Fracture network systems and methods of forming the same

Abstract

An example method to form a fracture system includes generating a back flow or at least a lower pressure in a first well at a first zone. The back flow includes flowing a material from the first zone towards an outlet of the first zone and the lower pressure includes actively decreasing the pressure in the first zone. It is noted that the back flow may cause the first zone to exhibit the lower pressure (i.e., the back flow causes the first zone to exhibit a lower pressure than if there was no back flow). The method also includes hydraulically stimulating a second well at a second zone. Hydraulically stimulating the second well may form a fracture network between the first zone and the second zone.

Description

FRACTURE NETWORK SYSTEMS AND METHODS OF FORMING THE SAMECROSS REFERENCE TO RELATED APPLICATION

[0001] This application claims priority to United States Patent Application Serial No. 63 / 595,582, entitled: Fracture Network Systems and Methods of Forming Same, filed November 2, 2023, pursuant to relevant portions of 35 U.S.C. §119 and 35 U.S.C. §120. The foregoing application is herein incorporated by reference in its entirety.BACKGROUND

[0002] Energy from the formation of Earth and radioactive decay causes the Earth’s crust to have thermal energy. The thermal energy of the Earth has been used to provide power and heat. For example, thermal energy has been used to provide heated baths since the Paleolithic times and to heat buildings since the Roman times.

[0003] Unlike other forms of renewable energy, geothermal energy provides power at a relatively constant rate regardless of the weather. However, generating geothermal energy can be expensive and inefficient. As such, users of geothermal energy continue to seek new and improved methods for generating geothermal energy.SUMMARY

[0004] Embodiments disclosed herein are related to methods to form fracture systems, for example, geothermal energy production. In an embodiment, a method to form a fracture system is disclosed. The method includes hydraulically stimulating a first well at a first zone. The method additionally includes, after hydraulically stimulating the first well at the first zone, generating a back flow in the first well at the first zone, in which the back flow generates a lower pressure in the first well that is less than a pressure in the first well before generating the back flow. The method also includes, while or after generating the back flow in the first well at the first zone, hydraulically stimulating a second well at a second zone. The second zone is a portion of the second well that is connected to the first zone of the first well using a fracture network.

[0005] In an embodiment, a method to form a fracture system is disclosed. The method includes hydraulically stimulating a first well at a first zone. The method additionally includes, after hydraulically stimulating the first well at the first zone, generating a low pressure in the first well at the first zone. The method also includes, while or after generating the low pressure1SUBSTITUTE SHEET (RULE 26)in the first well at the first zone, hydraulically stimulating a second well at a second zone. The second zone is a portion of the second well that is connected to the first zone of the first well using a fracture network. The low pressure is less than a pressure in the first zone before generating the lower pressure.

[0006] In an embodiment, a method to form a fracture system is disclosed. The method includes hydraulically stimulating the first well at the first zone. The method also includes, after hydraulically stimulating the first well at the first zone, generating a back flow in a first well at a first zone. The back flow generates a lower pressure in the first well that is less than a pressure in the first zone before generating the back flow. The method additionally includes, while or after generating the back flow in the first well at the first zone, hydraulically stimulating a second well at a second zone. The second zone is a portion of the second well that is connected to the first zone of the first well using a fracture network. The method also includes pumping at least one geothermal-rated proppant into at least one of the first well or the second well after hydraulically stimulating the second well at the second zone. Pumping at least one geothermal-rated proppant into at least one of the first well or the second well increases the pressure in the first zone and the second zone. While the pressure in the first zone and the second zone is increased, the method may include isolating the first zone from a remainder of the first well and isolating the second zone from a remainder of the second well. Further, the method includes flowing a clean fluid into at least one of the first well or the second well to remove excess the at least one geo-thermal rated proppant from at least one of the first well or the second well.

[0007] Features from any of the disclosed embodiments may be used in combination with one another, without limitation. In addition, other features and advantages of the present disclosure will become apparent to those of ordinary skill in the art through consideration of the following detailed description and the accompanying drawings.BRIEF DESCRIPTION OF THE DRAWINGS

[0008] The drawings illustrate several embodiments of the present disclosure, wherein identical reference numerals refer to identical or similar elements or features in different views or embodiments shown in the drawings.

[0009] FIG. 1 is a schematic illustration of a fracture system, according to an embodiment.

[0010] FIG. 2 is a flow diagram of an example method to form the fracture system, according to an embodiment.

[0011] FIG. 3 is a flow diagram of an example method to form the fracture system, according to an embodiment.DETAILED DESCRIPTION

[0012] Embodiments disclosed herein related to methods to form fracture systems, for example, geothermal energy production. An example method to form a fracture system includes hydraulically stimulating a first well at a first zone. Hydraulically stimulating the first well at the first zone may form fractures extending from the first zone. After hydraulically stimulating the first well at the first zone, the method includes generating a back flow or at least generating a lower pressure in the first well at the first zone. The back flow can include flowing a material from the first zone towards an outlet of the first zone and the lower pressure includes actively decreasing the pressure in the first zone. It is noted that the back flow may cause the first zone to exhibit the lower pressure (z.e., the back flow causes the first zone to exhibit a lower pressure than if there was no back flow). The method also includes hydraulically stimulating a second well at a second zone. The foregoing operation may take place while or may take place after generating the back flow in the first well. Hydraulically stimulating the second well may form a fracture network between the first zone and the second zone.

[0013] For example, hydraulically stimulating the second well at the second zone causes fracturing of a reservoir adjacent to the second zone. As used herein, “reservoir” refers to bedrock, other rocks, or other subterranean formations that extends around and between the wells. Such fracturing of the reservoir may include opening new fractures in the reservoir or reactivating natural fractures in the reservoir. The back flow and / or lower pressure in the first zone causes the fracturing to preferentially extend from the second zone to the first zone and the fractures extending from the first well. In other words, the back flow and / or lower pressure in the first zone causes more fracturing to preferentially occur between the first and second zones (z.e., form more flow paths between the first and second zones) than if there was no back flow and / or lower pressure in the first zone. As such, the fracturing of the reservoir caused by hydraulically stimulating the second zone causes a network of fractures to preferentially occur between the first zone and the second zone.

[0014] In an embodiment, the methods disclosed herein may be used to form fracture networks at a plurality of zones. For example, after forming the fracture networks between the first zone and the second zone, the method may include forming a fracture networks between a third zone of the first well and a fourth zone of the second well. In such an example, the third and fourth zones may be isolated from the first and second zones, respectively. The methodmay then include hydraulically stimulating the third zone and, after such stimulation, generating a back flow in a first well at a third zone or otherwise decreasing the pressure in the third zone. The method also includes hydraulically stimulating a second well at a fourth zone. The fourth zone is a portion of the second well that may be connected to the third zone using a second fracture network. Hydraulically stimulating the second well at the fourth zone may cause fracturing of the reservoir adjacent to the fourth zone. Such fracturing may preferentially extend from the fourth zone to the third zone and the fractures extending from the first well. As such, the fracturing of the reservoir at the fourth zone causes a network of fractures to preferentially occur between the third and fourth zones. It is noted that the methods disclosed herein may be used to form factures between additional corresponding zones of the first and second wells, without limitation.

