Systems and methods for electrical power generation

Power generation assemblies and methods relating thereto are disclosed. In an embodiment, the power generation assembly includes a thermoelectric generator, and a conductor configured to conduct electricity generated by the thermoelectric generator to the surface of a subterranean wellbore. The power generation assembly is to circulate a working fluid through a closed loop in the power generation assembly in response to the receipt of geothermal energy within a subterranean formation, to cause the thermoelectric generator to generate electricity.

Not applicable.

BACKGROUND

This disclosure generally relates to electrical power generation. More particularly, some embodiments of this disclosure relate to systems and methods for generating electrical power utilizing geothermal energy accessed from a bore extending from the surface into a subterranean formation.

Bore holes are commonly drilled from the surface to access minerals or other resources (e.g., oil, gas, water, etc.) that exist within subterranean formations. The internal heat of the Earth (e.g., residual heat from the Earth's formation, heat generated by radioactive elements beneath the Earth's surface, etc.) typically induces an increasing temperature gradient per increasing depth within such bore holes (e.g., at a rate of approximately 1° F. per 70 vertical feet in some locations). The elevated temperatures within these bore holes are potential sources of energy that may be harnessed to provide power (e.g., electrical power) at the surface.

BRIEF SUMMARY OF THE DISCLOSURE

Some embodiments disclosed herein are directed to a system including a power generation assembly. The power generator assembly is configured to be enclosed within a wellbore extending from the surface into a subterranean formation along a central axis. Wherein the power generation assembly includes a thermoelectric generator, and a conductor configured to conduct electricity generated by the thermoelectric generator to the surface. The power generation assembly is configured to circulate a working fluid through a closed loop in the power generation assembly in response to the receipt of geothermal energy within the subterranean formation, to cause the thermoelectric generator to generate electricity.

Other embodiments disclosed herein include a power generation assembly. In an embodiment, the power generation assembly includes a first barrier and a second barrier spaced from one another along a central axis. In addition, the power generation assembly includes a first chamber, a second chamber, and a third chamber. The first chamber, the second chamber, and the third chamber are bounded by the first barrier and the second barrier, and the second chamber is axially disposed between the first barrier and the second barrier. Further, the power generation assembly includes a central housing defining a central throughbore and an annular flow path in the second chamber. Still further, the power generation assembly includes a thermoelectric generator disposed within the second chamber radially between the central throughbore and the annular flow path, and a working fluid disposed in each of the first chamber, the second chamber, and the third chamber. The central throughbore and the annular flow path are in fluid communication with the first chamber and the third chamber. When the first chamber is exposed to a first temperature and the second chamber is exposed to a second temperature that is higher than the first temperature the working fluid flows through the central throughbore at a third temperature and flows through the annular flow path at a fourth temperature that is less than the third temperature.

Still other embodiments are directed to a method of generating electrical power. In an embodiment, the method includes (a) positioning a power generation assembly in a wellbore extending into a subterranean formation, and (b) transferring heat from the formation into a working fluid disposed within the power generation assembly. In addition, the method includes (c) circulating the working fluid within a closed loop in the power generation assembly as a result of (b). Further, the method includes (d) exposing a thermoelectric generator of the power generation assembly to a temperature gradient using the circulating working fluid during (c). Still further, the method includes (e) generating electric current with the thermoelectric generator as a result of (d).

Embodiments described herein comprise a combination of features and characteristics intended to address various shortcomings associated with certain prior devices, systems, and methods. The foregoing has outlined rather broadly the features and technical characteristics of the disclosed embodiments in order that the detailed description that follows may be better understood. The various characteristics and features described above, as well as others, will be readily apparent to those skilled in the art upon reading the following detailed description, and by referring to the accompanying drawings. It should be appreciated that the conception and the specific embodiments disclosed may be readily utilized as a basis for modifying or designing other structures for carrying out the same purposes as the disclosed embodiments. It should also be realized that such equivalent constructions do not depart from the spirit and scope of the principles disclosed herein.

