Fail safe regulator for deep-set safety valve having dual control lines

A sub-surface safety valve apparatus, comprising:

• a closure movable between closed and opened conditions relative to a bore in the sub-surface safety valve;
• a first actuator tending to close the closure in response to first hydraulic pressure communicated by a first control line to the sub-surface safety valve;
• a second actuator tending to act against the first actuator in response to second hydraulic pressure communicated by a second control line to the sub-surface safety valve;
• and
• a regulator repeatedly operable between at least two repeatedly operable conditions and regulating hydraulic communication between the first and second control lines in response to a pressure differential therebetween, the regulator in at least one of the repeatedly operable conditions permitting hydraulic communication from the first control line to the second control line in response to the second hydraulic pressure falling below a pressure level related to hydrostatic pressure associated with the first control line.

A sub-surface safety valve hydraulic control method, comprising:

• actuating the sub-surface safety valve open by communicating fist hydraulic pressure to the sub-surface safety valve via a first control line;
• offsetting hydrostatic pressure associated with the first control line by communicating second hydraulic pressure to the sub-surface safety valve via a second control line;
• and
• regulating a hydraulic pressure differential between the first and second control lines with at least two repeatedly operable conditions by—
• permitting in one of the repeatedly operable conditions hydraulic communication from the first control line to the second control line in response to the second hydraulic pressure falling below a pressure level related to the hydrostatic pressure associated with the first control line;
• and
• restricting in another of the repeatedly operable conditions hydraulic communication from the second control line to the first control line.