| 摘要 |
A ground subsidence wellhead has a lower wellhead assembly mounted on the ground for supporting a casing in tension and an upper wellhead assembly threaded to the top of the casing and spaced from the lower wellhead assembly. The lower assembly has a casing head with aconical bowl for receiving a slip. The slip is wedged between the casing head and casing by compression springs acting between the casing head and the slip, and has asymmetrical teeth for engaging the casing to prevent downward, but allow upward, movement of the casing in the slip.
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