Methods and systems for zonal isolation in wells   

Abstract: According to the invention, a method for isolating a zone inside a well is provided. The method may include providing a catch screen at a first location in the well and providing a fluid flow to the catch screen. The fluid flow may include a first fluid and a shape memory material. The first fluid may at least partially pass through the catch screen. The shape memory material may accumulate at the catch screen. The method may also include triggering the shape memory material such that it changes from a first shape to a second shape, thereby at least partially isolating one portion of the well from another portion of the well.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims priority to Provisional U.S. Patent Application No. 61/448,560 filed Mar. 2, 2011, entitled “DEVICES FOR ZONAL ISOLATION IN GEOTHERMAL WELLS,” the entire disclosure of which is hereby incorporated by reference, for all purposes, as if fully set forth herein.

The U.S. Government may have rights in this invention pursuant to DOE AWARD NO. 10EE0002771.

SUMMARY

In one embodiment, a method for isolating a zone inside a well is provided. The method may include providing a catch screen at a first location in the well and providing a fluid flow to the catch screen. The fluid flow may include a first fluid and a shape memory material and/or engineered material. The first fluid may at least partially pass through the catch screen. The shape memory material and/or engineered material (collectively referred to as “shape memory material” herein) may accumulate at the catch screen. The method may also include triggering the shape memory material such that it changes from a first shape to a second shape, thereby at least partially isolating one portion of the well from another portion of the well.

In another embodiment, a different method for isolating a zone inside a well is provided. The method may include providing a seal mechanism coupled with an elongated member, where the seal mechanism includes a shape memory material. The method may include inserting the elongated member into the well and triggering the shape memory material such that it changes from a first shape to a second shape, thereby at least partially isolating one portion of the well from another portion of the well.

In yet another embodiment, a different method for isolating a zone inside a well is provided. The methods may include providing a liquid mixture into the well and causing the liquid mixture to foam and set at a first location in the well, forming a porous open cell solid, thereby at least partially isolating one portion of the well from another portion of the well.

The present invention is described in conjunction with the appended figures:

FIG. 1 shows a visualization of a shape memory material compacted, encapsulated in a seal, and then returned to its original shape after trigger activation of the seal;

FIG. 2 shows one embodiment of the invention for isolating a zone inside a well which uses a shape memory material and a catch screen;

FIG. 3A shows another embodiment of the invention for isolating a zone inside a well which uses a shape memory material coupled with a drill pipe;

FIG. 3B shows another embodiment of the invention for isolating a zone inside a well which uses a shape memory material disposed inside a membrane coupled with a drill pipe;

FIG. 4 shows another embodiment of the invention for isolating a zone inside a well which uses liquid deployable foam which can set and cure inside the well;

FIG. 5 shows an Enhanced Geothermal System for power generation;

FIG. 6 shows four different types of zonal isolation in a well;

FIG. 7 shows deployment of the zone isolation system from FIG. 3B;

FIG. 8 shows deployment of the zone isolation system from FIG. 3A; and

FIG. 9 demonstrates additional features of the embodiment shown in FIG. 2.

DETAILED DESCRIPTION

Embodiments of the present invention include new apparatuses and methods for isolating zones in a well through the use of an engineered, controlled flow manufactured materials. An engineered material can provide a designed flow resistance that builds pressure internally as a fluid passes through it. In some embodiments, an engineered material can be used to build pressure in a well (or pipe) by limiting the fluid flow at particular locations.

A well may be defined as a subterranean hole drilled into the earth, and typically used for oil, gas, or geothermal energy exploration and production. It can be useful to isolate subterranean fluid flow to certain locations, or zones, within a well and to prevent flow in other areas. A well can also refer to a pipe or any other chamber within which fluid flows, even if not drilled into the earth.

