Bore hole mining

Minerals, in particular coal, that have been deposited in layers or along seams in the earth can be mined utilizing a large diameter bore hole drilling equipment. With the drilling equipment stationed on the surface of the earth, a drilling member is drilled down into the earth along the seam of the mineral deposit. If the mineral deposit extends at an angle to the earth, i.e. less than 90.degree., the drilling operation is conducted so as to drill at a similar angle to the earth. As the mineral deposits are broken up during the drilling operation, the broken fragments are removed from the drilled hole. After drilling has occurred for a certain distance in a forward direction, a creeping effect is induced in portions of the side walls of the drilled hole. The drilling member is then retracted from the drilled hole in such a manner so as to drill out any mineral fragments in the hole of the drilling member. These mineral fragments are then removed from the hole as the drilling member is retracted. The removal of the mineral fragments can best be accomplished utilizing an hydraulic flow mechanism for circulating fluid through the drilling member and removing the mineral fragments as they are drilled.

BACKGROUND OF THE INVENTION 
The present invention relates to the mining of mineral deposits, in 
particular coal mining. 
While various different types of mining procedures have been used over the 
years for the mining of coal, these procedures basically fall into two 
categories, underground mining and strip mining. In underground mining, 
there are several different types of procedures including room and pillar 
mining, long wall mining and hydraulic mining. In all of these procedures, 
however, tunnels in the earth are made through which the miners enter the 
earth to the location of the coal for carrying out the mining operation. 
In long wall and hydraulic mining operations the roof of the tunnel must 
be supported by leaving pillars in the seams. The pillars can reduce 
recovery by as much as 50%. 
In strip mining, huge areas of the earth must be removed in order to 
extract coal from along the coal seam. The area of the earth over which 
the strip mine extends depends upon the depth to which the coal seam is to 
be mined. The deeper the mining of the seam the wider the area of the 
earth that must be disturbed. 
Various attempts have also been made at conducting drilling operations 
between various tunnels underground; exemplary of such attempts are the 
embodiments illustrated in U.S. Pat. Nos. 3,167,354 and 4,123,109. In 
addition, some attempts have been made at subterranean hydraulic mining of 
mineral deposits such as shown in U.S. Pat. Nos. 3,874,733 and 4,092,045. 
Furthermore, with respect to the process of mixing the mineral deposits, 
such as coal, in a slurry for the purposes of transportation along a 
pipeline, such techniques are shown in U.S. Pat. Nos. 3,041,053 and 
3,924,895. 
With the increasing necessity for economically and efficiently obtaining 
sources of energy, it has become even more critical for finding new 
techniques for the mining of coal. Such problems are especially enhanced 
in light of the safety considerations in tunnel mining and the 
environmental concerns with strip mining. 
SUMMARY OF THE INVENTION 
An object of the present invention is to provide an improved procedure and 
associated equipment for the mining of coal in a more economic and 
efficient manner. 
Another object of the present invention is to provide an improved procedure 
for the mining of coal that avoids the dangers involved with tunnel mining 
and the environmental problems of strip mining. 
A further object of the present invention is to provide a procedure for the 
mining of minerals utilizing large shaft diameter drilling equipment 
arranged on the surface of the earth. 
Still another object of the present invention is to provide drilling 
equipment for drilling along a coal seam from the surface of the earth for 
the mining of such coal. 
Still a further object of the present invention is to provide a technique 
for mining coal utilizing reverse direction drilling equipment with a high 
torque drill bit attached at the end of a drill string. 
A still further object of the present invention is to provide a drilling 
system capable of mining coal by a drilling operation from the surface of 
the earth by breaking up the coal and extracting the broken coal from the 
drilled hole by circulating fluid through portions of the drilling system 
in the drilled hole. 
