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.

Description:
FIELD OF THE INVENTION 
       [0001]    The present invention relates to 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 a flowline protection system (FPS) at a remote wellhead. 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 well. The system provides a “black box” data recorder function that documents every system test, valve closure and ability of independent protection layers to contain the well topside pressure. 
       BACKGROUND OF THE INVENTION 
       [0002]    In the oil and gas industry, production fluid pipelines downstream of the wellhead are designed to minimize the cost of the pipeline and the cost of a conventional downstream pressure relief valve and flare system. It is therefore necessary that such pipelines be protected against excessive pressure that might rupture the pipe or lift pressure relief devices, which could result in excess flaring or environmental pollution. A design approach used to protect pipelines from over-pressure applies a short-section of thick-walled pipe close to the wellhead, with a dual layer of protection comprising an emergency shutdown (ESD) valve and a high integrity protection system (HIPS). The ESD valve is designed to provide a safe and orderly shutdown of the pipeline in the event process parameters require it. HIPS is typically an automated electro-hydraulic system employing pressure sensors to control the closure of valves to isolate a rapid build-up of pressure in order to protect the downstream pipe from an overpressure which may exceed the pipeline&#39;s pressure rating. A HIPS unit is preferably provided with standardized design and integrally constructed as a modular, factory-assembled unit. 
         [0003]    Prior art valve control techniques rely upon valve limit switches or valve stem position sensors to offer feedback during functional valve testing of the ESD valve and the HIPS valves. In some cases, differential pressure is also checked to confirm valve closure. However, the prior art does not disclose the use of differential pressure measurements across each of the safety systems independent protection layers within an assembled flowline protection system to provide useful and actional feedback of the status of each of the systems and to identify failures. 
         [0004]    It would be desirable to provide a wellhead flowline protection system that includes differential pressure transmitters across each of the safety systems independent protection layer and that incorporates those measurements within expert, state-based logic, local to the wellsite. 
         [0005]    It is therefore an object of the present invention to provide a wellhead flowline protection system and a method for the application of differential pressure indicating transmitters in conjunction with pressure sensors, pressure transmitters and position switches to monitor and control the integrated protection systems at remote wellheads. 
       SUMMARY OF THE INVENTION 
       [0006]    The above objects, as well as other advantages described below, are achieved by the method and apparatus of the invention which provides a flowline protection system comprising an emergency shutdown valve and a high integrity protection system (HIPS). The ESD valve is designed to provide a safe and orderly shutdown of the pipeline in the event process parameters require it. The HIPS offers an additional layer of protection to limit pressure exerted on the piping system connected to a wellhead. The HIPS of the present invention has an inlet for connection to the wellhead and an outlet for connection to the downstream piping system and, in a preferred embodiment, is constructed as a skid-mounted integral system for transportation to the site where it is to be installed. 
         [0007]    The ESD valve is monitored by a valve stem position switch, a downstream pressure switch, and an upstream pressure indicating transmitter, with a differential pressure indicating transmitter measuring differential pressure across the ESD valve. The instruments provide their measurements to a local control panel located at the wellsite. The HIPS comprises at least one set of two valves in series, each valve monitored by a valve stem position switch, and at least one dedicated set of redundant pressure switches located downstream of the valves and by an additional pressure indicating transmitter. In addition, a differential pressure indicating transmitter is placed across each of the HIPS valves, and another differential pressure indicating transmitter is placed across each of the at least one set of two valves that make up the assembled HIPS unit. These instruments also provide their measurements to the local control panel located at the wellsite. The local control panel provides a wellsite “black box” data recorder function that documents and time stamps valve movement and system performance. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0008]    The present invention will be further described below and in conjunction with the accompanying drawings in which: 
           [0009]      FIG. 1  is a schematic diagram of a wellhead flowline protection system in accordance with the invention; and 
           [0010]      FIG. 2  is a process flow diagram of steps carried out in monitoring and controlling a wellhead flowline protection system, using the system and method of the present invention; and 
           [0011]      FIG. 3  is a block diagram of a component of a system for implementing the invention, according to one preferred embodiment of the present invention. 
