Note: Descriptions are shown in the official language in which they were submitted.
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APPARATUS AND PROCESS FOR DRILLING A BOREHOLE IN
A SUBTERRANEAN FORMATION
CROSS REFERENCE TO RELATED APPLICATIONS
[001] This application claims priority to and relates to an earlier filed
United States
provisional application S.N. 61/556,986 which was filed in the United States
Patent and
Trademark Office on November 8,2011.
FIELD OF THE INVENTION
[002] The field of the invention is directed to apparatus and processes for
drilling a well by
employing reverse circulation of drilling fluid.
BACKGROUND OF THE INVENTION
[003] When conducting drilling to construct deep wells, the pressure of
drilling fluid or
drilling mud that is pumped down from the surface and into the open hole of
the formation
may be quite high. It is usually advisable to maintain a fluid/mud weight
above the
formation pressure to prevent gas "kicks" or influxes from the wellbore.
Furthermore, the
friction pressure of pumping into a drill string may be quite substantial.
Thus, pressure is
required to be applied to cause the drilling fluid and cuttings to flow
through the drill string,
out into the open hole, and up the annulus at an adequate rate.
[004] Too much pressure applied in this process can cause other problems. That
is, such
fluid pressure applied at the surface also is applied to the open hole of the
subterranean
formation. High pressures applied to an open hole of a formation may cause the
formation to
fracture, with a subsequent sudden loss of drilling fluid into the formation.
Such a sudden
loss of drilling fluid into the formation may have severe consequences. In
some instances,
there is a very narrow "window" of pressure that may properly be applied in
the drilling of a
well without exerting too much or too little pressure. That is, excess applied
pressure can
fracture the formation. On the other hand, inadequate pressure may not
properly carry the
drilled cuttings up the annulus to the surface. Thus, a pressure "window"
exists that
engineers must observe in planning the pressure to exert while drilling a
well.
[005] Sometimes, lost circulation materials or pills are applied into drilling
fluid, and such
materials travel out of the bit and adhere to the formation to prevent such
fluid loss into the
formation. But, such materials may damage the formation and reduce the ability
of the
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formation subsequently to produce oil and gas into the wellbore during
production
operations. Such damage to the formation is undesirable, and therefore the use
of such
materials is not always advisable.
[006] Operating within the mud weight "window" allows engineers to improve
drilling
efficiency and set casing at the best possible depth. If casing is set too
shallow, well
construction cost increases and well depth is limited. Sometimes, this may
cause the
production rate to be compromised. In other instances, the target formation
may not be
accessible. Techniques that widen or open the window to be employed are
desirable.
[007] Conventional drilling employs rotary rock bits to compress the rock,
causing the rock
to fracture into cuttings. Pulsed power drilling, however, is a method of
constructing a
wellbore by applying voltage into the rock of a formation, which causes the
rock to fail in
tension rather than compression. High voltage pulses employed in pulsed power
drilling may
cause an electrical arc in the rock that causes the rock to break in an
electro-crushing process.
One illustration of such a drilling technique is described in U.S. Patent
Publication No. US
2009/0050371 Al to Moeny et al. (See "Moeny"). In such applications, drilling
fluid flows
down the drill string and out through passages in the bit near the electrodes
and then up the
outside of the drilling apparatus within the annulus to bring rock cuttings to
the surface. (US
2009/0050371 Al, paragraph 0109).
[008] A technique or apparatus that is capable of reducing the risk of
formation damage and
allowing the use of a reduced bottom hole pressure in the drilling of deep
wells would be
very desirable. A drilling technique that is capable of allow cuttings to be
brought to the
surface using a reduced flow rate of flow of drilling fluid is highly
desirable.
[009] The invention is directed to improved drilling apparatus and processes.
SUMMARY OF THE INVENTION
[0010] An apparatus and process for drilling a borehole into a subterranean
formation with
reverse circulation of drilling fluid is provided. The apparatus employs a
means to transfer a
supply of electrical power downhole either from a cable running down the
bottom hole
assembly components or the use of "wired drill pipe" with the capability to
conduct electrical
energy downhole with electrical conductors incorporated into the drill pipe
body. The
apparatus comprises a tubular drill pipe extending into the subterranean
formation, the drill
pipe having an interior space and an annular space on the exterior of the
drill pipe. A bottom
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hole assembly is connected to the drill pipe, the bottom hole assembly
comprising a bit to
excavate the subterranean formation to form cuttings. A downhole motor is
provided, the
downhole motor being adapted for receiving electrical power from either the
cable extending
into the subterranean formation or the use of wired drill pipe supplying the
electrical power.
