Patent Application
20230332501
The present invention relates generally to hydraulic fracturing a rock mass as part of a method of establishing a block cave mine or extending an existing block cave.
The present invention relates particularly to hydraulic fracturing a rock mass by drilling a plurality of holes downwardly into the rock mass using a drill rig positioned on the ground above a proposed or existing block cave mine and then injecting a hydraulic fracturing fluid into the drilled holes from above-ground equipment as part of a method of establishing a block cave mine or extending an existing block cave mine.
The present invention also relates to a non-metallic casing for lining the drilled holes.
Block cave mining is an efficient technique that leverages gravity and induced stress to support the efficient extraction of ore from a rock mass.
Block cave mining methods, due to their low operating costs and high productivity, have historically been the preferred underground solution to profitably mine large, low-grade deposits.
Major drawbacks of block cave mining are high upfront mine establishment costs and long lead times to establish name plate production rates. Establishment costs typically range from US$2 billion to US$5 billion and take up to 7 years to reach production.
Establishment costs and times are exacerbated by increasingly complex ore bodies at depth, including depth related issues such as strength/stress ratios, material handling costs, seismicity, heat, etc.
Conventional block caves are established from two levels, namely an undercut level which functions to facilitate the creation of a void above a draw horizon to induce caving within the mine, and a lower extraction level from which draw bells are opened upwardly and connected to the undercut level, allowing caved ore to move downwardly through the draw bells into the extraction level and be removed from the extraction level.
Establishment of conventional block caves or extending existing block cave mines includes pre-conditioning a rock mass above the undercut and extraction levels of the mine.
Papers by Catalan et al., 2012a, Catalan et al., 2012b, Catalan et al., 2012c and Catalan (2015) define “pre-conditioning” a rock mass as the implementation of processes to modify the rock mass to enable better control or management of a block cave mine.
The term “modify” is used in this context to mean causing artificially induced changes to a rock mass through:
Conventional hydraulic fracturing a rock mass comprises drilling a plurality of holes into the rock mass from sub-levels below the ground and injecting a hydraulic fracturing fluid into the drilled holes and forming fractures in the rock mass that extend from the drilled holes. The fractures facilitate rock mass failure that assists in downward movement of rock mass during caving and reduce unwanted energy transfer through the rock mass as a consequence of seismic activity.
As used herein, the term “hydraulic fracturing” (also known as “hydrofracturing” or “fracking”) is understood to mean fracturing a rock mass by a pressurized fluid, such as water, that is injected into drilled holes extending into the rock mass.
The present invention provides an alternative method of hydraulic fracturing a rock mass as a part of the establishment of a block cave or extending an existing block cave mine and an installation for carrying out the method.
The present invention also provides a non-metallic casing for lining drilled holes formed in the method.
The above description is not an admission of the common general knowledge in Australia or elsewhere.
The invention is based on a realisation that hydraulic fracturing a rock mass from the ground above the rock mass is an effective alternative to conventional hydraulic fracturing technology for establishing a block cave mine or extending an existing block cave mine.
The invention includes:
In broad terms, the invention provides a method of hydraulic fracturing a rock mass as part of a method of establishing a block cave mine or extending an existing block cave mine that includes:
The fractures in the rock mass that are induced by the hydraulic fracturing method assist subsequent removal of the rock mass via the extraction level of the block cave mine.
The fractures in the rock mass that are induced by the hydraulic fracturing method also assist making the rock formation more seismic-safe by reducing the transfer of energy through the rock mass in a seismic event.
Hydraulic fracturing fluid injection step (b) may include perforating each hole so that injected hydraulic fracturing fluid flows through perforations into the rock mass and induces fractures in the rock mass.
Drilling step (a) may include casing each hole.
Drilling step (a) may include casing and lining each hole.
Hydraulic fracturing fluid injection step (b) may include perforating each cased and lined hole so that injected hydraulic fracturing fluid flows through the perforations into the rock mass and induces fractures in the rock mass.
The cased and lined hole may be perforated by any suitable perforating apparatus.
One example of a suitable perforating apparatus is a perforating gun having spaced explosive charges that can be initiated to from a perforate the immediate part of the cased and lined hole.
