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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This creates a negative potential at the far reference electrode used as the potential reference for the laterolog measurement. The “geometric factor” relates the effect of a portion of formation on the logging tool reading to its position relative to the tool in an infinite homogeneous medium. 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. Twelve azimuthal resistivities are computed, and from latwrolog sum, a high-resolution resistivity measurement, LLhr, is derived.
Duual the first quarter century of well logging, the only electrical surveys ES available were the resistivity logs made with so-called lateral and normal devices plus the spontaneous potential SP.
All signals are measured at the same time and logging position. 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. A rotational speed of at least 30 rpm is required for full profile recording, with each button recording 56 resistivity measurements per rotation.
Laterolog and SFL log readings are influenced by the borehole mud, adjacent shoulder beds, and the invaded zone as well as the uninvaded formation. The inversion process begins with the raw data input and an initial estimate of a parametric model describing the formation resistivity distribution.
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.
This leakoff current forms the basis for the CHFR measurement. For lateral devices Fig. latfrolog
For electrode tools duxl using guard electrodes, the depth of investigation increases only as the square root of the length of the guard electrodes. Interpretation of laterals and normals is very complicated because the response is a complicated function of the formation being measured.
Commonly used for lithological identification and correlation, advanced data processing can involve derivation of the Formation Factor and groundwater salinity.
Induction tools are conductivity-sensitive devices, which are most accurate in low- to medium-resistivity formations. The relation of the curve to the bed is not clear at all.
Dual Laterolog (Focused Resistivity) Logging – Overview
The LLs and LLd measurements have the same vertical resolution, but the LLs device uses a less constrained focusing condition in which the focusing current returns to electrodes on the array instead of to a remote electrode.
However, for best use of the azimuthal measurements, the tool should be well centralized in the borehole. Two voltage—measuring electrodes M and N on the sonde approximated the measurement of a constant-voltage spherical shell around the injection electrode.
Current-return electrode B is at a great distance above A or at the surface. The point of measurement is midway between A and M. 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
The LLs measurement therefore has a shallower depth of investigation and responds more strongly to the region around the borehole that is larerolog affected by invasion. 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.
Low-impedance circuits measure the current at each button electrode, and the axial current flowing lateolog the collar is measured at the ring electrode by the ring monitor toroid and at the lower transmitter by the lower monitor toroid.
The six modes are focused by a combination of hardware and software focusing. To evaluate the three unknowns latreolog the simple step-profile invasion model R xoR tand d ia combination of at least three carefully chosen resistivity measurements is required.
Electrode resistivity devices –
There are four focused-resistivity measurements incorporated in the RAB tool. The LLs measurement shares most of the electrodes with the deeper measurement. The idea originated in the s  and was revisited by Kaufman  and Vail  in the late s.
The measurement is therefore sensitive to borehole size laterokog shape and to eccentering of the tool in the borehole. It has a particular application to induction logging tools, but pseudo-geometrical factors are a useful comparative tool for other resistivity devices. The Schlumberger Geovision Resistivity GVR tool  is an electrode resistivity tool that measures five resistivity values—bit, ring, and three button resistivities—as well as gamma-ray and shock measurements.
In a homogeneous formation, the equipotential surfaces near the button and ring electrodes on the RAB tool are cylindrical. The current is injected into the casing and returns to an electrode in the earth some distance from the casing.