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Evaluating Injection Well Leaks: Environmental and Aquifer Impact in the Paris Basin

Impact of an injection well leak (Paris Basin).

Context:

The Paris Basin's injection well system, part of a Dogger doublet (Middle Jurassic) for urban heating, experienced prolonged leaks during high-flow operations. These leaks caused abnormal pressure drops and contamination in aquifers critical for industrial and drinking water use.

Key Indicators:

  • Location: Paris Basin.
  • Problem: Abnormal drop in injection pressures.
  • Detection: Logging of cased holes, casing diameter tools, and production logs (PLT).

Materiality of the Leak:

The leak affected two aquifer systems:

  1. Middle and Lower Eocene (EMI): A multi-layer aquifer with carbonate and sandy facies, unsuitable for human consumption but used for industrial purposes.
  2. Albian Aquifer: A strategic freshwater reservoir with alternating sandy and clayey layers, protected by mining regulations and used for drinking water supply and hydroenergy applications.

Both aquifers exhibit high productivity, with transmissivities exceeding 100 darcy-meters.

Modeling and Impact Assessment:

The study employed advanced heat and mass transfer modeling software (TOUGH2-V2, interfaced with mView) to simulate chemical and thermal contamination over a 9-month leak period.

Leak Parameters:

  • Volume: ~750,000 m³.
  • Temperature: 60°C.
  • Salinity: 20 g/NaCl equivalent.

The simulations characterized the invasion of contaminants and their spread within the aquifers.

Findings:

  1. Superficial Aquifer (EMI):
    • Extent of Impact: Limited to a 200 m radius from the leaking well.
    • Intensity of Contamination: Accounts for 83% of total leakage impact.
  2. Albian Aquifer:
    • Minimal Impact: Due to protective regulations and lower direct exposure.

Thermal and Pressure Fields:

The following figures illustrate the progression of pressure and temperature fields:

  • Figure 2: Regional-scale impact (aquifer thickness = 30 m).
  • Figure 3: Local-scale impact (aquifer thickness = 30 m).
  • Figure 4: Near-well pressure/temperature fields after sealing (304 days).
  • Figure 5: Long-term impact after sealing (10 years).
  • Figure 6: Extended long-term impact (100 years).

Conclusion:

The prolonged injection well leak in the Paris Basin caused localized thermochemical damage, with the superficial EMI aquifer bearing the brunt of the impact. The Albian aquifer, due to its strategic importance and regulatory protections, remained largely unaffected.

Sealing the leak mitigated long-term damage, with simulations indicating minimal contamination spread beyond the immediate vicinity of the well. These findings underscore the importance of rigorous monitoring and rapid response to leaks in geothermal and industrial water systems.