In addition, in more particular terms, the invention provides a method of hydraulic fracturing a rock mass as part of a method of establishing a block cave mine or extending an existing block cave mine that includes:
Step (c) may include perforating the casing of each drilled hole at spaced intervals along a section of the drilled hole.
The perforated holes may be in “frac clusters”, with multiple perforated holes at different heights forming a single cluster.
In addition, in more particular terms, the invention provides a method of hydraulic fracturing a rock mass as part of a method of establishing a block cave mine or extending an existing block cave mine that includes:
The method may include drilling a plurality of holes at the location and forming a cluster of holes at the location and carrying out the subsequent method steps on the cluster of holes at the location.
The method may include carrying out the drilling, casing and lining method steps (i.e. stage 1 method steps) with drill rig equipment at the location and forming the cluster of cased and lined holes and then, on completion of the method steps, moving the drill rig equipment to another location and repeating the method steps at the other location.
The method may include setting up hydraulic fracturing fluid injection equipment at the location after the drill rig equipment has been moved from the location and perforating the cased and lined holes and hydraulic fracturing the cluster of holes (i.e. stage 2 method steps) and then, on completion of the method steps, moving the hydraulic fracturing fluid injection equipment to another location and repeating the stage 2 method steps at the other location.
The drilled holes may be any suitable hole diameter, hole depth(s), and hole spacing(s).
Typically, the casing is a non-metallic casing.
As is described further below, the applicant has found that forming the casing from a non-metallic material provides an opportunity to balance the operational requirements for containing high pressure injection of hydraulic fracturing fluid and minimising or avoiding damage altogether to mine crushers and other equipment after the casing is processed downstream, i.e. after the casing moves downwardly through a block cave and is removed from the extraction level of the mine.
Perforation step (e) may include perforating the casing at any suitable spaced intervals along the length of the casing.
The perforations may be any suitable size and shape.
The perforations may be in “frac clusters”, with multiple perforations at each of a number of different heights forming a single cluster.
The hydraulic fracturing fluid may be any suitable hydraulic fracturing fluid.
Typically, water is the hydraulic fracturing fluid.
The invention may include selecting hydraulic fracturing fluids that are suitable for forming fractures having different sizes and shapes.
Different hydraulic fracturing fluids may be required in different situations.
One option is forming parallel fractures (preferred by miners)—slower flow rate and more viscous hydraulic fracturing fluids.
Another option is forming complex fractures (preferred by seismologists)—different hydraulic fracturing fluids and higher flow rates.
The method may include selecting parameters for the method having regard to a need to compromise between the different priorities of seismologists and mining engineers. Seismologists want to heavily fracture a rock mass—minimising energy transfer issues in a seismic event. Mining engineers do not want to heavily fracture a rock mass. Mining engineers prefer to fracture as rock mass to form comparatively larger fragments than those preferred by seismologists that will be able to move downwardly as block caving continues and be removed as reasonable-sized fragments, i.e. not fines, via draw bells. Inevitably, rock fragments that form in upper levels of a block cave mine will reduce in size due to fragment-fragment abrasion as the fragments move downwardly. Mining engineers do not want the fragments to be “fines” at the draw points.
While hydraulic fracturing technology has been previously employed during conventional block caving, it is initiated at block cave sub-levels and not from the ground. Given the logistical issues of underground operation, there is an upper limit on the lengths of casings used during conventional hydraulic fracturing—such as 1.5 m. In contrast, the method of hydraulic fracturing of the invention is not subject to the same logistical constraints because the operation is conducted above ground level. As such, significantly longer casings may be used—such as 9+m, and higher power/torque is able to be used for drilling, thereby making it possible to drill fewer holes per a given volume of rock mass compared to the number of holes required in an underground pre-conditioning operation.
Hydraulic fracturing a rock mass from the ground provides an opportunity to accelerate cave propagation, manage high rock stresses, and reduce early fragmentation size and downstream secondary breakage requirements.
Further to the above, a main purpose of hydraulic fracturing a rock mass is to fracture the rock mass to create fractures, effect a reduction in rock mass quality, reduce the modulus of elasticity of the rock mass, improve fragmentation, and reduce the capacity of the rock to transmit/convey stress.
