Detection of sub-basaltic sediments by a multi-parametric joint inversion approach

Abstract

In many parts of the world sedimentary horizons with potential for hydrocarbon are located below flood basalt provinces. However, the presence of high velocity basaltic overburden makes delineation of sediments difficult due to the low velocity layer problem. Electrical and electromagnetic methods have been used in such scenarios because of the good electrical conductivity contrast between basalts and underlying sediments. However, mapping of the target sediments becomes difficult when the layer is thin as the data errors due to inherent noise lead to equivalent solutions. To tackle such difficult situations, a joint inversion scheme incorporating seismic reflection and refraction, magnetotelluric and deep electrical resistivity datasets is presented. Efficacy of the scheme is tested for a model comprising a thin sedimentary layer sandwiched between a thick basalt cover and a granitic basement. The results indicate that the parameters of the target sedimentary layer are either poorly resolved or equivalent solutions are obtained by the inversion of individual datasets. Joint inversions of seismic reflection (RFLS) and refraction (RFRS), or DC and MT dataset pairs provide improved results and the range of equivalent solutions is narrowed down. Combination of any three of the above datasets leads to further narrowing of this range and improvements in mean model estimates. Joint inversion incorporating all the datasets is found to yield good estimates of the structure. Resolution analysis is carried out to appraise estimates of various model parameters obtained by jointly inverting different combinations of datasets.

Nature-inspired stochastic hybrid technique for joint and individual inversion of DC and MT data

“…10 ) with error 0.0899, 0.1658 and 0.3816, and their associated time 1.94 Sec 1.84 Sec and 1.85 Sec per model, respectively (Table 5 ). The mean model obtained from vPSOGWO are reasonably near to their true model and better than results analyzed by Manglik et al 39 . These findings show that the equivalency problem related to the sedimentary layer has been much minimized.…”

“…The DC and MT data were more reliable for better resolution in shallow and deeper structure, respectively. In comparison to the inverted model by Manglik et al 39 , Table 5 shows less amount of uncertainty in the thickness and resistivity parameters. As a consequence, the vPSOGWO successfully lowers the amount of uncertainty and produces a mean model with higher precision.…”

Integrating Electromagnetic Data with Other Geophysical Observations for Enhanced Imaging of the Earth: A Tutorial and Review

“…The target of both studies is to image sub-basalt sediments in a region south-east of the Faroe Islands along the so-called Flare6 line. The thickness of the basalt and the geometry of the sediments below is of great interest for hydrocarbon exploration (Christie and White 2008;Manglik et al 2009;Patro et al 2015) as it determines the potential prospectivity of the hydrocarbon reservoir. Both studies use a combination of seismic travel times and electromagnetic data for their inversion approach.…”