History Matching of a North Sea Flowline Startup

Abstract

Summary This paper presents a history match of the startup conditions measured for a buried offshore North Sea oil flowline. Wellhead and platform-arrival temperatures, pressures, and flow rates were predicted as the production rate varied during startup. The simulation study was performed with the new workstation version of OLGA® (Version 1.4), a transient and steady-state multiphase-fluid-flow simulator. The OLGA simulator rigorously models the transient hydraulic and heat-transfer effects that occur during flowline startup. The effects of surface production devices, such as variable area chokes, were included in this study. Results from steady-state and transient runs are compared with field data. Good agreement was obtained between field and predicted values. This study also illustrates the importance of the phase behavior of the oil, fluid properties, and heat transfer on the simulation performance. Simulated steady-state results compared favorably with results predicted by PIPEPHASE®, a steady-state multiphase-flow simulator. Introduction There is an increasing need to develop more oil and gas fields in harsh offshore environments. The special problems associated with offshore operations pose new challenges in the design and development of economical offshore production systems. Problems specific to the offshore environment include hydrates, wax deposition, and transient slugging. In an offshore cold-water environment, the transient effects during production system startup and shutdown become more pronounced. New transient simulation tools, such as OLGA, are becoming available that aid in the design and modeling of these transient effects. OLGA also can be used to predict the slugging and depressurization behavior of the flowline system to aid in the design of topside facilities. This study uses the OLGA transient multiphase-flow simulator to history match actual startup data from a North Sea field. The transient data matched included mass flow rate, platform temperature and pressure, and wellhead temperature and pressure. This type of data study is useful for designing treatment and prevention programs for hydrate and wax deposition in offshore flowlines.