Repurposing idle oil and gas wells for compressed air energy storage

Abstract

A compressed gas energy storage system which can also store thermal energy. The storage system can have a surface subsystem, a geological heat storage subsystem, and a compressed gas storage subsystem. The surface subsystem can comprise gas compression, gas expansion, and heat exchange functions. The geological heat storage subsystem can comprise a cold and hot zone in fluid communication with the surface subsystem. The compressed gas storage subsystem can also be in fluid communication with the surface subsystem. The systems and methods can be implemented in porous rock formations. This allows for the use of extremely large, natural formations rather than man-made salt caverns, as is the current state of the art. Existing wells drilled by oil and gas producers can be utilized, thereby drastically reducing cost and time for implementation. Further, use of sub-surface thermal management provides a complete solution for long term energy storage at high efficiency.

Description

APPLICATION FOR PATENTINVENTORS: IRAJ ERSHAGHIBIRENDRA JHADONALD L. PAULBHAVANI RAGH U RAMANTITLE:REPURPOSING IDLE OIL AND GAS WELLS FOR COMPRESSED AIR ENERGY 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 / 548,309 filed on November 13, 2023, titled “Repurposing Idle Oil and Gas Wells for Compressed Air Energy 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 system comprising a repurposed aquifer intersecting idle hydrocarbon well completion system that has been reworked to enable compressed air energy storage in the aquifer and also to eliminate any risk of hydrocarbon emission to the environment. Idle hydrocarbon well refers to a well originally completed for hydrocarbon production.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 also present 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 environmentalhazards 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. Storage in porous reservoirs is particularly suited for long duration because of low absolute costs as well as low marginal costs for increasing storage capacity.

[0011] While the porous reservoir may be either a depleted hydrocarbon reservoir or an aquifer, the latter is more attractive as it minimizes any potential contact of the air with hydrocarbons. This not only eliminates any potential flammability hazard, but it also allows atmospheric discharge of air from the turbines without costly treatments to remove environmental contaminants in the produced air.

[0012] Aquifer candidates selected for compressed air energy storage are typically those that contain non potable water and are confined and isolated from any underground drinking water sources. However, commercialization of this technology for long duration energy storage has been challenging mainly because of the very high costs of drilling new wells to access the subsurface aquifers for compressed air storage as well as the high cost of geological characterization of the formation and acquisition of subsurface data to build reservoir models for simulation and design of the compressed air energy storage system.

[0013] Thus, there are two urgent needs to be addressed: (a) the large and growing inventoryof idle and orphaned oil and gas wells that pose an environmental hazard and (b) the lack of a commercially viable long duration energy storage system to realize a net zero carbon grid.

[0014] The present invention meets these needs.SUMMARY OF THE INVENTION

[0015] The present disclosure relates generally to compressed gas energy storage, and more particularly to compressed gas energy storage systems which repurpose existing abandoned, orphaned, or idle hydrocarbon wells.

[0016] The systems and methods of the present disclosure provide for idle hydrocarbon well completion systems reworked to enable compressed air energy storage systems where the compressed air is stored in an aquifer layer that is intersected by the idle hydrocarbon well and confined by a first impermeable formation layer above it and a second impermeable formation layer below it and where the rework includes installation of one or more well barrier elements to prevent any leakage of hydrocarbon to the surface either via the casing or via the annular region behind casing. Additionally, the well barrier elements also prevent any leakage of the compressed air via the annular region behind the casing and prevent any contact of the compressed air with the hydrocarbon in the subsurface systems. Idle hydrocarbon well refers to a well which was originally completed for hydrocarbon production, but is no longer being used fort such a purpose.

[0017] In one embodiment of the present disclosure, the repurposed well completion system may comprise a first plug installed in the casing at a depth below the aquifer layer bottom depth as a well barrier element to hydraulically isolate the deeper hydrocarbon layer and prevent contact between the compressed air and the hydrocarbon.

