

[0040] Clause 14: The subsurface hydraulic storage system from clause 12, configured so that, in the passive mode of operation, the second electrical submersible pump is powered by the second power and control system to lift a downhole fluid to the surface.

[0041] Clause 15: The subsurface hydraulic storage system from clauses 12 or 13, wherein, in the active mode of operation, the second ESP is configured to be driven in rotation by the downhole fluid.

[0042] Clause 16: The subsurface hydraulic storage system from clauses 1-15, wherein the ESP includes a centrifugal pump and a motor configured to be reversibly operated as a turbine and a generator.

[0043] Clause 17: The subsurface hydraulic storage system from clauses 1-16, comprising a control device for switching between the active and passive mode of operations.

[0044] Clause 18: The subsurface hydraulic storage system from clause 17, wherein the control device is configured to switch between the active and passive mode of operations as a function of an electrical load of the electrical network.

[0045] Clause 19: The subsurface hydraulic storage system from clauses 17 or 18, wherein the control device includes the power and control system of the ESP, optionally the first and second power control systems.

[0046] Clause 20: The subsurface hydraulic storage system from any preceding clause, wherein the storage space is located downhole at a depth inferior to the target depth.

[0047] Clause 21 : A subsurface hydraulic storage method, including: in a first mode of operation: lifting a downhole fluid from a target depth in geological formation into a storage space situated at surface or downhole, using an electrical submersible pump (ESP); using a fluid to rotate a turbine connected to a generator, so that the turbine drives the generator, producing electricity, wherein said fluid is the downhole fluid or a working fluid that has been heated by the downhole fluid; injecting electricity produced by the generator into an electrical network; and in a second mode of operation: flowing the downhole fluid from the storage space to the ESP; driving the ESP with the downhole fluid flow so as to produce electricity; injecting the electricity produced by the ESP into the electrical network.

[0048] Clause 22: The subsurface hydraulic storage method of clause 21, wherein, in the first mode of operation, the ESP is powered by the electricity from the electrical network.

[0049] Clause 23: The subsurface hydraulic storage method of clauses 21 or 22, wherein, it comprises switching between the first and second mode of operation as a function of an electrical load of the electrical network.

[0050] Clause 24: The subsurface hydraulic storage method of clause 23, wherein the first mode of operation is activated when the electrical load is below a first threshold and the second mode of operation is activated when the electrical load is above second threshold, for instance equal to the first threshold.

[0051] Clause 25: The subsurface hydraulic storage method of any clauses 21-24, wherein the downhole fluid is lifted into the storage tank via a first flow path and is flowed to the ESP via the first flow path or via a second flow path.

[0052] Clause 26: The subsurface hydraulic storage method of any clauses 21-25, wherein the wellbore is a first wellbore, the ESP is a first ESP and the storage space includes a second wellbore, wherein a second ESP is disposed in the second wellbore and wherein the method includes lifting the stored downhole fluid to the surface using the second ESP in the second mode of operation.

[0053] Clause 27: The subsurface hydraulic storage method of clause 26, wherein the second ESP is connected to the electrical network, wherein the method includes, in the first mode of operation, flowing the downhole fluid through the second ESP, driving the second ESP with the downhole fluid flow so as to produce electricity, and injecting the electricity produced by the second ESP into the electrical network.

[0054] Clause 28: The subsurface hydraulic storage method of any clauses 21-27, wherein the storage space is situated at a depth inferior to the target depth. The power harvesting method according to one or more embodiments herein described.

[0055] Clause 29: The power harvesting system according to one or more embodiments herein described.

[0056] These described embodiments are examples of the presently disclosed techniques. Additionally, in an effort to provide a concise description of these embodiments, not all features of an actual embodiment may be described in the specification. It should be appreciated that in the development of any such actual implementation, as in any engineering or design project, numerous embodiment-specific decisions will be made to achieve the developers’ specific goals, such as compliance with system-related and business-related constraints, which may vary from one embodiment to another. Moreover, it should be appreciated that such a development effort might be complex and time consuming, but would nevertheless be a routine undertaking of design, fabrication, and manufacture for those of ordinary skill having the benefit of this disclosure.

[0057] The articles “a,” “an,” and “the” are intended to mean that there are one or more of the elements in the preceding descriptions. The terms “comprising,” “including,” and “having” are intended to be inclusive and mean that there may be additional elements other than the listed elements. Additionally, it should be understood that references to “one embodiment” or “an embodiment” of the present disclosure are not intended to be interpreted as excluding the existenceof additional embodiments that also incorporate the recited features. For example, any element described in relation to an embodiment herein may be combinable with any element of any other embodiment described herein. Numbers, percentages, ratios, or other values stated herein are intended to include that value, and also other values that are “about” or “approximately” the stated value, as would be appreciated by one of ordinary skill in the art encompassed by embodiments of the present disclosure. A stated value should therefore be interpreted broadly enough to encompass values that are at least close enough to the stated value to perform a desired function or achieve a desired result. The stated values include at least the variation to be expected in a suitable manufacturing or production process, and may include values that are within 5%, within 1%, within 0.1%, or within 0.01% of a stated value.

[0058] A person having ordinary skill in the art should realize in view of the present disclosure that equivalent constructions do not depart from the spirit and scope of the present disclosure, and that various changes, substitutions, and alterations may be made to embodiments disclosed herein without departing from the spirit and scope of the present disclosure. Equivalent constructions, including functional “means-plus-function” clauses are intended to cover the structures described herein as performing the recited function, including both structural equivalents that operate in the same manner, and equivalent structures that provide the same function. It is the express intention of the applicant not to invoke means-plus-function or other functional claiming for any claim except for those in which the words ‘means for’ appear together with an associated function. Each addition, deletion, and modification to the embodiments that falls within the meaning and scope of the claims is to be embraced by the claims.

