Application of pre-stack seismic waveform inversion and empirical relationships for the estimation of geomechanical properties in Ruby field, central swamp depobelt, Onshore Niger Delta, Nigeria

Abstract

Pre-stack seismic inversion, well log analysis approach and empirical relations were adopted in this study to better estimate geomechanical properties of Ruby field with minimum error. The use of conventional well log empirical method alone to evaluate geomechanical properties in oil/gas fields sometimes becomes problematic. Geomechanical properties were divided into: elastic moduli [Young’s modulus, shear modulus, bulk modulus and Poisson ratio (PR)] and rock mechanical strength properties (closure stress ratio (CSR), brittleness (BRI) and compressibility). Four geomechanical earth models (CSR, BRI, Young’s modulus and PR) were generated from the inversion analysis to understand the distribution of rock strength properties across the field. The results deciphered high Young’s, shear and bulk modulus in the reservoir zone compared to the cap/seal rocks and a decrease in PR. This implies that, the cap/seal are more ductile and less compressible than the reservoir rocks, indicating that the reservoirs are highly brittle. CSR result reveals high in cap/seal indicating that the cap/seal rock are harder to fracture and has a greater chance to withstand higher compressive stress before failing as opposed to reservoir rocks. The inverted earth model shows that, Young’s modulus and brittleness increase toward the northeastern part of the field, while CSR and PR increase toward the southwestern part of the field. These results suggest that harder, stiffer, highly compressible and easily fractured rocks are found in the northern and eastern part of the field as opposed to the southern to western part of the field that is ductile.

Developing a relationship between static Young’s modulus and seismic parameters

“…In this regard, the integration of geomechanics and seismic plays an essential role in estimating the stress field and mechanical properties of rocks across reservoir unit. It implies that the geomechanical parameters can be estimated from seismic data based on empirical relationships for dynamic-to-static conversion (Herwanger and Koutsabeloulis 2011;Gray et al 2012;Jiang and Xiong 2019;Sharifi et al 2019;Ugbor et al 2021). As a widely applied and fundamental rock property, Young's modulus (E s ) is important for geomechanical reservoir characterization.…”

Envelope-based constrained model for multiparameter pre-stack seismic inversion

“…As the primary method of reservoir quantitative interpretation (Denney, 2013), pre-stack seismic inversion shows strong applicability and effectiveness in parameter estimation. In recent decades, pre-stack inversion has significantly been developed (Buland and Omre, 2003;Downton and Ursenbach, 2006;Buland et al, 2008;Pérez et al, 2013;Grana 2016Grana , 2020Wang et al, 2019;Li et al, 2021), especially for the corresponding parameter inversion used observed seismic reflection data, as widely applied in reservoir exploration (Avseth et al, 2016;Okeugo et al, 2019;Ugbor et al, 2021;Shakir et al, 2022).…”