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The AAPG/Datapages Combined Publications Database

Southeast Asia Petroleum Exploration Society (SEAPEX)


Proceedings of the South East Asia Petroleum Expolration Society Volume IV, 1978
Pages 81-94

Geology of Bombay High and Adjoining Structures

Bhagwan Sahay


The Bombay offshore basin, a southern extension of the Cambay basin where oil and gas fields on land have been discovered came into existence during Upper Cretaceous time due to the faulting in the Deccan trap basement.

The first seismic surveys were undertaken in 1962-1963, followed by detailed surveys in 1972 and 1973 by CGG and GSI, respectively. As a result of these surveys, a number of structures, I.e. Bombay High, Bassein, Diu, Dahanu, and South Tapti, etc., were delineated. The Bombay High, the largest structure, is on a large palaeohigh which extends for over 100 km in a NW-SE direction with a faulted eastern flank and a gentle-dipping western flank. Besides the Bombay High, other important structures, like Bassein, Tarapur, Satellite, Diu, and small closures in DCS area, have also been evaluated by drilling. The stratigraphic column from a well In Bassein structure, where a full sedimentary section from Palaeocene-Recent was met, has been taken as a type section to illustrate the stratigraphy of Bombay offshore basin. On the Bombay High, no sediments earlier than late Oligocene were deposited.

The different seismic reflectors, H-1 to H-4, can be correlated from east to west and north to south, except for occasional variations. There is a considerable change in the fades between the wells drilled on different structures.

The oil and gas-bearing horizons of the Bombay High, Bassein, South Bassein, DCS and other structures are mostly micrite/biomicrite and chalky limestones. These range in age from Middle Miocene to Early Eocene and exhibit both primary and secondary porosity.

In view of: (a) occurrence of big oil/gas fields at Bombay High and South Bassein, (b) presence of a small oil field at Bassein and B-38, and (c) oil/gas indications in several other smaller structures, exploratory drilling Is contemplated to evaluate unexplored structures north, northwest, south and southeast of the Bombay High.

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