The Bonaparte Basin is located primarily offshore in coastal waters off the north coast of Australia, straddling the border between Western Australia and the Northern Territory. The offshore portion of the basin covers 250,000 sq km compared to just over 20,000 sq km onshore.
To date, production development offshore has relied on standalone systems, such as those established since the 1980s at the Challis-Cassini, Jabiru, Laminaria, Laminaria East, Corallina, Buffalo, and Elang-Kakatua oilfields in the Northern Territory and Commonwealth-administered portions of the basin.
Dr Michael R. Smith, Chief Executive of oil and gas forecasting company Energyfiles, says that a number of gas fields in the basin have not yet been developed due to their remote location, including Petrel, which was discovered in 1970, Tern which was discovered in 1971 and Sunrise and Troubadour which were discovered in 1974. There are a large number of other undeveloped oil, oil and gas, and gas discoveries in the region, says Dr Smith.
Santos holds interests in five permits in the southern Bonaparte, which contain the currently undeveloped Petrel and Tern gas fields. These fields have estimated recoverable reserves of 1.4 trillion cubic feet (Tcf). According to the Geological Survey of Western Australia’s Petroleum Explorer’s Guide to Western Australia, Tern and Petrel – which are located in Western Australian-administered waters – are currently being appraised for future development and an economic market is being sought.
Santos also holds interests in a further three permits in the northern Bonaparte containing the currently undeveloped Evans Shoal, Caldita and Lynedoch/Barossa gas resources. Santos operates the NT/P48 permit (Evans Shoal) and has a 40 per cent interest in both the NT/P61 and NT/P69 blocks (Caldita and Barossa/Lynedoch respectively), where ConocoPhillips is the operator.
Evans Shoal is a joint venture between Santos, Shell Development (Australia), Petronas and Osaka Gas Australia. Proved and probable recoverable dry gas resources at Evans Shoal are estimated to be around 6.6 Tcf.
In the ConocoPhillips-operated Caldita and Barossa fields, drilling of the Caldita-2 well in NT/P61 – located 6 km from the Caldita-1 discovery well, which was drilled in 2005 – commenced in early December 2006 and was completed in February 2007. Caldita-2 was drilled to a total depth of 3,973 m and confirmed the presence of gas in the western part of the Caldita structure. The well was plugged and abandoned as planned.
Testing of the Barossa-1 well in late 2006 confirmed the presence of gas and provided valuable reservoir and composition data. The well was drilled to a total depth of 4,310 m, with two drill stem tests completed. The first test, of a lower-quality reservoir interval, flowed gas at a rate of approximately 0.8 MMcf/d and the second test, of a higher-quality reservoir interval, flowed at a rate of approximately 30.1 MMcf/d. Barossa-1 was also plugged and abandoned as planned.
Santos said in early 2007 that the forward program for Evans Shoal, Caldita and Barossa was to complete the acquisition and processing of 3D seismic data over the structures by the end of the first quarter 2008, to determine the likely resource range and the development potential.
A Field Development Plan was approved in 2007 for the Blacktip gas field, located near Petrel and Tern in the Timor Sea, approximately 110 km off the coast of Northern Australia. Eni Australia, which is developing the Blacktip field, has signed a sales and purchase agreement with the Northern Territory’s Power and Water Corporation for the supply of gas from the field – through APA Group’s planned Bonaparte Gas Pipeline – to meet the Northern Territory’s long term gas requirements from 2009. The development of Blacktip began in June 2006. The field contains estimated recoverable reserves of 1.1 Tcf.
Further north, in the Northern Territory portion of the Bonaparte Basin close to the border with East Timor, Woodside has plans to develop its Greater Sunrise Gas Development, including the Sunrise and Troubadour fields (discovered in 1975 and 1974, respectively) which could begin production in 2011. The Greater Sunrise development contains estimated recoverable reserves of 7.7 Tcf.
Following ratification of a 50-50 revenue-sharing agreement between Australia and East Timor in February 2007, a development team was reconstituted to review all available data to determine if further appraisal work is required for Greater Sunrise. East Timor voted to ratify the International Unitisation Agreement and the treaty for Certain Maritime Arrangements in the Timor Sea, providing what Woodside said at the time was a “significant step forward”? for the company.
Development options include a brownfields expansion of the Wickham Point Bayu-Undan LNG plant at Darwin. Development is contingent on the project receiving legal, regulatory and fiscal certainty from the East Timorese and Australian governments. Woodside is also considering a world first floating LNG development for the Greater Sunrise fields.
The Bayu-Undan offshore gas and natural gas liquids field is located in shallow waters, about 500 km northwest of Darwin. The Bayu field was discovered in 1995 with the Bayu-1 exploration well and the Undan field was discovered later that year with the Undan-1 exploration well. The field is estimated to hold 3.4 Tcf of gas. Participants in the Bayu-Undan joint venture are ConocoPhillips (operator), Eni, Santos, Inpex and Tokyo Timor Sea Resources Pty.
The development of the field proceeded in two phases. The first phase, completed in 2004, consisted in the production of natural gas liquids (propane, butane and condensates). The second phase, completed in 2006, allows the production of natural gas that is conveyed, through a 500 km, 26 inch gasline, to the LNG plant at Wickham Point, Darwin, which has a capacity of 3.5 million tonnes/year. The LNG plant uses ConocoPhillips’ optimised cascade LNG process technology with associated storage and marine load-out facilities.
With its abundant resources, central location to Asian markets and an increasing number of major projects, the Bonaparte Basin looks set to continue rising as an Australian gas producing region.