Online Journal for E&P Geoscientists

Deshenenkov, Ivan S.^*1; Kozhevnikov, Dmitry A.¹; Kovalenko, Kazimir ¹
(1) Well Logging, Gubkin Russian State University of Oil and Gas, Moscow, Russian Federation.

We propose the adaptive technique for hydrocarbon saturation determination. Its essence is to configure interpretative algorithms on characteristic values of reservoirs resistivity. Developed petrophysical reservoir model significantly improves accuracy and reliability of the quantitative inverse problem solution.

Reservoir rocks hydrocarbon saturation calculation with resistivity log is substantially limited by information shortage about petrophysical characteristics of reservoirs mineral components.

The adaptive resistivity log data interpretation is forced to calculate the hydrocarbon share in the effective pore volume. Petrophysical assurance of this technique is relation between measured resistivity and changes in reservoir water-holding capacity (i.e. clay type and volume). It is necessary to specify three resistivity characteristic values. There are resistivities of the reservoir in case when all pore volume is filled with irreducible water, resistivities of water bearing reservoir and oil bearing reservoir with maximal available total porosity.

Resistivity characteristic values are determined according to the comparison of effective porosity with current reservoir resistivity. Then the share of hydrocarbon in the effective pore volume is calculated with modified Dakhnov-Archie equation without any empirical parameters. Calculation results depend on resistivity characteristic values as well as reservoir rock characteristic values, but not brine (formation water) resistivity. This fact significantly increases accuracy of the adaptive algorithm.

The statistical trials technique (Monte Carlo technique) shows that the total relative error of the hydrocarbon saturation determination with the adaptive technique is less in 1.2 - 1.6 times than in case of the conventional log data interpretation (conventional Dakhnov-Archie equation). Notably the error of saturation determination is maximal in poor-porous formation.

The adaptive technique provides tuning on lithological and petrochemical conditions of the particular reservoir in situ, including the wellbore construction influence; the adaptive technique doesn’t require any tools standardization in contrast to the conventional interpretation; it can be used for the old data re-interpretation. There is no need to specify reservoir components properties and volume contents. Interpretative models are stable under the influence of residual water saturation and formation water resistivity uncertainties.