Simulation Study of Subsea Control System Based on SimulationX

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1 Simulation Study of Subsea Control System Based on SimulationX Xin Wang, Xin Zuo*, Hua-qing Liang Department of Automation, China University of Petroleum, Beijing 02200, China *Corresponding author ( Abstract This paper studies the subsea multiplex electro-hydraulic control system, which consists of the surface equipments and subsea components. In order to reduce the risk of the system and increase the reliability of the hydraulic control system, software SimulationX is used to simulate the process of hydraulic control system. Analyze the gate valve s process of opening/closing based on the subsea hydraulic libraries in SimulationX. In addition, SimulationX provides us an effective method to get hydraulic pressure characteristics in subsea control module (SCM), which is important for the reliability of the SCM. Key words: Subsea control system, Multiplex electro-hydraulic control system, Return pressure, SimulationX. INTRODUCTION Most of the new oil fields are located in deep water and are generally referred to as deepwater systems. The control system can control valves on the manifold, Xmas tree and sea tube terminal, and collect the temperature/pressure (Zhou, 2009). In addition to meeting the basic function, equipments and control signals failure or other potential safety hazard occur, the control system must have the safety recovery function. Moreover, development of these fields sets strict requirements for verification of the various systems functions and specifications. The high costs and time involved in changing a pre-existing system due to the specialized vessels with advanced onboard equipment. A full scale test (System Integration Test-SIT) does not provide satisfactory verificat ion of subsea systems because the test, for practical reasons, cannot be performed under conditions which the system will operate (Liu, 2009). In this paper, we will pay attention to the subsea production control system, subsea mu ltiplex electrohydraulic control system has been the more efficient and reliable system for subsea oil&gas production system. Hydraulic control part provides hydraulic power for the hydraulic actuator, which the hydraulic circuit pressure effects the speed of response time of the gate valve opening/closing. We will build the model of hydraulic circuit in SCM and the hydraulic actuator, then hydraulic circuit and gate valve opening/closing process are analysied based on SimulationX. 2. SUBSEA PRODUCTION CONTROL SYSTEM DESCRIPTION Subsea production control system is generally divided into four categories: direct hydraulic control system, piloted hydraulic control system, multiplex electro-hydraulic control system and all electric control system. The first three systems, actuators under water are driven by hydraulic, the differences are that control signal generation, transmission and execution of processes. In the fourth system, actions under water are achieved by motor, but its reliability and the service life are not recognized by the industry. Currently the most widely used is multiplex electro-hydraulic control system. Figure presents a typical deepwater system for production of oil and gas. Subsea installations are linked with the surface vessel using an umbilical. Figure. Subsea control system for oil and gas production Figure 2 is the Sche matic diagram of multiplex electro-hydraulic. The hydraulic valves on the Xmas tree of 307

each well are controlled by an electro-hydraulic subsea control model (SCM) which receives hydraulic power, electric power, and co mmunications via umbilical.

2 each well are controlled by an electro-hydraulic subsea control model (SCM) which receives hydraulic power, electric power, and co mmunications via umbilical. SCM on the Xmas tree controls each valve on the tree, and collect data of temperature and pressure, then these data will be transmitted to the master control station(mcs) through umbilical cable (Hu, 202). Figure 2. The Schematic diagram of multiplex electro-hydraulic The main hydraulic equipment of multiplex electro-hydraulic: Hydraulic power unit (HPU), topside umbilical termination assembly (TUTA), umbilical, subsea umbilical termination assembly (SUTA ), flying leads, SCM and hydraulic actuator. 2.. Hydraulic Power Unit (HPU) HPU provides high/low pressure hydraulic for operation of valve under water. 2.2 Umbilical Umbilical cable is a pipe, connecting platform control equipment and subsea control system. It transmits electric, hydraulic, control signals and chemical reagent. Figure 3. Cross section of umbilical 2.3 Subsea Control Model (SCM) In order to monitor and control the subsea production system, every Xmas tree needs one SCM. The function of SCM has been illustrated in the previous. When need to open/close the valve on the tree, electro-hydraulic directional control valve (DCV) in the SCM gets the signal from SEM in the SCM, DCV changes the channel so that hydraulic drive actuator. SCM is so important that we call it the brain of subsea production system. 308

master valve (AMV), annulus wing valve (AWV), annulus access valve (AAV), production choke valve (PCV) and che mical injection valve (CIV).

3 Figure 4. Subsea Control Model 2.4 Valves On the Tree Figure 5 is the structure diagram of Xmas tree. SCM receives instruction from MCS in platform, control system drives surface-controlled subsurface safety valve (SCSSV), production master valve (PMV), production wing valve (PW V), annulus master valve (AMV), annulus wing valve (AWV), annulus access valve (AAV), production choke valve (PCV) and che mical injection valve (CIV). At the same time, valves positions, oil&gas flow and pressure information are transmitted to MCS by SCM and umbilical (Liu Guoheng, 202). Figure 5. Xmas tree-p&id 3. THE SUBSEA HYDRAULIC CONTROL SYSTEM Figure 6 is the simplified version of SCM hydraulic system. DCV controls hydraulic line on/off. Figure 6. SCM hydraulic system 309

