New Prospects for the Complex Geological Interpretation of the Spontaneous Polarization Method in Combination With Electrical Methods in the Sections of Oil Fields in the Volga-Ural Region and Western Siberia

The use of the spontaneous polarization (PS) method in combination with electrical and electromagnetic logging methods to solve the problems of assessing the saturation of reservoirs, determining carbonate, clay and open porosity of rocks (in combination with the method of natural radioactivity) is hampered by the low resolution of standard equipment recording the PS curve, the lack of evaluation of the quality of recording the PS curve and insufficient development methodological support for the geological and geophysical interpretation of the PS method.

A particular problem is the registration of the PS curve in high-resistance carbonate-terrigenous sections of the VolgaUral region. The method of selected PS potentials, proposed by H.G. Doll (Schlumberger company) in 1950 and tested at the Romashkinskoye field in Tatarstan, has not found wide application due to methodological difficulties.

Pilot tests of bi-gradient PS logging equipment (ABGKPS) in the carbonate-terrigenous section of the Volga-Ural region, and subsequent processing of its materials showed the high informative value of ABGK-PS and the prerequisites for its use in conditions where the practical use of standard PS logging is excluded due to its low informative value.

It is shown that the recording of ABGC-PS diagrams makes it possible, within the framework of geological interpretation, to assess the mineralization of reservoir water in the carbonateterrigenous section, which is extremely important for solving the problems of calculating hydrocarbon reserves.

A new algorithm is presented for the complex interpretation of borehole electrometry data and the method of bi-gradient (divergent) logging for estimating calculated parameters (porosity coefficients and oil and gas saturation), which does not require knowledge of the mineralization of reservoir water. The algorithm is implemented in the software “PH-PETROLOG”.

For a detailed division of the carbonate-terrigenous section into lithological differences and an assessment of the nature of reservoir saturation, it is proposed to supplement the complex of radioactive and acoustic logging with the complex ABGKPS + multi-probe lateral logging (for the carbonate part of the section) and ABGK-PS + multi-probe induction logging (for the terrigenous part of the section).

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