The Gorgon SCS project on Australia’s Northwest Shelf began injection in July 2020 and is one of the largest active projects, with a nominal injection capacity of 4 Mt per year. A plant on Barrow Island receives feed gas from the Gorgon and Io/Jansz Fields and separates the CO2 from natural gas.
The CO2 is then injected into sandstones of the Lower Dupuy Formation at a depth of approximately 2,500 m (See Figure below). In order to reduce pressure build-up in the storage reservoir, brine is extracted from the Lower Dupuy and reinjected into shallower sands of the Barrow Formation. Unfortunately, sand influx into the brine re-injection wells resulted in a shortfall in injected water volumes and hence, in the volumes of brine extracted from the storage reservoir.
This, in turn, increased the reservoir pressure in the Lower Dupuy, limiting CO2 injectivity and prompting the regulator to impose an injection rate limit to mitigate additional risks. Subsequently, Gorgon has not been able to meet its contractual obligations. The project had to acquire and surrender carbon credits to offset its target shortfall of 5.23 Mt of CO2 at an estimated cost in excess of US$100 million.
Gorgon is an example of a potential risk (sand influx) that was not sufficiently addressed in well planning. Additional analysis, including a possible pilot project, would have been useful in identifying the possible severity of this issue and how to best mitigate it.
