U.S. patent number 3,882,946 [Application Number 05/463,796] was granted by the patent office on 1975-05-13 for turbodrill.
Invention is credited to Jury Rolenovich Ioanesian, Rolen Arsenievich Ioannesian.
United States Patent |
3,882,946 |
Ioannesian , et al. |
May 13, 1975 |
TURBODRILL
Abstract
A turbodrill provided with at least two multistage hydraulic
turbines mounted one after another and operating in succession at
different speeds. According to the invention, the first element
along the path of the drilling fluid fed from the turbodrill is a
low-speed turbine and/or hydrodynamic braking stages mounted on a
solid shaft and capable of passing the total flow of the fluid. The
second element along the path of the drilling fluid is a high-speed
turbine capable of utilizing a high pressure drop and developing a
high torque, with the turbine being mounted on a hollow shaft
connected to a bit. Ahead of the high-speed turbine inlet, there is
mounted a device dividing the fluid coming from the low-speed
turbine into two flows, one being directed to the high-speed
turbine and the other being directed to the bit through the hollow
shaft of this turbine. The turbodrill allows a high pressure drop
to be utilized in the bit without increasing the pressure in the
delivery line of the mud pump and thereby providing for a hydraulic
effect without using a packing gland at low speeds of the bit and
high axial loads on the bottom hole.
Inventors: |
Ioannesian; Rolen Arsenievich
(Moscow, SU), Ioanesian; Jury Rolenovich (Moscow,
SU) |
Family
ID: |
23841403 |
Appl.
No.: |
05/463,796 |
Filed: |
April 24, 1974 |
Current U.S.
Class: |
175/107; 173/73;
415/903 |
Current CPC
Class: |
E21B
4/02 (20130101); F03B 13/02 (20130101); Y10S
415/903 (20130101) |
Current International
Class: |
E21B
4/00 (20060101); E21B 4/02 (20060101); F03B
13/00 (20060101); F03B 13/02 (20060101); E21b
003/12 () |
Field of
Search: |
;175/107 ;173/73
;415/502,503 |
References Cited
[Referenced By]
U.S. Patent Documents
Foreign Patent Documents
|
|
|
|
|
|
|
1,166,795 |
|
Nov 1958 |
|
FR |
|
1,195,283 |
|
Nov 1959 |
|
FR |
|
1,271,127 |
|
Jul 1960 |
|
FR |
|
1,053,444 |
|
Mar 1957 |
|
DT |
|
Primary Examiner: Brown; David H.
Attorney, Agent or Firm: Holman & Stern
Claims
What is claimed is:
1. A turbodrill for drilling oil and gas wells in an assembly with
a drilling unit comprising drill pipes, through which a drilling
fluid is supplied into the turbodrill and a mud pump for delivering
the drilling fluid into said drill pipes; said turbodrill,
comprising, in combination, a housing, at least two multistage
hydraulic turbines having different speeds, said turbines being
mounted in said housing one after another and operating in
succession; the low-speed turbine passing the total flow of the
drilling fluid coming from said drill pipes being located as a
first element along the path of said fluid; the next element along
the path of said fluid being the high-speed turbine utilizing a
high pressure drop and developing a high torque; a solid shaft on
which said low-speed turbine is mounted; a hollow shaft on which
said high-speed turbine is mounted and having one end connected to
a bit; a device dividing the fluid coming from said low-speed
turbine into two flows, one flow being directed to said high-speed
turbine and the other flow being directed through said hollow shaft
to said bit so that the turbodrill operates with a hydraulic effect
defined by the pressure drop in both the turbines and utilized by
the high-speed turbine without applying any substantial additional
load to said mud pump.
2. The turbodrill as claimed in claim 1, in which the device
dividing the fluid into two flows is a coupling connecting the
solid shaft with the hollow shaft for summing up the torques
developed by the turbine and transmitted to the bit; the
half-coupling secured on the solid shaft having openings for
bypassing a portion of the fluid running from the low-speed turbine
into the hollow shaft of the high-speed turbine.
3. The turbodrill as claimed in claim 1, in which the high-speed
turbine is made so that the inlet and outlet angles of the rotor
blades are substantially equal to each other and the inlet and
outlet angles on the stator blades are substantially equal to each
other.
