1. Department of Fossil Fuels and Environmental Geochemistry, Drummond Building, University of Newcastle, Newcastle upon Tyne NE1 7RU, United Kingdom, Materials and Process Simulation Center, Beckman Institute (139-74), Division of Chemistry and Chemical Engineering, California Institute of Technology, Pasadena, California 91125, and Institut Français du Pètrole, Geology and Geochemistry Research Division, 1-4 Avenue de Bois-Preau, 92852 Rueil-Malmaison, France