System and Method to Fracture and Seal Subterranean Formations

This application claims the benefit of U.S. Provisional Patent Application Nos. 63/648,429, filed May 16, 2024, and 63/745,658, filed Jan. 15, 2025, both of which are hereby incorporated by reference in their entirety herein.

The present disclosure relates generally to an energy storage system with a sealed subterranean storage zone in which to store a high-pressure working fluid until the energy is needed at the surface to perform useful work such as generating electricity, and more particularly to fracturing and sealing such zones.

While it is relatively easy for electrical power to move from place to place over long distances, electrical power demand is ever increasing in the United States as it is used, among other things, for lighting, heating, cooling, refrigeration, electronics, machinery, and some transportation systems. Moreover, the frequency of peak power events is increasing as the number of power-hungry devices attached to the North American power transmission grid increases. In the United States, much of the electricity is generated by burning natural gas as a fuel.

Energy storage is needed to balance the large variations in supply and demand to supplement the power generation systems currently in use. High summer temperatures, low winter temperatures, electric powered transportation methods, artificial intelligence (AI) data methods and the like are adding to the power needs of today. Large scale energy storage methods currently include compressed air energy storage (CAES), natural gas cavern storage, pumped hydro, chemical batteries, and subterranean energy storage. Each energy storage system uses different physics and mechanics to achieve the goal of providing energy when it is needed in sufficient quantity. Underground, cavern, natural gas storage is popular in Europe and other places around the world to store chemical energy until it is needed in the long heating season.

CAES relies on the elasticity of the working fluid and the thermal expansion of the working fluid at the surface to produce useful work. Accordingly, for hydraulic systems like CAES, PE (potential energy)=(1/2) kx, where: PE is the elastic potential energy (measured in joules, J) k is the spring constant (measured in newtons per meter, N/m) and x is the displacement from the equilibrium position (measured in meters, m).

Pumped hydro is the method of storing energy by pumping water to a higher elevation, storing it, then later allowing the water to fall under gravitational forces to spin a turbine/generator combination to produce electricity. Water is pumped up the hill during off-peak demand periods when electricity is available at a lower cost. For pumped hydro, (potential energy)=mass of water (m)×gravitational acceleration (g)×height difference (h).

Subterranean energy storage is similar to compressed air energy storage (CAES) in that the working fluid is stored underground, however the energy recovery mechanisms are quite different. Both systems can gain some geothermal energy from the earth to warm the working fluid. The subterranean energy storage relies on the elasticity of the earth and the overburden on the rock where the working fluid is stored and the thermal energy gathered by the working fluid.

In the construction phase of the subterranean energy storage system the well, the subterranean zone, and the surface facilities must be built and/or properly prepared for the operation phase. A subterranean zone can be made up of man-made hydraulic fractures, natural fractures, natural occurring caves, or other fluidically connected geologic features. Not all subterranean systems include fractured formations in the subterranean zone. Some are well sealed and do not require hydraulic fracturing or sealing.

For this technology any or all fluidically connected parts can be used to store high pressure fluid. The fluid stored may be used as the working fluid for a system to produce electricity or other useful work below ground or above ground.

The steps to prepare the zone, fracture, store high pressure fluid in the subterranean zone, and then move it to the surface equipment to perform useful work, desalinate water and generate electricity are described in applicant's earlier granted patents, U.S. Pat. Nos. 8,763,387, 9,481,519, 10,125,035 and 11,927,085, all of which are hereby incorporated by reference in their entirety herein. Also hereby incorporated in their entirety herein are applicants' U.S. Pat. No. 11,795,802 describing the creation of fractures in the subterranean zone, sealing it, and preparing it to store high-pressure working fluids which are later moved to the surface to perform useful work; and U.S. Pat. No. 12,123,293 describing other methods to fracture and seal the subterranean zone prior to utilizing it for storage of the high-pressure working fluid.