Minerals, in particular coal, that have been deposited in layers or along 
seams can be mined utilizing drilling procedures with the drilling rigs 
being located on the surface of the earth. The drilling system for such a 
mining operation in accordance with the present invention is composed of a 
large diameter drill rig capable of drilling at an angular orientation 
with respect to the vertical. As the drilling operation proceeds, the 
coal, or minerals, are broken into fragments. The broken coal fragments 
are removed from the drilled hole by a reverse dual string hydraulic 
method. The coal is then cleaned and the slurry concentration reduced for 
transportation in a slurry pipeline. Depending upon the terrain and the 
desired delivery point, the coal can be pumped or gravity fed to a loading 
terminal or user location. Once reaching such destination, the coal is 
then dried. 
Several factors will determine the economic advantages of utilizing such a 
drilling operation. Such factors include the total recoverable reserves, 
the angle and depth of the coal seam, the continuity of the coal seam, the 
thickness of the seam, surrounding formations, terrain, climate, 
availability of water supplies and the penetration rate for the drilling. 
Minerals deposited in thick seams which are vertical or near vertical are 
primary candidates for mining by drilling operations. In particular, 
bituminous coal deposits that are presently mined by long wall, hydraulic 
or strip mining methods can be mined utilizing the drilling operations and 
equipment of the present invention. 
After each hole is drilled, the hole can be refilled with proper roof 
supports. The roof supports are provided by placing cement plugs at 
regular intervals in the drilled holes and filling the space between the 
cement plugs with waste material from the mining excavation operations. By 
providing roof supports in this manner, adjacent drilled holes can be 
drilled closer together with additional reserves being produced. 
The drilling operation in the present invention is a safer operation than 
tunnel mining inasmuch as no underground personnel are utilized. 
Furthermore, the drilling operation of the present invention does not 
create the environmental problems of strip mining. In utilizing the 
drilling operation for the mining of coal, large areas of the earth need 
not be excavated in order to remove the coal. Furthermore, the drilling 
operation can be utilized for extracting coal from a deeper depth in the 
earth than possible with a strip mining operation. 
The method of the present invention utilizes drilling equipment that is 
arranged on the surface of the earth. In accordance with this operation, 
the drilling member is first drilled down into the earth for forming a 
large diameter hole and breaking up the mineral deposits as the drilling 
occurs. These broken mineral fragments are removed from the drilled hole 
as the drilling operation proceeds. During portions of the drilling 
operation, creep is induced in portions of the side walls of the drilled 
hole. After the drilling has continued for a certain distance into the 
hole, the drilling member is then retracted from the hole. As the drilling 
member is retracted, the mineral fragments which have fallen back into the 
hole above the drilling member due to the inducement of the creep effect 
in the side walls of the hole is drilled. These mineral fragments that are 
drilled as the drilling member is retracted are then removed from the 
hole. 
The creep effect to which reference is made in this application is an 
effect that occurs when the pressure from the earth surrounding the hole 
provides a sufficient force for causing portions of the side walls of the 
hole to partially cave-in. Such a cave-in of the side walls places 
additional mineral deposits into the hole which can then be extracted by 
the drilling operation. As further explained below, such a creep effect 
can be induced by decreasing the fluid level in the hole so that the 
pressure of the earth surrounding the hole on the walls is greater than 
the static fluid pressure in the hole thereby causing the cave-in. 
The removal of the mineral fragments from the hole is best accomplished by 
creating a fluid flow through the drilling member in the drilled hole. The 
flow of fluid carries the mineral fragments out of the hole. This fluid 
flow can be accomplished by utilizing dual wall string drilling equipment 
where water is fed into the hole through one chamber of the drill string 
and the water with the broken mineral fragments is then extracted from the 
hole through the other chamber of the drill string. The flow of fluid also 
travels across the cutting surface of the drilling bits so as to 
constantly wash away the broken mineral fragments so that such fragments 
are extracted from the hole. In addition, the washing of the cutting 
surface of the drilling member prevents the drilling member from becoming 
blocked or clogged by such mineral fragments. 
