Compressed air energy storage system using repurposed idle hydrocarbon wellbores for air storage

Abstract

A compressed gas energy storage system which repurposes existing hydrocarbon wells. The storage system can have a squeeze cemented annular section and a plug to create an air storage zone. Compressed air can be stored within this air storage zone. Further, use of sub-surface wells provides a complete solution for long term energy storage at high efficiency.

Description

APPLICATION FOR PATENTINVENTORS: STEVEN F. SCIAMANNABHAVANI RAGHURAMANBIRENDRA JHA TITLE:COMPRESSED AIR ENERGY STORAGE SYSTEM USING REPURPOSED IDLE HYDROCARBON WELLBORES FOR AIR STORAGESPECIFICATIONCROSS REFERENCE TO RELATED APPLICATIONS

[0001] The present application claims priority to and the benefit of co-pending US Provisional Patent Application Serial No. 63 / 548,313 filed on November 13, 2023, titled “Compressed Air Energy Storage System Using Repurposed Idle Hydrocarbon Wellbores For Air Storage.” This reference is incorporated in its entirety.FIELD

[0002] The present disclosure relates generally to compressed air energy storage, and more particularly to a compressed air energy storage (CAES) system comprising one or more repurposed idle hydrocarbon wells to enable wellbore air storage and further comprising surface expansion and power electronic systems to enable constant power output generation.BACKGROUND

[0003] A current problem is the growing inventory of idle hydrocarbon wells. Idle hydrocarbon wells are oil and gas wells that have not yet been plugged and are not producing, injecting, or otherwise being used for their intended purpose.

[0004] A count in the year 2020 recorded 230,000 approved idle oil and gas wells in the US. While these idle wells may have potential for future oil or gas production or associated uses, in many instances they are maintained as idle wells because of the high cost of properly plugging and abandoning them. If not properly monitored and maintained, however, they may pose a risk to the environment, public health, and safety. They alsopresent an elevated risk of becoming orphan wells.

[0005] Orphan wells are abandoned oil or gas wells that are no longer active, and which may or may not have a known owner. There are various types of orphan wells, such as abandoned wells with no owner of record (some drilled over many decades ago) or abandoned wells with an owner who has ostensibly sold the responsibility for that well to someone else or gone bankrupt. The state is then obligated to take on the cost of remediation of the orphan wells. The number of documented orphan wells in the in the US is about 100,000 with estimates of undocumented orphan wells varying from 300,00 to 800,000.

[0006] Both idle and orphaned wells carry the risk of emission of greenhouse gases such as methane as well as the risk of contamination of shallower freshwater aquifers and drinking water zones with hydrocarbons if they are not properly plugged and abandoned. The integrity of the cement sheath surrounding the well casing to prevent leakage of hydrocarbons over the long term diminishes especially in the case of wells that were not adequately cemented, e.g., older wells with casings partially cemented and using older cement compositions.

[0007] In many instances, even if the well is properly cemented, the chance of leakage that can develop via cracks in the cement sheath is present because of various earth movements. For wells that are planned for abandonment, other failures can also develop besides cement-related issues such as those caused by the corrosion or holes in the casing with time. However, the high costs associated with plugging and abandonment of idle wells make them a liability to the oil and gas operators and to the State, resulting in a mounting environmental challenge as the idle well inventory continues to grow.

[0008] Moreover, even for idle wells that have been conventionally plugged and abandoned, there is typically no provision for long term monitoring of any potential leaks that can develop over time. There is hence an urgent need to find a good solution for the large and growing inventory of idle and orphaned hydrocarbon wells and the environmental hazards associated with them.

[0009] Yet another current problem is the need for long duration energy storage to enable a net zero carbon grid. Renewable power sources are variable and intermittent, and their supply may not always match peak demand. Long duration energy storage from time scales of a few hours to time scales of weeks and months for seasonal storage is critical to achieve the goal of expending renewable sources and a net zero carbon grid.

[0010] Compressed air energy storage is a great candidate for long duration energy storage. In the charging cycle, ambient air is compressed and injected into underground caverns or porous reservoirs for storage. In the discharging cycle, when electricity is needed, the stored high-pressure air is produced to flow through turbines for power generation and discharged to the atmosphere.

