Bayu-Undan gas and condensate field, Bonaparte Basin The APPEA Journal 2000. Field: Bayu-Undan Gas and Condensate Field. Location: Bonaparte Basin, Timor Sea
Top of HRDZ: 400––500 ms
Pull-up: Strong
Intensity: High
Amplitude Anomalies: Weak A relatively small but intense HRDZ is located to the east of the Bayu-Undan Field, north-east of the Mistral–1 well (Fig. 4a). This anomaly is roughly circular to ovoid along strike (Fig. 4b and c), shows significant pull-up, and degraded stack response of the underlying reflectors (Fig. 4a). It is evident at both the top Paleocene (Fig. 4b) and base Miocene (Fig. 4c) horizons, suggesting that it formed during the Late Tertiary. Various models have been proposed for the origin of this anomaly, ranging from diagenetic alteration, perhaps induced by leaking hydrocarbons (Brooks et al, 1996), to a Late Eocene meteorite impact (Gorter, 1999). We favour a leakage-related origin; the localised nature of the anomaly may suggest that it is caused by leakage at the intersection of two fault trends. An older, north-south trending fault system is evident on seismic data in the Timor Sea and intersects with the more recent NE–SW and E–W faulting. This older fault system is most clearly seen near the Buffalo and Bayu-Undan fields, but is believed to extend over the Skua Field further to the south and west. The intense nature of the interpreted HRDZ suggests that the Mistral trap is strongly breached, though this needs to be confirmed independently by additional work, such as fluid inclusion studies or petrophysical analysis. Another low intensity anomaly is located immediately to the ENE of the Bayu–5 well (Figs 4b and c). This anomaly is significantly smaller and less intense than that associated with Mistral, perhaps suggesting that smaller amounts of hydrocarbons have leaked from this part of the Bayu trap. 
a)
b)
c)
Figure 4. HRDZs near the Bayu-Undan Field. a) Seismic strike line through Mistral HRDZ; b) Seismic horizon image (TWT) at Base Miocene horizon; c) Seismic horizon image (TWT) at Top Paleocene horizon. © This collection APPEA Limited 2000. Authors retain © in respect of their own contribution. |
