Note: Descriptions are shown in the official language in which they were submitted.
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BACKGROUND OF T~lE INVENTION
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I. Field_of the Inve-nt'ion: This invention relates in
general to rotary well drilling, particularly to shock
~ absorbing apparatus used in the drill string to minimize
vibrations transmitted from a drill bit, through the drill
-- 5 string and to the equipment at the surface of the earth.
II. Description of 'the Pr'ior Art: Shock absorbing appara-
tus used in the drill string of a rotary well drilling
apparatus may be classified into two types: (1) Shock
absorbers for oil well drilling and (2) shock absorbers for
hole drilling for other industrial purposes such as blast
hole drilling.
Representive of shock absorbers used in drilling oil
and gas wells may be seen in U. S. Patent Nos. 3,382,936 and
3,746,329. In these shock absorbers a gas cavity is formed
_ 15 between a mandrel and a tubular body for supporting the load
imposed upon the drill bit and for absorbing any shock
loading or vibrations that would otherwise be transmitted
between the drill bit and the equipment at the surface of
the earth. Due to the large hydrostatic pressure of the
liquid drilling fluids used to drill deep oil and gas wells,
it would be difficult to seal between thi~ large hydrosta~ic
pressure and the much lesser pressure of the gas inside the
apparatus. To solve this problem there is disclosed in
Patent 3,382,936 a pressure transmitting liquid chamber
which comtnunicates with the gas cavity inside the apparatus
and the ambient drilling fluid. As a consequence, the
liquid in the intermediate liquid chamber may be sealed much
easier than the gas due to the relatively high viscosity of
liquid when contrasted with gas. The liquid and gas inside
the apparatus is prevented from intermingling by use of a
movable and fluid responsive separation element, which in
U. S. Patent 3,382,936 was a flexible membrane or bag. When
~FD~ problems develop~ with this flexible membrane or bag, a solid
piston was invented to maintain separation between gas and
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liquid, as is disclosed in U. S. Patent 3,746,329. Sub-
sequently, there was disclosed another apparatus to accomplish
results similar to the above two apparatuses, and in addition
_.~ a reduction of torsional shock loadings and vibrations, as
may be seen with reference to U. S. Patent No. 3,998,443.
With respect to the industrial type shock absorber,
there is disclosed in U. S. Patent Nos. 4,055,338 and
4,145,034 a shock absorber particularly adapted for use with
a blast hole drill rig. Blast hole drill rigs are utilized
to drill shallow holes, approximately fifty feet deep, for
lowering and detonating explosives to disintegrate the earth
for mining. The shock absorber disclosed in the above two
patents is adapted to be placed in the drill string at a
location near the surface of the earth. As is the case with
shock absorbers used in oil and gas well drilling, gas is
utilized for carrying the load imposed upon the drill bit
and the shock loading or vibrations transmitted from the
drill bit to the surface of the earth and the equipment used
to motivate the drill bit. Since air ~s used as the cir-
culating medium to remove cuttings from the bottom of thebore hole, there is no need for an intermediate or pressure
transmitting liquid chamber inside such shock absorbers.
Rather, there are seals between the manclrel and tubular body
to seal the ~as inside thc apparatus and prevent lubricant
from exiting from the apparatus. 'l`lle lubricant is necessary
in order to provide adequate lubrication to the seals. In
the apparatus disclosed in U. S. Patent Nos. 4,05S,33~ and
- 4,1~5,034 the pressure of the lubricant in the lubricant
cavities is maintained intermediate the pressure of the
pressurized chamber and ambient. This is beneficial in that
none of the seals is exposed to a pressure differential as
large as the differential between the pressure inside the
pressurized chamber and atmospheric pressure. Hence, the
_ seals are exposed to less stress and deformation and can be
expected to have a longer life. In these devices a selected
. pressure is applied to the lubricant inside the lubricant
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cavities by injecting lubricant through a grease fitting.
The pressure in the lubricant cavities is independent of the
pressure in the load transmitting and shock absorbing chamber.
In such devices, because of depletion of lubricant, the
S lubricant pre~sure will eventually drop. After about eighty
to one hundred hours of operation, relubrication is necessary
and failure to relubricate can result in substantial damage
to the seals and to the shock absorber.
