ESTIMATING RATES OF POTENTIAL CO_2 LOSS FROM GEOLOGICAL STORAGE SITES FOR RISK AND UNCERTAINTY ANALYSIS

摘要

A key objective of geological storage of CO_2 in porous rock is its long-term subsurface containment in order to assist in the reduction of CO_2 emissions. Achievability of such containment can be assessed in risk and uncertainty analyses that consider the occurrence of unlikely events inducing leakage. Envisaged leakage mechanisms are flow driven by buoyancy and overpressure through permeable zones in the top seal of storage reservoirs, along permeable faults and damaged well bores. Seepage rates from natural CO_2 accumulations with non-optimum seals, flow rates from natural gas storage, and fluid discharge rates related to earthquakes can indicate potential leakage rates for risk and uncertainty analysis. For example, seepage from natural CO_2 accumulations occurs at fluxes of 0.00001 to 0.001 tonnes/yr/m~2 in the Otway Basin, Australia. Discharge from slowly flowing springs can peak at hundreds to thousands of tonnes/yr CO_2-equivalent after earthquakes but typically have short durations of days to months. Careful site selection that reduces leakage risk together with the planning for early leak detection and remediation can, in a risk and uncertainly analysis, lead to a high likelihood of project success.