Otway Project: geochemical monitoring
Hydrological & groundwater monitoring
Water levels and the chemistry of the shallow (unconfined Port Campbell Limestone) and deep aquifers (confined Dilwyn aquifer) are monitored to ensure early detection in the unlikely event of any injected CO2 leaking into these freshwater aquifers.
Seasonal variation, flow rate and direction of water-flows are recorded using dataloggers suspended from a steel cable a few metres below the existing water level in privately and state-owned shallow and deep water bores.
Groundwater sampling using a low flow pump will help identify any unusual chemical changes.
CO2 and methane compounds of the injection stream are “tagged” using chemical tracers in order to verify the CO2 plume behaviour. Tracers used are CD4 (perdeuterated methane), SF6 (sulfur hexaflouride) and Krypton.
These tracers enable researchers to identify the amount of time it takes CO2 injected at CRC-1 to travel to Naylor-1, track the movement of methane relative to CO2, provide additional information on the long term fate of injected CO2 and confirm that there has been no leakage to shallow aquifers, soils or the atmosphere.
Downhole fluid sampling
High quality well-bore fluid and gas samples are collected at reservoir pressure from multiple levels to detect the arrival of CO2 at the Naylor-1 site and to characterise chemical changes associated with this. Samples are analysed in laboratory for their chemical and isotopic composition.
During injection, the CO2 migrates from the CRC-1injection well to accumulate below the residual methane cap at the Naylor-1 monitoring well pushing the point of gas-water contact (GWC) down. Injection will stop when the injected CO2 is detected at U-tube 3.
The U-tube system was developed by Lawrence Berkeley National Laboratory (LBNL) and the CO2CRC. It was installed during the Naylor-1 workover completion.
The objectives of using the U-tube system are to:
- detect the arrival of CO2 at Naylor-1 through the identification of tracers injected at CRC-1 in order to characterise CO2 migration and behaviour within the Waarre C formation; and
- characterise chemical changes associated with the CO2 arrival.
The U-tube system consists of three tubes: one in the methane gas-cap, a second just below the current gas-water contact (GWC) and a third in the water leg. Each U-tube consists of two 1/4" stainless tubing lines from the surface down the Naylor-1 well, terminating in a 'T', which opens to the formation through a check valve and a filter.
To take a sample using a U-tube:
- U-tube is purged with nitrogen allowing formation fluid to fill the U-tube through the downhole check valve
- High pressure nitrogen (inert gas at 3200psi) is introduced to the drive leg of the ¼” tube of the U-Tube sampled closing the check valve and bringing the sample to surface at near formation pressure in the sample leg
- The high pressure fluid or gas is sampled using isotubes after going through monitoring probes at the surface facilities (yellow sea container). Secondary sampling of dissolved gas in the solution is possible from each of the 3 U-tubes