A pneumatically governed, wireline-retrievable subsurface safety valve directly operated by local tubing pressure change at the valve has been developed for natural gas storage wells. This paper provides a detailed operating theory and description of the valve, which utilizes a control chamber volume of well-effluent to maintain a history of well bore pressure. The "memorized" pressure is constantly compared to current flowing tubing pressure via a sensing piston. When an established differential pressure value is exceeded, the sensing piston allows valve closure and control of the well. A "flapper-type" closure valve with an automatic reset mechanism allows the tool to be placed back in service with manipulation of tubing pressure.

Application of this technology is best suited to gas storage wells with a routine flow rate change caused by seasonal variation in gas demand. In these wells a fixed-rate flow sensing valve is not preferred.

The viability of this technology has been demonstrated by prototype testing in a producing gas storage well.

This new concept will be of particular interest to gas storage well operators seeking simple, subsurface-controlled well protection.

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