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SU~RY OF THE INVENTION
The invention may be summarized as a shock absorberof the type having a tubular body and a mandrel reciprocally
~ rnounted in the body for rotation therewith. This shock
absorber has an annular chamber in the body cont~ining
fluid under pressure for absorbing load and shock. It
also has lubricant cavities between the seals containing
lubricant.
A piston is positioned between the mandrel and the
tubular body for movement responsive to pressure differential
between the load carrying and shock absorbing fluid in the
chamber and the lubricant cavities between the seals. The
piston is one form of means that may be used to exert a
portion of the pressure of the fluid in the load chamber
upon the lubricant. The pressure oE the lubricant is inter-
~~ 15 mediate the pressure in the load chamber and ambient. As a
consequence, the seal between the lubricant cavities and the
exterior of the tool is subjected to lower pressure differen-
tials and will have the potential for longer life.
The piston is a differential area piston, having a
reduced portion carried within a sleeve that is in contact
with the 1uid in the chamber. The piston has an enlarged
portion carried in the lubricant passage and communicates with
the lubricant in the lubricant cavities. The differential
areas assure lower pressure in the lubricant cavities than
in the pressurized chamber. This reduces the pressure drop
across the seal between the pressurized chamber and the
lubricant cavities, and also the pressure drop across
the seal between the lubricant cavities and ambient. Further,
selected pressures are maintained in the lubricant cavities
by movement of the piston even after loss of a relatively
large quantity of lubricant passed the seals.
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_ ~ ~ = N ~F ~HE DRAWINGS
Fig, 1 is a vertical sectional view of a shock
absorber constructed in accordance with this invention.
Fig. 2 is a partial, enlarged sectional view of a
portion of the shock absorber of Fig. 1.
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DESCRIPTION OF THE PREFI~RR~:D EMBODI~ENT
`Referring to Fig. 1, a threaded portion 11 protrudes
from the top sub 13 for connection to a drill string member
(not shown). A cylindrical barrel 15 is screwed to the top
sub 13, forming a tubular body in cooperation with top sub
13. A mandrel 17 is reciprocally and telescopingly received
in barrel 15. Mandrel 17 has a threaded lower end 19 for
connection to another drill string member (not shown). A
pressurized fluid chamber 21 between thc mandrel 17 and top
sub 13 supports the load placed on the drill string and
absorbs shock transmitted through the string from the drill
bit.
Top sub 13 has an axial passage 23 for transmitting
drilling fluid to the drill bit. A tube 25 is secured to
the lower end of top sub 13 and extends telescopingly into
an axial bore 27 in mandrel 17. A tubular shield 29 is
carried concentrically within tube 25. Shield 29 has a
smaller outer diameter than the inner diameter of tube 25,
providing an insulating clearance as explained in more
detail in U. S. Patent 4,145,034
A ventilatin~ passage 31 in top
sub 13 communicates the annular space between tube 25 and
shield 29 to the exterior. A char~ing port and valve means
33 is located in the top sub and extends into chamber 21 for
introducing gas under pressure. This valve may be similar
to that shown in U. S. Patent No. 3,382,936.
As explained in more detail in U. S. Patent No. 4,055,338,
a
floating piston-type separator 35 is moun~ed in chamber 21
for dividing the chamber into an upper gas region 37 and a
lower liquid region 39. A plurality of drive pins 41 are
located in grooves provided in the outer diameter of mandrel
17 and in the inner diameter of barrel 15 for rotating the
mandrel with the barrel. A retainer 43 is connected to the
top of the mandrel above drive pins 41 for retaining them.
Retainer 43 contacts a shoulder 45 when the tool is in the
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fully extended position, as shown in Fig. 1, preventing man-
drel 17 from disengaging itself from the barrel 15. A port
47 in barrel 15 allows liquid to be introduced into the
liquid region 39 of chamber 21.
A primary inner load seai ~9 is located in an annular
groove in bore 27 of mandrel 17 for sealing pressurized
fluid in the liquid region 39. A secondary inner seal 51 is
located in a groove in the bore 27 below the primary load
seal 49. Seal 51 will be adjacent the bottom of tube 25
when the mandrel 17 is at the fully extended positioi. A
Teflon band 52 between inner seals 49 and 51 reduces friction.
The exterior cylindrical surface of mandrel 17 below
drive pins 41 is in sliding contact with the inner wall c,f
barrel 15. Friction is reduced by a Teflon band 53. Bands
52 and S3 do not serve to sea; pressure. An outer primary
load seal 55 is located in a groove on the exterior surface
of the mandrel above band 53. A secondary outer load seal 57
is located below band 53. Seal 57 will be adjacent the
bottom of barrel 15 when the mandrel 17 is in the fully
extended position. Seals 49, 51, 55, and 57 are annular,
single resilient seals.
