Simultaneous AVO Inversion
In cases where there is an AVO response in the seismic, and in cases when there is little or no acoustic impedance contrast for the reservoir zone, a prestack inversion is needed to properly determine the reservoir extent and quality. RockTrace® extends the InverTrace® Plus approach to the inversion of prestack data. The number of stacks needed to obtain the desired results is determined in the Feasibility stage, but typically ranges from 3 to 10.
The workflow for RockTrace projects generally follow these steps:
- Load seismic angle or offset gather stacks, well logs, and velocity information
- Perform petrophysical and rock physics analysis on the well log data
- Estimate the seismic wavelet for each angle or offset using a multi-well estimation technique
- Build a geologic model to stabilize the low frequency component for P-Impedance, S-Impedance, and Density in the inversion
- Run the RockTrace inversion and QC the results
- Generate volumes such as Vp/Vs, LambdaRho and MuRho, and Fluid Index volumes.
- Analyze and interpret the results
Jason’s RockTrace™ simultaneous inversion dramatically improved the development plan in the Horn Mountain field by predicting sand quality through interpretation of Net-to-Gross volumes. The client needed to understand sand quality which varied across the field, largely as a function of shale content and sand cementation. Prior to performing the inversion the client was making drilling decisions based on seismic amplitudes.
Furthermore, the client changed their development drilling plan after discovering that the lower M Sands had better than expected Net-to-Gross.
This figure shows the Net-to-Gross as recorded in the wells compared to the Net-to-Gross computed and predicted from the seismic inversion. There is a very strong match for both the J Sands (green) and the M Sands (red) between the measured data and the inversion results.
When additional wells were added after the project was completed, the correlation actually increased slightly compared to the numbers shown here.