Unformatted text preview: asure of a formation’s capacity to transmit sound waves. Tool is consists of two transmitters & four receivers. Transmitter 1 starts to emit waves which received by two receivers. Then this process repeats again with transmitter 2 and the other two receivers. Tool is putted in center of borehole (no contact with hole). Quantitatively, the sonic log is used to evaluate porosity in liquid filled pores. The tool is only capable of measuring travel time. Many relationships between travel time and porosity have been proposed, the most commonly accepted is the Wyllie time average equation. The equation basically holds that the total travel time recorded on the log is the sum of the time the sonic wave spends traveling the solid part of the rock, called the rock matrix and the time spent traveling through the fluids in the pores. Фs= (∆t‐∆tma) / (∆tp‐∆tma) Where: Фs is sonic porosity, ∆t is Transit time in formation, ∆tma is Transit time through 100% of the rock matrix, ∆tp is that through 100% of the pore fluid. Calibration: The tool is calibrated inside the borehole opposite beds of pure and known lithology, such as anhydrite (50.0 ms/ft.), salt (66.7 ms/ft.), or inside the casing (57.1 ms/ft.). Values for ∆t and V in Wyllie’s time average equation: Names and mnemonics of common industry sonic tools: 57 Geology & Geophysics in Oil Exploration Mahmoud Sroor Geology & Geophysics in Oil Exploration Radioactive Tools:
Density Tool: Litho-Density Tool (LDT) These tools have a caesium-137 or cobalt-60 source emitting gamma rays at 0.662 MeV, a short-spaced and a long-spaced detector in the same way as the basic formation density tool. However, the detectors are more efficient, and have the ability to recognize and to count separately gamma rays which have high energies (hard gamma rays: 0.25 to 0.662 MeV) and gamma rays which have low energies (soft gamma rays: 0.04 to 0.0 MeV). Gamma ray enters the formation, then scattering & looses some of its energy then absorbed by a formation. Then, the d...
View Full Document
- Spring '10
- Geology, Volcano, Tephra, Volcanic Ash, Geology & Geophysics, Mahmoud Ahmed Sroor