| Patents for E21B 31 - Fishing for or freeing objects in boreholes or wells (3,788) |
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| 10/31/1991 | DE3941081A1 System involving lost rock drills and probes - employs drill of appropriate dia. with lateral slots for expulsion of drilled-out material |
| 10/22/1991 | CA1291189C Adjustable collet |
| 10/15/1991 | US5056609 Valve assembly for a downhole to remove bore hole subsidence |
| 10/09/1991 | EP0451058A1 Method and apparatus for discarding a tubing in an access well to a salt cavity for gas storage |
| 10/08/1991 | US5054833 Releasable overshot |
| 10/08/1991 | US5054832 Fishing tool for retrieving implements from a hole |
| 10/02/1991 | CN1055033A Drag analysis method |
| 10/01/1991 | US5052485 Jar mechanism |
| 09/17/1991 | CA1289061C Pipe connector and method of applying same |
| 09/05/1991 | WO1991013237A1 Drag analysis method |
| 09/03/1991 | US5044438 Wellhead bowl protector and retrieving tool |
| 08/20/1991 | US5040620 Methods and apparatus for drilling subterranean wells |
| 08/20/1991 | US5040598 Pulling tool for use with reeled tubing and method for operating tools from wellbores |
| 08/14/1991 | CN2082756U Grab-covering type fishing collar |
| 08/07/1991 | CN1053654A Intensely-magnetic waxproof viscosity-reducing rare-earth fishing tool |
| 07/24/1991 | CN1053278A Well casing flotation device and method |
| 07/23/1991 | US5033557 Hydraulic drilling jar |
| 07/10/1991 | CN2080556U Tool for taking bridge plug in or out of well |
| 07/09/1991 | US5029924 Well pipe extractor apparatus |
| 07/09/1991 | US5029642 Apparatus for carrying tool on coil tubing with shifting sub |
| 07/02/1991 | CA1285473C Latch and retrieving assembly |
| 06/30/1991 | WO1991009907A1 Polymer and asphalt reaction process and polymer-linked-asphalt product |
| 06/30/1991 | CA2072579A1 Polymer and asphalt reaction process and polymer-linked-asphalt product |
| 06/18/1991 | US5024277 Running tool for use in well bores |
| 06/11/1991 | US5022473 Adjustable fishing jar |
| 06/04/1991 | US5020599 Drilling tool |
| 05/15/1991 | CN1012627B Detachable permanent magnetic waxproof device for oil well |
| 05/07/1991 | US5013188 Process for replacing a length of buried pipe |
| 05/01/1991 | CA2028924A1 Anti-sand bridge tool and method for dislodging sand bridges |
| 04/27/1991 | CA2028516A1 Releasable well tool stabilizer |
| 04/24/1991 | CN2075694U Centrifugal salvage device for drill tool |
| 04/16/1991 | US5007479 Hydraulic up-down well jar and method of operating same |
| 03/20/1991 | EP0418057A1 Overshot fishing tools |
| 03/20/1991 | CN2073472U Latch jack with rope and drilling rod |
| 03/13/1991 | CN1011993B Cleaning device for internal surface of casing pipes |
| 03/05/1991 | US4997225 From a well |
| 03/05/1991 | CA1281025C Mechanical directional drilling jar |
| 03/01/1991 | WO1991003620A1 Well casing flotation device and method |
| 03/01/1991 | CA2065338A1 Well casing flotation device and method |
| 02/26/1991 | US4995458 Wear bushing retrieval tool |
| 02/12/1991 | US4991649 Oil well packer retriever |
| 02/06/1991 | CN2070815U Swing overshot |
| 02/04/1991 | WO1991002138A1 Apparatus for recovering a wellhead |
| 01/31/1991 | DE3923707A1 Machine for replacing underground pipes - consists of pipe thrust drive with starting and finishing pits |
| 01/30/1991 | CN1011430B Process for avoiding the equipment of well-drilling to block up in the well |
| 01/22/1991 | US4986361 Well casing flotation device and method |
| 01/02/1991 | EP0405799A1 A jar mechanism |
| 12/26/1990 | CN2068144U Rare-earth strong magnet anti-wax pour gluing fishing apparatus |
| 12/20/1990 | DE3940354A1 Underground pipe removal method - involves cutting through in lengthwise direction and forming space between it and earth |