Essentially, the first step is to collect and evaluate geologic data. Pilot wells may be drilled to collect various geologic data including core samples to verify models. Once a feasible well placement has been determined, one or more wells are drilled, then one or more casing strings are run and cemented in place. Completions are designed and placed in a manner that allows the working fluid to traverse between the wellbore and subterranean formation with the least restriction. In some instances, it may be necessary to sever the upper casing from the lower casing. There are many methods available today to perform this operation which may include techniques such as perforating, fracturing, water jetting, or others to establish a smooth fluid flow path into and out of the subterranean zone for the working fluid through the wellbore.

After the well is constructed, pressure pumping and fluid mixing equipment are moved to the location. One or more treatment schedules are injected into the target subterranean formation to artificially modify the permeability of the formation. At this time the formation can be sealed and prepared for the operation phase.

During the operation phase, a working fluid is injected down the well bore, and out into the fracture network of the subterranean zone. Energy is stored in the subterranean zone as high-pressure fluid. Fluid is pumped from a low-pressure storage area to a high-pressure subterranean zone where it can be used immediately or stored for a period of time before being moved to the surface to produce useful work. The high-pressure fluid can, for example, be used with a turbine/generator set to produce electricity. Low-pressure storage can be a subterranean zone located close to the surface. One or more wells might be used in the subterranean energy storage system. Some may be dedicated to injection or production flow, or a combination of these regimes depending on subterranean zone access and system demands. In any event, the fluid is stored there under pressure until all, or part of the fluid volume is returned to the surface. In most instances, this high-pressure fluid will be used to produce electricity. The output could be used to power a data center, an industrial plant, a manufacturing center, a food processing plant or some other medium to large scale facility needing energy.

Once such subterranean energy storage facilities are constructed and operational, the stored energy can be released to produce workable energy, such as electricity. In order to convert this stored energy as efficiently as possible, a control system needs to be utilized.

If the fracture is tough enough and does not leak too much, it may be acceptable to cycle the working fluid into and out of the subterranean zone without placing any sealing material in it.

It is important to note that the well bore can be vertical, near vertical, horizontal, near horizontal or at any angle. Likewise, the fracture opening or the subterranean zone, or the storage fractures can be vertical, near vertical, horizontal, near horizontal or at any angle relative to the well bore.

Historically, many different materials and techniques have been used in oil and gas wells to stop the flow of water from an underground zone into the well bore. It is important to control the flow of unwanted formation water from entering the well bore in large amounts as the water reduces hydrocarbon flow, increases corrosion, and decreases the life and profitability of the well. This technology goes back nearly 100 years and many different fluid systems are currently available. Such systems have been used in oil and gas wells for different phases of drilling, completion, and production engineering for lost circulation control, drilling fluids, plugging agents, fracturing fluids, water shut off, and water profile control.

By way of example, gel injection is the process of pumping chemical formulations of water, polymers, and crosslinking chemical agents. The gelation time can be controlled to ensure the materials are in the correct location when the gelation takes place to shut off a path for the formation water. Some gel injections contain a polymer like polyachrylamide.

In any event, it is a general object of the present disclosure to provide a system and method to store energy underground as a high-pressure working fluid.

It is another general object of the present disclosure to provide a system and method to store fluids underground in fractured and sealed subterranean zones.

It is yet another general object of the present disclosure to provide a system and method to store other useful fluids underground.

A more specific object of the present disclosure is to provide a system and method to seal a subterranean zone wherein the material is an equal density polysaccharide fluid developed for efficient placement of the water based and specialty polymer gel (WB SPG) technology.

Yet another more specific object of the present disclosure is to provide a system and method to seal a subterranean zone wherein the material is a silicone rubber containing polymers.

Yet still a further object of the present disclosure is to provide a system and method where the seal material is placed on the high-pressure side of the formation water.

These and other objects, features and advantages of this disclosure will be clearly understood through a consideration of the following detailed description.

According to an embodiment of the present disclosure, there is provided a system for the sealing of a subterranean zone for high pressure fluid storage. The system includes a zone having propagating fracture tips that are sealed by pumping a fluid from a wellbore. The sealing fluid consists of two fluids which have the same density but different viscosities. The viscosity of the carrier fluid being less than the acting fluid.

