GB1447993A - Low flow safety valve apparatus - Google Patents

Abstract

1447993 Valves SCHLUMBERGER TECHNOLOGY CORP 29 Oct 1973 [31 Oct 1972] 50172/73 Heading F2V [Also in Division E1] A downhole low flow well safety valve includes a throughflow mandrel 86 carrying a closure head 116 co-operable with a fixed seat 124, the mandrel being maintained in an upper flow-permitting position while the pressuredrop across a choke beam 138 is sufficient to overcome the bias of spring 98. When the flow rate falls to a predetermined value, e.g. upon closure of a separate safety valve in response to excess flow, the spring depresses the mandrel and the closure head engages a PTFE seal ring 128 at 120 and a metal disc 130 at 122, the closure head in this position presenting a net effective area on which the bottomhole pressure acts to hold the mandrel in its closed position. To re-open the valve, the production string is pressurized to depress a piston 146 to a position in which spring fingers 152 are forced radially into groove 156 in the mandrel by entry of projections 158 into a constricted portion 162 of the housing, the piston in its depressed position abutting the mandrel at 168. The production string pressure is then lowered and the bottomhole pressure eventually becomes effective to raise the piston which is accompanied by the mandrel due to the fingers engaging the shoulder 170. When the projections 158 move above shoulder 160, the fingers expand out of the groove under their own resilience and due to interaction of their ends 155 with the shoulder 170, and the piston eventually abuts shoulder 164. At this stage, the flow rate is unlikely to have reached a value sufficient to produce a pressure drop across the choke beam capable of resisting the force of the spring, and so the mandrel will be depressed but is prevented from reaching a fully-closed position by entry of pin 172 into the choke beam, the consequent increase in the pressure drop across the beam kicking the mandrel back upwards. This cycling of the mandrel continues with decreasing amplitude until the flow rate is restored to its normal value. The upper end of the mandrel carries a tubular element 104 which receives a sleeve 110 depending from sub 58 and defines therewith a dead space to prevent sand from settling on the piston.