Utilizing the drilling equipment of the present invention, it is possible 
to drill at an angular orientation with respect to the surface of the 
earth, with such angle being less than a right angle. By utilizing various 
stabilizers for stabilizing the drilling bit in order to prevent any 
substantial lateral movement, it is possible to conduct such drilling 
operation anywhere between 60.degree. up to 90.degree. with respect to the 
horizontal plane of the surface of the earth. Such stabilizing equipment 
includes a plurality of rollers and cylindrical members that are 
substantially the same size as the diameter of the hole being drilled. In 
order to allow the drilling bit to move into the earth, however, the 
stabilizer will be just slightly smaller, perhaps a few inches for a 
twenty foot diameter drill, than the diameter of the hole. For example, if 
the hole being drilled has a diameter of twenty feed then the stabilizer 
will be approximately 19 feet and 8 inches in diameter. 
The present limits for angular drilling with the various embodiments 
disclosed herein are 30.degree. from the vertical. Once the drilling 
assembly and drill string are more than 30.degree. from the vertical, the 
wall drag becomes in excess of 30% of the drilling assembly weight. The 
problems encountered when the wall drag becomes excessive are hole 
deviation (failure to follow the seam of the mineral deposit) and reduced 
penetration rates. If improved drilling assembly can be fabricated, it may 
become possible to drill at an angle of 45.degree. with respect to the 
vertical. 
In addition to the hydraulic equipment providing a fluid flow for removing 
the drilled mineral fragments, the fluid provided by the mechanism also 
fills the drilled hole. The provision of such fluids serves as a static 
balancing force against the pressures on the side walls from the 
surrounding earth during the normal drilling operation except when a creep 
effect is to be induced. In addition, with the drilling of coal, the 
provision of fluid in the hole acts as a safety device during the drilling 
operation. 
The drilling system of the present invention includes a primary drilling 
bit mechanism that is arranged at the forward end of the drilling string 
members that extend into the hole. A plurality of drilling bits, such as 
those of a gang drill, are arranged at the forward end of the drilling bit 
mechanism. In order to obtain a high torque device it is desirable if only 
the drilling bits themselves are rotated and not the entire drilling 
mechanism and drilling string members. For this purpose, an arrangement is 
provided for rotating the drilling bits down at the bottom of the hole 
being drilled instead of rotating such bits by rotating the entire 
drilling string from the surface of the earth. During the drilling 
operation, the drilling mechanism should be secured against lateral 
movement in order to enable the drilling to occur along a coal seam in the 
earth that extends at an angular orientation with respect to the surface 
of the earth. 
For the purpose of rotating the drilling bits, several different types of 
well known down-hole driving arrangements can be utilized. Such 
arrangements include drilling fluid drive bits and down-hole electric 
drilling motors. In accordance with the embodiments illustrated in this 
application, the drilling bits are fluid driven by the hydraulic fluid 
circulated through the drilling equipment which is utilized for removing 
the broken mineral fragments. 
In addition to the primary drilling bit mechanism, a secondary drilling bit 
mechanism can be arranged along the drilling string at a location above 
the primary drilling bit mechanism. This secondary drilling bit mechanism 
is arranged for enabling the mineral deposits to be drilled when 
retracting the drilling string from the drilled hole. For this purpose, 
raised bore drill bits facing in an upward direction can be utilized. 
These raised bore bits will drill out those mineral deposits that have 
fallen into the drilled hole due to the inducement of the creep effect in 
the walls of the drilled hole. 
In order to enable fluid to be circulated through the drilling equipment, 
dual wall drilling string members are utilized. The dual wall drilling 
string members have an inner chamber and an outer chamber. The fluid is 
circulated through one of these chambers, generally the outer chamber, 
across the surface of the drilling bits and back through the other 
chamber. Since the inner chamber is generally larger, the fluid with the 
broken mineral fragments are generally extracted through the inner chamber 
of the dual wall drilling string members. To assist in the circulation of 
the fluid, air also can be pumped into the chambers. Such air can create 
either the necessary pressure for maintaining the fluid flow across the 
drilled bit surfaces or can be used for so as to supply air into the inner 
chamber for helping to extract the fluid with the mineral fragments from 
such chamber. 
In utilizing the drilling mining operation of the present invention, the 
number of tons of coal per hour depends upon the diameter of the drill bit 
mechanism and the rate of drilling. Ideally, the diameter and drilling 
rate should be selected so as to produce at least 25 tons of coal per 
hour. In accordance with the preferred embodiment, the diameter of the 
drill should be selected in excess of 10 feet since such a drill can be 
operated at an extremely efficient and economical rate for producing coal 
well in excess of 25 tons per hour. For such purposes the typical rate of 
penetration would be at least 8 feet per hour. 
