Nonionic Surfactant Mixture for CO2 Foam Sweep Efficiency
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Solution Overview
Problem
Miscible carbon dioxide flooding for enhanced oil recovery faces issues such as poor sweep of subterranean formations due to gas bypassing and early breakthrough, exacerbated by traditional surfactants that can create emulsions and adsorb onto formation rock, leading to reduced foam formation and surfactant loss.
Innovation Solution
A mixture of two or more nonionic surfactants, prepared through alkoxylation reactions using a double metal cyanide catalyst, is injected into the subterranean formation with carbon dioxide to create a foam that enhances oil recovery by increasing the apparent viscosity of carbon dioxide and preventing gas channeling, while being soluble in carbon dioxide at typical oil recovery temperatures and pressures.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of operation
If traditional surfactants (e.g., ethoxy-sulfates) are used to create foam for miscible carbon dioxide flooding, then foam generation and gas channeling prevention are improved, but emulsion formation occurs that is difficult to break and causes permanent damage to the formation by irreversibly plugging pore throats
Solution Approach 1:
The patent changes the chemical nature of the surfactant from traditional anionic surfactants (ethoxy-sulfates) to nonionic surfactants with specific molecular structures (containing ethylene oxide and propylene oxide units). This parameter change in surfactant chemistry eliminates emulsion formation while maintaining foam generation capability, resolving the contradiction between ease of operation and harmful effects.
Solution Approach 2:
The patent introduces polarity-adjusted nonionic surfactants with specific hydrophilic-lipophilic balance (HLB) values tailored for different reservoir conditions. By optimizing the local chemical properties of the surfactant molecules (through controlled ethoxylation and propoxylation degrees), the system achieves effective foam generation without the harmful emulsion formation associated with traditional surfactants.
2Reliability
If anionic surfactants with high affinity to formation rock (e.g., carbonate) are selected to enhance foam stability, then foam formation is improved, but surfactant loss occurs due to adsorption into the formation rock
Solution Approach 1:
The patent extracts the problematic ionic character from traditional surfactant molecules and replaces it with nonionic structures. By removing the charged groups that cause strong adsorption to formation rock, the system maintains foam stability through optimized hydrophobic-hydrophilic balance while eliminating surfactant loss via adsorption.
Solution Approach 2:
The nonionic surfactant acts as an intermediary that provides the necessary foam-stabilizing properties without the harmful adsorption characteristics of anionic surfactants. The specific molecular structure (with controlled EO/PO ratios) serves as a mediator between foam stability requirements and surfactant retention in the reservoir.
3Productivity
If miscible carbon dioxide flooding is performed to reduce crude oil viscosity and increase hydrocarbon flow, then oil mobility is improved, but poor sweep occurs when gas flows through paths of least resistance, bypassing significant portions of the formation
Solution Approach 1:
The patent applies preliminary action by injecting the nonionic surfactant system before or with the carbon dioxide to pre-condition the formation. The surfactant creates stable foam that modifies gas flow patterns in advance, forcing the carbon dioxide to sweep through previously unswept portions of the formation rather than channeling through high-permeability paths.
Solution Approach 2:
The patent changes the physical parameters of the injected fluid system by introducing surfactant-induced foam, which dramatically increases the apparent viscosity of the carbon dioxide. This parameter change transforms the gas from a low-viscosity fluid that channels easily into a foam system with enhanced mobility control that achieves uniform sweep and contacts more crude oil.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
The nonionic surfactant mixture improves the sweep efficiency of carbon dioxide through the formation, increasing its residence time and contact with crude oil, thereby enhancing crude oil recovery and reducing surfactant loss, leading to more effective viscosity reduction and increased oil production.
Implementation Method 1
A foam can generate an apparent viscosity of 100 to 1,000 times that of the injected gas, therefore, the foam can inhibit the flow of the gas into that portion of subterranean formation that has previously been swept
Implementation Method 2
the nonionic surfactants are soluble in carbon dioxide and reduce the interfacial tension between the carbon dioxide and crude oil
Implementation Method 3
each nonionic surfactant is independently prepared by an alkoxylation reaction of a first epoxide, a second epoxide, and optionally a third epoxide where the first, second, and third epoxides are different from one another, and a linear or branched aliphatic alcohol
Data Source
AI summary
The present invention provides for a method of using a mixture of two or more nonionic surfactants for enhanced oil recovery and for an emulsion that includes carbon dioxide, a diluent and a mixture of two or more nonionic surfactants, where each nonionic surfactant is prepared with a double metal cyanide catalyst.