4. The turbodrill as calimed in claim 1, in which the high-speed
turbine has stator and rotor blades whose inlet and outlet angles
are less than the similar angles of the low-speed turbine
blades.
5. The turbodrill as claimed in claim 4, in which the high-speed
turbine is made so that the inlet and outlet angles of its rotor
blades are substantially eqial to each other and the inlet and
outlet angles of the stator blades are substantially equal to each
other.
6. The turbodrill as claimed in claim 1, in which the high-speed
turbine has blades whose radial heights are lower than those of the
low-speed turbine blades.
7. The turbodrill as claimed in claim 6, in which the high-speed
turbine is made so that the inlet and outlet angles of its rotor
blades are substantially equal to each other and the inlet and
outlet angles of its stator blades are substantially equal to each
other.
8. A turbodrill for drilling gas and oil wells in an assembly with
a drill unit comprising drill pipes, through which a drill fluid is
supplied into the turbodrill, and a mud pump for delivering the
drilling fluid into said drill pipes; said turbodrill comprising,
in combination, a housing, a low-speed turbine defining,
hydrodynamic braking stages and a high-speed turbine located in
said housing one after another and operating in succession; the
hydrodynamic braking stages being arranged first along the path of
the drilling fluid coming from said drill pipes and passing the
total flow of said fluid; the next element along the path of said
drilling fluid being the high-speed turbine capable of utilizing a
high pressure drop and developing a high torque; a solid shaft
mounting the hydrodynamic braking stages; a hollow shaft mounting
said high-speed turbine and one end of which is connected to a bit;
a device dividing the fluid coming from the low-speed turbine into
two flows, one of which is directed to said high-speed turbine,
while the other is directed through said hollow shaft to said bit
so that the turbodrill operates with hydraulic effect.
9. The turbodrill as claiamed in claim 8, in which the device
dividing the fluid into two flows is a coupling connecting the
solid shaft to the hollow shaft for summing up the torques
developed by the turbines and transmitted to the bit; the
half-coupling secured on the solid shaft having openings for
bypassing a portion of the fluid flow running from the low-speed
turbine into the hollow shaft of the high-speed turbine.
10. The turbodrill as claimed in claim 8, in which the high-speed
turbine has stator and rotor blades whose inlet and outlet angles
are less than the similar angles of the low-speed turbine
blades.
11. The turbodrill as claimed in claim 10, in which the high-speed
turbine is made so that the inlet and outlet angles of the rotor
blades are substantially equal to each other and the inlet and
outlet angles of the stator blades are substantially equal to each
other.
12. The turbodrill as claimed in claim 8, in which the high-speed
turbine has blades whose radial heights are lower than those of the
low-speed turbine blades.
13. The turbodrill as claimed in claim 12, in which the high-speed
turbine is made so that the inlet and outlet angles of its rotor
blades are substantially equal to each other and the inlet and
outlet angles of its stator blades are substantially equal to each
other.
14. A turbodrill for drilling gas an oil wells in an assembly with
a drilling unit comprising drill pipes, through which a drilling
fluid is supplied into the turbodrill, and a mud pump for
delivering said drilling fluid into said drill pipes; said
turbodrill comprising in combination, a housing, two multistage
hydraulic turbines operating with different speeds and hydrodynamic
braking stages arranged in said housing one after another and
operating in succession; the first element along the path of the
drilling fluid coming from said drill pipes being the low-speed
turbine and the hydro-dynamic braking stages which pass the total
flow of said fluid; the next element along the path of said
drilling fluid being a high-speed turbine capable of utilizing a
high pressure drop and developing a high torque; a hollow shaft
mounting said high-speed turbine and one end of which is connected
to a bit; and a device dividing the fluid coming from said
low-speed turbine and hydrodanymic braking stages into two flows,
one of which is directed into said high-speed turbine and the other
is directed through said hollow shaft to said bit so the turbodrill
operates with a hydraulic effect.
15. The turbodrill as claimed in claim 14, in which the device
dividing the fluid into two flows is a coupling connecting the
solid shaft with the hollow shaft for summing up the turbine
torques transmitted to the bit; the half-coupling secured on the
solid shaft having openings for bypassing a portion of the fluid
flow running from the low-speed turbine into the hollow shaft of
the high-speed turbine.
16. The turbodrill as claimed in claim 14, in which the high-speed
turbine has stator and rotor blades whose inlet and outlet angles
are less than those of the low-speed turbine blades.
