Pockmark reservoir, a new carbonate reservoir type from the Madura Sub-Basin, Indonesia

The Mid-Pliocene grainstones (MPG) constitute the first type of reservoir to produce oil in Indonesia. So far, most of the MPG wells have been abandoned due to the small scale reservoiring but industry still has expectations for this today. However, its formation mechanism and distribution are still debated. Using seismic data interpre-tation, the J110 Sequence of the Early Pliocene is widely developed throughout the East Java Island, the Madura Sub-Basin, the Madura Island and the southern volcanic arc area in a bathyal environment as a highly condensed layer during the "biogenic bloom" period, from -7.8-3.5 Ma. There was a big environment change due to the -3.5 Ma tectonic compression event. Diapirism caused by the compression event eventually led to formation of pockmarks (or mud volcano craters) developed along the crest of anticlines from onshore East Java east-ward to the offshore Mudura Sub-Basin. Globigerina tests accumulated in the pockmark by cold seepage winnowing mechanism finally as high-quality petroleum reservoirs.