Evaluating the influence of seal characteristics and rate of pressure buildup on modeled seal performance and carbon sequestration economics
Creators: name: Kalyanaraman, Nishanth
Publisher: name: The University of Texas at Austin
Year: 2008
Subjects: CO2 sequestration
Geologic storage of CO2
Seal model

description: This research investigates seal performance for carbon dioxide (CO2) sequestration in brine reservoirs. Numerical codes were adapted from the natural gas (methane) storage industry and modified for CO2 applications to investigate the factors influencing migration rates and magnitudes through a sealing layer resulting from pressure buildup in an underlying injection reservoir. The factors investigated include seal characteristics such as thickness and permeability as well as the characteristics of pressure buildup, such as rate and magnitude. The goal was to understand fundamental processes involved in CO2 migration through a seal and to determine how these factors affect CO2 migration rates and magnitudes through the seal and net volume retained. An expected result from this modeling indicates an approximately linear relationship between maximum pressure buildup and CO2 leakage. Unexpected conclusions include the non-linearity between seal thickness and CO2 leakage indicating that doubling seal thickness does not necessarily halve the leakage volume. Another non linear relationship is observed between seal permeability and CO2 leakage. In addition, it is shown that there is a minimum seal permeability that performs adequately (essentially no leakage) and permeabilities lower than that do not decrease seal risk. The integrated flow model developed is used to calculate the net volumes retained in the formation for different injection scenarios with a fixed injection volume and the results are integrated into the economic assessment of carbon sequestration. The second component of this thesis research addressed the economic implications of various injection scenarios, focusing on the various ways a fixed amount of CO2 could be used. An economic model was built to investigate the factors influencing the net present value of carbon sequestration in EOR and non-EOR projects. The factors investigated include the timing (duration) of different injection rates, CO2 credit received for successful storage, leaked CO2 fraction (output from seal performance model) and economic parameters such as CO2 price, operating and capital expenses and discount rate. The results from this analysis are that: 1) The CO2 leak rate calculated from the flow model is low for the conditions modeled and has negligible impact on the net present value when compared to CO2 credit and the timing of different injection rates; 2) longterm sequestration projects operating at low pressures may never become profitable with low CO2 credit and this provides an incentive to operate at higher injection pressures; 3) most regulators may favor lower injection pressures to avoid risks of leakage. Higher CO2 credits are needed to make these long-term projects attractive; and 4) for CO2 credits over $2.22/ tonne, it would be profitable to continue sequestration after EOR, providing a backstop for any economic risks of standard EOR projects