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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Final inversion results consist of the estimated resistivity structure satisfying all HDLL data and the ltaerolog quality indicators represented in terms of the importance of the formation parameter along with its corresponding error bounds.

Low-impedance circuits measure the current at each button electrode, and the axial current flowing down the collar is measured at laterolkg ring electrode by the ring latefolog toroid and at the lower transmitter by the lower monitor toroid. HALS laterolog and array induction openhole logs. Drillpipe conveyance produces the same effect, with the drillpipe becoming the “short circuit.

These combine multiple depths of investigation with 2D inversion of the data to give cual improved response in invaded thin beds with conductive mud. 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. Conversely, a laterolog tool is preferred when R xo is less than R t.

Use this section to provide links to relevant material on websites other than PetroWiki and OnePetro. More importantly, the surface current return and insulating bridle are no longer needed.

### Dual Laterolog Tool (EDLT) | LandSea – Open Hole and Cased Hole Logging Systems

A cylindrical focusing technique CFT is used to measure and compensate for this distortion by restoring the cylindrical geometry of the equipotential surfaces in front latrolog the measurement electrodes. Long guard electrodes are required to achieve the desired depth of investigation and measurement range. The most common normal spacings were 16 and 64 in. The measure current I 0 is emitted from the central A0 electrode, returning to an “infinitely distant” electrode, usually at the surface.

Thousands of them were run each year all over the world.

Focusing involves injecting current from guard or bucking electrodes to ensure that the current from the central measure electrode flows into laterilog formation rather than along the borehole. The six modes are focused by a combination of hardware and software focusing. If casing has been set in or below the resistive zone, it accentuates the “short circuit” effect of the borehole, and the Groningen effect is more pronounced.

The lateral device was designed to provide a deeper resistivity measurement than the normal tools, while at the same time improving the detection of thin beds. Resistivity logging probes involves the injection of laterologg current through a current electrode and measurement of the voltage drop at a potential electrode after passage through the rock. This focusing technique produces a response very similar to that of a wireline laterolog.

An automatic 2D inversion is available that yields the best results from the data in invaded thin beds.

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. 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 laterolof and gamma-ray measurements.

### Electrode resistivity devices –

The volume of formation between these two surfaces is constant, and because a potential difference of 2. Two voltage—measuring electrodes M and N on the sonde approximated the measurement of a constant-voltage spherical shell around the injection electrode.

Many charts called departure curves were published to aid in interpretation of the ES logs. LLd and LLs curves, with a very shallow resistivity measurement that reads R xo directly, may be sufficient. The inversion process is initiated by using the shallow measurements associated with short-spacing sensors to identify and evaluate the shallow-formation resistivity structure. Both logs share the same electrodes and have the same current-beam thickness, but different focusing currents give them different depths of investigation.

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 distance AO is the spacing of the lateral device.

Twelve azimuthal resistivities are computed, and fual their sum, a high-resolution resistivity measurement, LLhr, is derived. Two equipotential spheres are established around the I 0 survey current electrode; the first sphere is approximately 9 in. The SFL device uses two independent current systems.

If automatic corrections are not available, log-interpretation charts provided by the service company are used to manually correct the log readings for these influences. It uses small electrodes that can be combined with the dual-induction tool to provide shallow-investigation data for invasion evaluation.

## Dual Laterolog Service

For electrode tools focused using guard electrodes, the depth of investigation increases only as the square root of the length of the guard electrodes. A two-parameter inversion model can also be used in real time to solve for R t and d iwith R xo provided by the microcylindrically focused log MCFL measurements of the Platform Express tool. The inversion process begins with the raw data input and an initial estimate of a parametric model describing the formation resistivity distribution.

Resistivity logging is the recording,in uncased or recently cased sections of a borehole, of the resistivities or their reciprocals, the conductivities of the subsurface formations, generally along with the spontaneous potentials SPs generated in the borehole. The hardware injects the currents in a way that is as close to focused as possible. These are used as inputs to a 2D inversion to solve for formation resistivities.

The Schlumberger high-resolution laterolog array Laterplog tool consists of five laterolog arrays with different depths of investigation. The shallowest mode, RLA0, is mostly sensitive to the borehole and is used to estimate the mud resistivity. Modern interpretation methods include 2D inversion after the curves are digitized and iterative forward modeling for when they are not digitized.