| 摘要 |
<p>The invention relates to circulating subs for use in wellbores, particularly but not exclusively to circulating subs used during downhole drilling operations. The apparatus of the present invention is characterised by controlling means for controlling the movement of a sleeve between first (closed) and second (open) positions; the controlling means comprising: a control member (24) slidably mounted in a body (4) and moveable by fluid pressure in the body (4) in a first axial direction relative to the body (4); a spring (38) biasing the control member (24) in an opposite axial direction of the body (4); a pin (48) secured to one of the body (4) and the control member (24); and a control groove (32) in which a portion of the pin (48) is received formed in the other of the body (4) and the control member (24), the central groove (32) being shaped to limit axial displacement of the control member (24) in response to pressure variations in the body (4) such that only after a predetermined number of movements of the control member (24) to a first limit position is the control member (24) able to move to a second limit position to displace the sleeve (52) into the second position of the sleeve (52). The present apparatus thereby has the advantage over the prior art of being reliable and convenient to use, and compatible with the use of wireline or coil tubing tools. The apparatus may also be reset many times whilst remaining in a downhole position and is therefore less time consuming and less expensive to use than the prior art.</p> |
