Modelling Iodine Production Using Coupled Geochemistry in CMG GEM

Iodine production from subsurface brine reservoirs is governed by a complex interplay of fluid flow, gas solubility, and geochemical reactions. 

Using CMG’s GEM simulator, a fully integrated workflow was developed to:

• Model iodine production from brine systems 
• Capture gas dissolution effects (CH₄, CO₂) 
• Simulate mineral reactions controlling iodine release 
• Evaluate water injection and recycling strategies 

Outcome: A predictive framework that enables operators to optimize iodine recovery, reduce uncertainty, and better manage reinjection strategies.

Why Iodine Modeling Matters

Iodine is a strategic resource used in:

• Pharmaceuticals and medical imaging 
• Electronics and advanced materials such as Perovskite solar cells
• Energy storage technologies 

Unlike hydrocarbons, iodine is:

• Dissolved in formation water (brine) 
• Produced indirectly through fluid movement and chemical reactions 

This makes iodine production highly sensitive to:

• Reservoir flow patterns 
• Water recycling strategies 
• Subsurface geochemistry 

Operational Context

In typical iodine-producing reservoirs:

• Natural gas and iodine are co-produced with water 
• Gas is separated at surface 
• Produced water is fully reinjected 

Key Implication: The reservoir behaves as a circulating reactive system, not a depletion-driven system.

The Challenge

Conventional simulation approaches:

• Track pressure and flow 
• Ignore chemical reactions and aqueous processes 

As a result, they cannot:

• Predict iodine concentration changes 
• Capture mineral-driven iodine release 
• Evaluate long-term recycling effects 

Solution: CMG GEM Coupled Workflow

CMG GEM enables a fully integrated modeling approach, combining:

1. Fluid Flow

• Multiphase flow in porous media 
• Injector-producer interaction 

2. Gas Solubility

• Methane and CO₂ dissolution into brine 
• Modeled using Henry’s Law, accounting for: 
  • Pressure 
  • Temperature 
  • Salinity 

3. Geochemistry

• Aqueous reactions (e.g., iodide transport) 
• Mineral reactions: 
  • NaI dissolution → iodine release 
  • Precipitation under changing conditions 

4. Geomechanics (Optional but Enabled)

• Pressure-induced deformation 
• Subsidence and stress effects 

Model Overview

Reservoir Description	Fluid & Chemistry	Operational Strategy Modeled
2D cross-sectional model	Water-saturated system (~100%)	Water Injection: 100 m³/day
Depth: ~1000 m	Methane-dominated gas phase	Water Production: 100 m³/day
Thickness: ~160 m	Iodine present as iodide (I⁻) in brine	Voidage Replacement Ratio = 1
Layered system (Kv/Kh = 0.1)		100% water recycling

 

This creates a dynamic circulation system, where injected water continuously alters reservoir chemistry.

Key Results

1. Iodine Mobilization Driven by Reactive Transport
As shown in Figure 1, NaI dissolution is concentrated along injector–producer flow paths, indicating that iodine release is directly controlled by sweep efficiency and flow connectivity.

Insight: Iodine production depends on

• Flow pathways 
• Mineral dissolution dynamics 

2. Injection Alters Reservoir Chemistry

Injected water: 

• Dilutes iodine concentration 
• Triggers additional mineral reactions 

Insight: Recycling creates both production support and dilution effects

3. Pressure & Mechanical Effects

As shown in Figure 2, strong pressure gradients develop between the injector and the producer, driving flow and inducing measurable vertical displacement. It highlights the coupled impact of injection on both fluid movement and reservoir deformation.

Insight: Long-term operations can impact

• Reservoir structure 
• Flow pathways 

4. Long-Term Production Behavior

• Short-term: Stable iodine production 
• Mid-term: Decline due to dilution 
• Long-term: Complex behavior from recycling and redistribution 

Insight: Figure 3 shows a non-linear iodine production profile, where early-time stability is followed by dilution-driven decline and late-time redistribution effects, demonstrating the impact of continuous water recycling on iodine concentration.

Key Takeaways 

• Iodine production is geochemistry-driven, not purely flow-driven 
• Mineral buffering (NaI) plays a critical role in sustaining production 
• Water recycling introduces both benefits and risks: 
  • Sustains reservoir pressure 
  • Alters chemistry and concentration 
• Gas solubility influences aqueous chemistry, impacting iodine availability 

Best Practices

• Incorporate geochemistry when modeling dissolved resources 
• Use Henry’s Law-based solubility models for gas–water systems 
• Explicitly model: 
  • Mineral phases 
  • Aqueous reactions 
• Treat water injection systems as closed-loop reactive systems 

Conclusion

This study demonstrates that:

• Accurate iodine production forecasting requires coupling flow, geochemistry, and operational strategy.
• CMG GEM provides a unified platform to model this complexity, enabling operators to design injection strategies that directly control iodine recovery rather than reacting to uncertain production behavior.