1. University of Cambridge Department of Earth Sciences, , Downing Street, Cambridge CB2 3EQ, UK
2. Universität Potsdam Institut für Geowissenschaften, , 14476 Potsdam-Golm, Germany
3. University of Bristol School of Earth Sciences, , Wills Memorial Building, Queens Road, Clifton, Bristol BS8 1RJ, UK
4. BP Institute for Multiphase Flow , , Madingley Road, Cambridge CB3 0EZ, UK
5. University of Cambridge , , Madingley Road, Cambridge CB3 0EZ, UK
6. University of Cambridge Department of Applied Mathematics and Theoretical Physics, , Centre for Mathematical Sciences, Wilberforce Road, Cambridge CB3 0WA, UK