Annulus flow commonly occurs in oil wells where well fluids flow between an inner and an outer pipe in the well. An extreme example is the Macondo accident. Although annulus flow is common in drilling, production and well intervention, our understanding of multiphase annulus flow is rudimentary compared to flow in circular pipes. The present knowledge is based on small scale, low pressure studies, mostly for vertical flow. Even this sparse knowledge is hardly built into commercial simulators. A new project is currently undertaking experimental and numerical studies of the fundamental physics of annulus flows. A new six-camera X-ray tomography system is mounted on IFE's Well Flow Loop and used to reveal internal flow structures for a wide range of gas-liquid and oil-water flows. The initial campaign is reported in the current paper.
On the 20th of April 2010, explosion and fire killed 11 people on the Deepwater Horizon oil rig in the Gulf of Mexico and began a human, economic and environmental disaster. After two days in flames, the rig sank and left the drilling riser on the sea floor leaking oil and gas from the well through the gap between the riser and the drill-string.
Immediate concerns were raised regarding the amount of oil being discharged to sea, and this number has also played a significant role in the legal proceedings. One of many techniques that were applied was based on using a multiphase flow simulator to match the observed slug frequency out of the sunken riser. There are, however, serious flaws to this approach, the most apparent being the lack of reliable multiphase flow models for flow in annuli, that is, flow between the inner and the outer pipe. Commercial multiphase flow simulators lack the ability to correctly predict pressure drop in annulus flow, even for single phase flow. Well design is thus based on crude assumptions with large uncertainty and high error margins. This may lead to inefficient well design and high risk of production problems.
