Changes

==Porosity==

==Porosity==

Each of the porosity tools—density, compensated neutron, sonic, and photoelectrical effect—can be used to estimate porosity when lithology and fluid properties are known. (Methods for estimating porosity from these devices individually are described in the chapter on “[[Standard interpretation]]” in Part 4.) When both porosity and lithology are unknown, two or more of the devices can be used together to determine both porosity and lithology. (The most common methods for determining both porosity and lithology are described in the chapter on “Lithology from Logs” in Part 4.) Table 4 shows the resolution and applications of porosity devices.

Each of the porosity tools—density, compensated neutron, sonic, and photoelectrical effect—can be used to estimate porosity when lithology and fluid properties are known. (Methods for estimating porosity from these devices individually are described in [[Standard interpretation]].) When both porosity and lithology are unknown, two or more of the devices can be used together to determine both porosity and lithology. (The most common methods for determining both porosity and lithology are described in [[Lithology from Logs]].) Table 4 shows the resolution and applications of porosity devices.

{| class = "wikitable"

{| class = "wikitable"

===Sonic===

===Sonic===

Sonic devices measure the velocity of various acoustic waves, most notably compressional, shear, and Stoneley waves. The velocity of the waves is a function of the elastic properties and the density of the formation. Logs normally present the inverse of velocity, called the ''interval transit time'' or ''delta t'' (Δ''t''). A number of empirical relationships have been developed to relate compressional velocity to porosity (which are explained in the chapter on “Standard Interpretation” in Part 4).

Sonic devices measure the velocity of various acoustic waves, most notably compressional, shear, and Stoneley waves. The velocity of the waves is a function of the elastic properties and the density of the formation. Logs normally present the inverse of velocity, called the ''interval transit time'' or ''delta t'' (Δ''t''). A number of empirical relationships have been developed to relate compressional velocity to porosity (which are explained in [[Standard Interpretation]]).

Two versions of the compressional sonic device are available: the compensated sonic and the full waveform sonic (FWS). The full waveform sonic contains an array of receivers that are used to determine both compressional and shear velocities. Sonics are available in a variety of transmitter-to-receiver spacings from 3 to [[length::12 ft]] or more. The longer spacings are capable of investigating deeper into the formation. Both the conventional sonic and the full waveform sonic devices are used to measure compressional velocity. A typical presentation of compressional sonic measurements is shown in the log in Figure 1.

Two versions of the compressional sonic device are available: the compensated sonic and the full waveform sonic (FWS). The full waveform sonic contains an array of receivers that are used to determine both compressional and shear velocities. Sonics are available in a variety of transmitter-to-receiver spacings from 3 to [[length::12 ft]] or more. The longer spacings are capable of investigating deeper into the formation. Both the conventional sonic and the full waveform sonic devices are used to measure compressional velocity. A typical presentation of compressional sonic measurements is shown in the log in Figure 1.