Wellhead flowline protection system

Abstract

A system and method for the application of differential pressure indicating transmitters in conjunction with pressure sensors, pressure transmitters and position switches to monitor and control the flowline protection systems at remote wellheads. The system communicates with a local control panel in proximity to the wellhead, as well as to a central control room at the processing plant supplied by the wells. The system provides a black box data recorder function that documents every system test, valve closure, and the ability of the independent protection layers to contain the wellhead topside pressure. In addition, the system provides a means to limit release of hydrocarbons via a conventional pressure relief and flare system, and documents high pressure events when pressure relief valve setpoints are reached.

We claim: 
     
         1 . An automated flowline protection system for protecting a flowline at an oil or gas wellhead, the flowline protection system comprising an emergency shutdown system, a high integrity protection system, and a local control panel;
 the emergency shutdown system comprising: an emergency shutdown valve installed downstream of the wellhead on a high pressure segment of the flowline; an emergency shutdown valve actuator; an emergency shutdown valve stem position switch that monitors the position of the emergency shutdown valve; a first pressure transmitter installed on the high pressure segment of the flowline between the wellhead and the emergency shutdown valve; a first pressure switch installed on the high pressure segment of the flowline downstream of the emergency shutdown valve and upstream of the high integrity protection system; and a first differential pressure indicator installed across the emergency shutdown valve; wherein the emergency shutdown valve actuator, the emergency shutdown valve position switch, the first pressure transmitter, the first pressure switch, and the first differential pressure indicator interface with the local control panel; and   the high integrity protection system comprising: at least one set of a first and second inline valve installed in series on the high pressure segment of the flowline, downstream of the emergency shutdown system; a first inline valve actuator; a second inline valve acuator; a first and second inline valve stem position switch respectively monitoring the positions of the first and the second inline valves; a second pressure transmitter and a second and a third pressure switch installed downstream of the high integrity protection system and upstream of a spec break separating the high pressure segment of the flowline from a downstream lower pressure segment of the flowline; a second and a third differential pressure transmitter installed respectively across the first and the second inline valves; and a fourth differential pressure transmitter installed across the series installation of the first and the second inline valves; wherein the first and the second inline valve actuators, the first and the second inline valve position switches, the second pressure transmitter, the second and the third pressure switches, and the second, the third, and the fourth differential pressure indicators interface with the local control panel.   
     
     
         2 . The system of  claim 1  in which the high pressure segment of the flowline is rated for a maximum operating pressure that corresponds to a maximum shut-in pressure of the wellhead. 
     
     
         3 . The system of  claim 1 , wherein the local control panel is configured such that in the event of an overpressure at the well as indicated by any of the first, second, or third pressure switches, the local control panel signals the emergency shutdown valve actuator to close the emergency shutdown valve and the local control panel monitors the emergency shutdown valve stem position switch, and monitors and records pressure to confirm that closure of the emergency shutdown valve has occurred, and
 if the local control panel determines that the emergency shutdown valve fails to close following the overpressure event, the local control panel signals the first and second inline valve actuators of the high integrity protection system to close the first and second inline valves, and the local control panel monitors the first and second inline valve position switches, and monitors and records pressure to confirm that closure of the first and second inline valves has occurred, and   if the local control panel determines that neither of the inline valves closes following a failure of the emergency shutdown valve to close following the overpressure event, the local control panel signals that manual isolation of the flowline protection system is required.   
     
     
         4 . The system of  claim 3 , wherein:
 the local control panel includes a clock;   records a timestamped record of all signals to the emergency shutdown valve actuator to close the emergency shutdown valve and timestamps all movements of the emergency shutdown valve as indicated by the emergency shutdown valve stem position switch; and   records a timestamped record of all signals to the first and second inline valve actuators of the high integrity protection system to close the first and second inline valves, and timestamps all movements of the first and second inline valves as indicated by the first and second inline valve position switches.   
     
     
         5 . The system of  claim 1 , wherein the local control panel is programmed to perform functional testing of the emergency shutdown valve and the first and second inline valves of the high integrity protection system. 
     
     
         6 . The system of  claim 5 , wherein:
 the local control panel includes a clock;   records a timestamped record of all functional testing signals to the emergency shutdown valve actuator to close the emergency shutdown valve and timestamps all movements of the emergency shutdown valve as indicated by the emergency shutdown valve stem position switch; and   records a timestamped record of all functional testing signals to the first and second inline valve actuators of the high integrity protection system to close the first and second inline valves, and timestamps all movements of the first and second inline valves as indicated by the first and second inline valve position switches.   
     
     
         7 . The system of  claim 1 , wherein the local control panel includes a clock, and monitors, timestamps, and records maximum upstream to downstream pressure rise during a high pressure event. 
     
     
         8 . The system of  claim 1 , further comprising a pressure relief valve and flare system downstream of the spec break, wherein the local control panel includes a clock, and wherein the local control panel monitors, timestamps, and records flaring that occurs when any of the second pressure transmitter and the second and the third pressure switch installed downstream of the high integrity protection system and upstream of a spec break indicate a downstream pressure that exceeds the setting of the pressure relief valve and flare system. 
     
     
         9 . The system of  claim 1 , wherein the local control panel includes a clock, and wherein the local control panel is configured to monitor for leaks in the flowline, emergency shutdown system, or high integrity protection system, and to timestamp and record any detected leaks.