DETAILED DESCRIPTION OF EXEMPLARY EMBODIMENTS

The following discussion is directed to various exemplary embodiments. However, one of ordinary skill in the art will understand that the examples disclosed herein have broad application, and that the discussion of any embodiment is meant only to be exemplary of that embodiment, and not intended to suggest that the scope of the disclosure, including the claims, is limited to that embodiment.

The drawing figures are not necessarily to scale. Certain features and components herein may be shown exaggerated in scale or in somewhat schematic form and some details of conventional elements may not be shown in interest of clarity and conciseness.

In the following discussion and in the claims, the terms “including” and “comprising” are used in an open-ended fashion, and thus should be interpreted to mean “including, but not limited to . . . .” Also, the term “couple” or “couples” is intended to mean either an indirect or direct connection. Thus, if a first device couples to a second device, that connection may be through a direct connection of the two devices, or through an indirect connection that is established via other devices, components, nodes, and connections. In addition, as used herein, the terms “axial” and “axially” generally mean along or parallel to a given axis (e.g., central axis of a body or a port), while the terms “radial” and “radially” generally mean perpendicular to the given axis. For instance, an axial distance refers to a distance measured along or parallel to the axis, and a radial distance means a distance measured perpendicular to the axis. As used herein, the terms substantial, substantially, generally, about, approximately, and the like mean +/−10%. Finally, any reference to up or down in the description and the claims is made for purposes of clarity, with “up”, “upper”, “upwardly”, “uphole”, or “upstream” meaning toward the surface of the wellbore or borehole and with “down”, “lower”, “downwardly”, “downhole”, or “downstream” meaning toward the terminal end of the wellbore or borehole, regardless of the wellbore or borehole orientation.

As previously described above, elevated temperatures found within the lower regions of subterranean boreholes are a potential thermal energy source that may be harnessed to generate power (e.g., electrical power) for use at the surface. One common type of borehole that is formed in a subterranean formation is that associated with an oil and gas well. Typically, these wells may be drilled to a depth of 5000 to 10000 feet below the surface (depending the specific location), and may have a bottom hole temperature close to or over 300° F. There are a great number of such wells that have been drilled to access oil and gas reserves worldwide over the last two centuries. Once hydrocarbon production ceases or falls below an economic threshold, these wells are typically plugged (e.g., with cement/plugs, etc.) and abandoned. The costs for performing these operations may be considerable in some circumstances. However, these abandoned wells may still serve as an effective access point for the geothermal energy stored within the Earth. Therefore, embodiments disclosed herein include systems and methods for generating electrical power from the geothermal energy emitted into a subterranean wellbore, such as, for example, an abandoned oil and gas well). In addition, as will be described in more detail below, the systems and methods disclosed herein may also be utilized to generate electrical power from other sources of thermal energy (i.e., other than a geothermal energy source).

Referring now toFIG.1, a geothermal power generation system according to some embodiments is shown. System10generally includes a wellbore12extending into a subterranean formation6from the surface4. Wellbore12includes a central axis15, a first end or upper end12a, and a second or lower end12bopposite upper end12a. Upper end12ais disposed at the surface4, and lower end12bis disposed within the subterranean formation6. In this embodiment, wellbore12is substantially vertical, such that axis15is generally aligned with the vertical direction (e.g., along the direction of gravity). However, in other embodiments, one or more sections or portions of wellbore12may be non-vertically oriented (e.g., lateral). A casing or liner pipe16(or more simply casing16) is disposed within wellbore12and is secured in place. In some embodiments, casing16is cemented within the wellbore12so as to prevent formation fluids (e.g., oil, gas, water, etc.) from migrating to the surface4between the casing16and the wall of wellbore12. A plurality of perforations18extend through casing16and into formation6to provide a pathway for formation fluids into casing16and ultimately the surface4.