17. The turbodrill as claimed in claim 16, in which the high-speed
turbine is made so that the inlet and outlet angles of its rotor
blades are substantially equal to each other and the inlet and
outlet angles of its stator blades are substantially equal to each
other.
18. The turbodrill as claimed in claim 14, in which the high-speed
turbine has blades whose radial heights are lower than those of the
low-speed turbine blades.
19. The turbodrill as claimed in claim 18, in which the high-speed
turbine is made so that the inlet and outlet angles of its rotor
blades are substantially equal to each other and the inlet and
outlet angles of its stator blades are substantially equal to each
other.
Description
BACKGROUND OF THE INVENTION
The present invention relates to drilling machines and, more
particularly, to turbodrills used for drilling oil and gas
wells.
The present machine can be used both for drilling the wells by a
rock bit characterized by a high pressure drop, i.e., jet bits, and
for drilling the wells by bits characterized by low pressure
drops.
PRIOR ART
The turbodrills known in the drilling practice are not suitable for
drilling with jet bits, since so far there is packing gland that
could be reliable at high pressure drops.
A turbodrill with a rotary housing having three multistage
hydraulic turbines mounted in succession and rotating a bit is
known in the art. The turbines operate with different speeds. The
high-speed turbine is located as a first element along the path of
the drilling fluid fed from the drill pipes, a moderate-speed
turbine is located as a next element, and the last element is a
low-speed turbine, with all these turbines operating with the same
fluid flow rate.
Since the known turbodrill has a rotary housing, the packing gland
is located in its upper portion above the inlet of the fluid into
the high-speed turbine.
Such an arrangement of the packing gland is disadvantageous, since
it operates at a pressure drop equal to the sum of the turbine and
bit pressures. It is known, however, that even when drilling by
conventional rock bits operating at low pressure drops, the packing
gland of the turbodrill becomes inoperative within a short period
of time. For this reason, the jet bits operating at very high
pressure drops can not be practically used with such
turbodrill.
Furthermore, with the known turbodrill, the mud pump, besides the
deleterious resistances in the drill string and annular space, has
not overcome the pressure drop of the turbine and the bit and this
increases the pressure in the delivery line of the pumps.
It should further be noted that the presence of turbines operating
with different speed but at the same flow rate does not improve the
power characteristics of the turbodrill and does not provide for
drilling with a high pressure drop in the bit.
Attempts were made to develop a turbodrill in which the flow is
divided for obtaining a hydraulic effect in the bit without an
additional increase in the pressure in the delivery line of the mud
pump. This device, however, has a number of disadvantages which do
not allow the required effect to be obtained.
In this turbodrill, a part of the flow enters the turbine, while
another part of the flow bypassing the turbine enters the bit
through a hollow shaft. The part of the flow having been used in
the turbine, is also supplied to the bit and with this object in
view a packing gland is provided in the bottom portion of the
turbodrill.
Thus, the high-pressure and low-pressure flows are mixed in the bit
and this, first, reduces the hydraulic effect and, second, requires
special bits with passages for the high-pressure and low-pressure
streams. Furthermore, the supply of only a part of the flow to the
turbine results in the following undesirable phenomena. When using
a low-speed turbine, limited torques are developed on the shaft of
such a turbodrill. Therefore, the drilling operation is effected
with low bit weights, and this makes a rock bit very inefficient.
When there is employed a high-speed turbine developing a high
torque on the shaft, it results in a high speed of the machine and
this is not good for a rock bit.
OBJECT AND SUMMARY OF THE INVENTION
The main object of the present invention is to provide a turbodrill
which would allow to realize a high pressure drop in the bit
without a considerable additional increase in the pressure in the
delivery time of the mud pump.
Another object of the invention is to provide a turbodrill which
would enable the drilling operation to be performed at a low speed
of the bit and high axial load on the bottom hole.
Still another object of the invention is to provide a turbodrill
which would operate with a hydraulic effect without using a packing
gland.
