|Publication number||US3889959 A|
|Publication date||Jun 17, 1975|
|Filing date||Aug 2, 1973|
|Priority date||Aug 7, 1972|
|Also published as||CA978177A, CA978177A1, DE2339391A1|
|Publication number||US 3889959 A, US 3889959A, US-A-3889959, US3889959 A, US3889959A|
|Inventors||Persson Jan Edvard|
|Original Assignee||Atlas Copco Ab|
|Export Citation||BiBTeX, EndNote, RefMan|
|Patent Citations (5), Referenced by (22), Classifications (25), Legal Events (2)|
|External Links: USPTO, USPTO Assignment, Espacenet|
United States Patent 1191 Persson 1 EARTH DRILLING APPARATUS  Inventor: Jan Edvard Persson, Nacka, Sweden  Assignee: Atlas Copco Aktiebolag, Nacka,
Sweden 22 Filed: Aug. 2, 1973 21 Appl. No.: 384,953
 Foreign Application Priority Data Aug. 7, 1972 Sweden 10239/72  References Cited UNITED STATES PATENTS 3/1940 Seamark 277/31 3/1952 Sausa 251/5 X 3,145,995 8/1964 Adamson et a1. 166/53 X 3,492,007 1/1970 Jones 166/84 X 3,614,111 10/1971 Regan 251/1 X 1 June 17, 1975 Primary Examiner-Martin P. Schwadron Assistant Examiner-Richard Gerard Attorney, Agent, or Firm-Flynn & Frishauf  ABSTRACT A drilling apparatus for pressure drilling through the earth, comprising a drill string, a casing tube assembly, a rotary drilling machine with mechanized drill string handling and a liquid handling system. The liquid han- 'dling system comprises means for controlling the casing tube pressure and the liquid level within the drill string during withdrawal and disconnection of the drill string. At disconnecting a drill string section, a pressure air impulse is introduced into the flushing channel thereof so as to lower the liquid level and thereby avoid liquid over-flow at the top of the casing tube. A back-flow restricting valve prevents rapid rising of the liquid level within the drill string. A preventer unit having a pressure balanced packing sleeve seals off the upper end of the casing tube; the contact pressure of said packing sleeve is automatically and continuously adapted to the actual casing tube pressure by means of a pressure responsive control valve which is arranged to release the packing sleeve from pressure in response to decreasing casing tube pressure.
12 Claims, 4 Drawing Figures PATENTEDJUN 17 I975 SHEET Fig. 1
PATENTEDJUN 17 I975 3, 9 959 SHEET 2 HllllllllH SHEET PATENTEDJUN 17 I975 4 U \\/A/ L PATENTEIJJUHH ms -:BBSBSS SHEET 1 EARTH DRILLING APPARATUS This invention relates to a drilling apparatus for pressure drilling through the earth, and more particularly to a device for maintaining the drill hole pressure during withdrawal and disconnection of the drill string.
An object of the invention is to provide a preventer unit for sealing off the casing tube during drilling and vertical travel of the drill string, the preventer being provided with a long-life packing sleeve.
A further object of the invention is to provide a means for controlling the contact pressure of the preventer unit packing sleeve with respect to the casing tube pressure.
Further objects and advantages of the invention will be apparent from the detailed description and the drawings BRIEF DESCRIPTION OF THE DRAWINGS FIGS. 1 and 2 schematically show a drilling apparatus according to the invention, FIG. 1 showing the drilling apparatus in its drilling position, and FIG. 2 showing the drill string withdrawing position and also showing a pressure air injection device;
FIG. 3 is a longitudinal section through a preventer unit according to the invention, the preventer unit being shown in its active, as well as in its non-active position; and
FIG. 4 shows a longitudinal section through a pres sure control valve intended for adapting the contact pressure of the preventer unit in correspondence to the actual pressure in the casing tube.
DETAILED DESCRIPTION The drilling apparatus shown in FIG. 1 comprises mainly a drill string 1, a drilling machine 2 for rotating the drill string 1, a casing tube assembly 3 and a liquid handling system 4.
The drill string 1 is constituted by a number of conventional drill tube sections and is terminated at its forward or lower end by a core tube provided with an annular diamond bit. (Not shown). At its rear or upper end, the drill string 1 is provided with a water swivel 5 and adjacent its forward end, the drill string is provided with a backflow restricting valve 6. The valve 6 has to be located above the core tube.
