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Three-phase slug flow in horizontal pipelines downstream of restrictions
Zhou, Denghong
Zhou, Denghong
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2023
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Abstract
Valves are widely used in transportation systems for various reasons. In oil and gas pipelines, they regulate the flow rates or pressures to meet facility requirements or ensure safe transportation. However, their effect on multiphase flow behavior is still not well understood. A major purpose of this study is to systematically investigate the choking effect on downstream multiphase flow behaviors for three-phase slug flow. To achieve this goal, a flow loop consisting of a 43-ft long horizontal pipe with a 2.067-in. inner diameter was constructed, with a 2-in. ball valve installed at the inlet of the test section. Flow patterns, phase distributions, and pressure drop were measured at the test section 123 pipe diameters downstream of the valve. The instrumentation includes a high-speed camera, an Electrical Capacitance Volume Tomography system for phase distribution monitoring, and differential pressure transducers for pressure drop measurements in the test section and across the valve. A total of 67 tests for oil-water two-phase flow and 106 tests for gas-oil-water three-phase slug flow were conducted to systematically investigate the effects of the inlet choke opening, water cut, gas, and liquid superficial velocities on the downstream fluid flow behaviors.
Based on the experimental observations, new models were proposed for oil-water and gas-oil-water flows in horizontal pipes, respectively. The model for oil-water flow focuses on semi-dispersed flow that demonstrates a dispersion layer on top with a free water layer at the bottom. The model for gas-oil-water three-phase flow focuses on slug flow, in which the slug body and film region demonstrates some stratifications in the liquid phase. Parametric studies show that the new three-phase slug flow model captures well the effects of choking opening, water cut, liquid and gas flow rates on the pressure gradient. Both models outperform other existing models.
In summary, this study provides valuable insights into how an inlet choke affects the downstream fluid flow behavior for oil-water two-phase and gas-oil-water three-phase flows in horizontal pipes at different flowing conditions. It also offers two new hydraulic models for predicting phase holdup and pressure gradient with a focus on flow patterns that lack deep understanding.
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