- Industry: Oil & gas
- Number of terms: 8814
- Number of blossaries: 0
- Company Profile:
A technique in which an ultrasonic transducer, in transmit mode, emits a high-frequency acoustic pulse towards the borehole wall, where it is reflected back to the same transducer operating in receive mode. The measurement consists of the amplitude of the received signal, the time between emission and reception, and sometimes the full waveform received. Tools that use this technique either have multiple transducers, facing in different directions, or rotate the transducer while making measurements, thereby obtaining a full image of the borehole wall. Pulse-echo techniques are used in the borehole televiewer. In cased hole, the waveform is analyzed to give indications of cement-bond quality and casing corrosion.
Industry:Oil & gas
A technique in which a tracer is injected into the flow stream of a production or injection well to determine fluid paths and velocities. Radioactive tracers have been used from the 1940s and are still common for determining flow profiles in injection wells. Tracers with high neutron-capture cross section, such as borax or high-salinity water, were introduced in the 1970s to record injection/pulsed neutron logs. In multiphase production wells, special tracers were introduced in the 1990s to move with only one phase, so as to give a phase-velocity log. Radioactive tracers with different energies are used to track the development of fractures, or other processes, in the multiple-isotope log. <br><br>Tracer measurements are used qualitatively to determine the movement of fluids behind pipe, or quantitatively to determine fluid-flow velocity within the pipe.
Industry:Oil & gas
A technique in which a slug of material is introduced into the flowstream of a producing well to determine the flow rate of one or more of the fluids. The marker has specific properties, such as high neutron capture cross section, that allow it to be detected by sensors of a production logging tool. Some markers are specifically designed to be soluble in only one fluid phase, so that they can be used to produce a phase-velocity log. The term refers to nonradioactive markers, in contrast to the more traditional radioactive markers, or tracers.
Industry:Oil & gas
A technique in nuclear magnetic resonance (NMR) logging based on the shift in the T<sub>2</sub> distributions, or spectra, acquired with different echo spacings. The technique is usually used to detect gas or light oil. These fluids have a significant diffusion relaxation. A measurement made with a standard short echo spacing will give a signal from these fluids at a certain T<sub>2</sub>. A measurement made with a long echo spacing will cause more diffusion relaxation and a shorter T<sub>2</sub>. Other fluids, with minor contribution from diffusion, will not be changed. Gas and light oil can therefore be identified by the shift between the two T<sub>2</sub> distributions.
Industry:Oil & gas
A technique in nuclear magnetic resonance (NMR) logging that is based on the difference between the T<sub>2</sub> distributions, or spectra, acquired at different polarization times. The technique often is used to detect gas or light oil. These fluids have long T<sub>1</sub> that exceed 1 s. A measurement made with a long polarization time will polarize much of these fluids and give significant signal at the appropriate T<sub>2</sub>. A measurement made with a short polarization time will polarize little of these fluids and will give a much smaller signal. Other fluids, with shorter T<sub>1</sub>, will be polarized in both cases, so that a difference in signal at the appropriate T<sub>2</sub> identifies gas or light oil.
Industry:Oil & gas
A technique in nuclear magnetic resonance (NMR) logging based on a long echo spacing, specially chosen to enhance the diffusion of formation water. Echo spacings in standard NMR logs are too short to allow any significant diffusion relaxation from water. Long echo spacings, for example 3 s, cause diffusion relaxation to limit the maximum T<sub>2</sub> from water. They also limit the maximum T<sub>2</sub> from light hydrocarbons. However, there is a certain range of viscosity of medium oil that is less affected. The enhanced diffusion technique therefore permits the identification of some medium oils.
Industry:Oil & gas
A technique for utilizing fractal geometry to produce reservoir descriptions.
Industry:Oil & gas
A technique for the semiquantitative mineralogical analysis of a sample of rock by measuring the diffraction peaks in X-rays diffracted by the sample. The position of the diffraction peaks is a measure of the distance between discrete crystallographic diffracting planes within minerals, while their intensity indicates the quantity of the mineral. The technique is only semiquantitative because the size and shape of the diffraction peak are strongly influenced by the geometry of the measurement, for example orientation of the minerals, and sample preparation. Fine particles such as clays must be separated from larger particles and measured separately if they are to be detected properly. To reduce errors associated with preferred orientation of minerals, samples are most commonly ground to a powder before analysis, a technique known as powder X-ray diffraction.
Industry:Oil & gas
A technique for recording the formation compressional slowness based on the transit time between transmitter and receiver. In the most basic wireline sonic measurement, an acoustic transducer emits a sonic signal, of between about 10 and 30 kHz, which is detected at two receivers farther up the hole. The time between emission and reception is measured for each receiver, and subtracted to give the traveltime in the interval between the two receivers. If the receivers are two feet apart, then this time is divided by two to give the interval transit time, or slowness, of the formation. This type of measurement is also known as first motion detection. <br><br>This technique works because the first arrival at the receiver is a wave that has traveled from the transmitter to the borehole wall, where it has generated a compressional wave in the formation. Some of this wave is critically refracted up the borehole wall, generating head waves in the borehole fluid as it progresses. Some of these strike the receiver, arriving in most cases well before any signal traveling directly through the mud. Furthermore, if the logging tool is parallel to the borehole wall, the traveltime in the mud is cancelled by taking the difference between the traveltime to the two receivers. Problems of irregular hole or a tilted tool are avoided by using borehole compensation. <br><br>The depth of investigation depends on the slowness, the transmitter-to-receiver spacing and the presence or absence of an altered zone. It is generally within the invaded zone, and of the order of several inches.
Industry:Oil & gas
A technique for recording sound at different positions in the borehole to generate a noise log. The measurement technique uses a microphone to record signals in the audible range approximately 20 to 20,000 Hz. In some circumstances, the frequency of the signal can be related to the source of noise and the flow regime, while the amplitude of the signal can be related to the flow rate. The useful signal lies approximately between 100 and 5000 Hz, with lower frequencies generally representing background and mechanical noise. The measurement may record the total signal over all frequencies, the signal at a single frequency, or consist of a set of measurements over different frequency ranges.
Industry:Oil & gas
