WO2024064303A1

WO2024064303A1 - Methods and materials for employing fractures in mining operations

Info

Publication number: WO2024064303A1
Application number: PCT/US2023/033409
Authority: WO
Inventors: Howard Schmidt; Cliff MAURONER
Original assignee: Howard Schmidt; Mauroner Cliff
Priority date: 2022-09-22
Filing date: 2023-09-21
Publication date: 2024-03-28

Abstract

Methods for augmenting mining operations with hydraulic fractures. The methods may comprise forming one or more hydraulic fractures near an ore body, which may be filled with an impermeable material, thereby forming an artificial aquitard or a barrier to contaminant migration. The methods may also comprise forming one or more hydraulic fractures within an ore body, injecting a proppant material into the fractures, and cycling a solution through the fractures to perform in-situ mining, or cycling a working fluid through the fractures to provide a mode of heat exchange. The methods may further comprise forming one or more hydraulic fractures at a site of interest to locally influence stress fields in order to prepare the site for material extraction, or disposing within the fractures an energetic material, and detonating the energetic material to extend a single fracture, to form multiple fractures, or to highly fragment rock.

Description

Methods and Materials for Employing Fractures in Mining Operations

CROSS-REFERENCE TO RELATED APPLICATIONS

[0001] This application claims priority to U.S. Provisional Application No. 63/408,939 filed on September 22, 2022, which is incorporated herein by reference.

STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT

[0002] Not applicable.

BACKGROUND OF THE INVENTION

Field of the Invention

[0003] The present invention relates to mining operations. More particularly, the present invention relates to the use of one or more hydraulic fractures across a range of surface and subsurface mining applications.

Background of the Invention

[0004] For centuries, mining operations have enabled societies to extract from the Earth a rich variety of naturally occurring, non-renewable minerals including fuel sources such as coal; valuable metals including gold and silver; industry-critical metals such as iron ore, copper, and various rare-earth metals; stone-based materials including marble, granite, or gravel; and a variety of other materials having utility or value. These materials may typically be formed naturally through long-duration rock cycles, or may be present in solutions found at, near, or below the Earth’s surface, and regions across the world may host these materials in varying concentrations in reserves, which may be commercially exploitable through mining processes.

[0005] Mining operations may be broadly characterized as surface operations or subsurface operations. Examples of surface mining operations include strip mining, open-pit mining, placer mining, or mountaintop mining, while subsurface mining may often be associated with construction of some form of mine shaft enabling access to the minerals of interest, which may be removed through a variety of known techniques. One or more of these methods of mining may be suitable for producing a given mineral or accessing a deposit of interest, and each method may bring with it a number of inherent risks, examples of which may include soil, water, or air contamination; risks to the biodiversity of the surrounding environment; or health or safety risks to the persons involved in the mining operation. Further, as limited quantity, non-renewable resources, the mined materials may exhibit, or be expected to exhibit, a peak in production, where for example, as the resource is produced, the material may become more difficult to access or production yields may begin to fall, which may cause long-term supply of the material to decline.

[0006] Under certain circumstances, paradigm-shifting technologies may be developed which may favorably transform the cost profiles associated with an industry. Innovations in hydraulic fracturing have introduced such a paradigm shift in oil and gas production, enabling access to a rich supply of hydrocarbon reserves at highly favorable costs. In more recent times, fracturing technologies have been extended to fundamentally transform grid-scale energy storage infrastructure in the form of geomechanical pumped storage systems, presenting sizable cost and siting advantages over traditional pumped hydro storage projects. More recent advances in fracturing methodologies have the potential to bring transformative benefits to a range of industries centered around geological sciences, and consequently there is a need in the art for methods of bringing the transformative benefits of fracturing innovations to long-established practices associated with mining operations.

BRIEF SUMMARY OF SOME OF THE PREFERRED EMBODIMENTS

[0007] These and other needs in the art are addressed in one embodiment by a method of forming one or more hydraulic fractures nearby an ore body, and filling the one or more hydraulic fractures with an impermeable material, thereby forming an artificial aquitard.

[0008] These and other needs in the art are addressed in one embodiment by a method of forming one or more hydraulic fractures within an ore body, injecting a proppant material into the one or more hydraulic fractures, and cycling a solution through the one or more hydraulic fractures, or one or more wellbores, to perform in-situ mining.