| 12/20/1990 | DE3940321A1 Replacement of underground metal pipes - is achieved by cutting old pipe into two halves, forcing halves apart and inserting new pipe |
| 12/04/1990 | US4974690 Adapter for drilling strings with controllable air passage |
| 11/28/1990 | CN2066483U Device for grapping stone from well |
| 11/13/1990 | US4969514 Apparatus for retrieving pipe sections from a well bore |
| 11/06/1990 | US4967844 Selectively operable ball valve and production packer system |
| 11/06/1990 | CA1275915C Running and pulling tool |
| 10/24/1990 | CN1010114B Flushing method for hydrographic and engineering geological well drilling |
| 10/23/1990 | US4964464 Anti-sand bridge tool and method for dislodging sand bridges |
| 10/10/1990 | EP0391541A1 Wear bushing retrieval tool |
| 10/03/1990 | CN2063164U Grinding and milling combined fishing device |
| 10/03/1990 | CN2063163U Fishing device for pipe well |
| 10/02/1990 | US4960173 Releasable well tool stabilizer |
| 09/25/1990 | US4958691 Fluid operated vibratory jar with rotating bit |
| 08/28/1990 | CA1273288A1 Safety valve for an oil well, and tooling for operating said valve |
| 08/14/1990 | US4947534 Apparatus and method for salvaging concentric piping members |
| 08/07/1990 | US4945985 Pipe down-hole retrieval tool |
| 08/01/1990 | EP0380263A2 Fishing jar |
| 07/31/1990 | US4944543 Ice auger extractor for retrieving augers or similar devices from a bore hole |
| 07/11/1990 | CN2059180U Regenerating drill for waste driven well |
| 07/10/1990 | US4940089 Latching device |
| 07/03/1990 | CA1271134A1 Retrieving mechanism |
| 06/12/1990 | CA1270191A1 Line moving apparatus for wireline supported tools |
| 06/06/1990 | CN1042752A Detonation assembly for explosive wellhead severing system |
| 05/09/1990 | EP0367240A1 Adaptor for drilling strings with a controllable air passage |
| 04/25/1990 | CN2056442U Drill rod automatic gripe/knee-braced device |
| 04/24/1990 | US4919219 Remotely adjustable fishing jar |
| 04/18/1990 | CN2056189U Automatic fishing tool for casing core barrel |
| 04/18/1990 | CN1007633B Viscosity-decreasing and wax-coagulation-preventing device in petroleum transporting pipe |
| 04/11/1990 | CN1041202A Detachable permanent magnetic waxproof device for oil well |
| 04/04/1990 | CN2055533U Permanent-magnet broken-rod fishing tool for well drilling |
| 03/28/1990 | CN2055175U Wheel type well dredge machine |
| 03/21/1990 | CN1040653A Apparatus for avoiding stuck drilling equipment and method of determining probability of unsticking stuck drill pipe |
| 03/20/1990 | US4909320 Detonation assembly for explosive wellhead severing system |
| 03/07/1990 | CN2054071U Double-cylinder type overshot for steel wire |
| 02/14/1990 | EP0354716A1 Apparatus and method for avoiding a drill string becoming stuck during drilling |
| 01/10/1990 | CN2050890U Submersible pump for washing well |
| 01/02/1990 | US4890682 Apparatus for vibrating a pipe string in a borehole |
| 12/26/1989 | US4889199 Downhole valve for use when drilling an oil or gas well |
| 12/26/1989 | US4889198 Drilling jar latch |
| 12/20/1989 | CN2049675U Eccentric valve fishing tool |
| 12/20/1989 | CN2049674U Fishing tool for inclinometer in well |
| 12/06/1989 | CN2048894U Electroheating deblockage apparatus for oil well |
| 11/28/1989 | US4883120 Latching tool for retrieving wellbore devices |
| 11/28/1989 | US4883119 Mechanical latching device operated by dead weight and tension |
| 11/28/1989 | US4883118 Combination tubing cutter and releasing overshot |
| 11/22/1989 | CN2048109U Rotary magnetizing device |
| 11/14/1989 | US4880066 Assembly for directional drilling of boreholes |
| 11/08/1989 | CN2047300U Enveloping type gripper for catching things fallen in well |
| 10/31/1989 | US4877085 Manually operated spear apparatus |
| 10/04/1989 | CN2045421U Multifunction fishing cylinder |
| 09/26/1989 | CA1261819A1 Extraction device for pneumatically actuated drilling tools |