Enhanced Oil Recovery Using Polymer Alternating CO₂ Gas Injection: Mechanisms, Efficiency, and Environmental Benefits

Abstract

In light of the depletion of conventional oil reserves and rising global warming, the CO 2 -EOR has garnered global attention among stakeholders for its potential to evolve into a net carbon-negative technique for extracting residual oil. CO 2 -EOR is a method of extracting additional crude oil beyond primary and secondary recovery from the reservoir using CO 2 as an injection fluid. Among CO 2 -EOR methods, water alternating gas (WAG) injections have been adopted in over 90% of CO 2 -EOR projects worldwide due to improved mobility control and better volumetric sweep efficiency as compared to conventional gas and water injections. However, the sweep efficiency can be further improved by substituting water with the polymer, owing to its greater viscosity. This paper aims to study the mechanisms involved in the miscible and immiscible displacement of medium crude oil by polymer alternating gas (PAG) injection. The miscibility of crude oil with CO 2 was determined using slim tube experiment. The oil displacement mechanism by CO 2 injection was studied by using interfacial tension (IFT) measurements and the rheology of crude oil under different CO 2 equilibrium pressure conditions. Observations revealed that as the CO 2 equilibrium pressure increased, there was a reduction in the IFT between the crude oil and the CO 2 system, attributed to the exchange of CO 2 and intermediate hydrocarbons (HCs) across the interface. The rheological studies of crude oil indicated a decreasing trend in oil viscosity with increasing CO 2 pressure, thereby improving the oil mobility. The solubility of CO 2 in oil and the swelling factor were quantified for different CO 2 saturation pressures using pressure decay data and the density of the CO 2 -saturated crude oil. The rheological and injectivity studies of the polymer were conducted using hydrodynamic dimension analysis, resistance factor, and residual resistance factor to assess the flowability of the polymer within the core. In the case of immiscible PAG, an additional 26% of OOIP was recovered following waterflooding, while 42% of the oil was recovered under the miscible mode. Furthermore, the CO 2 net utilization factor was greater for PAG in the miscible mode compared to that in the immiscible mode. In summary, PAG has huge potential to extract medium oil from low-permeable carbonates, and its efficiency is highly dependent on the mode of CO 2 injection, polymer hydrodynamic dimensions, and mobility control offered by the polymer.

Utilization of CO2-captured poly(allylamine) as a polymer surfactant for nanoarchitecture production in a closed CO2 cycle

“…In this process, the polymer facilitates oil movement toward production wells by alternating with CO 2 to displace oil. 90–92 The conversion of the CA-captured PAA into the polymer surfactant is accompanied by CO 2 release, which can be controlled by adjusting the ratio of the ion exchanger. The ion exchange in water causes the surfactant to self-assemble into nanoobjects, which are expected to effectively displace oil when used in the PAG injection method.…”

Utilizing Artificial Intelligence Techniques for Modeling Minimum Miscibility Pressure in Carbon Capture and Utilization Processes: A Comprehensive Review and Applications

“…The implementation of CO 2 – EOR can be done under several schemes, including the injection of miscible/immiscible CO 2 , water alternating CO 2 gas injection (WAG CO 2 ), polymer alternating gas CO 2 (PAG), simultaneous water CO 2 gas injection, foam assisted CO 2 , low salinity water–surfactant–CO 2 , and hybrid schemes with surfactant polymer (SP). − Most CO 2 – EOR processes are commonly confronted to satisfy two objectives consisting of maximizing ORF and minimizing the production of CO 2 (this latter means the increase in the storage performance). − However, it is worth mentioning that many published studies and experimental tests demonstrated the superiority of the miscible type (single–phase flow) of CO 2 – EOR processes in reaching higher ORF compared to the immiscible type (two–phase flow). , The suitable design of a CO 2 – EOR process depends greatly on the so-called minimum miscibility pressure (MMP) since this parameter allows the determination of the injection type, i.e., miscible or immiscible. MMP represents the cutoff pressure at reservoir temperature (T R ) above which miscibility between the reservoir fluid and the injected gas occurs after multiple contacts. − …”

Effect of Imidazolium-Based Ionic Liquids on the Sandstone Reservoir’s Wettability: Implications for CO2 Geo-Storage

“…In recent years, numerous studies have been conducted to modify the oil-wet and/or CO 2 -wet reservoirs using various chemicals, including surfactants, nanofluids, acids like stearic acids, pH-altering agents, and smart fluids with variations in ionic composition. ,,,− These chemicals demonstrated a significant alteration in wettability, thereby improving the ultimate storage potential of CO 2 through capillary and structural mechanisms. However, concerns regarding the economic feasibility, scalability, and deliverability of such chemicals deep within reservoirs present several challenges.…”