[0018] An annular section behind the casing spanning at least the thickness of the aquifer layerinterval, can extend some distance into the first impermeable formation layer and some distance into the second impermeable formation layer, and can be used as an additional well barrier element by squeeze cementing to fill any cracks in the cement or the casing. This serves to prevent any leakage of the compressed air and / or the hydrocarbon along the annular region behind the casing.

[0019] The squeeze cemented annular section spanning the aquifer interval may be perforated to connect the compressed air storage zone in the aquifer layer to the wellbore to enable injection and production of compressed air. A production tubing running through the casing from the well head to a depth between the top and bottom depths of the aquifer layer may be used to inject and produce the compressed air during the charging and discharging cycles of the compressed air energy storage system. A packer may be set in the annulus between the production tubing and the casing at a depth above the aquifer layer top depth to hydraulically isolate and contain the compressed air in the tubing.

[0020] Other aspects and embodiments are described in further detail below.BRIEF DESCRIPTION OF THE DRAWINGS

[0021] The detailed description will be better understood in conjunction with the accompanying drawings as follows:

[0022] FIG. 1 is a depiction of a compressed air energy storage system using repurposed hydrocarbon wells intersecting an aquifer layer in conformance with one example embodiment of the disclosure.

[0023] FIG. 2 is an example of a reservoir site selected to simulate a 5MW compressed air energy storage system and shows the top view of the reservoir with a set of selected idle wells.

[0024] FIG. 3 is an embodiment of the system where the well barrier elements include thesqueezed cement sections in the annulus and one plug.

[0025] The embodiments of the present disclosure are detailed below with reference to the listed Figures.DETAILED DESCRIPTION OF THE EMBODIMENTS

[0026] 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.

[0027] 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.

[0028] 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 teaching persons 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.

[0029] 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.

[0030] 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.”

[0031] The word “about” means plus or minus 5% of the stated number.

[0032] 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.

[0033] When methods are disclosed or discussed, the order of the steps is not intended to be limiting, but merely exemplary unless otherwise stated.

[0034] 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.

[0035] 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, and publications 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.

[0036] The embodiments of the present disclosure generally relate to compressed gas energy storage, and more particularly to compressed gas energy storage systems which repurpose existing abandoned, orphaned, or idle hydrocarbon wells.

[0037] This disclosure describes an idle hydrocarbon well completion system reworked to enable a compressed air energy storage system where the compressed air is stored in an aquifer layer that is intersected by the idle hydrocarbon well and confined by a first impermeable formation layer above it and a second impermeable formation layer below it. The workover can include one or more well barrier elements to prevent any leakageof hydrocarbon to the surface either via the casing or via the annular region behind casing. The well barrier elements also prevent any leakage and flow of compressed air along the annular region behind the casing and prevent any contact of the compressed air with the hydrocarbon in the system. Leakage of fluids in the annular region behind casing can occur due to cracks and fissures in cement or cracks in casing due to the age of the wells.

[0038] Impermeable formation layer here refers to rock formations, for example shale formations, that act as flow barriers to fluids because of their extremely low permeabilities. In addition to the first and second impermeable formation layers that provide vertical confinement, the reservoir can also have other geological structural features, such as pinched out layers, impermeable regions, sealed faults etc., that can trap and facilitate storage of large volumes of compressed air through lateral confinement.

[0039] Aquifer candidates selected for compressed air energy storage are those that contain non potable water and are hydraulically isolated from any underground drinking water sources as well as the deeper hydrocarbon layer. The deeper hydrocarbon layer may be partly or fully depleted. Idle hydrocarbon well as used in this disclosure refers to a well originally completed for hydrocarbon production. Hydrocarbon as used in this disclosure refers to either oil or gas or a combination of both phases.

[0040] Figure 1 shows one embodiment of a compressed air energy storage system using repurposed idle hydrocarbon wells 140 to store compressed air in a subsurface aquifer 150 that they intersect. The hydrocarbon wells 140 were drilled previously to extract hydrocarbon from the deeper hydrocarbon layer 160.

[0041] The charging cycle of the compressed air energy system compresses ambient air with compression system 110 captures heat via heat management system 130 and injects it into the subsurface aquifer for storage using the repurposed wells 140.