An annular groove or inner lubricant cavity 59 is
formed in tlle bore 27 of mandrel 17 between the inner seals
49 and 51. Similarly, an outer annular groove, or outer
lubricant cavity 61 is formed on the exterior cylindrical
surface of mandrel 17 between outer seals 55 and 57. The
lubricant cavities include the annular clearance space that
exists between the primary and secondary seals. A lateral
passage 63 is drilled from the exterior of mandrel 17 to
inner lubricant cavity 59, then sealed by a steel plug. A
lateral passage 65 is drilled inwardly a sele~ted distance
from the outer lubricant cavity 61. A longitudinal passage
67 intersects passages 63 and ~5. Longitu~.'nal passage 67
extends upwardly from lateral passage 63, and is plugged at
the end, creating a standpipe for compressing air located in
the passages. A grease fitting 69 is mounted at the bottom
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of longitudinal passage 67 for the introduction of grease
into the pn~ssages ~nd c.~vitics.
There are three additional longitudinal passages 71
(only one showTI~ that extend into a recess 73 formed near the
top of mandrel 17. Recess 73 is in communication with
the liquid region 39 of the pressurized chamber 21. The
longitudinal passages 71 are connected by lateral passages
75 to the outer annular lubricant cavity 61. Since the
outer lubricant cavity 61 is in communication with the inner
lubricant cavity 59 by way of passage 65, the longitudinal
passages 71 will also be in communication with both the
inner and outer lubricant cavities. ~ach lateral passage 75
intersects each longitudinal passage 71 at a selected
distance from the bottom of the longitudinal passage.
Referring to Fig. 2, each longitudinal passage 71
contains a sleeve 77. Sleeve 77 is located at the top of
the annular passage 71 and sealed in passage 71 by seal 79.
_ Sleeve 77 has an enlarged upper end 81 that fits securely
within an enlarged upper portion in the longitudinal passage
71. Sleeve 77 has a reduced diameter lower portion 83 that
fits tightly within a reduced diameter portion of passage
71. The enlarged and reduced portions 81 and 83 define a
shoulder 85 in passage 71 that faccs upwardly and prevents
~ sleeve 77 from moving downward. Retainer 43 limits the up-
ward movement o~ sleeve 77. When sleeve 77 contacts retainer
43, its seal 79 will still be locate(l within longitudinal
passage 71.
A piston 87 is reciprocally and sealingly carried in
sleeve 77. Piston 87 has an upper reduced diameter portion
~ 30 89 that is tightly an~ slidingly received in the inner bore
of sleeve 77. Seal 91 on the reduced portion 89 prevent~s
the leakage of fluid ~rom the liquid region 39 to the longi-
tudinal passage 71. Piston 87 has an enlarged portion 93
intermediate its ends that is tightly received within
passage 71. The enlarged portion 93 contains a seal 95 to
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prevent the leakage of fluid past this portion in passage
71. The diameter and thus the cross sectional area of the
enlarged portion 93 is larger than the diameter and cross
sectional area of the reduced portion 89. Preferably the
S cross sectional area of the enlarged portion 93 is two and
one-half tilnes the cross sectional area of the reduced
portion 89. This differential area will transmit approxi-
mately 40% of the pressure in the chamber 21 to the lubricant
cavities 59 and 61.
The lower end 97 of piston 87 is of smaller diameter
than longitudinal passage 71. The length of the lower end
97, froln t'ne bottom to enlarged portion 93, is greater
than the distance from the bottom of longitudinal passage
71 to lateral passage 75. This enables lubricant to be
pumped through lateral passage 75, and around the clearance
between lower end 97 and longitudinal passage 71 to urge
the piston 87 upward when lower end 97 is in contact with
the bottom o~ longitudinal passage 71.
To prepare the tool for use, after assembling, a
measured amount of liquid, which may be conventional hydraulic
oil, is introduced tllrougll charge port 47 into the liquid
__ region 39, while trapped air is let out through a bleeder
hole (not shown). The liquid fills liquid region 39, in-
cluding the spaces around the drive pins 41, and the space
in the recess 73 of the mandrel 17. Piston separator 35
will move upward to a selected level about one inch above
retainer 43. The liquid is substantially incompressible.
