Patent Description:
With the advent of improved drilling techniques for drilling to greater depths in a formation and higher toleration of temperatures, numerous advances have been made to allow for the formation of specific well configurations.

To elevate the efficiency of well positioning the unification of drilling techniques, working fluid chemistry, wellbore conditioning unit operations together with flow rate, sequencing inter alia must be combined to achieve efficient heat recovery in the most complex and varied thermal gradients in a given formation.

The present invention facilitates the ability to recover thermal energy regardless of thermal gradient anomalies and complexities.

In terms of the evolution of the art, one of the earlier developments is realized in Moe, <CIT>. There is disclosure regarding a wellbore configuration which includes a plurality of heat absorbing holes within a geothermal area. The disclosure is silent regarding casing or liners, however it is limited to utilization of a fractured zone, angular disposition of the heat absorbing holes being parallel to each other and further limitations. The teachings specifically state:
"The magnitude of the sloping angle will depend on several factors, for instance the temperature gradient in the rock, the length of the heat absorbing hole and the water flow rate. Calculating the angle will be well within the capabilities of the skilled person and will therefore not be detailed here. The angle would normally lie between <NUM>° and <NUM>°, preferably it will be about <NUM>°.

Furthermore, in order to maximize the extraction of heat from a given volume of rock, at least substantial parts of the heat absorbing holes extend parallel to each other. More preferably, the heat absorbing holes are arranged in one layer or, if necessary, in a plurality of vertically spaced layers. Providing an array of vertically spaced layers, each layer having a plurality of heat absorbing holes, allows for increasing the capacity of the plant without spreading the holes over a wide area. This is of considerable importance if the volume of earth available for exploitation is not large.

The supply and return holes <NUM>, <NUM> are interconnected by four heat absorbing holes <NUM>, each having a diameter of <NUM> and being approximately <NUM> long. The spacing between these holes <NUM> may be <NUM>-<NUM>. They have been drilled starting out from the supply hole <NUM> and terminate at or near the return hole <NUM>. A fracture zone <NUM> has been established in this area to provide flow communication between the holes <NUM> and <NUM> since it would be difficult to hit the return hole <NUM> directly when drilling the heat absorbing holes <NUM>.

The teachings also teach a difficulty regarding the connection of the inlet and outlet as emphasized. As a disadvantage, the Moe arrangement would not provide sufficient teaching regarding unrestricted access to a gradient regardless of its anomalies and thus the disclosure is limited to specific scenarios.

The document teaches a closed loop thermal energy recovery arrangement in a variety of rock types at higher temperatures, one of which is solid rock which is differentiated in the disclosure of Shulman:
"This invention relates to novel methods and apparatus employing liquid circulation in a closed pipe loop system by which the thermal energy in subterranean hot rock is extracted, i.e. mined, and brought to the surface for utilization. Said hot rock may be solid, fissured or fractured and dry or wet but essentially free of mobile fluid. By this invention, the thermal energy is transferred from the hot rock to relatively cold liquid flowing in one or more of a plurality of distantly separated heat conducting pipe loops that descend from a manifold at the surface into the hot rock and then join together with the bottom of a riser through which the heated fluid returns to the surface.

The wellbore configurations are not discussed in any details with complex patterns or disposition of the heat recovering conduits. The arrangement relies on piping in the wellbore configuration for fluid transportation through the arrangement for thermal recovery from the formation. Another disadvantage is seen by the positioning of the manifold on the surface rather than inherently within a downhole network of wellbores.

Brown, in <CIT>, teaches a fracturing process for forming a fractured zone in hot dry rock. Super critical CO2 is used as a working fluid to convey the absorbed energy from the geothermal formation. The fluid communication is not in a closed loop where there is an interconnecting segment in fluid communication between an inlet well and an outlet well where the working fluid is isolated from the formation. In the Brown arrangement, the formation itself indiscriminately communicates with the inlet and outlet wells. This is further evinced by the fact that Brown teaches:
" Finally, the hot dry rock circulating system is completed by drilling the two or more production wells to intersect the reservoir near each end of the elongated reservoir region as defined by the "cloud" of microseismic event locations defining the shape of the fractured hot dry rock reservoir. All the wells would be appropriately completed with casing to the surface and then purged of drilling fluids and other water-based materials, again using gaseous carbon dioxide.

From this passage the use of casing is identified as is an intersection of wells, but not with each other as in a closed loop, but rather with a man-made reservoir within the formation.

<CIT> discloses a geothermal plant. There are teachings in the patent regarding specific requirements for the production sections of the configuration being in a specific disposition relative to a concentric inlet/outlet well arrangement. The disclosure does not provide instruction regarding conditioning of the wellbores during or after drilling or possible directions for interconnecting segments to exploit the thermally productive zone without restriction.