To optimise the recovery of mineral deposits, adjacent bore holes should be 
drilled on a relatively close pattern. To accomplish this, bore holes are 
drilled in an alternating arrangement with the center line spacing of such 
holes on a 250% of hole diameter arrangement for the first set of holes. 
Once the first set of holes are drilled and subsequently plugged with 
cement plugs separated by waste material, the second set of holes are 
drilled on a center line spacing of 125% of hole diameter from the center 
of the holes of the first set of holes. By utilizing this method of hole 
spacing, a substantial percentage of in place reserves, e.g. 65%, can be 
recovered.

DESCRIPTION OF THE PREFERRED EMBODIMENTS 
A schematic illustration of a coal mining operation in accordance with the 
present invention as illustrated in FIG. 1. As shown in that figure, a 
drilling system 2 is used for drilling into a coal seam in the earth. 
Inasmuch as most coal seams extend at an angle, the drilling assembly is 
shown drilling at an angle into the earth. 
Drilling system 2 includes a drilling rig assembly 12 mounted on a platform 
14. As the system is utilized, drilling bit assembly 16 drills into the 
earth for breaking up the coal formation into fragments that can be 
removed from the hole. The drilling bit assembly is mounted on the end of 
a drill string 18, which can be made up of a plurality of string members 
with additional members being added as the drilling bit assembly proceeds 
into the earth. 
In accordance with the operation of the present invention, it is preferable 
for the drill string 18 not to rotate and for the rotational drive forces 
to be applied directly at the bit assembly 16. For this purpose any one of 
several different types of downhole drilling drivers can be utilized. 
During normal operation of the drilling procedure, the drilled hole is 
filled with fluid up to level 19; the purpose of such fluid will be 
explained further below. 
After the coal is drilled out of the hole, it is cleaned, i.e. separated 
from the various rocks and earth that were removed with the coal at a 
cleaning station 4. The coal is then prepared in a slurry form at station 
6 for transmission through a slurry pipeline 8. The coal slurry passing 
through pipeline 8 can either be forced through the pipeline due to 
gravity if the loading station is downhill or can be pumped by a pump 10. 
The coal eventually travels to a station where it is either loaded for 
further transportation or actually utilized. Various techniques for 
transporting coal in a slurry form are known in the art, such as shown for 
example, in U.S. Pat. No. 3,924,895. 
As will be explained in greater detail below, during the drilling 
operation, the drill bit assembly 16 first drills into the hole in a 
forward direction. After the bit assembly has advanced by a predetermined 
distance, a creep effect is induced in a portion of the side walls of the 
drilled hole. The creep effect to which reference is made herein is a 
partial cave-in effect that occurs when the pressure on the walls of the 
drilled hole exceeds the static pressure within the hole. 
As previously indicated, the hole is filled with fluid to a level 19 during 
normal drilling operation. The fluid within the hole provides a static 
balancing pressure that prevents any caving-in of the side walls of the 
hole. The pressure for such cave-in effect is created by that portion of 
the earth above the drilled hole that applies a force due to the weight of 
the earth such as represented by arrow A in FIG. 1. If the fluid level in 
the drilled hole is allowed to drop to a sufficiently low level then the 
force of the earth above a portion of the wall of the drilled hole will 
cause such wall portion to partially cave-in. This expands the hole and 
places additional coal into the hole which then can be drilled out. 
After such a partial cave-in, or creep, has been accomplished, a reversed 
drilling operation can be carried out. For this purpose, drill bit 
assembly 16 can be provided with drill bits facing in an upwards direction 
along the drilling path. Exemplary of the type of drill bits that can be 
utilized for this purpose are raised bore bits. The drill string with the 
drilling bit assembly is then retracted from the drilled hole with the 
upwardly facing drilling bits drilling out the coal that has caved into 
the hole. Thus, coal can be mined from the hole both when advancing the 
drilling bit assembly in a forward direction and when retracting such 
assembly from the hole. During both operations, the drilled coal fragments 
are hydraulically removed from the drilled hole. 
