At present, the sidetracking depth zone is usually located without any rigorous substantiation based on the logging data only.

However, as practice has vividly showed, this does not always enable us to “hit the target”, so to speak. This situation can be explained by the following factors:

1. Electric logs used to determine the sidetracking depth do not always meet the strict sidetracking depth selection criteria because as the well is operated the data obtained after the drilling and logging procedures may vary due to the changes in the initial oil deposits discovered in a formation or any other place. Besides, the registered oil content may be replaced with water or gas. If we add the possibility of oil deposit replenishment to the equation, then the credibility of logging data will simply “sink” in the chorus of critical remarks.

2. Moreover, the sidetracking depth is selected without taking into account whether the gas deposit is located “above” or “below” the oil-containing formation.

Meanwhile, the location of the gas-containing formation “above” the oil interlayer could offer extra energy for expulsion of fluid from the formation right into the wellbore.

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