Flow assurance studies for CO2 transport

In order to compensate for the relative lack of experience of the CCTS community, Flow Assurance studies of new CO2 pipelines and networks are a very important step toward reliable operation. This report details a typical approach for Flow Assurance study of CO2 transport pipeline. Considerations to take during the design of a pipeline are highlighted, with an emphasis on operability of the system. The steady state aspects of a pipeline operation are first addressed, putting some highlight into the nature of CO2 flow in wells, and its intrinsic effects on pipeline outlet conditions. Two-phase flow in the wells cannot be avoided for a wide range of reservoir pressures, and the implications of this on the operability of a pipeline are being discussed. Specific aspects relating to the injection into multiple wells are also looked at. It is concluded that it is not more challenging than a single well operation and that balancing effects between wells may even rend the operability of the entire system simpler. Finally, transient phenomena during dynamic operations are addressed, with special emphasis on an Emergency Shut Down process as a worst transient scenario. Again, the worst case is obtained in the case of a single well, as the presence of additional wells provide a buffering effec

Mitigation of Terrain Induced Slugging Using Mixer Devices

The present work focuses on experimental evidence of slug mitigation via various devices. The slug mitigation potential of a number of mixers was tested using a laboratory scale air/water setup to compare their effect on the incoming slugs just upstream of the separator inlet. Dedicated methods and key performance indicators were developed to characterize the slug properties and evaluate the mixers effectiveness. Such mitigation is especially interesting for the purpose of producing oil and gas from thin oil rims, in which wells are often drilled following the geological structure of the oil-bearing layer. These wells consequently contain many long, near-horizontal sections, through which the transport of the oil gas mixture often takes the form of slug flow, i.e. Large volumes of liquid travelling at the velocity of the gas phase. As the gas cannot bypass the slugs, they are generally produced to the topside facilities, where they have a detrimental effect on the mechanical integrity of the equipment and on the metering accuracy due to their large volume. Mitigating slug flow has therefore great potential in optimizing the production from thin-oil rims on the short term. The present study shows that consistent reductions can be obtained on pressure fluctuations due to slugging, highlighting the benefit of these devices. It was observed that the slug speed could be significantly reduced, as well as the liquid hold-up within the slugs, especially when gas lift is used in conjunction with the devices. The physical mechanisms behind these effects are isolated, leading to optimization of the device geometry, for application to full scale. The demonstrated potential of the mixer devices can yield a quantifiable reduction of the impact of slugging on mechanical integrity and metering accuracy. As a consequence, production limitations due to slugging problems can be alleviated, resulting in potential for increase in oil production rates from thin oil rims

Effect of drag-reducing polymers on Tubing Performance Curve (TPC) in vertical gas-liquid flows

This paper discusses the effect of drag reducing polymers on the Tubing Performance Curve (TPC) of vertical air-water flows at near atmospheric conditions. The effect of polymer concentration, liquid and gas flow rates on the pressure drop curve (Tubing Performance Curve) was investigated experimentally. The results showed that polymers tend to reduce the interfacial roughness, which is counter productive in most cases as it increases the range where gravity dominates the flow. However, at higher gas rates, experiments suggest that lower the wall-liquid shear stress translates into a decrease in the pressure drop, making the use of polymers beneficial to extract early gas at a faster rate. These results can be explained by an analytical model. The derived understanding of the effect of polymers on 2-phase flows can be generalized to other flow regimes and holds promises as a valuable way to address other multiphase production issues

Cold restart of viscous multiphase flowline by hot water flushing

The main objective of this paper is to understand the physical processes of shut-in and restart of viscous multiphase flowline. For this purpose, experiments were performed on shut-in and restart processes in the Multiphase Flow Rig at Statoil's research Centre in Porsgrunn. Real crudes were used with oil viscosity up to 30,000 cP at room temperature. Different physical processes were identified that significantly influence the shut-in and restart. The performance of the numerical tools (OLGA code and CFD) is assessed against the experimental data and theory. The OLGA code is found to predict well the shut-in process, but over-predicts the restart time. © BHR Group 2013

The shape and motion of gas bubbles in a liquid flowing through a thin annulus

We study the shape and motion of gas bubbles in a liquid flowing through a horizontal or slightly inclined thin annulus. Experimental data show that in the horizontal annulus, bubbles develop a unique ‘tadpole-like’ shape with a semi-circular cap and a highly stretched tail. As the annulus is inclined, the bubble tail tends to vanish, resulting in a significant decrease of bubble length. To model the bubble evolution, the thin annulus is conceptualised as a ‘Hele-Shaw’ cell in a curvilinear space. The three-dimensional flow within the cell is represented by a gap-averaged, two-dimensional model, which achieved a close match to the experimental data. The numerical model is further used to investigate the effects of gap thickness and pipe diameter on the bubble behaviour. The mechanism for the semi-circular cap formation is interpreted based on an analogous irrotational flow field around a circular cylinder, based on which a theoretical solution to the bubble velocity is derived. The bubble motion and cap geometry is mainly controlled by the gravitational component perpendicular to the flow direction. The bubble elongation in the horizontal annulus is caused by the buoyancy that moves the bubble to the top of the annulus. However, as the annulus is inclined, the gravitational component parallel to the flow direction becomes important, causing bubble separation at the tail and reduction in bubble length