In FIG. 2, one embodiment of a portion of the drilling system of the 
present invention is illustrated. As shown, a drilling mechanism 20 is 
mounted on drill string member 18 which extends below the ground level. 
Drilling mechanism 20 includes on its lower end a drilling bit mechanism 
22 which has a plurality of individual drilling bits. In order to secure 
the drilling mechanism against lateral movement during the drilling 
operation, a plurality of stabilizer members can be arranged around the 
drill string. Such stabilizing members can include a plurality of rollers 
24 and stabilizer rings 26. While only one set of stabilizer members have 
been illustrated, a plurality of such members can be provided. 
A plurality of circular weights 28 and 30 also are arranged along the drill 
string in the area adjacent to the drilling bit mechanism. Such weights 
help to press the drilling bit mechanism with the drilling bits against 
the bottom of the hole being drilled. Here again a plurality of such 
weights can be provided depending upon the hardness of the particular coal 
seam being drilled. Mounted above the weights can be additional rollers 
and circular stabilizing members. At the top of drilling mechanism 20 is a 
cap 29. In the space between cap 29 and weight 28 surrounding drilling 
string 18 can either be additional weights and/or additional stabilizer 
members. 
The particular type of drill bit arrangement utilized on drill bit 
mechanism 22 is a set of gang drill bits 32. The gang drill bit assembly 
has a plurality of assemblies 34, 36, 38 and 40. Each of these 
subassemblies of bits is individually rotated by a fluid flow across each 
assembly. In addition each of the subassemblies has a plurality of 
rotating individual drill bits such as bits 42 and 44. 
In order to drive the drill bits, fluid is fed along the drill string 
members to the area of the subassemblies. This fluid also serves to remove 
the drilled coal fragments during the drilling operation. Furthermore, the 
fluid also fills the drilled hole for providing the static balancing force 
for preventing the walls of the hole from caving in except when it is 
desired to induce a creep effect. 
For the purpose of enabling fluid to be fed into the drilled hole and then 
extracted therefrom, dual wall string members are utilized. The string 
members that form drill string 18 have an outer chamber 46 and an inner 
chamber 48. Fluid is fed into outer chamber 46 through fluid inlet 50 
which is arranged above the ground. The fluid then travels down along the 
outer chamber of the dual wall string members until it reaches fluid 
chamber 55, as shown in FIG. 2. Fluid from chamber 55 then travels under 
weir 53 into a fluid drive line 56. The fluid flows along drive line 56 
and is diverted into two separate lines 58 and 60. The flow of fluid is 
maintained in only one direction by a ball check valve 61 in order that 
the fluid along with any coal fragments cannot flow back into chamber 55 
from the area of the drilling operation. The flow of fluid through the 
line then travels down to the area of the subassemblies. By creating a 
propelling force along guide impeller 63 and rotating bracket 62, the 
subassembly is rotated. The fluid also flows over the individual drill 
bits, such as bits 42 and 44, for rotating these bits. In addition, as the 
whole subassembly is rotated, the drill bits rotate as they roll along the 
coal being drilled. 
As the drilling operation proceeds, the fluid with the coal fragments are 
drawn back into the drill string members through a return line 64. Return 
line 64 leads back into inner chamber 48 of drill string 18. To assist in 
the withdrawl of the fluid with the coal fragments from chamber 48, an air 
pressure force is created by air emitted through outlet 66 of an air line 
52. The slurry with the coal fragments is then emitted from the drilling 
system through an outlet 54. 
A modified embodiment of the drilling mechanism is illustrated in FIG. 3. 
In this figure those elements that are the same as those in FIG. 2 are 
identified by the same reference numerals the primary distinctions between 
the drilling mechanism 68 illustrated in FIG. 3 and the drilling mechanism 
20 illustrated in FIG. 2 reside in the air flow system that is employed. 