These and other objects are attained by providing a turbodrill
comprising at least two multistage hydraulic turbines mounted one
after another and operating in succession with different speeds,
said turbines rotating a bit, according to the invention, a
low-speed and/or hydrodynamic braking stages, through which passes
the total flow of a drilling fluid, are mounted on a solid shaft as
a first element along the path of said drilling fluid supplied from
the drilling pipes, with the next element along the path of the
drilling fluid being a high-speed turbine mounted on a hollow shaft
and made with a possibility of utilization of a high pressure drop
and development of a high torque on the shaft; mounted ahead of
said high-speed turbine inlet is a device dividing the flow of
fluid coming from the low-speed turbine into two flows, one of
which is directed to the high-speed turbine, while the other is
directed to the bit through the hollow shaft of this turbine.
The concept of a "low-speed" or "high-speed" turbine is defined by
the peripheral speed of the rotor when running idle, with a flow
rate of 1 dm.sup.3/ sec.
The mutual arrangement of the turbines, when the low-speed turbine
is located first along the path of the fluid and the high-speed
turbine is the last along the same, as well as the fact that the
first turbine operates with a total flow rate and the second,
developing high torques, operates with a part of this flow, make it
possible to obtain a high torque and comparatively low speed of the
turbodrill shaft suitable for rock bits.
The division of the incoming fluid into two flows, one of which is
fed into the high-speed turbine from which it passes through the
holes in the turbodrill housing directly into the space between the
housing and the well wall, while the other flow passes directly to
the bit, makes it possible to provide a turbodrill without packing
glands and to obtain a hydraulic effect on the bit without any
substantial increase in the pressure in the delivery line of the
mud pump.
From the technological point of view, the device for division of
the fluid into two flows is expedient to be made in the form of a
coupling connecting the shafts of the low-speed turbine and/or
hydrodynamic braking stages with the shaft of the high-speed
turbine for summing up the turbine torques transmitted to the bit.
For this purpose, a half-coupling mounted on the solid shaft has
openings for admitting a portion of the fluid supplied from the
low-speed turbine into the hollow shaft of the high-speed
turbine.
Due to the face that the couplings between the shafts in the
turbodrills are obligatory components, it is most expedient
technologically, to use them for division of the flow, with these
components being removable.
When the turbodrill is to be used for drilling a deep well, the
low-speed turbine is preferably provided with hydrodynamic braking
stages in which the stator and rotor blades have the equal inlet
and outlet angles and are inclined at the same angle to the plane
normal to the turbodrill axis.
When drilling very deep wells, all stators and rotors mounted on
the solid shaft are preferably made with blades having equal inlet
and outlet angles and inclined at the same angle to the plane
normal to the turbodrill axis.
Use of such stators and rotors allows the speed of the turbodrill
shaft to be controlled within a wide range and makes it possible to
select the most expedient operating conditions for the bit
depending on the depth of the well, the type of the bit, the
character of the drilled rock, and the properties of the drilling
fluid.
In the high-speed turbine stators and rotors, the outlet angles of
blades must be less with respect to the plane normal to the
turbodrill axis than the corresponding angles of the low-speed
turbine. The blades' radial heights of the high-speed turbine are
also expedient to have lower than those of the low-speed turbine.
The expediency of such a construction is dictated, on the one hand,
by the necessity of designing a hollow shaft of the largest
possible diameter and, on the other hand, by the fact that with a
low radical height of the turbine blades with specified outlet of
angles of the rotors and stators, the turbine pressure drop is
increased and this makes it possible to utilize the high pressure
drops which are required for efficient operation of the jet
bits.
In order to increase the pressure drop, which can be utilized in a
jet bit with its speed being reduced, the inlet and outlet angles
of the rotor and stator blades of the high-speed turbine are to be
made substantially equal to each other. The pressure drop in the
turbines having blades of such a shape increases with a decrease in
the speed of the turbodrill shaft. In this case, a higher amount of
drilling fluid will be supplied into the nozzles of the jet bit.
The pressure drop in the bit will increase correspondingly and this
increases the efficiency of the hydraulic jet.