In this embodiment, wellbore12is abandoned, and thus is plugged to prevent formation fluids from progressing into casing16and up to surface4. In particular, in this embodiment cement14fills the lower portion of wellbore12, from lower end12bto a point above perforations18. In other embodiments, a mechanical plug or seal may be placed within casing16above perforations18to similarly prevent the flow of formation fluids to surface4via casing16. In still other embodiments, a combination of mechanical plugs and cement may be used to plug and abandon wellbore12.

Referring still toFIG.1, as previously described above, the internal temperature gradient of the Earth's crust results in an increasing temperature gradient when moving along axis15from the surface4within wellbore12, from upper end12atoward lower end12b. Thus, the temperature within wellbore12may be higher proximate lower end12bthan it is proximate upper end12a. Thus, system10also includes a power generation assembly100that is installed within wellbore12(particularly within casing16) and is configured to harness the temperature difference within the wellbore12to generate electrical power. Once generated, the electrical power may be conducted to the surface4via a conductor52(or a plurality of conductors) and delivered to a final location50, which may include a local power grid, one or more batteries, capacitors, or other power storage assemblies.

It should be appreciated that power generation assembly100is enclosed or encapsulated within wellbore12. Thus, in this embodiment, each of the components of power generation assembly100are disposed downhole (e.g., within wellbore12) such that only electric current (e.g., via conductor52) is brought back up to the surface4. As a result, power generation assembly100may require little to no surface space. The details of one embodiment of power generation assembly100will now be discussed in more detail below.

Referring now toFIG.2, an embodiment of power generation assembly100is shown installed within casing16of wellbore12(seeFIG.1). Power generation assembly100includes a first or upper barrier110, a second or lower barrier122, and a third or middle barrier120. Each of the barriers110,122,120are axially spaced from one another along axis15and each sealingly engages with the inner wall of casing16. In this embodiment, lower barrier122is proximate to and axially above cement14and perforations18, and middle barrier120is axially disposed between upper barrier110and lower barrier122. Thus, upper barrier110is uphole of middle barrier120and lower barrier122, middle barrier120is downhole of upper barrier110and uphole of lower barrier122, and lower barrier122is downhole of each of the upper barrier110and middle barrier120.

A first or upper chamber112is defined between upper barrier110and middle barrier120, a second or lower chamber114is defined between lower barrier122and cement14, and a third or middle chamber150is defined between middle barrier120and lower barrier122. Thus, upper chamber112is uphole of middle chamber150and lower chamber114, middle chamber150is downhole of upper chamber112and uphole of lower chamber114, and lower chamber114is downhole of each of the upper chamber112and middle chamber150. In this embodiment, because power generation assembly100is installed and incorporated within casing16wellbore12, barriers110,120,122comprise plugs that are installed within casing16.

Upper chamber112may be disposed within an axial section or portion of wellbore12that is at a first temperature, and lower chamber114may be disposed within an axial section or portion of wellbore12that is at a second temperature that is higher than the first temperature. For example, in some embodiments, the first temperature about the upper chamber112may range from 70° F. to 120° F., and the second temperature about the lower chamber114may range from 180° F. to 300° F. The axial length of chambers112,114,150may be adjusted so as to place the upper and lower chambers112and114, respectively, at predetermined depths to achieve a desired temperature difference therebetween.

Referring still toFIG.2, middle barrier120includes a central throughbore121extending axially therethrough. In addition, lower barrier122includes a first or upper end122a, a second or lower end122bopposite upper end122a, a first port124extending axially between ends122a,122b, and a second port126also extending axially between ends122a,122bthat is separate from the first port124. A first conduit127extends axially from lower end122btoward cement14(e.g., first conduit127extends axially downward or downhole) and is in fluid communication with first port124. A second conduit128extends axially from upper end122atoward middle barrier120(e.g., second conduit128extends axially upward or uphole) and is in fluid communication with second port126. Thus, the first conduit127and first port124define a first flow path through lower barrier122from middle chamber150to lower chamber114, and second conduit128and second port126define a second flow path through lower barrier122from middle chamber150to lower chamber114.