[0015] The fracture systems formed according to the methods disclosed herein may be used to produce geothermal energy. For example, a thermal energy transport fluid (e.g., water) may be injected into at least one injection well. The injection well includes one of the first well or the second well. The thermal energy transport fluid may flow between the injection well to at least one production well (the other of the first or second well) through the reservoir using the fractures formed in the reservoir. The thermal energy transport fluid may receive thermal energy from the reservoir as the thermal energy transport fluid flow through the reservoir. The thermal energy transport fluid may then flow out of the production well. The heated thermal energy transport fluid flowing out of the production well may be used to produce energy using conventional geothermal energy production techniques.

[0016] The methods disclosed herein to form fracture systems may be an improvement over conventional methods to form fracture systems. For example, conventional methods to form fracture systems often form “short circuits” in the fracture networks thereof. The short circuits of such conventional methods result in imbalanced flow through the reservoir by forming highly permeable paths that bypass significant portions of the reservoir. The methods disclosed to form fracture networks may also form short circuits therein. However, it is currently believed that the methods disclosed herein are significantly less likely to form short circuits therein compared to at least some conventional methods to form fracture networks. For example, the methods disclosed herein include using back flow or at least lower pressures in the first well to cause the fractures to preferentially extend from the second zone to the first zone and the fractures extending therefrom. In other words, less fracturing of the reservoir occurs in locations of the reservoir that are not between the first and second zone. It is believed that such fracturing decreases the likelihood of short circuits forming in the reservoir comparedto conventional methods of forming fracture systems. It is also believed that such fracturing decreases the likelihood that one fracture network (e.g., the fracture network between the first and second zones) are interconnected with another fracture network (e.g., the fracture network between the third and fourth zones). Avoiding interconnecting adjacent fracture networks may decrease the likelihood of forming short circuits.

[0017] FIG. 1 is a schematic illustration of a fracture system 100, according to an embodiment. The fracture system 100 may be formed using any of the methods and systems disclosed herein. The fracture system 100 includes a first well 102, a second well 104, and at least one fracture network 106 extending therebetween. The at least one fracture network 106 includes one or more fractures (e.g., reactivated natural fractures and / or new fractures) extending into a reservoir 108 and at least some of the fractures form flow paths between the first and second wells 102, 104.

[0018] In an example, the first well 102 is positioned below the second well 104. It is currently believed that selecting the first well 102 to be below the second well 104 may facilitate formation of the fracture networks 106 (illustrated schematically as triangles) extending from the first and second wells 102, 104 into the reservoir 108 using the methods disclosed herein in most geological scenarios and production schemes. However, it is noted that the second well 104 may be located below the first well 102 in certain geological scenarios and production schemes.

[0019] In an example, the first well 102 is an injection well and the second well 104 is a production well. It is currently believed that selecting the first well 102 to be the injection well and the second well 104 to be the production well facilitates flow of the thermal energy transport fluid through the reservoir 108 in most geological scenarios. However, again, it may be beneficial to select the first well 102 to be the production well and the second well 104 to be the injection well in certain geological scenarios. In an embodiment, the first and second wells 102 may include a casing, such as a cemented casing.

[0020] As previously discussed, the first and second wells 102, 104 extend into the reservoir 108. The reservoir 108 includes a subterranean formation exhibiting temperatures suitable for geothermal energy production. The reservoir 108 may include any suitable subterranean formation, such as shale, sandstone, limestone, igneous rocks, metamorphic rocks, or any other suitable subterranean formation. The reservoir 108 may include or not include natural fractures extending therein. It is noted that the reservoir 108 including natural fractures may facilitate formation of the fracture networks 106 when the natural fracturesextend between the first and second wells 102, 104 since it may be easier to reactive natural fractures than form new fractures.

[0021] The first and second wells 102, 104 include active portions. The active portions of the first and second wells 102, 104 are the portions of the wells that have one or more fracture networks 106 extending therefrom. At least the active portions of the first well 102 and the second well 104 may exhibit a similar trajectory. That is, at least the active portions of the first well 102 and the second well 104 may extend generally parallel to each other. In an embodiment, the active portions of the first and second wells 102, 104 may be angled (as shown) or horizontal since such angled or horizontal active portions of the first and second wells 102, 104 may more efficiently extract thermal energy from a volume of the reservoir 108 than if the first and second wells 102, 104 were vertical.

[0022] The active portions of the first and second wells 102, 104 may follow the formation minimum stress orientation of the reservoir 108 or may be generally orthogonal (e.g., ± 30° or less, ± 20° or less, or ± 10° or less) to a prominent fracture set strike. The active portions of the first and second wells 102, 104 may be at least a distance D below a surface 110 of the earth from which the first and second wells 102, 104 extend. The distance D may be about 30 meters or more, such as about 50 meters or more, about 100 meters or more, about 200 meters or more, about 300 meters or more, about 400 meters or more, about 500 meters or more, about 750 meters or more, about 1 km or more, about 1.25 km or more, about 1.5 km or more, about 2 km or more, about 3 km or more, about 4 km or more, about 5 km or more, or in ranges 30 meters to about 100 meters, about 50 meters to about 200 meters, about 100 meters to about 300 meters, about 200 meters to about 400 meters, about 300 meters to about 500 meters, about 400 meters to about 750 meters, about 500 meters to about 1km, about 750 meter to about 1.25 km, about 1 km to about 1.5 km, about 1.25 km to about 2 km, about 1.5 km to about 3 km, about 2 km to about 4 km, or about 3 km to about 5 km.

[0023] The active portions of first and second wells 102, 104 are spaced from each other by a distance d. The distance d may be relatively constant e.g., vary by about 100 meters or less, about 75 meters or less, about 50 meters or less, about 25 meters or less, or about 10 meters or less) along the lengths of the active portions. The distance d may be about 15 meters or more, about 25 meters or more, about 50 meters or more, about 75 meters or more, about 100 meters or more, about 125 meters or more, about 150 meters or more, about 175 meters or more, about 200 meters or more, about 250 meters or more, or in ranges of about 15 meters to 35 meters, about 25 meters to about 50 meters, about 35 meters to about 75 meters, about 50 meters to about 100 meters, about 75 meters to about 125 meters, about 100 meters to about150 meters, about 125 meters to about 175 meters, about 150 meters to about 200 meters, or about 175 meters to about 250 meters. The distance d may be selected for a variety of reasons. For example, the distance d may be selected to be less than the distance D to prevent the fracture networks 106 forming between the wells and the surface 110. Also, generally, the distance d is selected to be as large as possible since increasing the distance d increases the thermal energy transferred from the reservoir 108 to the thermal energy transport fluid. However, the distance d may be limited based on the other factors, such as the composition and density of the reservoir 108, the expected pressure in the first well 102 while forming the fracture networks, and the method used to hydraulically stimulate the second well 104 while forming the fracture networks 106, among others. In an example, the distance d may be about 100 meters to about 160 meters, such as about 120 meters to about 150 meters. It is currently believed that the methods disclosed herein may form fracture networks 160 in most geological scenarios when the distance d is about 100 meters to about 160 meters or, more preferably, about 120 meters to about 150 meters. It is noted that the methods disclosed therein for forming the fracture system 100 may be greater than other conventional methods of forming fracture systems due to the back flow and / or lower pressure in the first well 102 during fracturing.