[0042] In the generating cycle, the stored air can be produced from repurposed wells 140,heated by heat management system 130, and expanded through turbines in an expansion system 120 to generate electricity when needed.

[0043] Prior to starting the compressed air injection and production cycles, a compressed air storage cushion must be built in the aquifer layer 150 to provide pressure support for the required injection and production rates which in turn are determined based on the design specifications for the power capacity, cycle durations and storage duration of the compressed air energy storage system.

[0044] Typical compressed air storage cushion volumes are 10 to 100 times the injection and production cycle air volumes. For an advanced adiabatic compressed air storage system such as the example shown in Figure 1, heat released during a charging compression cycle may be captured via a heat management system 130 comprising one or more heat exchangers and stored in a hot thermal store and used later to heat the expanding air during a generating cycle. Another example of a heat management system 130 is a cold- water tank as a 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 a generating cycle and the cold water returned to the cold-water tank to close the water loop.

[0045] Selection of candidate reservoir sites:

[0046] Potential candidate reservoir sites are those that contain idle hydrocarbon wells that pass through an aquifer layer and which were originally drilled to extract hydrocarbon from the deeper hydrocarbon layers that are now partially or fully depleted and no longer economical to produce from.

[0047] Geological and petrophysical analysis of available archived subsurface geophysical well logs, cement bond logs and drilling reports of the idle wells may be used to identify the presence of impermeable shale layers above and below the aquifer layer as well as other geological structural features that can trap and facilitate storage of the compressedair.

[0048] Available salinity data of the aquifer may be reviewed to ensure it is not a potential underground source of drinking water or connected to current drinking water networks. The permeability and porosity of the aquifer as well as the number and location of the available idle wells are important consideration factors to assess if the candidate site can meet the injectivity and productivity requirements and hence the design power capacity of the compressed air energy storage system.

[0049] Selection of candidate idle hydrocarbon wells for repurposing for compressed air energy storage is based on their location in the reservoir and guided by reservoir models and simulations to ensure they can meet the flow and pressure requirements of the compressed air injection and production cycles. The areal extent of the aquifer is another important factor to ensuring sufficiency of storage volume of compressed air needed for the design power capacity and storage duration.

[0050] Reservoir Simulation of a compressed air energy system:

[0051] Figure 2 is an example of a potential candidate reservoir site for a 5MW compressed air energy storage system and shows the top view of the reservoir site with a set of selected idle wells. For this 5MW system, there are four water wells for water depletion Wl, W2, W3, W4 and four compressed air wells Al, A2,A3,A4 for compressed air injection and production.

[0052] Based on the available archived subsurface geophysical information, a preliminary reservoir model was built to demonstrate the viability of the reservoir site for a 5MW compressed air energy storage system for an 8-hour charge and a 16-hour discharge cycle duration. The storage aquifer layer for this exemplary candidate has 28% porosity, is 80 ft thick with horizontal and vertical permeabilities of 340 mD. and 68 mD, respectively. It is confined between an 80 ft caprock layer above (a first impermeable layer) and a 20 ft thick bedrock layer (a second impermeable layer) below, with both layers having a very low permeability of O.lmD.

[0053] The initial aquifer reservoir pressure is 66.7 atm and the temperature is 46.1 C. ASPEN simulations of the surface compressor and expansion subsystems for a 5MW advanced adiabatic compressed air energy storage system gave the requirement of air production rates from the reservoir in the discharge cycle and the air injection rates during the charging cycle.

[0054] Prior to beginning the compressed air injection and production cycles, a compressed air storage cushion must be developed in the aquifer layer to provide pressure support for the injection and production rates required for the 5MW plant. The volume of the compressed air storage cushion is typically in the range of 10 to 100 times the injection or production cycle volumes and the actual size will depend on the reservoir structure, relative permeabilities of air and water in the aquifer and the position and location of the wells.

