Hydrodynamic considerations for carbon storage design in actively producing petroleum provinces: An example from the Gippsland Basin, Australia

The Australian offshore Gippsland Basin has been investigated by the CO2CRC for its potential to store large volumes of CO2 from new coal-fired power developments in the Latrobe Valley (Gibson-Poole et al., 2006). The Gippsland Basin has been producing hydrocarbons since the 1960s and the depletion and decommissioning of some of the major oil fields is likely to coincide with the need for storage of anticipated CO2 emissions of up to 50 million tonnes annually for a 40 year injection period (Gibson-Poole et al., 2006). This will necessitate several individual storage sites to be used both sequentially and simultaneously, but timed such that existing hydrocarbon assets will not be compromised.Potential injection targets lie within the interbedded sandstones of the Upper Latrobe Group, regionally sealed by the Lakes Entrance Formation (Gibson-Poole, et al., 2006). A hydrodynamic evaluation of the Upper Latrobe Aquifer System (the Latrobe Group) mapped the hydraulic head distribution of the virgin formation water flow system and the impact on that system of the extraction of large volumes of gas and oil (Hatton et al., 2004; Underschultz and Johnson, 2005). They determined that offshore oil and gas production have resulted in significant, although short-term (tens to hundreds of years) alteration of the formation water flow system.This paper outlines a study investigating whether the local hydraulic gradients induced by pressure depletion in the vicinity of hydrocarbon production are sufficient to alter the buoyancy driven migration of injected CO2. The methodology developed by Hubbert (1953) to determine the ability of geologic structures to hold hydrocarbons under varying hydrodynamic conditions was applied to CO2 storage. An average density of injected CO2 calculated from in-situ pressure and temperature conditions in the Latrobe aquifer was applied to both virgin and production affected hydrogeological environments. The results suggest that the location of reservoir spill points and the migration direction of CO2 in the Latrobe aquifer would change continually due to the transient nature of the production impact on the formation water flow system. Therefore, it is not sufficient to calculate a static volume available for CO2 storage within structural closures. The production lifetime of and the potential pressure interference between petroleum fields has to be taken into account when selecting sites for CO2 geological storage.