[0024] The first well 102 and the second well 104 may include one or more zones. The zones of the first and second wells 102, 104 are regions thereof from which the fracture networks 106 extend from. In an embodiment, the first well 102 includes a first zone 112 and the second well 104 includes a second zone 114. The first and second zones 112, 114 may include any region of the first and second wells 102, 104. For example, as illustrated, at least one of the first zone 112 or the second zone 114 is a region of the first well 102 or second well 104 that are furthest from a surface 110 of the earth into which the first and second wells 102, 104 extend from. Alternatively, at least one of the first zone 112 or the second zone 114 are regions of the first well 102 or the second well 104 that is not furthest spaced from the surface 110.

[0025] The second zone 114 is a portion of the second well 104 that may be connected to the first zone 112 of the first well 102 using the first fracture network 106a. In an embodiment, the second zone 114 is a portion of the second well 104 closest to or at least proximate to the portion of the second well 104 that is closest to the first zone 112. In such an embodiment, the relative proximately of the first zone 112 and the second zone 114 facilitates formation of a first network 106a. In an embodiment, the second zone 114 is a portion of the second well 104 that has an advantageous subterranean formation extending between it and the first zone 112. An advantageous subterranean formation may include, for example, natural fractures or anothersubterranean formation that may be easier to hydraulically stimulate than another subterranean formation.

[0026] The first fracture network 106a may extend in the reservoir 108 between the first and second zones 112, 114. The first fracture network 106a may include a plurality of fractures (e.g., fissures, cracks, void spaces, etc.). At least some of the fractures extend between the first zone 112 and the second zone 114. In an embodiment, a greater quantity of the fractures extend between the first zone 112 towards the second zone 114 than any similarly sized area extending from the first zone 112 and the second zone 114.

[0027] At least some of the fractures extending between the first and second zones 112, 114 form flow paths through which any thermal energy transport fluid may flow. For example, the first fracture network 106a allows the thermal transport fluid to flow into the reservoir 108 from the injection well and from the reservoir 108 into the production well. The working fluid flowing through the reservoir 108 removes thermal energy from the reservoir 108 (e.g., is heated) thereby allowing thermal energy to be removed from the reservoir 108. The first fractured system 106a allows increases fluid connectivity between the first and second wells 102, 104 which, in turn, increases the thermal energy transferred to the thermal energy transport fluid.

[0028] The first well 102 may include one or more additional zones in addition to the first zone 112 and the second well 104 may include one or more additional zones in addition to the second zone 114. Fracture networks 106 may extend between corresponding ones of these additional zones of the first well 102 and the second well 104. Except as otherwise disclosed herein, these additional zones of the first and second wells 102, 104 and the fracture networks 106 extending between such zones may be the same or substantially similar to the first and second zones 112, 114 and the first fracture network 106a. For example, the first well 102 may include a third zone 116 and the second well 104 may include a fourth zone 118. The fourth zone 118 includes a portion of the second well 104 that may be connected to the third zone 116 of the first well 102 using a fracture network. The third zone 116 and the fourth zone 118 are distinct from (e.g., positioned closer to the surface 110) than the first zone 112 and the second zone 114, respectively. A second fracture network 106b may extend between the third and fourth zones 116, 118. The second fracture network 106b may be distinct and isolated from the first fracture network 106a which may prevent or at least limit short circuiting through the reservoir 108, for example, due to the higher pressure trapped in the fracture network 106a, which would act as a high pressure buffer to prevent new fractures propagating into this zone area. One geothermal rated plug can be set by methods like coiled tubing unit or wireline unitbetween zone 112 and zone 116 on the first well 102, and the other plug can be set between zone 114 and zone 118 on the second well 104 after the fracture network 106a is completed. The second fracture network 106b is distinct and isolated from the first fracture network 106a when the void spaces of the first fracture network 106a does not intersect with or intersect with a limited number of the void spaces of the second fracture network 106b.

[0029] In an embodiment, at least one of the first well 102 or the second well 104 includes a casing defining at least a portion of the walls thereof. The casing may include, for example, a cemented casing (e.g., geothermal cement configured to provide an insulated barrier between the wells and the reservoir). The cemented casing may have one or more perforations or fractures extending therethrough such that fluids (e.g., the working fluid or the thermal energy transport fluid) may flow through the casing. In an embodiment, at least one of the first well 102 or the second well 104 does not include a casing.

[0030] The system 100 is illustrated as including two wells, namely a single first well 102 and a single second well 104. However, in an embodiment, the fracture system 100 may include a plurality of first wells 102 and / or a plurality of second wells 104. In an embodiment, the fracture network(s) 106 extending from one first well 102 may only extend between said first well 102 and one of the plurality of second wells 104 or may include fracture networks extending between said first well 102 and two or more of the plurality of second wells 104 (e.g., a first fracture network extending from said first well 102 to one second well 104 and a second network system extending from said first well 102 to another second well 104 or fracture networks extending from said first well 102 to one second well 104 and another second well 104). Similarly, in such an embodiment, one of the plurality of second wells 104 may include fracture network(s) extending only between said second well 104 and one of the plurality of first wells 102 or may include fracture networks extending between said second well 104 and two or more of the plurality of first wells 102.

[0031] The system 100 may include one or more components configured to generate geothermal energy. For example, the system 100 may include an injection string inserted into one of the first well 102 or the second well 104 and a production string inserted into the other of the first well 102 or the second well 104. The injection string is configured to provide a thermal energy transport fluid into the fracture networks 106 and the production string is configured to receive the thermal energy transport fluid from the fracture networks 106. The injection string and the production string may be in fluid communication with a thermal energy transport fluid reservoir that is configured to hold the thermal energy transport fluid. The thermal energy transport fluid may include, for example, liquids, gelled liquids, gases, slurries,emulsions, organic compounds (e.g., hydrocarbons, oil, etc.), nanoparticle mixed with a liquid, water, or combinations thereof. The system 100 may also include a power plant coupled to the injection and production strings. The power plant may be configured to generate electrical energy using the thermal energy extracted from the reservoir 108. Examples of components that may be used in the system 100 are disclosed in U.S. Patent No. 9,726,157, the disclosure of which is incorporated by reference herein, in its entirety.

[0032] The fracture system 100 extending into the reservoir 108 may be formed using any of the methods disclosed herein. FIG. l is a flow diagram of an example method 200 to form the fracture system 100, according to an embodiment. The example method 200 may include one or more operations, functions, or actions as illustrated by one or more of blocks 205, 210, and / or 215.

[0033] The example method 200 may include (e.g., begin with) block 205, which recites “hydraulically stimulating the first well 102 at the first zone 112.” The example method 200 may include block 210, which recites “after hydraulically stimulating the first well 102 at the first zone 112, generating a back flow in the first well 102 at the first zone 112.” The example method 200 may also include block 215, which recites “while or after generating the back flow in the first well 102 at the first zone 112, hydraulically stimulating the second well 104 at the second zone 114.”

