Note: Descriptions are shown in the official language in which they were submitted.
78~
BACKGROUND OF THE PRESENT IN~ENTION
The present invention relates generally to hydraulic
mining tool apparatus and more particularly to an improved
hydraulic mining tool and method of hydraulically mining
unconsolidated mineral formations such as tar sands.
Recent technology has been developed which permits the
recovery of subterranean mineral deposits by use of hydrau-
lic mining techniques. Basically, such hydraulic mining
techniques are characterized by the use of a high velocity
liquid stream which is discharged directly into the sub-
terranean mineral deposit to dislodge minerals from their
surrounding mineral bed. The freed minerals form a resul-
tant slurry with the discharged liquid stream which may be
pumped by various means, upward to ground surface and sub-
sequently processed by surface separation systems. As the
slurry is removed from the formation, a mining cavity or
void is formed in the mineral bed which dependent upon the
size and type of the particular formation, may extend to
100 feet in diameter throughout the height of the mineral
bed. Examples of such hydraulic mining tools are disclosed
in U.S. Patent 3,951,457 issued to Redford, U.S. Patent
No. 3,439,953 issued to Pfefferle, and my
Canadian Patent 1,130,020 entitled Downhole PumP with Bottom
Receptor.
As to date, such hydraulic mining techniques have been
primarily utilized to recover minerals such as uranium,
coal, or potash which typically possess sufficient consoli-
dation in their natural formation state so that as the
mining cavity or void is formed in the subterranean forma-
tion, the surrounding mineral bed remains in its stabilized
consolidated condition, thereby defining a "clean" mining
cavity. Thus, in such consolidated formations, the over-
burden is continuously supported by the consolidated mineral
bed and the hydraulic mining tool may be freely rotated
and vertically reciprocated within the borehole and mining
cavity throughout the mining process. However, in the
hydraulic mining of unconsolidated mineral formations such as
tar sands,unique mining problems exist which to a great
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extent has rendered the existing hydraulic mining tool
technology commercially infeasible.
In contrast to the above mentioned consolidated mineral
formations, unconsolidated formations such as tar sands,
typically are non-uniform in composition and often fail to
possess the necessary degree of stabilization to maintain
a "clean" mining cavity during the hydraulic mining opera-
tion. This failure of the ~mconsolidated formations and
in particular tar sand formations, is due to the individual
sand grains of the formation being stabilized primarily by
the compressive forces generated by the weight of the over-
burden, with the cementation forces existing between
individual sand grains being extremely small in magnitude.
As the subjacent portions of the tar sand mineral bed are
removed during the hydraulic mining process, the overburden
compressive force balance within the mineral formation is
disturbed which, due to only minimal cementation forces
existing between the individual sand grain, often results
in a "cave-in" or "compaction situation" whereby the sur-
rounding mineral bed catastrophically falls in and aroundthe drill string and into the mining cavlty.
When hydraulically mining in relatively shallow
unconsolidated formations, the occurrence of such a com-
paction situation within the mineral bed often permits the
overburden to migrate downward into the borehole and mining
cavity, wherein it mixes with the mined mineral slurry and
is subsequently transported upward to ground surface during
the mining process. As will be recognized, the mining of
the non-mineral bearing overburden reduces the overall
efficiency of the mining process and if substantial, renders
the cost effectiveness of the hydraulic mining process
commercially infeasible. Further, in those instances where
the downward migration of the overburden is acute, a
~eneral subsidance of the overburden may be experienced
whereby the overburden fails to support the necessary
surface mining equipment.
Alternatively when mining in deep unconsolidated mineral
formations (i.e., greater than 500 feet below ground surface),
individual sand grains located proximal the borehole often
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dislodged from the mineral bed by frictional drag forces
exerted by the rotating mining tool and drill string.
Through prolonged duration, these frictional drag forces
often disturb the fragile cementation forces existing
between sand grains and result in the entire surrounding
mineral bed falling in and compacting around the mining
tool. Due to the depth in which the mining operation is
occuring, substantial pressure is applied along the entire
length of the drill string which generates substantial
torque on the mining tool during rotation. Such high
tortional forces have heretofore required the intermittent
shut down of the drilling operation or,in extreme instances,
have caused a complete structural failure or twist off of
the mining tool within the formation. Such intermittent
discontinuance of the mining operation significantly de-
creases overall operating efficiency while a twist-off
condition typically results in the mining tool being
irretrievably lost within the mineral formation.
