Full waveform sonic analysis

Full waveform sonic analysis

To complement our interpretation of borehole image logs we can deliver indicators of mobility and possible open fracturing by deriving these indicators from low-frequency Stoneley waveform log data.

Initially both indicators tend to be qualitative in nature, mainly because mudcake membrane barriers vary in thickness and stiffness and fracture-invading drilling-fluid filtrates can have dynamic viscosities that differ from those of undisturbed reservoir fluid. With sufficient additional permeability-calibration information we can achieve semi-quantitative indicators, still bearing strong sensitivity to hydraulically-open fracturing effects.

Where fracture density in some intervals might exceed resolution of Stoneley mobility and potential fracture indicators we would expect both indicators to show increases driven by integration of fracture density together with severity of individual open fractures.

We would expect any fracturing severe enough to cause recordable drilling-fluid losses during overbalanced drilling to also affect both indicators as long as borehole-fluid density during logging was similarly overbalanced enough to maintain fracture expansion, although it would also be reasonable to expect dampening effects from remaining fracture-clogging lost-circulation materials beyond mudcake.

We can deliver and apply quality-assured compressional and shear slowness data and bulk density data to compute mechanical properties: including velocity ratio (vp:vs), Poisson’s ratio (ν), bulk modulus (K), shear modulus (μ), Young’s modulus (E) and Lamé’s lambda (λ) constant. This can help clients appreciate mechanical stratigraphy. Overbalanced drilling can disturb borehole-local rock properties, especially for fractured cases.

We can also compute fastest and slowest flexural shear from full-waveform aligned and crossed dipole waveform log data.

For quality assurance we would appreciate (at client’s discretion and if available) access to any potentially pertinent information: such as drilling fluid properties and loss records; mud log or cuttings evaluations; core photographs, CT scans, minipermeametry scanning data, plug measurement data; LWD data, including any high-resolution images; all other log data, including high-resolution images, and wireline formation pressure and mobility testing results; geological reports, well completion reports, and fracture characterization reports.