Interpretation of seismic inversion using ternary diagram: Seismic lithology identification

Abstract

Considering the demand for lithology identification in quantitative seismic interpretation, I introduced ternary diagrams based on rock physics modelling to derive lithology from seismic data. For this purpose, physical and acoustic parameters of minerals were utilized to reconstruct the most common rocks in hydrocarbon reservoirs, including source, reservoir and caprock. Subsequently, the generated rocks were input into a ternary diagram based on easily obtained parameters from seismic data, including acoustic impedance, V_P/V_S ratio and lambda–mu–rho parameters. Next, two ternary diagrams were implemented according to the elastic parameters for reservoir (and source) and caprock identification. The theoretical results indicated that the proposed ternary diagrams can be applied for interpreting seismic inversion data to discriminate limestone from sandstone and shale using lambda–rho. Additionally, mu–rho can serve as a criterion to differentiate dolomite from limestone and anhydrite (or sandstone from shale and limestone). The obtained ternary diagram was validated using ultrasonic and well-log data from blind wells and subsequently used to interpret 3D seismic data. For this purpose, acoustic impedance was calculated using a simultaneous inversion method from pre-stack data and converted to elastic parameters, which were then input into the ternary diagrams. The validation procedures yielded promising results and demonstrated that ternary diagrams can effectively identify different lithologies compared to conventional binary cross-plots. The advantage of the proposed diagrams lies in their comprehensiveness and generality, making them compatible with seismic limitations and applicable to a wide range of sedimentary rocks. The findings of this research can enhance the interpretation of seismic inversion results when mineral fraction or petrophysical interpretation is unavailable. Finally, the advantages and limitations of the methodology were discussed, and the impact of reservoir heterogeneities and fluid types on ternary diagrams was analysed. It was concluded that the proposed diagrams are not restricted to specific depositional settings and can be developed for the seismic interpretation of unconventional reservoirs and igneous rocks through the implementation of the mentioned methodology.