Thus, there exists a substantial need in the art for
an improved hydraulic mining methodand apparatus specific-
ally adapted for use in unconsolidated mineral formations
which prevents downward migration oE the overburden, reduces
frictional drag forces exerted on the mineral bed, and
prevents extremely high tortional forces being generated
on the mining tool during the hydraulic mining operation.
SUMMARY OF THE PRESENT INVENTION
The present invention comprises an improved apparatus
and method of hydraulically mining which specifically
addresses and alleviates the above referenced deficiencies
associated in the hydraulic mining of unconsolidated
mineral formations. More particularly, the present inven-
tion comprises the formation of a consolidated, stabilized
region or zone adjacent the overburden/mineral bed inter-
face which extends radially outward into the formation in
a generally disc-shaped configuration. In the preEerred
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embodiment, this stabilized zone is formed by injecting a
suitable liquid bonding agent radially outward in the
formation which after a sufficient curing period, bonds
the individual overburden particles together to yield a
consolidated, stabilized region. By such a procedure, the
stabilized region forms in effect a rigid platform which
artificially increases the cementation forces existing
between the individual formation particles thereby increas-
ing the support of the overburden and preventing the down-
ward migration of the same during the mining operation.
In addition, the present invention contemplates theuse of a non-rotating protective sleeve which is telescop-
ingly positioned along the length of the drill-string
extending from ground surface to a location adjacent the
mining tool. By use of the non-rotating protective sleeve,
the mineral bed in the area adjacent the length of the borehole
is substantially isolated from rictional drag forces
caused by the rotation of the drill string and, hence, the
cementitious forces existing between the individual sand
~0 grains o the ~ormations are not disturbed. As such, the
possibility of a "faLl-in" or "cornpaction situation" within
the formation is substantially reduced.
In addition to the reduced drag-force benefits made
possible by its use, the protective sleeve forms a protective
shroud surrounding the length of the drill-string which
upon confronting a fall-in condition, shields the major
length of the drill-string from direct interaction with
the compressive forces exerted by the mineral formation.
Hence, even upon encountering a fall in condition during
the mining of deep mineral formations the tortional forces
exerted upon the mining tool are maintained at a minimum
value. In addition, the protective sleeve permits the
rapid withdrawal of the mining tool from the formation and
if necessary may be sacrificed and left within the formation
while recovering the mining tool and drill-string.
Further, the present invention discloses a novel
method of hydraulically mining an entire mineral bearing
area or oil field wherein multiple boreholes are formed in
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the formation at laterally spaced intervals with the
spent tailings from the currently mined borehole being
returned into the previously mined borehole cavity. As
such, environmental pollution considerations are reduced
and the surface configuration and habitation of the entire
oil field drilling site is maintained substantially in
it's natural state.
DESCRIPTION OF DRAWINGS
These as well as other features of the present inven-
tions will become more apparent upon reference to the
drawings wherein;
~5 Figure 1 is a cross-sectional view taken through a
mineral formation depicting the overburden and mineral bed
and illustrating the initial step of drilling a borehole
from ground surface to a depth adjacent the interface
between the overburden and mineral bed;
Figure 2 is an enlarged cross sectional view taken
about the in~erface between the overburden and mineral bed
oE Figure 1 and depicting the manner in which the stabi-
lized consolidated region is formed in the formation;
Figure 3 is a cross-sectional view of the mineral
formation depicting the subsequent step of extending the
borehole downward into the mineral bed and the insertion
of the protective sleeve within the borehole;
Figure 4 isan enlarged cross-sectional view of the
mineral bed depicting the relative orientation of the
mining tool and drill string with the protective sleeve;
Figure 5A is a schematic representation depicting the
position of the hydraulic mining tool and protective
sleeve at the initiation of the actual hydraulic mining
process;
Figure 5B is a schematic representation of the mineral
bed depicting the initial formation of the mining cavity
cavity within the formation;
Figure 5C is a schematic representation of the mineral
bed depicting the configuration of the mining cavity after
a prolonged mining operation;
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Figure 5D is a schematic representation of the mineral
bed illustrating the manner in which the mining tool and
protective sleeve may be reciprocated vertically upward
within the mineral bed to begin the formation of an addi-
tional mining cavity;
Figure 6 is a cross-sectional view depicting the
method of forming multiple boreholes within the mineral
formation which are laterallly spaced from one another and
illustrating the manner in which the tailings Erom the
currently mined borehole are returned to fill the mining
cavity of a previously mined borehole.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT
_
Referring tc Figure 1, there is shown a mineral for
mation 10 composed generally of an overburden 12 and mineral
bed 14 which by way of example comprises a unconsolidated
tar sand formation. Preparatory to the actual hydraulic
mining operation, the ini~ial step in the method of the
present invention is a formation of a borehole 16 which
initiates ad~acent ground surface 18 and preferably extends
a short distance beyond the interface 20 between the over-
burden 12 and mineral bed 14. The borehole 18 may be
formed by any conventional method but by way of preferred
embodiment is produced by use of an auger sized to yield
an effective borehole diameter of approximately 20 inches.