Other objects and advantages of the present invention will be
apparent from the following detailed description of one particular
embodiment of the invention with reference to the accompanying
drawings.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is a general view of the turbodrill according to the
invention, in longitudinal section; with the bottom components of
the turbodrill being connected along the line I--I;
FIG. 2 is a longitudinal section of the stator and rotor of the
low-speed turbine;
FIG. 3 is a shape of the stator blades of the low-speed
turbine;
FIG. 4 is a shape of the rotor blades of the low-speed turbine;
FIG. 5 is a longitudinal section of the stator and rotor with the
equal inlet and outlet angles of the blades and located at the same
angle to the plane normal to the turbodrill axis;
FIG. 6 is a shape of the stator blades disposed at an angle of
90.degree. to the plane normal to the turbodrill axis;
FIG. 7 is the same of the rotor blades;
FIG. 8 is a longitudinal section of the stator and rotor of the
high-speed turbine;
FIG. 9 is a shape of the stator blades of the high-speed turbine
and;
FIG. 10 is the same of the rotor;
DETAILED DESCRIPTION OF THE INVENTION
The present invention is a turbodrill for drilling oil and is gas
wells and used as a component of a drilling unit which also
comprises drill pipes through which the drilling fluid delivered by
a mud pump passes to the turbodrill.
The turbodrill comprises two multistage hydraulic turbines
operating in succession at different speeds and mounted one after
another in a housing 1 (FIG. 1).
According to the invention, a low-speed turbine 2 is mounted as a
first element along the path of the drilling fluid coming from the
drill pipes (not shown). This turbine is secured on a solid shaft 3
and is fixed thereto by means of a nut 4. The shaft 3 is fixed with
respect to the housing 1 by means of radial bearings 5. The total
flow of drilling fluid fed to the turbodrill passes through the
low-speed turbine 2.
A high-speed turbine 6 is mounted after the low-speed turbine along
the path of the drilling fluid. A hollow sectional shaft 7
connected to bit 8 is used for mounting the turbine 6.
Mounted before the inlet of the high-speed turbine 6 is a device
for the division of the fluid coming from the low-speed turbine 2
into two flows.
The device dividing the fluid into two flows is a coupling
consisting of two half-couplings 9 and 10 connecting the shafts 3
and 7 of the turbines 2 and 6, respectively, for summing up the
torques developed by the turbines and transmitted to the bit 8.
The half-coupling 9 is secured on the solid shaft 3 and has
openings providing communication between a space 12, separating the
turbines, and are space 13 of the shaft 7 of the high-speed turbine
6 and serving for by passing a portion of the fluid coming from the
low-speed turbine 2 into the hollow shaft 7 of the high-speed
turbine 6.
Both half-couplings 9 and 10 form a coupling transmitting the
torque from the solid shaft 3 to the hollow shaft 7.
When drilling deep wells, it is necessary to run the turbodrill
and, therefore the bit 8, at low speeds. In this case, the
low-speed turbine performs two functions: it not only develops a
torque on the solid shaft 3 but also limits the speed of the
high-speed turbine 6, thus serving as a hydrodynamic brake.
Depending on a required speed of the bit 8, the low-speed turbine 2
may have the blades of different shapes.
In order to obtain average revolutions, blades 14 of a stator 15
and blades 16 of rotor 17 of the low-speed turbine 2 should be made
of the shapes shown in FIGS. 3 and 4.
In order to obtain a lower speed of the bit 8, the solid shaft 3
should be provided with a part of the stages with a shape of the
blades 14 and 16 of the stators 15 and rotors 17 shown in FIGS. 3
and 4 and with another part of the stages with a shape of blades 18
of stators 19 and blades 20 of rotors 21 shown in FIGS. 6 and
7.
In order to obtain the lowest speed, the solid shaft 3 must be
equipped with stators 19 and rotors 21 with the blades 20 and 18 of
the shapes shown in FIGS. 6 and 7. Shown in FIGS. 3 to 10 by an
arrow A is a direction of rotation of the turbodrill shaft, while
an arrow B shows the direction of the fluid flow.
The high-speed turbine 6 is capable of utilizing a high pressure
drop and provides for a high torque on its shaft 7. For this
purpose, the outlet angles .alpha..sub.1 of blades 22 of stators 23
and the outlet angles .alpha..sub.1 of blades 24 of rotors 25 of
the turbine 6 are less than the similar angles .alpha..sub.2 of the
blades 14 of the stators 15 and the angles .alpha..sub.2 of the
blades 16 of the rotors 17 of the low-speed turbine 2.
What is more, the high-speed turbine 6 has blades 22 and 24 whose
radial heights h.sub.1 (FIG. 8) are lower than the radial heights
h.sub.2 (FIG. 2) of the blades 14 and 16 of the low-speed turbine
2.