Hydraulic fracturing assists in ensuring sufficient initiation of a block cave as it reduces the rock mass quality and reduces the critical hydraulic radius required before caving commences.
Hydraulic fracturing not only helps to degrade the rock mass strength to reduce the critical hydraulic radius required before cave initiation, it also helps to manage stress levels within the rock mass thereby reducing magnitude and frequency of mining induced seismicity.
A more broken, “softer” and elastic rock mass has less capability to convey/transmit rock stress and therefore actual stress levels encountered are generally reduced.
Hydraulic fracturing also assists in improving early fragmentation and therefore reduces the need for secondary breakage of oversized fragments during mining production activities.
In broad terms, the invention also provides a hydraulic fracturing equipment installation positioned at a location on the ground above a rock mass and operable for hydraulic fracturing the rock mass as part of a method of establishing a block cave mine or extending an existing block cave mine, the installation including:
More particularly, although not by any means exclusively, the invention provides a hydraulic fracturing equipment installation positioned at a location on the ground above a rock mass and operable for hydraulic fracturing the rock mass as part of a method of establishing a block cave mine or extending an existing block cave mine, the installation including:
The drill rig equipment may include equipment operable for lining the drilled holes with a casing, such as a metallic or a non-metallic casing.
The drill rig equipment may include equipment operable for forming a lining, such as of a concrete material, in an annular space between the casing and a hole wall.
Typically, the installation includes the following equipment:
The invention also provides a block cave mine that includes the above-described hydraulic fracturing equipment installation located on the ground above a rock mass at a block mine establishment stage or an extension stage of an existing block cave mine and operable for hydraulic fracturing the rock mass as part of a method of establishing a block cave mine or extending an existing block cave mine.
The block cave mine may be any suitable mine.
By way of example, the block cave mine may be as described and claimed in International (PCT) Patent Application No. PCT/AU2021/050255 in the name of the applicant, and the disclosure in the PCT specification is incorporated herein by cross-reference.
The invention provides a non-metallic casing for use in a hydraulic fracturing method, the non-metallic casing comprising a non-metallic material having a maximum pressure resistance of 90 MPa.
The invention provides a non-metallic casing for use in a hydraulic fracturing method of establishing a block cave mine or extending an existing block cave mine, the non-metallic casing comprising a non-metallic material.
The non-metallic material may have a maximum pressure resistance of 90 MPa.
The invention also provides a coupling for connecting together axially-aligned non-metallic casings in end-to-end relationship.
The invention also provides an assembly of two axially aligned casings connected together in end-to-end relationship via a coupling.
As used herein, the term “maximum pressure resistance” refers to the maximum pressure from a hydraulic fracturing fluid that the non-metallic casing is able to withstand without failure of the casing.
Whilst the use of strong metals such as steel may otherwise satisfy the requirement for high-pressure resistance, the applicant has realised that its use in a block cave would present significant operational complications because of downstream processing issues.
In particular, metallic casings would end up in underground crushers and on conveyor belts, resulting in causing damage to the crushers and conveyors and other equipment and potentially threaten the safety of personnel.
Accordingly, the non-metallic casing is preferably formed to withstand high internal pressures, i.e. has sufficient high-pressure resistance, during injection of hydraulic fracturing fluid and to fracture in a mine crusher without causing significant damage to the crusher.
The non-metallic casing may be made of any suitable non-metallic material that has mechanical properties that allow a plurality of the casings to be coupled together and inserted into a drilled hole and:
The non-metallic casing may be a polymeric material.
The non-metallic casing may be a composite material comprising a polymeric material matrix and a reinforcement dispersed in the matrix.
The reinforcement may be in the form of fibres.
The non-metallic casing may comprise a fibre-reinforced composite material.
In one embodiment, the fibre-reinforced composite material includes glass fibres.
In another embodiment, the fibre-reinforced composite material includes carbon fibres.
In another embodiment, the fibre-reinforced composite material includes a polymeric matrix, such as an epoxy material.
Typically, the casing is elongate with a central bore that extends between open ends and has a uniform circular transverse cross-section along the casing from one open end to the other open end of the casing.
The casing may be any suitable length, any suitable diameter, and any suitable wall thickness.
The casing may be at least 6 m, typically at least 8 m, more typically at least 9 m.
