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.

Highlights

  • Over the years, the evaluation of geomechanical properties in the Niger Delta oil and gas field has been neglected

  • Another advantage of the seismic-driven geomechanical model is that Prestack seismic inversion provides additional means to constrain the uncertainties of mechanical properties in the 3D space and better account for local variation introduced by complex geological structures (Xiaohui et al 2016)

  • This study focuses on the estimation of geomechanical properties from well data using empirical equations and seismic data using prestack time-migrated seismic waveform inversion in Ruby field reservoir competent assessment

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Summary

Introduction

The evaluation of geomechanical properties in the Niger Delta oil and gas field has been neglected. One fundamental advantage of using Prestack simultaneous waveform inversion is the ability of the inversion process to remove the effect of wavelet from the seismic data (removal of side lobe and tuning effect introduced by wavelet) and produce high-resolution image of the subsurface (Margrave et al 1998; Veeken and Silva 2004; Moosavi and Mokhtari 2016) Another advantage of the seismic-driven geomechanical model is that Prestack seismic inversion provides additional means to constrain the uncertainties of mechanical properties in the 3D space and better account for local variation introduced by complex geological structures (Xiaohui et al 2016). Seismic inversion method provides the most detailed view of the earth’s subsurface and its applications in the Niger Delta over the years have yielded increase in oil production (Dagogo et al 2016; Akpan et al 2020a, b)

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