[0011] Depending on how the heat of compression and the heat needed for expansion are handled, various thermodynamic schemes of CAES are possible such as diabatic, adiabatic and isothermal and combinations / modifications of those. Large capacity CAES plants store the compressed air in large volume underground caverns and reservoirs.

[0012] For small capacity CAES plants (typically those with capacity less than 50MW), compressed air storage has been proposed in above ground storage vessels or underground drilled wells. The commercialization of small capacity CAES plants has been constrained due to the high capital cost per kW of both the above ground storage vessels, as well as, for the drilling of new wells that need to be completed with high- cost wellbore casing to meet the high-pressure requirements.

[0013] Furthermore, there are permitting and siting challenges as well as footprint considerations for surface storage. Reuse of idle geothermal wells has been proposed to save on up-front capital cost and use geothermal heat from active geothermal wells during the generation cycle, but this scenario is constrained to siting on active geothermal fields. Yet another major challenge with all the current proposed solutions for small capacity CAES plants is the declining air pressure in the storage reservoir as the stored air is withdrawn during the generating cycle which results in decliningvoltage and generated power and makes connection to power grids a challenge.

[0014] Thus, there are two urgent needs to be addressed: (a) the large and growing inventory of idle and orphaned oil and gas wells that pose an environmental hazard and (b) the lack of a cost-effective small capacity CAES system that can provide constant power output to enable connection to the grid.

[0015] The present invention meets these needs.SUMMARY OF THE INVENTION

[0016] The present disclosure relates generally to small capacity CAES systems comprising one or more repurposed idle hydrocarbon wells to enable wellbore air storage and further comprising surface wellhead, expansion and power electronic systems to enable constant and grid connectable power generation.

[0017] In one embodiment of the present invention, the compressed air energy storage system comprises a set of one or more repurposed idle hydrocarbon wells that have been reworked to hydraulically isolate the hydrocarbon producing zones from the wellbore completion system and to enable storage of compressed air within the cased wellbore. It further comprises a surface wellhead system on each well that comprises a pressure choke that throttles the incoming constant flow rate but declining pressure air from the well to supply constant pressure air. The constant pressure air streams from the set of one or more wells are fed to a multistage air expansion system to enable constant power generation during the generating cycle.

[0018] In another embodiment of the present invention, the surface wellhead system of each repurposed idle well comprises a small turboexpander-generator and a power converter subsystem. The inlet air pressure to the small turboexpander-generator is declining but the air flow out of the small turboexpander-generator is controlled at a constant pressure. This air flow from one surface wellhead system is combined with similarlygenerated constant air pressure streams from the other wells and feeds into a multistage air expansion system to generate a first power output stream with constant power capacity (kW) during the generating cycle.

[0019] Further, the pressure drop across the small turboexpander-generator generates a second power output stream with declining capacity (kW) because the inlet air pressure is declining. The second power output stream has a declining voltage and feeds a power converter to produce a third power output stream at a constant voltage but with declining electrical current (& power).

[0020] The first power output stream and the third power output streams from the individual wellheads is routed to a power management system comprising a battery, rectifier and inverter to provide a constant power output to the grid over the generation cycle. The power management system ensures a constant level of power output supply to the grid by either using make-up power from the battery to supplement when power output is low (i.e. at the end of the generating cycle) or storing it when it is high (i.e. at the beginning of the generating cycle).

[0021] Other aspects and embodiments are described in further detail below.BRIEF DESCRIPTION OF THE DRAWINGS

[0022] The detailed description will be better understood in conjunction with the accompanying drawings as follows:

[0023] Figure l is a depiction of an advanced adiabatic compressed air energy storage system with air storage in repurposed idle hydrocarbon wells to enable storage of compressed air within the cased wellbore and surface wellhead, expansion and electronics systems to generate constant power output in the generating cycle.

[0024] Figure 2 is an embodiment of the disclosure with a surface wellhead system comprisingof a pressure choke that throttles the incoming constant flow rate but declining pressure air from the well to supply constant pressure air to feed an air expansion system for constant power generation.