[0055] It is preferable to maintain the pressure close to the initial aquifer pressure, but it should never exceed the fracture pressure of the aquifer formation. Reservoir simulation for the exemplary candidate site described here for the 5MW plant included the following three operation stages:

[0056] Depletion of water and initiation of compressed air storage cushion stage of two- months duration. This involves simultaneous water production from the four water wells Wl, W2, W3, W4 and compressed air injection into the four compressed air wells Al, A2, A3, A4 to allow faster compressed air storage cushion creation while maintaining the air injection pressure close to the initial aquifer pressure and always below the fracture pressure.

[0057] Compressed air storage cushion growth stage of four-months duration to grow the compressed air storage cushion by shutting in the water wells and continuing to inject compressed air at the rate of 2.787E+6 standard cubic feet / day per well during this period. The resulting compressed air storage cushion volume was about 100 times the required total daily air production volume for a 5MW plant.

[0058] The compressed air injection / production cycling stage was simulated for a duration of 12 months. Compressed air was injected at the rate of 18.26E+6 standard cubic feet / day per well for 8 hours during the charging cycle and produced at the rate of 9.13E+6 standard cubic feet / day per well for 16 hours during the discharge cycle in each of the four wells for 5MW power generation.

[0059] Reservoir simulations showed strong pressure support over the 12 months of compressed air injection / production cycling with pressure variations of + / - 3.5 atm respectively, thus validating the feasibility of this candidate site and idle wells to support generation of 5MW power for 16 hours every day. It is to be noted that operating strategies to build the compressed air storage cushion and carry out the compressed air injection and production cycles can vary depending on the reservoir structure, features, and properties as well as the available idle wells and their location. While the example above demonstrates the site feasibility for a 5MW system, scale up to higher capacities of 100 MW or more is possible by increasing the volume of the compressed air storage cushion and the number of idle wells to increase injection and production rates of the compressed air. A larger compressed air storage cushion volume also enables longer duration storage of energy.

[0060] Reworking the well completion system for compressed air energy storage:

[0061] The workover requirements of the well completion system to repurpose it for a compressed air energy storage systems includes: (a) enabling compressed air injection into and compressed air production out of the compressed air storage cushion in the aquifer, (b) prevention of any leakage of hydrocarbon to the surface through inside the casing, (c) prevention of any leakage of hydrocarbon into and flow along the annular region behind casing (d) prevention of any leakage of compressed air into and flow along the annular region behind the casing and (e) 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.

[0062] Figure 3 is one embodiment of the invention that shows a repurposed idle hydrocarbonwell passing through an aquifer 3200 and a now depleted hydrocarbon containing layer 3400. The aquifer is a saline aquifer with water that is non potable. Further, the aquifer layer is confined between a first impermeable formation layer 3100 and a second impermeable formation layer 3300 and is hydraulically isolated from any freshwater layers closer to the surface and from the depleted hydrocarbon zone below.

[0063] The repurposed well can comprise typical elements of a well, such as casing 310, tubing 320, old cement 330, and a packer 340. The repurposed well completion system may also comprise a first plug 370 installed in the casing at a depth below the aquifer layer 3200 bottom depth as a well barrier element to hydraulically isolate the deeper hydrocarbon layer and prevent contact between the compressed air and the hydrocarbon. 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. While the embodiment of Figure 3 shows only the one depleted hydrocarbon layer below the aquifer, it is possible that there are other hydrocarbon layers between the second impermeable layer and the depleted hydrocarbon layer that may or may not have been previously producing. Tn such scenarios, the first plug 340 serves as a well barrier to isolate the other hydrocarbon layers too.

[0064] 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 3, a squeeze cemented annular section 350 behind 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 compressed airand / or the hydrocarbon along the annular region behind the casing.

[0065] This squeeze cemented annular section 350 behind the casing should span at a minimum the aquifer layer 3200 interval, but preferably should also have a first extension into the first impermeable layer 3100 and a second extension into the second impermeable layer 3300 as shown. The impermeable layers 3100, 3300 have cap rock like properties, are tightly consolidated and have sufficient strength to withstand stresses of normal well operations and have negligible flow through them.

[0066] Hence, extending the squeeze cementing region into these layers ensures there is very low risk of well barrier integrity loss through creations of conduits for leaks through the annular region. The first plug 370 is also preferably set against the second extension of the squeeze cemented section to leverage the strength of the impermeable layer and its resistance to stresses as shown in this embodiment.

