Facies Distribution and Petroleum Geology of the Bombay Offshore Basin, India

Abstract

In view of the recent oil and gas dicoveries in the Bombay Offshore basin, its detailed geology has been worked out in terms of its source rock and reservoir potential. An agewise, layer‐cake lithofacies analysis and five depositional model maps from Paleocene to Middle Miocene age, together with a number of paleotectonic sections has led to the reconstruction of a xeneralized depositional model of the basin as a whole. This proposed depositional model envisages the Bombay Offshore basin as a shelf‐to‐basin carbonate model. During Paleogene and Early Neogene time the clastic supply by the proto‐Narmada river from the NE resulted in delta progradation up to the Dahanu depression, which was a region of pro‐deltas and lagoons with a considerable thickness of finer clastics. Beyond the Dahanu depression, the Bombay High and Bassein‐Alibag‐Ratnagiri shelf remained open carbonate platforms, while the DCS area was the locale of shelf‐edge carbonate build‐up. The potential targets for exploration are the deltaic sandstone to the north in the Tapti area—particularly where the sandy facies interfingers with the shales and the porous limestone horizons in the Bombay Platform, Bassein‐Alibag‐Ratnagiri shelf and the DCS trend. The Dahanu depression is thought to be the main source rock area.

Seismological constraints on the structure and composition of western Deccan Volcanic Province from converted phases

“…On the contrary, the stations closer to the coast exhibit large P M s delays (0.3s–0.7s) with respect to MUL and show a thick crust (>38 km) with the thickest crust (41 km) observed at KOP, which is on the coast. Absence of surface sediments in the coastal plains, lack of evidence for the presence of Mesozoic sediments beneath the traps in the Mumbai offshore [ Basu et al , 1982] and along the DSS profiles at Koyna, together with the absence of complexities in the observed RFs indicate little possibility of thick sediments contributing to the observed delays. However, the shallow, large amplitude P to S conversions observed at several stations may possibly reflect the presence of thin layers of pre‐trap Mesozoic sediments and/or variations in the thickness of the low velocity traps.…”

Tholeiitic dykes in the Seychelles and the original spatial extent of the Deccan

“…The same goes for studies of the Indian shelf (e.g. Biswas 1982;Basu et al 1982), where the basalt cover is shown as continuous or only rarely penetrated by Archaean inliers. Such a continuous basalt cover would not be expected if much rifting occurred after volcanism had ceased.…”

The Late Eocene‐Early Miocene Unconformities of the NW Indian Intraplate Basins and Himalayan Foreland: A Record of Tectonics or Mantle Dynamics?

“…The BMU is documented and regionally mapped in the Barmer, Cambay, Kutch (Chowdhary, ; Chowdhary & Singh, ; Kundal et al, ), and Bombay (Mumbai) Basins (Basu et al, ; Mehrotra et al, ; Mohan, ; Wandrey, ) as an erosional event of generally decreasing erosional depth southward (Figure , panels 5–7). In subsurface data sets, it is recognized as a regional seismically correlatable reflection event (Figure ).…”