The backflow restricting valve 6 is in fact a check valve provided with a restricted by-pass opening through which the drill string is slowly tilled up when it is lowered down into a water containing hole. The bypass opening should be of such a size that the drill string is filled up with water as it has reached the bottom of the hole. Thereby, the drilling operation can be started immediately.
The drilling machine 2 comprises a housing 7, a motor 8, a rotating chuck 9, a feeding device 10 for accomplishing longitudinal movements of the drilling machine and a stationary chuck 11. The drilling machine 2 is intended for positive feeding, retracting and disconnecting the drill string. Such a drilling machine is shown in Swedish patent No. 324,747, corresponding to US. Pat. No. 3,613,804.
The casing tube assembly 3 comprises a casing tube 12, a gate valve 13 located at the upper end of the easing tube and intended for closing the casing tube when the drill string is withdrawn. The casing tube assembly also comprises an emergency preventer 14 of a conventional type for sealing off the casing tube 12 when the drill string 1 is present therein but stationary. Finally, the casing tube assembly comprises a preventer unit 15 according to the invention, the object of which is to seal off the casing tube 12 during drilling and withdrawal of the drill string. The main component of the preventer unit 15 is an annular pressure fluid actuated packing sleeve 17 (see FIG. 3). The preventer unit 15 is herebelow described in detail.
The liquid handling system 4 is intended for providing the drill hole with flushing medium through the drill string 1. The liquid handling system 4 comprises means for restricting the return flow in order to establish an over-atmospheric pressure in the drill hole. For that purpose the liquid handling system 4 is split up into two main branches, namely one feed branch 18 and one re turn branch 19. The feed branch 18 comprises a pump P2, a manometer M2 and a flow meter F1 and is connected to the water swivel 5 through a conduit 21.
The return branch 19 of the liquid handling system 4 is connected to the casing tube 12 through a conduit and comprises a flow meter F2, a manometer M3 and a variable restricting device S2. Moreover, the return branch 19 contains a more sensitive flow meter 22 which is connected downstream of the restricting means S2. Flow meter 22 is provided with an outlet conduit 23 containing a variable restricting means S3. Further, the sensitive flow meter 22 includes a vessel having one of its walls made of a transparent material. Through this wall, the liquid level within the vessel is observable from the outside. Rising or sinking of the liquid level indicates variations in the return flow. The vessel is also provided with an overflow outlet D6 through which drill hole gas is exhausted. Owing to the fact that the return flow branch 19 of the liquid handling system is closed up to the flow meter 22, it is possible to control the gas outlet. Such a gas is very often unhealthy.
The return flow branch 19 also contains a constant pressure valve T2 which is arranged in parallel with the flow restricting means S2 and connected to the threeposition valve V4. During intermittent flow in the system the valve T2 is put into action by shifting the valve V4.
The return flow branch 19 of the liquid handling system 4 also contains a variable displacement pump P3 and two additional outlets D3 and D4. The outlet D3 contains a flow restricting means S4 and the outlet D4 contains a safety valve T1 the opening pressure of which is adjustable and normally set on the top pressure limit of the casing tube. This part of the system, together with the flow meter F2 and the manometer M3, is suspendable from the rest of the system by means of a valve V3.
The pump P3 is driven by a pressure compensated hydraulic motor (not shown) and is intended to be put into work in order to maintain the drill hole pressure and thereby avoid collapsing of the drill hole wall if the regularly working pump P2 is stopped or if the liquid loss in the hole rapidly increases. In the latter case, the pump P3 can be supplied with a thicker flushing liquid in order to obtain a choking up of the high-porous formations.
The feed and return flow branches 18 and 19, respectively, are interconnected by a conduit comprising a three-position valve V2 and a manometer M4 which is intended for calibration purposes.
Furthermore, the drilling apparatus comprises a pressure fluid system for actuating the preventer unit 15. This pressure fluid system comprises a pump P1 and is connected to the casing tube 12 via a pressure control valve S1.
The pressure control valve S1 comprises a housing 31 and a spring biased valve piston 32 (see FIG. 4). The valve piston 32 is biased in one direction partly by means of a pressure spring 33 and partly by the casing tube pressure through a pressure sensing conduit 99. The biasing force of the spring 33 is adjustable by a screw 35. The valve piston 32 is also exposed to a counter-directed force constituted by the pressure from the pump P1. The pump pressure actuated end of the valve piston 32 is of a smaller diameter than the opposite end and is provided with a valve seat portion for cooperation with an annular seat 34 in the housing. The housing 31 is provided with an outlet D2 which is so located that, when the piston 32 is pushed away from the seat 34 by the pump pressure, the pump is drained through the outlet D2.
