The most important part of geological exploration work is to ensure a reliable assessment of hydrocarbon reserves, which is based on petrophysical core studies. In the case of unconventional reservoirs and reservoirs with hard-to-recover reserves, the determination of porosity is a basic, fundamental condition for their successful study, since a reliable determination of this parameter, the value of which is many times lower than in traditional reservoirs, critically affects the assessment of the resource base (the effect of small numbers). In the Russian Federation, the most widespread assessment of the porosity of core samples in laboratory conditions is carried out using the liquid saturation method (state standard GOST 26450.1-85) when core samples are saturated with formation water (model) or kerosene, as well as the gas-volumetric method (for helium) and the NMR method. These methods are well-proven for traditional reservoirs, with their relatively large porosity values; for reservoirs with hard-to-recover reserves the situation does not look so positive. Weak methodological basis for performing porosity measurements in the case of low values, lack of unification of measurement conditions and methods, insufficient qualifications of specialists, lithologic-mineralogical and petrophysical features of the objects of study, lead to a significant discrepancy in the results of porosity measurements both by different methods and by different laboratories. To correctly assess the results obtained and the reasons for their discrepancies, knowledge of both characteristics of the object being studied, and measurement techniques and features of the equipment, is required. The article discussed the Rosneft Oil Company experience in development of a technology for assessing void space using petrophysical methods on core samples for various reservoirs, including unconventional ones, as well as the complex structure of void space.
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