Sasanof Prospect, Offshore Western Australia, PRM 12.5%
The Sasanof Prospect is a large, seismic amplitude supported, structural-stratigraphic trap in the high-quality reservoir sands of the Cretaceous Lower Barrow Group on the Exmouth Plateau.
The Prospect is on trend and directly updip of the Mentorc Gas Field which contains a certified 2C 378 Bcf of gas and 16.4 MMbbls of condensate (2C) and covers an area of 18 km2. The liquids rich, low C02 Mentorc Field is the eastern fault block and is “filled to spill” into the updip Sasanof Prospect to the west.
The Sasanof Prospect covers an area of up to 400 km2 and is estimated by ERCE to contain a 2C Prospective Resource of 7.2 Tcf of gas and 176 MMbbls of condensate (P50 recoverable) with a 32% Chance of Success (CoS). (See PRM announcement of 7 December 2021 for full ERCE report details)
The Prospect is supported by Direct Hydrocarbon Indicators (DHIs) with strong seismic amplitudes defining the prospect area and the reservoir is anticipated to be of high quality and effectively sealed at the top of the Lower Barrow Group.
The reservoir is predicted to be a series of coarsening upward sandstone cycles with a gross thickness of 80m at the well location. The well will drill through the reservoir section and reach total depth within the Lower Barrow Group shales.
Sasanof Location Map
Sasanof West to East Cross Section
MENTORC GAS FIELD – DOWNDIP PLAY OPENING DISCOVERY
The Mentorc Gas Field is a downdip discovery adjacent to the eastern edge of the greater Sasanof Prospect. Two wells have been drilled on the field, these being the original discovery well and a subsequent appraisal well that underwent full dynamic production testing.
Mentorc was discovered in 2010 and opened up the play within the topsets of the top Lower Barrow Group. The field consists of multi Darcy (> 10 Darcy) and high porosity (average porosity 27%) reservoir sands that are over 100 m thick and contain a 60 m gas column. The field was identified by strong amplitudes on the Glencoe 3D seismic survey. Subsequent analysis showed the flat-spot amplitude cutoff and gas water contact correspond to within 1 m. Mentorc contains a Gaffney Cline certified 2C 378 Bcf (P50 585 Bcf GIIP) and 2C 16.4 million barrels of condensate (P50 26 MMbbls CIIP).
SASANOF PROSPECT TECHNICAL BACKGROUND
The Sasanof Prospect is covered by several high-quality modern 3D seismic surveys. The Glencoe 3D survey is the most technically advanced and analysed data set over Sasanof.
Western Gas has considerably enhanced the seismic data with reprocessing and inversion projects. One of the key geophysical advantages, and reasons for recognising Sasanof as a significant play, is over 20 wells in and surrounding the Equus blocks have been used to calibrate the Glencoe 3D geophysical response. The data is now considered of excellent quality.
A key focus has been on the analysis of the amplitudes including a comprehensive Rock Physics and Quantitative Interpretation (QI) study by the industry leading seismic processing company DownUnder Geosolutions (DUG). One of DUG’s main conclusions from its QI study was that “updated lithology and fluid predictions confirm the prediction of gas in Sasanof”.
The Sasanof trap is a structural-stratigraphic trap on the edge of the Barrow Delta front. The structure dips to the east and north and is closed to the south by erosion of the topsets on the back delta plain. The key updip closure, to the west, is provided by a combination of incised shale-filled distributary channels and pinch-outs of the deltaic topset sands. The Sasanof-1 well location has been chosen on a 4-way dip closed structure on an upthrown fault block, within the overall stratigraphic trap.
The Sasanof reservoir section comprises the top set sands of the Barrow Delta and successful analogues include the Van Gogh Oil Field on the North West Shelf and numerous producing Alaskan, Siberian and Pakistani stratigraphically trapped giant fields.
The reservoir thickness prediction, based on seismic inversion data, varies from 30 m to 120 m over the 400km2 area. The reservoir quality is excellent in all the nearby Barrow Group delta front wells. The top seal is proven at Mentorc and at numerous other fields in the Northern Carnarvon Basin.
The predicted hydrocarbon charge is based on the discovered fields either side of the Sasanof location. To the west, the Pinhoe and Royal Oak gas fields have almost the same high liquids, low CO2 gas composition as the downdip Mentorc field to the east of Sasanof. The geochemical similarities indicate a related hydrocarbon source has charged all the valid traps in this area, via vertical fault migration.
Based on Western Gas analysis, Sasanof has a geological chance of success of 32%
The Sasanof-1 well will be a vertical well with single casing string design and will be drilled to a total depth of approximately 2500 m in 1070 m of water.
In the success case, the well will be comprehensively evaluated, fluid samples and pressure measurements will be recovered to allow for the certification of resource volumes. The well will be fully plugged and abandoned, with caprock isolation, upon completion of evaluation activities.