<CIT>, teach a closed loop heat recovery arrangement for transferring heat from a well casing into the fluid. The text indicates:.

The text provides a general teaching regarding sealing, but includes casing in the heat recovering sections of the wellbore configuration. The text indicates:
"According to some embodiments, methods for producing geothermal energy described herein may include portions of wells that are not cased with metal pipe but, instead, the walls of such portions may be formation rock that has been sealed with hardened sealant and the well wall in such portions being defined by the boundary of such hardened sealant which, in some embodiments, will cause the diameter of the well in such portions to be larger, and in some cases much larger, than in the metal cased portion of such wells.

The reference mirrors the teachings of Shulman, supra, and does not provide instruction regarding intersection of wells, the absence of casing and/or liners or geometric variation in the disposition of the heat recovering segments of the wellbore arrangement to accommodate any thermal gradient pattern.

A further method of providing a geothermal wells system can be found in the document <CIT>.

It would be desirable to have a method of forming a wellbore configuration that can be user adapted to the anomalies of the gradient pattern as opposed to being confined to specific wellbore designs that are adapted to the limitations of the existing equipment and methods for recovering thermal energy.

The present inventive methods disclosed herein after ameliorate the noted limitations and provide previously unseen degrees of freedom to efficiently capture thermal energy from within a thermally productive formation.

One object of one embodiment of the present invention is to provide an improved method for configuring wells and well systems in a thermally productive formation for recovery of thermal energy there from for subsequent use.

Another object of one embodiment of the present invention is to provide a method for configuring wellbores in a thermally productive geologic formation, comprising:.

The conditioning is effected by at least one of continuously, discontinuously, during, after and in sequenced combinations of drilling of at least one of drilling the inlet well and the outlet well.

In greater detail, conditioning may include introducing at least one composition not native to the formation and a unit operation and combinations thereof.

To augment the effectiveness of the method, one may dynamically modify the conditioning operations responsive to signalling data from at least one of the drilling operations of the inlet and outlet wells.

Depending on the specific situation the unit operation may include controlling the temperature of drilling fluid, pre-cooling a rock face in the formation being drilled, cooling drilling apparatus and modifying pore space of wellbores formed from drilling in the formation.

Modification of the pore space may include activating the pore space for subsequent treatment to render it impermeable to formation fluid ingress into the interconnecting segment or egress of the working fluid into the formation, sealing the pore space during drilling in a continuous operation, sealing pore space during drilling in a discontinuous operation and combinations thereof.

Operational conditioning modification may also be based on signalling data from signalling between the inlet well and the outlet well.

Optionally, another unit operation includes forming conduits in the formation relative to a longitudinal axis of an interconnecting segment and in fluid communication therewith for augmenting thermal recovery with the working fluid. The conduits may have a terminal end and positioning of the conduits of an interconnecting segment may be in thermal contact with the adjacent conduits of an adjacent interconnecting segment of another well. The conduits may contain natural buoyancy-driven convection which enhances the effective radius of the heat-collecting interconnecting segment and increases overall heat transfer from the rock volume.

The conduits may be fractures, single bores, auxiliary segments, or multiple radial bores extending radially from an interconnecting segment.

When arranged with a vertical component the conduits act as convection cells, where natural buoyancy-driven convection enhances the effective radius of the heat-collecting interconnecting segment. The conduits are typically <NUM> inches ( <NUM> )in diameter or greater, and may be <NUM> inches ( <NUM>)or equal to the diameter of the interconnecting segment itself.

As another option, conduits of an interconnecting segment may be connected for fluid communication with the adjacent conduits of an adjacent interconnecting segment of another well.

A further object of one embodiment of the present invention is to provide a well configuration suitable for recovering thermal energy from a thermally productive geologic formation through circulation of fluid there through, comprising:.

In one embodiment, the auxiliary segment includes a selectively operable valve for allowing stored heated fluid circulation access to the interconnecting segment and may further include a selectively operable outlet in fluid communication with at least one of the conversion device and an adjacent well configuration.

The configurations may be a plurality of well configurations in a concentric and spaced relation, a plurality of well configurations in a spaced laterally offset parallel planar relation and may further include at least one of a common inlet well and a common outlet well.

For the thermal energy collection, the interconnecting segments are utilized and the configurations can provide a plurality of interconnecting segments in fluid communication with the inlet well and the outlet well with a plurality of spaced apart arrays of interconnecting segments in a predetermined pattern.

