Influence of Effective Stress on Absolute Permeability of Ultralow-Permeability Rocks

Abstract

The great potential of unconventional hydrocarbon resources in the world is realized in shale formations represented by fractured low-permeability and ultralow-permeability reservoirs. The development of shale formations in the energy depletion mode leads to an increase in effective pressure, which has a significant effect on the permeability of low-permeability and ultralow-permeability reservoirs. A laboratory estimation of the influence of effective pressure on the absolute permeability of different litological compositions rocks with permeability from 0.1 nD to 1 mD was carried out. Absolute gas permeability was determined by the pulse decay method and the modified steady-state method under pressure conditions. The results showed that an increase in the effective pressure from 7 to 45 MPa leads to a decrease in the absolute permeability of low-permeability and ultralow-permeability reservoirs by 1.8 – 100 times, depending on the initial permeability of core samples and their lithology. Reliable correlations of absolute permeability and effective pressure for reservoirs of different types have been identified. Correlations can be used to design well flow rates for the entire period of shale formations development.