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Площадь: 137047.06 км²
Kerala-Konkan basin
Kerala-Konkan basin lies south of the Mumbai Offshore area, the main productive oil province of India.
Kerala-Konkan Basin developed after the break-up of west Gondwana into Madagascar and Indian continents. A series of linear rifts, horsts and grabens developed parallel to the dominant basement fabric NNW-SSE (see Figure 1).There were significant tectonic events that affected the imprint of the newly formed western Indian basins such as: a) the rifting away from Madagascar; b) the reorientation of drainage system from east to west which affected the sediment supply to the west coast; c) uplift, extension and subsidence caused by the Deccan/Reunion mantle plume; d) the northward drift of India and development of its western coast carbonate systems and finally; e) the collision of India with the Himalayas.
The rifting between Madagascar and India led to development of clastic deposition over an already developed sag basin. With progressive rifting the basin went through a shallow marine stage which was disrupted by volcanism, uplift, extension and subsidence associated with the Deccan/Reunion mantle plume (Biswas, 1982). Continuous rifting took place as India, drifted into higher latitudes, contemporaneous with development of carbonate systems off the western coast. Afterwards, during midEocene the collision of the Indian and Asian tectonic plates occurred, the Himalayan uplift and reactivation of the western coast basins of India also took place. These events led to a period of clastic sedimentation over the rift basin followed by a five million year long span of volcanism, that originated the depositional environment of carbonates in the west coast, as opposed to the very active clastic sedimentation offshore the east coast still active nowadays. The Mesozoic sediments under the so-called Deccan basalt in the western flank of India are in actuality covered by flood basalts that were intense at the Tertiary-Cretaceous boundary and which have impacted the whole of west India. Interpreting the structuring of Mesozoic sediments under basalt either by seismic surveys or well drilling has been difficult due to homogenous and massive nature of the basalt. Deccan basalt blankets the Kutch, Saurashtra, Bombay and Kerala-Konkan basins. Our DISCover surveys are fundamental for the comprehensive seismic interpretation all along the western flank of the Indian peninsula deepwater realm.
Figure 1: Location and morphology of the Kerala-Konkan Basin in the southwest coast and southern tip off India. The basin is affected by the basalt flood events near its K/T boundary
Deepwater Stratigraphy
The litho-stratigraphy of the basin explains two different events of sedimentation before and after the Deccan basalt eruption, these are: (i) Sandstone dominated continental deposition (ii) Sandstone, shale and coal dominated deltaic/ marginal marine deposition (iii) Sand, shale and limestone dominated marine deposition (Shah et al, 2009). Sediments which are above the basalt are alteration of clastic and carbonate sediments. Lithology is mainly affected by marine transgressions, regressions pulses and Tertiary column sedimentation is mostly under the influence of Himalayan uplift.
It is interesting to note the divergence of the sedimentary columns between east and west India offshore basins (Figure 2). In the east coast basins of India the sediments are strikingly similar all with successive sequences of open marine clastics laid down during Upper Cretaceous, Tertiary and Plio-Pleistocene. This stratigraphy differs from the west coast due to the remarkable predominance of carbonates in these basins, which were starved during the Tertiary (Fainstein et al., 2008).
Figure 2: Generalized stratigraphy of the west coast Mumbai High consisting mostly of carbonates and shales, differs greatly compared with the dominant clastic stratigraphy of the east coast Krishna-Godavari Basin.
In the sub-basalt section, oil migration from source to reservoir requires pathways that are through windows of seals below reservoirs. Faults should provide the conduits that permit migration of oil from source to reservoir. In the western coast the predominant reservoirs are carbonates above basalt and carbonates and sands below basalt. These were deposited in several pulses of marine transgression associated with vertical uplift of the basins. The most important basin offshore in the West Coast is the Mumbai basin, the main producing area in India containing the giant Mumbai High field, This field discovered in 1974 is geologically unique its main producing reservoirs are Miocene carbonates. Deepwater wells are yet to be drilled in this province.
The modern technology seismic over-under reveals many distinct characteristics within the Tertiary and Mesozoic sections (see Figs. 3 & 4). Furthermore strong amplitude events are seen deep seated within the Mesozoic layers and a remarkable change in seismic bandwidth differentiates the Tertiary from the Mesozoic strata
Figure 3: The wonderful imaging of Mesozoic strata under basalt is clearly demonstrated in this in-line seismic section. A sizable anticline structure is delineated under an erosion unconformity represented by the Cretaceous/Tertiary boundary. Numerous faults compartmentalize sedimentary strata. High-amplitude anomalies on Mesozoic may represent earlier lava flowage (Reunion) event;
Figure 4: Southwest- Northeast line displays a volcanic ridge dome and the adjacent marginal Mesozoic basin. Tertiary cover is uniform the high amplitude reflection is the signature of carbonate platform. Shallow to deepwater subsidence of the basin occurred recently. Tertiary sequences are detached from Mesozoic sequences.
Petroleum Systems Assessment of Regional Data
In deepwater there are two rather distinct lithologies that were shaped before and after the Deccan flood basalt events. Modeling of a basin in two dimensions representing a reasonable cross-section of the focused portion of the basin, requires the basic geometry elements of the basin. These were obtained as per the description above with experimental offshore regional dip seismic lines acquired with state-of-theart technology and processed synthesized by Kirchhoff PSDM depth migration (Fig. 5), along with a synthetic seismogram based on density data (Fig. 6). Thickness of the basalt and the sub-basalt sediments are therefore based on the synthetic seismogram and on the interpretation of seismic section.
Figure 5 Seismic section synthesized by Kirchhoff PSDM. Basalt is represented by distinct bright and bold reflections. Sub-basalt dimmer amplitudes represent Mesozoic sediments;.
Figure 6: A regional synthetic view of the Kerala-Konkan, based on the interpretation of seismic and density data.
Data source:Modern Seismic Imaging and Basin Modeling Reveals Sub-Basalt Hydrocarbon Potential Offshore India. Somen Mishra, Roberto Fainstein, Rajesh Kalra, Radhakrishna Munukutla, Jyoti Shah, B.P.Wygrala S.Chandrashekkar4 and C.Visweswara Rao. 2022
Следующий Бассейн: Waipoga