As the pump P1 has a determined flow capacity, the pressure in the system which is the pressure acting upon the packing sleeve 17 of the preventer unit is dependent on the size of the drainage opening. The drainage opening is defined by the seat 34 and the valve piston 32. Oppositely, the opening force acting upon the valve piston is dependent on the pressure in the system. The size of the drainage opening is also dependent on the counter directed force of the spring 33 and the casing tube pressure which act upon the opposite end of the valve piston. Thus, the latter is acted upon by two oppositely directed fluid pressures and gives at a certain setting of the spring force a greater drainage opening when the pressure in the casing tube decreases. The result of that is that the pressure in the system as well as the pressure acting upon the packing sleeve 17 decreases. The relationship between the pressure in the casing tube and the pressure in the liquid system can be adjusted by means of the screw 35. The pressure fluid system can be drained to an outlet D1 by means of a valve V1.
Moreover, the pressure fluid system contains a manometer M1 and a conduit for connection with the return flow branch 19 of the liquid handling system, which conduit contains a check valve T3.
Referring to FIG. 3, the preventer unit 15 comprises a housing 40 which is provided with a central opening for the drill string 1. Within the housing 40 there is rotatably mounted a retainer ring 41 which is connected to the pressure fluid system through an opening 42 in the housing 40.
The packing sleeve 17 is rigidly secured in the retainer ring 41 in such a way that pressure fluid from the pump P1 has access to its outside for applying a radial contact force and make it engage the drill string with its inside. To the left in FIG. 3, the packing sleeve 17 is shown in its pressure released rest position and to the right in the same figure the packing sleeve 17 is shown in its active position.
As seen in FIG. 3, the packing sleeve 17 is provided with two axially spaced contact portions 45 and 46 which are intended to cooperate with the drill string when the packing sleeve is pressurized. i
During axial movement of the drill string 1, the packing sleeve 17 slides along the drill string. In order to limit the friction force arising upon the packing sleeve 17, the latter is provided with a number of small diameter leakage openings 43 which are located intermediate the contact portions 45 and 46. Through these leakage openings 43, pressure fluid is able to leak out between the packing sleeve 17 and the drill string 1. Thereby. a pressure balancing of the packing sleeve is accomplished. By this arrangement not only a limitation of the contact pressure between the packing sleeve and the drill string is obtained but also a lubrication of the contact surfaces.
As the difference between the actuating pressure of the packing sleeve 17 and the drill hole pressure is less than the difference between the actuating pressure and the atmosphere, the sleeve 17 may very well be nonsymmetric, which means that it is thicker at its upper end than at its lower end. In order to obtain an equal pressure balancing and lubrication of the packing sleeve 17 throughout its length, the leakage openings may be placed somewhat closer to that end of the packing sleeve which is closest to the drill hole. The packing sleeve 17 may very well be made of rubber or plastic. As water is used as pressure fluid in the system, it is very easy to obtain lubrication of the retainer ring 41 by using bearing surfaces made of rubber, plastic and the like. By this arrangement the bearing surfaces of the retainer ring do not have to be packed in.
FIG. 2 shows the same drill equipment as FIG. 1 but in FIG. 2 it is shown in position withdrawal of the drill string. In this position, the water swivel 5 is disconnected from the rear end of the drill string and a hydraulically operated air injection device 50 is fitted. The object of this device is to connect the drill string 1 to a pressure air source. To obtain a proper connection between the air injection device and the drill string, the drilling machine 2 is provided with a coupling sleeve 48 which extends rearwardly from the rotatable chuck 9.
The air injection device 50 comprises a swing arm 49 upon which is mounted a tapered connecting member 51. The connecting member 51 is movable by means of the swing arm between an active position (as in FIG. 2) and a non-active position (as in FIG. 1) and is provided with a conical outer surface 53 for cooperation with the rear end of the coupling sleeve 48. The swinging arm 49 is actuated by means of a hydraulic cylinder 52 which is connected to a pump 54 via a control valve 55.
The pressure air system which communicates with the connecting member 51 comprises a compressor 57, a pressure air tank 58 and a control valve 59.
The operation order of the above described drilling equipment is the following.
