The Sunrise-Troubadour fields, containing between 10 and 16 tcf of retrograde gas condensate, are located in the Timor Sea, 450 km to the northwest of Darwin, Australia. The 80-m-thick, Middle Jurassic siliciclastic reservoir is entrapped in a fault-bounded structural closure that has 180 m of vertical relief and covers an area of 75 50 km. The volumetric significance of this field was identified through an intense late 1990s appraisal campaign. This paper presents the geoscientific results of this campaign and their implications for project evaluation and development planning.

Reservoir quality, continuity, and connectivity are the essential subsurface determinants of the size of these accumulations. These parameters were primarily controlled by depositional environment. Overall, the reservoir succession is of moderate net to gross (approximately 30%); however, most of the gas is contained in two high net-to-gross sublayers. The latter main gas-bearing subintervals are interpreted to have been deposited during lowstand episodes, the lower unit being represented by an incised valley complex and the upper by attached, forced-regressive shoreface deposits. Deposition in this limited accommodation setting has resulted in lateral reservoir continuity and broad sheetlike stratigraphy. Lithologically, the reservoir comprises very fine- to coarse-grained quartzarenites and sublitharenites that are interbedded with variably brackish to open-marine shales. The whole succession displays an overall upward increase in marine influence.

The main phase of faulting and trap formation occurred during the Quaternary. Detailed fault modeling indicates a low likelihood of compartmentalization in this extensive structural high. Variations in both hydrocarbon maturity and condensate yield across the field indicate nonequilibration of the recently emplaced hydrocarbons that have been derived from a mature (1.3–1.4 %R_o) Middle Jurassic marine kerogen source rock. Pressure analysis indicates a tilted gas-water contact that sits above a dynamic aquifer.

Reservoir geologic data have been matched to seismic amplitude variation with offset (AVO) effects to constrain depositional modeling via statistical inversion techniques. This has then been fully integrated with mapped and probabilistically modeled subseismic faults into dynamic reservoir simulations. The work flow involved the identification of key uncertainties and the detailed, focused evaluation of these parameters. This in turn provides confidence in reservoir volumes and behavior, despite widely spaced well data. Development planning is in progress, with commercial production planned for this decade.