The article discusses issues related to the assessment of irreversible creeping deformation effect on the compressibility of reservoirs, which, by definition, is considered elastic and is determined in standard experiments. Standard experiments are used regularly in the industry, and the results of these experiments are widely used for hydrodynamic modeling of field development and the hydrocarbon reserves assessment. Laboratory studies of the dependence of effective pressure on reservoir properties and rock samples porosity were carried out. A laboratory complex allows determining permeability with simultaneous measurement of sample deformation under the influence of crimping pressure. In the experiments, core samples of terrigenous deposits of the Tyumen suite of the field in Western Siberia (Rosneft Oil Company asset) were used. It is shown if the phenomenon of rock creeps under a load that exceeds the historical maximum is not taking into account it leads to an increase in uncertainty in determining the rocks compressibility. It is discussed how deformation hysteresis and rock permeability reduction under cyclic changes in effective pressure depend on the method and duration of measurement. The duration of the experiments depends on many factors, including subjective ones, which contributes to an increase in uncertainty in determining the studied rocks compressibility. However, creep tests are often, but not "generally" included in compressibility tests as additional steps. In this connection, it is recommended to conduct a series of test experiments for new and little-studied deposits to determine the possibility and rate of creeping deformation.
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