At the start of the drilling operation, the lower part of the drill string 1 containing the drill bit, the core tube and the backflow restricting valve 6 is introduced through the drilling machine 2 and the casing tube assembly 3. Thereafter, the drilling operation is carried out in a conventional manner in that the chuck 9 rotates the drill string 1 at the same time as the feeding device 10 forces the drill string 1 downwards. The feed branch 18 of the liquid handling system 4 is connected to the drill string by means of the water swivel 5. During drilling, the safety preventer l4 and the gate valve 13 are fully opened, while the preventer unit 15 is activated by the pressure fluid system pump P1. The drill hole is continuously flushed by a liquid delivered by the pump P2, the feed pressure being indicated at the manometer M2 and the fluid flow being indicated at the flow meter F1. The flushing liquid is pumped down the hole through the interior of the drill string 1 and returns to the surface at the outside of the drill string. As the drill hole is closed by means of the preventer unit 15, the flushing liquid is forced out into the return flow branch 19 of the liquid handling system 4 Because of porosity in the penetrated formations, losses of flushing liquid always occur, which means that the return flow is less than the feed flow. The actual return flow is indicated on the flow meter F2.
During drilling, the valve V3 is open, the valve V2 is closed between the feed branch l8 and the return flow branch 19 and the valve V4 is open toward the flow restricting means S2. The pressure in the return flow branch 19 is indicated on the manometers M4 and M3.
At the beginning of the drilling operation, the flow restricting means S2 and S3 is set so as to match an estimated return flow or so as to match a certain loss of liquid in the drill hole. The restriction means S2 gives a desirable return flow pressure. The restriction means S3 should be set so that the liquid level within the vessel 22 remains stationary at a certain level. If a considerable increase or decrease in the flush liquid losses occurs, it could be observed upon the flow meter F2. On the other hand, if the liquid losses in the drill hole are diminutive, it could be observed upon the flow meter 22. The flow meter 22 is very sensitive because of the fact that even a very little change in return flow is indicated as a successive rising or sinking of the liquid level. This high sensitivity makes it possible to discover gas inflow into the drill hole at an early stage which is very important from the safety point of view, because the operators get more time for taking precautionary measurements in order to avoid blow-outs.
In order to maintain the liquid pressure in the drill hole, when the water swivel 5 and the feed branch 18 of the liquid handling system is disconnected from the drill string 1, the valve V2 is closed toward the water swivel and the valve T2 is activated by shifting the valve V4. By this arrangement the liquid pressure in the drill hole is maintained.
Owing to the fact that the hydrostatic pressure within the drill hole increases as the depth of the drill hole increases, the pressure of the flushing liquid has to be adapted thereto in order to control occurring gas inflow into the drill hole. For making the preventer unit seal off the drill hole around the drill string at increasing pressure, a higher contact pressure has to be applied upon the packing sleeve 17. This pressure adaptation is accomplished by the pressure control valve S1 which communicates with the casing tube 12 through the pressure sensing conduit 99. As the casing tube pressure increases, the pressure required to obtain drainage of the pump Pl also increases. This means that the drainage of the pump P1 decreases and the pressure in the pressure fluid system as well as the contact pressure of the preventer unit packing sleeve 17 increases. The actual pressure in the pressure fluid system can be observed on the manometer M1 and could be adapted manually by setting of the screw 35 of the pressure control valve S1.
At withdrawal and disconnection of the drill string 1, which is carried out in a common way by cooperation between the chucks 9 and 11 of the drilling machine and the feeding device 10, the water swivel 5 is disconnected, whereby the liquid pressure within the drill string ceases. In order to prevent the liquid within the chine above the preventer unit 15, the connecting member 51 is swung into engagement with the coupling sleeve 48. Pressure air is introduced into the drill string in the form of a pressure air impulse. The purpose of the pressure air impulse is to press down the liquid level within the drill string a certain distance below the uppermost drill string joint. Then, the air injection device is disconnected by shifting of the valve 55 and the uppermost drill string section is disconnected. As soon as the disconnected drill string section has been removed, the pressure air system is reconnected to the drill string.
The liquid level within the drill string has to be lowered to such a low level that a pressure that may remain in the drill string, is not able to raise the liquid level up to the section joint that has just been broken during the time interval when the air injection device is removed. The liquid level rising speed depends on the size of the by-pass opening of the backflow restricting valve 6. If the by-pass opening through'this valve 6 has a proper size the liquid level does not reach the upper end of the drill string and any liquid overflow does not occur. At the top of the casing tube assembly 3, there is mounted a funnel 56, the object of which is to collect overflowing liquid in the case the liquid level rises too fast in the drill string. The funnel is provided with an outlet D7 through which liquid is drained to the tank.