A still further object of one embodiment of the present invention is to provide a method of forming a well configuration suitable for recovering thermal energy from a thermally productive geologic formation through circulation of fluid there through, comprising:.

For the intersection drilling, drilling independently from the inlet well and the outlet well to form an interconnecting segment between the inlet well and the outlet is conducted by electromagnetic signalling.

Electromagnetic signalling devices will be utilized for the signalling and will be selectively positioned in predetermined location combinations of the inlet well, the outlet well, the detritus segment and the interconnecting segment.

The devices may be operated in a predetermined sequence.

Further, the method includes signalling a well in progress with signalling from a previously formed adjacent well.

The method is well suited to recovery of thermal energy from a geothermal formation having a temperature of not less than <NUM>.

For efficiency and flexibility of deployment in a formation, circulation of fluid within the interconnecting segment may be performed in the absence of casing and liners.

A plurality of interconnecting segments in embodiments can be in fluid communication with the inlet well and the outlet well, with the configuration having a plurality of spaced apart arrays of interconnecting segments in a predetermined pattern.

Optionally there may be a step of selectively circulating the fluid from one array as a slipstream to an inlet point of a spaced second array prior to discharge at the outlet well common to all arrays. In this way, the slipstream preheats fluid from the inlet well prior to circulation in the spaced second array.

The slipstream may also be distributed to an adjacent well configuration for thermal augmentation of the adjacent well.

Having thus generally described the invention, reference will now be made to the accompanying drawings, illustrating preferred embodiments.

Similar numerals used in the Figures denote similar elements.

The technology has applicability in the wellbore formation, drilling and energy recovery areas of technology.

Referring to <FIG>, shown is a schematic representation of a closed loop well system <NUM> disposed within a thermally productive formation <NUM>. The system <NUM> includes an inlet well <NUM>, an interconnecting well segment <NUM> and an outlet well <NUM> in closed loop fluid communication with an energy processing device <NUM> positioned on the surface,S. The outlet well may be co-located with the inlet well at the device <NUM> or located distally as shown by the dashed line <NUM> for alternate connection. A working fluid is circulated through the system <NUM> in order to absorb thermal energy from within the formation <NUM>.

For efficiency, the interconnecting well segment <NUM> is not cased or lined and does not include any other pipe or related mechanical arrangements. The outlet well <NUM> and inlet well <NUM> may be cased or otherwise made to comply with accepted practices known to those skilled in the art. Any detritus that evolves from use of the arrangement may be collected in segments <NUM>.

Energy processing device <NUM> may process the energy for other uses broadly denoted by numeral <NUM>, stored at <NUM> or passed on to an electrical grid <NUM> which optionally may include solar devices <NUM> and/or wind devices <NUM> in any suitable combination.

In respect of the spatial orientation of the wells within a thermally productive formation, reference may be had to <FIG>. In the illustration, elements have been removed for clarity, however it will be understood that the illustration is to convey the disposition of the interconnecting segment <NUM> may have relative to at least one of the plane of the inlet well <NUM> and outlet well <NUM>.

In the Figure, the interconnecting well segment <NUM> may be positioned at any angle within any of the planes ( X-Y ), ( X- (-Y) ) ( (-X)- Y) ( (-X) - (-Y) ), ( X-Z ), ( X- (-Z) ), ( Z- (-X) ), ((-X)- (-Z)), ( Z-Y ), ( Z- (-Y)), ((-Z)-(-Y)) and ((-Z)-Y) and may also be disposed to have an X,Y and Z coordinate for cross plane disposition. For purposes of explanation the positive x axis will represent the inlet well <NUM>. The well may be disposed at any angle alpha or beta in a range which does not impede operation of the well <NUM>. This is equally true for outlet well <NUM>. The inlet wells <NUM> and outlet wells <NUM> communicate with the surface ,S, as referenced in respect of <FIG>.

Any number of interconnecting segments16 may be disposed within the space discussed. Other well configurations will be discussed in the advancing Figures. The quantity and spatial positioning will depend on the thermal gradient of the formation <NUM>.

Advantageously, the observation of the drilling by intersection between the inlet well <NUM> and outlet well <NUM> by independent drilling operations to form the interconnecting segment <NUM>, the absence of liners, casing, etc. within the interconnecting segment with conditioning of the drilling operation, results in configuration freedom to maximally recover thermal energy.

<FIG> illustrates an example of the steps involved in sensor ranging the inlet well and outlet well in a formation for intersection through the formed interconnecting segment. Although the example references an interconnecting segment, it will be understood that the methodology relates to multiple interconnecting segments formation in any pattern as discussed in respect of <FIG>. The individual interconnecting segments are fully utilizable to have sensor communication there between to guide the drilling of subsequent interconnecting segments with a given well system or those being formed in a proximate system within the formation.

