Electric Logging through Casing String
This method determines specific electrical resistance of rocks behind the metal wall of the casing string.
Differences in voltage, caused by flow of an applied current on rocks around the well, is measured with an acoustic logging
of resistances in a cased well. A current traverses through electrodes of the logging to the metal caseing string which plays
the role of a huge electrode. The reverse current electrode is placed on the surface. As a rule, it is a string cellar of a
neighbouring well. Connection of measuring and current electrodes with the inner surface of the casing string is provided by
hydrolic system of the device. This system creates excessive working pressure, as compared with well pressure, presses
hard-face sharpened tags of electrodes into the body of a colomn. In this case the influence of casing string and
circulating fluid is absent.
Conditions of applying this method: in vertical and deviating holes cased by five- or six-inch steel columns
filled with any type of solutions or in dried wells.
Technical characteristics of EKOS 31-7 Device:
- measuring range of specific resistances of rocks - from 1 to 100 Ohm•m
- point registration, step-type behaviour on depth - from 0.4 to > 1.0 m
- column current - not less than 5 A
- device current: direct current - 250 mA; impulse current 7-10 Hz - to 1 A
- pressure in hydrolic system vs well pressure - 0.5 – 0.6 MPa
- depth fixing is carried out with the help of RK facilities with a collar locator.
Usage:
- determination of specific electrical resistance of rocks in oil and gas wells cased with steel columns, including at low
mineralization and small porosity, when it is difficult to get precise data by nuclear logging
- determination of water-oil (WOC), gas-oil (GOC) and gas-water (GWC) contacts, as well as determination of
oil and gas saturation factor (OGSF)
- monitoring of oil and gas fields and subsurface waters
- determination of missed productive layers and zones of secondary saturation.