Subsequent to the formation of the borehole 16, a tubular
drill casing 22 having a maximum outside diameter slightly
less than the diameter of the borehole 18 is inserted
within the borehole 18 extending from ground surface 18 to
a position adjacent the lower end of the borehole 16. The
casing 22 is preferably formed of metal or cement and is
maintained stationary within the formation 10 by conventional
means such as casing shoes (not shown). As will be recog-
nized, due to the casing 22 extending throughout the length
of the overburden 12~once installed, fall-in of the over-
burden 12 into the borehole 16 is substanially eliminated.
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1:1L78~9S
Subsequent to the implacement of the casing 22, the
ne~t manipulate step of the present învention is the for-
mation of an artificially stabilized or consolidated zone
adjacent the interface 20 between the overburden 12 and
mineral bed 14 which serves to provide subjacent support
for the overburden 12 during the mining process. Refer-
ring to Figure 2, the detailed structure and procedure
utilized to produce this stabilized region may be described.
As shown, the casing 22 adjacent its lowermost end is pro-
vided with a plurality of apertures 30 which extendradially outward through the cylindrical wall of the casing
22. The apertures 30 may be formed in the casing 22 either
during manufacture of the casing and, hence, prior to
insertion of the casing 22 within the borehole 18 or subse-
quently after the casing is set in the Eormation 10 by useof conventional gun-perforation or jet-perforation tech-
niques. As best shown in Figure 2, the plural apertures
30 are preferably located at a distance spaced from the
lowermost end of the drill.casing 22 and positioned so as
to be in the general plane of or slightly above the over-
burden/mineral bed interface 20.
A mechanical packer 32 (indicated by the phantomlines
in Figure 2) is inserted downward from ground surface 18
through the length of the casing 22 and rigidly positioned
at the lower~ost end of the casing 32. Such mechanical
packers are well-known in the art, and with reference to
this particular application, is utilized to completely
close off or block the lowermost end of the casing 22 at
~ an area vertically below the plural apertures 30. With
the packer 32 implaced within the casing 22, a suitable
bonding agent may be pumped under pressure, downward from
ground surface 18 through the interior oE the casing 22
wherein it is directed through the apertures 30 and urged
radially outward into the formation 10 (as indicated by the
arrows in Figure 2). By controlling injection pressure as
well as the volume of the bonding agent introduced into the
formation, the bonding agent may be squeezed radially outward
into the formation forming a disc-shaped region 40
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substantially co-axial about the borehole 16. A variety of
bonding agents may be utilized for this purpose, and are
characterized by remaining substantially pliable or fluid
during the initial injection process to sufficiently migrate
radially outward into the formation and subsequently cure
or harden to bond the injected formation into a substantially
regid consolidated region. Examples of such bonding agents
are catalyst activated silica jells such as "SAND FIX", a
registered trademark of the Halliburton Company for a multi-
10 step organic chemical resin process, or "SAND SET", aregistered trademark of the Halliburton Company for a pre-
mixed plastic compound which hardens to form a strong
perMeable consolidation.
In the preferred embodiment, the effective diameter of
15 the artificially consolidated region 40 (and, thus, the
amount of bonding agent injected into the formation 10),
may be predetermined to insure thal: sufficient support will
be yielded for the overburden 12 in an amount proportional
to the amount of mineral bèd 14 desired to be mined in the
20 actual hydraulic mining process. ~owever, for the majority
oE hydraulic mining applica~ions, Lt is anticipated that
the effective diameter of the consolidated zone 40 will
range from approximately 10 to 60 Eeet, thereby preventing
any downward migration or subsidence of the overburden 12
25 into the mineral b2d 14.
