Sonic log will provide important information about the physical structure of a rock matrix. The ability of sound to travel within and through rock or sand and gravel depends on the physical structure of the matrix.
Because the total transit time from the transmitter to the receiver includes the path thru the borehole fluid + formation + borehole fluid, Borehole compensated (two or four receiver) logging tools are used. Borehole compensation is accomplished mathematically by subtracting the borehole transit time. It gives information resulting young’s modulus, bulk modulus, shear modulus, Poisson ratio, and Porosity.
Tool design philosophy & applications
The full wave form sonic tool has been specifically designed for the water, mining and geotechnical industries. Its specification make it ideal for cement bond logs (CBL), for the measurement of permeability index and as a specialist tool to carry out deep fracture identification.
During logging, a series of high frequency sonic impulses are emitted by the tool. Following their passage through the borehole fluid and formations, these impulses are detected by receivers at various distances from the transmitter. At each receiver, the arriving waveform is digitally sampled according to a set of predefined tool configuration parameters (sample rate, sampling period, gain).
The digitized waveforms are subsequently transmitted to the surface acquisition and recording system.
Sonic logs are widely used to provide formation porosity/permeability and mechanical properties.
Under suitable conditions S-wave and Stoneleys wave arrivals can be detected.
The tool must only be operated in fluid-filled hole and does no necessary need to be centralized.
Detection of poor or missing cement behind casing
Porosity and permeability
Variation of rock strength
Indication of fractures and permeability in hard rocks.
High energy of transmission to give a greater depth of penetration
Lower frequency of operation for greater penetration, and tube wave recording especially for CBL
Ability to record a long wave train for Tube wave reflection acquisition, which allows the determination of fracture aperture and permeability index.
Truly modular construction allowing variation of receiver/transmitter combinations
Higher logging speeds due to higher rate of data communication