In some embodiments of the invention the shape memory or engineered material can be a man-made porous material, possibly of a polymeric and/or elastic nature. Any material may be used in which an engineered porosity can be created and used to at least partially affect the pressure differential in the embodiments described herein. Merely by way of example, the following materials may be employed: organic polymers, inorganic polymers, epoxies, silicones, rubbers, etc. Devices that are used in a downhole environment to isolate well areas and withstand pressures produced by downhole fluids and/or gases are typically called packers and/or Zonal Isolation Devices (ZID\'s).

Some embodiments of the invention provide a new type of ZID or packer for use in oil, gas, and/or geothermal wells that is composed of multiple components. Such a ZID can use an engineered porous seal material to create well flow isolation at discreet locations within a well between the wellbore and the well casing or drill pipe.

In some embodiments, the engineered seal material that creates the isolation (seal) can be delivered into the well (1) as a monolithic piece attached to a work pipe, (2) as discrete pieces (possibly 0.1 inches to 2 inches) carried into position with a liquid, (3) as discrete pieces contained by a removable containment barrier that is attached to a work pipe, or (4) by flowing the engineered material in liquid form directly into the well at which point it forms the seal. Once placed, the seal material can allow flow through the porous internal structure, but seal off most flow around the seal material. In some embodiments, annular flow (flow between the seal and the well and/or pipe) is primarily eliminated or reduced in comparison with other seals. In some embodiments, well flow is not stopped but is significantly reduced, thus allowing gradual pressure build-up along the length of the seal and reducing localized high pressure points on the formation common with other types of packers, that can result in localized damage or failure to the formation and potentially compromise the ability of a packer to maintain a differential pressure. A larger distribution of the pressure along the length of the ZID can reduce the chance of fracturing the formation in unwanted locations.

In some embodiments, the seal material may be compacted during delivery and held in place by a skin or encapsulant. The seal material can remain compacted until the encapsulation is released by a chemical, thermal, shape memory behavior, pressure environment, well chemistry (pH) or mechanical trigger. See FIG. 1 for a visualization of this process. In some embodiments, the compacted, non-triggered material can allow high flow to continue to carry more material into place. When the trigger is activated, the seal material expands to fill the annulus between the wellbore formation and the drill pipe, creating the engineered low-flow porous seal.

Depending on how the seal material is delivered downhole, a deployable catch screen may be used at certain locations along the length of the ZID to catch or retain seal material pieces and hold them in place until triggered. FIG. 2 shows this embodiment of the invention.

The delivery of seal material can be accomplished through a number of mechanisms. In some embodiments, combinations of mechanisms may be employed to deliver the seal material.

In one embodiment, the seal material can be flow delivered (FIG. 2). Discreet particles of the seal material can be contained within fluid such as water, mud and other liquids. The fluid with the particles may then be pumped downhole and restrained by a catch screen (or filter) to accumulate seal material in a desired location.

In some embodiments, the delivery of seal material can be delivered attached to a work pipe (FIG. 3A). The seal material can be fabricated as a monolith and can be rigidly attached to the work pipe. Attachment of the seal material can be made through mechanical or adhesive means. In one example, the work pipe may be fabricated in 40 ft. discreet lengths, and can include the attached seal material to be delivered downhole through a work string per standard oil field practices.

In other embodiments, the delivery of seal material can be delivered unattached with a work pipe (FIG. 3B). The seal material, in discreet chunks or sizes, can be contained along the length of a work pipe through the use of a skin or containment barrier over the outside of the seal material. The seal material may not be rigidly bonded or attached to the work pipe. A containment barrier can be used to hold the seal material to the work pipe. The work pipe, for example can come in 40 ft. discreet lengths, can have the contained seal material delivered downhole through work string per standard oil field practices.

In some embodiments, the delivery of seal material can be flow delivered in-situ with a downhole seal formation (FIG. 4). Liquid and/or solid components for polymer seal material can be mixed on site of a well and are mixed and pumped in liquid form into the well bore annulus. The seal material can flow into place in well and can react in-situ using well bore environmental conditions to achieve reaction and cure.