Subsequent to the formation of the consolidated region
40, the mechanical packer 32 is removed from the interior
of the drill casing 22 and a conventional drilling apparatus
such as an auger (not shown) is lowered downward within the
30 casing 22 and utilized to extend or drill the borehole 16
deeper into the mineral formation 14. As best shown in
Figure 3, the borehole 16 is preferably extended to the
total depth desired to be mined in the mineral bed 14,
typically ranging from 300 to 5,000 feet below ground surface.
35 Of course, the actual distance of the borehole will be dependent
upon the height of the particular mineral bed 14.
With the borehole 16 extended to total depth within the
mineral bed, a protective sleeve or shroud 42 is inserted
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downward from ground surface 18 into the formation 10. The
sleeve 42 is preferably formed of plural, tubular steel
pipe sections which are connected in an end for end orien-
tation. The ouside diameter of the pipe sleeve is sized
slightly less than the inside diameter of the drill casing
22 while the inside diameter is slightly greater than the
outside diameter of the mining tool 50 (shown in Figure 4).
As shown, the sleeve 42 extends throughout the entire of
length of ~he casing 22 and substantially throughout the
length of the borehole 16, terminating at a vertical distance
spaced from the lower end of the borehole 16. The upper
end of the sleeve 42 is preferably connected to a suitable
lifting and/or lowering mechanism such as a hydraulic jack
(not shown) which prevents the sleeve 42 from rotating in
the ormation and permits the sleeve 42 to be selectively
reciprocated axially throughout thevlength of the borehole 16.
With the consolidated region 42 formed adjacent the
overburden/mineral bed interface 20 and the protective
sleeve 42 positioned within the mi.neral bed 14, the hydraulic
mining tool 50 (shown in Figure 4) may be inserted from
ground surface 18 downward through the protective sleeve
42 to be disposed within the mineral bed 14, at a vertical
elevation below the end of the protective sleeve 42. As is
well knownin theart~e hydraulic mining tool is mounted at
its uppermost end to a drill string 52 which includes
internal conduits and piping (not shown) extending from
ground surface 18 to the mining tool 50. In operation,
the drill-string 52 and mining tool 50 is rotated by con-
ventional means located above ground surface 18 and a high
velocity liquid, such as water, is channeled downward
through the internal conduits of the drill strin~ and dis-
charged radiàlly outward through one or more venturi jets
54 formed on the mining tool 50 to dislodge the sand particles
from the mineral bed 14. The dislodged sand par-icles form
an aqueous slurry with the liquid discharge, which may be
raised upward to ground surface by way of a pump disposed
within the interior of the mining tool 50. A more detailed
description of the operation of such hydraulic mining tools
is disclosed in U.S. Patent No. 3,951,457 issued to Redford
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'I~L7~3~L95
and my Canadian patent application 355,024, now Patent
1,130,200 entitled Downhole Pump with sOttOm Receptor.
In Figures 5A through 5D, the particular mining processes
occuring as well as the benefits made possible by the method
of the present invention may be recognized. As shown in
Figure 5A, the mining tool 50 is initially positioned to
extend to the total depth of the borehole 16 and is disposed
directly within the mineral bed 14. It is an important
10 feature of the present invention that the lower end of the
protective sleeve 42 is maintained at a height vertically
above the venturi cutting jets 54 of the mining tool 50
which height corresponds to the particular height of the
mineral bed 14 desired to be initially mined.