[0034] The blocks included in the described example method 200 (and the blocks of the other methods disclosed herein) are for illustrative purposes. In some embodiment, the blocks may be performed in a different order, may be combined together, and / or separated into different blocks. In some embodiments, the example method 200 (and the other methods disclosed herein) may include additional blocks, such as forming the first and second wells 102, 104 or any of the other blocks disclosed herein.

[0035] Block 205 recites “hydraulically stimulating the first well 102 at the first zone 112.” During block 205, a working fluid flows into the first zone 112 of the first well 102. The working fluid may increase the pressure sufficiently that hydraulic fracturing or hydraulic shearing occurs to open new fractures or reactivate natural fractures in the subterranean formation. The new fractures or reactivated natural fractures extend away from the first zone 112. Block 205 may not be configured to form fractures that extend all the way between the first zone 112 and the second zone 114. Instead, block 205 is configured to form fractures that extend partially between the first and second zones 112, 114. For example, block 205 may include forming fractures that extend about 1% to about 99% (e.g., about 1% to about 50%, about 25% to about 75%, or about 50% to about 99%) of the distance d between the first zone112 and the second zone 114. In some examples, one or more fractures extending from the first zone 112 may reach the second zone 114. However, in such examples, the fractures extending from the first zone 112 to the second zone 114 typically form poor flow paths such that the second zone 114 still needs to be hydraulically stimulated in block 215. Block 205 may be performed using any suitable equipment, such as plug and perf equipment, a sliding sleeve, straddled perforation equipment, or any of the other equipment disclosed herein.

[0036] In an embodiment, block 205 include non-hydraulically forming perforations or other types of fractures extending from the first zone 112 before hydraulically stimulating the first well 102. In an example, the first well 102 may include a casing. The perforations or other types of fractures may form flow paths through the casing. Such flow paths may facilitate hydraulically stimulating the first well 102 through the casing. In an example, the perforations or other types of fractures may also extend into the subterranean formation. In an embodiment, the perforations or other fractures are only formed or preferentially formed in a portion of the first zone 112 that generally faces the second zone 114 thereby further causing the fractures extending from the first zone 112 to preferentially extend towards the second zone 114. In an embodiment, the perforations or other fractures may extend circumferentially around the first zone 112. The perforations or other fractures may be formed using any suitable technique, such as the perforating guns of a plug and perf technique.

[0037] During block 205, a working fluid is pumped into the first zone 112. The working fluid pumped into the second zone 114 may include any suitable fluid. For example, the working fluid may include liquids (e.g., water), gelled liquids, gases, slurries, emulsions, organic compounds, any other fluid, or combinations thereof. In an embodiment, the working fluid may include a proppant mixed therein that is configured to maintain the fractures open. In an embodiment, the working fluid does not include a proppant mixed therein. It is currently believed that omitting the proppant from the working fluid (at least until the first and second zones 112, 114 are in fluid communication with each other) facilitates formation of the fractures between the first and second zone 112, 114 than if the working fluid included the proppant.

[0038] The working fluids pumped into the first zone 112 increases a pressure in the first zone 112. The pressure in the first zone 112 is increased until the pressure causes new fractures or reactivates old (e.g., natural) fracture in the subterranean formation. In an embodiment, the working fluid may be pumped into the first zone 112 until a pressure in the first zone 112 is sufficiently high to cause fracturing of the subterranean formation. However, the pressure of the working fluid in the first zone 112 is selected to be low enough that the fractures are unlikelyto extend all the way to the second zone 114. For example, the pressure of the working fluid in the first zone 112 is calculated to cause fractures to extend from the first zone 112 a selected distance from the first zone 112.

[0039] In an embodiment, block 205 may include detecting the pressure of the first zone 112, for example, using a pressure transducer. The detected pressure in the first zone 112 may be used to determine if additional quantities of working fluid need to be provided or removed from the first zone 112. For instance, the quantity of working fluids provided to the first zone 112 may be increased or decreased if the pressure in the first zone 112 is too low or too high to form the fractures extending a selected distance from the first zone 112. The detected pressure may also indicate the formation of fractures since the pressure may decrease when fractures are formed.

[0040] In an embodiment, block 205 may include isolating the first zone 112 from the remainder of the first well 102 e.g., isolate from the fourth zone 118). Isolating the first zone 112 from the remainder of the first well 102 causes the fractures to extend from the first zone 112 instead of another zone of the first well 102 (e.g., the third zone 116). Isolating the first zone 112 from the remainder of the first well 102 decreases the volume of the first well 102 that must be pressurized. The first zone 112 may be isolated from the remainder of the first well 102 using any suitable technique. In an example, the first zone 112 may be isolated from the remainder of the first well 102 using a cemented casing. Based on the fracturing procedure, the wellbore of the first well 102 is sealed with cemented casing and only the portion of the first zone 112 that is perforated is hydraulically fractured. Further examples of devices and methods of isolating the first zone 112 from the remainder of the first well 102 are disclosed in U.S. Patent No. 10,551,091, the disclosure of which is herein incorporated by reference, in its entirety. In an embodiment, block 205 does not include isolating the first zone 112 from the portions of the first well 102 between the first zone 112 and the surface 110. Block 205 may not include isolating the first zone 112 from the portions of the first well 102 between the first zone 112 and the surface 110 when the first well 102 includes a casing and the casing of the portions of the first well 102 between the first zone 112 and the surface 110 is not perforated.

[0041] In an embodiment, block 205 may include removing at least some of the working fluid from the first zone 112 and the fractures extending therefrom before block 310. However, as will be discussed in more detail below, the back flow generated during block 210 may remove the working fluid from the first zone 112 and the fractures extending therefrom.

[0042] Block 210 recites “generating a back flow in a first well 102 at a first zone 112.” The back flow generated during block 205 may be formed using any suitable technique. Forexample, the back flow may be generated by removing a fluid (e.g., the working fluid) from the first zone 112. The back flow generated in the first zone 112 may decrease the pressure in the first zone 112 than if no back flow was generated in the first zone 112. For example, the back flow may create a pressure differential (the difference between the pressure in the first zone 112 before the back flow and the pressure in the first zone 112 during or immediate after generating the back flow) of about 5 kPa to 100 kPa, such as about 5 kPa to about 10 kPa, about 7.5 kPa to about 12.5 kPa, about 10 kPa to about 15 kPa, about 12.5 kPa to about 17.5 kPa, about 15 kPa to about 20 kPa, about 17.5 kPa to about 22.5 kPa, about 20 kPa to about 25 kPa, about 22.5 kPa to about 30 kPa, about 25 kPa to about 40 kPa, about 30 kPa to about 50 kPa, about 40 kPa to about 60 kPa, about 50 kPa to about 70 kPa, about 60 kPa to about 80 kPa, about 70 kPa to about 90 kPa, about 80 kPa to about 100 kPa. It is noted that the pressure differential may be less than 5 kPa or greater than 100 kPa. The back flow formed during block 210 may also decrease the pressure in the fractures extending from the first zone 112.

