Perm Journal of Petroleum and Mining Engineering (Jun 2019)
Study of secondary alterations of visean reservoir rocks of Solikamsk Depression in condition of stabilization of ancient oil-water contacts
Abstract
A model of multi-stage formation of Visean oil deposits in Solikamsk depression in condition of stabilization of ancient oil-water contacts is provided. When reservoir rocks stay in condition of oil-water zones for extended periods of time, oxidizing processes actively develop, as result of which oil saturated reservoirs undergo non-reversible changes in rock wettability. After inflow of new portions of hydrocarbons and formation of modern oil-water contact residual products of oil oxidation are formed as solid bitumen. Cases of absence of reservoir bitumenosity in ranges of ancient oil-water contacts are explained by active fluid exchange in reservoirs. It is established that high specific resistance values in terrigenous reservoirs of Visean deposits in Solikamsk depression, exceeding 600 Ohm*m, are related to their hydrophobization in conditions of ancient oil-water contacts. Electrical laterlog results are compared with evaluation of rock wettability based on X-ray core tomography and microscopic analysis of thin sections. For Visean high-ohmic reservoirs of Shershnevskoe deposit statistically significant excess of rock porosity comparing to standard geophysical section is established. For ranges with resistivity 600 Ohm*m – at porosity over 18 %. In average, excess porosity in high-ohmic section is over 3 %, which is probably due to predominance of reservoir deconsolidation (dissolution) processes over their cementation at levels of ancient oil-water contacts. For Visean operational objects of Shershnevskoe deposit geological model is built on basis of resistivity data, separating zones (volumes) of different wettability type reservoir development. In general, the established zones of development of hydrophilic and hydrophobic reservoirs are of regular spatial arrangement. Geological models built with regard to rock wettability may be used to optimize reservoir management technologies at oil operational objects.
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