- Industry: Oil & gas
- Number of terms: 8814
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A log that shows the magnitude of the correction applied to the long-spacing detector of a density measurement. When delta rho is above a certain value, typically +/- 0. 15 g/cm<sup>3</sup>, the correction may no longer be accurate, and needs to be examined in more detail. Delta rho is also used as a qualitative indicator of borehole rugosity.
Industry:Oil & gas
A log provided by a casing collar locator tool that generally incorporates a gamma ray log to correlate the relative position of casing string features, such as the location of a pup joint, with the reservoir or formation of interest.
Industry:Oil & gas
A log recorded using an electrical wireline. In this sense, the term refers to any log recorded on a wireline, whether it measures an electrical quantity or not. The term dates from the early days of logging when the only logs were the spontaneous potential and resistivity from conventional electrode devices.
Industry:Oil & gas
A log run for the purpose of correlating between wells. The most common logs used for this purpose are the gamma ray, the resistivity and the acoustic log; the most common depth scales are 1/500 and 1/1000, or 2 in. /100 ft (5 cm/30 m) and 1 in. /100 ft (2. 5 cm/30 m).
Industry:Oil & gas
A log showing the depth or relative position of casing or tubing collars that is used to correlate depth for depth-sensitive applications such as perforating or isolation treatments. Indications are provided by a collar locator tool and correlations are made with previous baseline logs, such as the gamma ray log, or the casing or tubing running tally prepared during the installation process.
Industry:Oil & gas
A log that has been generated from digital data some time after the actual acquisition of the data. It is distinct from the acquisition log. Some of the parameters for processing the log may or may not be different from those of the acquisition log.
Industry:Oil & gas
A log or a recording in which the complete signal received at an acoustic transducer is recorded. With full-waveform recording, it is possible to determine the slowness not only of the first arrival but also of later arrivals. In borehole sonic logging, these may be the shear, flexural and Stoneley waves. The waveforms are recorded by an array of receivers in an array-sonic tool, and processed with a suitable technique such as slowness-time coherence.
Industry:Oil & gas
A log of the resistivity of the formation, expressed in ohm-m. The resistivity can take a wide range of values, and, therefore, for convenience is usually presented on a logarithmic scale from, for example, 0. 2 to 2000 ohm-m. The resistivity log is fundamental in formation evaluation because hydrocarbons do not conduct electricity while all formation waters do. Therefore a large difference exists between the resistivity of rocks filled with hydrocarbons and those filled with formation water. Clay minerals and a few other minerals, such as pyrite, also conduct electricity, and reduce the difference. Some measurement devices, such as induction and propagation resistivity logs, may respond more directly to conductivity, but are presented in resistivity.
Industry:Oil & gas
A log of the high-frequency (on the order of 25 MHz) dielectric properties of the formation. The log usually includes two curves the relative dielectric permittivity, symbolized by epsilon which is unitless, and the resistivity in ohm-m. At the frequency used, water molecules have a strong effect on the dielectric properties, so that both relative dielectric permittivity and conductivity increase with the volume of water present. Relative dielectric permittivity can be used to distinguish hydrocarbons from water of any salinity. However, the effect of salinity is more important than the salinity effect with the high-frequency electromagnetic propagation log, and the interpretation is more complex. The advantage of the dielectric propagation log is that the lower frequency permits a larger depth of investigation and therefore an analysis of the undisturbed zone.
Industry:Oil & gas
A log of photoelectric absorption properties. The log measures the photoelectric absorption factor, P<sub>e</sub>, which is defined as (Z/10) <sup>3. 6</sup> where Z is the average atomic number of the formation. P<sub>e</sub> is unitless, but since it is proportional to the photoelectric cross section per electron, it is sometimes quoted in barns/electron. Since fluids have very low atomic numbers, they have very little influence, so that P<sub>e</sub> is a measure of the rock matrix properties. Sandstones have low P<sub>e</sub>, while dolomites and limestones have high P<sub>e</sub>. Clays, heavy minerals and iron-bearing minerals have high P<sub>e</sub>. Thus, the log is very useful for determining mineralogy. In interpretation, PEF is normally converted to the simpler volumetric cross section, U in barns/cm<sup>3</sup>, by taking the product of PEF and density. <br><br>The log is recorded as part of the density measurement. The depth of investigation is of the order of one inch, which is normally in the flushed zone. PEF can be affected by heavy minerals such as barite in the mudcake or mud filtrate. PEF logs were introduced in the late 1970s.
Industry:Oil & gas