[0009] These and other needs in the art are addressed in one embodiment by a method of forming one or more hydraulic fractures, which may be closely spaced, in proximity to, or within, an ore body, and circulating a fluid through the one or more fractures so as to circulate ore or other materials of interest out of a subsurface region, through a wellbore, for processing at or near a surface of the earth from which the wellbore may be drilled. [0010] These and other needs in the art are addressed in one embodiment by a method of forming one or more hydraulic fractures in proximity to an ore body, and injecting a resistant material into the one or more hydraulic fractures in order to increase stability of desired locations prior to the site being excavated.

[0011] These and other needs in the art are addressed in one embodiment by a method of forming one or more hydraulic fractures at a site of interest to locally influence stress fields in order to prepare the site for material extraction.

[0012] These and other needs in the art are addressed in one embodiment by a method of forming one or more hydraulic fractures nearby a mineral reserve, and filling the hydraulic fracture with a sealing material to form a barrier to prevent contaminant migration or migration of other subsurface plumes such as carbon dioxide (CO2) or coal combustion residuals (CCR).

[0013] These and other needs in the art are addressed in one embodiment by a method of forming one or more hydraulic fractures near an ore deposit, disposing within the one or more hydraulic fractures an energetic material, and detonating the energetic material to extend a single fracture, to form multiple fractures, or to highly fragment rock.

[0014] These and other needs in the art are addressed in one embodiment by a method of forming one or more hydraulic fractures within a site exhibiting temperature gradients and cycling a working fluid through the one or more hydraulic fractures in order to provide a mode of heat exchange.

[0015] The foregoing has outlined rather broadly the features and technical advantages of the present invention in order that the detailed description of the invention that follows may be better understood. Additional features and advantages of the invention will be described hereinafter that form the subject of the claims of the invention. It should be appreciated by those skilled in the art that the conception and the specific embodiments disclosed may be readily utilized as a basis for modifying or designing other embodiments for carrying out the same purposes of the present invention. It should also be realized by those skilled in the art that such equivalent embodiments do not depart from the spirit and scope of the invention as set forth in the appended claims.

BRIEF DESCRIPTION OF THE DRAWINGS

[0016] For a detailed description of the preferred embodiments of the invention, reference will now be made to the accompanying drawings in which: [0017] FIG. 1 illustrates an embodiment of an artificial base aquitard formed below an ore body of interest; and

[0018] FIG. 2 illustrates an isometric view of an embodiment of a system of vertical artificial aquitards formed down-dip of an ore body of interest.

[0019] FIG. 3 illustrates a plan view of an embodiment of a system of vertical artificial aquitards formed down-dip of an ore body of interest.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0020] Fractures may be formed by injecting an incompressible fluid into a formation under significant pressure, thereby causing the rock to split. Research into the effects of employing explosive techniques in forming systems of multiple fractures has been performed and is known in the art. For example, in the publication entitled “In-Situ Evaluation Of Several Tailored-Pulse Well Shooting Concepts,” Richard A. Schmidt et al., Sandia National Laboratories (SPE/DOE 8934), presented at the Society of Petroleum Engineers Unconventional Gas Recovery Symposium, May 1980, the entire contents of which are incorporated herein by reference thereto, detailed comparisons of resulting permeability effects are presented for a series of full-scale tests performed across varying multiple-fracture systems. While an orientation of a fracture may generally correlate to local stress fields present within the formation, methods have been developed to initiate and propagate fractures in desired orientations which may be suitable for an application of interest. In practice, it has been found that a horizontal fracture can be initiated and propagated a significant distance even where the natural fracture direction may be vertical. Often, fractures may be propped in order to improve fluid conductivity through known or novel methods. U.S. Patent Application Nos. 17/145,666, filed January 11, 2021; 18/128,004, filed March 29, 2023; and 18/134,851, filed April 14, 2023, the entire contents of which are incorporated herein by reference thereto, disclose a range of methods of developing fractures and preparing fractures for service.

[0021] Mining operations present an opportunity to employ a single hydraulic fracture, or a plurality of hydraulic fractures formed in a series or cluster, in unique ways to augment or replace traditional methods of mining. Under certain conditions, it may be suitable to form a series of fractures in one or more desired directions, for example horizontal, vertical, or combinations thereof, from one or more wellbores drilled into or nearby an ore body. Across the field of mining, hydraulic fractures may be employed to perform a range of roles integral to in-situ mining operations, preparing a site for traditional mining processes, in processes incorporating explosive materials, and in projects incorporating heat extraction or heat exchange.

