The GCAH-1 geothermal production well, part of a doublet system with the GCAH-2 injector well, has experienced a gradual decline in productivity over its operational lifespan. This performance drop has raised critical questions about reservoir behavior, well integrity, and the impact of operational practices.
This study focuses on three key objectives:
- Modeling production tests to assess changes in well performance.
- Analyzing heat transfer mechanisms between the geothermal reservoir and the wellhead.
- Simulating long-term impacts of 30 years of operation on mass and heat transfers, pressure, and temperature fields.
Key Findings
Reservoir Properties and Well Performance
Production tests conducted in 2013 revealed that the reservoir’s transmissivity and hydrodynamic properties remained consistent with initial conditions from 1984. However, anomalies were detected in the upper casing of the GCAH-1 well. A 0.5 mm deposit layer was identified in a 300 m section of the casing, potentially contributing to increased pressure losses and reduced flow rates.
Thermochemical Mechanisms
The analysis ruled out compaction or sedimentation of suspended particles as primary causes. Instead, thermochemical clogging, driven by the precipitation of mineral species such as calcium carbonates, iron sulfides, and other crystalline deposits, emerged as a plausible explanation. This phenomenon may have been exacerbated during periods when corrosion inhibitors were not used.
Operational Insights
Simulations indicated that the productivity drop was not due to a permeability barrier in the reservoir. Instead, the deposits in the casing likely caused localized flow restrictions. Interestingly, well performance temporarily recovered after shutdowns, suggesting that operational pauses could influence deposit behavior.
Proposed Solutions
To address the identified issues, the study recommends:
- Enhanced monitoring of thermochemical properties in the geothermal loop.
- Regular cleaning of well casings to mitigate deposit formation.
- Injection of inhibitors to prevent mineral precipitation and maintain flow efficiency.
Conclusion
The decline in GCAH-1 well productivity is primarily attributed to fouling within the well casing rather than changes in the reservoir. By addressing these challenges through improved operational practices and targeted interventions, the long-term sustainability of geothermal systems can be ensured.