The seal can be made from any number of materials. In some embodiments, the seal material can include a porous polymer material, for example, an open cell foam. An open cell foam can include, merely by way of example, silicone, polysiloxane, epoxy, and polyurethane foams. In some embodiments, the seal material can be a porous ceramic material. In some embodiments, components of the seal material can be selected such that they form a polymer material once downhole. In some embodiments, the seal material can have a pore size between about 10 microns and about 1000 microns. In some embodiments, the seal material can include porous particles such as polymer foam spheres. In other embodiments, the seal material may be any combination of the above described materials, and/or possibly include materials not discussed herein.

The seal material can have a number of operational properties. For example, the seal material can be porous; elastically compressible; may expand when triggered by mechanical, chemical or thermal means; and/or when expanded, it may still allow some amount liquid flow through pores.

For example, the seal material can comprise open cell epoxy foams, open cell silicone foams, shape memory foams, porous polymer or elastomeric balls, porous ceramic balls, in-situ formed epoxy or silicone foams, discreetly bonded foams, and/or monolithic foams unattached, attached or bonded to work pipe. In some embodiments, the seal material can comprise of any or all of the above and/or can be reinforced with non-continuous fibers or other reinforcements.

The seal material can be reinforced with elements that alter the materials performance, including mechanical, thermal, and chemical resistance characteristics. In some embodiments, reinforcements can include particles, discreet objects, non-continuous fibers (chopped fibers), random oriented fiber mats, and/or continuous fiber reinforcements. In some embodiments, reinforcement materials can include ceramic, carbon, glass, polymer (Kevlar). In some embodiments, reinforcements can range in size from nano-scale to macro-scale.

A skin or encapsulating material may be used according to some embodiments (see FIG. 1). The skin may include a material that contains the seal material and/or reacts to the forces of the compressed seal material or other external forces during downhole delivery. The skin material may be porous or non-porous. In some embodiments, the seal material may have the capability of being triggered to at least partially release itself from the seal material so that the compacted or compressed seal material is allowed to expand.

In some embodiments, the skin or encapsulant material can include a sealed elastomer with high strain capability; a hard shell, continuous or mesh-like material; and/or a wire or tape material wrapped around to form a cage.

In some embodiments, an elastomeric skin can be used to enclose the seal material and compact the same through use of reduced internal pressure. In some embodiments, for example, the skin can be sealed. In some embodiments, a hard shell skin can be placed on the compacted seal material and can react with material forces through mechanical means. In some embodiments, the skin does not need to be sealed, allowing liquids to permeate the skin and affect the seal material.

In some embodiments, the skin materials can include a thin walled silicone rubber elastomer, a hard shell polymer coating, polymer capsules, ceramic capsules, metallic capsules, metallic wire, and/or inorganic or organic fibers.

An encapsulant trigger, for example, can be a physical, mechanical, or chemical process used to remove the skin or encapsulant material at the correct time that allows the seal material to expand to its unconstrained or uncompacted state. A trigger can work in conjunction with the skin material, may not harm or physically alter the seal material, and/or can be time controllable to enable removal of the skin only at the desired time once the seal material is in place downhole. In some embodiments, a skin material can be triggered, for example, using a solvent flow, well chemistry (e.g. pH), an acid or corrosive flow, heat activation, explosive charges, sonic waves (sonification), acoustic energy, electro-magnetic waves, and/or vibration.

A catch screen can be a screen that allows fluid flow to pass through but contains seal material particles and holds them in the proper location when flowed downhole. In some embodiments, the catch screen can be located on outside of drill pipe and screens particles in the annular space between the formation and the drill pipe.

The catch screen, for example, can be capable of rigidly attaching to the drill pipe, can be capable of surviving the downhole journey without damage, can be open or deployed and make contact with formation wall, and/or can catch the seal material particles while still allowing fluid flow.

