For many years, the pipeline industry has worked on leak detection technologies to accurately predict and mitigate the occurrence of leaks in pipelines. However, this is not an easy task since many systems have different characteristics and the existing technologies have specific ranges of applications. Nevertheless, the technological progress has reduced the gap between accurate leak predictions and false alarms in single-phase systems. A new challenge has been growing leak detection technologies with multiphase production systems since many of the current leak detection techniques limit their applications to single-phase systems. Although, there are some technologies that claim multiphase capabilities; it is not clear yet how they overcome the challenges imposed by the hydrodynamics of a multiphase system. Therefore, the main objective of this paper is to assess a multiphase system and simulate leak events to gain a better understating of its hydrodynamic behavior during the transient leak event.

The studied multiphase system operates with three phases: oil, water, and gas; thus, flow patterns vary from stratified to severe slugging for some operating conditions and locations. The 30-in. pipeline system starts from an offshore production-separation platform which is located approximately 55 miles offshore and delivers its production to a separation processing plant on-shore. A leak condition was simulated in the middle of the trunkline to determine its effect on the hydrodynamics of the system and both ends facilities. Different gas oil ratios (GOR) and pipeline pressures were evaluated to determine the effect of those conditions on the leak detectability. One key parameter to accurate determination of a leak is to precisely differentiate or filter a leak signal (pressure, flow rate, pressure wave, etc.) from normal pipeline data noise. In this case that was even more challenging since a slugging condition was observed in the normal operation of the multiphase system which generates flow and pressure fluctuations that could overlap the leak data. This paper presents the results obtained for the steady-state prior leakage and transient leakage cases. In addition, a sensitivity analysis of different gas oil ratios is presented as well to map out its effect on the leak detectability.

Introduction and Background

A concern for operating a multiphase production system under higher pressures and gas-oil-ratios was expressed during a capacity increase study since that would reduce its reliability and integrity while increasing the operational risk. The offshore field demonstrated a potential for producing 5-7% more crude oil and gas than that of its original design capacity and the capacity study indicated a good feasibility of operating at those conditions. Therefore, a risk assessment of the system was required to ensure it function within safety compliance and quantify the risk associated with these new operating conditions. In addition, a part of the IMP possible mechanical failures (leaks) and their effect has to be evaluated to determine the consequence of a leak and how to better control it. Consequently, a leak simulation analysis was conducted to understand how the system will behave under leak conditions, to estimate the time to possibly detect a leak with the current technology, and to get an approximation of the amount of product spill for mitigation actions.

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