| Description |
Simulating in situ pyrolysis requires an understanding of rock mechanics, reservoir engineering, thermodynamics, heat transfer, reaction kinetics, and mass transfer. In order to account for the possibility of subsidence, a model of poroelasticity is also required for oil shale. Poroelastic models couple deformation of porous media with fluid flow in and out of pores, while accounting for stress-response of the fluid. When pyrolyzed, kerogen in oil shale decomposes into lighter molecular weight organic compounds, such as bitumen, oil, gas, and char. Pyrolization greatly reduces the mechanical capability of oil shale, while producing oil and gas. A simulation which accounts for the mechanical transformation and deformation of oil shale during in situ pyrolysis was implemented using Itasca Consulting Groups FLAC3D. While a weakening, increasingly porous rock matrix might be expected to collapse, the compression is counteracted by growing pore fluid pressure. Due to its large residence time, a significant fraction of the oil produced in situ is likely to be lost through decomposition. In this simulation, the stresses of pore pressure and confining pressure mostly cancelled each other out. The analysis results may reflect the complexity of the problem more than they shed light on the true nature of in situ pyrolysis. In principle, increasing pore pressures could cause fractures to open during pyrolysis, but the simulation is not equipped to represent flow from zone to zone via fracture. Should fracturing be predicted, a module has been developed to relieve excess pressure by bleeding fluid into noncommunicated fractures for each zone. Alternatively, if tensile pressure is predicted, and fluid has been stored in the simulated fractures, the module will release fluid back into the geometry, thus preserving mass balance in the system. |
