![]()
Abstract A four-layer model was developed for horizontal and near horizontal oil-water flows. The four layers consist of pure water, oil-in-water dispersion, water-in-oil dispersion, and pure oil. The two dispersed layers are known to have significantly different viscosities. Therefore, the four-layer model provides a more comprehensive description and better modeling of the phase distribution and velocity profile as compared to earlier modeling efforts using two- and three-layers. Furthermore, the four-layer model uses a more accurate estimate of the mixture layer viscosities as compared to prior work using a simple volumetric averaging approach. The definition of the boundary between the two mixture layers was based on experimental phase-inversion measurements.
This four-layer model is based on experimental work performed on horizontal oil-water flows in a 10-cm diameter and 40-m long pipeline. Flow characteristics including pressure gradient, phase distribution and velocity profile across the pipe, and phase inversion point were measured for an oil and ASTM seawater system. Input water cuts between 0 to 100% were examined at mixture velocities ranging from 0.4 m/s to 3.0 m/s. The system was maintained at 25°C and 0.136 MPa. The model predictions are in good agreement with the experimental data. A multi-layer model is also proposed as the general form of segregated flow model, which can be used for Computational Fluid Dynamics (CFD) modeling efforts. CFD using a preliminary multi-layer model provided reasonable estimates of pressure drop.
Introduction Compared with gas-liquid flows, a lot fewer studies have been performed on pipeline flows of two immiscible liquid phases. In the case of gas-oil-water systems, the two liquid phases are usually treated as a single mixed fluid without considering interaction between oil and water. However, with the common occurrence of oil-water flows in the oil field, the distinct behavior of the oil-water flows must be considered when designing and operating wells, production facilities and pipelines.
Flow mechanisms of oil-water are significantly different from those of gas-liquid systems. These different mechanisms arise largely because oil and water have physical properties (density and viscosity) which are similar as compared to gas-liquid flows where the two phases have very different physical properties. For example, the often encountered slug flow for gas-liquid horizontal flows are rarely observed for oil-water flows in horizontal pipes1–3. Furthermore, oil-water flows exhibit other behaviors such as the formation of dispersions or emulsions, and phase inversion. The well-developed models for gas-liquid system, thus, can not be directly applied to oil-water system.
Two relatively simple models, the homogenous model and the two-layer segregated model, have been widely used both for organizing experimental results and for predicting design parameters for oil-water flows. For extremely low flow rates, oil and water flow as pure phases in two well-separated layers, and the two-layer segregated model is suitable. At relatively high flow rates, oil and water are completely and uniformly mixed throughout the pipe cross-section and the homogeneous flow model can be applied, provided that the mixture viscosity is known.
However, in most oil-water flow cases, the mixture velocities are neither extremely low nor extremely high, but of moderate speeds where non-trivial flow patterns exist; for example semi-segregated, semi-mixed and mixed flow patterns as shown in Figure 1. Based on this observation, Vedapuri4 developed the three-layer model to predict the pressure drop and hold up, and he showed that predicted water film thickness agreed with the experimental data. The three-layer model consists of a pure water layer, a pure oil layer, and an intermediate mixture layer.
Site News