[0025] Figure 3 summarizes calculated single well power capacity values for various storage and withdrawal rate scenarios using the embodiment of FIG. 2.

[0026] Figure 4 is an embodiment of the disclosure with a surface wellhead system comprising a small turboexpander-generator and a power converter subsystem. The power output stream 1 from the multistage expansion system and the generated power output stream 3 from individual wellheads is routed to a power management system comprising a battery, rectifier and inverter to provide a constant power output to the grid.

[0027] Figure 5 is an embodiment of the system where the well barrier elements include a squeezed cement section in the annulus and a plug.

[0028] The embodiments of the present disclosure are detailed below with reference to the listed Figures.DETAILED DESCRIPTION OF THE EMBODIMENTS

[0029] Before explaining the present disclosure in detail, it is to be understood that the disclosure is not limited to the specifics of particular embodiments as described and that it can be practiced, constructed, or carried out in various ways.

[0030] While embodiments of the disclosure have been shown and described, modifications thereof can be made by one skilled in the art without departing from the spirit and teachings of the disclosure. The embodiments described herein are exemplary only, and are not intended to be limiting.

[0031] Specific structural and functional details disclosed herein are not to be interpreted as limiting, but merely as a basis of the claims and as a representative basis for teachingpersons having ordinary skill in the art to variously employ the present embodiments. Many variations and modifications of embodiments disclosed herein are possible and are within the scope of the present disclosure.

[0032] Where numerical ranges or limitations are expressly stated, such express ranges or limitations should be understood to include iterative ranges or limitations of like magnitude falling within the expressly stated ranges or limitations.

[0033] The use of the word “a” or “an” when used in conjunction with the term “comprising” in the claims and / or the specification may mean “one,” but it is also consistent with the meaning of “one or more,” “at least one,” and “one or more than one.”

[0034] The word “about” means plus or minus 5% of the stated number.

[0035] The use of the term "optionally" with respect to any element of a claim is intended to mean that the subject element is required, or alternatively, is not required. Both alternatives are intended to be within the scope of the claim. Use of broader terms such as comprises, includes, having, etc. should be understood to provide support for narrower terms such as consisting of, consisting essentially of, comprised substantially of, and the like.

[0036] When methods are disclosed or discussed, the order of the steps is not intended to be limiting, but merely exemplary unless otherwise stated.

[0037] Accordingly, the scope of protection is not limited by the description herein, but is only limited by the claims which follow, encompassing all equivalents of the subject matter of the claims. Each and every claim is hereby incorporated into the specification as an embodiment of the present disclosure. Thus, the claims are a further description and are an addition to the embodiments of the present disclosure.

[0038] The inclusion or discussion of a reference is not an admission that it is prior art to the present disclosure, especially any reference that may have a publication date after the priority date of this application. The disclosures of all patents, patent applications, andpublications cited herein are hereby incorporated by reference, to the extent they provide background knowledge; or exemplary, procedural or other details supplementary to those set forth herein.

[0039] The embodiments of the present disclosure generally relate to systems and methods for a constant power output and grid connectable CAES system comprising a set of one or more repurposed idle hydrocarbon wellbores for compressed air storage and one or more surface wellhead expansion and power electronic systems.

[0040] While the systems and methods are described for repurposed idle hydrocarbon wells, the are applicable to any idle wells such as geothermal wells or water wells. Further while the systems and methods are described for a compressed air energy storage system, they are also applicable to compressed gas energy storage systems that include other gases such as carbon dioxide, nitrogen, hydrogen, and natural gas.

[0041] Figure 1 shows one embodiment of the disclosure using an advanced adiabatic CAES process integrated with repurposed idle hydrocarbon wellbore storage of compressed air and surface wellhead, expansion and electronics systems to generate constant power output in the generating cycle. Compression system 110 can feed compressed air into a thermal storage and heat exchange system 130, which then stores the compressed air in Idle hydrocarbon wells 140. When recovering energy, the compressed air can be routed through the thermal storage and heat exchange system 130, through the wellhead system 120, and to an expansion and electronics system 150 for power generation.

