SU217318A1 - Device for divergent micrologging of borehole - Google Patents

Abstract

A DEVICE FOR A DIVERGENT MICRO-CARRIAGE WELL, containing a probe with current and two measuring electrodes, placed on a pressure shoe, and an electronic circuit including an auto-regulator, designed to maintain a constant derivative of the potential difference between the measuring electrodes, and to measure: , characterized in that, in order to simplify the device and increase the measurement accuracy, in it the probe is made in the form of ring electrodes, coaxially arranged around the central point measuring electrode, the outer ring electrode is volumetric and current, and the inner one is measuring.

Description

(Ls

h

1C

00 CX)

The known devices for micro-, logging and microstage well logging, containing a probe with point electrodes, placed on a pressure shoe, and measuring scale, give measurement results that are significantly affected by the mudcake and the borehole wall geometry.

The proposed divergent micro-logging device makes it possible to obtain measurement results that are less affected by these factors than measurement results by any other devices. This is ensured by the presence of a three-electrode probe, in which the current and one of the measuring electrodes are annularly molded. The current electrode ring is volumetric and coaxially located around the second annular measuring electrode and the central point measuring electrode. Thus, the probe design provides an extremum in. potential measurement point and does not require the use of an autoregulator to maintain the extremum.

Fig, 1 shows a diagram of the proposed device; figure 2 - it: probe,,. ,

The device consists of ground equipment and downhole tool. Ground equipment contains a block. Power 1 and registration unit 2 and 3, coming from the downhole signal device.

The downhole device includes a probe containing a current electrode and two measuring electrodes M and N, and an electrode circuit. Electrode A is made in the form of a volumetric ring, coaxially located around the measuring electrodes and in contact with the movement of the well with the wall of the well. The electrode M is made in the form of a flat ring mounted in the probe shoe.

The downhole device electronic circuit consists of an auto regulator assembled on lamps 4–8 and used to power the current electrode A of the probe and to maintain a constant potential difference between the Mi electrodes of the N probe and the amplifier of the measured signal assembled on the lamps 9, 10 and slingshook for amplification and matching with the parameters of the potential cable of the electrode N. In addition, this circuit includes a master oscillator on the lamp 11, which is used to supply an alternating current to the modulator of the auto-regulator, and a switching circuit 12 on the relay for remote control of the measurement process. The device is designed to work on single-core cable.

To describe the operation of the device

We use a cylindrical coordinate system whose origin is located at the center of the electrode N and whose axis 1 is perpendicular to the plane of the shoe. In this case, the current coming from the electrode A into the cavity in which the measuring electrodes M and N are located, gradually spreads into the formation along the axis direction. Based on the well-known equation of electrodynamics d, it is easy to establish that the change in current intensity in the elementary portion of the cavity in the radial direction to the electrode. N is equal to the strength of the current flowing into the reservoir within this elementary area, i.e.

AZ.y

dp

Further, the potential on the surface of the shoe with coordinates and g is equal to

  3 () Rn,

where Н „is the resistance exerted on the current JnCf) within the measuring electrodes (resistance of the near-wellbore zone of the formation). Change Elec | (the potential of the potential in the range of -VALUE in the direction of the coordinate is equal to.

3 (rVR, jf, h

where RP is the resistance to current J (h) of an elementary part of the space of a shoe cavity with a coordinate r ..

Differentiating expression (3) with respect to f, taking into account the fact that all the parameters of this expression are in general functions of the coordinate P, and substituting the result of differentiation, as well as extrusion (2) into equation (1), we obtain. -,

 | dRc ftiov) RC

U (r) 0. dr RcdTlTir

Taking into account, this cavity in which the measuring electrodes are located is located inside the side electrodes.

Claims (1)

A DEVICE FOR DIVERGENT MICRODIGGING OF WELLS, containing a probe with a current and two measuring electrodes placed on a pressure shoe, and an electronic circuit including an autoregulator designed to maintain the constancy of the second derivative of the potential difference between the measuring electrodes / s and for measuring the potential of the central measuring electrode, characterized in that, in order to simplify the device and improve the accuracy of measurements, the probe is made in the form of ring electrodes, coaxially arranged GOVERNMENTAL around the central point of the measuring electrode, wherein the outer electrode is annular volume and is a current and measuring the internal g.