Note: Descriptions are shown in the official language in which they were submitted.
1260~S~;
Background of the Invention
The present invention relates to a method and appa-
ratus for drilling in earthen formations for the produc-
tion of gas, oil, and water. The system is also useful in
mining operations and anywhere it is necessary to drill a
hole of a particular diameter into the earth. In parti-
cular, the present invention relates to a method and
apparatus for fluid jet-assisted mechanical drilling or
mechanically-assisted fluid jet drilling. Although the
invention is described herein in connection with gas and
oil well drilling, the principles and concepts disclosed
apply equally to other forms of drilling.
In oil and gas well drilling, the cost of equipment
and labor is extremely high. In order to minimize the
cost of this phase of oil and gas production, it is desir-
able to drill the holes through earthen formations, as
rapidly as possible commensurate with good drilling prac-
tices. In drilling earthen formation holes, particularly
in harder formations (which are more difficult to drill)
and as the depth of the hole increases, there are a number
of operating problems that tend to make the cost of such
holes more expensive. Also, there are a number of trade-
offs and drilling factors which must be considered in
order to maximize the rate of penetration of the drill bit
and minimize the cost.
The primary sources of drilling forces which affect
the rate of penetration during drilling are: (1) the
torque provided by the rotation of the drill bit as it
bores its way through the earthen formation, (2) the
weight, supplied by that portion of the drill assembly
known as the drill collar, acting on the drill as it
presses against the formation, and (3) the pressure of the
drilling fluid which is delivered to the drill bit through
the drill string.
As the depth of the well increases, the drilling
forces available to the drill bit as a result of the rota-
lZ6~:)455
tion of the drill bit and the pressure of the drilling mud
are reduced because of transmission losses between the
drilling rig and the bit. Furthermore, as the hole gets
deeper, the earthen formations become more di~ficult to
drill. Therefore, the rate of penetration decreases.
To maintain the rate of penetration the weight acting
on the drill bit and its torque can be Lncreased. How-
ever, where the weight on the drill bit i8 increased, the
drill bit wear~ out much faster. It then becomes
necessary to replace the drill bit more frequently. This
is also a very undesirable trade-off since the entire
drill string must be removed from the hole in order to
replace the drill bit. For holes of 10,000 feet or more,
replacing the bit often takes one or more days and is very
costly
Placing additional weight on the drill bit is also an
undesirable trade-off because increased weight causes the
bit to drill in unwanted directions (directional insta-
bility), which may cause expensive operating problems.
High pressure fluid jets provide a means of increasing
the rate of penetration by increasing power levels at the
bit without increasing directional control requirements.
There are methods in current practice that use fluid jets
to increase drilling rates. These methods involve
increasing the fluid presQure of the conventional drilling
mud stream from 2000 pounds per square inch (psi) to
approximately 4000 psi. The added pressure is used to
increase the velocity of the fluid leaving the nozzles.
However, this is done only to assist in the removal of the
cuttings, not to penetrate the rock. This method is
commonly known as jet drilling and generally results in
increased rates of penetration of about 30Z to 50% over
conventional approaches.
Experimental approaches have investigated higher
~i 35 pressure fluid jets as a means to assist the drilling
process by actually cutting the rock with the jet. In one
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program in which target pressures of 15,000 psi were
attempted, the rates of penetration increased by factors
of 2 to 4 but apparently the system held together only for
a short time duration. The system was designed to
increase the entire mud stream pressures from pump through
jet nozzles. This required surface power sources of
around 5000 horsepower (hp) at mud flow rates of about 400
gallons per minute (gpm). Numerous operating problems
ensued because of elevated pressures. Both pump and
transmission systems (drilling assembly) failed in a rela-
tively short time. The approach was proven to be tech-
nically effective, but not practical.
Summary of the Invention
The present invention comprises a drilling method and
apparatus which achieves the advantages of jet drilling
without the attendant disadvantages. This invention com-
prises a hybrid system which couples the advantageous
effects of a fluid jet and a mechanical drill bit in a
dual-fluid system. The resulting combined jet and mechan-
ical drill provides a dramatic increase (up to five times)
in the drilling rates available with conventional
techniques, without increasing the weight acting on the
drill bit or experiencing the related directional control
problems.