[0042] For an advanced adiabatic CAES process shown in Figure 1, heat released during the charging compression cycle may be captured via one or more heat exchangers and stored in a hot thermal store and used later to heat the expanding air during the generating cycle. One example of a heat management system is a cold-water tank as the source for cold water to capture the heat of compression through one or more heat exchangers and a pressurized insulated hot water tank as a thermal store for the heat. The heat can subsequently be transferred in heat exchangers from the hot water thermal store to the expanding air in the generating cycle and the cold water returned to thecold-water tank to close the water loop.

[0043] Wellbore casings may comprise one or more casing sections such as surface casing, intermediate casing, production casing, or production liner in the order of decreasing diameter and increasing depth. Cased wellbore depths may be in the range of 7000 to 10,000 feet. Standard casing sizes run from an outer diameter of 4.5 inches to 20 inches and are categorized based on yield strength, tensile strength and hardness. Minimum yield strength for a common J-55 type casing grade is 55000 psi (3742 atm) and yield pressure rating for a 7-inch OD is 3740 psi (254.4 atm). An N-80 26 Ib / ft casing has a minimum yield stress of 80,000 psi and a yield pressure rating of 6340 psi (431 atm). These carbon steel casings can also withstand temperatures as high as 200C.

[0044] Repurposing idle well for CAES with wellbore storage

[0045] The reworking requirements of the well completion system to repurpose it for a compressed air energy storage systems includes: (a) hydraulic isolation of the hydrocarbon layer from the cased section of the wellbore both inside the casing and the annular region outside the casing by installation of well barrier elements, (b) enabling compressed air injection into and compressed air production out of the wellbore, (c) enabling storage of compressed air in the wellbore for long durations of 10 hours plus, and (d) prevention of any contact of the compressed air and the hydrocarbon gases anywhere in the system to eliminate any possibility of formation of potentially explosive air-hydrocarbon mixtures.

[0046] The repurposed well completion system may comprise a first plug installed in the casing close to the depth of the casing bottom. The plug serves as a well barrier element to hydraulically isolate all deeper hydrocarbon layers and prevent any contact between the compressed air and the hydrocarbon. The plug may be cement based and may optionally include one or more special additives to enhance its functional properties as needed to withstand harsh conditions such as corrosive environments, high temperature environments or high stress environments. The plug may also be set using non-cement formulations such as for example low temperature melting alloys, thermosettingpolymers etc. Additional one or more plugs may also be set at depths below the first plug at depths above the hydrocarbon layer to provide additional well barrier elements.

[0047] Placing a plug in the cased wellbore by itself may not be sufficient to hydraulically isolate the hydrocarbon layer as leakages may also occur in the annulus outside the casing. Especially for old wells, stresses from normal well operations such as for example pressure testing, stimulation, injection and production could cause cracks in the cement as well as debonding induced micro annuli in the cement sheath surrounding the casing. The annular region cement may also become brittle over time and more susceptible to leak paths. A first squeeze-cemented annular section behind the casing at a depth near the bottom depth of the casing can be used as a well barrier element to fill any cracks and gaps in the cement and prevent any leak induced flow of the hydrocarbon from deeper layers along the annular region behind the casing. Additional one or more squeeze-cemented sections may also be set at depths below the first squeeze-cemented section and at depths above any individual hydrocarbon layers to provide additional well barrier elements.

[0048] The compressed air storage is in the cased wellbore section between the first plug and the wellhead. Casing integrity in this section is critical to ensure the stored compressed air does not leak and can withstand repeated pressure cycling of the CAES process at the storage temperature. A wellbore-reservoir model incorporating the wellbore trajectory and the geology of the surrounding reservoir layers may be used to understand the CAES induced stress fields and sensitivity to trajectory deviation. Well logs (for example acoustic and ultrasonic logs) may be used to evaluate the cement sheath integrity and the quality of the bonding at the cement / casing and cement / formation interfaces. Casing logs may be used to analyze for any casing sections damaged due to corrosion. Casing mechanical integrity may be reinforced through application of casing patches and liners in sections more vulnerable to stress as well as in the damaged casing sections. Hydraulic pressure test may be conducted to test for leaks and the effectiveness of the rework. Compressed air may also be use for static and cyclical pressure testing.

