| 摘要 |
A wellbore traction apparatus 20 comprises traction elements, preferably wheels 14, for engagement with a wellbore wall 16, and drive means, preferably a motor 25. The apparatus 20 is selectably operable in a free-rolling mode in which the wheels 14 are configured to move freely of the motor 25; and a driven mode, in which operation of the motor 25 moves the apparatus 20 in relation to the wellbore. The apparatus is particularly suitable for deploying a tool string in a wellbore. The motor 25 may be coupled and decoupled with the wheels 14 via a clutch mechanism. The apparatus 20 preferably includes at least one magnet 18 to maintain contact of the wheels 14 with the (metallic) wellbore wall 16. The motor 25 may be engaged with the wheels 14 when there is insufficient gravitational force for the apparatus 20 to freely roll down the wellbore. |