[0043] The back flow may reduce the pressure in the first zone 112 and the fractures extending therefrom for a variety of reasons. For example, the back flow may remove the working fluid that was used to hydraulically stimulate the first zone 112 during block 205. The removal of the working fluid may decrease the pressure in the first zone 112 and the fractures extending therefrom. Once the working fluids are removed, the back flow allows the pressure in the first zone 112 and the fractures extending therefrom to be controlled.

[0044] The decreased pressure in the first zone 112 and the fractures extending therefrom caused by the back flow may cause the fracture networks 106 formed by hydraulically stimulating the second well 104 (as discussed with regards to block 215) to preferentially extend from the second well 104 to the first well 102 and the fractures extending from the first well 102. As previously discussed, preferentially causing the fracture networks 106 to extend between the first and second wells 102, 104 may prevent the short circuiting of the fracture system 100 and may facilitate transfer of thermal energy from the reservoir 108 to the thermal energy transport fluid.

[0045] In an embodiment, block 205 may include flowing a back flow fluid into the first zone 112, while simultaneously removing the back flow fluid from the first zone 112. In such an embodiment, flowing the back flow fluid into the first zone 112 allows a continuous back flow to be present in the first zone 112. It is noted that block 205 may still decrease the pressure in the first zone 112 even though the back flow fluid is being provided to the first zone 112 simultaneously with removing the fluid from the first zone 112. Flowing the back flow fluid into the first zone 112 during block 205 may provide several benefits. For example, thecontinuous back flow in the first zone 112 may facilitate detection of flow path being successfully formed between the first and second zones 112, 114. For instance, as will be discussed in more detail with regards to block 210, working fluids that are used to hydraulic stimulate the second zone 114 may enter the first zone 112 when the fluid flow paths are successfully formed between the first and second zones 112, 114. Such working fluids entering the first zone 112 may be moved by the continuous back flow towards sensors that detect such fluids. As such, the continuous back flow may better detect the formation of the fluid flow paths between the first and second zones 112, 114. Further, flowing the back flow fluids into the first zone 112 during block 205 may allow for better control of the pressure in the first zone 112 during the method 200. For example, flowing the back flow fluids into the first zone 112 may allow the pressure in the first zone 112 to be increased or decreased (as needed) and even cause the pressure in the first zone 112 to be increased above initial pressure in the first zone 112 (e.g., to facilitate removal of the fluids used to stimulate the second zone 114).

[0046] Any suitable back flow fluids may be flowed into the first zone 112 during block 205. In an example, nitrogen (N2) may be flowed into the first zone 112 during block 205. At the surface 110, the nitrogen pumped into the first well 102 may initially be a liquid thereby allowing the nitrogen to be more density stored. The liquid nitrogen may be heated as the liquid nitrogen flows down the first well 102 due to the elevated temperature of the subterranean formation thereby gasifying at least a portion of the liquid nitrogen. Any liquid nitrogen that reaches the first zone 112 will be quickly gasified due to the temperature of the reservoir 108. The gaseous nitrogen may quickly displace any of the working fluid that remains in the first zone 112 and the fractures extending therefrom. Nitrogen may be used as the back flow fluid since it is inert, relatively cheap, readily available, and can be easily stored in its liquid phase thereby decreasing the volume of the storage container that holds the nitrogen. That said, the back flow fluid may include any other suitable fluid. In an example, the back flow fluid may alternatively include carbon dioxide (CO2), since carbon dioxide is relatively inert and cheaply available. In another example, the back flow fluid may include argon or another inert or noble gas though the quantity of such back flow fluids may be limited due to cost. In yet another example, the back flow fluid may include atmospheric gas since atmospheric gas is cheaper and more readily available than nitrogen and does not require a storage container to hold the atmospheric gas. However, the oxygen found in atmospheric gas may cause combustion in the first zone 112 if the first zone 112 includes a combustible material e.g., gas or oil in the subterranean formation) due to the elevated temperature of the reservoir 108 and may therefore cause oxidation of the equipment. In an example, the back flow fluidmay include a combination of fluids, such as nitrogen gas mixed with argon, other inert or noble gases, atmospheric air, or any other suitable fluid.

[0047] Block 210 may be performed using any suitable equipment. In an embodiment, tubing may be disposed in the first zone 112. The tubing may include, for example, coiled tubing, fracturing down tubulars, drill pipe, or any other suitable tubing. The tubing may be in fluid communication with a pump. The tubing and the pump may collectively remove fluids (e.g., the back flow fluid provided to the first zone 112 and any other fluid in the first zone 112) from the first zone 112. In an example, the tubing and the pump are also configured to provide the back flow fluids to the first zone 112 during block 205. In such an example, the tubing and the pump may be in fluid communication with a reservoir of the back flow fluid such that the tubing and the pump may remove the fluid from the reservoir of the fluid and provide the back flow fluid to the first zone 112. It is noted that the tubing may include coiled tubing when the tubing both removes the fluid from and provides the fluid to the first zone 112 since, unlike at least some tubing, the coiled tubing is able to perform both tasks.

[0048] Block 215 includes, “while or after generating the back flow in the first well 102 at the first zone 112, hydraulically stimulating the second well 104 at the second zone 114.” Though the herein described method permits stimulation of the second well 104 while back flow in the first well 102 is still being generated, it should be noted it may be more prudent and safer to stimulate the second well 104 at the second zone 114 after the back flow is completed on the first well 102 at the first zone 112. That is, a fracture connection developed between the first and second zones 112, 114, could cause a serious problem on the back flow operations, such as pressure spikes, that could damage the equipment creating the back flow. Additionally, a back flow completed on the first zone 112 can further assure that a sufficiently low pressure in the first zone 112 will attract the fracture connection from the second zone 114. During block 210, a working fluid flows into the second zone 114 of the second well 104. The working fluid may increase the pressure in the second zone 114 sufficiently that hydraulic fracturing or hydraulic shearing occurs to open new fractures or reactive natural fractures in the subterranean formation. The lower pressure in the first zone 112 and the fractures extending from the first zone 112 attracts the new fractures and reactivated fractures formed during block 215 such that the new fractures or reactive natural fractures preferentially extend from the second zone 114 to the first zone 112 and the fractures extending from the first zone 112 to form the fracture network 106a. In other words, block 210 connects the first zone 112 and the second zone 114 together such that, after block 215, the thermal energy transport fluid may flow between thefirst and second zones 112, 114. Block 215 may be performed using any suitable equipment, such as plug and perf equipment, a sliding sleeve, or straddled perforation equipment.

[0049] In an embodiment, block 215 includes non-hydraulically forming perforations or other types of fractures extending from the second zone 114 before hydraulically stimulating the second well 104. In an example, the second well may include a casing. The perforations or other types of fractures may form flow paths through the casing. Such flow paths may facilitate hydraulically stimulating the second well 104 through the casing. In an example, the perforations or other types of fractures may also extend into the subterranean formation. In an embodiment, the perforations or other fractures are only formed or preferentially formed in a portion of the second zone 114 that generally faces the first zone 112 thereby further causing the fracture network 106a to extend between the first and second zones 112, 114. In an embodiment, the perforations or other fractures may extend circumferentially around the second zone 114. The perforations or other fractures may be formed using any suitable technique, such as the perforating guns of a plug and perf technique.

