Leveraging High-Frequency Full-Waveform Inversion (FWI) for Reservoir Quality Discrimination

The paper presents a reprocessing project in the Sarawak Basin, Malaysia, that uses high-frequency full-waveform inversion (FWI) to improve the resolution of the velocity model to distinguish reservoir quality and facies change. The legacy data was processed in 2018 and led to a successful oil discovery in XI well. The reprocessing was aimed to identify the reservoir extension beyond XI. X2 well was subsequently drilled after XI but failed to find any hydrocarbon. Since X2 was drilled concurrently with this reprocessing, it served as a blind well for velocity validation after the drilling. This project ran FWI up to 38Hz and the inverted velocity contains high-frequency details such as beddings, faults, and geological structures. The FWI velocity correlated well with XI and X2 sonic velocities, confirming its robustness and accuracy. The 38Hz FWI velocity shows higher velocity at the reservoir section of X2, suggesting a tighter reservoir compared to XL The result also suggests better reservoir is located at the northern side of the fault block. This paper concluded that high-frequency FWI velocity can be used as a useful interpretation tool to indicate facies change and reservoir quality and aid the critical decision-making process such as determining the drilling locations.