Abstract
Imaging below the basalt for hydrocarbon exploration is a global problem because of poor penetration and significant loss of seismic energy due to scattering, attenuation, absorption and mode-conversion when the seismic waves encounter a highly heterogeneous and rugose basalt layer. The conventional (short offset) seismic data acquisition, processing and modeling techniques adopted by the oil industry generally fails to image hydrocarbon-bearing sub-trappean Mesozoic sediments hidden below the basalt and is considered as a serious problem for hydrocarbon exploration in the world. To overcome this difficulty of sub-basalt imaging, we have generated dense synthetic seismic data with the help of elastic finite-difference full-wave modeling using staggered-grid scheme for the model derived from ray-trace inversion using sparse wide-angle seismic data acquired along Sinor–Valod profile in the Deccan Volcanic Province of India. The full-wave synthetic seismic data generated have been processed and imaged using conventional seismic data processing technique with Kirchhoff pre-stack time and depth migrations. The seismic image obtained correlates with all the structural features of the model obtained through ray-trace inversion of wide-angle seismic data, validating the effectiveness of robust elastic finite-difference full-wave modeling approach for imaging below thick basalts. Using the full-wave modeling also allows us to decipher small-scale heterogeneities imposed in the model as a measure of the rugose basalt interfaces, which could not be dealt with ray-trace inversion. Furthermore, we were able to accurately image thin low-velocity hydrocarbon-bearing Mesozoic sediments sandwiched between and hidden below two thick sequences of high-velocity basalt layers lying above the basement.
Highlights
The Deccan Volcanic Province (DVP) of India is an important large igneous province in the world, as it marks the Cretaceous–Paleocene (* 65 Ma) boundary, which has witnessed a major global climate change (Courtillot et al 1988; Keller et al 2008)
We have extended the results to build complete pre-stack depth migration (PSDM) seismic image along the profile with fine-scale horizons of sub-trappean Mesozoic sediments hidden below the thick basalts as trap, sedimentary basin as well as the basement configuration
The present study mainly focuses the imaging of complex subsurface geological structures beneath highly heterogeneous and thick column of rugose basalt layers
Summary
The Deccan Volcanic Province (DVP) of India is an important large igneous province in the world, as it marks the Cretaceous–Paleocene (* 65 Ma) boundary, which has witnessed a major global climate change (Courtillot et al 1988; Keller et al 2008). The tomographic imaging for the first time has clearly brought out a smooth and minimum-structure velocity model along the 90-km-long wide-angle seismic profile in this highly complex Deccan trap with a meaningful interpretation of the presence and extension of sub-trappean Mesozoic sediments favorable for hydrocarbon accumulation, hidden below the thick and highly heterogeneous basalts (Behera and Sen 2014). To overcome difficulties associated with sub-basalt imaging and accelerate hydrocarbon exploration activities in the Deccan Volcanic Province of India, we have adopted a robust elastic finite-difference full-wave modeling approach using staggered-grid scheme (Virieux 1986) This approach is capable of computing synthetic seismic data (shot gathers) using numerical simulation of elastic wave propagation through different layers having thick rugose basalts and thin hydrocarbon-bearing sub-trappean Mesozoic sediments in the Deccan trap-covered region of India as imaged by Behera and Sen (2014) with the help of robust tomographic inversion technique. Basalt interface (direct arrivals, primary reflections, multiples, mode-conversions, diffractions, groundrolls, scattering, etc.) using numerical simulation of elastic wave propagation through the model and generation of full-wave synthetic seismic data for sub-basalt imaging of Mesozoic sediments
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