[0050] During block 210, a working fluid is pumped into the second zone 114. The working fluid of block 210 may include any of the working fluids disclosed herein. The working fluids pumped into the second zone 114 increases a pressure in the second zone 114. The pressure in the second zone 114 is increased until the pressure causes new fractures or reactivates old (e.g., natural) fractures in the subterranean formation. These fractures formed by the increase pressure grow until the second zone 114 is in fluid communication with the first well 102. For example, the fractures formed during block 210 may grow until the fractures formed during block 210 reach the fractures extending from the first zone 112 (as formed during block 205) or reach the first zone 114 itself. Due to the back flow in the first zone 112, these fractures preferentially expand towards the fractures formed during block 205 and the first zone 112. Once the second zone 114 is in fluid communication with the first zone 112, the working fluid may no longer pumped into the second zone 114 and the pressure in the second zone 114 is allowed to decrease.

[0051] Block 215 may include detecting when the first and second zones 112, 114 are in fluid communication with each other. In an embodiment, block 210 may include detecting a pressure in the second zone 114 using a pressure sensor. The pressure in the second zone 114 may suddenly drop when the second zone 114 is in fluid communication with the first zone 112 due to the working fluid flow into the first zone 112. In an embodiment, block 210 may include detecting a pressure in the first zone 112 using a pressure sensor. The pressure in the first zone 112 may suddenly increase when the second zone 114 is in fluid communication withthe first zone 112 since the working fluid is flowing into the first zone 112. It is noted that the lower pressure in the first zone 112 may make it easy to detect the increased pressure in the first zone 112 caused by the working fluid entering the first zone 112. In an embodiment, block 210 may include detecting the presence of the working fluid in the first zone 112, such as with a moisture sensor or other sensor. It is noted that the back flow in the first zone 112 may cause the working fluid to quickly reach the moisture sensor or other sensor once the working fluid enters the first zone 112.

[0052] In an embodiment, block 215 may stop flowing the working fluid into the second zone 114 as soon as it is detected that the first and second zones 112, 114 are in fluid communication with each other. In an embodiment, block 215 may continue to flow the working fluid into the second zone 114 for a period of time, until the pressure in the first zone 112 or the second zone 114 is at threshold value, or until an additional quantity of working fluid is pumped into the second zone 114. Continuing to pump the working fluid into the second well 114 even after the first and second zones 112, 114 are in fluid communication with each other may cause additional fractures to form or increase the size of the fractures. However, continuing to pump the working fluid into the second well 114 even after the first and second zones 112, 114 are in fluid communication with each other may be less efficient at forming the fractures than before the first and second wells 102, 104 are in fluid communication with each other. As will be discussed in more detail below, block 215 may continue to flow the working fluid into the second zone 114 while also mixing proppant with the working fluid after detecting that the first and second zones 112, 114 are in fluid communication with each other.

[0053] Block 215 may include isolating the second zone 114 from the remainder of the second well 104 (e.g., isolate from the fourth zone 118). Isolating the second zone 114 from the remainder of the second well 104 causes the second fracture network 106a to preferentially extend the second zone 114 to the second zone 114. This prevents or at least inhibits the second fracture network 106a from connecting with other fracture networks and allows the system 100 to include more fracture networks with, at most, limited connections between the fracture networks. The first zone 112 may be isolated from the remainder of the second well 104 using any suitable technique. In an example, the second zone 114 may be isolated from the remainder of the second well 104 using a geothermal rated plug or cement plug. Further examples of devices and methods of isolating the second zone 114 from the remainder of the second well 104 are disclosed in U.S. Patent No. 10,551,091, the disclosure of which was previously incorporated herein. In an embodiment, block 215 may not include isolating the second zone114 from the portions of the second well 104 between the second zone 114 and the surface 110 when the second well 104 includes a casing and the casing of the portions of the second well 104 between the second zone 114 and the surface 110 is not perforated.

[0054] Block 210 may be performed using any suitable equipment. In an embodiment, block 210 may be performed using plug and perf equipment, a sliding sleeve, or straddled perforation equipment. In an embodiment, block 210 may be performed using tubing (e.g., any of the tubing disclosed herein) disposed in the second zone 114, a pump in fluid communication with the tubing, and a reservoir of the working fluid.

[0055] FIG. 3 is a flow diagram of an example method 300 to form the fracture system 100, according to an embodiment. Except as otherwise disclosed herein, the example method 300 is the same as or substantially similar as any of the other methods disclosed herein. The example method 300 may include one or more operations, functions, or actions as illustrated by one or more of blocks 305, 310, 315, 320, 325, and / or 330. The blocks including in the described example method 300 (and the blocks of the other methods disclosed herein) are for illustrative purposes. In some embodiment, the blocks may be performed in a different order, may be combined together, separated into different blocks, or include additional blocks.

[0056] The example method 300 may include (e.g., begin with) block 305, which recites “hydraulically stimulating the first well 102 at the first zone 112.” The example, method 300 may also include block 310, which recites “after hydraulically simulating the first well 102 at the first zone 112, generating a back flow in the first well 102 at the first zone 112.” The example method 300 may also include block 315, which recites “while or after generating the back flow in the first well 102 at the first zone 112, hydraulically stimulating the second well 104 at the second zone 114.” The example method 300 may also include block 320, which recites “pumping at least one geothermal-rated proppant into at least one of the first well 102 or the second well 104 after hydraulically stimulating the second well 104 at the second zone 114.” The example method 300 may also include block 325, which recites “pumping a cleaning fluid into at least one of the first well 102 or the second well 104 to remove excess geo-thermal rated proppant from at least one of the first well 102 or the second well 104.” The method 300 may also include block 330, which recites “plugging the first well 102 and the second well 104 to isolate the first zone 112 from the rest of the first well 102 and the second zone 114 from the rest of the second well 104.”

[0057] Blocks 305, 310, and 315 are the same or substantially similar to one or more of the corresponding blocks of the method 200. For example, block 305 may be the same as orsubstantially similar to block 205, block 310 may be the same as or substantially similar to block 210, and block 310 may be the same as or substantially similar to block 315.

