Low-Dimensional Modeling of Two-Phase Flow in Pipelines

Multiphase flow in pipelines is an ubiquitous part of any oil and gas production system. Developing fast, yet accurate multiphase flow models having utility in system design, control design, and system health-monitoring is therefore an important engineering and scientific challenge, particularly when the pipelines are parts of a complex subsea architecture. Presented in this dissertation are multi-physics reduced-order fluid and thermal models of one-dimensional transient two-phase flow in pipelines. The proposed fluid model is comprised of a steady state multiphase flow mechanistic model in series with a transient reduced-order single-phase flow model. The low-dimensional model parameters are realized by developing equivalent fluid properties (i.e., viscosity, density and bulk modulus) that are a function of the flow pattern, steady-state pressure gradient, and liquid holdup identified through the mechanistic model. The fluid model is then coupled with a two-phase flow heat transfer model via a multi-physics integration block used to update the fluid properties along the pipeline based on the predicted pressure and temperature conditions. The model ability to reproduce the dynamics of multiphase flow in pipes is first evaluated upon comparison to OLGA. The two models show a good agreement of the steady-state response and the period of oscillation indicating a similar estimation of the pipeline natural frequency. However, they present a discrepancy in the overshoot values and the settling time due to a difference in the calculated damping ratio. Both models are then compared to transient two-phase flow data collected at the National University of Singapore flow loop. It is concluded that the low-dimensional model is characterized by a superior overall performance when compared to OLGA. The developed model accuracy improves when considering a higher order but is associated with a higher simulation time. The established multi-physics models are used for the design, modeling, simulation, and optimization of multiple-wells subsea architectures with a High Integrity Pressure Protection System (HIPPS) as an alternative to reduce the subsea capital expenditure (CAPEX). The utility of the developed low-dimensional models is the reduced computational burden of estimating transient multiphase flow in pipelines, thereby enabling real-time estimation of pressure, temperature, and flow rate.