A central housing152is disposed within middle chamber150. In particular, central housing152is disposed axially between upper barrier110and lower barrier122and extends axially through central throughbore121in middle barrier120. Housing152includes a first or upper end152a, a second or lower end152bopposite upper end152a, and a central throughbore154extending axially between ends152a,152b. Upper end152ais disposed within upper chamber112and lower end152bis disposed within middle chamber150proximate lower barrier122. Therefore, second conduit128coupled to lower barrier122extends into throughbore154of central housing152.

An annular pocket158is defined within housing152that is radially formed between a radially inner annular wall156and a radially outer annular wall159. Radially inner annular wall156forms a portion of central throughbore154. A thermoelectric generator180is disposed within pocket158radially between annular walls156,159that is configured to generate electric current when exposed to two different temperatures. Specifically, generator180generates electric current when a radial temperature gradient is applied thereto via the Seebeck Effect. The construction of a thermoelectric generator (e.g., like generator180) is well known and therefore, the details of such a construction are not described in detail herein; however, in general, electric generator180includes dissimilar metallic materials that are exposed (during operation of power generation assembly100) to different temperatures via radial annular walls156,159to thereby generate electric current which is conducted to the surface4(e.g., via conductor52shown inFIG.1).

An annular flow path160is defined radially between casing16and radially outer annular wall159that extends axially from middle barrier120to a manifold region162within middle chamber150that is axially disposed between lower end152bof central housing152and lower barrier122. The manifold region162is also in fluid communication with central throughbore154of housing152via lower end154bof central housing152and with lower chamber114via first port124and first conduit127. Thus, annular flow path160is in fluid communication with lower chamber114via manifold region162. In addition, annular flow path160is in fluid communication with upper chamber112via a flow path164defined between upper barrier120and central housing152. Flow path164is an annular flow path that includes a U-bend166. As will be described in more detail below, U-bend166prevents or restricts gases from flowing or advancing axially upward from annular flow path160into upper chamber112during operations.

Referring still toFIG.2, during operations, a working fluid, such as, for example a refrigerant is circulated within power generation assembly100to expose thermoelectric generator180to two different temperatures. As a result, thermoelectric generator180may generate electric current which is supplied to the surface (e.g., surface4) via a suitable conductor or conductors (e.g., conductor52shown inFIG.1).

In particular, in this embodiment, the working fluid circulated within power generation assembly100may comprise a multi-component fluid, such as, for example, a two component fluid. Thus, the working fluid may comprise a first fluid and a second fluid. The first fluid may have a first boiling point, and the second fluid may have a second boiling point that is higher than the first boiling point. In the following example, the circulated fluid within power generation assembly comprises an ammonia and water mixture; however, it should be appreciated that other fluid combinations may be used in other embodiments, and the ammonia-water mixture discussed below is merely one potential example multi-component working fluid that may be circulated within power generation assembly100.

In addition, initially the annular flow path160may be charged with a gas that is different from the components of the working fluid. In some embodiments, the gas charged within annular flow path160may be inert. In the following particular example, the gas charged within annular flow path160is helium; however, it should be appreciated that other gases may be used in other embodiments. It should also be appreciated that the gas charged within annular flow path160(e.g., helium in the following described example) pressurizes the working fluid within power generation assembly180such that during the following operations, the circulated working fluid is maintained at a substantially constant pressure. In some embodiments, the pressure of the working fluid circulated within power generation assembly180may be maintained within range of −14.7 psig (−1 bar) to 150 psig (10 bar) during operations. In other words, the circulation of the working fluid within power generation assembly180(which is described in more detail below) is achieved via changes in state (e.g., from liquid to gas or from gas to liquid) and via the transfer of thermal energy, and not from an induced differential pressure (e.g., such as from a mechanical pump, compressor, or the like).

