Interval velocities that were derived from Full Waveform inversion (FWI) were utilised to predict the rock strength for the deep section of a planned wellbore. The objective of the rock strength prediction is to optimize bit selection and bit trip planning for drilling. The well is planned to be drilled in the Northern Carnarvon Basin on the Australian North West Shelf. Laboratory-derived calibration of uniaxial compressive strength (UCS) is available from relevant offset wells at depths of approximately 4000m TVDMSL. Using the laboratory data, the appropriate empirical relationships for calculating UCS from sonic velocities can be identified for already drilled wellbores in the area. In these offset locations, UCS profiles derived from FWI velocities are scaled to closely match the UCS derived from downhole data. The same scalar is applied when UCS is calculated for an extracted FWI velocity profile in the planned drill location. Together with a lithology profile created through seismic interpretation, a rock strength profile is predicted at the planned drill location to depths that have previously not been drilled in the area.
AAPG Datapages/Search and Discovery Article #90324 © 2018 AAPG Asia Pacific Region GTW, Pore Pressure & Geomechanics: From Exploration to Abandonment, Perth, Australia, June 6-7, 2018