       
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       [0012]    Referring to  FIG. 1 , a flowline protection system  1  is installed at a petroleum wellhead  2  to protect the integrity of flowline  3 , prevent the loss of petroleum product and prevent environmental damage, as well as reducing the occurrence of activation (lifting) of conventional pressure relief systems. Flowline protection system (FPS)  1  comprises an emergency shutdown (ESD) system  4 , a high integrity protection system (HIPS)  5 , and local control panel  10 . 
         [0013]    ESD  4  includes an ESD valve  20 , monitored by position switch  30 , a pressure transmitter  40  that is tapped from flowline  3  downstream of valve  20 , and a differential pressure indicating transmitter  50  that is placed across valve  20 . The instrumentation interfaces with local control panel  10 . The actuator for valve  20  is not shown, but also interfaces with local control panel  10 . 
         [0014]    HIPS  5  includes redundant inline valves  21  and  22 , each monitored by a valve stem position switch,  31  and  32 , respectively. Redundant pressure transmitters  41 ,  42  are tapped from flowline  3  downstream of valves  21  and  22 . Differential pressure indicating transmitters  51  and  52  are placed across valves  21  and  22 , respectively, and differential pressure indicating transmitter  53  is placed across both valves  21  and  22 . The instrumentation interfaces with local control panel  10 . The actuators for valves  21  and  22  are not shown, but also interface with local control panel  10 . 
         [0015]    ESD  4  is placed upstream of HIPS  5 . ESD  4  has a lower trip setting than HIPS  5 . Pressure indicating transmitter  60  is tapped off flowline  3  upstream of ESD  4 , while pressure indicating transmitter  61  is tapped off flowline  3  downstream of HIPS  5 . Pressure indicating transmitters  60 ,  61  also interface with local control panel  10 . A specification break  6  is placed in flowline  3  downstream of HIPS  5 , at a junction between high-pressure upstream piping and lower-pressure downstream piping. 
         [0016]    Downstream of specification break  6  is a conventional pressure relief and flare system  7 . Pressure relief and flare system  7  includes a pressure relief valve that will have a setpoint above that of FPS  1 . That is, ESD  4  and HIPS  5  will activate before pressure relief and flare system  7  activates. 
         [0017]    During normal operation, all valves  20 ,  21 ,  22  will be open and position switches  30 ,  31 ,  32  will correctly identify that. Pressure transmitters  40 ,  41 , and  42  will all indicate a consistent normal pressure, such as 500 psig, and the differential pressure indicating transmitters  50 ,  51 ,  52 ,  53  will indicate 0 psig (i.e., no difference between the upstream and downstream pressures they are monitoring). Local control panel  10  will indicate safe and normal operation. 
         [0018]    In the event of an overpressure at the well due to downstream blockage, the ESD system should trip first on increasing pressure, as it has a lower trip setting than the FPS. If it trips, then ESD valve  20  should close, which should be indicated by valve stem position switch  30 . Pressure transmitter  40  will indicate the pressure downstream of valve  20 , and differential pressure indicating transmitter  50  shall indicate the pressure difference between the upstream and downstream sides of valve  20 . If valve  20  correctly trips and closes, the downstream flowline  3  shall be pressurized at a level below the HIPS or the pressure relief valve setpoint. The differential pressure indicating transmitter  50  will indicate a differential of the wellhead shut-in pressure and the downstream flowline pressure. Local control panel  10  will indicate trip of ESD  4 , that it requires reset, and will record the time and date of the event. 