[0049] Higher temperature wellbore storage of the compressed air reduces the load on the surface thermal storage system. The wellbore-reservoir model may be used to simulate the heat loss from the wellbore which depends on the wellbore geometry and the conductivities of the surrounding layers, including cement and rock layers. While initial heat losses may be high, it is expected that over time with repeated CAES injection and production cycles, the formation will slowly heat up and result in reduced heat loss. Insulating and corrosion resistant casing liners may be deployed in high heat loss regions of the casing to conserve the thermal energy of the stored compressed air.

[0050] A sensor system comprising one or more sensors may be deployed to monitor any leakage of hydrocarbon to the surface. The hydrocarbon may be present in the produced air stream, or it may leak through the annular section behind the casing and be detected in the surface environment around the well head or in the surface casing vent valve assembly. The sensor system may also detect flow of compressed air in the surface casing valve assembly indicating leakage of compressed air in the annular region behind the casing.

[0051] Embodiments for constant power output in the CAES generating cycle:

[0052] An example candidate well with a 8.625 in OD J-55 type casing to a depth of 8000 feet and a 7 inch OD production J-55 type casing to a depth around 10000 feet stores about 21,400 kg of air at 200 atm and a temperature of 46C. Continuous withdrawal of air from the wellbore in the generating cycle, however, causes a decline in the wellbore air pressure and hence reduces the speed of the first stage expansion turbine in the CAES multistage expansion system. This results in decreasing voltage and electrical current and hence decreasing power output making it difficult to connect to the grid. Further, the decreasing inlet air pressure to the first stage turbine of the multistage expansion system reduces its efficiency.

[0053] Figure 2 is an embodiment of the invention that addresses this issue to enable constant power output generation from the system during the generation cycle. It comprises a surface wellhead system comprising of a wellhead pressure choke on each wellborethat that throttles the incoming constant flow rate but declining pressure air from the well to supply constant pressure air. The constant pressure air streams from the set of one or more wells are fed to the multistage expansion system to enable constant power generation. Air from a wellbore 210 is exiting at declining pressures as the wellbore is emptied. It is passed through a wellbore choke 220 to keep the pressure constant. Constant pressure air 240 is combined with constant pressure air from other wells 230 and routed to a multistage expansion system 250. From here, discharge air 260 can be vented to atmosphere and generated power 270 can be sent to the grid.

[0054] Figure 3 summarizes calculations of single well power output capacity for the example candidate well with the well head pressure choke outlet pressure set to 65 atm. It is assumed that a 5 atm pressure differential is required for air to flow from well to the surface and hence the air withdrawal from the wellbore is stopped when the pressure in the wellbore drops to around 69 atm.

[0055] The withdrawal rate hence determines the duration of the generating cycle. For various constant withdrawal rates, even as pressure in the wellbore drops from 200 to around 69 atm, the supply of air to the expansion system is at the constant pressure of 65 atm ensuring a constant voltage and power generation that is grid connectable. ASPEN simulations indicate that with an initial storage pressure of 200 atm and air preheated to 130 C prior to each expansion stage, this example well can generate 100 to 140 kW power for 10 to 14 hours storage duration with a three-stage expansion system. A 1MW capacity CAES plant may thus require around 7 tolO wells.

[0056] By selecting wells with a higher casing yield pressure rating, the storage and hence power capacity per well may be increased proportionately as shown for the case where the initial storage pressure is 400 atm.

[0057] The embodiment of Figure 2 combines flows out of individual wellhead chokes to feed the multistage expansion system. Other embodiments are possible whereby there are multiple expansion systems where each is fed by a subset of wells and the generated power is combined to supply the grid. The stored compressed air withdrawal fromindividual wells may also be done in a staggered manner to feed the multistage expansion system and generate constant power at a lower capacity level but for a longer duration. Such configurations offer more flexibility to meet varying power demand and duration needs.

[0058] Scaling up to a 10 MW capacity may be done by either integrating multiple CAES systems comprising one or more repurposed wells or with a single CAES system comprising the entire set of repurposed wells. A techno-economic analysis for the integrated system and the assessment of site characteristics such as well layout, interwell distances, and capacity per well may be used to design the integrated system.

