The laterolog was put into service in , predating the induction log by 6 or 7 years, Logarithmic scales appeared for the dual laterolog and later tools to. Dual laterolog resistivity measurements; Laterolog anomalies; Azimuthal dual laterologs. 2 Array electrode tools; 3 Shallow focused. Description. The QLDLL3 Dual Laterolog tool provides a time multiples dual spacing focused resistivity measurement with two different.
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Both logs share the same electrodes and have the same current-beam thickness, but different focusing currents give them different depths of investigation. The measurements are taken while the tool is stationary and take approximately a minute per station. Sual the apparent paradox of measuring formation resistivity through the highly-conductive steel casing, tools are now available that can measure the formation resistivity to considerable accuracy.
There are four focused-resistivity measurements incorporated in the RAB tool.
Many charts called departure curves were published to aid in interpretation of the ES logs. Current-return electrode B is at a great distance above A or at the surface. The voltage measured is approximately equal to the potential gradient at the point of measurement 0, midway between M and N.
The volume of formation between these two surfaces is constant, and because a potential difference of 2. In practice, N or B may be placed in the hole at a large distance above A and M [the voltage measured is practically the potential of M because of current from Areferred to an infinitely distant point]. A mild Groningen effect may be difficult to identify from the LLd curve alone. This focusing technique produces a response very similar to that of a wireline laterolog. Modern interpretation methods include 2D inversion after the curves are digitized and iterative forward modeling for when they are not digitized.
He has extensively travelled throughout the world and is now based in South Australia. The separation is not a clear function of invasion, but is also a function of bed thickness. Cased-hole resistivity is becoming accepted for applications including contingency logging, reservoir monitoring, and evaluation of old producing wells.
Two equipotential spheres are established around the I 0 survey current electrode; the first sphere is approximately 9 in. A Hz alternating current passes through the toroidal-coil lower transmitter that is 1 ft from the bottom of the tool, inducing a voltage in the collar below. These resistivity measurements are repeated using current from the lower transmitter.
Lategolog laterolog is generally recommended for holes drilled with very conductive drilling muds i.
Electrode resistivity devices –
Because the DLL measure current is AC albeit very low frequencyskin effect reduces the volume around the well where the measure and focusing current can flow. Because lateroloog information can often be obtained by reinterpreting old ES logs, this chapter includes discussion of the principles and responses of the ES latreolog.
The measurement is therefore sensitive to borehole size and shape and to eccentering of the tool in the borehole. The point of measurement is midway between A and M. Resistivity logging probes involves the injection of electrical current through a current electrode and measurement of the voltage drop at a potential electrode after passage through the rock. Little of the current is able to return to the remote electrodes through the highly resistive formation, with the majority flowing in the conductive mud in the borehole.
This requirement results in the ft [8. Because it has no bridle, it does not suffer from Groningen effect.
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The inverse arrangement made it more practical to record measurements by the two normals and the lateral simultaneously. The LLs measurement shares most of the electrodes with the deeper measurement. The intermediate measurements are used to derive the radial-invasion profile.
The data are usually stored downhole for later retrieval, although a compressed image and selected button data may be transmitted to the surface in real time together with the ring and bit resistivities and gamma-ray measurements. Using inversion processing, measurements of different vertical resolution and depths of investigation are combined in a single interpretation process to provide an accurate resistivity distribution image.
These combine multiple depths of investigation with 2D inversion of the data to give much improved response in invaded thin beds with conductive mud. The deep azimuthal measurement operates at the same frequency as the deep laterolog measurement, and the currents flow from 12 azimuthal current electrodes to the surface. Both the measure current and measure voltage V 0 are varied and measured, but their product power I 0 V 0 is kept constant.
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Resistivity logging involves the measurement of electrical properties of the rock. This is equivalent to replacing the azimuthal electrodes with a single cylindrical electrode of the same height. The high-resolution LLhr curve reads almost as deeply into the formation as a deep laterolog Laterlog curve, particularly when R yo is less than R t.
This is achieved by operating LLs and LLd at different frequencies. Commercial tools were introduced in by Schlumberger  and Baker Atlas. Long guard electrodes are larerolog to achieve the desired depth of investigation and measurement range. The SFL device uses two independent current systems. In practice, both modern laterolog and induction-logging tools are suitable for most logging conditions, and it is no longer practical to make a specific recommendation for one type in preference to the other, except in extreme conditions.
Duzl effect is known as “squeeze” for conductive beds and “antisqueeze” for resistive beds, and it leads to horn-like distortion of resistivity readings at bed boundaries.
In the early s, a new dual laterolog that had an additional laterolig segmented current electrode was introduced. The apparent resistivities RLA1 through RLA5 are all sensitive to the formation, becoming progressively deeper in investigation.
It uses small electrodes that can be combined with the dual-induction tool to provide shallow-investigation data for invasion evaluation. To estimate R t under a variety of different logging conditions and in different formations, a simple three-parameter, step-profile invasion model is often used. Laterolog devices see the more resistive zones, and induction tools see the more conductive zones.