Abstract
In the determination of the porosity of the rock bulk drilled through the oil well, we compare the measured physical quantities and the calculated quantities given by the idealized, theoretical rock model. The comparison gives stochastical equations. Supposing that the measured log is a random variable with expected value given by the theoretical model and with known variance, we can determine the statistical estimation of the volume fraction of the porosity and other mineral components and the variance of those quantities. If we involve the exact, theoretical material balance equation into the system of stochastical equations, as a stochastical equation tending to zero standard deviation, then the variance of the porosity and other mineral components will be decreased. The consideration of the material balance equation requires the use of the cyclical determinant instead of the regular determinant.