[0022] In-situ applications, including solution mining and leach mining, present opportunities of particular interest to incorporate fracturing techniques in mining operations. In these applications, one or more chemical solutions may be cycled into an ore deposit and subsequently extracted in order to dissolve a mineral of interest which is removed from the deposit along with the solution, and leak-off of the solution into the surrounding formation may be a problem commonly encountered.

[0023] In embodiments, certain in-situ mining operations may benefit from employing fractures filled with impermeable material in order to form artificial aquitards. In an embodiment, an artificial base aquitard may be formed to collect fluid introduced to an ore body by initiating and propagating a fracture at a bottom of a wellbore drilled into, or near, an ore body, propagating the fracture horizontally, and filling the fracture with an impermeable material. Under certain conditions, propagating the fracture with a high radius to depth ratio may cause edges of the fracture to tip upwards towards the free surface (see “Crack tip behavior in near-surface fluid- driven fracture experiments” by Bunger, A. P., Detoumay, E., & Jeffrey, R. G. (2005), Comptes Rendus Mecanique, 333(4), 299-304), which may provide the fracture with a shape similar to a bowl, which may be ideal for collecting fluids. In embodiments, additional horizontal and/or vertical fractures may be formed to surround the target in-situ zone in order to surround portions of the ore body, or otherwise channel or direct flows of fluids via high-conductivity paths formed through the in-situ zone.

[0024] In embodiments which may or may not comprise artificial aquitards, an ore body of interest may be prepared for in-situ mining by forming one or more fractures in a region proximal to, surrounding, or including the ore body and circulating a fluid through the prepared region and returning the circulated fluid to the surface for processing of materials of interest which may be carried to the surface by the circulated fluid. In such embodiments, subsurface leaching may be reduced or eliminated, and the method of preparing the region through use of energetic materials and fractures in this manner may substantially increase the volume of ore which may be accessible via the wellbore.

[0025] FIG. 1 illustrates an example embodiment of such an application, wherein wellbore 110 may be drilled to extend from surface 100 to a desired depth 115 which may be located below an ore body of interest. In embodiments, one or more fractures 120 may be formed to extend horizontally from wellbore 110 at one or more desired depths 115, which may thereby generate region 130 proximal to, surrounding, and/or including the ore body of interest which may become fractured by energetic materials. In embodiments, an artificial base aquitard 140 may be formed at desired depth 115 underneath region 130 as shown, and in the manner just described. Such an embodiment may render region 130 suitable for mining, for example by circulating pulverized material up and out of wellbore 110. In an example application employing such embodiments, it may be desirable to re-bore wellbore 110 after triggering energetic materials, so as to provide wellbore 110 with a diameter suitable to be configured with tubing, which may be appropriate for continuous circulation of a fluid, the fluid having a viscosity suitable for lifting and producing rubble, gravel, and/or other materials from the ore body. In in-situ applications employing such embodiments, it may be desirable to inject the fluid into region 130 from a depth located above region 130 and extract the fluid and materials of interest from region 130 at a depth located below region 130, while in ore extraction applications employing such embodiments, it may be desirable to inject the fluid into region 130 from a depth below region 130 and extract the fluid and materials of interest from region 130 at a depth above region 130.

[0026] FIGS. 2 and 3 illustrate isometric and plan views, respectively, of an example embodiment employing a system of vertical artificial aquitards which may be employed to restrict or block fluid flow down-dip from an ore body. In embodiments, wellbore 210 may be drilled to a desired depth 215, which may be located below an ore body of interest. One or more horizontal fractures 220 may be formed to extend horizontally from wellbore 210 at one or more desired depths 215, which may generate region 230 proximal to, surrounding, and/or including the ore body of interest which may become fractured by energetic materials. In such embodiments, a natural or artificial base aquitard 240 may be located or formed below the ore body of interest. As shown, one or more vertical artificial aquitards 250 may be formed in a desired arrangement nearby region 230, which may form a barrier to channel or block fluid flow down-dip from region 230. A fluid may then be circulated into and extracted from region 230 in a manner similar to that just described in the embodiment illustrated in FIG. 1, as may be appropriate for in-situ applications or ore extraction applications.

