Analysis and optimisation of the wastewater reinjection system at the Keshen gas field

Poor-quality reinjected water has caused significant formation damage in the Keshen ultra-deep HP/HT gas field. This damage has led to progressively increasing injection pressure and declining injectivity, threatening sustainable gas field water disposal. In this study, we systematically analyzed water quality and operational data from injection wells. Based on this analysis, we developed a theoretical filter-cake model to describe solid particle accumulation and its impact on reservoir impairment. We also proposed an integrated remediation strategy that combines surface water treatment optimization (demulsification, flocculation, and filtration) with periodic downhole acid stimulation. Preliminary field evidence suggests that this strategy is associated with significant recovery in post-treatment injectivity indices. These findings indicate that the integrated approach may contribute to remediating near-wellbore damage and restoring long-term injectivity in complex HP/HT reservoirs.