[0059] The terms “approximately,” “about,” and “substantially” as used herein represent an amount close to the stated amount that still performs a desired function or achieves a desired result. For example, the terms “approximately,” “about,” and “substantially” may refer to an amount that is within less than 5% of, within less than 1% of, within less than 0.1% of, and within less than 0.01% of a stated amount. Further, it should be understood that any directions or reference frames in the preceding description are merely relative directions or movements. For example, any references to “up” and “down” or “above” or “below” are merely descriptive of the relative position or movement of the related elements.

[0060] The present disclosure may be embodied in other specific forms without departing from its spirit or characteristics. The described embodiments are to be considered as illustrative and notrestrictive. The scope of the disclosure is, therefore, indicated by the appended claims rather than by the foregoing description. Changes that come within the meaning and range of equivalency of the claims are to be embraced within their scope.

Claims

CLAIMS1. A subsurface hydraulic energy storage system comprising: a reservoir configured to store a downhole fluid; a turbine coupled to a generator, wherein geothermal heat from the downhole fluid is configured to drive the turbine and the generator, and the generator is electrically connected to an electrical network; an electrical submersible pump (ESP) installed at a target depth in a wellbore in a geological formation, and electrically connected to a power control system, wherein the power control system is electrically connected to the electrical network, wherein the ESP is in fluid communication with the reservoir, and the ESP is configured in an active mode of the subsurface hydraulic energy storage system to utilize electrical power from the electrical network to pump the downhole fluid comprising the geothermal heat from the geological formation to the reservoir.

2. The subsurface hydraulic energy storage system of claim 1, wherein the turbine is in fluid connection with the ESP and the reservoir, and the downhole fluid directly drives the turbine.

3. The subsurface hydraulic energy storage system of claim 1, comprising a heat exchanger and a working fluid circuit, wherein the downhole fluid is configured to transfer the geothermal heat to the working fluid circuit via the heat exchanger, the working fluid circuit comprises the turbine, and a working fluid of the working fluid circuit directly drives the turbine.

4. The subsurface hydraulic energy storage system of claim 3, wherein the working fluid vaporizes in the heat exchanger.

5. The subsurface hydraulic energy storage system of claim 1, wherein the ESP is configured in a passive mode of the subsurface hydraulic energy storage system to provide electrical power to the electrical network based at least in part on a return flow of the downhole fluid from the reservoir to the geological formation through the ESP.

6. The subsurface hydraulic energy storage system of claim 1, wherein the power control system comprises a variable speed drive (VSD).

7. The subsurface hydraulic energy storage system of claim 1, wherein the reservoir comprises a storage tank at a surface of the geological formation.

8. The subsurface hydraulic energy storage system of claim 1, wherein the ESP is a first ESP and the reservoir comprises a second wellbore with a second ESP, wherein the second ESP is configured in an active mode of the subsurface hydraulic energy system to provide electrical power to the electrical network based at least in part on the flow of the downhole fluid from the first ESP to the second wellbore, and the second ESP is configured in a passive mode of the subsurface hydraulic energy system to utilize electrical power from the electrical network to pump the downhole fluid from the second wellbore to the first wellbore.

9. The subsurface hydraulic energy storage system of claim 1, comprising a control device for switching between an active mode and a passive mode of the subsurface hydraulic energy storage system based at least in part on an electrical load on the electrical network, wherein the ESP is configured in the active mode to utilize electrical power from the electrical network to pump the downhole fluid to the reservoir, the turbine is configured in the active mode to provide electrical power to the electrical network, and the ESP is configured in the passive mode to provide electrical power to the electrical network based at least in part on a return flow of the downhole fluid to the geological formation from the reservoir through the ESP.

10. A method of operating a subsurface hydraulic energy storage system, comprising: in an active mode of operation, performing the following steps: lifting a downhole fluid from a target depth in a wellbore in a geological formation into a reservoir using an electrical submersible pump (ESP), wherein lifting the downhole fluid comprises driving the ESP with lifting electricity is provided by an electrical network, and the downhole fluid comprises geothermal heat;driving a turbine connected to a generator with the geothermal heat, wherein driving the turbine drives the generator to produce geothermal electricity; and providing the geothermal electricity from the generator to the electrical network, wherein the geothermal electricity is greater than the lifting electricity; and in a passive mode of operation, performing the following steps: directing a return flow of the downhole fluid from the reservoir to the geological formation through the ESP; driving the ESP with the return flow of the downhole fluid, wherein driving the ESP produces downhole electricity; and providing the downhole electricity to the electrical network.I L The method of operating the subsurface hydraulic energy storage system of claim 10, comprising switching between the active mode and the passive mode as a function of an electrical load on the electrical network.

12. The method of operating the subsurface hydraulic energy storage system of claim 11, comprising switching to the active mode when the electrical load is below a first threshold, and switching to the passive mode when the electrical load is greater than or equal to the first threshold.

13. The method of operating the subsurface hydraulic energy storage system of claim 10, wherein the wellbore comprises a first wellbore, the ESP is a first ESP, the reservoir comprises a second wellbore having a second ESP, wherein the passive mode of operation comprises driving the second ESP with a portion of the downhole electricity to direct the return flow of the downhole fluid from the reservoir to the geological formation through the first ESP.

14. The method of operating the subsurface hydraulic energy storage system of claim 10, comprising transferring the geothermal heat from the downhole fluid to a working fluid in a working fluid circuit comprising the turbine.

15. The method of operating the subsurface hydraulic energy storage system of claim 14, wherein the working fluid comprises water, and transferring the geothermal heat from the downhole fluid to the working fluid vaporizes the water.

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