3D Energi Limited released prospective resource estimates for Monarch Prospect, located in the Otway Basin within VIC/P79 exploration permit, where the Company is in Joint Venture with ConocoPhillips Australia SH2 Pty Ltd. The full prospectivity of Monarch has only now been revealed by recent reprocessing of ~1135km2 of the La Bella and Investigator 3D seismic surveys over key leads and prospects in VIC/P79. 3D Energi retains a 20% participating interest in VIC/P79. The Monarch Prospect is a tilted fault block located on the margin of the Voluta Trough, a major depression directly adjacent to the Mussel Platform, with the two being separated by the northwest-southeast trending Tartwaup-Mussel Fault System.

Within VIC/P79, a chain of prospects has previously been delineated along the southern edge of the Mussel Platform, collectively referred to as the La Bella Complex. Monarch is the deepest prospect in the chain, which progressively shallows towards the east (Rosetta, Trident and Defiance, respectively) and culminates in the La Bella gas discovery. The principal reservoir at Monarch is the Waarre C reservoir, which serves as the main gas reservoir in the Otway Basin.

The Waarre unit thickens and deepens rapidly across the north-south trending fault separating Monarch from Rosetta, with the top of the Waarre C located at ~3000m depth at the Monarch crest. The La Bella MC3D reprocessing has revealed previously unseen DHIs, principally in the form of an interpreted flat spot within the Waarre C reservoir likely representing a gas-water contact. A second potential flat spot was also observed within the deeper Waarre A reservoir.

Flat spots are flat or tilted reflections that cut across the naturally inclined/dipping seismic reflections and coincide with the contact between the gas within the reservoir and the water beneath (namely they represent the gas-water contact). Examples of Otway gas fields with flat spots include Thylacine, Geographe and Minerva. Some of these examples are tilted, such as Minerva, most likely due to overburden velocity variations caused by the channelling.

As previously mentioned, gas fields in the Otway are typically amplitude supported. However, no major amplitude response is observable on reprocessed seismic at the top Waarre C reservoir at Monarch, except for a narrow band of high amplitudes along the western margin of the structure. Despite the significant uplift in image quality, the overall lack of amplitude at the top Waarre C reservoir is likely due to some remaining noise in the data above Monarch and Rosetta, potentially caused by internal heterogeneity within the channel in the overburden.

Seismic reprocessing delivers on image quality and the definition of Monarch: Previous explorers have overlooked the significant exploration potential of Monarch due to the challenge of discerning seismic reflections beneath the significant noise (seismic multiples) present in legacy data beneath extensive Tertiary channelling. This noise is particularly evident across the central La Bella 3D survey, reducing the seismic data quality beneath. For the first time, the Joint Venture has obtained a clear and continuous image of the seismic reflections in the Monarch Prospect, as well as Rosetta Prospect directly to the east.

The La Bella MC3D Reprocessing Project has applied the latest processing and imaging techniques, including Full Waveform Inversion and shallow water demultiple technology, resulting in a significant improvement in image quality beneath the channel. The presence and quality of 3D seismic in Otway Basin exploration are critical to successful exploration. By utilising 3D seismic, Operators within the Otway Basin have reported world-class success rates in drilling prospects supported by Direct Hydrocarbon Indicators in the offshore Otway Basin, with reported success rates of 100% respectively, within permits located adjacent to VIC/P793,4. Prior to the La Bella MC3D Reprocessing Project, no prospective resource estimates were provided for Monarch as poor data quality hampered an accurate evaluation.

Given the significant uplift in image quality of seismic reflections beneath the channel, in conjunction with the observation of a likely gas-water contact in the structure (coinciding with a flat spot), TDO is now able to provide a more accurate prospective resource assessment. Monarch now forms a material part of the VIC/P79 portfolio as the larger prospect (by volume) that has been identified in the permit to date. TDO estimates a prospective resource of 316 Bcf (gross best estimate)5 within the Waarre C reservoir; however, in the event of more favourable reservoir properties the high estimate could reach as much as 506 Bcf.

The prospective resource estimate considers only the Waarre C reservoir, however, additional prospectivity may exist within the deeper Waarre A reservoir based on the potential observation of a second flat spot. The new prospective resource estimate at Monarch upgrades the total VIC/P79 in-permit prospective resource base to 849 Bcf (gross best estimate), with 571 Bcf (gross best estimate) located within the La Bella Complex. All prospective resource estimates to date have been identified on 3D seismic within the eastern half of the permit and proximal to infrastructure.