| Description |
The purpose of this research is to present an analysis of the leakage potential of sequestering CO2 in a reservoir that exhibits faulting, but may or may not have a fault penetrating the reservoir seal. A hypothesis is that CO2 injected into the reservoir will leak through a fault system. The questions addressed by this thesis are: (1) Under what conditions will CO2 leak through a fault and how much will leak under different conditions? (2) How much time is required for CO2 to migrate through an unbroken seal formation? (3) Under what conditions will permeable reservoirs above the target reservoir intercept or "catch" CO2 leaking through a fault? (4) Is injecting into two reservoirs preferable to injection into one? Questions (1) and (4) were addressed with site-specific models, whereas questions (2) and (3) were addressed with generic hydrogeologic models. Simulations using multi- and single-continuum models were used to analyze the leakage potential from a geological storage reservoir. Fault conduits and geologic formation porosities and permeabilities were used as constraining parameters in a sensitivity analysis. Model results highlighted that a fault above (but not penetrating) the injection reservoir increases the seepage velocity through a seal, causing a greater risk of CO2 leakage due to the increase of pressure during injection (question (1) above). Simple 1-D seal models illustrate that un-fractured, low-permeability formations are very effective at trapping CO2 for decades and longer, depending on permeability (question (2) above). Additional simulation results illustrated that with a penetrating fault through a seal facilitating direct CO2 leakage, a ratio of fault to medium permeability of two orders of magnitude difference or greater will, in many if not most cases, recapture the CO2 in shallower formations, reducing or eliminating leakage to the surface (question (3) above). Finally, this analysis suggests that a single-reservoir injection (question (4) above) is best since a stacked reservoir would decrease the overall risk of CO2 leakage during and after injection, highlighted by results of the question (3) analysis. |