The outer diameter of the casing may be at least 10 cm.
In an embodiment, the non-metallic casing includes a tapered threaded section on at least one end thereof.
The axial length of the threaded section may be any suitable length.
The tapered threaded section may extend over a longitudinal distance of greater than 5 cm, typically greater than 8 cm.
The tapered threaded section may extend over a longitudinal distance of between 5 and 25 cm, typically between 8 and 15 cm.
The tapered threaded section may taper from an outer diameter of less than 15 cm, typically less than 12 cm.
The tapered threaded section may taper at an angle of between 0.5° and 2° to the longitudinal axis of the casing.
By way of example, an outer surface of each end section of each coupling may taper inwardly towards that end of the casing and be formed with an external thread. The threaded ends sections may be coated with a material such as acetal or silicone to facilitate forming a seal with the coupling when two axially aligned casings are located in the coupling.
The coupling may include a cylindrical sleeve with open ends.
An internal surface of the sleeve may taper inwardly from the ends towards the centre, i.e. so that the internal diameter of the sleeve decreases inwardly from the ends of the sleeve towards the centres of the sleeve.
The internal surface of the sleeve may include a flat land in central section of the sleeve mid-way between the open ends of the sleeve. The purpose of the flat land is to prevent insertion of casings too far into the coupling, such that there is a small axial gap between the ends of the casings in the coupling.
In an embodiment, the non-metallic casing includes a thermoplastic liner.
The thermoplastic liner may comprise polyethylene or any other suitable thermoplastic material.
The non-metallic casing may include alternating circumferential ribs and longitudinal ribs.
The circumferential ribs provide resistance to hoop stresses in the casing.
The longitudinal ribs provide resistance to longitudinal stresses in the casing.
The invention also provides a method of manufacturing the non-metallic casing described above, the method including forming a casing from a non-metallic material and forming a threaded coupling on at least one end of the casing.
A benefit of the invention is an opportunity to de-couple pre-conditioning a rock mass for a block cave mine from underground operations that are required to establish a block cave mine or to extend an existing block cave mine. Specifically, with the invention the hydraulic fracturing required to pre-condition a rock mass can be carried out from an above-ground installation ahead of any underground operations. This is a benefit because of the cost and time and logistical complexity associated with working underground on block cave establishment and block cave extension operations.
Another benefit of the invention is an opportunity to carry out the hydraulic fracturing method of the invention with comparatively larger and higher-powered drilling rigs and other equipment than can be used in underground pre-conditioning operations and without the constraints of using equipment underground. Therefore, there is an opportunity to complete pre-conditioning of a given rock mass with the hydraulic fracturing method and equipment installation of the invention more quickly than is possible with underground pre-conditioning operations.
Another related benefit of the invention is an opportunity to drill larger diameter and fewer holes for a given volume of rock mass than is possible with underground pre-conditioning operations arising from the opportunity to use comparatively larger and higher-powered drilling rigs and other equipment than can be used in underground pre-conditioning operations. Drilling fewer holes provides an opportunity for higher pre-conditioning rates compared to those in underground pre-conditioning operations. In addition, drilling larger holes makes it possible to form larger perforations in lined and cased holes and, therefore more extensive hydraulic fracturing of a rock mass.
Other benefits of the invention include opportunities for:
There are similarities and differences between the hydraulic fracturing technology of the invention for use in establishing and extending block cave mines and hydraulic fracturing technology used in the oil/gas industry, including the following similarities and differences:
In order that the inventions are more fully explained, embodiments of (a) a method of hydraulic fracturing a rock mass as part of a method of establishing a block cave mine or extending an existing block cave mine and an hydraulic fracturing equipment installation for carrying out the method in accordance with the invention (b) a non-metallic casing in accordance with the invention, and (c) a block cave mining method and a block cave are described with reference to the accompanying drawings, in which:
In order to carry out the embodiment of the method of hydraulic fracturing a rock mass as part of the embodiment of the method of establishing a block cave mine or extending an existing block cave mine in accordance with the invention, it is necessary to:
In the embodiment described below in relation to
The area may be any suitable sized location depending on a given mine plan. The numbers of holes in each cluster at each location may be any suitable number of holes. In the trial described below, 3 holes were drilled at a location. Typically, the number of holes will be a function of a range of factors, including required hole spacings, and the extent to which equipment for stages 1 and 2 can be positioned to drill multiple holes and to access the holes, respectively.
