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The Dorado Oilfield
The location area and sub-basin that the Dorado Oilfield is located, the hydrocarbon discoveries made in the area, and the size of discovery well Dorado-1 and appraisal wells Dorado-2 and Dorado-3 are highlighted throughout the section. Exploration of the under-surveyed Bedout Sub-basin was aimed at the Triassic Lower Keraudren Formation fluvio-deltaic sediments. The lack of production infrastructure in the 1970s impeded discoveries to be made due to the erosional truncation trap set up by a major canyon system. Today, however, we have the technology to discover the high-quality reservoirs, source rocks, and hydrocarbon fluids in this frontier basin. Moving forward, Santos Limited Energy and Carnarvon Petroleum combine their resources for the purpose of discovering major oil and gas in the Bedout sub-basin of the Roebuck Basin. The natural gas energy company, Santos Ltd., produces the second to largest amount of oil and gas independently with 80% interest in the Dorado project. Carnarvon Petroleum is an oil and gas company where they are soon to discover the largest oilfield known to Western Australia's North West Shelf using their latest data and technology holding 20% interest.

Study Area
The Dorado Oil and Gas Field is located in the Bedout Sub-basin situated 160 kilometers offshore of Port Headland, Western Australia (NWS) and has a water depth of about 90 meters. The shallow-watered Bedout Sub-basin encompasses an area of about 15,000 km2 with reservoirs located at depths of 4000 meters in the Caley, Baxter, Crespin, and Milne formations. These formations are classified as clastic sedimentary units of the Middle Triassic Lower Keraudren Formation. North of Dorado is Bedout High with the Beagle sub-basin to the west and Lambert Shelf to the south. Previous exploration in the 1970s shows the presence of high quality reservoirs, source rocks, and hydrocarbon fluids indicating high reservoir productivity of condensate rich gas.

Geologic Setting
The Bedout Sub-basin is oval shaped and located north of the Dorado Canyon where wells Dorado-1, Dorado-2, and Dorado-3 are drilled and named after. The Dorado Canyon Older uplifted rocks are seen towards the surface with about 4 km exposed. Dorado wells are located in a shallow water environment that is about 95 meters deep. Recent research suggests that the Upper Paleozoic section across the North West Shelf is likely a part of the East Gondwana interior rift setting. This Carboniferous-Permian intercontinental rift was later modified by Upper Permian extension.

Stratigraphy
This is an area of interest to drill due to the porous and permeable sands making this a good area for the source rock to mature and produce hydrocarbons over time. Dorado is located beneath the Hove Unconformity in the Lower Keraudren Formation. The Lower Keraudren is made up of mainly Triassic aged sediment with little Permian and Jurassic aged grains. This area is a fluvial depositional environment due to the preservation of facies in stratigraphy exemplifying deposits being eroded, modified, and destroyed by river processes. In the Middle Triassic, there is a creation of a fluvio-deltaic basin in the Lower Keraudren. There also seems to be rich gas-condensate and oil migrating from the source rock to the Caley, Baxter, Crespin, and Milne reservoirs due to secondary migration.

Dorado-1 & Dorado-2
Dorado-1 is a discovery well meaning the first well to produce oil in this new field. In order to understand the extent and size of the hydrocarbon accumulation, the appraisal well, Dorado-2, is drilled. Santos proves the size and span of the reservoir and sets the boundaries of the area to evaluate rocks, fluids, and production rates. The stratigraphy in the Bedout sub-basin gives the Dorado wells such a success due to the permeable and porous carrier beds and reservoir rocks. In drilling the Dorado-2 appraisal well, there is high confirmation of oil and gas production in the area with 40 m of net oil pay in the Main Caley formation, 11 m of oil pay in the Upper Caley sands, and 32 m of gas pay in the gas-bearing Bazter and Milne sandstones underlying the Upper and Main Caley formations. In Dorado-1, the condensate rich gas yields in the Upper Caley, Crespin, and Milne formations range from 190 to 245 bbl/MMCF. Dorado-2 has similar interval results referring to the Baxter formation with a condensate rich gas yield of 70 to 90 bbl/MMCF. There is no indication of the Upper Caley, Crespin, or Milne formations in Dorado-2. These appraisal results prove to Santos Ltd. and Carnarvon Petroleum Ltd. that the Dorado hydrocarbon discovery is bigger than anticipated making prospective wells in the surrounding area more profitable. Dorado-1 is being kept as a future production well while Dorado-2 is plugged, and they will come back to drill Dorado-3 in the future. Overall, Dorado-1 and Dorado-2 wells are oil-bearing in the upper zone and gas-bearing in the underlying sandstone formations with an oil-water contact depth of 4,003 m. Further research is needed to confirm the hydrocarbons in the region, but there is confirmation that all wells are operating properly and in compliance.

Dorado-3
The Dorado-3 appraisal well confirms where the main oil pool in the field is located. From the initial flow test, it proves that the Main Caley formation is the major oil reservoir in the area. The test results show that the Caley sands have a maximum rate of 11,100 b/d of oil along with 21 MMCF/d of gas across an 11-m thick section 3,999 to 4,015 m from a total net reservoir interval of 53 m. This proves that this is one of the most oil-rich, high quality reservoirs found off the North West Shelf of Australia, and the highest ever flow rates are coming from the appraisal well tests underlying the Baxter reservoir. The test results also indicate that the flow rate in the Caley formation is at the higher end of its pre-drill expectations and support major progress toward needing front-tier tools and engineering design come 2020. Dorado-3 is plugged and abandoned making a great conclusion to the 2019 drilling program in the Bedout sub-basin.

Seismic Data
The Dorado prospect is a combination of a structural and stratigraphic trap created by the Middle Triassic Main Caley Unconformity. Seismic data of Dorado shows development of the largest entrenched valleys with accumulation on the northern flank. 3D seismic surveys were done showing the incised valley system allowing closures to properly be mapped; however, there is a constant struggle to explore more of the uncharted Bedout Sub-basin due to the poor seismic data quality. The poor seismic data is due to the shallow-water depths and hard carbonate seafloor which contaminates and disrupts the data. Entrapment and sealing mechanisms are key to exploration success.

Future Discoveries
The discoveries talked about in the Wilkinson articles prove that the appraisal results show a large hydrocarbon discovery in the Bedout sub-basin. This huge and daunting discovery makes Santos Ltd. and Carnarvon Petroleum Ltd. want to take on this project in the future. In 2019, Santos Ltd. and Carnarvon Petroleum Ltd. want to drill a third well, Dorado-3.

Conclusion
The Dorado Oilfield has opened up a variety of exploration opportunities with the drilling of appraisal wells Dorado-2 and Dorado-3. With the drilling of these wells, they have become more reliable and predictable reservoirs. Work on the oilfield is ongoing with mature rocks from the Jurassic to Palaeozoic. Exploration opportunities are taking forth to successfully take on the trapping styles and reservoirs that Dorado has to offer with the Lower Keraudren formation as the major focus of exploration.

Quote
"This is a country that is at once staggeringly empty and yet packed with stuff. Interesting stuff, ancient stuff, stuff not readily explained. Stuff yet to be found." - Bill Bryson, In a Sunburned County