[0059] While the embodiment shown in Figure 2 generates power at constant output enabling connection to the power grid, it is penalized by a need for a high volume of working air cushion because withdrawal stops when the storage pressure approaches the choke outlet pressure, thus reducing the power output capacity per well. There is also an energy loss incurred across the choke due to the throttling induced pressure drop.

[0060] Figure 4 shows another embodiment of this invention where the surface wellhead system of each well comprises a small turboexpander-generator and a power converter subsystem.

[0061] The inlet air pressure of wellbore air 410 to the small turboexpander-generator 420 is dropping but the air flow out 440 of the small turboexpander-generator is controlled at a constant pressure (and can be combined with constant pressure air from other wells 430) to feed into the multistage expansion system 450 similar to that in embodiment of Figure 2 to generate discharge air 460 and a power output stream 482 to a power management system 480 with constant capacity (kW) throughout the generating cycle which generates power to the grid 484.

[0062] The small turboexpander-generator 420 converts the pressure drop across it to generate a second power output stream 488 with declining power output (kW) because the inlet air pressure is declining. The second power output stream 488 feeds a power converter486 to produce a third power output stream 487 which is at constant voltage but with declining electrical current (& power). The power output stream 482 from the multistage expansion system and the third power output stream 487 (along with similar power output streams from other wells 485) from each of the individual wellheads are routed to the power management system 480 comprising a battery, rectifier and inverter to provide a constant power output to the grid.

[0063] The power management system 480 ensures a constant level of power output supply to the grid 484 by either using make up power from the battery to supplement when power output is low or storing it when it is high. This approach uses power electronics similar to that utilized by distributed photovoltaic solar systems (eg. commercial & large rooftop PV) enabling them to provide a constant power output to the grid. Variations in solar energy due to diurnal cycles and other elements such as cloud cover and rain which results in varying voltage, current and hence power output from each solar panel.

[0064] The declining power output from individual wells as they depressurize is analogous to the varying power output from individual solar panels as the sun transits from high noon to sunset). Power output levels (kw) are approximately in the same range for both systems and hence power electronic systems developed in the solar industry for integrating individual photovoltaic panels within a solar system may be deployed for the embodiment described here.

[0065] The embodiment of Figure 4 is estimated to yield a 15-20% increase in the per well delivered energy relative to the delivered energy of the embodiment of FIG. 2 that uses a wellhead pressure choke. A further increase of 10-15% in the delivered energy may be enabled by letting the wellbore pressure drop to pressures as low as 5 atm by using a second small turboexpander coupled to the same generator.

[0066] Other embodiments are possible comprising multiple multistage expansion systems where each is fed by a subset of wells and the generated power is combined to feed the grid. The individual wells may also be operated in a staggered manner to generate constant power at a lower capacity level but for a longer duration. Such configurationsoffer more flexibility to meet varying power demand and duration needs.

[0067] Figure 5 is one embodiment of the invention that shows a repurposed idle hydrocarbon.

[0068] The repurposed well can comprise typical elements of a well, such as casing 310, tubing320, old cement 330, and a packer 340. The repurposed well completion system may also comprise a first plug 370 installed in the casing as a well barrier element to hydraulically isolate the deeper hydrocarbon layer and prevent contact between the compressed air and the hydrocarbon.

[0069] The plug can be cement based and may optionally include one or more special additives to enhance its functional properties as needed to withstand harsh conditions such as corrosive environments, high temperature environments or high stress environments. The plug may also be set using non-cement formulations such as for example low temperature melting alloys, thermosetting polymers etc. The first plug 340 can serve as a well barrier to isolate the other hydrocarbon layers below.

[0070] Placing a plug in the cased wellbore by itself may not be sufficient to hydraulically isolate the hydrocarbon layer as leakages may also occur in the annulus outside the casing. Especially for old wells, stresses from normal well operations such as for example pressure testing, stimulation, injection and production could cause cracks in the cement as well as debonding induced micro annuli in the cement sheath surrounding the casing. The annular region cement may also become brittle over time and more susceptible to leak paths. As shown in the embodiment of Figure 5, a squeeze cemented annular section 350 behind the casing can be used as a well barrier element to fdl any cracks and gaps in the cement and prevent any leak induced flow of the compressed air and / or the hydrocarbon along the annular region behind the casing.

