Impact of reservoir parameters and wellbore permeability uncertainties on CO2 and brine leakage potential at the Shenhua CO2 Storage Site, China

Abstract

This paper describes a system-level risk assessment for the Shenhua CO2 storage site, China, using the National Risk Assessment Partnership Integrated Assessment Model for Carbon Storage (NRAP-IAM-CS). We begin by determining the optimal number of Monte Carlo (MC) simulations to achieve CO2 and brine leakage result convergence. Then, we calculate mass CO2 and brine leakage to the atmosphere and a hypothetical shallow aquifer. Finally, we assess the geochemical impacts in the event of leakage as if there were a shallow freshwater aquifer at the Shenhua site. Simulation results show that leakage results tend to stabilize after 300 Monte Carlo simulations. When the three wells on site are assigned a permeability of 10−11 m2 (representing significantly leaking wells), moderate CO2 and brine leakages occur, and the percentage of CO2 leakage exceeds the threshold value we set based on the Intergovernmental Panel on Climate Change (IPCC). This is, however, unlikely to be the case for the Shenhua site. For all the other scenarios, the CO2 leakage is trivial although there is still the possibility of CO2 leakage into the groundwater aquifer exceeding the 1% threshold over 1000 years, assuming constant legacy wellbore permeability. For the significantly leaking scenario, there is a 10% probability to have a moderate (2.7 × 107 m3) leakage-affected volume in the shallow aquifer with the pH below 6.5, and a large (1.4 × 108 m3) volume with the total dissolved solids (TDS) above 500 ppm, hence pH and TDS may be considered for site monitoring plans. Based on the simulation results, there is a very low probability of significant CO2/brine leakage through the existing wells at the Shenhua CO2 storage site.