CA2896812A1 - In-situ leaching of ore deposits located in impermeable underground formations - Google Patents

Abstract

A method and system of in-situ leaching of ore deposits located within underground formations comprising non-porous and impermeable rock. The method includes hydraulically fracturing the impermeable formation containing an ore deposit to create a fractured zone within the formation. Then a flowable explosive is introduced into the fractured zone and detonated to rubblize the fractured zone to create a permeable zone within the formation that is suitable for in-situ leaching of the ore deposit.

Description

IN-SITU LEACHING OF ORE DEPOSITS LOCATED IN IMPERMEABLE
UNDERGROUND FORMATIONS
FIELD OF THE INVENTION
[001] The present invention relates generally to mining ore, and more particularly, relating to a method of in-situ leaching of uranium deposits located in non-porous, impermeable underground formations.
BACKGROUND OF THE INVENTION

[002] Currently, uranium deposits are mined using open-pit mining, underground mining, and in-situ leaching. The present application is directed toward in-situ leaching. In-situ leaching (ISL), also referred to as solution mining, is well-known, and example methods are described in U.S. Patent Nos. 3,309,140;
4,185,872; 4,239,286; and 4,285,548, the entirety of each are incorporated herein by reference. Generally speaking, in-situ leaching is a process where uranium is recovered from an underground deposit through wellbores that are drilled into the deposit. A leaching solution is pumped into the deposit to dissolve the uranium and is then pumped to the surface where the solution is processed to separate the uranium from the solution.

[003] In-situ leaching mining of uranium is preferred over the other mining methods for several reasons. These reasons include lower development and operating costs, reduced hazard to workers, smaller work force, and less expensive remediation, among others. Currently, in-situ leaching of uranium is performed on deposits located in sedimentary rock formations due to the natural porosity and permeability of sedimentary rock. While current mining is limited to sedimentary rock formations, there are significant uranium deposits located in non-sedimentary rock formations. These include deposits located in non-porous, impermeable metamorphic and igneous rock formations.

[004] The industry has avoided these deposits because in-situ leaching requires a porous, permeable formation so that the leaching solution can flow through the formation to dissolve the uranium. According, there is a need for in-situ leaching of uranium deposits located in underground formations of non-porous, impermeable rock, such as, metamorphic or igneous rock formations.
SUMMARY OF THE INVENTION

[005] Embodiments of the present invention provide a method and system of in-situ leaching of ore deposits located in impermeable underground formations. These underground formations include non-porous and impermeable igneous or metamorphic rock, for example, that contain valuable ore deposits, such as uranium that heretofore have not been recovered by in-situ leaching.

[006] In general, in one aspect, a method of in-situ recovery of uranium disposed in an underground formation comprising non-porous impermeable rock includes:
a) hydraulically fracturing the underground formation, thereby creating a fractured zone along said uranium deposit;
b) introducing a flowable explosive into said fractured zone;

c) detonating said explosive, thereby creating a permeable zone;
d) injecting a recovery solution into said permeable zone; and e) recovering said recovery solution from said permeable zone.

[007] There has thus been outlined, rather broadly, the more important features of the invention in order that the detailed description thereof that follows may be better understood and in order that the present contribution to the art may be better appreciated.
BRIEF DESCRIPTION OF THE DRAWINGS

[008] In the drawings:

[009] Figure I is a cross-section of an in-situ leaching mine constructed in accordance with an embodiment of the present invention;

[010] Figure 2 is a flow chart illustrating a method of forming a permeable zone within a non-permeable formation in accordance with an embodiment of the invention;

[011] Figure 3 is a cross-section of an underground formation after the underground formation has been hydraulically fractured in accordance with an embodiment of the present invention; and

[012] Figure 4 is a cross-section of an underground formation after detonation of an explosive within a fractured zone of the underground formation, creating a permeable zone in the formation.
DETAILED DESCRIPTION OF THE INVENTION

[013] Embodiments of the present invention provide an in-situ leaching mining method for the recovery of ore deposits located within underground formations comprising non-porous and impermeable rock, such as igneous and metamorphic rock formations.

[014] With reference to FIG. 1, there is illustrated a cross-section of an in-situ leaching mine 100 operating to recover ore deposit 102, such as uranium, located within underground formation 104 that has been constructed in accordance with an embodiment of the present invention. Conventionally, leaching solution 106 is injected into the underground formation 104 through injection well 108. Then after flowing through the underground formation 104, ore rich solution 110 is recovered at the surface from the underground formation through production wells 112. In practice, the mine 100 may include any number of configurations of injection wells and production wells based upon the geologic formation containing the ore deposit 102.

[015] Unconventionally, the underground formation 104 containing the ore deposit 102 is a non-porous and impermeable rock formation that has been operated upon using the methods disclosed herein such that the ore can be recovered from the formation utilizing conventional in-situ leaching techniques.

[016] Particularly, the methods disclosed herein create a highly porous and permeable zone 114 in the underground formation 104 along the ore deposit 102 such that an in-situ leaching mining process can be performed to extract the ore deposit from the formation that otherwise would not be possible. For illustrative and discussion purposes only, zone 114 is shown entirely disposed within the ore deposit 102.

