| 摘要 |
<p>A safety valve (10) adapted for placement above a wellhead. The valve has a housing (11) having coaxial upper (24) and lower (23) vertical housing passages, the diameter of the upper and lower passages being sufficiently large to pass a tubing hanger (4) with tubing for landing in the wellhead. The valve also has a control element means disposed between said upper and lower vertical housing passages for preventing or allowing fluid flow through a passage smaller than the lower vertical housing passage and for providing full diametrical access via the upper housing passage to the lower housing passage. In a ball control element embodiment of the invention, a rotatable ball (21) is disposed between upper and lower passages and lateral outlets in the housing. The ball has a removable insert (22) such that in one position of the ball, the insert can be removed to provide full bore access in line with the well. The housing may be incorporated with the tubing head or may be attached to the top of the tubing head. During insertion of or workover of tubing, a blowout preventer may be attached to the top of the valve housing. The ball may be rotated for closing off the flow path from the well below. A christmas tree may be installed after the blowout preventer is removed. </p> |