The methodology of this invention, to solve the pro-
blems encountered by the earlier experimenters, is to
separate the power stream used for drilling from the end
stream used for removing cuttings from the bore hole. The
process takes a relatively small side stream from the
total mud stream, raises it to much higher pressure, e.g.,
20,000 psi or higher, transmits it via a dual conduit
drilling assembly to a drill bit modified with a series of
small nozzles, and recombine the two fluid streams at the
bottom of the hole to form a conventional drilling fluid
that is circulated back to the surface to repeat the
cycle. As a result, a low horsepower, (for example,
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approximately 600 hp compared to 5000 hp when the entire
mud stream is pressurized) highly effective jet power
stream is provided at the bit that adds drilling capacity
at the bottom of the hole and increases the rates of pene-
tration by a factor of 5 or more over conventionalsystems.
The drilling mud, containing the rock chips and
debris, is filtered at the top of the well in the normal
process. The side stream portion is filtered even further
for use as a high pressure fluid. It may be necessary to
clarify the side stream by decreasing suspended solid~
content and eliminating particle sizes larger than, for
example, 300 microns. As an alternative to filtered or
clarified drilling mud, any fluid that the high pressure
tS pumps can handle without excessive wear and tear, and that
won't plug the nozzle at the drill bit, can be utilized as
the high pressure fluid.
Thus, the present method and system comprises a closed
system in which the drillilng fluid, including mud and high
pressure fluid, continuously circulate, Because these two
fluids mix at the drill bit, the drilling mud may be con-
centrated so that the final solution contains the proper
additives for those particular drilling conditions. This
drilling mud concentration is accomplished at the surface
where the additives are added to the mud before it is
pumped down the drill pipe.
The volume of the high pressure fluid under the system
of the present invention is much less than the total
drilling mud volume as in prior art jet drilling
systems. The volume of the high pressure fluid is on the
order of 25 - 75 gpm as opposed to 300 - 400 gpm for the
total drilling mud stream. In addition, the high pressure
of the jet fluid (for example, on the order of 15,000 -
25,000 psi or even higher) can be achieved at these lower
volumes by means of only 200 - 900 hp. This compares with
3,000 - 6,000 hp under prior systems. Thus, there is a
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significant reduction in the horsepower requirements for
jet cutting by the present drilling system. Because of
this tremendous reduction in horsepower, even higher
pressures, such as 40,000 - 50,000 psi, can be achieved in
the jet fluid without uneconomical horsepower requirement~
when low flow rates are maintained.
There are several other associated advantages of the
present drilling method. Because the high pressure fluid
is filtered or clarified such that the abrasives and mud
additives are reduced, there is minimal abrasion and wear
on the pumping equipment and the drill string conduits.
Furthermore, because of the lower flow rates and the
positioning of the jet nozzles with respect to the
drilling bit, there is no overcut. This aids in main-
taining good hole straightness. Moreover, the concentric
conduit, having the high pressure fluid within the outer,
drilling mud fluid, minimizes any safety hazards
associated with the high plressures of the fluid jet.
Because low volume - high pressure systems are safer
than high volume - high pressure systems, and because the
use of a concentric dual conduit drilling assembly puts
the high pressure - low volume power stream inside of a
conduit which in turn is inside of regular drill pipe,
further increasing safety, the jet drilling system herein
. ~ 25 described i8 able to meet the demand for a safe, econo-
mical method that will increase rates of penetration at
depth and in hard to drill earthen formations.
The present method and apparatus is also highly advan-
tageous because it can be easily integrated into conven-
tional drilling systems. Moreover, conventional drilling
can be continued without bit replacement should softer
~; formations be encountered. Also, because the rate of
al~ penetration for the present method is so high, the delays
and high expense associated with "fishing" may be eli-
; 35 minated. Fishing occurs when an object is lost at the
bottom of the well and must be retrieved before drilling
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can continue. With the higher drilling rates achieved
under the present system, the obstruction potentially can
be drilled around or a new hole drilled with economic
results.
Furthermore, under the present system, controlled
directional drilling is faster. This is because the gra-
vitational force component supplied to the conventional
drill bit by the weight of the drill string decreases
since gravity is no longer acting directly in line with
the direction of the bit. Power levels to the bit are
further reduced by the increased friction of the drill
pipe and drill collar as it lays against the side of the
hole. Because increases in power level are supplied, in
the present invention, by high pressure fluid which is not
affected by the change in hole direction, the present
; invention produces faster directional hole drilling than
conventional approaches.
The present invention also contemplate~ an improved
drill bit system. In prior jet drilling systems, the
fluid jet acted on the rock independent of the mechanical
cutter. In the present invention, however, the fluid jet
acts in concert with the mechanical cutter. Two
mechanisms are proposed.
