Offshore oil and gas prospect
The Dorado oil and gas discovery is located in the WA-437-P exploration permit in the Commonwealth waters offshore Australia.
The prospect is a part of the Phoenix project acreage, which is jointly owned by Santos (80%, operator) and Carnarvon Petroleum (20%).
The final investment decision (FID) on the project is expected to be reached in late 2020.
Dorado oil and gas discovery is located in the Bedout basin within the Caley Member, offshore Western Australia. It is situated approximately 160km north of Port Hedland, near the Pilbara region of Australia.
The Phoenix project acreage covers 22,000km², comprising the WA-437-P permit and neighbouring WA-435-P, WA-436-P and WA438-P blocks, collectively termed as the Greater Phoenix Area.
The Dorado prospect was discovered by the Dorado-1 discovery well in July 2018. The discovery well is located less than 20km up-dip of the Roc-1 and Roc-2 discoveries located within the WA-437-P permit.
Dorado-1 discovery well was drilled to a measured depth of 4,044m using the Ensco-107 drilling rig.
The well yielded condensates ranging between 70 barrels per million standard cubic feet (Mscf) and 245Mscf. Following wireline testing, it showed the presence of a net oil pay thickness of 79.6m.
The well was drilled with the objective to analyse the presence of additional hydrocarbons in the Baxter and Milne sandstones within the Caley Member.
Dorado is estimated to contain 448 million barrels of oil-equivalent (Mboe), making it the third biggest oil field in the greater North West Shelf.
The Dorado-2 appraisal well was drilled to a total depth of 4,573m using the Noble Tom Prosser drilling rig in 91m-deep waters. It is located approximately 2.2km from the Dorado-1 well to target reservoirs in a down-dip location.
The well was designed to intersect potential hydrocarbons in the Baxter and Milne reservoirs and hydrocarbon-water contacts in the main Caley Reservoir. It encountered 85m of net reservoir in the Caley Formation and 32m of net pay in the Baxter and Milne sandstones.
The well also intersected an oil-water contact in the Caley reservoir, enabling the refinement of the recoverable oil resource and extracting high-quality oil comparable to those discovered in Dorado-1.
Secondary target condensate rich gas was extracted from Baxter reservoir and wireline logging showed the presence of a hydrocarbon column with no gas-water contact. The Crespin reservoir was water-wet, while the Milne reservoir samples indicated the presence of oil.
The development plan for the Dorado oil and gas discovery includes the drilling of deviated wells using a jack-up drilling rig. The wells will be tied-back to a floating production, storage and offloading vessel (FPSO), which will hold the produced oil to be transported for refining and sale.
The produced oil is expected to be sold in the Asian market, whereas the gas could be transferred to Western Australia through the existing gas infrastructure in the region.
Initial works for long lead time items have commenced, while the concept development will be drafted based on further drilling results.
The Ensco-107 is a jack-up drilling rig built by Keppel FELS in 2006. The vessel is classified as an A.B.S. A-1 self-elevating mobile offshore drilling unit capable of operating in water depths of 350ft to 400ft, with a maximum drilling depth of 30,000ft.
The rig is equipped with a Varco SLX 18 ¾” 10,000Psi well control system and Keppel FELS self-positioning fixation system. It can operate at a transit speed of 4.5kt to 5kt and is designed to accommodate 112 people.
The Noble Tom Prosser drilling rig used to drill the Dorado-2 well is a jack-up drilling rig owned by Noble Corporation and built by Jurong Shipyard in 2014. It features Friede & Goldman’s JU3000N design and is classified as an ABS +A1 self-elevating drilling unit.
The rig is capable of drilling in water depths of 400ft to a maximum drilling depth of 35,000ft. It is equipped with a Cameron control system and five units of Caterpillar C-175-16 engines.
MMA Offshore was contracted for the provision of vessels for drilling, while Noble Corporation and ENSCO Australia were contracted for providing the drilling services.
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