EXPLOITING GEOTHERMAL ENERGY THROUGH HEAT RECOVERY BY CIRCULATING WORKING FLUID IN PURPOSE-BUILT SYSTEM OF MULTILATERAL WELLS

Abstract

The present invention relates to heat extraction from a hot dry rock system using a single well with multilaterals in a closed loop circulation. More particularly, it relates to geothermal heat collector systems. A working fluid is circulated through a single well (106) with several lateral heat absorbing branches (113). These branches are sidetracked off the main wellbore (111) and completed using a slotted lateral sealed bore junction and hanger assembly completion (114) installed in the main wellbore (111). The lateral heat absorbing branches (113) are tied in and completed in a tubing mono assembly, comprising of the well (106) and lateral heat absorbing branches (113). The tubing assembly is hung off in a slotted tubing hanger assembly (112) that is installed in the bottom section of the main wellbore (111). The hanger assemblies are equipped with circulation ports and open hole rock slips. The heat extraction is done through direct contact between the working fluid and the formation.

Claims

1-10. (canceled)

11. A plant for extracting geothermal energy from hot dry rock by circulating a working fluid through a single well with several lateral heat absorbing branches comprising: lateral heat absorbing branch or branches that is or are sidetracked off the main wellbore and completed using a slotted lateral sealed bore junction and hanger assembly completion installed in the main wellbore, heat absorbing branches that are tied in and completed in a tubing mono assembly, comprising of the main wellbore and lateral heat absorbing branches; and lateral tubing assembly that is hung off in a slotted open-hole tubing hanger assembly installed in the bottom section of the main wellbore, said hanger assemblies are equipped with circulation ports and open hole rock slips, wherein heat extraction is done through direct contact between the working fluid and the formation.

12. The plant according to claim 11, wherein each lateral tubing assembly, is connected to and extending from the corresponding slotted lateral sealed bore junction and hanger assembly completion.

13. The plant according to claim 12, wherein the bottom hole assembly is equipped with guide and downhole choke.

14. The plant according to claim 11, wherein orientation and direction of lateral heat absorbing branches are adapted according to formation geology.

15. The plant according to claim 11, wherein a substantial part of the lateral heat absorbing branches may be located parallel to each other or may extend downwards from the main wellbore.

16. The plant according to claim 12, wherein a lateral heat absorbing branch is spatially distributed at least 50 m from the nearest heat absorbing branch.

17. The plant according to claim 13, wherein a lateral heat absorbing branch is spatially distributed at least 50 m from the nearest heat absorbing branch.

18. The plant according to claim 11, wherein surface wellhead has an inlet port for well injection through the injecting tubing, and a port for the circulated heated working fluid in the return annulus.

19. The plant according to claim 11, wherein the flow direction in the injection tubing and return annulus may be reversed to enable among others removal of sediments.

20. The plant according to claim 11, wherein the working fluid for extracting thermal energy from hot dry rock is treated depending on local conditions and requirements to avoid bacterial growth, the treatment may include filtration, exposure to Ultraviolet (UV) light and the use of biocides.

21. A method for extracting and producing geothermal energy from hot dry rock by circulating a working fluid through a single well with several lateral heat absorbing branches comprising: a lateral heat absorbing branch bore sidetracked off the main wellbore; retrievable whipstocks are used to sidetrack each lateral heat absorbing branch bore off the main wellbore; and each heat absorbing branch is completed using a slotted lateral sealed bore junction and hanger assembly completion installed in the main wellbore, immediately below the entrance of the heat absorbing branch.

Description

DESCRIPTION OF THE DRAWINGS

[0027] FIG. 1 gives a general schematic of the geothermal plant layout according to the invention.

[0028] FIG. 2 is a schematic side view of the subsurface view of the plant and a typical well path, here shown with the lower main wellbore at an angle.

[0029] The main wellbore is to be drilled to Total Depth (TD) into the geological HDR formation. The wellbore will be open to formation except the upper part of the wellbore which will be cased off with a surface casing (108) for structural and thermal insulation purposes.

[0030] When the main well has reached TD the drilling and installation of the lateral wells will start, the number and length of which will depend upon the designed plant energy project deliveries.

DETAILED DESCRIPTION

[0031] A plant for exploiting geothermal energy by pumping and circulating working fluid through the center of preinstalled injection tubing installed in a drilled well down to the Earth surface.

[0032] As shown in FIG. 1, the plant will consist of a surface wellhead 105, heat exchanger 103, surface heat/energy consumers 101 and 102, a circulating/injection pump 104, surface fluid returns from well 107, the well 106 being drilled into said geological formation, the lower part of the well being drilled vertically or at an angle pending geological formation.

[0033] The lateral heat absorbing branches 113 are sidetracked off the main wellbore 111, using retrievable whipstocks and completed with slotted lateral sealed bore junction and hanger assembly completions 114 equipped with circulation ports and open hole rock slips.

[0034] The subsequent laterals and main wellbore will be equipped with lateral tubing assemblies 115, completed with downhole tubing circulating chokes 116 and designed for optimum and full circulation of the total injected volume of working fluid via the return annulus 110 between injection tubing 109 and main wellbore 111.

[0035] Eventually, all the lateral heat absorbing branches 113 are tied back in an slotted open-hole tubing hanger assembly 112, to be tied back to surface via the injection tubing 109, to be used for working fluid injection.

[0036] As working fluid is circulated from surface down the injection tubing 109 to the geological formation, through the lower section of the main wellbore 111, and through the lateral heat absorbing branches 113, the return annulus 110 between the installed injection tubing 109 will fill with working fluid in contact with the hot geological formation.

[0037] The continued injection of working fluid from the surface will ensure transportation of heated working fluid from the formation back to the surface via the tubing annuli of the lateral heat absorbing branches 113 and the return annulus 110 of the injection tubing 109.

[0038] The spacing and figuration between all the lateral heat absorbing branches 113 must be drilled at least 50 m away from the nearest heat absorbing branch.

[0039] The total length of the heat absorbing areas of the main wellbore 111, and particularly the lateral heat absorbing branches 113, will depend on the designed plant energy deliverables, as well as the optimization of geothermal contact and return of heated working fluid circulation.

[0040] All multilateral sealed bore circulation junction tubing hanger assemblies that are installed to be adequately slotted to ensure required annulus circulating area is available, not to restrict the design return circulation rate of volume of heated working fluid.

[0041] FIG. 2 shows the lower section of the wellbore 111 being drilled vertically, alternatively directionally drilled at an angle dependent on the geological formation, the subsequent lateral heat absorbing branches 113 being sidetracked off the main wellbore 111.

[0042] To avoid any bacteriological growth or contamination of the working fluid (water) circulated through the plant, the treatment of the fluid will depend on local conditions and requirements. The treatment will mainly be based on filtration of fluid and exposure to Ultraviolet (UV) light and the use of biocides.

TABLE-US-00001 Terminology 101 Surface heat/energy consumer 102 Surface heat/energy consumer 103 Heat exchanger 104 Injection/circulating pump 105 Surface wellhead 106 The well 107 Surface fluid returns from well 108 Surface casing 109 Injection tubing 110 Return annulus 111 Main wellbore 112 Slotted tubing hanger assembly 113 Lateral heat absorbing branches 114 Slotted lateral sealed bore junction and hanger assembly completion 115 Lateral tubing assembly 116 Downhole tubing circulating choke