pH-Switch Viscoelastic Foam for Acidic Gas EOR Salt Tolerance
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Solution Overview
Problem
Existing foam systems for enhanced oil recovery using acidic gases suffer from poor stability and viscosity issues due to the repulsion between anionic and nonionic surfactants, leading to inefficient recovery factors, especially in high mineralization environments.
Innovation Solution
A viscoelastic foam system comprising a pH-switch surfactant, such as long-chain hydrocarbyl amines, is introduced to enhance interaction with anionic surfactants under acidic conditions, increasing viscosity and stability, utilizing the pH-altering effect of acidic gases to improve foam performance.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If anionic surfactants are used to enhance foam stability through electrostatic repulsion, then foam stability is improved, but salt resistance deteriorates due to precipitation in high mineralization environments
Solution Approach 1:
The patent changes the charge state parameter of the surfactant by using pH-switchable surfactants that transition from neutral to charged states. At reservoir pH conditions, the surfactants become charged and provide electrostatic repulsion for foam stability, while at injection pH, they remain neutral for better solubility and salt resistance. This parameter change resolves the contradiction between foam stability and salt resistance.
Solution Approach 2:
The patent introduces dynamic pH-switchable surfactants that can dynamically change their charge state in response to pH changes. These surfactants are neutral at injection pH for good solubility but become charged at reservoir pH to provide electrostatic repulsion and foam stability, thus adapting to different environmental conditions and resolving the contradiction between salt resistance and foam stability.
2Adaptability or versatility
If nonionic surfactants are compounded with anionic surfactants to improve salt resistance, then salt resistance is improved, but foaming performance deteriorates due to low ionization degree
Solution Approach 1:
The patent uses pH-switchable surfactants that dynamically change from nonionic to ionic forms based on pH. At injection conditions, they remain nonionic for good salt resistance and solubility. At reservoir conditions, they switch to ionic forms to provide strong foaming performance through electrostatic repulsion, thus resolving the contradiction between salt resistance and foaming performance.
Solution Approach 2:
The patent changes the ionization parameter of the surfactant by using pH-responsive materials. The surfactants transition from nonionic (low ionization) at injection pH to ionic (high ionization) at reservoir pH, thereby achieving both good salt resistance during injection and excellent foaming performance in the reservoir environment.
3Reliability
If anionic-nonionic surfactants are used to achieve high ionization degree, then foaming performance is improved, but viscosity-increasing effect deteriorates due to repulsion between anionic groups
Solution Approach 1:
The patent uses pH-switchable surfactants that are nonionic at injection pH (avoiding repulsion and maintaining viscosity) but become ionic at reservoir pH (providing strong foaming performance). This dynamic switching resolves the contradiction between foaming performance and viscosity-increasing effect by separating these functions in different stages of the process.
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 system stabilizes foam and increases viscosity, enhancing the recovery factor by more than 20% through improved plugging performance and sweep efficiency in porous media.
Implementation Method 1
when acidic gases such as CO2 are used as gas sources, they dissolve in aqueous solution, causing the pH to drop significantly
Implementation Method 2
under the action of an acidic substance, the protonation degree and hydrophilic-lipophilic balance of the compounding with an anionic surfactant can be well achieved
Implementation Method 3
The anionic surfactant sodium α-olefin sulfonate is most commonly used because the negative charges between its anions repel each other, enhancing the liquid film separation pressure and making the foam less likely to become thinner and break
Implementation Method 4
the negative charges between its anions repel each other, enhancing the liquid film separation pressure
Implementation Method 5
the compounded system does not have a viscosity-increasing effect on the system... has excellent foaming performance but also has good viscosity-increasing effect on the system
Data Source
AI summary
A viscoelastic foam system for an acidic gas switch improves the recovery factor. The viscoelastic foam system for an acidic gas switch has a pH-switch surfactant, a hydrocarbyl anionic surfactant and water. The pH-switch surfactant is at least one of long-chain hydrocarbyl amines. After the viscoelastic foam system meets the acidic gas, the interaction between the pH-switch surfactant and the hydrocarbyl anionic surfactant is enhanced, the viscosity increases, and the formed foam has better stability and plugging performance. When the viscoelastic foam system is injected at 1.0 PV, the apparent viscosity of the foam formed in the rock core is ≥270 mPa·s, which can increase the recovery factor by more than 20%, and the long-chain hydrocarbyl amine improves the salt tolerance of the single anionic surfactant, so that the applicable mineralization range of the system is increased to 10-200 g/L.