By providing the cross communication between the wells, the inlets, the outlets and interconnecting segments, trajectory drift is minimized to facilitate accurate intersection of the wells being drilled. Sensors may also be utilized in the detritus capture segments <NUM> , not shown and discussed ingreater detail herein after.

Referring now to <FIG>, a cross section of an interconnecting segment <NUM> is shown disposed with formation <NUM>. Extending from the segment <NUM> are or conduits <NUM> extending into the formation <NUM>. Conduits <NUM> may be voids either in fluid communication with the interior <NUM> of segment <NUM> or sealed without fluid communication with the interior <NUM>. It has been found that the conduits <NUM> are useful to enhance the thermal recovery capacity of the interconnecting segment when working fluid is circulated there though as well in periods of quiescence. Positioning and quantity of the radially extensions will be dictated by formation characteristics to maximize thermal recovery without structural/mechanical compromise of the segment <NUM>. Where adequate, if pre-existing fissures, cracks, fractures or contained areas of permeability are encountered, they may be used to function as conduits. Theses may also occur during drilling of the segment <NUM>.

<FIG> illustrates an example where the conduits <NUM> are arranged in a generally helical pattern with the dotted points representing those extending outwardly from the plane and those crossed points being representative of the extensions on the opposed surface extending away from the plane. This is exemplary; the pattern with be ascertained from gradient data amongst other germane parameters.

<FIG> illustrates a further example where a plurality of segments <NUM> are disposed within formation <NUM>. In the example, the extensions <NUM> of adjacent segments may be arrange in close proximity to fill a given area <NUM> with extensions to effectively increase the volume of the gradient from which thermal energy may be recovered. The conduits <NUM> act as a convection cell of buoyancy driven flow which direct thermal energy into the interior <NUM> of segments <NUM>. The extensions can be arranged for adjacent positioning or interdigitated with other conduits <NUM>.

As a further embodiment, the individual segments <NUM> may be connected by the conduits <NUM>, the connection being generally denoted by numeral <NUM>. In this manner, the arrangement has the appearance of a ladder when viewed perspectively.

Turning now to the well configuration possibilities, <FIG> illustrates a generally toroidal well configuration generally denoted by numeral <NUM> disposed within formation <NUM>.

In this arrangement, inlet well <NUM> is in fluid communication with a main inlet hub well <NUM> which is connected to each of the interconnecting segments <NUM>. Suitable valve devices ( not shown, but generally represented by numeral <NUM> ) may be incorporate in some or all of the looped segments <NUM> for fluid flow redirection and other control.

The arrangement <NUM> also includes a main outlet hub well <NUM> connected in a similar manner as that indicated for main inlet hub well <NUM> with a similar valving feature (not shown).

Within the structure, each looped segment <NUM> may be operated as a single unit to recover thermal energy.

As an operational alternative, the flow of working fluid within arrangement <NUM> may be circulated in a generally helical pattern through the whole arrangement with sequencing of periods of quiescence to allow for maximum thermal recovery. Such flexibility allows for connection to, for example the energy processing device <NUM>. This facilitates on demand power when the energy is converted to electricity and overcomes the limitations associated with baseload power peak delivery issues.

<FIG> illustrates a further embodiment of a well configuration denoted by numeral <NUM>. The general shape is that of a saddle where the interconnecting looped segments are adjacent one another with an arcuate presentation. The inlet well <NUM> may be connected to each of the looped segments <NUM> in a hub or manifold arrangement <NUM> or valved at <NUM> for selective operation. In a similar manner, outlet <NUM> may connected in the same fashion.

<FIG> illustrates yet another possible variation generally in the form of an inverted parabola.

<FIG> illustrates another well system configuration where the inlets <NUM> may be singular from distant points in the configuration or joined at <NUM>. Similarly, outlets <NUM> may be combined at <NUM>. For colocation, the outlets <NUM> and inlets <NUM> may be extended for geographic proximity.

<FIG> illustrates a general cone shaped configuration where the outlet well <NUM> may be at the bottom portion of the configuration or the top as shown in dashed line. The lower parts of the looped segments <NUM> may be connected together or independent.

<FIG> illustrates yet another configuration in the general form of a whisk. In this embodiment, the segment loops <NUM> may have a concentric inlet <NUM> and outlet <NUM> with fluid flow from the inlet in the direction of arrow <NUM> and outlet flow at <NUM>. This arrangement allows for a large volume of the formation to be " mined" for heat in the formation <NUM> outside of the configuration and in the formation volume <NUM> within the configuration. One of the advantages with this configuration are that all of the intersections happen with a single borehole or "mother bore" and electromagnetic signalling can be simplified, even accomplished with permanent devices placed in the mother bore or passively. Another advantage is only a single vertical bore is required to house both the inlet and outlet flow streams.

