Fluid communication between different formations due to ineffective isolation of the well
Unintentional aquifer inter-connection (originally separated by impermeable layers) via the wellbore or disturbance of non-targeted aquifers with fluid intrusion (geothermal fluid, testing fluid, drilling mud, etc.) is a risk that can appear when drilling wells. The consequences of this phenomenon may include potential aquifer and freshwater resource contamination and depletion, loss in geothermal potential, affect other underground uses, ground elevation at surface from formation swelling, collapse or landslides from formation dissolutions. The phenomena are driven by differential pressures between layered aquifers and can be caused by well barrier and integrity failures due to poor cementation practices, mechanical damage during well development, corrosion and scaling, geo-mechanical disturbances, thermal stress and material failure or degradation, and aging over the life cycle of operations. It can be triggered during the drilling process and through all life stages of a geothermal project. It can also result from improper reinjection applications. Ref: Geoenvi D2,1
Informations
- Category: Environmental risks
- Id: F-2
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Phases:
- Drilling / Testing
- Exploitation / Development
- Post-closure
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Consequences:
- Economic / Performance / Acceptability
- Health / Safety / Environment
Mitigation
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Prevention:
- Isolation of well from surrounding formation (double casing, cementation of the casing annulus)
- Use of external casing packer between aquifers
- Use water-based mud to avoid pollution of an aquifer with drill mud
- Follow states of the art when decommissioning of wells
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Monitoring:
- Monitoring of corrosion, cement work, water level or pressure and geochemical properties of untargeted aquifers intersected, well parameters (flow rate, temperature and pressure)
- Monitoring of abandoned wells
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Corrective measures:
- Apply protocol of corrective measures in case of leaks either in the injection or production wells (adapt production or injection depending on situation encountered) and remediation with work over (patch for ex)
More information is available on the project deliverable (link), or navigate on the online version.
