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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The volume of formation between these two surfaces is constant, and because a potential difference of 2. Final inversion results consist of the lqterolog resistivity structure satisfying all HDLL data and the statistical quality indicators represented in terms latterolog the importance of the formation parameter along with its corresponding error bounds.
This model consists of a flushed zone of resistivity R xo and a sharp boundary at diameter d iwith the uninvaded zone of resistivity R t. Because the borehole is generally more conductive than the formation, the current tends to stay in the mud, and the measurement responds primarily to the volume of mud in front of each azimuthal electrode.
The Latetolog measurement shares most of the electrodes with the deeper measurement.
These are used as inputs to a 2D inversion to solve for formation resistivities. The most common normal spacings were 16 and 64 in. Mud resistivity and tool standoff are also measured. The high-resolution LLhr curve reads almost as deeply into the formation as a deep laterolog LLd curve, particularly when R yo is less than R t.
Focussing of the electrical injection current laterolgo achieved through auxiliary electrodes whose job is to create a sheet like injection. 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.
A cylindrical focusing technique CFT is used to measure and compensate for this distortion by dhal the cylindrical geometry of the equipotential surfaces in front of the measurement electrodes. Deep measurements associated with the longest sensor spacings are used in evaluating the uncontaminated formation resistivity structure.
Many charts called departure curves were published to aid in interpretation of the ES logs. These combine multiple depths of investigation with 2D inversion of laerolog data to give much improved response in invaded thin beds with conductive mud. The inversion process is initiated by using the shallow measurements associated with short-spacing sensors to identify and evaluate the shallow-formation resistivity structure.
The relation of the curve to the bed is not clear at all. 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.
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A rotational speed of at least 30 rpm is required for full profile recording, with each button recording 56 resistivity measurements per rotation. In a homogeneous formation, the equipotential surfaces near the button and ring electrodes on the RAB tool are cylindrical.
Conductivity in the borehole has a strong influence on an induction measurement, but little influence on a laterolog measurement. Although most of the current returns through the casing, some laterolot fraction of it will leak off from the outside of the casing and will return through the earth.
Because new information can often be obtained by reinterpreting old ES logs, this chapter includes discussion of the principles and responses of the ES measurements. The idea originated in the s  and was revisited by Kaufman  and Vail  in the late s. The Groningen effect was named after the large Dutch gas field where the anomaly was first identified.
The voltage difference is now measuring the resistance of the casing, R 1. He has extensively travelled throughout the world and is now based in South Australia.
Twelve azimuthal resistivities are computed, and from their sum, a high-resolution resistivity measurement, LLhr, is derived. The inherent vertical resolution is sharper—24 in. 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.
An automatic 2D inversion is available that yields the best results from the data in invaded thin beds. All of the measurements are combined in the equation.
Resistivity and spontaneous SP logging. 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. 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 laterloog log MCFL measurements of the Platform Express tool.
Dual Laterolog Tool (EDLT) | LandSea – Open Hole and Cased Hole Logging 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 laterilog to the other, except in extreme conditions. Cased-hole resistivity is becoming accepted for applications including contingency logging, reservoir monitoring, and evaluation of old producing wells. Three independent, borehole-corrected resistivity measurements with appropriately chosen depths of investigation contain enough information from the formation to reliably solve for R t using this model.
The measure current I 0 is emitted from the central A0 electrode, returning to an “infinitely distant” electrode, usually at the surface. However, in layered formations, there is a tendency for current to flow preferentially in the more conductive beds and avoid the more resistive beds. A mild Groningen effect may be difficult to identify from the LLd curve alone. The SFL device measures the laterooog of the formation near the borehole.