Effect of retrograde condensation and stress sensitivity on properties of condensate gas reservoirs

In the production process of low permeability condensate gas reservoir, the reverse condensate action and stress sensitivity will lead to the decrease of reservoir permeability and gas well productivity. However, there are few studies on the effect of retrograde condensation and stress sensitivity on permeability. In this study, the stress-sensitive experiments using the method with constant confining pressure but variable inner pressure were carried out on three cores from the BZ gas field in southwestern Bohai Sea. The test result that use the nitrogen as the experimental fluid represent the effect of core skeleton damage on reservoir permeability during formation pressure drop, and the test result that use the condensate gas as the experimental fluid represent the effect of core skeleton damage and retrograde condensation on reservoir permeability. The results reveal that when the formation pressure drops to the dew point pressure, retrograde condensation damage is the main cause of permeability decline. And the effects of core skeleton damage will increase as the formation pressure drops and exceed the retrograde condensation damage when the net stress is greater 7 MPa. When the net stress reaches 20 MPa, the core skeleton damage accounts for more than 90% of the total damage. Furthermore, the gas well production was calculated considering stress sensitivity and retrograde condensation based on the experimental results, the result shows that gas well production decreases by 97.65% when retrograde condensation is considered. This study can provide a reference for quantitative evaluation of the retrograde condensation and stress sensitivity in the production process of condensate gas reservoir.