- Industry: Oil & gas
- Number of terms: 8814
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Referring to a log of porosity based on the effect of the formation on fast neutrons emitted by a source. Hydrogen has by far the biggest effect in slowing down and capturing neutrons. Since hydrogen is found mainly in the pore fluids, the neutron porosity log responds principally to porosity. However, the matrix and the type of fluid also have an effect. The log is calibrated to read the correct porosity assuming that the pores are filled with fresh water and for a given matrix (limestone, sandstone or dolomite). It is presented in units of porosity (vol/vol or p. U. ) for the matrix chosen. Older logs were presented in counts per second or API units. The depth of investigation is several inches, so that the log reads mainly in the flushed zone. <br><br>The neutron porosity log is strongly affected by clay and gas. Hydrogen occurs in clays and hydrated minerals as well as pore fluids. Gas has a low hydrogen density, so that gas zones have a very low apparent porosity. The measurement is based on either thermal or epithermal neutron detection. Thermal neutrons have about the same energy as the surrounding matter, typically less than 0. 4 eV, while epithermal neutrons have higher energy, between about 0. 4 and 10 eV. Being a statistical measurement, the precision is greatest at high count rates, which in this case occurs at low porosity. <br><br>Neutron porosity logs were introduced in the early 1940s. The first tools were known as neutron-gamma tools, since the detector measured the gamma rays emitted on capture. Neutron-neutron tools, using a thermal neutron detector were introduced in about 1950.
Industry:Oil & gas
Referring to a borehole-compensation scheme for sonic logs that combines measurements taken when the logging tool is at two different depths in the borehole. In normal borehole-compensation schemes, the effects of caves and sonde tilt are minimized by combining measurements from a second transmitter (T2) above a pair of receivers with those from the first transmitter (T1) below the receivers. This arrangement makes the logging tool unacceptably long for the long-spacing sonic log. In the depth-derived system, T2 is located below T1, at a distance equal to the receiver spacing. T1 is fired and the transit time between the receivers at depth z (TT1z) is recorded as usual. Then when T1 and T2 are at depth z, both are fired sequentially and the difference in time for their signals to reach one of the receivers is recorded (TT2z). The average of TT1z and TT2z is borehole-compensated since the acoustic signals traveled in opposite directions for the two measurements.
Industry:Oil & gas
Referring to a fluid with several different immiscible fluids (oil, water or gas).
Industry:Oil & gas
Referring to a flow or other phenomenon with only one component, normally oil, water or gas.
Industry:Oil & gas
Radial distance from the wellbore to the outer tip of a fracture penetrated by the well or propagated from the well by hydraulic fracturing.
Industry:Oil & gas
Product of fracture permeability times fracture width for a finite-conductivity fracture.
Industry:Oil & gas
Production of formation fluid through the casing-tubing annulus.
Industry:Oil & gas
Pressure registered on equipment or devices when fluid flows through.
Industry:Oil & gas
Predictable variation of a property of a material with the direction in which it is measured, which can occur at all scales. For a crystal of a mineral, variation in physical properties observed in different directions is anisotropy. In rocks, variation in seismic velocity measured parallel or perpendicular to bedding surfaces is a form of anisotropy. <br><br>Often found where platy minerals such as micas and clays align parallel to depositional bedding as sediments are compacted, anisotropy is common in shales.
Industry:Oil & gas