Referring still toFIG.2, during operations of one specific implementation, a mixture of ammonia and water (as previously described above) is disposed within lower chamber114as the working fluid. As previously described above, lower chamber114is disposed at a lower depth within the wellbore12and thus is exposed to relatively high geothermal temperatures. As a result, geothermal energy is transferred from the formation (e.g., formation6inFIG.1), through casing16and into the lower chamber114(see e.g., arrows170inFIG.2) so that the ammonia-water mixture within lower chamber114boils and emits ammonia-water vapors.

The ammonia-water vapors are then flowed (e.g., via natural convection) axially upward through second port126and second conduit128and are emitted into throughbore154of central housing152(see e.g., arrows172inFIG.2). The expansion of the ammonia-water vapors into throughbore154and the relatively lower temperature within throughbore154(e.g., compared to lower chamber114), cause the water component of the vapors to condense within throughbore154and settle axially downward into manifold region162(see e.g., arrows174inFIG.2). Conversely, the ammonia vapors emitted from second conduit128(which have a lower boiling point than the water) continue upward in a gaseous state and are emitted from throughbore154into upper chamber112via upper end152aof central housing152(see e.g., arrows176inFIG.2). Therefore, during operations, the radially inner wall156of annular pocket158within central housing152is exposed to the relatively high temperatures of the ammonia and water vapors flowing through throughbore154. In some embodiments, the radially inner wall156may be exposed to temperatures ranging from 180° F. to 300° F. during these operations.

Referring still toFIG.2, upon entering upper chamber112, the heated ammonia vapors are exposed to the relatively lower temperatures of upper chamber112that result from the relatively lower temperature of the formation (e.g., formation6inFIG.1) at the shallower depth of chamber112. Accordingly, upon entering the upper chamber112, thermal energy is transferred from the ammonia vapors back into the formation (see e.g., arrows171inFIG.2) such that the ammonia vapors cool and condense to a liquid that then flows through flow path164into annular flow path160. As previously described, the annular flow path160is filled with a gas, which in this example comprises helium. The helium is prevented from flowing back up through flow path164into upper chamber112by liquid ammonia that is disposed within U-bend166of flow path164. Upon entering annular flow path160, the ammonia liquid is exposed to the helium gas and therefore expands (e.g., evaporates) or diffuses back into a gaseous state as it generally flows or progresses axially downward through annular flow path160toward manifold region162(see e.g., arrows178inFIG.2).

The evaporation of the ammonia liquid into gas within annular flow path160cools the ammonia significantly so that the annular wall159defining annular flow path160is exposed to relatively low temperatures. For example, in some embodiments, the radially outer wall159may be exposed to temperatures ranging from −40° F. to 0° F. during these operations. Thus, thermoelectric generator180is exposed to a relatively large temperature difference or gradient between the radially inner wall156and radially outer wall159of annular pocket158. For example, in some embodiments, the temperature difference between the radially inner wall156and radially outer wall159may range from 175° F. to 340° F. Because the electrical current generation of thermoelectric generator180may be directly proportional to the temperature difference that is applied thereto, this relatively large temperature difference may allow thermoelectric generator180to generate a relatively large amount of electric current. In addition, thermoelectric generators (e.g., such as generator180) may also operate a greater efficiencies in lower temperature environments. Thus, by additionally cooling the working fluid (e.g., ammonia) as it flows through the annular flow path160, the overall temperature exposed to the thermoelectric generator180may be decreased such that generator180may operate at an enhanced efficiency.

Referring still toFIG.2, as the evaporated ammonia vapors flow axially downward toward manifold region162, they are once again condensed back into a liquid such that the liquefied ammonia may be mixed with the liquid water within manifold region162(which was condensed from throughbore154as previously described above—see e.g., arrows174). Thereafter, the ammonia-water mixture may be flowed from manifold region162back into lower chamber114via first port124and first conduit127(see e.g., arrows179inFIG.2) such that the above described cycle may be repeated.

