Comprehensive Rock Physics, Petrophysics workflow to correct Sonic Logs for improved seismic QI: Study using wells of Krishna Godavari basin

Abstract

Rock physics analysis uses well log data as direct measurement of physical properties of the subsurface formations. Hence, in seismic reservoir characterisation they do not suffer the same level of scrutiny as seismic. Mud-filtrate invasion during drilling contaminates porous formation affecting log responses in non-intuitive ways. Ignoring invasion effect on well logs prior to quantitative petrophysical interpretations may led to erroneous reserve estimates as well as well-to-seismic misties. In addition, sonic logs are prone to ambiguity incorporated by weak waveform generation and non-unique coherence picking. This gives rise to non-unique compressional and shear slowness data. To correct the invasion affected logs, we have designed a workflow that effectively improves the recorded data. This workflow uses modified Gassmann (1951) fluid replacement modelling (FRM) method for sonic data correction. In addition, following an improved coherence picking we get a further updated sonic slowness. Using the corrected data in synthetic seismic generation enables us to achieve substantial improvements in synthetic-seismic correlation values. Furthermore, use of updated data results in a better three way matching with vertical seismic profiling (VSP) data.