Soil gas monitoring - an effective tool for CO₂ leak detection in the shallow subsurface

Abstract

Geoscience Australia and C02CRC have constructed a greenhouse gas controlled release facil ity at an experimental agricultural station maintained by CSIRO Plant Industry at Ginninderra, Canberra. Two shallow subsurface CO2 release experiments have been performed at this facility to date. The purpose was to simulate a (controlled) leakage scenario from a CO2 storage site to further develop and verify shallow and near surface monitoring techniques. This was facilitated by the installation of a 100 m long slotted horizontal well, divided into six packer zones, at 2 m depth in the shallow subsurface. CO2 was released into the soil via the well at a rate of 144 kg/d and 216 kg/d respectively. for a period of nine weeks during the first (28 March-30 May 2012) and eight weeks during the second experiment (26 October-21 December 2012). Presented will be the results of the soil gas monitoring work including soil gas analysis, isotopic composition analysis, fixed gas relationships and krypton tracer monitoring. The study demonstrates that together these methods are an effe ctive way to detect and characterise CO2 leakage in the shallow subsurface against natural background CO2 levels.