According to an embodiment of the present disclosure, there is also provided a method for sealing a subterranean zone for storing high pressure fluid. The method consists of selecting a subterranean zone for fluid storage, fracturing the zone and creating fracture tips therein, providing a first fluid and a second fluid wherein the fluids have the same densities but different viscosities, pumping a sealing fluid consisting of the two fluids into the zone and sealing the fracture tips.

According to an embodiment of the present disclosure, there is provided a system for the sealing of a subterranean zone for high pressure fluid storage. The system includes a zone with rock faces and fracture tips that are sealed by a fluid pumped from the surface, through the well and out into he subterranean zone which consists of rock faces and/or fracture tips that are sealed by a sealing fluid. A push fluid is used to place the sealing fluid which has the same density but will have higher different viscosity at all shear rates

One or more embodiments of the subject disclosure will now be described with the aid of numerous drawings. Unless otherwise indicated, use of specific terms will be understood to include multiple versions and forms thereof.

It is to be understood that hydraulic fracturing is a process used in oil and gas wells for pumping fluids and solids through a wellbore and out into a zone breaking open rock to provide paths for hydrocarbons to move into the well and up to the surface. In this storage application method and system, the zone can be fractured and sealed with the proper sealing material as part of a fluid system. A desired subterranean zone is thereby created in which to hold fluids at high pressure for long or short durations for the purpose of storing energy.

illustrates an embodiment of a method and systemfor storing fluid underground for the purpose of energy storage. As shown, a wellwith fractured and sealed subterranean zonesis connected to a surface facilitywhich is connected to a fluid storage mechanism. The surface facilitywill contain at least one pump and one turbine/generator set for converting high pressure fluid to generate electricity. The usable work outputis shown above the surface facility.

illustrates an embodiment of a method and systemfor storing fluid underground for the purpose of energy storage. As shown, a wellwith fractured and sealed subterranean zonesis connected to a surface facilitywhich is connected to a fluid storage mechanism. The surface facilitywill contain at least one pump and one turbine/generator set for converting high pressure fluid to generate electricity. The energy inputis shown above the surface facility. The energy inputis being used to pump the working fluid into the welland into the fractured and sealed subterranean zoneswhere it will be stored until it is needed.

is a simplified block diagram of the system showing energy input A, geothermal energy input B, the stored fluid, and the energy output.

One embodiment of this system consists of the application of an organically crosslinked polyacrylamide, or polyacrylamide created through copolymerization with other monomers, for geomechanical pumped storage reservoir creation and lifecycle maintenance. An example of the invention includes the application of polyethyleneimine (PEI) cross-linking a copolymer of acrylamide and tert-butyl acrylate (PAtBA), which we will also refer to as a Water-Based (WB) Specialty Polymer Gel (SPG) or WB SPG for abbreviation.

An equal density polysaccharide fluid was developed for efficient placement of the WB SPG technology at the propagating fracture tip and for optimized sealing of the fracture, as well as cleanup of the fracture void for water storage. Accordingly, a method has been developed for sealing a subterranean zone for high pressure fluid storage. It is a method of pushing fluids to grow fracture volume and push WB SPG technology to the propagating front of the fracture.

Achieving proper displacement of one fluid (WB SPG technology fluid) by another push fluid (polysaccharide fluid) requires two physical phenomena. Unless dealing with vertical deep fracture sealing and steering a downward fracture direction where the density of the sealing fluid is higher than the density of the push fluid, the density of the second fluid must essentially equal the density of the first fluid. This is necessary to prevent buoyancy, or density gradient, effects from allowing one fluid to pass over another in the horizontal fracture space. And, the viscosity of the second fluid (polysaccharide) must be greater than the viscosity of the first fluid (WB SPG technology) in the sequential fluid train at all shear rates that will occur anywhere within the subterranean area during all pumping and placement exercises.