A downhole pump is powered by the motor, the downhole pump being configured
for reverse
circulating drilling fluid and cuttings upwards through the interior space of
the drill pipe.
[0011] In one embodiment of the invention, the apparatus comprises a mechanism
for
removing excavated cuttings from the drilling fluid and then recirculating the
drilling fluid
downwards through the annular space on the exterior of the drill pipe. The bit
may comprise
a rotary rock bit. In other applications, the apparatus may have one or more
electrodes
configured for applying a pulsed voltage to excavate the formation with
applied pulsed
power. The downhole pump may be a positive displacement pump. In some
applications,
such as certain pulsed power bit applications, the bit may not rotate.
[0012] In some embodiments of the invention, the cross sectional area of the
interior space of
the drill pipe is less than the cross sectional area of the annular space,
thereby minimizing the
drilling fluid flow rate that is required to carry excavated cuttings upwards
through the
interior space of the drill pipe.
[0013] A downhole generator may be provided, in one embodiment of the
invention, for
applying pulsed power to the bit. The drilling fluid may comprise an
electrically insulating
formulation having a low level of electrical conductivity. In some
applications, the drilling
fluid comprises a carbon-based material.
[0014] A process is disclosed for drilling a borehole into a subterranean
formation with
reverse circulation of drilling fluid. The process comprises extending a
tubular drill pipe into
the subterranean formation, the drill pipe having an interior space and an
annular space on
the exterior of the drill pipe, the drill pipe having a proximal end near the
top of the wellbore
and a distal end with an attached bottom hole assembly. An electrical cable or
wired drill
pipe extends into the well to supply power to downhole apparatus. The bottom
hole
assembly may comprise a drilling bit. A pump and a motor are provided within
the borehole,
the pump being powered by the motor. The pump is in fluid communication with
the interior
of the drill pipe. It may be possible to circulate drilling fluid from the
annular space to the
interior space of the drill pipe. Drilling fluid with cuttings may be pumped
upwards through
the interior space of the drill pipe. In some embodiments of invention,
excavated cuttings
may be removed from the drilling fluid near the top of the wellbore and re-
circulated
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downward through the annular space. A control system may be employed to
regulate the
pulse repetition rate of the electrodes.
BRIEF DESCRIPTION OF THE FIGURES
[0015] Figures are provided to illustrate specific embodiments of the
invention, but the
invention is not limited to only the embodiments illustrated in the Figures,
but may extend to
other variations that would be appreciated by a person of skill in the art of
drilling.
[0016] Fig. 1 illustrates a schematic of one embodiment of the invention that
employs a
pulsed power drilling bit;
Fig. 1A shows a perspective view of the pulsed power drilling bit employed in
the apparatus
of Fig. 1;
Fig. 2 shows an alternate embodiment of the invention with a drilling
apparatus that employs
a rotary rock drill bit; and
Fig. 2A shows a more detailed view of the rotary rock drill bit.
DETAILED DESCRIPTION OF THE INVENTION
[0017] The present invention may employ pulsed power drilling apparatus or
rotary rock
drilling apparatus with reverse circulation drilling. Reverse circulation
drilling refers to
drilling wherein the drilling fluid is passed down the annulus to the outside
of the drill string
or drill pipe, and then circulated upwards through the drill pipe towards the
upper end of the
wellbore.
[0018] As used herein, "drilling" is defined as excavating or otherwise
breaking and driving
through a subterranean formation substrate. As used herein, "bit" and "drill
bit" are defined
as the working portion or end of a tool for providing cutting, drilling,
boring, or breaking
action on a substrate, such as rock. As used herein, the term "pulsed power"
is that which
results when electrical energy is stored (e.g., in a capacitor or inductor)
and then released so
that a pulse of current at high peak power is produced.
[0019] Referring to Fig. 1, a drilling apparatus 18 is disclosed for entry
into a wellbore 19 of
a subterranean formation 20. A tubular drill pipe 22 is provided with an
interior space 24
inside the pipe, and an annular space 26 outside the drill pipe 22. A bottom
hole assembly 28
is connected to the drill pipe 22 and is located, during drilling, at the
lower portion of the
wellbore 19. A bit 30 is configured to contact and break the rock of
subterranean formation
20. Fig. 1 shows a pulsed power bit 30, but other bits may be employed as
further described
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herein. Drilling fluid is circulated in reverse flow direction, such that the
fluid with cuttings
flows along direction arrow 40, and then along direction arrow 32. Cuttings
are dislodged by
the bit 30 and transferred by way of drilling fluid along arrow 32 to upwards
in the wellbore
19. A cable 36 is provided for providing a steady source of electricity to
downhole motor 34,
which drives downhole pump 38 to move the drilling fluid.
