Exploration in the southwest Malita Graben: initial results and remaining potential

Abstract

In 2011, Total E&P Australia and Petronas Carigali drilled two exploration wells in permit WA-403-P in the northern Bonaparte Basin. Both wells targeted the Middle-Jurassic play of the Elang/Plover formations that have yielded all commercial discoveries in the area. Notably, the wells were drilled in a less-explored area near the axis of the basin, targeting reservoirs at or more than 4,000 m. Pre-drill, the critical risks were recognised as burial-related reservoir degradation and cross-fault leakage into Upper Jurassic to Lower Cretaceous sands. The first well, Durville-1, was drilled on a poorly imaged three-way dip closure to the south of the Flamingo High. A gas column with high CO2 content was encountered in thick, high net-to-gross sands of lowermost Berriasian age. Drilling was terminated before the Elang Formation was reached. The second well, Laperouse-1, was drilled on a well-imaged fault block near the southern margin of the Malita Graben. The structure was formed in the Late Jurassic and lacks recent fault activation; thus, it was anticipated that early hydrocarbon charge might protect the reservoir from severe diagenesis. Laperouse-1 encountered a thick succession of Tithonian to Berriasian water-bearing sand packages; it reached total depth in the Elang Formation. The WA-403-P drilling campaign has confirmed the presence of thick Cretaceous sandstone in the area, although significant discrepancies in reservoir quality are observed between Durville-1 and Laperouse-1.