         [0019]    If ESD  4  fails to trip in response to an overpressure, such as 800 psig, then the pressure will rise until the blockage results in a HIPS  5  trip, which will close valves  21  and  22 , and which closure will be indicated by position switches  31 ,  32 . Pressure transmitters  41 ,  42  will indicate the pressure downstream of valves  21 ,  22 , and differential pressure indicating transmitters  51 ,  52 ,  53  will indicate the pressure difference each is experiencing. If valve  21  correctly closes, then pressure transmitters  41 ,  42  will indicate the pressure within the downstream flowline  3 , differential pressure indicating transmitter  51  (across valve  21 ) will indicate a differential of the wellhead shut-in pressure and the pressure of downstream flowline  3 . Differential pressure indicating transmitter  52  (across valve  22 ) will not indicate any differential pressure, as the upstream overpressure will be sealed off by valve  21 . Differential pressure indicating transmitter  53  (across both valves  21  and  22 ) will indicate a differential of the wellhead shut-in pressure and the pressure of downstream flowline  3 . If valve  21  fails to close but valve  22  does close, then differential pressure indicating transmitter  51  would not indicate a differential, but differential pressure indicating transmitter  52  would indicate the full differential, as would differential pressure indicating transmitter  53 . In either case, local control panel  10  will indicate failure of ESD  4  to trip, will indicate that HIPS  5  has tripped and requires reset, and will record the date and time of all valve responses. There can also be cases where the downstream pressure exceeds the pressure setpoints of ESD  4  and HIPS  5  for a short period that reaches the downstream pressure relief valve lift setting. This does not change the operation of the ESD or HIPS layers of protection. 
         [0020]    The black box function of local control panel  10  tracks the maximum upstream to downstream pressure rise during a high pressure event. 
         [0021]    In the event of an overpressure in the downstream piping, followed by failure of both ESD  4  and HIPS  5 , the pressure indicating transmitters  60 ,  61  would both indicate the pressure relief valve setting, and the differential pressure indicating transmitters  50 ,  51 ,  52 ,  53  would not indicate any differential. Local control panel  10  would indicate a failure of ESD  4  and HIPS  5 , and that manual isolation of wellhead  2  is required. Local control panel  10  would also timestamp occurrences of downstream pressure exceeding the setting of pressure relief and flare system  7 , so as to document the venting of the well. 
         [0022]    In an alternate embodiment, not shown, HIPS  5  can include two sets of redundant inline valves, the two sets being assembled in parallel, such that for testing purposes one of the sets can be isolated and the valves closed while the other set of valves remains open to allow uninterrupted flow from the wellhead. All valves within the parallel flow paths would be monitored by local control panel  10 , as described above. 
         [0023]    In another embodiment, local control panel  10  supports functional testing of ESD  4  and HIPS  5  systems. Furthermore, the black box functions of the local control panel include time stamping all ESD  4  and HIPS  5  valve movements, whether they occur as part of a functional test, or through a safety demand. 
         [0024]    In another embodiment, local control panel  10  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, in support of a leak detection and repair reporting program. 
         [0025]      FIG. 2  shows a process flow diagram of a method  200  of monitoring and controlling a wellhead flowline protection system. In step  205 , local control panel  10  monitors normal conditions, confirming that position switches indicate that the ESD valve  20  and HIPS valves  21  and  22  are open, and confirming that the pressure switches, pressure transmitters, and differential pressure transmitters are reporting numbers that are within tolerance. If the conditions remain normal, method  200  advances to step  210 , in which local control panel  10  indicates that conditions are normal, such as via a green pilot light on local control panel  10 . As long as conditions remain normal, method  200  will continue to loop back through step  205 . 
         [0026]    If local control panel  10  notes an overpressure condition, method  200  advances to step  215 , in which local control panel  10  signals for a trip of ESD valve  20 . The method  200  advances to step  220 , monitoring valve stem position switch  30 , the pressure switches, pressure transmitters, and differential pressure transmitters to confirm that ESD valve  20  has tripped. If ESD valve  20  is confirmed as tripped, method  200  advances to step  225 , in which local control panel  10  confirms the trip of ESD valve  20 , such as via a red pilot light on local control panel  10 . Method  200  then awaits a reset by an operator or maintenance personnel. 
         [0027]    If a trip of ESD valve  20  is not confirmed, method  200  advances to step  230 , in which local control panel  10  signals for a trip of HIPS valves  21  and  22 . The method  200  advances to step  235 , monitoring position switches  31 ,  32 , the pressure switches, pressure transmitters, and differential pressure transmitters to confirm that at least one of HIPS valves  21  and  22  have tripped. If HIPS valve  21  or  22  is confirmed as tripped, method  200  advances to step  240 , in which local control panel  10  confirms which HIPS valves have tripped, such as via red pilot lights on local control panel  10 . Method  200  then awaits a reset by an operator or maintenance personnel. 