[0058] Block 320 recites “pumping at least one geothermal-rated proppant into at least one of the first well or the second well after hydraulically stimulating the second well at the second zone.” Block 320 may be performed after blocks 305, 310, and 315, such as after the first zone 112 is in fluid communication with the second zone 114. The geo-rated proppant (“proppant”) flowed into the first well 102 or the second well 104 may maintain the first fracture network 106a open after block 310. For example, the proppant may help create and maintain unique favorable and independent flow paths from the first zone 112 to the second zone 114. In an example, the proppant may be pumped into the well that forms the production well. In such an example, the proppant may be preferentially located at or near the portion of the first fracture network 106a that is adjacent to the production well. During use, the relatively hot water pumped into the production well remove less thermal energy from the rocks of the first fracture network 106a adjacent to the production well which, due to thermal expansion, causes minimal shrinkage of the rock adjacent to the production well. Meanwhile, the relatively cold water pumped into the first fracture network 106a from the injection well causes relatively significant shrinkage of the rock adj acent to the inj ection well due to thermal expansion. The passageways of the first fracture network 106 adjacent to the injection well is less likely to collapse during use compared to the passageways of the first fracture network 106 adjacent to the production well due to greater shrinkage of the rock adjacent to the injection well relatively to the minimal shrinkage of the rock adjacent to the production well. As such, the proppant preferentially located at or near the portion of the first fracture network 106a that is adjacent to the production well prevents or at least inhibits collapsing the passageways near the production well where, without the proppant, the passageways are more likely to collapse.

[0059] The proppant may include any suitable geothermal -rated proppant. For example, the proppant may include sand (e.g., treated sand), another ceramic material, another solid material, or combinations thereof. Prior or concurrent with block 320, the proppant may be mixed with fracking fluid, such as a gel, foam, or slickwater-based fracking fluid. Mixing the proppant with the fracking fluid help flow the proppant into the first well 102 or the second well 104 and flow the proppant into the first fractured network 106a.

[0060] Whether the proppant is provided to the first well 102 and / or the second well 104 may depend on whether the first well 102 or the second well 104 is the production well. For example, generally, the proppant is provided to the production well and, thus, the proppant may be provided to the first well 102 or the second well 104 that is selected to form the productionwell. That said, the proppant may be provided to the injection well, for example, depending on the subterranean formation.

[0061] In an embodiment, block 320 includes mixing the proppant with the working fluid of block 315 after a connection between the first and second wells 102, 104 is detected. For example, the working fluid may continue to be pumped into the second zone 114 after the connection between the first and second zones 112, 114 is detected. After detecting the connection, the proppant may be mixed with the working fluid such that the continuous supply of the working fluid to the second zone 114 also provides to proppant to the second zone 114.

[0062] In an embodiment, block 320 may include providing the proppant to one of the first well 102 or the second well 104 until the proppant is detected in the other of the first well 102 or the second well 104. In other words, block 320 may include ceasing to provide the proppant to the first well 102 or the second well 104 after the proppant is detected in the other of the first well 102 or the second well 104. Detecting the proppant in the other of the first well 102 or the second well 104 ensures that the proppant is present throughout the first fracture network 106a and that at least substantially all of the first fracture network 106a is maintained open by the proppant. In an embodiment, block 320 may include ceasing to provide the proppant to one of the first well 102 or the second well 104 as soon as the proppant is detected in the other of the first well 102 or the second well. In an embodiment, block 320 may include providing a preselected quantity of the proppant into one of the first well 102 or the second well 104. In other words, block 320 may include ceasing to provide the proppant to the first well 102 or the second well 104 after the preselected quantity of the proppant is provided. The preselected quantity of proppant may be calculated based on the expected volume of proppant needed to interconnect and maintain the first fracture network 106a. In an embodiment, block 320 may include providing the proppant after the proppant is detecting until a selected time after the proppant is detected or after an additional quantity of proppant is provided.

[0063] Block 325 recites “pumping a cleaning fluid into at least one of the first well 102 or the second well 104 to remove excess geo-thermal rated proppant from at least one of the first well 102 or the second well 104.” For example, after block 325, excess proppant (e.g., proppant that is not maintaining the first fracture network 106) and, optionally, other contaminants may be present in at least the first zone 112, the second zone 114, and the first fracture network 106a. Pumping the cleaning fluid to remove excess proppant increases the quantity of proppant that is present in the first fracture network 106a, facilitates plugging the first and second zones 112, 114, as discussed in more detail below, and facilitate moving tubing in the wellbore. Examples of the cleaning solution may include clean stimulation fluid.Alternatively or additionally, at least some of the excess proppant and other contaminants may be bullheaded or otherwise swept into the injection well perforations or the injection well sleeves. In an embodiment, block 325 does not include removing the cleaning fluid from the first well 102, the second well 104, and the first fracture network 106a. Instead, the cleaning fluid moves any excess proppant from the wellbore into the fracture network 106a and increases the pressure in the first zone 112, the second zone 114, and the first fracture network 106a. In other words, block 325 may include pumping the cleaning fluid and the proppant from the first well 102 or the second well 104 into the reservoir 108.

[0064] In an embodiment, the method 300 may include block 330. Block 330 recites “plugging the first well 102 and the second well 104 to isolate the first zone 112 from the rest of the first well 102 and the second zone 114 from the rest of the second well 104.” Block 330 may be performed when a pressure in the first zone 112, the second zone 114, and / or the first fracture network 106a is elevated. For example, providing proppant to the first well 102 or the second well 104 in block 320 and / or flowing the cleaning fluid into at least one of the first well 102 or the second well 104 in block 325 increases the pressure in the first zone 112, the second zone 114, and the first fracture network 106a. As such, block 330 may be performed during or immediately after blocks 320 and / or 325 while the pressure is elevated in the first zone 112, the second zone 114, and / or the first fracture network 106a. In an example, plugs may be used to isolate the first and second zones 112, 114. Isolating the first and second zones 112, 114 may maintain the elevated pressure in the first zone 112, the second zone 114, and the first fracture network 106a after block 320 and / or block 325. The elevated pressure in the first zone 112, the second zone 114, and the first fracture network 106a may prevent or at least inhibit fractures generated while forming other fracture networks (e.g., the second fracture network 106b) from expanding towards and becoming connected with the first zone 112, the second zone 114, and the first fracture network 106a. In other words, the elevated pressure of the first zone 112, the second zone 114, and the first fracture network 106a prevents or inhibits different fracture networks from being interconnected. Preventing or inhibiting different fracture networks from becoming interconnected by decreasing the risk of forming short circuits in the system 100.

[0065] In an embodiment, the block 330 may be split into two or more blocks. For example, block 330 may be split into a first block and a second block. The first block may include plugging one of the first well 102 or the second well 104 and the second block may include plugging the other of the first well 102 or the second well 104. The second block may be performed at some time after the first block. In a particular example, the first block includesplugging whichever of the first well 102 or the second well 104 forms the production well and the second block includes plugging whichever of the first well 102 or the second well 104 forms the injection well. In such an example, the first block may be performed before block 325 while the second block is performed during or after block 325. Plugging the production well before block 325 prevents or at least inhibits the cleaning fluid from becoming dislodged from the first fracture network 106a while the cleaning fluid is pumped into the injection well.

