Biotechnology has had a major effect on improving crude oil displacement to increase petroleum production. The role of biopolymers and bio cells for selective plugging of production zones through biofilm formation has been defined. The ability of microorganisms to improve the volumetric sweep efficiency and increase oil recovery by plugging off high-permeability layers and diverting injection fluid to lower-permeability was studied through experimental tests followed by multiple simulations. The main goal of this research was to examine the selective plugging effect of hydrophobic bacteria cell on secondary oil recovery performance. In the experimental section, water and aqua solution of purified Acinetobacter strain RAG-1 were injected into an oil-saturated heterogeneous micromodel porous media. Pure water injection could expel oil by 41%, while bacterial solution injection resulted in higher oil recovery efficiency; i.e., 59%. In the simulation section, a smaller part of the heterogeneous geometry was employed as a computational domain. A numerical model was developed using coupled Cahn–Hilliard phase-field method and Navier–Stokes equations, solved by a finite element solver. In the non-plugging model, approximately 50% of the matrix oil is recovered through water injection. Seven different models, which have different plugging distributions, were constructed to evaluate the influences of selective plugging mechanism on the flow patterns. Each plugging module represents a physical phenomenon which can resist the displacing phase flow in pores, throats, and walls during Microbial-Enhanced Oil Recovery (MEOR). After plugging of the main diameter route, displacing phase inevitably exit from sidelong routes located on the top and bottom of the matrix. Our results indicate that the number of plugs occurring in the medium could significantly affect the breakthrough time. It was also observed that increasing the number of plugging modules may not necessarily lead to higher ultimate oil recovery. Furthermore, it was shown that adjacent plugs to the inlet caused flow patterns similar to the non-plugging model, and higher oil recovery factor than the models with farther plugs from the inlet. The obtained results illustrated that the fluids distribution at the pore-scale and the ultimate oil recovery are strongly dependent on the plugging distribution.
Oil trapping behavior during the pre-flush stage is critically important to evaluate the effectiveness of matrix acidizing for the oil well stimulation. In this study, the visco-capillary behavior of the two-phase flow in the pore-scale is analyzed to investigate the influence of wetting properties for a natural rock sample. A two-dimensional model, based on Cahn–Hilliard phase-field and Navier–Stokes equations, was established and solved using the finite element method. A stability phase diagram for log capillary number (Ca)–log viscosity ratio (M) was constructed and then compared with the reported experimental works. The maximum and minimum ranges of capillary number and viscosity ratio to identify both viscous and capillary fingering regions were found to be Log M ≈ −2.5, Log Ca ≈ −5, and Log M ≈ −0.5, Log Ca ≈ −5, respectively. However, the most stable displacement region was found to be located at Log M ≈ 0.5 and Log Ca ≈ −2. Furthermore, the impact of four independent variables, including pore volume of injection (1 < PV < 5), capillary number (−6 < Log Ca < 0), viscosity ratio (−5 < Log M < 2), and contact angle (π/6<θ<5π/6), on recovery factor (RF) was investigated using central composite design of response surface methodology. For the chosen range of independent variables, the optimum conditions for the immiscible two-phase flow (e.g., RF > 0.95) occurred at Log M > 0, −4.5 < Log Ca < −2, PV > 1, θ > π/6 condition. It is worth mentioning that for Log M< 0, the optimum condition occurred at Log M ≈ 0, Log Ca ≈ −3.5, PV ≈ 4, and θ ≈ π/6.
Gas flooding through the injection of CO2 is generally performed to achieve optimum oil recovery from underground hydrocarbon reservoirs, and CO2 capturing and storage. In fact, the second purpose is aimed at reducing the greenhouse effect in the atmosphere and achieving NetZero. Due to the laborious operational circumstances governing the gas injection process under miscibility conditions such as pressure maintenance, many reservoirs are situated in near-miscibility gas flooding operations. In this research, the displacement of oil through carbon dioxide injection under near-miscibility conditions is scrutinized exclusively at the pore scale. In this regard, based on the correlations and data available in the literature, first, the criteria of the near miscibility region are specified. Then, two separate numerical approach are implemented to examined the behavior of CO2-oil at lower-pressure limit of specified region. First, Phase-field coupled with Navier-Stokes equation is used to investigate the CO2-oil displacement by capturing the diffusive interface properties and hydrodynamic properties of fluids. Next, the effect of CO2 mass transfer into the oil phase is incorporated by coupling classical Fick’s law to the system of above equations to track the viscosity reduction of oil and the variation of CO2 diffusion coefficient using TDS module respectively. To better recognize the oil recovery mechanism in pore-scale, qualitative analysis indicates that interface is moved into the bypassed oil due to low interfacial tension in the near-miscible region. Moreover, behind the front ahead of the main flow stream, the CO2 phase can significantly displace almost all the bypassed oil in normal pores and effectively decrease the large amounts in small pores. This is because of mass transfer and capillary cross-flow mechanism caused by simultaneous CO2 and oil flow through the diffusive interface between the phases. The quantitative results also confirmed that taking mass transfer into account in pore-scale simulation and strengthening the diffusion term enhanced oil recovery from 92% to over 98%, approaching the output of miscible gas injection. The outcome of this research emphasizes the significance of applying the CO2-EOR process under near-miscible operating conditions.
Gas flooding through the injection of $$\text{CO}_{2}$$ CO 2 is generally performed to achieve optimum oil recovery from underground hydrocarbon reservoirs. However, miscible flooding, which is the most efficient way to achieve maximum oil recovery, is not suitable for all reservoirs due to challenge in maintaining pressure conditions. In this circumstances, a near-miscible process may be more practical. This study focuses on pore-scale near-miscible $$\text{CO}_{2}$$ CO 2 –Oil displacement, using available literature criteria to determine the effective near-miscible region. For the first time, two separate numerical approaches are coupled to examine the behavior of $$\text{CO}_{2}$$ CO 2 –oil at the lower-pressure boundary of the specified region. The first one, the Phase-field module, was implemented to trace the movement of fluids in the displacement $$\text{CO}_{2}$$ CO 2 –Oil process by applying the Navier–Stokes equation. Next is the TDS module which incorporates the effect of $$\text{CO}_{2}$$ CO 2 mass transfer into the oil phase by coupling classical Fick’s law to the fluids interface to track the variation of $$\text{CO}_{2}$$ CO 2 diffusion coefficient. To better recognize the oil recovery mechanism in pore-scale, qualitative analysis indicates that interface is moved into the by-passed oil due to low interfacial tension in the near-miscible region. Moreover, behind the front ahead of the main flow stream, the $$\text{CO}_{2}$$ CO 2 phase can significantly displace almost all the bypassed oil in normal pores and effectively decrease the large amounts in small pores. The results show that by incorporating mass transfer and capillary cross-flow mechanisms in the simulations, the displacement of by-passed oil in pores can be significantly improved, leading to an increase in oil recovery from 92 to over 98%, which is comparable to the result of miscible gas injection. The outcome of this research emphasizes the significance of applying the $$\text{CO}_{2}$$ CO 2 -EOR process under near-miscible operating conditions.
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