[0027] In other embodiments of in-situ applications, one or more horizontal fractures may be formed in a target zone and filled with proppant in order to provide channels through which solutions or leaching agents may be cycled within the zone via one or more wellbores drilled to provide access to the zone, and pumped back to the surface. Similarly, a series of connecting, closely spaced horizontal fractures can be formed along or across a target zone in order to expand or maximize the amount of surface area exposed to in-situ solutions within the zone, through which the solution may be circulated via one or more wellbores providing access to the target zone. [0028] The use of fracturing techniques in mining operations may also be of interest in preparing a site for traditional forms of mining. In an embodiment, one or more fractures may be formed at a site of interest to locally influence stress fields in order to prepare the site for material extraction. In another embodiment, one or more fractures may be spaced at desired locations, or along a desired path, prior to tunneling in order to facilitate excavation. In a further embodiment, one or more fractures may be formed surrounding a site of interest which may then be filled with a sealing material in order to prevent contaminant migration. An additional further embodiment may comprise a method of forming one or more hydraulic fractures in proximity to an ore body, into which a resistant material may be injected, which may increase stability of one or more desired locations surrounding or including the ore body prior to the site being excavated through traditional methods, for example highwall mining.

[0029] Fracturing can also be employed in conjunction with energetic, or explosive, materials. In embodiments, the energetic material may be selected to control or provide a desired detonation velocity, and may be used to extend a single fracture, to form multiple fractures, or to highly fragment rock, which may be accomplished for example with increasing detonation speed. In certain embodiments, fracturing processes may be used in place of blast mining. Detonating material may also be used in fractures employed during in-situ applications to generate rubble in a fracture which may serve as a proppant, thereby allowing high volume flow through the fracture and increasing surface area for chemical reactions. Such rubble-filled vertical fractures may be used to support thermal convection for heat exchange or geothermal heat extraction.

[0030] Hydraulic fractures may also be utilized in embodiments where heat transfer may be an objective of developing a site, horizontal or vertical fractures may be formed through though this method in order to create self-propped channels with high conductivity. When coupled with one or more boreholes, such embodiments can serve as subsurface heat exchangers or be utilized for heat extraction. The method of providing heat transfer or heat exchange capability through one or more hydraulic fractions may be particularly attractive to industrial applications which may include, for example, data center cooling or waste heat rejection.

[0031] Although the present invention and its advantages have been described in detail, it should be understood that various changes, substitutions and alterations may be made herein without departing from the spirit and scope of the invention as defined by the appended claims.

Claims

CLAIMS What is claimed is:

1. A method of forming an artificial base aquitard to collect a fluid introduced to an ore body, comprising: drilling a wellbore in proximity to an ore body; initiating a fracture at a bottom of the wellbore; propagating the fracture horizontally; filling the fracture with an impermeable material to form an artificial base aquitard; introducing a fluid into the ore body; and collecting the fluid in the artificial base aquitard.

2. The method of claim 1 , wherein the propagating comprises propagating the fracture with a high radius to depth ratio.

3. The method of claim 1, wherein the wellbore comprises a plurality of wellbores, the fracture comprises a plurality of fractures, and the artificial base aquitard comprises a plurality of artificial base aquitards which surround one or more portions of the ore body.

4. The method of claim 3, wherein the plurality of base aquitards is formed in locations which allow channeling a flow of the fluid through the ore body.

5. A method of producing a mineral of interest from an ore body, comprising: drilling a wellbore in proximity to an ore body; forming a horizontal fracture at a bottom of the wellbore; filling the fracture with proppant to form a channel through which a fluid may be circulated through the ore body; cycling the fluid from the wellbore into the ore body to dissolve a mineral of interest located in the ore body; returning the fluid to the wellbore, wherein the fluid includes the mineral of interest; and retrieving the fluid from the wellbore, thereby producing the mineral of interest at a surface from which the wellbore was drilled. The method of claim 5, wherein the wellbore comprises a plurality of wellbores, and the fractures comprise a plurality of fractures formed along or across the ore body. The method of claim 6, wherein the plurality of fractures connect and allow the fluid to circulate through the connected plurality of fractures before the fluid is retrieved from one of the plurality of wellbores. A method of forming an artificial vertical aquitard to collect a fluid introduced to an ore body, comprising: drilling a wellbore in proximity to an ore body and down-dip from said ore body; initiating a fracture along the wellbore proximal to the ore body; propagating the fracture vertically; filling the fracture with an impermeable material to form an artificial vertical aquitard; introducing a fluid into the ore body via a second wellbore; and collecting the fluid in a natural or artificial base aquitard. The method of claim 8, wherein the wellbore comprises a plurality of wellbores, the fracture comprises a plurality of fractures, and the artificial vertical aquitard comprises a plurality of artificial vertical aquitards which surround one or more portions of the ore body. The method of claim 9, wherein the plurality of artificial vertical aquitards is formed in locations which allow channeling a flow of the fluid through the ore body.