Enhanced Oil Recovery (EOR)
EOR increases oil recovery rates significantly, extending the productive life of reservoirs, and it enables recovery of oil from mature fields that have undergone primary and secondary recovery. EOR techniques are broadly classified into three main categories:
- Thermal Recovery
Thermal Recovery involves the application of heat to reduce the viscosity of heavy oil, making it easier to flow. Steam is injected into the reservoir to heat the oil. The method commonly used in heavy oil and bitumen reservoirs.
- Gas Injection
Gas Injection involves the injection of gases to either miscibly or immiscibly interact with the oil, improving its mobility. It includes carbon dioxide (CO₂) injection: CO₂ mixes with the oil to reduce viscosity and swell the oil, helping it flow to production wells. Hydrocarbon gas injection: Lighter hydrocarbons are injected to mix with reservoir oil. Nitrogen injection: Primarily used to maintain pressure or in miscible displacement. The method is effective in light and medium oil reservoirs.
- Chemical Injection
Chemicals are injected to improve oil displacement efficiency. It includes polymer Flooding: Polymers increase water viscosity, improving the sweep efficiency. Surfactant-Polymer Flooding: Surfactants reduce oil-water interfacial tension, aiding oil mobilization. Alkaline Flooding: Alkaline solutions react with certain crude oils to form surfactants in-situ. The method is applied in reservoirs with favorable chemical interactions
Challenges of EOR
- High cost of implementation and operation.
- Requires advanced technology and infrastructure.
- Environmental concerns, including risks of water contamination and CO₂ handling.
- Reservoir-specific constraints, such as temperature, pressure, and oil properties.
The integration of EOR with geomechanics involves understanding and managing the mechanical behavior of the reservoir and surrounding rocks during EOR processes.
Geomechanical Considerations in EOR
- Reservoir Stress Changes:
- Fluid Injection: Techniques like steam, CO₂, or chemical injection increase pore pressure, altering the effective stress in the reservoir and potentially inducing deformation.
- Stress Redistribution: Changes in stress may cause fractures, faults activation, or compaction.
- Rock-Fluid Interactions:
- Thermal Expansion: In thermal EOR, injected heat causes thermal expansion of the rock matrix, affecting stress and permeability.
- Chemical Reactions: Chemicals can alter rock integrity through mineral dissolution or precipitation.
- CO₂-Induced Changes: CO₂ injection can lead to chemical interactions with carbonate rocks, weakening the formation.
- Reservoir Deformation:
- Compaction: High-pressure EOR methods can lead to reservoir compaction, impacting porosity and permeability.
- Subsidence: Surface subsidence can result from reservoir compaction, especially in unconsolidated formations.
- Fracture Dynamics: Geomechanics determines whether induced fractures propagate or stay controlled.
- Caprock Integrity:
- Maintaining the seal's integrity is critical to preventing leakage during CO₂ or fluid injection.
- Fault Reactivation:
- Pressure changes may reactivate existing faults, potentially leading to seismic events or reservoir compartmentalization.
EOR plays a crucial role in meeting global energy demand while also addressing environmental sustainability challenges. Integrating geomechanics with EOR ensures enhanced recovery while minimizing risks, making it an essential aspect of modern reservoir management. Therefore, one of the main topics of the first international conference on geoenergy and the fifth national petroleum geomechanics conference is enhanced oil recovery.
Researchers are invited to send their articles in these fields to the first international geoenergy conference and the fifth petroleum geomechanics conference.
