Towards a Frequency Distribution of Effective Permeabilities of Leaky Wellbores

Abstract

The risk of leakage along existing wellbores associated with CO2 sequestration depends strongly upon the leakage path permeabilities. If enough buildups of surface casing pressure (SCP) and rates of surface casing vent flow (SCVF) recorded on intermediate wellbore casing strings are available, a frequency distribution of leakage path permeability values can be obtained. Uncertainty about the location of the leak source results in a range of leakage path permeability values for each measurement of SCP or SCVF. Most permeability values exceed intact cement permeability, consistent with the presence of cracks or other defects in the formation/cement/casing interface. Assuming the gas migration path through leaky wellbores in hydrocarbon reservoirs is analogous to the leakage path for CO2 plumes, the distribution of inferred permeabilities enables quantitative estimation of CO2 leakage fluxes.