In some embodiments, the catch screen, for example, can comprise of a metallic mesh with metal spring bow fingers and mechanical release, and have a metal drill pipe collar. In some embodiments, the catch screen, for example, can consist of a metallic mesh with composite spring bow fingers and mechanical release, and have a metal or composite drill pipe collar. In some embodiments, either of the above concepts can be used with a shape memory metal or polymer composite actuation release. In some embodiments, the metallic mesh with metal spring bow fingers can be coated with ceramic and may not need an actuation release.

The following provides descriptions of various specific embodiments of the invention. These embodiments are provided as examples only. Any given feature of one embodiment may or may not be present in all embodiments. Additionally, any given feature of one embodiment may be implemented in other embodiments.

One key renewable energy resource being exploited is geothermal energy. Currently, commercial geothermal reservoirs are referred to as a hydrothermal energy because the water and the heat are naturally occurring. Unlike wind and solar power, geothermal energy is not affected by changing weather and is therefore always available to meet power demands. Thus, this process offers an environmentally benign, reliable source of energy.

In the U.S., geothermal power is currently produced from relatively shallow wells located primarily in California and Nevada. In these locations, geothermal energy is produced under nearly “ideal” circumstances, which include porous rock and an ample supply of sub-surface water. For geothermal energy to be more widely utilized, and to tap into the large potential offered by generating power from the heat of the earth, deeper wells will be necessary to reach the hot, dry rock located up to 10 km beneath the Earth\'s surface. To utilize this resource, water will be introduced into the well to create a geothermal reservoir. This approach is known as an Enhanced Geothermal System (EGS).

EGS reservoirs as shown in FIG. 5 are typically at depths of 3 to 10 km, and the temperatures at these depths have become a limiting factor in the applications of some technologies. For example, reliable zonal isolation for high-temperature applications at high differential pressures is needed to conduct mini-fracs and other stress state diagnostics.

Zonal isolation can be useful for many EGS reservoir development activities. However, to date, the capability has not been sufficiently demonstrated to isolate sections of the wellbore to: (1) enable stimulation; and (2) seal off unwanted flow regions in unknown EGS completion schemes and high-temperature (>200° C.) environments. Furthermore, zonal isolation devices have been classified into two main categories: Full borehole isolation devices and annulus isolation devices.

Potential uses of the zonal isolation devices described herein may be: 1) fracking or stimulation, 2) cement casing formation, 3) cold zone seal-off, and 4) zonal flow control, as illustrated in FIG. 6. These intended use subdivisions define differing operating parameters such as required pressure differential, operating temperature, operating lifetime, device geometry, and/or device delivery method. FIG. 6 shows (a) a single device used in the stimulation process, (b) a straddle configuration sealing of the annulus used for stimulation and pressure leak-off testing, (c) a full cross-section isolation device used to control flow in boreholes or naturally occurring fractures, and (d) a full cross-section device which can be used to create casings.

Another factor that may be considered besides the specific downhole conditions and the specific zonal isolation process desired by the operator, is understanding what processes the well operator is willing to employ to install and remove the zonal isolation device, and what processes can be employed to prepare the well for the insertion, activation, or removal of the zonal isolation device. For example, is the well operator willing and able to cool the well in the region where the zonal isolation device will be installed which might allow the device to be thermally triggered. Other trigger conditions may or may not be deliverable by the well operator.

The porous material implemented in the seal may be responsible for creating the pressure differential in the well and transferring the corresponding loads into the borehole wall. To accomplish this within any given length requirement, the porous material may need to exhibit particular microstructure characteristics. The density and pore size of the material will be at least partially responsible for determining the ability to create the desired pressure differential and transferring the loads into a length of the borehole.

Furthermore, the material may exhibit chemical stability at operational temperatures while saturated with water. The material may be very consistent and have predictable properties over a wide range of temperatures. The downhole environment will also introduce a number of contaminants into the system other than water; therefore the material may also be resistant to attack from chemicals such as hydrocarbons and dilute acids or bases.