[0071] The first plug 370 is also preferably set within the squeeze cemented section to leverage the strength of the section and its resistance to stresses as shown in this embodiment.

[0072] Squeeze cementing can also be used to prevent leaks across casing that may bedamaged and pitted because of corrosion. Yet another option for repairing damaged casing sections is to use casing liners or patches. Well logs (for example acoustic and ultrasonic logs) may be used to evaluate the cement sheath integrity and the quality of the bonding at the cement / casing and cement / formation interfaces. Casing logs may be used to analyze for any casing sections damaged due to corrosion. In one embodiment of the invention, such well log information may be used to identify additional annular regions behind the casing to be squeeze cemented or casing sections to be patched.

[0073] A tubing 320 may be run through the casing from the well head to a depth between the top and bottom depths of the aquifer layer and may be used to inject and produce the compressed air during the charging and discharging cycles of the compressed air energy storage system as shown.

[0074] A packer 340 may be set in the annulus contain the compressed air in the casing between the packer 340 and the first plug 370 and within the tubing 320.

[0075] In an optional embodiment of the invention, a second plug 380 can be installed in the casing below the first plug 370 and the space between the two may be filled with a fluid such as for example a completion fluid. This provides an additional well barrier to reinforce the first plug 370 well barrier and ensure there is no leak of high pressure compressed air below the first plug 370 and no leak of hydrocarbon up the casing past the first plug 370.

[0076] Filling the space with a liquid leverages the fact that the diffusion of any leaked gas in liquid medium is about 4 orders of magnitude lower than in a gas medium. The second plug 380 can be set closer to the top depth of any depleted hydrocarbon perforations 390 such that it serves as a well barrier close to the source of any hydrocarbon emission. The second plug may be set using cement or non-cement-based formulations.

[0077] Using compressed air in the embodiments described above is advantageous as air can be easily drawn from the ambient environment for compression and storage and can also be released back to the environment after expansion. These systems, however, mayalso be applicable to compressed gas energy storage systems using any other suitable gas including but not limited to carbon dioxide, nitrogen, hydrogen, and natural gas.

[0078] While the embodiments here are described for a compressed air energy storage system operated as an advanced adiabatic system, they are equally applicable to compressed air energy storage systems with isothermal or near-isothermal compression and isothermal or near-isothermal expansion schemes. They are also applicable to compressed air energy storage systems where the heat of compression is fully or partly rejected to the environment and the heat of expansion is provided by a thermal store system that converts renewable energy when it is available to thermal energy and stores it for later use to heat the expanding gas in the discharge cycle..

[0079] While the present disclosure emphasizes the embodiments, it should be understood that within the scope of the appended claims, the disclosure might be practiced other than as specifically described herein.

Claims

CLAIMSWhat is claimed is:

1. A compressed air energy storage system comprising: a) a hydrocarbon well spanning; b) an air storage zone in the hydrocarbon well; and c) a barrier element.

2. The system of claim 1, wherein the barrier element comprises at least one of: a) a plug; or b) a squeeze cemented annular section spanning at least the aquifer layer.

3. The system of claim 1, wherein a first plug is installed within the squeeze cemented annular section.

4. The system of claim 3, further comprising a second plug installed below the first plug, wherein the space between the first plug and the second plug is filled with a fluid.

5. The system of claim 4, wherein the fluid is a brine completion fluid.

6. The system of claim 1, further comprising: a) tubing running through the casing; and b) a packer set in the annulus between the tubing.

7. The system of claim 6, wherein the tubing is insulated.

8. The system of claim 1, further comprising a sensor system of one or more sensors to detect hydrocarbon presence at surface.

9. A method for storing energy in a compressed air system comprising: a) choosing a hydrocarbon well; b) creating a squeeze cemented annular section; c) creating an air storage zone in the squeeze cemented annular section; d) installing a first plug; e) storing air within the air storage zone.

10. The method of claim 9, wherein the first plug is within the squeeze cemented annular section.

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