Well-Test Interpretation for Fracture-Vuggy Gas Condensate Reservoirs Using Wellhead Shut-In Pressure Data and Wellbore Flash Calculations

Abstract

To reduce the operational cost and risk of conventional downhole testing, this study presents an integrated well-test interpretation workflow that uses wellhead shut-in pressure data to characterize formation flow conditions in real time. Fluid mass- and heat-transfer equations are established for the wellbore, and a heat-conduction equation is established for the formation. Flash calculations are used to capture condensate phase changes inside the wellbore, while wave propagation and seepage mechanics are integrated into the formation flow model. This yields a coupled wellbore–formation flow system, and a corresponding numerical solution method is proposed according to the mathematical characteristics of the governing equations. Using this model, an interpretation method for wellhead-pressure testing in fracture-vuggy condensate-gas wells is established to determine critical reservoir parameters, including permeability, skin factor, cave location, and cave volume. The results show that converting measured wellhead pressure to bottomhole pressure after shut-in introduces an error during the initial shut-in period; this error gradually decreases with increasing shut-in time. Validation against a field well shows that the overall relative pressure error is less than 2%. Interpreted wellbore storage and near-wellbore cave volume exhibit errors within 5%, while formation permeability, distant cave volume, and cave location are essentially unaffected. The skin-factor difference is 0.55 (dimensionless; relative difference 20.1%), which should be interpreted with caution because skin factor is strongly controlled by early-time data. The model is adaptable to various wellbore types in fracture-vuggy condensate-gas reservoirs. Compared with traditional downhole testing, the proposed method substantially reduces operational hazards and expenses while providing accurate results, offering a low-risk, low-cost, and efficient technical solution for optimizing deep gas-field development.