RE: Chess Board2 Feb 2024 12:17
SundaGas Banda Unipessoal Lda (“SundaGas”) operates the offshore TL-SO-19-16 Production Sharing Contract (PSC),
offshore Timor-Leste, which contains the Chuditch-1 gas discovery, drilled by Shell in 1998 on 2D seismic. The Chuditch-1
well encountered a 29m gas column at the top of a good quality Plover Formation reservoir section, under the regional Lower
Cretaceous Echuca Shoals and Wangarlu Formation sealing shales. The gas was interpreted to be trapped in a three-way
fault-bound structure, with the well located in a downdip position. Shell exited the area in 2001, likely due to lack of
commercialisation options for gas at that time, and no further drilling has taken place although a 3D seismic survey was
acquired in 2012. SundaGas signed the PSC in 2019 and on initial evaluation of the legacy 2D and 3D PSTM seismic data,
Chuditch was estimated to hold about 700 Bcf of recoverable gas resource. Adjacent faulted and low relief four-way dip closed
traps were also identified but were observed to be partially coincident with bathymetric highs even after depth conversion.
Imaging of the near top reservoir Darwin seismic event was also extremely poor close to fault zones, particularly in the area
between the Chuditch discovery well and the crestal bounding fault, the position of which itself was uncertain.
To address these issues, 1,270 km2 of vintage 3D seismic data has been reprocessed to PSDM during 2021-2022, including
the application of Full Wavefield Inversion. Significant effort was put into velocity model building, to resolve the issues created
in large part by the shallow section. This project was carried out by TGS Imaging UK and resulted in a significant uplift in data
quality, such that the Chuditch field can be clearly imaged for the first time (Figures 1 and 2).
A number of observations are emerging from ongoing interpretation of these data:
• The Chuditch discovery appears substantially larger than previously assessed, with P50 estimate of recoverable
gas resources of approximately 1.1 Tcf, significantly greater than resource estimates from earlier mapping.
• Adjacent prospects have either been enhanced, modified or removed on the new 3D PSDM mapping compared to
earlier vintages. These additional features are anticipated to hold further mid-case prospective gas resources of
approximately 2.1 Tcf in total.
• Subsurface risks associated with these resources have been significantly reduced on the improved new seismic
dataset.
• The Wangarlu Fm. shales appear to behave in a ductile fashion, with faults in the underlying Permian to Lower
Cretaceous being dislocated from the Upper Cretaceous and Tertiary, explaining structural differences and the
regionally effective nature of the seal.
The uplift achieved through seismic reprocessing, and the resulting realisation that the Chuditch field appears to be materially
largely than previously thought, means less appraisal drilling is likely to be required to