Assessment of the geological factors influence on the oil-productive of terrigenous reservoirs of the Vereyian horizon of the Melekess depression

Abstract

Abstract The article presents study results of terrigenous reservoirs of the Vereiskian horizon of Tatarstan. The sandstones and silty sandstones are composed by grains of quartz, feldspars, clay minerals and organic remains cemented with calcite. Rocks were formed under the conditions of marine paleobasin coastal part with normal salinity. The migrated aggressive solutions partially leached out the carbonate cement from sediment, realizing the reservoir-filtration potential inherent in rocks. The oil fluids that filled the pore space practically did not interact in any way with the mineral skeleton of terrigenous reservoirs at the chemical level. Thus, the influence of the rocks mineral component on the properties of oils is completely excluded. In oil-saturated reservoirs, from which good oil inflows are obtained, light fractions of hydrocarbons prevail, boiling away at temperatures of 200-320°C. In the reservoir rocks, from where the watered oils are obtained, there are medium and heavy fractions of hydrocarbons, boiling at temperatures of 320-450°C. In unproductive sandy reservoirs with immobile viscous oil, only heavy fractions of hydrocarbons, which boiling at temperatures above 450°C, prevail. Thus, the oil recovery of terrigenous reservoirs is determined not by the composition of host rocks, but by the degree of oils oxidation contained in them.