In the described embodiment, the drill rig equipment required for stage 1 is transported to and operated at one location, i.e. the
The embodiment of the hydraulic fracturing equipment installation layout shown in
Basically, the above-mentioned equipment, including the equipment of the drill rig equipment is standard equipment that is used in the oil/gas industry and that has been adapted, i.e. modified, as required to be suitable for use drilling and lining multiple spaced-apart holes in hard rock geology in typical block cave mine locations. It is noted that the adaption of oil/gas industry equipment required knowledge and understanding of factors relevant to hard rock geology.
It is noted that the invention is not limited to the particular layout of equipment shown in
Stages 1 and 2 of the method are carried out as follows at each location in the described embodiment:
In general terms, the method of hydraulic fracturing the rock mass using the installation shown in
In more particular terms, an embodiment of the method of hydraulic fracturing the rock mass using the installation shown in
Steps (a) to (d) are stage 1 method steps and steps (e) and (f) are stage 2 method steps.
With reference to
With reference to
Typically, the casing 21 is 9 m, but may be any suitable length.
The diameter of the bore 31 and the wall thickness of the casing 21 may be any suitable values depending on the performance requirements for the casing 21.
Typically, the outer diameter of the casing is at least 10 cm, but may be any suitable diameter.
The axial length of the threaded section 25 may be any suitable length.
The tapered threaded sections 25 may extend over a longitudinal distance of greater than 5 cm, typically greater than 8 cm.
The tapered threaded sections 25 may extend over a longitudinal distance of between 5 and 25 cm, typically between 8 and 15 cm.
The tapered threaded sections 25 may taper from an outer diameter of less than 15 cm, typically less than 12 cm.
The tapered threaded sections 25 may taper at an angle of between 0.5° and 2° to the longitudinal axis of the casing 21.
The end sections of each casing 21 and the couplings 23 in
With particular reference to
As can best be seen in
The couplings 23 may be formed from one material.
The couplings 23 may also be formed from different materials to optimise the performance requirements for the couplings 23. This is the case with the embodiments of the couplings 23 shown in the Figures, with the sleeves being formed from one material and the internal threaded sections being formed from other materials.
The threaded ends sections 25 are typically coated with a material such as an acetal or silicon to facilitate forming a seal with the couplings 23 when the casings 21 are located in the couplings 23.
It can readily be appreciated that, in use, a 2nd casing 21 can be connected to a 1st casing 21 in end-to-end relationship by the following steps:
It is noted from
The material selection for the casing 21 and the coupling 23 is an important consideration.
The casing 21 is formed from a non-metallic material having a maximum pressure resistance of 90 MPa.
In the case of the embodiment shown in
The coupling 23 shown in
The applicant, via a consulting engineering company retained by the applicant, has carried out successful test work on prototype casings 21 formed from non-metallic materials mentioned above and the couplings 23 mentioned above.
The test work included pressure testing to assess whether the casings 21 and couplings 23 could survive hydraulic fracturing fluid pressures up to 10,000 psi and crush tests to assess whether the casings 21 and couplings 23 would damage mining equipment such as crushers.
The applicant has determined that non-metallic casings can be formed (a) to withstand high internal pressures, i.e. has sufficient high-pressure resistance, during injection of hydraulic fracturing fluid and (b) to fracture in a mine crusher without causing significant damage to the crusher.
Details of one particular casing 21 formed from a glass reinforced epoxy resin matrix (E-CR glass fibre and aromatic amine-cured epoxy resin) and designed to operate at an internal hydraulic fracturing fluid pressure of 10,000 psi are set out in the following Table 1.
The test work carried out to date has indicated that it is possible to operate successfully with non-metallic casings 21.
The applicant has completed a confidential trial of an embodiment of a method of hydraulic fracturing a rock mass and an embodiment of a hydraulic fracturing equipment installation in accordance with the invention at the Cadia mine of the applicant in New South Wales, Australia.
The trial results greatly exceeded expectations.
