Reinjection of spent geothermal fluid back into the reservoir is essential for a sustainable field. Scale and corrosion in these lines and wells reduce injectivity and raise pumping energy.
Why do problems arise in reinjection?
As the fluid passes through the plant it cools and loses steam; silica concentration rises and saturation is exceeded. Residence time in holding tanks gives silica time to polymerise. Colloidal silica and metal silicates then build up on line surfaces and in the formation around the well, lowering injectivity. Air entering tanks and pump suctions accelerates corrosion, and the released iron combines with silica to make scale heavier.
Symptoms
- Reinjection pressure rising at the same flow
- Falling well injectivity index
- Frequent filter blockage, white–grey scale inside the line
- Higher pump energy consumption
Control programme
- Setting reinjection temperature against the silica saturation limit
- Dosing a silica-specific inhibitor and dispersant
- Controlled pH management where needed
- Shorter tank residence times and prevention of oxygen ingress
- A programme designed together with the corrosion inhibitor
| Monitoring | What it shows |
|---|---|
| Injectivity index | Plugging of well and formation |
| Monomeric / total silica | Polymerisation and inhibitor effect |
| Turbidity and suspended solids | Colloidal silica and corrosion products |
| Dissolved oxygen and iron | Air ingress and corrosion |
Frequently asked questions
Can lost injectivity be recovered?
Partly; chemical cleaning or acidising can improve it, but the lasting solution is preventing scale from forming.
Why is lowering reinjection temperature risky?
A lower temperature yields more power but increases silica saturation; the limit should be set together with the chemical programme.
Where is the programme dosed?
Usually after the plant outlet and before tanks and pumps; the exact point depends on the site layout.
Related guides
- Geothermal power plant chemicals (overview)
- Calcite scaling in geothermal wells
- Silica and metal silicate scaling
- Corrosion in geothermal systems
- Downhole dosing via capillary tubing
- Heat exchanger and ORC fouling
- Geothermal heating and greenhouse systems
- Sulphide scales (stibnite, iron sulphide)
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