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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Electrode resistivity devices
Duncan Cogswell, Executive Director at Borehole Wireline, is a qualified geologist who has worked in borehole geophysical logging for mineral exploration, mining and groundwater since The intermediate measurements are used to derive the radial-invasion profile.
Focusing involves injecting current from guard or bucking electrodes to ensure that the current from the central measure electrode flows into the formation rather than along the borehole. The hardware injects the currents in a way that is as close to focused as possible. The azimuthal resistivity measurements are sensitive to tool eccentering in the borehole and to irregular borehole shape. The shallowest mode, RLA0, is mostly sensitive to the borehole and is used to estimate the mud resistivity.
For normal devices Fig.
Electrode resistivity devices –
By having all currents return to the tool body rather than surface, Groningen effect is eliminated and shoulder-bed effect reduced. Individually selected azimuthal resistivities can be used in the same manner where the logged interval is azimuthally anisotropic or includes highly dipping thin beds. The measurement is therefore sensitive to borehole size and shape and to eccentering of the tool in the borehole.
LLd and LLs curves, with a very shallow resistivity measurement that reads R xo directly, may be sufficient. 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.
The current switch is changed to position 2. Commercial tools were introduced in by Schlumberger  and Baker Atlas. Commonly used for lithological identification and correlation, advanced data processing can involve derivation of the Formation Factor and groundwater salinity. 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.
The Schlumberger high-resolution laterolog array HRLA tool consists of five laterolog arrays with different depths of investigation.
In addition, the current from each azimuthal electrode is focused passively by the currents from its neighbors. The inversion latrrolog is initiated by using the shallow measurements associated with short-spacing sensors to identify and evaluate the shallow-formation resistivity structure.
Resistivity and spontaneous SP logging. The borehole corrections must always be made first, followed by bed-thickness corrections and finally invasion corrections of the determination of R tR xoand d i. Both logs share the same electrodes and have the same current-beam thickness, but different focusing currents give them different depths of investigation. These recordings are duual for correlation of the strata and detection and quantitative evaluation of possibly productive horizons.
This is equivalent to replacing the azimuthal electrodes dua a single cylindrical electrode of the same height. The laterolog is generally recommended for holes drilled with very conductive drilling muds lateeolog.
The inversion process begins with the raw data input and an eual estimate of a parametric model describing the formation resistivity distribution. These combine multiple depths of investigation with 2D inversion of the data to give much improved response in invaded thin beds with conductive mud. It has a particular application to induction logging tools, but pseudo-geometrical factors are a useful comparative tool for other resistivity devices.
A beam thickness of only 28 in. It graphically compares the relative contributions of the invaded zone to the tool responses and their relative depths of investigation. The point of measurement is midway between A and M.
Resistivity logging involves the measurement of electrical properties of the rock. A rotational speed of at least 30 rpm is required for full profile recording, with each button recording 56 resistivity measurements per rotation.
Dual Laterolog (Focused Resistivity) Logging – Overview
However, in layered formations, there is a tendency for current to flow preferentially in the more conductive beds and avoid the more resistive beds. The Baker Atlas high-definition lateral log HDLL tool  acquires 8 potential and 16 first differences, and computes 14 second differences. An LLhr log can therefore replace an LLd log for interpretation, especially where its vertical resolution is an advantage.
When the GVR tool is positioned directly above the bit, the resistivity measurement has a resolution of approximately 2 ft [61 cm], which is usually adequate for “geostopping”—stopping drilling precisely at casing or coring depths. 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.
The most common normal spacings were 16 and 64 in. A constant-power measuring system ensures measurement accuracy over a wide range of resistivities from 0.
Borehole and shoulder effects are minimized by the use of laterolog-style focusing.
Dual Laterolog Tool (EDLT) | LandSea – Open Hole and Cased Hole Logging Systems
Laterolog tools are resistivity devices, which are most accurate in medium- to high-resistivity formations. This is achieved by regulating the currents generated by the upper and lower transmitters for zero axial current flow at the ring monitor electrode, which avoids current flow along the borehole and focuses the duwl current into the formation. In an alternate version of the lateral, the positions of the current and voltage electrodes are interchanged. The current near the injection electrode spread out radially from the electrode.
The six modes are focused by a combination of hardware and software focusing. 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]. The LLs measurement shares most of the electrodes with the deeper measurement.
The measurements are taken while the tool is stationary and take approximately a minute per station. 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. Since then, new logging methods have been developed to measure values much closer to R xo and R t.
In addition to providing a visual image of formation lamination and anisotropy, the azimuthal images can be used to estimate the gross formation dip and to correct deep resistivity measurements in dipping beds.
The Groningen effect was named after the large Dutch gas field where the anomaly was first identified.