Such favorable viscosity conditions are proven through viscosity measurements (Grace M5600 viscometer, R1B1 Couette configuration) over the shear rates of 0.001 sec-1 to 1600 sec-1 while at the pressures anticipated downhole.

These fluids can be used in the construction, fracturing phase, or added to the working fluid being cycled into and out of the subterranean zone, or they may be pumped in as a repair to seal a leaking subterranean zone. These fluids can be shear thickening, shear thinning, or Newtonian fluids.

It is important to note that the well bore can be vertical, near vertical, horizontal, near horizontal or at any angle. Likewise, the fracture opening, or the subterranean zone can be vertical, near vertical, horizontal, near horizontal or at any angle relative to the well bore.

The seal is designed to hold pressure from one direction. The pressure differential is zero or higher from the inside of the fluid storage area to the outside of the seal. Seal material is sometimes placed in an oil or gas well when a zone is experiencing a high water cut. This is done to reduce the water produced and thus decrease the operating cost. The seal holds pressure from one direction. The producing zone is the high-pressure side and the fracture or fluid path to the well is the low-pressure side.

Another embodiment of this system includes the application of silicone rubber containing polymers in subterranean long duration energy storage construction. The system is employed as a fluid by which the hydraulic fracture may be formed, sealed, and repaired.

A method has been developed for sealing a subterranean zone for high-pressure fluid storage based upon these two fluid technologies.

An 8.8 lb/gal silicone rubber containing polymer and a setting time greater than 6 hours has been achieved. The setting time is adjustable. The second is an 8.8 lb/gal polysaccharide fluid developed for efficient placement of the silicone rubber containing polymer at the propagating fracture tip and any leak point in the subterranean zone for optimized sealing of the fracture, as well as cleanup of the fracture void for fluid storage.

It will be appreciated that the fluid densities used herein are not fixed limitations. Densities may range from any achievable value, from about 8 lb/gal to about 18 lb/gal.

The system includes the application of silicone rubber containing polymers to create subterranean structures through a method of at least two fluids having specially optimized density and rheological properties to create a subterranean void capable of storing water for use in long duration energy storage.

Three variants of silicone rubber containing polymers are noted by way of example. The silicone rubber containing polymer as a neat material. Silicone rubber containing polymer w/ Microfine Solids. Macro solids bound by silicone rubber containing polymer w/ Microfines.

In some embodiments, the push fluid, a polysaccharide fluid, may contain solid particles and/or microfines.

An embodiment of silicone rubber containing polymers are comprised of liquid silicone rubber with additives to control the crosslinked material's physical and mechanical properties. These additives could include granules of cross-linked liquid silicone rubber, non-cross linked high consistency rubber, cross linked high consistency rubber suspended in the pre-crosslinked liquid silicone rubber. In addition, solids particles including but not limited to silica, Fe2O3, Fe3O4, and Al could be suspended in the liquid silicone rubber to control material's physical and mechanical properties.

Several silicone rubbers exist but a preferred embodiment is cured or platinum-cured liquid silicone rubbers. In addition, a thinner, Polydimethlysiloxane (PDMS) oil, is added to the cured liquid silicone to engineer the liquid viscosity, cured material strength, elasticity, and cure time to match downhole conditions. Mass percentages of thinner range from 10% to 90%. Pushing fluids to grow fracture volume and push silicone rubber containing polymers to the propagating front of the fracture may be necessary. By way of example, achieving proper displacement of one fluid, a silicone rubber containing polymers, by another push fluid, a polysaccharide fluid, requires two physical phenomena.

One, the density of the second fluid must essentially equal the density of the first fluid. This is necessary to prevent buoyancy, or density gradient, effects from allowing one fluid to pass over another in the horizontal fracture space. And, two, the viscosity of the second fluid (polysaccharide) must be greater than the viscosity of the first fluid (polymer containing silicone rubber) in the sequential fluid train at all shear rates that will occur anywhere within the subterranean area during all pumping and placement exercises.