Water injection into saline aquifers as a proxy for potential CO2 injection in Taranaki, New Zealand

The underground storage of carbon dioxide in saline aquifers is the main target for the storage of large volumes of CO2 globally, and this approach also has potential in New Zealand. The injection of water produced in conjunction with oil and gas extraction into saline aquifers has similarities to the injection of CO2 into deep saline aquifers, but has not previously been assessed as an analogue in New Zealand. This report presents a compilation of publicly available data on volumes and rates of the re-injection of produced water into saline aquifers in the onshore Taranaki region along with a simple conversion to equivalent volumes of CO2. To date, a total of 18 Mt of produced water or approximately 9 Mt of CO2 equivalent has been re-injected, with this process continuing. There are primarily three saline aquifer intervals that have been used for deep-well re-injection, the Matemateaonga, Mount Messenger and Tikorangi formations. The Matemateaonga Formation has the longest history of use as a saline aquifer for deep-well water injection with a total of 14 Mt of water or 7 Mt of CO2 equivalent injected at three sites (Kapuni, Waihapa and McKee fields) followed by the Tikorangi Formation (2.87 Mt water, 1.4 Mt CO2 equivalent) and then Mount Messenger Formation (1.1 Mt water, 0.55 Mt CO2 equivalent). The daily average volumes injected range from as little as 23 tonnes of water (11 tonnes CO2) up to 1046 of tonnes water (523 tonnes CO2). These data suggest that it would be feasible for the injection of CO2 into deep saline aquifers to be undertaken in onshore Taranaki. This is consistent with early regional assessments undertaken by Arnot et. al. (2009). However, much more detailed, site-specific assessments would be required before any such project could proceed. (auth)