Permeability prediction during hydrocarbon production is a rather important problem. The decrease in permeability due to depletion reserves and the drop in reservoir pressure (increase in effective pressure) leads to an increase in the time of oil or gas production. A large number of works have been devoted to the problem of permeability reduction due to effective pressure. Establishment of permeability models is carried out by various methods including coreflooding tests and field well tests. The results of previous studies have shown that permeability has a power-law or exponential dependence on effective pressure, however, the difficulty in predicting permeability is due to hysteresis, the causes of which remain not fully understood. To model permeability, as well as explain the causes of hysteresis, some authors use mechanical models of the reservoir, which cannot be applied with small fluctuations in effective pressures in the initial period of hydrocarbon production. In this work, we analyzed data from well tests at one of the fields in the north of the Perm region and came to the conclusion that in the initial period of production, the permeability of the reservoirs largely depends on the amount of fluid produced. Based on the well test data of the terrigenous reservoir, a model was obtained that describes the change in permeability in the initial period of oil production. To confirm the model, coreflooding tests of samples of the terrigenous reservoir were carried out according to a specially developed program. Coreflooding results showed high convergence of the model obtained from well test data. With computed tomography (CT) and scanning electron microscope (SEM), the properties and structure of the pore space of the cores were studied and it was found that the main reason for the decrease in the permeability of low-clay rocks in the initial period of production is the migration of natural colloids.