Rigorous Simulation Model of Kerogen Pyrolysis for the In-situ Upgrading of Oil Shales

Oil shale is a vast, yet untapped energy source, and the pyrolysis of kerogen in the oil shales releases recoverable hydrocarbons. In this dissertation, we investigate how to increase process efficiency and decrease the costs of in-situ upgrading process for kerogen pyrolysis, which is applicable to the majority of the oil shales. In-situ upgrading processes include (a) Shell In-situ Conversion Process (ICP), (b) ExxonMobil Electrofrac, and (c) Texas A&M (TAMU) Steamfrac. We evaluate these three processes in realistic scenarios using our newly developed multi-phase, multi-component, nonisothermal simulator.

Kerogen pyrolysis is represented by 6 kinetic reactions resulting in 10 components and 4 phases. Expanding TAMU Flow and Transport Simulator (FTSim), we develop a fully functional capability that describes the kerogen pyrolysis and the accompanying system changes. The simulator describes the coupled process of mass transport and heat flow through porous and fractured media, and accurately accounts for phase equilibria and transitions. It provides a powerful tool to evaluate the efficiency and the productivity of the in-situ upgrading processes.

We validate our simulator by reproducing the field production data of the Shell ICP implemented in Green River Formation. We conduct the sensitivity analyses of the presence and absence of pre-existing fracture system, oil shale grade, permeability of the fracture network, and thermal conductivity of the formation. Validated model has the oil shale grade of 25 gal/ton, fracture domain permeability of 150 md, and formation thermal conductivity of 2.0 W/m-K.

In the application cases, we analyze the significant factors affecting each process. In the Shell ICP, the ExxonMobil Electrofrac, and the TAMU Steamfrac, we study the effects of heater temperature, electrical conductivities of injection material, and steam injection strategy, respectively. We find that the best case of the Shell ICP showed the highest energy efficiency of 144 %. The best cases of the ExxonMobil Electrofrac and the TAMU Steamfrac show the energy efficiency of 74.1 %, and 54.1 %, respectively. We obtain positive Net Present Value (NPV) in the TAMU Steamfrac by much less number of wells than the Shell ICP and the ExxonMobil Electrofrac, though it has the lowest energy efficiency.