Three methods of possible deployment for the seal materials of the invention are, merely by way of example: (1) delivery by the work pipe and triggering to expand; (2) delivery piecewise by fluid flow and triggering to expand once in position; and/or (3) delivery by work string or fluid flow and synthesizing (foaming) in place. For the first two methods of deployment a flexible material such as CTD\'s TEMBO® Shape Memory Polymer Foam Material (TEMBO® Foam) would be necessary. For the third method of deployment, other materials such as porous organic/inorganic materials become a possibility in addition to foamed polymers.

Delivery of a porous plug as a zonal isolation device can be accomplished in at least three ways. In oilfield and other applications, an embodiment of the invention may be installed on the outside of a drill string in a compacted state, lowered into the open hole, and then deployed out such that it seals against the walls in a temperature-driven process. FIG. 7 illustrates a work string delivery process. For the temperatures and pressures required for an EGS zonal isolation, this delivery method may be very challenging. Therefore, if the device is to be delivered on a work string, an additional method of constraining the device before deployment can be considered. Coatings which dissolve in water or other common mild solvents or chemicals used in well drilling may be utilized to deploy the device. Additionally, other deployment or radial expansion mechanisms may be used for both deployment and to provide radial pressure onto the borehole wall.

The second delivery method of the porous shape memory material, shown in FIG. 8, would be to flow or release particles of the material into place while pumping through a drill string and capture the material in place with a screen blocking the annulus.

A third method would be to form the porous plug downhole via a chemical synthesis foaming reaction. As seen in FIG. 4, this type of delivery would afford easy delivery of liquids or liquids with suspended particulates.

The structure or macroscopic composition of the ZID plug can also be divided into different concepts. The porous plug may be monolithic, in which case it would be delivered on the work pipe or as a liquid and foamed as described above. The plug also could be composed as a polylithic structure, formed from many deployed capsules to give a packed particle composition. It may also be a composite monolithic structure formed from particles of porous materials adhered to each other, thereby forming the plug.

Three key differences make embodiments described herein more effective and operationally viable than a fine-grained porous plug. First, the shape memory foam material can be compacted and frozen or constrained into shape before delivery, expanding in place and creating internal pressure in the plug. The internal pressure created by the spring-back output pressure of the foam applies force against the well bore, allowing it to react to differential pressure more effectively than a simple particulate. Second, the shape memory material is internally porous, and therefore can be delivered in large pieces, allowing it to be captured and accumulate much more quickly than a fine-grained material. Finally, the material can be formulated to closely match the specific gravity of the carrier liquid. For an unbalanced plug either above or below the insertion point, the specific gravity could be biased to help the particles either rise or sink into position. Or, for a balanced plug both could be used to simultaneously form a plug both above and below the insertion point.

FIG. 9 represents the cross section of an open-hole wellbore, with a drill string pipe (labeled “A”) inserted to just below the zone to be isolated. The pipe includes a capture screen, indicated by label “B” that deploys out from the pipe. Large particulate pieces of porous material packaged in a compressed state, indicated by label “C” may be flowed down the pipe using cooled water as a carrier. These pieces may circulate out of the pipe and upward to be captured by the screen. After the pieces are captured, the compressed porous materials may be triggered to expand, completely filling the desired length of annular space and putting a light radial pressure on the drill pipe and borehole walls to keep the porous plug in place and transfer any pressure differential created by the slowing of water flow directly into the borehole wall.

Selection of materials and material development for a porous zonal isolation device is done to allow a device that can be installed, build the pressure gradient, survive the temperatures, resist the forces applied, and be easily removed from the wellbore. In particular, the high temperatures required for EGS may necessitate materials that are developed specifically for this purpose. Also, since shape memory materials are temperature activated, different materials may be necessary depending on the temperatures encountered in a particular well. For this reason, materials may be used which allow for operating temperatures of up to 300° C.