As previously mentioned, an annular diamond bit is used and a core is formed throughout the hole. For that purpose, a single-walled core tube is used in order to obtain greatest possible core diameter. This means that the drill string has to be withdrawn from the drill hole every time the core tube has to be emptied. However, the drilling machine of the above described type, is especially well fitted for that purpose in that handling of the drill string sections is fully mechanized, and connection and disconnection of the drill string section is carried out very fast.
On the other hand, the single-walled core tube makes it possible to use a thin-walled drill bit which requires quite a little power with regard to rotation as well as feeding movements. Furthermore, this method makes it possible to continuously obtain information about the penetrated formations.
With the shown drilling apparatus a light and lowviscous flushing liquid is used, the density of which substantially corresponds to that of water. However, the flushing liquid contains some additives for instance for transportation of drill cuttings and for stabilizing the drilled hole. For the stabilizing purpose, the cuttings produced are used as reinforcement in the drill hole walls. The invention is not limited to the shown and described embodiment but can be freely varied within the scope of the claims.
What I claim is:
l. Preventer unit for establishing a seal between a casing tube and a drill stem during pressure drilling through the earth, comprising an elastic packing sleeve rotatably mounted on the casing tube, the outside of said packing sleeve communicating with a pressure fluid source for applying a contact pressure upon the drill string, said preventer unit further comprising a pressure control valve which is connected to said fluid pressure source as well as to the casing tube pressure and which is arranged to automatically adapt the packing sleeve contact pressure in response to the casing tube pressure by controlling a pressure fluid source drainage.
2. Preventer unit according to claim 1, wherein the pressure control valve comprises a housing containing a slidable valve piston, a valve seat and a drain outlet, said valve piston being provided with a valve seat matching surface at its one end which communicates with said pressure fluid source, while its other end communicates with the casing tube pressure, said drain outlet being connected to said pressure fluid source via the valve seat. I
3. Preventer unit according to claim 2 wherein the packing sleeve is provided with at least one leakage opening through which pressure fluid has access to the inner surface of the packing sleeve.
4. Preventer unit according to claim 1,wherein the packing sleeve is provided with at least one leakage opening through which pressure fluid has access to the inner surface of the packing sleeve.
5. Preventer unit according to claim 4, wherein the packing sleeve has two axially spaced contact portions between which said leakage opening is located.
6. Preventer unit according to claim 4 wherein said at least one leakage opening extends from a radially outer surface of the packing sleeve to the inner surface of the packing sleeve. i
7. Preventer unit according to claim 4 wherein said packing sleeve is thicker at its upper end than at its lower end and wherein said at least one leakage opening is located closer to the lower end of said packing sleeve than to the upper end thereof.
8. Preventer unit according to claim 1 wherein said packing sleeve is thicker at its upper end than at its lower end.
9. Preventer unit according to claim 1 wherein said pressure control valve controls said pressure fluid source drainage so as to cause the packing sleeve contact pressure to increase in response to increasing casing tube pressure.
10. Preventer unit according to claim 9 wherein said pressure control valve decreases the pressure fluid source drainage in response to increasing casing tube pressure.
11. Preventer unit according to claim 1 wherein said pressure control valve controls said pressure fluid source drainage so as to cause the packing sleeve contact pressure to decrease in response to decreasing casing tube pressure.
12. Preventer unit according to claim 11 wherein said pressure control valve increases the pressure fluid source drainage-in response to decreasing casing tube pressure.
