- Industry: Oil & gas
- Number of terms: 8814
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The electrical device used on the axle of a spool or reel to provide electrical continuity between the rotating reel core and the stationary reel chassis. When using a coiled tubing string equipped with an electrical conductor, such as required during coiled tubing logging operations, a collector is fitted to the reel axle to allow connection of the surface data-acquisition equipment.
Industry:Oil & gas
The effective resistivity of the formation water or the mud filtrate, as it affects the electrochemical potential. The electrochemical potential is the main source of the spontaneous potential log. The equivalent water resistivity, or equivalent resistivity, is defined as the reciprocal of the activity of a solution, so that the formula for the electrochemical potential, E<sub>c</sub>, can be written as:<br><br> E<sub>c</sub> = - K log<sub>10</sub> (R<sub>mfe</sub> / R<sub>we</sub>)<br><br>where K is a coefficient, and R<sub>mfe</sub> and R<sub>we</sub> are the equivalent water resistivities. The importance of R<sub>mfe</sub> and R<sub>we</sub> is that they are equal to the actual water resistivities for NaCl solutions above about 0. 1 ohm-m. In salty waters below 0. 1ohm-m, the equivalent resistivity is lower by an amount that depends on temperature and salinity. In fresh waters, divalent ions such as Ca<sup>++</sup> and Mg<sup>++</sup> have a strong effect on E<sub>c</sub>. R<sub>we</sub> is then related to R<sub>w</sub> by an empirical transform that assumes average concentrations of these ions. For fresh mud filtrates, it has been common practice to set R<sub>mfe</sub> = 0. 85 * R<sub>mf</sub>.
Industry:Oil & gas
The effect on a propagation resistivity or induction log of charge buildup at the boundary between two formation layers with different dielectric properties. In a vertical well with horizontal layers, the current loops generated by the tool in the formation are parallel to the layers and do not cross bed boundaries. However, with an apparent dip between borehole and formation, the loops cross the bed boundaries and generate a charge buildup at the boundaries. The charge buildup acts like a secondary transmitter that increases the measured resistivity. The result is a spike to high resistivity as the tool crosses the bed boundary. In deviated or horizontal wells, polarization horns on measurements-while-drilling propagation logs often are used to detect a bed boundary. <br><br>The spike increases with apparent dip and resistivity contrast between beds. The magnitude of polarization spikes varies with tool type and spacing, being larger for the propagation tools.
Industry:Oil & gas
The effect on a laterolog whereby the current lines are no longer properly focused but spread out at a certain distance into the formation. The effect occurs opposite a high-resistivity bed with low-resistivity shoulders. The result is that laterolog devices, in particular deep devices, tend to read too low and have less depth of investigation. Shoulder bed correction charts correct for these effects in certain well-defined situations, such as no invasion in horizontal beds with vertical wells.
Industry:Oil & gas
The effect of a sharp change in the borehole diameter, such as that caused by a cave or rugose hole, on an induction log. In smooth boreholes of constant diameter, the effect of the borehole is well understood and can be corrected for. However, a sharp increase in diameter over a small depth interval can induce signals on one coil in the array and not in others. This signal is not handled by the normal borehole correction and may result in a spike on the log. The spike usually is significant only when the resistivity is high and the contrast between formation and borehole resistivity is very large. The spike also depends on the design of the array or the processing.
Industry:Oil & gas
The dynamic simulation of fluids through a reservoir model over time. When the simulation correctly recreates the past reservoir performance, it is said to be "history matched," and a higher degree of confidence placed in its ability to predict the future fluid behavior in the reservoir.
Industry:Oil & gas
The duration that a cement slurry remains in a fluid state and is capable of being pumped. Thickening time is assessed under downhole conditions using a pressurized consistometer that plots the viscosity of a slurry over time under the anticipated temperature and pressure conditions.
Industry:Oil & gas
The drop in reservoir pressure or hydrocarbon reserves resulting from production of reservoir fluids. At times, a strong waterdrive will maintain reservoir pressure to a substantial degree so that reserves diminish without a corresponding pressure decline.
Industry:Oil & gas
The depth of the first reliable reading of a curve on a log. For the typical bottom-to-top survey, the curve readings before the tool is picked up from the bottom of the hole are not reliable--they are straight lines that do not represent the formation at the depth indicated. With several logging tools in a tool string, the first reading of each curve will be at a different depth, depending on the measure point of each tool.
Industry:Oil & gas
The depth or time between successive measurements by a sensor. For measurements-while-drilling (MWD) logs, the sampling interval is most commonly a time. For wireline measurements, it is most commonly a depth.
Industry:Oil & gas
