In the paper, the authors suggest a technique to identify reservoir rocks in the Vendian-Cambrian carbonaceous deposits of the Siberian Platform and analyse one of the major reasons of their unsuccessful penetration based on examination of core and well logging data on the Chaykinskaya-367 parametric well. To identify a reservoir, it is suggested to analyse the composition of mobile fluids in the porous-cavernous matrix of carbonaceous rock. However, this is not sufficient to receive stable inflow from the interval under study. The inflow indicates occurrence and openness of fractures that serve as major channels of formation fluid flow. Openness of fractures is controlled by formation pressure and tangential stress in the near-wellbore environment. The paper provides that formation pressure in the Osa, Yuryakh, and Preobrazhenskoye horizons can be less than tangential stress, which evidently results in closure of vertical fractures and substantial decrease in or absence of fluid inflow, which can be observed in actual practice.