|Cited Patent||Filing date||Publication date||Applicant||Title|
|US2192805 *||Mar 18, 1936||Mar 5, 1940||Cecil Seamark Lewis Mervyn||Casing head equipment for bore holes or wells|
|US2590215 *||Feb 21, 1947||Mar 25, 1952||Sausa Frank C||Variable throat restricter valve|
|US3145995 *||Apr 24, 1959||Aug 25, 1964||Halliburton Co||Well service cable sealing apparatus|
|US3492007 *||Jun 7, 1967||Jan 27, 1970||Regan Forge & Eng Co||Load balancing full opening and rotating blowout preventer apparatus|
|US3614111 *||Oct 23, 1969||Oct 19, 1971||Regan John||Tool joint stripping stationary blowout preventer with a retrievable packing insert|
|Citing Patent||Filing date||Publication date||Applicant||Title|
|US3963077 *||Jun 18, 1975||Jun 15, 1976||Faulkner Ben V||Method of preventing well bore drilling fluid overflow and formation fluid blowouts|
|US4577700 *||Apr 16, 1984||Mar 25, 1986||Mobil Oil Corporation||Method and system for displacing drilling fluid from a drill string in a well drilling system|
|US5074518 *||Nov 2, 1990||Dec 24, 1991||Hydratech||Proportional annular B.O.P. controller|
|US5944122 *||Dec 4, 1997||Aug 31, 1999||Driltech Inc.||Methods and apparatus for controlling an air compressor in a drill string flushing system|
|US6112810 *||Oct 31, 1998||Sep 5, 2000||Weatherford/Lamb, Inc.||Remotely controlled assembly for wellbore flow diverter|
|US6374925||Sep 22, 2000||Apr 23, 2002||Varco Shaffer, Inc.||Well drilling method and system|
|US6527062||Apr 17, 2002||Mar 4, 2003||Vareo Shaffer, Inc.||Well drilling method and system|
|US7026950||Feb 27, 2004||Apr 11, 2006||Varco I/P, Inc.||Motor pulse controller|
|US7597328 *||Oct 22, 2003||Oct 6, 2009||Dean Foote||Seal assembly for reciprocating shaft|
|US8430175 *||Jan 30, 2008||Apr 30, 2013||Eni S.P.A.||Equipment for intercepting and diverting a liquid circulation flow|
|US8448711 *||Sep 23, 2010||May 28, 2013||Charles J. Miller||Pressure balanced drilling system and method using the same|
|US20040188949 *||Oct 22, 2003||Sep 30, 2004||Dean Foote||Seal assembly for reciprocating shaft|
|US20040217879 *||Feb 27, 2004||Nov 4, 2004||Varco International Inc.||Motor pulse controller|
|US20100012317 *||Jan 21, 2010||Smith International, Inc.||Rcd hydraulic stripping adapter|
|US20100084142 *||Jan 30, 2008||Apr 8, 2010||Eni S.P.A.||Equipment for intercepting and diverting a liquid circulation flow|
|US20120073826 *||Mar 29, 2012||Miller Charles J||Pressure balanced drilling system and method using the same|
|CN103196686A *||Mar 19, 2013||Jul 10, 2013||西南石油大学||Down-hole annular blowout preventer experiment bench|
|CN103573256A *||Sep 18, 2013||Feb 12, 2014||西南石油大学||Underground blowout preventer experiment bench device and operation method thereof|
|CN103573256B *||Sep 18, 2013||Feb 10, 2016||西南石油大学||一种井下防喷器实验台架装置及其操作方法|
|EP0159827A2 *||Mar 28, 1985||Oct 30, 1985||Mobil Oil Corporation||Process and apparatus for drill stem breakout during drilling operation|
|EP2150681A1 *||Apr 4, 2008||Feb 10, 2010||Siem Wis As||Seal for a drill string|
|WO1989009869A1 *||Mar 28, 1989||Oct 19, 1989||Weatherford U.K. Limited||An apparatus for, and method of, filling well casings|
|U.S. Classification||277/324, 175/64, 175/212, 251/1.2, 173/74, 175/218, 175/25, 166/387|
|International Classification||E21B33/02, E21B33/03, E21B33/08, E21B33/06, E21B21/16, E21B21/08, E21B21/00|
|Cooperative Classification||E21B21/16, E21B33/03, E21B21/08, E21B33/06, E21B33/08|
|European Classification||E21B33/03, E21B21/16, E21B33/06, E21B33/08, E21B21/08|
|Feb 23, 1981||AS02||Assignment of assignor's interest|
Owner name: ATLAS COPCO AB
Effective date: 19810212
Owner name: CRAELIUS AKTIEBOLAG, SUNDBYBERG, SWEDEN
|Feb 23, 1981||AS||Assignment|
Owner name: CRAELIUS AKTIEBOLAG, SUNDBYBERG, SWEDEN
Free format text: ASSIGNMENT OF ASSIGNORS INTEREST.;ASSIGNOR:ATLAS COPCO AB;REEL/FRAME:003838/0265
Effective date: 19810212