Porosity and cell size of the material may also be critical to generate a pressure gradient by resisting the flow but yet not block the flow completely. Sand beds have been studied to understand the interaction of particle size and porosity on flow resistance. Flow resistance through a sand bed is known by its inverse, hydraulic conductivity, and varies by orders of magnitude based on the particle size. For extremely small particles the flow resistance becomes nearly infinite. To generate a reasonable pressure gradient, fine or very fine sand can be used with a particle size in the range of 0.05 mm to 0.25 mm. Shape memory materials with a cell size in this range may have a similar hydraulic conductivity. This drives the material to a very fine texture, but has been achieved with shape memory materials and other porous materials for other applications. An existing material with cell size of roughly 0.2 millimeter was tested in a simple set-up showed hydraulic conductivity in the appropriate range.

To flow the materials into place, it may be necessary to have materials with a specific gravity close to one—that of water. This can be achieved because the polymer materials naturally have a specific gravity less than 1 but can be adjusted with dense fillers to match the requirement. Also, the specific gravity of the capsule as a whole can be adjusted with liquid fillers such as salt water. In the unbalanced example shown in FIG. 10, the specific gravity may be slightly less than the carrier fluid (mostly water) but not too low or the particles may not tend to carry downwards in the pipe under low flow conditions. Also, since the shape memory particles will expand once in place, the specific gravity of the pieces may be adjusted by sealing them with a membrane to prevent immediate water saturation.

To resist the forces applied, the particles may be installed with an internal pressure and by shear forces into the well bore walls. The stiffness of the material at temperature may define how much pressure per length of plug can be applied when the material expands. To meet practical size limitations, the material may have to generate between a few psi and a few hundred psi per inch through flow resistance. The material may also have compression stiffness in this same range.

Finally, removal of the porous material from the well bore can be considered. With a screen capturing the material that can be actuated, the screen would be removed and flow under the material would destabilize at the top surface and be pumped out in the original pieces to be recaptured and used again. An alternate removal scheme may involve circulation of a substance, possibly a solvent, through the porous zonal isolation device to dissolve or otherwise decompose the plug material. The polymer materials could be quickly dissolved by solvents currently accepted for use in the oil industry, or elsewhere. Another alternative would be to drill out the device if it is unable to be removed by solvent or under flow. Another alternative in a geothermal well would be to keep the material in place with constant cooling of the well due to flow through the plug, and then allow the material to decompose when flow is stopped and the material heats up to the temperature of the formation.

A number of polymeric materials may have properties that satisfy the various temperature and environment conditions. These polymeric materials include, merely by way of example, MR series, EPDM, Polyimide, BMI, Cyanate Ester, Silicones, and PEEK. These foamed polymeric materials have traits and/or properties which may be critical to the zonal isolation device performance. Operating temperature depends on the glass transition temperature, decomposition temperature and effect of temperature variance on the mechanical properties. The foam structure of a material considers the ability to control the foam structure in a desired manner with regard to aperture and cell size, relative density or “openness,” even distribution, and density. The mechanical properties depend on shear strength, maximum compressive strain, and output pressure at incremental values of strain. Lastly, the resistance to water may be important to the chemical stability throughout the temperature range as well as the effects water saturation has on the mechanical properties.

Polymers, metals and ceramics are all possible encapsulation candidate materials. However, at this stage, more development is needed to determine the desired porous seal material properties so that a full evaluation of all potential candidates can be considered.

In addition to possible material candidates, a number of possible trigger mechanisms are possible. This includes trigger by heat, chemical reaction, solvent, explosive charges, ultrasonic vibration, or some combination of these. For example, the reaction rate for chemical reactions which may strip the encapsulation material can be increased by vibration, and heat, which allow more mobility of atoms. Vibration and heat allow the reactants to get physically close enough to react by way of clearing away the products of the already reacted materials. This allows for unreacted materials to more readily physically meet and react, thereby increasing the reaction rate.

The invention has now been described in detail for the purposes of clarity and understanding. However, it will be appreciated that certain changes and modifications may be practiced within the scope of the appended claims.