What Does Acoustic Log Data Analysis Mean?
Acoustic log data analysis in the context of in-situ stress refers to the analysis of data gathered from acoustic logging. Minimum horizontal stress changes with depth due to the pore fluid pressure in the vertical direction, and rock lithology. This stress can be measured by acoustic log data analysis or diagnostic fracture testing. Minimum horizontal stress (sh) is one of the principal stresses that confined underground formations are subjected to.
Stresses in underground formations are not uniform and change in magnitude based on direction. The stresses are generally compressive, anisotropic and non-homogenous.
Trenchlesspedia Explains Acoustic Log Data Analysis
Acoustic log data can be used to derive a considerable amount of information regarding the lithology and structure. Analysis of acoustic signal may include amplitude changes, velocity ratios of the various components of the waveform, and frequency-dependent effects.
A borehole has two main wave categories — refracted and guided waves. Refracted waves travel through the fluid from the transmitter and are refracted at the borehole wall from where they travel through the rock till refraction takes place again through the fluid back to the receiver. Guided waves on the other hand travel in the fluid at the interface of borehole wall/fluid.
Acoustic waveforms are recorded digitally and a variable-density log can be made. The variable-density log (VDL) or three-dimensional (3‑D) velocity log is recorded photographically. The variations in the darkness of the record are related to the changes in the amplitude of the cycles in the waveform.