In drilling mechanism 68, air is fed in through inlet 52 directly into 
outer chamber 46 of the drill string member. The air then travels along 
with the fluid down into chamber 74. Chamber 74 is thus pressurized for 
helping to force the fluid through drive line 56 for rotating the drilling 
bit subassemblies. Air along with the coal slurry can be sucked back into 
line 64 for extracting the coal fragments. For enabling the air to be 
drawn into the extraction line and inner chamber 48 of the drill string 
member, air inlet ducts 70 and 72 are provided at the top of chamber 74. 
The operation of this modified embodiment of the drilling mechanism is 
similar to drilling mechanism 20 as previously described above. 
Another modified embodiment of a drilling mechanism is shown in FIG. 4. 
Drilling mechanism 76 has a drilling bit mechanism 22 similar to the gang 
drill mechanism previously described above. Arranged above the drilling 
bit mechanism are weights 78 and 80 and stabilizing members 82, 84 and 86. 
While only one rotating stabilizer mechanism 86 is illustrated, a 
plurality of such members could be utilized. At the top of the drilling 
mechanism 76 are raised bore bits 88. Such raised bore bits are used for 
drilling the coal that falls back into the hole due to the inducement of 
creep during the drilling operation. Thus, as drilling mechanism 76 is 
retracted from the hole, raised bore bit 88 drill out the coal in the 
hole. Raised bore bits 88 also can be utilized on those drilling 
mechanisms illustrated in FIGS. 2 and 3. Thus, with the inclusion of such 
raised bore bits, the drilling of coal can be accomplished in both 
directions, i.e. as the drilling bit mechanism 22 advances into the earth 
and as it is retracted from the earth. During both operations, the broken 
coal fragments can be removed from the hole by circulating fluid through 
the hole and through the drill string members such as previously described 
above. 
During the drilling operation, it is desirable to drill a plurality of 
holes as close together as possible. On the other hand, sufficient solid 
ground must be provided for enabling the drilling rig to be mounted on the 
earth above the hole. In order to satisfy both requirements, a drilling 
pattern such as illustrated in FIG. 5 can be utilized. As shown, the holes 
are drilled along a coal seam 90. First, a first set of holes, 92, 94 and 
96 are drilled. The first set of holes are then plugged by cement plugs 
separated by waste material that has been excavated from the hole and 
separated out from the coal. After the first holes have been replugged, a 
second set of holes, 98 and 100 are drilled. After drilling the second set 
of holes, these holes also can be plugged in the same manner as the holes 
of the first set. The spacing between the holes of the first set is 250% 
of the diameter D of the hole. The second set of holes are then spaced so 
that their center point is separated from the center point of the adjacent 
first holes by a distance L that is equal to 125% of the diameter D of the 
holes. In this manner, approximately 65% of the coal can be recovered from 
the coal seam. 
Accordingly, in utilizing the drilling equipment described above, the 
drilling bit is first drilled into the earth in a direction extending 
along a coal seam with the drilling bit breaking up the coal. The broken 
coal fragments are then extracted from the hole utilizing the flow of 
fluid through the drill string members and across the face of the bits of 
the drilling bit mechanism. After the drilling bit mechanism has advanced 
a certain distance into the earth, the fluid level in the hole is dropped 
and creep is induced in portions of the walls of the drilled hole. Such 
wall portions then partially cave in thereby filling part of the hole with 
additional coal which can be drilled out. Care must be taken not to cause 
too much coal to cave into the hole thereby making it impossible to drill 
in an outward direction. The drilling bit is then retracted from the hole 
at which time further drilling in the hole is carried out. The coal broken 
during the reverse drilling operation is removed from the hole with the 
flow of fluid through the hole. The holes are plugged after being drilled 
with spaced concrete plugs and waste material from the drilling operation 
after the drilling bit has been retracted. A new hole is then drilled in a 
direction extending along the coal seam. 
The present invention may be embodied in other specific forms without 
departing from the spirit or essential characteristics thereof. The 
present embodiments are presented merely as illustrative and not 
restrictive, with the scope of the invention being indicated by the 
attached claims rather than the foregoing description. All changes which 
come within the meaning and range of equivalency of the claims are 
therefore intended to be embraced therein.