In the first mechanism, a jet assisted mechanical
system, the fluid jet is configured with respect to each
cutting tooth so that the jet is parallel and close to the
cutti~g plane of the tooth and strikes the earthen forma-
tion at the cutting surface/rock interface. Thus, the
fluid jet serves the important function of cleaning the
surface of the rock so that the cutting tooth can avoid
crushing cut rock and efficiently apply the cutting
force. With conventional drilling methods, more than 75X
~ of the cutting power is used up in crushing chips and
;~ rocks which have already been cut. This expenditure of
power i8 wasteful and reduces the drilling rate. By the
use of a fluid jet aimed at the cutter/rock interface,
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lZ604S5
previously cut rock is cleaned from the cutter, thus pro-
viding direct con~act between the formation and the dril~
bit, thereby vastly increasing the drilling rate.
An important advantage of the present fluid
jet/mechanical drill bit is that the cutter forms cracks
which may be propagated by the water jet. In particular,
the fluid jet improves drilling in ductile failure condi-
tions by encouraging the formations of cracks in the
rock. This reduces pressure and horsepower requirements
and improves bit life at the same time.
In accomplishing these advantages, the distance
between the fluid jet and the substantially parallel
cutting to the plane is approximately 0.5 - 3 millimeters
and is located approximately 5 to 50 millimeters from the
desired target. It should also be noted that a submerged
jet is involved in this invention since the drilling mud
surrounds the cutting environment. It has been found that
any power 1088 in the fluild jet due to its submerged state
is due more to the dispersion of the jet by the drilling
mud than the interference of the mud itself. Thus, in the
present invention, a long chained polymer of approximately
0.1 to 2% solution may be added to the high pressure fluid
in order to maintain the cohesiveness of the fluid jet.
This also reduces the friction and wear on the drill
string conduit, pump valves, etc.
In the second mechanism, a mechanically assisted jet
system, the fluid jets are located between the cutting
teeth and actually form grooves in the rock. This facil-
itates the formation of cracks and chips by the mechanical
cutting teeth, In ~oth systems the jet is 5-50 milli-
meters from the cutting plane, commonly known as the
stand-off distance.
In summary, the drillLng method and apparatus of the
present invention increases the drilling rate of conven-
tional drill rigs by up to five times the usual amount,
while at the same time reducing the horsepower require-
1260455
ments of previous drilling systems by an order of magni-
tude.
Brief Descri tion of the Drawin 8
P R
Figure 1 is a schematic view illustrating the overall
drilling method and apparatus of the present invention
including the components at the well head and the drill
string.
Figure 2 is a sectional view of a portion of the drill
string illustrating the dual conduits thereof with the
high pressure conduit concentrically arranged within the
lower pressure drilling mud conduit, and also illustrating
the mixture of the two fluids rising in the annulus of the
hole.
Figure 3 i8 a perspective view of a conventional drag
bit which has been modified to receive jet nozzles at the
cutting plane of each tooth.
Figure 4 is a close-up, cross-sectional view taken
along line 4-4 of Figure 31illustrating the position of
the fluid ~et with respect to the cutting plane at the
cutter/rock interface.
Flgure 5 is a close-up sectional view illustrating an
alternate positioning of the fluid jet between cutting
teeth.
Detailed Description of the Invention
Referring to Figure 1, there is shown a conventional
drilling rig with the additional components necessitated
by the method and apparatus of the combined jetlmechanical
drill of the present invention. The components of the
conventional drilling system include the drill string 10
(both above ground and below ground portions), the drill
pipe handler 12 for attaching the individual sections of
the drill pipe 14, the mud cleaning system 16 shown in the
lower right hand portion of Figure 1, and the separation
system 20 located at the upper right hand portion of
Figure 1. The mud cleaning system cycles the drilling mud
back into the well through the swivel 18 located at the
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~6045~i
top of the drill string 10. The separation system 20
further filters and clarifies the drilling mud so that it
serves as the high pressure fluid for the jet drill.
The above ground portions of the drill string 10
include the swivel 18, as mentioned above, which permits
the drlll string to rotate while passing drilling fluid
through the conduit of the drill pipe 14. In the present
invention, a conventional swivel has been modified to
include a dual rotary hose system for the injection of
both the lower pressure drilling mud through one hose 22
and the high pressure jet drill fluid through a second
hose 24.
