Gorgon Project: Subsurface Evaluation of Carbon Dioxide Dsposal under Barrow Island

Abstract

The Gorgon Project is a major LNG development to be based in Northwest Australia. Gas will be produced from several offshore gas fields located in the Greater Gorgon Area with processing facilities to be located on Barrow Island. The reservoir fluids of several of the fields contain carbon dioxide (CO2) which will be extracted from the produced gases prior to liquefaction into LNG. The Gorgon Joint Venture participants have proposed to geologically dispose of the produced reservoir CO2 from the gas processed at the Barrow Island LNG plant. The CO2 injection project was extensively documented and subjected to public comment as part of the Gorgon Project Environmental Impact Assessment Process. Following this process the WA Environmental Protection Authority found that the environmental risks associated with the CO2 injection project were acceptable and recommended that CO2 injection must proceed as an integral component of the Gorgon Project. The target formation for geological disposal of this carbon dioxide is the Dupuy Formation, a Jurassic saline reservoir, deep beneath Barrow Island. The evaluation of the Dupuy Formation for the disposal of carbon dioxide was focused on characterising the reservoir and narrowing subsurface uncertainties not addressed by legacy oil exploration and development. Data acquisition was targeted to reduce major subsurface uncertainties including a seismic pilot to assess acquisition methods (including 4-D seismic) and an extensively evaluated appraisal well. Robust geological description, hydrodynamic, static and dynamic reservoir models have been used to gauge the impact of CO2 injection on development decisions. Key drivers for this development have been maximising per well injection of CO2 and ensuring containment of CO2 within the reservoir. Through effective subsurface and economic evaluation, a phased and flexible development plan for CO2 disposal has been developed to meet these objectives. Introduction The Gorgon Joint Venture is an unincorporated joint venture of three major international oil companies; Chevron (Operator, 50% interest), ExxonMobil (25%) and Royal Dutch Shell (25%). The Gorgon Project is a major capital LNG project that will produce gas from several offshore fields in the Greater Gorgon Area, off the Northwestern coast of Australia. Figure 1 shows the development plan for the Gorgon Project. The Gorgon and Io/Jansz gas fields will be developed initially as a subsea development with a tie back to Barrow Island. On Barrow Island the raw gas will be received and undergo liquefaction into LNG for export. Production of gas is also being actively considered for supply into the West Australian domestic market. The Gorgon Project has needed to overcome several technical challenges during the concept selection phase of development:The project has one of the longest sub-sea tie-backs in the world (145kms) in water depths greater than 1km and challenging terrain with the pipeline crossing the continental shelf;Barrow Island is a remote location and a Class A Nature Reserve;The nearest major logistical staging point (Perth, Australia) is over 1200km away from Barrow Island;Strict quarantine barriers to prevent environmental contamination;Finally, the Gorgon gas field has a significant component of CO2 in the reservoir fluid composition, with approximately 14% of Gorgon reservoir fluids being CO2.

The Future of Low-Carbon Electricity

“…This means that pressure in the receiving formation increases over a large area, and existing brines are displaced away from the injection site (79). Thus, pressure build-up limits practical storage capacity in many cases (80,81), which has spurred development of pressure management concepts generally (82), and brine withdrawal plans at the Australian Gorgon sequestration project specifically (83). Regulations also recognize the novel aspects of sequestration, typically requiring thorough understanding of site-specific risks (84), which has driven much research into the potential impacts of CO 2 sequestration and risk assessment (85,86).…”

Progress in monitoring strategies for risk reduction in geologic CO2 storage

“…The target injection zone is the upper massive sandstone and lower unit of the Dupuy Formation. The Dupuy storage units are overlain by siltstones and shales that form a continuous regional seal (Flett et al, 2008(Flett et al, , 2009. Recent plans for this site include pressure monitoring as part of a pressure management system, to allow injection of 200 million standard cubic feet (0.01 t) per day of CO 2 at an average rate of up to 3.65 million tons per year (Trupp et al, 2013).…”

Have We Overestimated Saline Aquifer CO2Storage Capacities?

“…This strategy has been proposed by various authors, in order to store CO 2 in rather small structures in Browse Basin, Australia [25]; as a pressure relief strategy for the Gorgon Australian project [26]; or as a way to increase Utsira CO 2 storage capacity [19].…”