• Nagendra Pratap Singh

      Articles written in Journal of Earth System Science

    • Use of genetic algorithm in reservoir characterisation from seismic data: A case study

      Satya Prakash Maurya Nagendra Pratap Singh Kumar Hemant Singh

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      In the present paper, a seismic inversion based on genetic algorithm (GA) is performed to characterise the reservoir using seismic data only from the Blackfoot field, Alberta, Canada. The algorithm is first tested on synthetically generated data to optimise the GA parameters. The error analysis between the inverted and the expected results suggested that the performance of algorithm is exceptionally satisfactory. Thereafter, the inversion is performed for real seismic data from the Blackfoot field. The seismic data is first inverted for acoustic impedance section and then it is transformed into the velocity and density sections using the relation derived from the well-log data. The interpretation of the inverted/derived results depicts a low-amplitude anomaly zone between 1055 and 1065 ms time interval, which is characterised as a reservoir. The results demonstrate the efficacy and applicability of the GA in reservoir characterisation from the seismic data alone. This study is very helpful for the offshore projects where the information about well logs are missing.

    • Seismic modelling of $\rm{CO_{2}}$ fluid substitution in a sandstone reservoir: A case study from Alberta, Canada


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      The prime objective of this study is to find the suitable petrophysical parameters which depict the maximum change in seismic amplitude due to fluid substitution. Therefore, in the present study thepetrophysical parameters are analysed to detect the most sensitive parameters due to fluid substitution. The analysis is performed in three steps: In the first step, the Gassmann fluid substitution is performedand a considerable change in velocity, density, impedance, lambda–mu–rho parameters and Shuey’s parameters is examined. The study shows that the most sensitive parameters are $A$ (intercept), whichshows the maximum drop of 22% with respect to $\rm{CO_{2}}$ injection, and $B$ (gradient), which shows the maximum increase of 10% with $\rm{CO_{2}}$ injection in the formation. Thereafter, in the second step, the seismic forward modelling is performed to examine the changes in seismic amplitude by the fluid substitution in the formation. The analysis depicts that the seismic amplitude increases steadily with increasing $\rm{CO_{2}}$ saturation. The amplitude increases by 4% at 20% $\rm{CO_{2}}$ injection, by 8% at 50% $\rm{CO_{2}}$ injection and the seismic amplitude increases by 12% at 100% $\rm{CO_{2}}$ injection in the target zone. Finally, in the third step, the numerical modelling is performed to assess the ability of seismic methods to detect the $\rm{CO_{2}}$ plume accurately by injecting $\rm{CO_{2}}$ plume of cylindrical shape. The analysis shows that the $\rm{CO_{2}}$ plume can be detected more prominently by analysing the impedance volume rather than the seismic amplitude section. This study is helpful in deciding which parameters should be monitored carefully in fluid replacement modelling projects.

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