[0020] Fig. lA shows a perspective view of the bit 30, which in the embodiment
of Fig. lA
is a pulsed power bit 30. For drilling larger holes, a conical bit may be
employed, especially
if controlling the direction of the hole is a primary concern. Such a bit 30
may comprise one
or more sets of electrodes for creating the electro-crushing arcs and may
optionally comprise
mechanical teeth to assist the electro-crushing process. One embodiment of the
conical
electro-crushing bit has a single set of electrodes arranged coaxially on the
bit, as shown in
Fig. 2A. In this embodiment, conical bit 30 comprises a center electrode 48,
the surrounding
electrode 44, the housing 42 and mechanical teeth 46 for drilling the rock.
Either or both
electrodes may be compressible. The surrounding electrode may have mechanical
cutting
teeth 50 incorporated into the surface to smooth over the rough rock texture
produced by the
electro-crushing process. In this particular embodiment of the invention, the
inner portion of
the hole is drilled by the electro-crushing portion (i.e., electrodes 48 and
44) of the bit 30, and
the outer portion of the hole is drilled by mechanical teeth 46. This results
in high drilling
rates, because the mechanical teeth have good drilling efficiency at high
velocity near the
perimeter of the bit, but very low efficiency at low velocity near the center
of the bit. The
geometrical arrangement of the center electrode 48 to the ground ring
electrode 44 is conical.
It should be recognized that many types of pulsed power bit configurations
could be
employed in the practice of the invention, and the invention is not limited to
only the
configuration shown in Fig. 1A. U.S. Patent Publication No. US 2009/0050371 Al
to Moeny
et al. (See "Moeny") describes various embodiments and technical
specifications that may be
employed in the application of pulsed power drilling, and is incorporated
herein by reference.
Further, other pulsed power drilling apparatus and techniques may be employed.
Other
embodiments of the invention may employ rotary rock bits that do not employ
pulsed power,
as further described herein in connection with Figs 2 and 2A.
[0021] Fig. 2 shows an alternate embodiment of the invention of drilling
apparatus 60 that
employs a rotary rock bit to break the rock to form a borehole by compression
upon the rock
within subterranean formation 77. In this embodiment, a tubular drill pipe 52
comprises an
interior space 72 and an annular space 70 on the exterior of the drill pipe
52. A power cable
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54 extends into the wellbore 53 and supplied electrical power to downhole
motor 56, which
drives downhole pump 58, which transports drilling fluid. A bottom hole
assembly 62 is
positioned upon the end of drill pipe 52, and comprises a bit 64. In the
embodiment of Fig. 2,
the bit 64 is a rotary rock bit. A reverse circulation process is employed to
circulate the
drilling fluid along direction arrow 66 and then into the interior space 72 of
the drill pipe 52.
Drilling fluid picks up rock cuttings generated by bit 64 and transports them
along direction
arrow 68 and arrow 74 upwards in drill pipe 52 in a reverse circulation flow
direction.
[0022] Fig. 2A illustrates rotary rock bit 64, which in this particular
example is a tricone
style bit 64. The bit 64 has teeth 76 for contact with rock of the
subterranean formation 77.
[0023] As described previously, in the first illustrated embodiment of the
present invention,
as shown in Figs. 1 and 1A, a drill bit is provided upon which is disposed one
or more sets of
electrodes. In this particular embodiment, the electrodes are disposed so that
a gap is formed
between them and the electrodes are disposed on the drill bit so that they are
oriented along a
face of the drill bit. Electrodes between which an electrical current passes
through a mineral
substrate (e.g., rock) are not on opposite sides of the rock. Also, in this
embodiment, it is not
necessary that all electrodes touch the mineral substrate as the current is
being applied.
[0024] The electrodes of the embodiments shown in Figs. 1-1A are disposed on a
bit and
arranged such that electro-crushing arcs are created in the rock. High voltage
pulses are
applied repetitively to the bit to create repetitive electro-crushing
excavation events. Electro-
crushing drilling can be accomplished, for example, with a flat-end
cylindrical bit with one or
more electrode sets. These electrodes can be arranged in a coaxial
configuration, as one
example.
[0025] The electrocrushing drilling process does not require rotation of the
bit, but in some
instances bit rotation may be desirable. The electro-crushing drilling process
is capable of
excavating the hole beyond the edges of the bit without the need of mechanical
teeth. In
addition, by arranging many electrode sets at the front of the bit and varying
the pulse
repetition rate or pulse energy to different electrode sets.
[0026] The invention may be provided in other arrangements not specifically
shown or
described in this specification but within the general spirit and scope of the
invention.
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