But, in practice, one of ordinary skill would readily appreciate that zone 114 could be formed in many different configurations to achieve desired in-situ leaching of the ore deposit. As a non-limiting example, zone 114 could be created so as to entirely encompass the ore deposit 102.

[017] In FIG. 2, a flow chart illustrates a method 200 according to an embodiment of the invention. At step 202, a borehole or multiple boreholes are drilled into the formation as determined based upon various factors, including geology of the formation and ore deposit. At step 204, after the one or more boreholes are formed, a hydraulic fracturing operation is performed on the formation utilizing one or more of the previously formed boreholes to fracture the formation and create one or more fracture zones. For the purpose of herein, hydraulic fracturing, hydrofracking, fracking, or hydroshearing meaning forcing opening of fissures in the underground formation. Further, one of ordinary skill in the art will readily appreciate that any number of known hydraulic fracturing methods can be used according to the geology of the formation

[018] At step 206, after fracturing the formation, a flowable explosive is introduced into the fractured formation through one or more of the boreholes and is caused to flow into the fissures of the one or more fracture zones that were formed in the formation during the prior fracturing operation. For the purpose of herein, flowable explosive means any explosive material that can be pumped or otherwise caused to flow into the formation. As a non-limiting example, nitroglycerine, astrolite, and nitromethane are types of flowable explosives that may be used.

Additionally, the flowable explosive could be granular or a liquid mixed with a granular. Finally, it is important to note that step 206 must be performed after step 204 to form the fissures that the explosive is caused to fill.

[019] At step 208, after the flowable explosive is introduced into the one or more fracture zones, the explosive is detonated causing further fracturing of the formation or otherwise rubblization of the fracture zones, thereby forming permeable zones. For the purpose of herein, rubblization means fragmenting the formation into a finer-grain matrix that has a high permeability than the formation beyond the rubblized zone. Detonating the fracture zones may cause one or more of the boreholes formed in step 202 to collapse which may need to be reestablish as desired for the completion of the in-situ leaching mine. And steps 202 through 208 may be repeated as necessary to complete development of the mine.

[020] After the forgoing method has been completed on the underground formation, the in-situ leaching mine can be completed according to known methods by completing leaching solution injection wells and solution recovery wells according the site plan as developed according the geology of the formation and the ore deposit. In certain instances the one or more bores formed during step may be completed either as injection or recovery wells based upon the site plan and the geology of the formation and ore deposit.

[021] With reference to FIG. 3, there is representatively illustrated an enlarged, cross-section of an underground formation after the underground formation has been hydraulically fractured, for example as in step 204 discussed above.
Particularly, borehole 302 has been drilled into the formation 304, and as illustrated, also into the ore deposit 306 that is located within the formation. As further illustrated, the formation along ore deposit 306 includes a fracture zone, generally indicated by broken line 308, which includes numerous fissures 310 formed into the formation during the fracturing step.

[022] With reference to FIG. 4, there is representatively illustrated an enlarged, cross-section of an underground formation after detonation of the explosive, for example as in step 208 discussed above. Particularly, the fracture zone, such as fracture zone 308 of FIG. 3, has been rubbilized by detonation of the explosive, thereby creating a permeable zone 402 in the underground formation 404 along the ore deposit 406. In the permeable zone 402, the formation has been fragmented into a finer-grain matrix of rubble 408 that allows in-situ leaching of the ore located in the permeable zone. As further illustrated, borehole 410 has been reestablished and may be further completed as either a leaching solution injection well or a leaching solution recovery well.

Claims (9)

CLAIMS:

1. A method of forming an in-situ mine comprising the steps of:
hydraulically fracturing a non-porous, impermeable formation containing an ore deposit, thereby creating a fractured zone;
introducing an flowable explosive into said fractured zone; and detonating said explosive, thereby causing rubblization of at least a portion said fractured zone.

2. The method of claim 1, wherein said flowable explosive is a liquid explosive.

3. The method of claim 2, wherein said liquid explosive is nitroglycerin.

4. The method of claim 1, wherein said formation comprises metamorphic or igneous rock.

5. A method of in-situ recovery of uranium disposed in an underground formation comprising non-porous, impermeable metamorphic or igneous rock:
hydraulically fracturing the underground formation, thereby creating a fractured zone along said uranium deposit;
introducing a flowable explosive into said fractured zone;
detonating said explosive, thereby creating a permeable zone;
injecting a recovery solution into said permeable zone; and recovering said recovery solution from said permeable zone.

6. The method of claim 5, wherein said flowable explosive is nitroglycerin.

7. The method of claim 5, wherein said formation comprises metamorphic or igneous rock.

8. A method of in-situ recovery of a uranium deposit located within an underground formation of non-porous, impermeable metamorphic or igneous rock, the method comprising the steps of:
forming a wellbore into the underground formation approximate the uranium deposit;
hydraulically fracturing the underground formation along a portion of said wellbore, thereby creating a fractured zone within the underground formation along the uranium deposit;
injecting a flowable explosive through said wellbore and into said fractured zone;
detonating said flowable explosive, thereby creating a permeable zone along the uranium deposit;
injecting a recovery solution into said permeable zone; and recovering said recovery solution from said permeable zone through a production well.

9. The method of claim 8, wherein said flowable explosive is nitroglycerin.