         [0028]    If neither of HIPS valves  21  and  22  trip, method  200  advances to step  245 , in which local control panel  10  indicates that the downstream pressure reached the pressure relief valve setting and that manual isolation is required. 
         [0029]    If a reset is required as a result of steps  225 ,  240 , or  245 , this is accomplished by step  250 . The method  200  will continue to loop back through step  250  until a reset is accomplished. When an operator or maintenance personnel conducts the appropriate actions, ensuring that the pressures are within tolerance, and all equipment and instrumentation is in working condition, the valves are reopened, and the system reset to step  205 . 
         [0030]      FIG. 3  shows an exemplary block diagram of a computer system  400  installed in local control panel  10 . Computer system  400  includes a processor  420 , such as a central processing unit, an input/output interface  430  and support circuitry  440 . Optionally, a display  410  and an input device  450  such as a keyboard, mouse or pointer are also provided. The display  410 , input device  450 , processor  420 , and support circuitry  440  are shown connected to a bus  490  which also connects to a memory  460 . Memory  460  includes program storage memory  470  and data storage memory  480 . Note that while computer  400  is depicted with direct human interface components display  410  and input device  450 , programming of modules and exportation of data can alternatively be accomplished over the interface  430 , for instance, where the computer  400  is connected to the central control room at the processing plant supplied by the wells, or via a detachable input device as is known with respect to interfacing programmable logic controllers. 
         [0031]    Program storage memory  470  and data storage memory  480  can each comprise volatile (RAM) and non-volatile (ROM) memory units and can also comprise hard disk and backup storage capacity, and both program storage memory  470  and data storage memory  480  can be embodied in a single memory device or separated in plural memory devices. Program storage memory  470  stores software program modules and associated data, and in particular stores a first software program module  310  that monitors for normal pressure and calls for the trip of the ESD valve in the event of overpressure; a second software program module  320  that monitors whether the ESD valve has tripped when called to do so, and if not, that calls for the HIPS valves to trip; a third software program module  330  that monitors whether at least one of the HIPS valves have tripped when called to do so, and if not, signals that manual isolation is required; and a fourth software program module  340  that monitors for a manual reset of tripped valves. Software program modules  310 - 340  incorporate the logic recited above in the paragraphs that describe  FIG. 1 . Local control panel  10  includes black box data recorder functions, monitoring the performance of the well and associated ESD and HIPS systems. 
         [0032]    In a preferred embodiment, support circuitry  440  of local control panel  10  includes a fully self-contained battery backup. The battery backup integrates with solar charging panel  445  that provides power at wellsites that are not supplied with utility power. Solar charging panel  445  is preferably mounted remotely from local control panel  10 . 
         [0033]    Thus, it can be seen that with this combination of isolation valves, position switches, pressure transmitters, pressure indicating transmitters, and differential pressure indicating transmitters, local control panel  10  will be able to recognize whether conditions are normal, or whether there is a high pressure demand with proper response by ESD  4 , or whether there is a high pressure demand with a failure of ESD  4  but with a proper response by HIPS  5 , or whether there is a high pressure demand with a failure of both ESD  4  and HIPS  5  that resulted in activation of pressure relief and flare system  7 . 
         [0034]    Another feature of the invention is that pressure indicating transmitter  61  works with local control panel  10  to identify the maximum pressure experienced by flowline  3  during a high pressure event, because even if the ESD and/or HIPS function as required at their setpoints, it is important to know the maximum downstream pressure reached to assess the likelihood of damage to flowline  3  downstream of specification break  6  and to determine if the pressure relief valve lifted, resulting in release of hydrocarbons. 
         [0035]    The system and method can be used for new construction, or can be retrofitted to existing construction at wellsites with reliable power or at remote wellsites without a reliable power supply. 
         [0036]    Although various embodiments that incorporate the teachings of the present invention have been illustrated in the figures and described in detail, other and varied embodiments will be apparent to those of ordinary skill in the art and the scope of the invention is to be determined by the claims that follow.