[0067] Squeeze cementing can also be used to prevent leaks across casing that may be damaged 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.

[0068] Referring again to the embodiment in Figure 3, the squeeze cemented annular section 350 that spans the aquifer layer interval may be perforated with new perforations 360 to connect the compressed air storage zone 3210 in the aquifer layer to the wellbore. The perforations may be across the entire interval of the aquifer thickness as shown or optionally only a partial upper section of the aquifer interval may be perforated if for example the reservoir simulation shows it to be a preferable way to minimize water coproduction with compressed air during the discharge cycle. A tubing 320 may be run through the casing from the well head to a depth between the top and bottom depths ofthe 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.

[0069] A packer 340 may be set in the annulus between the tubing and the casing at a depth above the aquifer layer top depth to hydraulically isolate and contain the compressed air in the casing between the packer 340 and the first plug 370 and within the tubing 320. Preferably the packer is set against the first extension of the squeeze cemented section 350 to leverage the formation rock strength of the first impermeable layer 3100 and its resistance to stresses.

[0070] In an optional embodiment of the invention, a second plug 380 can be installed in the casing between the first plug 370 and the depleted hydrocarbon layer 3400 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. 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 the 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.

[0071] The injection air stream out of the compressor may be cooled to the reservoir temperature or can be higher if there are no adverse effects of injecting higher temperature air into the aquifer. To conserve the heat energy of the compressed air during injection and production and minimize heat loss though the wellbore tubing to the surrounding formation, one may utilize insulated tubing.

[0072] Hydraulic pressure tests may be carried out to test casing integrity and monitor for leaks across the installed well barriers. Additional pressure testing using compressed air may also be conducted to monitor for leak of compressed air past the first plug into the casing section below or leaks along the annular section behind the casing if the casingintegrity is poor. This leaked air could migrate up to surface if the cement integrity is poor and may be detected in the surface casing vent valve assembly.

[0073] A sensor system comprising one or more sensors can be utilized 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 can also detect flow of compressed air in the surface casing valve assembly indicating leakage of compressed air in the annular region behind the casing.

[0074] One option for detecting flow at the surface casing valve assembly is a bubble test where one end of a hose is connected to the surface casing vent valve and the other end is submerged under water. Optionally, monitoring the annular pressure with the surface casing vent valve closed can give an indication of leak if the pressure builds up. The sensor system may also include specially configured housing assemblies and methods on the surface to enable concentration of any leaked hydrocarbons in the environment for better detection of their presence. Further the sensor system may be a combination of surface and sub-surface sensors and may be configured in a network. The sensing system may have functionalities to automatically sample and sense either continuously or at defined time intervals and may be equipped with alarm systems to generate alerts. Optionally the sensing system may include functionality for manual collection of samples for analysis at fixed time intervals.

[0075] 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, may also 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.

[0076] While the embodiments here are described for a compressed air energy storage system operated as an advanced adiabatic system, they are equally applicable to compressedair 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.

[0077] 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 a first impermeable layer, an aquifer layer, a second impermeable layer, and a hydrocarbon layer, wherein the hydrocarbon layer is below the first impermeable layer, the aquifer layer, and the second impermeable layer; b) an air storage zone in the aquifer layer fluidly connected to 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) perforations in squeeze cemented annular section; b) tubing running through the casing to a depth between the top and bottom depths of the aquifer layer; and c) a packer set in the annulus between the tubing and the casing at a depth above the aquifer layer top depth.

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 spanning a first impermeable layer, an aquifer layer, a second impermeable layer, and a hydrocarbon layer, wherein the hydrocarbon layer is below the first impermeable layer, the aquifer layer, and the second impermeable layer;b) creating a squeeze cemented annular section spanning at least the aquifer layer; c) creating an air storage zone in the aquifer layer; d) perforating the squeeze cemented annular section; e) installing a first plug within the squeeze cemented annular section below the perforation; f) storing air within the air storage zone.

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