Field works. Example 7.

Well logging

The following types of logging were used: resistivity logging, SP logging, gamma ray logging, temperature logging and resistivimetry.

Resistivity logging was carried out using standard lateral sonde A 0.9 M 0.1 N and potential sonde M 0.9 A 0.1 N. The stationary and remote electrode was situated on the surface close to wellhead. Potential and current electrodes should be made from stainless steel.

SP logging was carried out using potential sonde. The stationary electrode was situated about 10-15 m from wellhead to reduce the effect of casing on data results.

Temperature logging was carried out using borehole thermometer come with combination sonde.

Resistivimetry was carried out using small symmetric sonde.

Gamma ray logging was carried out using integral method by scintillational sensor (the length is 130 mm). To recalculate velocity values of gamma rays in terms of exposure dose rate (EDR) mcR/h, was used standard source calibration. Three integrating time constants of EDR (3, 6 and 12 sec) were measured during logging.


Results of geophysical carotage investigation

According to well log data, on the model of Riphean rocks clearly allocated three masses:

  • The upper mass includes sandstones with thin interbed of siltstones; interbedded members of sandstones and siltstones, silt-sandstones with interbed of siltstones with predominance of sandstones;
  • The medium mass includes interbedded members of siltstones, aleuropelites, aleuronic-clay slate, argillites; thin interbedded layer of argillites and siltstones; siltstones layer with carbon.
  • The lower mass, mostly, presented by sandstones.

Boundary between upper and medium masses for log data is reflected by resistivity values decrease and small radioactivity increase. Boundary between medium and lower masses is reflected by strongly resistivity values increase. Within the lower mass allocated interbeds with low resistivity. Among them, there are high and constant radioactivity values. Jointly radioactivity increase and resistivity decrease associate with clay horizon. Resistivity decrease with constant radioactivity, probably, associates with excessive fissuring. Rock mass reflected by higher resistivity values than host rocks. Massive resistivity is heterogeneous. Within the mass zones of jointing have resistivity values typical for some sandstone. Rock mass have anomaly low values of radioactivity. Two-dimensional inversion result obtained with the use of ZondCHT