Positioned in such a manner, the hydraulic mining process
is initiated with the mining tool 50 being rotated and the
hydraulic mining fluid being discharged radially through
the venturi jets 54 and into the formation 14 in the manner
previou~ly described. During the initial period of the
20 mining process, the sand particle~; o the mineral bed 16
located in the vicinity of the mining tool 50 are dislodged
and subsequently transported in a slurry mixture upward to
ground surface 18, whereby a substantially conical shaped
void or mining cavity 70 is formed within the mineral bed 14
25 (as illustrated in Fugure 5B). As the mining process continues
the volume of the mining cavity 70 increases with the surrounding
mineral bed 14 falling downward from the side surfaces of
the cavity toward the bottom of the cavity (as depicted by
the phantom lines in Figure 5C). This fall-in condition
30 within the mining cavity 70 is enhanced by the frictional
drag forces exerted on the surrounding mineral bed 14 by the
rotating mining tool 50 which disturb the relatively weak
crementitious forces of the mineral bed 14. However, due to
the non-rotating protective sleeve 42 forming a shroud over
35 the major portion of the drill string 52 of the mining tool
50, these frictional drag forces are exerted only in the
particular area of the mineral bed in which the mining tool
50 extends beyond the sleeve 42 (i.e. the area desired to
be mined within the mineral bed) and not through the entire
40 formation. As s~ch~ by axially positioning the protective
11~71~ 5
shroud 42 at a height above the mining tool 50, a controlled
fall-in or compaction situation can be provided during the
mining process. This controlled fall-in situation signifi-
cantly prevents the catastrophic compaction heretofore
experienced in the hydraulic mining of unconsolidated
mineral formations.
Further, due to the protecti~e sleeve 42 extending
along the major length of the drill string 52, in those
instances when a complete compaction or fall-in situation
10 occurs, the pressure and, hence, the torque exerted on the
mining tool apparatus is only exerted on the portion of the
mining tool 50 and drill-string 52 extending beyond the end
of the protective sleeve 42 and not along the entire length
of the drill-string 52 as heretofore associated in the art.
15 Thus, even upon con~ronting a complete fall-in situation
during the rnining operation, the maximum torque exerted on
the mining tool 50 is maintained at a minimum which reduces,
if not completely eliminates, the possibility of twist-off
of the mining tool 50 during the minin~ operation.
Once the initial conical shaped mining cavity 70 is
mined to a maximum volume, the mining t? 50 is raised
vertically upward to an elevation above the initial cavity
70 as depicted in Figure 5D. As the mining ~ool 50 is raised
vertically upward, the protective sleeve 42 is similarly
25 raised to a position above the mining tool 50 to define a
second area within the mineral bed 14 which is desired to
be mined. The hydraulic mining process may then again be
initiated causing the formation of a second conical shaped
mining cavity 70A in the mineral bed 14 which, as depicted
30 in Figure 5D, is spaced vertically above the initial cavity
70. As will be recognized, this process may be continued
throughout the elevation of the mineral bed 14 thereby
forming consecutive mining cavities 70, 70A, 70B, etc.,
within the mineral bed which are generally co-axial with
35 the borehole 16.
As the consecutive mining cavities 70, 70A, etc., are
formed in the mineral bed 14 and progress upward toward the
interface 20 between the overhurden 12 and mineral bed 14 !
the artificially consolidated region 40 (shown in Figure 6),
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serves to provide a platform-like structure which supports
the overburden 12 and prevents any downward sifting of the
overburden 12 into the borehole and mining cavity 70. As
such, the overburden is maintained in its initial state or
condition with only the mineral bed 14 being mined during
the hydraulic mining process which further prevents any
downward subsidance of the overburden 12. Once the entire
depth of the mineral bed 14 is mined in such a manner, the
minlng tool 50 and drill-string 52 may be removed from the
borehole 16 in a relatively simple procedure with the
protective shroud 42 bearing the major compressive forces
of the overburden 12. Subsequently, the protective sleeve
42 may be additionally removed from the formation or alter-
natively left therein and sacrificed within the formation.
By use of the process of the present invention, it will
be recognized that the entire mineral formation 10 may be
initially provided witha plurality of boreholes 16A, 16B,
and 16C as shown in Figure 6. As a hydraulic mining process
is conducted in one of plural boreholes 16C, the mined
material transported upward to ground surface may be separated
by conventional means and the non-~mineral bearing drill
tailings i.e. (sand particles) may be returned directly
into a previously mined borehole 16B. This process may be
continued for each of the previously mined boreholes 16A
such that the tailings removed from the mineral bcd 16 are
continously returned back to the subterranean formation.
As such, the minority of any adverse environmental considera-
tion caused by the dril tailing are eliminated by use of the
-present invention.
In summary, the present invention comprises a substan-
tial improvement in the art of hydraulic mining which is
specifically adpated for economical recovery of unconsolidated
mineral formations which eliminates the downward sifting of
overburden into the mining cavity, prevents substantial
torque being exerted on the tool, and provides a controlled
rate of recovery of the mineral formation.
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