_ 'rhen a gas such as nitrogen is introduced into the gas
region 37 through charging por~ and valve 33. The gas is
pressurized to a selected initial charge pressure that is
typically between 700 psig (pounds per square inch gage)
and 1500 psig, depenling upon the loading to be supported by
the shock absorber. The piston separator 35 will equalize
the pressure in the gas region 37 with the liquid region 39.
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If there is no lubricant in lon~ltudinal passage 71,
the pressure in chamber 21 will force each piston 87 down-
ward until its lower end 97 is in contact with the bottom of
the longitudinal passage 71. The length of sleeve 77 is
selected so that seal 91 of the reduced portion 89 will
still be located within sleeve 77. The enlarged portion
seal 95 will be located slightly above the point where
- lateral passage 75 intersects the longitudinal passage 71.
A lubricant, such as a molybdenum-based grease is
introduced through grease fitting 69. The lubricant fills
lateral passages 63, 65 and 75, longitudinal passages 67 and
71 and the cavities 59 and 61. As pressure is applied to
the substantailly incompressible lubricant, it compresses
air in the upper portion of longitudinal passage 67, above
lateral passage 63. It also flows around the end 97 of
piston ~7 and pushes upwardly on the enlarged portion 93
until the piston 87 and sleeve 77 contact the bottom of
- retainer 43. The pressure in lubricant cavities 59, 61 will
peak once this contact is made, Preferably no more than 700
... 20 psig is applied during filling with grease,
Once completely filled, the pressure in the lubricant
passages and spaces should be 40% of the charge pressure in
the pressurized chamber 21, because of the difference in
areas at seals 91 and 95 of piston 87. Pr~mary load seals
49 and 55 prevent the liquid in liquid region 39 from entering
the lubricant cavities 59 and 61. The pressure differential
across the primary load seals will be the pressure in the
pressurized chamber 21 less the pressure in the lubricant
cavities 59 and 61, or approximately 60% o~ the pressure in
the pressurized chamber 21. The secondary load seals 51 and
57 prevent leakage of lubricant to the exterior, which is at
atmospheric pressure. The pressure drop across these seals
will be the pressure in the lubricant cavities 59, 61 less
the ambient or atmospheric pressure.
In operation, the threaded portion 11 of top sub 13 is
connected with the kelly or an upper drill string member.
The threads 19 of mandrel 17 are connected with a depending
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drill string member that supports the drill bit. Applying
weight or force to the bit causes an increased pressure in
liquid region 39. The resulting pressure differential
across piston separator 35 causes its upward movement,
compressing gas in gas region 37 of chamber 21 until the
pressures are equalized. Shock loadings are dampened by the
compression of the gas in gas region 37. During drilling,
the mandrel 17 rotates in unison with the barrel 15, however
moves telescopingly in response to the shock and changes in
loading.
Piston ~7 has its upper face in communication with the
liquid in liquid region 39, and its lower face in communi-
cation with the lubricant of the lubricant cavities 59 and
61. Piston 87 separates the liquid from the lubricant, and
transmits the force exerted by the liquid in the liquid
region 39 to the lubricant in the lubricant cavities 59, 61.
If the pressure fluctuates in liquid region 39, this fluc-
~ tuation will also be transmitted to the lubricant cavities
59, 61 by reciprocation of piston 87.
As the lubricant is depleted, the piston 87 moves
further downward, still transmitting 40% of the pressure
force to the lubricant cavities 59, 61. Once the piston end
97 contacts the bottom of longitudinal passage 71, it is no
longer able to transmit force, thus relubrication is necessary.
Actual field tests have shown that the shock absorber of
this invention is able to operate approximatcly 10 ~imes
as many hours between servicing ~han the types shown in U. S.
Patent Nos. 4,055,338 and 4,145,034.
It should be apparent from the foregoing that an
apparatus having significant advantages has been provlded.
Tlle piston arrangement provides a positive pressure in the
lubricant areas, thus reducing the pressure drop across a
single load seal. It maintains the pressure in the lubri-
cant cavities for a longer time period than in the prior art
tool. The piston arrangement is simple in construction, and
readily adaptable to existing shock absorbers of this nature.
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While the invention has been shown in only one of its
forms, it should be apparent to those skilled in the art
that it is not so limited but is susceptible to various
changes and modifications without departing from the spirit
thereof.
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