The drlll strlng 10 also includes a normal kelly
sectlon 26 for imparting rotatlon to the drill string 10
;and a serles of lnter-connected drill plpe 14. The drill
plpe of the present lnvention has been modified, as will
be explained ln more detail in connectlon with Figure 2,
to comprise a dual conduit system. Indlvldual sections of
the drill pipe are lnterconnected at tool joints 64, only
one of whlch is illustrated ln Figures 1 and 2. As wlth
conventional drilling rigs, the below ground portlon of
the drlll string 10 includes a welghted drill collar 28
whlch provides gravitatlonal welght actlng on the drill
blt and a MWD (measurement whlle drilling) collar (not
shown) which gathers vital information at the bottom of
the well and transmits it up through the hole to a monitor
30. Finally, at the bottom of the hole, the drill bit 32
-~ is attached to the end of the drill string 10. The drill
bit of the present invention is described in more detail
in connection with Figures 3-5.
: A conventional mud cleaning system 16 as shown in
~; Flgure 1 includes a solids/fluid separator 34 (sometimes
~ referret to as a "shale shaker") located above a tank
36. The drllling mud i8 pumped from the well through a
condult 38 to the shaker 34. The cuttings and other ma;or
solids 40 which are contained in the drilling mud as it
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12604~5
emerges from the hole are dumped into a cutting~ pit 42.
The drilling mud may or may not receive a secondary treat-
ment 44 before being pumped back into the well. The
amount and types of mud treatment depend on the individual
drilling operation, geographic location, type of drilling
mud, and a number of other factor~. Typically, however,
the mud may be passed through mechanical or vacuum de-
gasing equipment and then through a series of hydro-
cyclones which remove successively finer solid components
from the mud stream. Such de-sanding and de-silting
cyclones can remove virtually all material greater than 40
microns and about 50% of the material greater than 15-20
microns. De-silting cyclones frequently remove the barite
~in weighted drilling mud~ and other additives which then
; 15 must be replenished before the mud is ready to be pumped
back into the well. Furthermore, sufficient additives
must be added to the mud so that it is slightly concen-
trated as it goes back down the well.
At this point, the drilling mud is pumped by means of
pumps 46 to the normal pressure of 3,000-5,000 psi through
; a conduit 48 back to the low-pressure rotary hose 22 of
the swivel 18. The drilling mud is slightly concentrated
a8 it re-enters the well so that when it mixes with the
high pressure fluid at the bottom of the well it will have
the proper concentration to perform its usual work of bit
- cooling, cuttings removal, and hole maintenance.
; Still referring to Figure 1, the separation system 20
~ of the present invention provides the high pressure fluid
3.~ for the jet assisted drilling. Unlike drilling mud, the
high pressure fluid may need to be of higher clarity than
the mud since suspended solids could cause serious erosion
and damage to pumps and other exposed equipment. In this
system a portion of the drilling mud stream, about 10-25%,
is drawn through a conduit 50 to a decanting centrifuge 52
which removes fine colloidal material from the drilling
mud. Such centrifuges can remove material in the 3-5
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1260~55
micron range to provide a clarified fluid for pressuri-
zation purposes. Further clarification involves the use
of gravity sedimentation techniques (not shown), including
the use of thickeners, clarifiers and flocculating agents
to neutralize the surface charges on the colloidal par-
ticles. The clarified liquid may be distilled, if
necessary, utilizing waste heat from the drilling rig
power source and then passed through ultra filtration
devices or used directly as the fluid source for the high
pressure pumps. The appropriateness of further treatment
would be considered separately for each type of mud system
and would depend on the adequacy of the solids control
system available in the mud cleaning system.
Preferably, the high pressure liquid would contain
1S particles only .015 inches or less and would be not any
larger than one half the diameter of the jet nozzles
(shown in Figures 4 and 5). The clarified fluid is then
conducted through a conduit 54 to a conventional inten-
sifier 56 which pressurizes the fluid to at least 20,000
psi at a flow rate of 25-75 gallons per minute. At these
levels, only about 200-900 hp is required in the inten-
sifier 56 or the pumping system. The pressurized fluid is
then passed through a high pressure conduit 58 to the high
pressure rotary hose 24 of the swivel 18.
Thus, it can be seen that the method and apparatus of
the present invention contemplates a closed system in
which two fluids are continuously circulated, being sepa-
rated, mixed and separated again.
