Sub-basalt Imaging of Hydrocarbon Bearing Mesozoic Sediments Using Ray-trace Inversion of First-arrival Seismic Data and Elastic Finite-difference Full-wave Modeling along Sinor-Valod Profile of Deccan Syneclise, India.

KARABI TALUKDAR1 and LAXMIDHAR BEHERA1*

1CSIR-National Geophysical Research Institute (CSIR-NGRI), Uppal Road, Hyderabad-500007, India.

E-mail: laxmidhar@ngri.res.in (*Corresponding Author)

 

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 (Fig. 1a). The full-wave synthetic seismic data generated have been processed and imaged using conventional seismic data processing technique with Kirchhoff pre-stack time (PSTM) and depth migrations (PSDM). 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 allow 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 (Fig. 1b).

                                                                                                                                            

Paper Published in Pure and Applied Geophysics (2018), Vol. 175, Issue 8, pp. 2931-2954

https://doi.org/10.1007/s00024-018-1831-z external link

 

Fig. 1 (a) Geology map of the Deccan Syneclise region having Sinor-Valod seismic profile (solid black line) with wide-angle SPs (SP1, SP2 marked as red dots) acquired for sub-basalt imaging. (b) The corresponding PSDM seismic image obtained by generation of full-wave synthetic seismic data using staggered-grid elastic finite-difference modeling superimposed on the velocity model derived along the Sinor-Valod seismic profile show the presence of hydrocarbon bearing Mesozoic sediments hidden below the thick column (> 2.0 km) of basalts.