Estimating Permeability From Sonic Log

Estimating Permeability From Sonic Log

Estimating Permeability From Sonic Log

An innovative permeability derivation method and workflow has been developed using the Stoneley wave attenuation mechanism. This method offers a more accurate and sensitive approach to estimating formation permeability. Here are the key aspects and details of the methodology and findings:

Basis of the Method:
- Stoneley-Wave Characteristics:
- The method is based on the relationship between Stoneley-wave propagation characteristics and formation permeability. Specifically, as formation permeability increases, Stoneley-wave velocity decreases while its attenuation increases.

Workflow Components:
1. Extraction of Stoneley-Wave Attenuation:
- Stoneley-wave attenuation is rigorously extracted from the waveform data obtained through monopole sonic measurements.
2. Inversion to Permeability:
- The extracted Stoneley-wave attenuation is then quickly inverted to determine the permeability of the formation.

Sensitivity Analysis:
- Sensitivity Comparison:
- The sensitivity of Stoneley-wave velocity and attenuation to different model parameters was analyzed. The findings showed that Stoneley-wave attenuation is significantly more sensitive to permeability changes than Stoneley-wave velocity.
- Borehole mud velocity has a strong influence on Stoneley-wave velocity but weakly affects Stoneley-wave attenuation. Therefore, Stoneley-wave attenuation is a more effective parameter for permeability inversion.
- The sensitivity analysis highlighted the advantages of using Stoneley-wave attenuation over velocity for permeability inversion due to its higher sensitivity to permeability changes.

Inversion Methodology:
The current inversion method consists of three major steps:
1. Estimate Stoneley-Wave Attenuation:
- Frequency-dependent Stoneley-wave attenuation is estimated from monopole sonic measurements.
2. Build a Forward Simulation Model:
- A forward simulation model is constructed using standard logs (gamma ray, caliper, resistivity, density, neutron, and sonic data). The theoretical Stoneley-wave attenuation is calculated under an initial permeability value using full Biot theory.
3. Iterative Comparison and Optimization:
- The measured Stoneley-wave attenuation is compared with the theoretical values, and the optimal permeability is determined through iterative processes.

Workflow Diagram:

Conclusion:

This innovative method utilizing Stoneley-wave attenuation for permeability derivation provides a reliable and sensitive tool for reservoir characterization. The method enhances the ability to estimate permeability in the absence of core data, making it a valuable asset for reservoir simulation and management.