Logistically, the trial achieved much faster drilling, more fractures per shift, and much more volume pre-conditioned, i.e. fractured, when compared to the current underground hydraulic fracturing methods.
By way of context, as noted above, the primary purpose of hydraulic fracturing applied at Cadia to date has been to reduce the risk of seismicity by creating more fractures in competent rock. Hydraulic fracturing is seen as one of the most effective techniques to decrease seismic risk during the mine development phase and during cave operations. Current practice at Cadia is to drill and fracture from underground. This is consistent with established underground mining industry practice.
The background lithology at the Cadia mine is volcanoclastic to andesitic volcanics. Three major structure groups occur near to the trial site: Carbonate Fault 5, Sericite-Chlorite-Clay shears and Cadia East Intrusive Dykes. Basically, the lithology is hard and abrasive. Volcaniclastics averaged 133 MPa, with the upper end of the range being 269 MPa. The silica content of 60.7% meant that there was a high abrasivity index. The Cadia conditions were seen as extreme by the drill bit suppliers and the drilling consultant retained by the applicant for the trial.
The hydraulic fracturing equipment installation for the trial was as described above in relation to
The scope of the trial was as follows:
Key parameters of the trial are set out below in Table 2.
The trial completed 3 of the 4 planned holes, with drilled hole details as follows:
The fourth planned hole was not drilled because the results with the preceding three holes were positive and a decision was made by the project team that the fourth hole was not required.
In addition, each of the three drilled holes was drilled using directional drilling technology.
Before the commencement of the trial, the project team identified a list of main project risks and assessed the outcomes versus these risks at the completion of the trial. Table 3 summarises the technical risks and outcomes.
Directional drilling was recognised by the project team as an important drilling option for the trial to ensure accurate drilling in order to steer around existing underground openings and to hit the target hydraulic fracturing zones.
The actual versus drilled paths were an excellent result on all three drill holes and a significant finding for what can be achieved through directional drilling.
The ability to steer around existing or planned underground openings or to avoid unfavorable structures or lithology opens opportunities compared to conventional rotary or diamond drilling.
The first drill hole RE006 was used as an initial trial to determine what drill bits may work across certain rock types. The three main types of drill bit used on RE006 were:
a. PDC: Pol-crystalline diamond composite
b. TCI: Tungsten Carbide Insert bit arranged as a Tri-cone
c. Hybrid: Combination of PDC and TCI
A total of nine bits were used on RE006.
The information gained was invaluable and allowed much better bit selection aligned to hole depth intervals and rock types for the subsequent drill holes.
By the end of the third hole RE007, the project team was confident that it had achieved a drilling “recipe” of key learnings that combined the proven oil/gas industry downhole equipment (drill bits, downhole motor, collars, stabilisers, etc) along with the operating parameters (torque, weight on bit, pumping rate, drilling fluids, etc) that could be applied on future hydraulic fracturing programs. Therefore, as noted above, the project team decided that the fourth planned hole was not required.
After drilling, casing and lining the holes, the next stage in the trial involved hydraulic fracturing each hole.
The hydraulic fracturing steps for each hole comprised forming 5 frac clusters along a section of the hole, with each cluster comprising multiple perforation sets spaced apart by 4 m, with each perforation set comprising multiple perforations around the perimeter of the hole at that height.
It is noted that the invention is not confined to this number of frac clusters and perforation sets and spacings between the sets. For example, there may be more or fewer frac clusters and different numbers of perforation sets per frac cluster and different spacings between perforation sets and different numbers and sizes of perforations in each perforation set. The particular selection made for the trial was based on carrying out sufficient hydraulic fracturing to test the method.
A wireline crew used a truck-mounted winch to lower tools downhole and control these tools via signal cable (the wireline). The tools included perforating guns incorporating explosive charges and bridge plugs to seal off sections of drilled, cased and lined holes.
A fracturing crew was responsible for operating a high-pressure pumping system and associated treating iron and valving in order to provide up to 140 MPa fracturing pressure at flow rates up to 20 barrels per minute (53 litres per sec) into drilled, cased and lined holes.
The “Plug & Perf” procedure was based on oil and gas industry technology. Perforations were created in the drill hole cased and lined walls using shaped explosive charges at 4 m spaced intervals.
