This paper proposes a work flow to address the challenges of over pressure in pipelines using the industry standard multiphase transient simulator. Electric submersible pumps (ESPs) are commonly used to increase the productivity of the wells, which, in turn, will generate higher shutoff pressure in the event of sudden wellhead and subsea line valve closures. The topside piping or the subsea line must be protected from overpressure during valve closures with the ESP still in running condition, so that the pressure does not reach beyond the maximum allowable operating pressure (MAOP) of the pipeline. Hence, it is critical to estimate the peak pressure surge, time to reach peak pressure, emergency shutdown (ESD) set point, and high-integrity pressure-protection system (HIPPS) initiation time.
The topside piping is normally designed with an MAOP significantly lower than the ESP shutoff pressure. In the event of sudden closure of wellhead platform valves or the valves located at the end of a subsea pipeline, the pipeline will be pressurized equivalent to the shutoff pressure of the ESP. In general, to protect the topside piping, several layers of protection are provided, with ESD and HIPPS being very common. The proposed workflow demonstrates the use of a multiphase transient simulator to estimate the peak pressure reached upon wellhead valve closure and the time required to reach the peak pressure for different scenarios so that the ESD initiation set point can be selected optimally. Once the ESD sequence activates, the pressure response in the piping during shutdown also can be estimated in an accurate manner. Further, in case the ESD system fails to respond, the workflow identifies the time to activate the HIPPS system, which will be based on the MAOP and time needed for HIPPS to activate. The workflow has been used extensively in major oil projects with ESP-operated wells to address their ESD and HIPPS activation set-point selection as a part of HAZOP closeout.
The workflow underscores the role of transient simulations in predicting the peak pressures, timing, and optimal ESD and HIPPS activation time to protect wellhead piping, thereby providing critical information to address piping/pipeline integrity challenges.