3D Model3D Model Structures ofStructures of Oil Shale Kerogen and Sand Tar AsphaltenesOil Shale Kerogen and Sand Tar Asphaltenes

Ian S.O. Pimienta1, Anita M. Orendt1, Ronald J. Pugmire2, and Julio C. Facelli1,3

1Center for High Performance Computing and 2Departments of Chemistry and of Chemical and Fuels Engineering and 3Biomedical Informatics, University of Utah, Salt Lake City, Utah 84112

IntroductiIntroductionon Kerogen is a mixture of organic chemical compounds

that make up a portion of the organic matter in sedimentary rocks. It is insoluble in normal organic solvents because of the large molecular weight (upwards of several thousand Daltons). When heated in the Earth’s crust (oil window ca. 60 ° - 120 °C; gas window ca. 120 ° - 150 °C) some types of kerogen release hydrocarbons in the form of crude oil or natural gas, collectively known as fossil fuels. Kerogens can also be found in rocks such as shale, as oil shale deposits. Asphaltenes are molecular substances found in crude oil. They are one of the major components in heavy oils, tar sands, and biodegraded oils (15%) which are expected to feature prominently in the world’s energy mix in the decades to come.

The objective of this study is to develop 3D structures of kerogens and asphaltenes that can be used to model their interaction with the inorganic matter of the rock for the purpose of identifying novel means of extracting them with a smaller carbon footprint.

Acknowledgements: An allocation of computer time from the Center for High Performance Computing at the University of Utah is acknowledged. This work is supported by a grant from the U.S. Department of Energy, National Energy Technology Laboratory. DE-FE0001243

All structure minimizations were performed using the molecular mechanics packages in HyperChem (MM+ force field) and the RHF/STO-3G level of theory in GAMESS.

The simulated annealing procedure was employed to generate several monomer conformations.

Models consisting of up to 12 kerogen units were generated.

Several different 3D asphaltene models were created based on available literature 2D models of asphaltenes from different sources.

The 3D images were generated using VMD.

Computational Computational DetailsDetails

The figure consists of 12 kerogen units (20402 atoms). The atom colors are as follows: C - teal, O - red, N - blue, S - yellow, H - gray. The tubes represent the molecule’s backbone and the spheres represent the atoms.

3D globular local structures of kerogen were obtained due to folding of the long aliphatic chains in the Siskin model.

From a molecular standpoint, separation of the seven distinct molecular units in the Siskin model could be difficult due to lack of accessibility of the smaller fragments from the surface.

The flexible bridge between aliphatic and aromatic groups in asphaltene molecules gives rise to several conformational structures.

Initial calculations suggest that parallel stacking in asphaltene units is the preferred orientation due to strong - interactions.

Molecular dynamics simulations are presently underway to determine how many asphaltene units per stack are present.

Evaluation of 3D molecular models will be based on ability to use model to reproduce experimental data on actual kerogen and asphaltene samples.

ResultResultss

Campana Mid-Continent U.S. San Joaquin Valley

Loydminster W. Maya Heavy Canadian

Parallel Stack Anti-parallel Stack Inverted StackThe atom colors are as follows: C - gray, O - red, N - blue, S - yellow, H - white. The tubes represent the molecule’s backbone and the spheres represent the atoms.