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Widespread deposition of platform and reefal carbonates of the Baturaja limestone formation occurred during the Miocene epoch in the South Sumatra basin. Although significant oil and gas deposits have been discovered in the porous facies, porosity within the Baturaja limestone has been observed to vary widely between tight platform facies and highly porous reefal facies, making predrill prediction of porosity an important exploration objective. I use amplitude‐versus‐offset seismic modeling to distinguish between porous and tight Baturaja limestone facies. Amplitude variations with offset for reflections from two Baturaja reefs in the South Sumatra basin were studied: one, a proven gas reservoir, the other, an interpreted reef that had not yet been drilled at the time of study. The seismic data were processed judiciously to preserve and enhance amplitude effects, which were then modeled using the Bortfeld approximation for reflection coefficients. A key assumption was that the [Formula: see text] ratio of limestone depends primarily on minerology rather than on porosity or pore‐fluid content. The modeling showed that porous and tight limestone facies have unique and different reflection-coefficient variation patterns with angle of incidence. Good agreement was found between observed data and the modeling results, indicating that the modeling of amplitude variations with offset can be used as a lithology discriminant. In the second case, a predrill prediction of porosity was confirmed by subsequent drilling.

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This special section on Southeast Asia features geophysical topics that cover several of the magnificent geotectonic provinces of the region. Southeast Asia is the site of the world's largest archipelago, which features more than 20,000 islands extending east to west more than 3500 miles. The extent of the offshore regions of the archipelago is many times greater than its land area. The Sunda Shelf, with its numerous Tertiary basins in the western part of the archipelago, contains areas of India, Myanmar, Thailand, Laos, Cambodia, Vietnam, Malaysia, Singapore, the Philippines, Brunei, West Indonesia, and their offshore regions that extend from the Andaman Sea to the Makassar Strait. By contrast, eastern Sunda, with its pre-Tertiary basins, embraces the islands along and north of the Banda Arc, from Sulawesi to western Papua in Indonesia and Timor-Leste and surrounding seas ( Figure 1 ). The most distinguishing tectonic features of the archipelago are related to the collision of the Indo-Australian Plate with the Sunda Shelf and the areas east of it. Numerous volcanoes and earthquake epicenters trace an extensive arc of collision-related subduction zones, which makes this one of the most tectonically active regions in the world. Back-arc and other basins within the stable parts of the Sunda Shelf are the sites of significant hydrocarbon accumulation, primarily within the territorial boundaries of Indonesia and Malaysia.