Patent ID: 9347286
Filing Date: 2016-05-24
CPC Classification: E21B

Claim Text:
1. A flow stop valve for placement in a downhole tubular operating in a dual fluid density system, wherein the flow stop valve is in communication with a pressure difference between fluid outside the downhole tubular and inside the downhole tubular at the flow stop valve, or between fluid above and below the flow stop valve inside the downhole tubular, wherein the flow stop valve comprises: a first valve element arranged such that the pressure difference acts across at least a portion of the first valve element, wherein the first valve element comprises a first passage to transmit fluid from a first port in a first side of the first valve element through a second side of the first valve element to a first chamber, the first port being positioned adjacent to a low pressure flow region when the flow stop valve is in an open position such that the low pressure flow region is in fluidic communication with the first chamber via the first port and the first passage; a second valve element, wherein the low pressure flow region is at least partially defined in a gap between the second valve element and the first valve element when the flow stop valve is in the open position, and wherein the first valve element is configured to move in a downhole direction with respect to the second valve element to actuate the flow stop valve from a closed position to the open position; and a resilient member disposed in the first chamber, the resilient member applying a biasing force on the first valve element, the biasing force being oriented so as to force the first valve element toward the second valve element, such that the biasing force causes the flow stop valve to actuate to the closed position when the pressure difference is below a threshold value.