The hollow shaft 7 of the multistage high-speed turbine 6 is made
sectional. A part of the shaft 7 connected to the bit 8 is a
spindle consisting of a body 26, secured to the housing 1 of the
turbodrill by means of connecting subs 27 and 28, and a shaft 29.
One end of the shaft 29 has a thread for connection with the bit 8,
while the other end thereof is used for connection by means of
half-couplings 30 and 31 with a shaft 32 serving as a next part of
the shaft 7 of the turbine 6. The shaft 32 is connected to the
shaft 7 by half-couplings 33 and 34.
Mounted in the spindle is a multistage bearing 35 taking the
hydraulic load due to the pressure drop in the turbines 2 and 6 and
transmitting the axial load to bottom hole 36.
The connecting sub 27 has openings 37 for admitting the drilling
fluid, having been operated in the high-speed turbine 6, into the
well 38.
The turbodrill can be made so that the drilling fluid used in the
high-speed turbine 6 is fed into the well 38 through an annular
space 39 provided between the body 26 of the turbodrill spindle and
the sshaft 29 of the spindle.
When drilling with a jet bit, the flow of fluid fet into the hollow
shaft 7 passes directly into the bit since the nozzles of the bit 8
are in communication with the space of the shaft 7 of the turbine
6. In this case, the passage cross sections of the jet bit nozzles
are selected to that the cooperating pressure in the bit
corresponds to the pressure drop in the high-speed turbine 6.
When drilling with a conventional bit, ahead of this bit, there is
mounted a removable nozzle 40 from which the fluid is fed into the
central hole of the bit.
The diameter of the nozzle 40 is selected taking into account the
pressure equal to the pressure drop in the high-speed turbine
6.
In face, the diameters of the jet bit nozzles or the diameter of
the removable nozzle 40 mounted ahead of the convention bit 8,
define the portion of fluid which will be fed through the hollow
shaft 7 to the bit 8 and the portion of fluid which will be fed to
the high-speed turbine 6 bypassing the bit 8.
The inlet angles .alpha..sub.3 (FIG. 10) and the outlet angles
.alpha..sub.1 of the blades 22 of the stators 23 (FIG. 8) of the
high-speed turbine 6 are substantially equal to each other and the
inlet angles .alpha..sub.3 (FIG. 10) and the outlet angles
.alpha..sub.1 of the blades 24 of the rotors 25 (FIG. 8) of the
same turbine are also equal to each other. In this case, the
pressure drop in the turbine 6 increases with a reduction in its
speed.
Therefore, in the process of turbodrilling, the speed of the bit 8
goes down with an increase in the load on the bottom hole 36 (FIG.
1) and therefore, the distribution of the total flow between the
turbine 6 and the bit 8 will be varied. From this it follows that
the higher the load on the bottom hole, i.e., the lower the bit
speed, the higher amount of fluid is fed into the bit; and hence
the higher the operating pressure in the jet bit.
Since the high-speed turbine 6 develops a high torque, it can be
made of two sections whose bodies are connected by subs 41 and 42
so that even when a part of the fluid flow fed into the turbodrill
passes through this turbine, a high torque required for drilling
with the bit 8 is developed on the hollow shaft 7. At the same
time, since this turbine is made with a possibility of utilization
of a high pressure drop, it also performs the function of a packing
gland limiting the amount of fluid fed into the well by-passing the
bit 8.
The present turbodrill operates as follows; working drilling fluid
delivered by the mud pumps through the drill pipes and the upper
sub 43 of the turbodrill enters the low-speed turbine 2, which
passes the total flow of the fluid. From the low-speed turbine 2,
the fluid is fed into the space between the turbines, from which a
portion of the fluid through the device dividing the fluid flow is
supplied into the hollow shaft 7, while the other portion of the
fluid is fed into the high-speed turbine 6. The fluid, having been
run in the turbine, through the openings 37 is directed into the
well 38, while the other flow through the hollow shaft 7 and the
nozzle 40 of the bit 8 is directed onto the bottom hole 36 of the
well 38 cooling the bit 8 and carrying out the cuttings to the
surface.
From the above, it can be seen that the present turbodrill has a
high torque at a limited shaft speed and provides for operation
with high-pressure jet bits without substantial loading of the mud
pump.
Furthermore, the present construction of the turbodrill allows it
to be made without a high-pressure packing gland since its function
is performed by the high speed turbine.
* * * * *