Electric casing Logging (Nanoscale Logging)

Technical characteristics of the logging tool

Scheme of work

Through the current electrodes B, A1 and A2, the power supply of the probe installation is supplied, using the measuring electrodes Nud and M1-M5 located on the probe installation, potential differences are measured and the specific resistivity of the rock is calculated. When the device is lowered into the well and when moving from point to point, the levers with electrodes are in a closed state, when measured, the levers open and cut into the well wall using a percussion mechanism.

The method of electric logging (nanoscale logging) allows us to solve the following problems:

• determination of the coefficient of current oil and gas saturation;
• assessment of the composition of the inflow from the facility;
• identification of idle intervals.

Features of interpretation and issuance of conclusions

The first step is to assess the reliability of the resistance values obtained by recording and to link the point-by-point recording to depth.

Reliability is estimated by formations whose electrical resistance does not change over time (water-saturated reservoirs, impermeable intervals). Snapping to the section is carried out using a module for measuring natural gamma radiation of rocks and a locator of couplings built into the device.

The second stage is the justification of the current mineralization of water saturating the rock.

Knowledge of water resistance is necessary to calculate the current coefficient of oil and gas saturation. Experience has shown that with an operational interpretation, the interpreter, as a rule, does not have information about the real mineralization of the mixture of injected and produced water. These data appear after the test.

There are several ways to justify the salinity (electrical resistance) of water:

• average salinity of associated water in the field;
• the use of analysis of associated water from neighboring wells;
• determination of current mineralization (chlorine content) in a particular well by additional well logging methods.

The third stage of interpretation is the calculation of the coefficient of current oil and gas saturation and the forecast of the composition of the inflow.

This stage is implemented if there is reliable information about the petrophysical dependences of the water saturation coefficient on resistance (Archie equation) and the relative phase permeability coefficients for oil and water for the studied object of exploitation.

The operational conclusion gives the coefficients of the current oil saturation, the nature of the saturation of the studied formation and the predicted value of the amount of water in the inflow. The conclusion is supplemented by a geological and geophysical tablet.

Interpretation example: