ABSTRACT: Impact of fault seal prediction study on exploration and development in Iron Duke Field, Brunei Darussalam

Konert, Robert J., Daan den Hartog Jager, Roslinda Dato Hj Kifli, DK Siti Hajar Pg Hj Zainal , Brunei Shell Petroleum, Seria, Brunei

The Iron Duke field, discovered in 1984, is located 30 km offshore Brunei Darussalam. It has a total estimated reserve of 14 million m3 of oil and 21 billion m3 of gas in Upper Miocene shallow marine sandstones. Current production is 1700 m3/day liquids and 0.8 million m3/day gas. 25 wells have been drilled in the Iron Duke area, with a major development drilling campaign currently ongoing.

Iron Duke is a structurally complex field, dominated by a system of SW-NE trending collapse faults, subsequently tilted towards the NW and intersected by an oblique fault trend related to deep-seated wrench displacement. Drilling results indicate that sealing capacity may vary both vertically and laterally, even along a single fault.

The complex fault behaviour has made it difficult to predict hydrocarbon contacts in different blocks. Further uncertainty is caused by presence of hard overpressures (>20kPa/m) below the main reservoirs, complicating well design and increasing drilling costs. Reduction of uncertainties could be achieved by the use of fault imaging techniques, identification and enhancement of direct hydrocarbon indicators and application of tools to predict fault sealing capacity.

Fault sealing capacity has been assessed through technical studies, using seismic and well data, focussing on shale gouge ratio and cross fault juxtapositions. The resulting improvement in the geological model is expected to reduce the risk of future development, appraisal and exploration activities. These studies have a direct impact on the development strategy of the area and aim at maximising the value of the asset throughout its lifecycle.

AAPG Search and Discovery Article #90913©2000 AAPG International Conference and Exhibition, Bali, Indonesia