The explosive charges were arranged in a perforating gun on the surface, then lowered to specific depths on a wireline system. The gun also included a 10,000 psi-rated plug which was used to seal off the previously-treated section of the hole below. In this way, only a 20 m section of drill hole was preconditioned at a time (One stage=5×4 m spaced fracs).
The “Plug & Perf” procedure is illustrated in
This procedure was repeated to form 5 perforation sets (see
At this point, the perforating gun 43 was removed to surface and the whole casing was pressurised down to the lowest bridge plug using high pressure pumps.
Two, 1,600 kW diesel-powered pumps (not shown) were located at the surface for this purpose. Each pump could deliver 3,000 litres per minute at up to a maximum 100 MPa (15,000 psi) pressure at the surface.
A 100 MPa rated “Frac Head” was then installed on each drilled hole enabling controlled application of flows and pressures within a contained system.
After a calculated duration of flow at a set flowrate, small plastic ‘bio-balls’ 71 (see
A second set of balls 71 was dropped and was drawn into and closed the perforations in the perforation set 61, and the process was repeated until the five×perforation sets 55, 57, 59, 61, 63 in the first frac cluster were fractured across the 20 m high section of the first frac cluster.
The actual downhole pressures achieved during the trial reached around 138 MPa (or 20,000 psi).
When hydraulic fracturing the first frac cluster was completed, the master valve was closed to isolate fracturing iron and wing valves were opened to allow flowback of hydraulic fluid from the hole to commence. Flowback continued until the well head pressure dropped to 700-1000 psi. Once the well head pressure was within this range, the frac tree master valve was opened and a RIH with bridge plug and casing gun assembly was lowered to a desired depth as per approved frac design and the bridge plug was expanded as described above in relation to the first frac cluster.
The procedure described above in relation to perforating and hydraulic fracturing the first frac cluster was repeated for the second frac cluster.
The above-described perforating and hydraulic fracturing the first and second frac clusters was repeated to form each of the five frac clusters.
An external contractor provided a seismic monitoring service at site and processed the results. The main activities of the contractor included:
The process followed by the contractor on each drill hole was as follows:
The contractor generated considerable data in real time and for later processing and evaluation. The data indicated that the trial was a success. There was successful hydraulic fracturing in a controlled pattern, with the results exceeding expectations.
The combined results of seismic processing for one of the drilled holes, namely drill hole RE007, are shown in
The Figure shows the volume of rock stimulated by the hydraulic fracturing at each pumping stage. The different regions 75, 77, 79, 81, 83 in the Figure show the results of fracturing each of the five clusters of five perforation sets.
The Figure shows that the zone pre-conditioned during the trial far exceeded the planned dimensions of a cylinder with radius 100 m. This is a positive result.
The overall volume pre-conditioned is the key parameter, rather than measuring individual fracture radius. The Figure shows that hydraulic fracturing when applied in an underground hard rock environment does not create a singular flat fracture as a disc emanating from a drill hole but rather a cloud of multiple fractures with a vertical extent of between 30-40 m at each frac stage.
When the multiple in-situ structures, joints, infills and other discontinuities that are known to exist in the Cadia orebody are taken into account, this outcome of a wide zone of seismicity with events appearing at different times and not always radiating outwards from the source perforations would follow the anisotropic nature of the rock mass.
Many modifications may be made to the embodiments of the invention described in relation to the Figures without departing from the spirit and scope of the invention.
By way of example, whilst the embodiment of the invention described in relation to the Figures include forming a plurality of holes as a cluster at one location and hydraulic fracturing the holes at that location, the present invention is not limited to this embodiment and extends to embodiments in which a single hole is drilled and hydraulically-fractured at one location and this process is repeated at each successive location.
| Number | Date | Country | Kind |
|---|---|---|---|
| 2020902989 | Aug 2020 | AU | national |
This application is a national-stage application under 35 U.S.C. § 371 of International Application No. PCT/AU2021/050932, filed Aug. 23, 2021, which International Application claims benefit of priority to Australian Patent Application No. 2020902989, filed Aug. 21, 2020.
| Filing Document | Filing Date | Country | Kind |
|---|---|---|---|
| PCT/AU2021/050932 | 8/23/2021 | WO |
