| 摘要 |
<p>A pressure-actuated head for detonating a gun for perforating a well bore is suspended on a tubing string for lowering down the well. The head includes a detonator pin (24) biased towards a detonator (16) but restrained by dogs (32) maintained in position by sleeve (31) until detonation is required. Detonation is effected by causing or allowing a pressure differential to develop across piston (41) which is sufficient to overcome shear pins (35), retraction of the sleeve (31) being assisted by spring (39). Fluid communication between chambers (44, 45) on respective sides of piston (41) is via choke (52) which is smaller than choke (47) which permits fluid communication between chamber (44) and variable-volume chamber (42b). The choke system allows chamber (45) to be pressurised, but a sudden reduction in well bore pressure to allow the pressure differential across piston (42) to be created slowly.</p> |