As a result, during operations with power generation assembly100, a working fluid (e.g., a refrigerant such as the ammonia-water mixture previously described above) is continuously circulated in a closed-loop at a relatively constant pressure to thereby expose thermoelectric generator to a large temperature gradient. Accordingly, through use of the geothermal temperature gradient along axis15of wellbore12, power generation assembly180may generate electric current that is conducted to the surface4via a suitable conductor or conductors (e.g., conductor52inFIG.1).

In the embodiment described above, power generation assembly100(seeFIG.2) is incorporated within the casing16of a subterranean wellbore12. However, in other embodiments, the power generation assembly (e.g., assembly100) may be a self-contained unit or assembly that is constructed at the surface (e.g., surface4inFIG.1) and lowered into the wellbore (e.g., wellbore12). For example, referring now toFIG.3, a power generation assembly200is shown. Power generation assembly200is generally the same as power generation assembly100, and thus, components of power generation assembly200that are shared with power generation assembly100are identified with like reference numerals and the description below will focus on the features of power generation assembly200that are different from power generation assembly100.

Primarily, power generation assembly200omits upper barrier110and instead includes an outer housing202that has a central axis205and surrounds each of the middle barrier120and lower barrier122. As a result, outer housing202also partially defines each of the chambers110,114,150previously described above. In particular, outer housing202includes a first or upper end202a, and a second or inner end202bopposite upper end202a. Upper chamber110is defined within housing202between upper end202aand middle barrier120, and lower chamber114is defined within housing202between lower end202band lower barrier122. In addition, middle chamber150is defined within housing202axially between middle barrier120and lower barrier122. Further, because barriers120,122are disposed within housing202, they may be mechanical plugs that engage with the inner wall of housing202or they may be incorporated or integrated within the walls of housing202itself.

Referring still toFIG.3, operations with power generation assembly200are substantially the same as those described above for power generation assembly100, and thus, the details of which are not repeated herein in the interests of brevity. However, because power generation assembly200is a self-contained unit, assembly200is first lowered into a wellbore (e.g., wellbore12inFIG.1) such that upper and lower chambers110and114, respectively, are disposed at appropriate depths so as to be exposed to a desired temperature difference due to the geothermal temperature gradient of a subterranean wellbore. Once the desired temperature difference is achieved between upper and lower chambers110and114, respectively, operations with power generation assembly200(particular the circulation of fluids therein) may be conducted in substantially the same manner as previously described above so that electric current is generated by thermoelectric generator180. Upon the cessation of operations (e.g., at the end of power generation operations altogether or during maintenance periods), the power generation assembly200may be simply pulled to the surface (e.g., surface4) via appropriate lifting equipment.

In addition, because power generation assembly200is a self-contained unit within outer housing202, it may be operated to generate electrical power in other environments that include a temperature gradient, other than a subterranean wellbore (e.g., wellbore12). For example, power generation assembly200may be placed in any location or apparatus that exposes chambers110,114to different temperatures to thereby drive the circulation of the working fluid contained therein (e.g., ammonia and water as previously described above) to result in the generation of electrical power via thermoelectric generator180as previously described above. For example, power generation assembly200may be operated in an industrial facility (e.g., chemical plant, refinery, manufacturing facility, etc.) where fluids or materials are circulated at various temperatures in furtherance of other manufacturing or chemical processing operations.

Through use of the power generation assemblies described herein (e.g., power generation assemblies100,200), electrical current may be generated from an existing temperature gradient. In some embodiments, the existing temperature gradient may be a temperature gradient disposed within a subterranean wellbore (e.g., such as that associated with an oil and gas well) generated by geothermal energies drawn from the interior of the Earth. Accordingly, these existing temperature gradients may be harnessed to generate electricity for use in other processes or locations.