A Case Study on Gas Breakthrough and Gas Well Reactivation in Carbonate Rock Water-Invaded Gas Reservoirs of Longmen Block, Southwest China

Introduction: The reactivation of water-flooded gas wells in low-porosity, low-permeability carbonate reservoirs remains a significant challenge in the natural gas industry. This study aims to establish a quantitative evaluation method to assess the unblocking potential of such wells, providing a key theoretical basis for targeted measures. Recent patents have focused on chemical methods for wettability alteration, yet a comprehensive quantitative chart linking reservoir conditions to well performance is still lacking. Method: This research utilized a series of core physical simulation experiments, including porosity- permeability tests, gas breakthrough pressure measurements, and nuclear magnetic resonance (NMR) analysis. Data from 31 core samples from the Longmen Block were integrated with production dynamic data from typical wells (TD-12# and TD-19#) to establish quantitative relationship charts. Results: The results indicate that: (1) The reservoir is typical low-porosity (avg. 2.24%) and low-permeability (avg. 2.06 mD), requiring water saturation within 10 m of the well to be reduced below 80% for effective gas flow; (2) NMR experiments revealed a power-function relationship between the critical pore throat radius of movable water and the pressure gradient; (3) Evaluation based on the chart showed that TD-12# is difficult to unseal under current conditions, while TD-19# could increase its movable reservoir volume by 872.55 m3 through wettability reversal (contact angle from 30° to 83°). Discussion: The “pressure gradient - residual water saturation - breakthrough pressure gradient” chart formed in this study demonstrates good applicability and aligns with production data. It effectively bridges the gap between laboratory core data and field-scale well performance. Conclusion: The quantitative evaluation chart provides a reliable tool for screening candidate wells and optimizing drainage gas production and wettability reversal measures in water-flooded carbonate gas reservoirs.