[0066] The methods disclosed herein (e.g., methods 200 and 300) may be repeated (in whole or in part) to form a plurality of fracture networks in the reservoir 108. Forming a plurality of fracture networks in the reservoir 108 may allow for greater quantities of thermal energy transfer fluid to flow through the reservoir 108 at any given time and remove more thermal energy from the reservoir 108 at any given time than if only the first fracture network 106a is formed in the reservoir 108. In an example, after forming the first fracture network 106a using any of the method disclosed herein, any of the methods disclosed herein may be used to form a second fracture network 106b that is distinct from (e.g., is not connected to or has limited connections with) the first fracture network 106a. Forming the second fracture network 106b may include hydraulically stimulating the first well 102 at the third zone 116; after hydraulically stimulating the first well 102 at the third zone 116, generating a back flow in the first well 102 at the third zone 116; and, while or after generating the back flow in the first well 102 at the third zone 116, hydraulically stimulating the second well 104 at the fourth zone 118. The method of forming the second fracture network 106b may also include any of the other blocks or acts disclosed herein. In an embodiment, a third fracture network (not labeled) may be formed after forming the second fracture network 106b using any of the methods disclosed herein, and so forth.

[0067] The methods disclosed herein may include removing the one or more plugs from the first well 102 and the second well 104. For example, the methods disclosed herein may include removing the plugs from the first well 102 and the second well 104 formed during block 330. It is noted that removing the plugs may include removing a plurality of plugs from each of the first well 102 and the second well 104 when, as previously discussed, the methods 200 and / or 300 are repeated to form a plurality of fracture networks. Removing the plugs allows a working fluid to be pumped into whichever of the first well 102 or second well 104 that forms the injection well, through the one or more fracture networks 106, and into whichever of the first well 102 or second well 104 forms the production well. The plugs may be removed using any suitable technique, such as using coiled tubing.

[0068] The methods disclosed herein (e.g., methods 200 and 300) may include setting up pressure control valves in whichever of the first well 102 or second well 104 that forms the injection well on one or more perforation clusters, in order to allow a quantity of injection fluid to be pumped into each fracture network 106 formed in accordance with the methods described herein (e.g., first fracture network 106a, second fracture network 106b, etc.), at either a preset pressure or an adjustable pressure. This pressure can be controlled, for example, through a pressure activated mechanism and / or via sensors that are provided in the set up pressure control valves in order to achieve preferable fluid flow in the formed fracture networks 106.

[0069] While various aspects and embodiments have been disclosed herein, other aspects and embodiments are contemplated. The various aspects and embodiments disclosed herein are for purposes of illustration and are not intended to be limiting.

[0070] Terms of degree (e.g., “about,” “substantially,” “generally,” etc.) indicate structurally or functionally insignificant variations. In an example, when the term of degree is included with a term indicating quantity, the term of degree is interpreted to mean ± 10%, ±5%, or ±2% of the term indicating quantity. In an example, when the term of degree is used to modify a shape, the term of degree indicates that the shape being modified by the term of degree has the appearance of the disclosed shape. For instance, the term of degree may be used to indicate that the shape may have rounded corners instead of sharp comers, curved edges instead of straight edges, one or more protrusions extending therefrom, is oblong, is the same as the disclosed shape, etc.

Claims

CLAIMSWhat is claimed is:

1. A method to form a fracture system, the method comprising: hydraulically stimulating a first well at a first zone; after hydraulically stimulating the first well at the first zone, generating a back flow in the first well at the first zone wherein the back flow generates a lower pressure in the first well that is lower than a pressure in the first well before generating the back flow; and while or after generating the back flow in the first well at the first zone, hydraulically stimulating a second well at a second zone; wherein the second zone is a portion of the second well that is connected to the first zone of the first well using a fracture network.

2. The method of claim 1, wherein the first well is an injection well and the second well is a production well.

3. The method of claim 1, wherein at least a portion of the first well and at least a portion of the second well are angled or horizontally oriented.

4. The method of claim 1, wherein the first well is below the second well.

5. The method of claim 1, wherein the first zone is spaced from the second zone by about 100 meters to about 160 meters.

6. The method of claim 1, wherein generating the back flow in the first well includes flowing nitrogen gas into the first zone.

7. The method of claim 1, wherein coiled tubing generates the back flow in the first well at the first zone.

8. The method of claim 1, wherein hydraulically stimulating the second well at the second zone includes using a plug and perf or sliding sleeve.

9. The method of claim 1, wherein generating the back flow in the first well at the first zone and hydraulically stimulating the second well at the second zone is performed without using a proppant.

10. The method of claim 1, wherein at least one of generating the back flow in the first well at the first zone or hydraulically stimulating the second well at the second zone is terminated after detecting an increase in pressure at the first zone of the first well.

11. The method of claim 1, wherein at least one of generating the back flow in the first well at the first zone or hydraulically stimulating the second well at the second zone is terminated after detecting a decrease in pressure at the second zone of the second well.

12. The method of claim 1, further comprising pumping at least one geothermalrated proppant into at least one of the first well or the second well after hydraulically stimulating the second well at the second zone.

13. The method of claim 12, further comprising stopping pumping the at least one geothermal-rated proppant into the second well after a preselected quantity of the at least one geothermal-rated proppant is pumped into the second well.

14. The method of claim 13, wherein stopping pumping the at least one geothermalrated proppant into at least one of the first well or the second well after the at least one geothermal-rated proppant is detected in the other of the first well or the second well.

15. The method of claim 12, further comprising flowing a clean fluid into at least one of the first well or the second well to remove excess the at least one geo-thermal rated proppant from at least one of the first well or the second well.

16. The method of claim 12, further comprising, during or after pumping the at least one geothermal-rated proppant, plugging the first well and the second well to isolate the first zone from the rest of the first well and the second zone from the rest of the second well.

17. The method of claim 1 , further comprising, after generating the back flow in the first well at the first zone and hydraulically stimulating the second well at the second zone: generating a back flow in the first well at a third zone, the third zone being isolated from the first zone; and while or after generating the back flow in the first well at the third zone, hydraulically stimulating the second well at a fourth zone, the fourth zone being isolated from the second zone; wherein the fourth zone is a portion of the second well that is connected to the third zone of the first well using a fracture network.

18. A method to form a fracture system, the method comprising: hydraulically stimulating a first well at a first zone; after hydraulically stimulating the first well at the first zone, generating a low pressure in the first well at the first zone; and while or after generating the low pressure the first well at the first zone, hydraulically stimulating a second well at a second zone;wherein the second zone is a portion of the second well that may be connected to the first zone of the first well using a fracture network; and wherein the low pressure is less than a pressure in the first zone before generating the lower pressure.

19. A method to form a fracture system, the method comprising: hydraulically stimulating the first well at the first zone; after hydraulically stimulating the first well at the first zone, generating a back flow in a first well at a first zone, wherein the back flow generates a lower pressure in the first well that is less than a pressure in the first zone before generating the back flow; and while or after generating the back flow in the first well at the first zone, hydraulically stimulating a second well at a second zone, wherein the second zone is a portion of the second well that is connected to the first zone of the first well using a fracture network; pumping at least one geothermal-rated proppant into at least one of the first well or the second well after hydraulically stimulating the second well at the second zone, wherein pumping at least one geothermal-rated proppant into at least one of the first well or the second well increases the pressure in the first zone and the second zone; while the pressure in the first zone and the second zone is increased, isolating the first zone from a remainder of the first well and isolating the second zone from a remainder of the second well; and flowing a clean fluid into at least one of the first well or the second well to remove any excess of the at least one geo-thermal rated proppant from at least one of the first well or the second well.

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