Rock physics attribute analysis for hydrocarbon prospectivity in the Eva field onshore Niger Delta Basin
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ORIGINAL PAPER-EXPLORATION GEOPHYSICS
Rock physics attribute analysis for hydrocarbon prospectivity in the Eva field onshore Niger Delta Basin Alexander Ogbamikhumi1 · Nosa Samuel Igbinigie1 Received: 1 April 2020 / Accepted: 5 August 2020 © The Author(s) 2020
Abstract Direct hydrocarbon indicator (DHI) expressions observed on seismic could arise due to various geological conditions. Such expression could lead to misinterpretation as hydrocarbon presence if not properly analyzed. This study employs rock physics attributes analysis to evaluate an identified prospect in the undrilled area of the studied reservoir. Prospect identification was actualized by analyzing structural and amplitude maps of the reservoir, which revealed a possible roll over anticline at both the exploited and prospective zone, with a very good amplitude support that conforms to structure. Well-based cross-plot analysis adopted four cross-plot techniques for feasibility study to test the applicability of rock physics for prospect evaluation in the field; Lambda-Rho versus Lambda-Rho/Mu-Rho ratio; Mu-Rho versus Lambda-Rho; and Poisson Ratio versus P-impedance. The result presented Poisson ratio, Lambda-Rho and Lambda/Mu-Rho ratio as good fluid indicator and Mu-Rho as a viable lithology indicator. As such, they were selected for seismic-based attribute and cross-plot analysis to validate the identified prospect. The results from seismic-based analysis showed consistency in the expression of the analyzed attribute at both the exploited and prospective zone. The seismic-based cross-plot analysis result was similar to the well-based analysis and was able to confirm that the observed amplitude expression in the exploited zone is an indication of hydrocarbon-bearing sand. Keywords Rock attribute · Cross-plot · Seismic inversion · Prospect validation · Rock physics
Introduction Seismic acoustic inversion and cross-plot analysis are effective tools in reservoir characterization. Avseth et al. (2008) define impedance inversion as a tool that offers insight into subsurface interpretation process, converting reflection amplitudes into more meaningful variations in layer properties (elastic properties), which can be related directly to the well log data after pertinent scale considerations has been made (Bosch et al. 2009). These established relationships are in turn incorporated to estimate rock attribute that can be employed to discriminate lithology and fluid for a typical field evaluation, especially in undrilled areas. Rock properties are the physical properties of rocks that influence the propagation of seismic wave. They basically * Alexander Ogbamikhumi [email protected] Nosa Samuel Igbinigie [email protected] 1
Department of Geology, University of Benin, Benin City, Edo State, Nigeria
include compressional wave velocity, shear wave velocity, density and their numerous derived attributes which include P-wave impedance, Poisson’s ratio, S-wave impedance, etc. (Dewar and Pickford 2001). The observed amplitudes on seismi
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