HIGH flying Carnarvon Petroleum Limited has identified a number of follow-up targets totalling more than 600 million barrels with the confirmation of the exciting potential associated with this year’s Dorado-1 oil discovery off the north-west coast of Western Australia.
Carnarvon, which drilled Dorado-1 in a JV with Santos’ takeover target Quadrant Energy in the underexplored Bedout Basin has now his completed its initial assessment of the follow-up oil prospects that are in close vicinity to the oil discovery at Dorado-1.
Carnarvon says the Dorado discovery has unlocked a significant new play type with the discovery of high quality oil, gas and condensate in multiple stacked, high quality sandstone reservoirs that are set-up and trapped by what is now known to be a shale filled channel “Dorado Canyon”.
The company said preliminary mapping of the extent of this Dorado Canyon, and the similar Apus Canyon, has identified numerous other prospects that have been significantly de-risked because of the success of the Dorado-1 well.
Three key, nearby prospects have been further evaluated and volumetric and risking analysis undertaken. Carnarvon said Dorado and these three prospects are expected to attract significant Joint Venture focus in 2019 and 2020.
The company said the high quality of the reservoirs discovered at Dorado, with porosities averaging around 20% for the Caley reservoir, combined with the quality of the light oil (around 500 API) has meant that prospective resources have been estimated to have high recovery factors averaging around 43%.
The follow up prospects include:
Roc South, has been identified as a very similar trap to Dorado, similarly situated up-dip of the Roc discoveries and relying on the Dorado Canyon for sealing and setting up the prospect. The reservoir packages are expected to be thicker at Roc South compared to Dorado, although the smaller areal extent means the overall volumes are anticipated to be smaller than Dorado.
Given the very similar seismic characteristics between Dorado and Roc South and what is anticipated to be an identical oil sourcing mechanism, Carnarvon says the Roc South prospect has a relatively high chance of geological success.
With the crest of Roc South being around 13 km from the crest of the Dorado structure, and the two structures being even closer at lower levels, drilling success at Roc South would naturally lead to this structure being developed along with the Dorado discovery.
Recoverable oil from the Roc South prospect is estimated at 56 million barrels (Gross Pmean)
The Pavo structure is situated around 40km from the Dorado discovery and current analysis suggests that this trap consists of a single reservoir layer, leading to a more modest potential size of 82 million barrels of oil (Pmean, gross).
Given the proximity to a well drilled by previous permit holders, Keraudren-1, the technical attributes of this prospect are better known and hence this well has a higher geological chance of success. Keraudren-1 encountered the Hove seal and below 100’s of metres of high porosity and permeable sands and as such is unlikely to have stacked sands like Dorado and hence volumes are calculated at one single Caley level only. This prospect was evaluated on modern 2D seismic data.
Similar to the Dorado discovery that is situated only a few kilometres away, the Apus prospect (see Figure 1) is made up of number of potential stacked reservoirs in the Caley, Baxter, Crespin and Milne sands occurring over a considerable area.
When the individual sands are arithmetically added, the mean recoverable volume of oil of 612 million barrels (gross) is substantial.
The Apus reservoirs are trapped by the Hove seal and Apus Canyon, with oil being potentially sourced from below the Dorado Canyon.
The Dorado, Apus and Pavo traps are analogous to major hydrocarbon traps set up by the Marlin submarine canyons in the Gippsland Basin. Here, fine-grained marine sediments similarly provide the necessary top and side-seal. The Marlin channel sets up the Fortescue, Halibut, Cobia, Mackerel and Marlin fields (estimated ultimate recoveries of 100’s of million to almost one billion barrels of oil per field).