|INDIA DEEP FOCUS - INVESTIGATING SUB-BASALT PLAYS THROUGH INTEGRATION OF HIGH-RESOLUTION GEOPHYSICAL DATA|
1Fugro Geoscience, 2Fugro Robertson Ltd
The West coast of India is generally regarded as under-explored, this is particularly true of the Kerala-Konkan basin where exploration has been restricted to the shelf and relatively unsuccessful to date. Recently attention has turned to the deepwater portion of the basin and the exploration potential associated with the sub-basalt sedimentary sequences; however the current understanding of the region is based on sub-optimal heritage information.
In conjunction with the Directorate General of Hydrocarbons (DGH) of India, Fugro has initiated the India Deep Focus project to acquire 2D long offset seismic data on the West coast of India, from the Indus Fan in the North to the Mannar Basin in the South. Phases I & II of India Deep Focus is shown below in Figure 1.
High-resolution potential fields data was acquired along with the seismic data to aid interpretation of the Deccan Trap basalts and regional geology. This new geophysical data has been integrated with the available well data, scientific literature in the public domain and analysis of the regional palaeogeographic evolution based on the Fugro Robertson Plate Wizard™ project. The aim of this process was to construct a coherent understanding of the regions geological history and hence the identification of a potential deepwater hydrocarbon province, focussing on the sub-basalt section.
The seismic data was acquired during the period May-June 2009 and subsequently processed by Fugro Geoscience India Pvt Ltd. The data is of high quality with a good range of amplitude variation; the seismic record length is 13 seconds two-way-time.
Early work to identify the age of the oceanic crust offshore West India indicates the continental shelf is relatively narrow (Figure 2). This suggests a relatively simple plate tectonic history dominated by the break-up of Gondwana and rifting between India and Madagascar. Shortly afterwards the Seychelles rifted from NW India and the Deccan traps were extruded. A recent publication by Carmichael et al. (2009) suggests the continental shelf is not as narrow as previously thought, but this paper does not cover the Kerala-Konkan basin.
Consequently, the geophysical data collected for the India Deep Focus project has been analysed for evidence of the continent-ocean boundary (COB), notably the presence of Seaward Dipping Reflectors (SDRs). An area of SDRs has previously been identified offshore West India by Roberts (2008) in the south of the India Deep Focus area. SDRs have been identified in volcanic passive margins around the world (eg. Faroe Islands) and interpreted as being related to seafloor spreading at the edge of the COB. The identification of the COB using the potential fields data and changes in the crustal signature is complicated by the presence of low density crust beneath the Laxmi and Chagos-Laccadive ridges, which has been related to volcanism.
Utilising Fugro's geophysical data it has been possible to produce a detailed geological history for the West coast of India. A period of massive crustal instability appears to have occurred in the proto-Indian Ocean which accounts for some of the discrepancies encountered during compilation of the regional geological history. It also suggests a potential deepwater hydrocarbon province is present.
Synthetic Aperture Radar data used has been used to interpret the presence of seeps and identify areas where a petroleum system maybe active. The seeps identified as potential natural slicks occur beneath a significant syn-rift section and in some cases are associated with faults which were reactivated during the Tertiary. The presence of deep Mesozoic grabens offshore of the Kerala-Konkan basin, and evidence of oil seeps, suggests that a previously unrecognized petroleum system is active beneath the Deccan Trap basalts.
CARMICHAEL, S.M., S. AKHTER, J.K. BENNETT, M.A. FATIMI, K. HOSEIN, R.W. JONES, M.B. LONGACRE, M.J. OSBOURNE and R.S.J. TOZER. 2009. Geology and hydrocarbon potential of the offshore Indus Basin, Pakistan. Petroleum Geoscience 15, 107-116.
EGOROV, V. and YALAMANCHILI S.V. (RAO). 2009 India Deep Focus – West Coast of India Gravity and Magnetic Data Interpretation. Interim Interpretation report. Unpub. Microsoft PowerPoint presentation, 50 slides.
FUGRO ROBERTSON LIMITED. 2010. Plate Wizard™
Müller, D.R., Roest, W.R., Royer, J-Y, Gahagan, L.M. and Sclater, J.G. 1997. Digital Isochrons of the Worlds Ocean Floor. Journal of Geophysical Research v. 102, 3211-3214.
ROBERTS, G. 2008a. Deepwater West Coast India – The Opening Up of a New Play. Geo Expro 5(5) 52-58.
Singh, N.K. and Lal, N.K. 1993. Geology and Petroleum Prospects of Konkan-Kerala Basin In Proc. Second Seminar on Petroliferous Basins of India v.2 (Ed. Biswas et al.)