Referring to Figure 2 there is shown a section of the
drill pipe 14 located within the hole and just below the
surface of the ground. As discussed above, the drill pipe
is concentric, with the high pressure conduit 60 con-
taining the jet drill fluid located within the outer
conduit 62 which conducts the concentrated drilling mud to
the bottom of the hole. This configuration promotes the
safety of the present invention by locating the high pres-
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1260455
sure conduit 60 within the drill pipe 14. Two sections of
the drill pipe 14a and 14b are joined at a tool joint 64
by a threaded connection. At this location, the joined
portions 60a and 60b of the high pressure conduit are
connected by a stab joint 66 connection and high pressure
~eals 68.
The arrows within the drill pipe 14 indicate that the
flow of fluid therein is downward. Also shown in Figure
2, as indicated by the arrows, is the drilling mud of
normal concentration rising in the annulus 70 of the hole
after the concentrated drilling mud in conduit 62 has
mixed with the high pressure fluid in conduit 60 at the
bottom. The mud is pumped to the mud cleaning and separa-
tion systems 16 and 20, respectively, (shown in Figure 1)
1 through a conduit 38 at the surface.
Figure 3 illustrates a conventional drag bit 32 which
has been modified to receive fluid iet nozzles to provide
a jet assisted mechanical drill; although the principles
of the present invention can also be utilized with other
types of drilling bits. The bit 32 is located at the end
of the drill string, as shown in Figure 1. The cutting
surface 76 of the drag bit 32 contains a number of stra-
tegically located cutting teeth 78, each having a coated,
inclined cutting surface 80 manufactured from a very hard
material, such as polycrystalline diamond compact (PDC).
As the bit 32 rotates, these teeth 78 bite and cut into
the formation. The fluid jet nozzles 82 are located
immediately adjacent the cutting plane 80 of the teeth 78,
shown in more detail in Figure 4, to provide a jet
assisted mechanical drill. Also, in the cutting surface
76 of the drag bit 32 is found a number of large holes 90
where the concentrated drilling mud exits. The high
pressure conduit 60 is manifolded at the bit 32 to the
openings 82 which form the fluid jets. Likewise, the low
pressure conduit 62 is manifolded to the holes 90.
Because of the rotary action of the drill bit 32 and the
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respective pressures of the high pressure fluid and the
drilling mud itself, the fluid and the mud mix instan-
taneously at the bottom of the well in order to provide a
drilling mud of normal concentration.
Figure 4 illustrates the interaction of the high
pressure fluid jet stream and a cutting tooth 78 on the
drag bit 32 of the jet assisted mechanical drill. The
tooth 78 is shown having a standard mounting in a recess
of the cutting surface 76 of the drag bit 32 and is pro-
vided with a PDC cutting plane 80. The jet nozzle 82 is
located so that the fluid jet (indicated by arrow 94) is
parallel to the cutting surface 76 and aimed at the
cutter/rock interface 96. In this embodiment, the cutter
78 opens a crack or deformation in the formation which is
then propagated by the fluid jet 94. Cuttings and splash-
back of the jet 94 are away from the cutter surface 76 to
minimize erosion and wear on the cutter surface 80. The
jet 94 may be located anywhere from 0.5-3 millimeters in
front of and parallel withlthe cutting plane 80 and
approximately 5 to 5U millimeters from the target which is
the cutter/rock interface 96. In addition to cleaning the
cuttings and dirt from the interface area, the fluid jet
94 also c0018 the cutting plane 80 and the tooth 78 in
order to vastly increase the drilling rate and life of the
bit 32. Preferably, the fluid contains a long chain
polymer in order to maintain the integrity of the jet 94
in its submerged conditions.
Figure 5 illustrates an alternate arrangement for the
fluid jets 94 which are between a pair of cutting teeth
78. In this configuration, a mechanically assisted jet
drill, the jets 94 actually form grooves 98 in the rock
which facilitate the formation of cracks and chips by the
mechanical cutting teeth 78. In this embodiment, as in
that of Figure 4, the jets preferably are about 5 to 50
millimeters from the target. Although the jet locations
shown in Figures 4 and 5 are preferred, other locations
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12604~;5
can also accomplish the advantages of the present inven-
tion, namely, increased drilling rate and extended bit
life.
In conclusion, it can be seen that the present inven-
tion dramatically improves the typical drilling rates by
providing a high pressure fluid jet stream acting in com-
bination with a conventional mechanical cutter. Further-
more, the fluid jet i8 economically provided by diverting
and clarifying only a small portion of the total drilling
mud stream and then combining the two fluids at the drill
bit.
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