A B C D E F G H I J K L M N O P Q R S T U V W X Y Z All
Gavarshetty, C. P.
- Stratigraphy and Sedimentation of Bombay Offshore Basin
Authors
1 ONGC, Priyadarshini, Eastern Express Highway, Bombay 400022, IN
Source
Journal of Geological Society of India (Online archive from Vol 1 to Vol 78), Vol 40, No 5 (1992), Pagination: 415-442Abstract
Correlation of seven chronostratigraphic sequences in over 300 wells drilled in the six structural blocks constituting the Bombay Offshore Basin has helped in defining the stratigraphy, paleogeography and facies distribution and suggesting a model for shelf carbonate deposition. The sequences correlated are: Paleocene-Early Eocene, Middle-Upper Eocene, Lower Oligocene, Upper Oligocene, Lower Miocene, Middle Miocene and Middle Miocene-Holocene.
The most significant observations arc 1) Surat depression and its southward extension through other grabens up to Ratnagiri block contain a restricted marine, paralic and continental shale, sand and coal facies of 500-3000 m. thickness, deposited during syn-rift. Paleocene-Early Eocene phase. This is the principal source rock in the basin. 2) The main reservoirs are the Miocene limestones in Bombay High and Middle Eocene and Lower Oligocene limestones in other areas. 3) The main sandstone reservoirs are in the Oligocene sequences in Daman-Tapti area of Surat depression and in the Paleocene-Lower Eocene sequence in Heera-Bassein and Ratnagiri blocks. 4) By tracing the clastic dispersal.pattern, it is shown that Saurashtra basin and Shelf Margin basin with their excessive Upper Oligocene-Holoccne fill are less favourable than the rest of the basin in hydrocarbon potential.
A homoclinal ramp model is suggested for the shallow shelf carbonate deposition. The suggested carbonate depositional model indicates that the platfonn areas are susceptible to shale incursions from the east which could affect the reservoir properties of limestone in many areas. Almost all the major carbonate pay zones are associated with unconformities and diastems and the principal porosity is telogenetic.
Keywords
Stratigraphy, Sedimentation, Carbonates, Bombay High.- Lithostratigraphy and Hydrocarbon Prospects of the Olpad Formation of Paleocene-Early Eocene Age in Ahmedabad-Mehsana Tectonic Block, Cambay Basin
Authors
1 Geology section, Oil & Natural Gas Corporation Limited, Mehsana Project, Mehsana - 384 002, IN
2 Geology section, Oil & Natural Gas Corporation Limited, EBG, Priyadarshini, Bombay, IN
3 Geology section, Oil & Natural Gas Corporation Limited, ERBC, RDS Project, Sibsagar, IN
Source
Journal of Geological Society of India (Online archive from Vol 1 to Vol 78), Vol 49, No 4 (1997), Pagination: 371-388Abstract
The Olpad Formation of Paleocene-Early Eocene age represents the oldest Tertiary clastic deposits. in the Mehsana area, North Cambay Basin. This unit is characterised by its heterogeneous lithologic association of volcanic conglomerate, volcanic wacke, trapwash, siltstone and shale, deposited by alluvial fan systems along fringes of palaeohighs and lacustrine to brakish water condition in the existing palaeolows. Recent exploratory drilling proved the occurrence of hydrocarbons in this formation. This significant find has prompted the necessity of identifying potential hydrocarbon reservoirs. The formation has been subdivided into three lithostratigraphic units (Unit I - III in descending order) based on sedimentary facies and well log characteristics. The reservoir characteristics of the sediments of Olpad Formation has been worked out based on sedimentological, SEM and XRD studies.
Lithostratigraphic correlation, structural configuration and thickness variation have been discussed. The study reveals that the distribution of different lithostratigraphic unit is controlled by tectono-sedimentation factors and the volcanic wacke lithofacies of Unit-I and III constitute the reservoir rock in the Olpad Fonnation. The study led to the identification of Umiwa. Khambel and Gamanpura as prospective areas for future exploration for structural-cum-stratigraphic traps.