Turning to <FIG>, a wellbore system sector is schematically depicted generally denoted by numeral <NUM>. Sector <NUM> is within a thermally productive formation <NUM>, with the positioning of different wellbore configurations positioned in predetermined zones to maximize gradient coverage. In the example, the sector <NUM> provides a stacked and spaced arrangement of looped segments <NUM> sharing a common inlet well <NUM> and common outlet well <NUM>.

Depending on the parameters, fluid circulation may follow the pattern denoted A through F. In this manner, at least a portion of heated fluid from top looped segments <NUM> may preheat the fluid entering bottom looped segments <NUM>. Alternatively, each of the looped segments <NUM> and <NUM> can be operated independently.

In respect of the remaining configurations, the toroidal configuration <NUM> may receive heated fluid from the outlet <NUM> of the stacked arrangement <NUM>, <NUM> as denoted by the dashed lines <NUM> or simply have an independent inlet well <NUM> denoted by the chain line <NUM>.

The whisk configuration may have an independent inlet well <NUM> and a bottom positioned outlet well <NUM> or the inlet well may be common with that of the toroidal configuration as denoted by numeral <NUM>.

Finally, the saddle configuration may include a common outlet well with the toroidal configuration at <NUM>.

It will be understood that all inlet wells <NUM> and outlet wells <NUM> will extend to the surface or conversion device <NUM> (<FIG>) for operation. In the <FIG>, the wells <NUM>,<NUM> are truncated for purposes of clarity in the illustration.

The sector <NUM> is exemplary only as are the wellbore configurations and common and independent combinations. With the intersecting directional drilling, the conditioning operations and sensor guided drilling, any pattern or configuration can be synthesized to exploit even the most irregular, disparate multizonal gradient distributions. All of these features when unified with the fact that the instant technology does not include piping liners or other mechanical arrangements within the heat recovering interconnecting segments, immediately removes geometric constraints for the configurations thus allowing the mining of any gradient in any rock formation.

<FIG> is another example of a well arrangement <NUM> to recover thermal energy from a specific volume of the formation <NUM>. In the example, the detritus segments <NUM> may include sensors <NUM> to transmit information regarding detritus accretion. In this manner, the working fluid may be compositionally altered to incorporate chemical additives to mitigate/repair any compromised areas with the well system. The arrangement of the interconnecting segments <NUM> may disposed in a spaced array as shown to recover thermal energy.

Further, as illustrated in <FIG> auxiliary segments <NUM> may be in fluid communication with a respective segment <NUM> to which it is attached and incorporate a valve mechanism <NUM> to allow for selective operation. The auxiliary segments <NUM> may be used to store heated working fluid selectively used as a thermal driver in the arrangement for the well system in the example or used via suitable interconnection to another well system ( not shown in this Figure). As illustrated, the auxiliary segments <NUM> may be positioned in a coplanar disposition with the segment to which it is attached or in an orthogonal plane as shown in dashed lines in the Figure. Suitable variations to this are envisioned depending on the gradient features.

<FIG> illustrate grouped well systems <NUM> in different angular dispositions with in the formation. In the grouped configurations, the systems <NUM> are modularized within a specific volume of the formation <NUM> thus allowing for a small footprint and convenient general co-location of the inlet well <NUM> and outlet well <NUM>. Within the module, inlet wells <NUM> and outlet wells may be common to individual well systems or common for all modules in the system <NUM>.

<FIG> provides for the possibility of interconnecting auxiliary segments <NUM> between adjacent wells at <NUM> or thermal supplementation from one outlet <NUM> to an inlet <NUM> of an adjacent well.

Claim 1:
A method for configuring wellbores in a thermally productive geologic formation (<NUM>), comprising:
drilling independently in said formation a well having an inlet well (<NUM>) and an outlet well (<NUM>), the outlet well being separate from the inlet well;
signalling between said inlet well and said outlet well during drilling to intersect to form a continuous well having interconnecting segments between said inlet well and said outlet well, and detritus segments (<NUM>) such that one detritus segment is formed at an intersection of each pair of two upper and lower interconnecting segments and at the lowest point of each pair of two upper and lower interconnecting segments, said interconnecting segments having a predetermined angular configuration relative to said inlet well and said outlet well within said formation; and
conditioning at least said interconnecting segments to facilitate thermal recovery by working fluid flow therethrough without casing or liner material in said interconnecting segments.