4 In production operation, the valve action time has an important influence on subsea control system s stability and reliab ility. In the process of gate valve opening and closing, hydraulic supply pressure and return pressure will change, and it is significant for selection of hydraulic components. 3. Deepwater Gate Valve In subsea production, gate valve has hydraulic cav ity and spring chamber. In the process of opening, its flow equation is: A A dy Q () dt Its time equation: A A L t (2) Q In the process of closing, its flow equation is: Its time equation is Q A A dy (3) t dt A A L (4) Remarks: Q is the flow in the process of opening, A is the piston area, A is the piston rod area, y is the piston position, Q is the flow in the process of opening. 3.2 Return Pressure of HP Hydraulic System Q Figure 7. SCM HP hydraulic system In the closing process of gate valve, spring push the valve stroke and then close the gate valve. In figure 7, compensator compensates sea water pressure. Define sea water pressure is Psea, pressure of check valve is P, compensator s pressure is same with Psea, when the valve was fully opened, the pressure of return line is: P P P (5) r In this paper, assume that the high pressure pump flow of HPU is 6.5L/min, and the low pressure pump is 3.5L/min. The diameter of a pipe is /2 inch, long of umbilical is 2.5Km. P is 290 psi. 4. SIMULATION OF THE SUBSEA HYDRAULIC CONTROL SYSTEM The SimulationX Global Subsea Center is an alliance of ITI and Agito providing offshore-specific SimulationX libraries (Wang, 202), comprehensive consulting and engineering services. The Subsea Hydraulic Library is an intuitive library where the user can find the most used special components in a subsea hydraulic system. sea 30

5 Figure 8. Schematic simulation of hydraulic system 4. Simulation of Gate Valve Opening/Closing Process Figure 9 is simulation of one valve s processing of opening and closing. Set up the stroke length of gate valve modular in simulation 5-/8, other parameters are the default settings. Figure 9. Schematic simulation of hydraulic system Figure 0 is the spring chamber pressure in opening process of gate valve, spring cavity hydraulic shock between 0 to 2 seconds then stable after 2 seconds. Figure 0. Spring chamber pressure in opening process of gate valve Figure shows that it takes about 2 seconds for the process of opening. 3

6 Figure. Valve stroke length in the process of opening In addition, the close signal starts at 200 seconds, Figure 2 is the valve stroke length curve in the process of opening/closing. It takes about 3 seconds for closing. Figure 2. valve stroke length curve in the process of opening/closing Figure 3 is the flow curve of hydraulic cavity in the process of opening/closing, hydraulic shock at beginning of opening/closing time. Figure 3. Flow curve of hydraulic cavity in the process of opening/closing 4.2 Simulation of Accumulator s Hydraulic Pressure From Figure 4-5, accumulator s hydraulic pressure decrease during the opening process of gate valve, then recovery along with time. 32

7 Figure 4. Flow curve of accumulator in the process of opening Figure 5. Flow curve of accumulator in the process of opening/closing 4.3 Simulation of Hydraulic Supply/Return Pressure From figure 6-7, hydraulic line s pressure changes along with the motion curve of gate valve stroke, and its return hydraulic pressure will change on the basis of subsea equipment, such as gate valve, check valve. Figure 6. Pressure curve of hydraulic line in the process of opening/closing 33

8 Figure 7. Pressure curve of return line in the process of closing 5. CONCLUS ION In this paper, subsea multiplex electro-hydraulic control system has been studied. Subsea hydraulic control system provides hydraulic power for the hydraulic actuator, which the hydraulic circuit pressure effects the speed of response time of the gate valve opening/closing. The hydraulic actuator model has been build and its opening/closing process has been studied based on SimulationX, and gets following conclusions: () Gate valve has hydraulic cavity and spring chamber, in the opening process, valve stroke length needs less time to get the target than the flow pressure of hydraulic cavity; (2) In the closing process of gate valve, the time for the valve length to get the off state, is approximately consistent with the time for flow curve to get stable; (3) Hydraulic return pressure is determined by the check valve and the sea pressure. REFERENCE Carre, D., & Osullivan, J. (2009) Moho Bilondo: Subsea Production System Experience. Offshore Technology Conference. Offshore Technology Conference. Hu Xuefeng (202) The composition and analysis of multiplex electro-hydraulic. Shipbuilding of China,53(), pp. 2. Liu Baosheng (2009) SimulationX Multidisciplinary modeling and simulation tools. Digital Manufacturing Industry, (9), pp.34. Liu Guoheng,Luo Xiaolan (202) The top horizontal Xmas tree underwater plug design elements. China Petroleum Machinery,40(), pp. 37. Wang Hongjun (202) SimulationX and hardware s Application in the loop simulation in the research design of servo press. Journal of Mechanical engineering, 48(6), pp. 5. Yasseri, S. (204). Application of systems engineering to subsea development. Underwater Technology, 32(2), pp Zhou Meizhen (2009) Hydraulic control researchof subsea actuator. China offshore platform, 24(3), pp. 3. Zhao, H. L., Wang, X.(204) Dynamic simulation research on deepwater gate valve actuator based on simulationx. Ocean Engineering Equipment & Technology. 34

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OIL & GAS Introduction to Subsea Production Systems 04 Christmas Tree (XT) Systems August 2015 DNV GL 2013 August 2015 SAFER, SMARTER, GREENER Christmas Tree Systems Onshore tree Offshore tree Subsea tree