No abstract

Miscible hydrocarbon (HC) rich gas injection is a common EOR technique included in the development plan of many Abu Dhabi oil fields. This technology, that provides a very high oil recovery, requires the supply of a gas that is very valuable for other uses or its commercialization. Utilization and storage of flue gases rich in CO2 and N2 can play a key role in lowering the overall reservoir emissions by coupling carbon capture and storage (CCS) with EOR techniques. Thus, the substitution of hydrocarbon gas by these gases is of great environmental and industrial interest. Nevertheless, the change of the injection gas is not straightforward and requires a previous study to ensure the gas miscibility. The aim of this piece of research is to estimate the minimum miscibility pressure (MMP) of the studied gas, in order to clarify if miscibility conditions are achieved at reservoir pressure. Thus, a comprehensive study was performed applying three different approaches to predict/estimate the MMP: Empirical correlations from the literature based on experimental results. Experimental measurements with Slim Tube tests. Computer modeling based on equations of state for phase-behavior calculations. Miscibility of CO2 and N2 was successfully investigated through the three approaches. In the case of CO2, miscibility at reservoir pressure was totally ensured at 120°C since MMP was estimated to be the bubble pressure of the studied oil, more than 100 bar below reservoir pressure. Otherwise, the conclusion of the nitrogen miscibility studies is that N2 gas flooding is not a feasible EOR technique since MMP is far above reservoir pressure. Before completely discarding the use of nitrogen, miscibility of mixtures of HC rich gas and N2 was first studied by PVT simulations. Thermodynamic modelling was compared against experimental Slim Tube tests evaluating HC+N2 mixtures. Laboratory work led to conclude that mixtures with 42% of N2 could be injected at miscible conditions and revealed that simulations overestimate the minimum miscibility pressure of the studied gas mixtures. Finally, miscibility of CO2 and N2 mixtures with typical compositions of flue gases from post-combustion processes were studied using the thermodynamic model retuned with previous experimental measurements. This work presents a thorough study of minimum miscibility pressure of CO2 and N2 in oil from Abu Dhabi, which is the first step of any EOR project coupled with CCS. The developed methodology covered the three different approaches and the results provide a broad comparison amongst correlated, measured and simulated MMP.

No abstract

Polymer flooding is a well-established EOR technique widely implemented in sandstone reservoirs. Sulfonated acrylamide-based copolymers recently proved their potential in harsh HT/HS carbonate reservoirs with pilot tests upcoming in the Middle East. While polymer flooding is often classified as a tertiary recovery method, the present study aims to evaluate EOR efficiencies in secondary and tertiary recovery scenarios. The polymer selection process and characterization in porous media are described in detail. The study was conducted on a lab-scale at a temperature of 120°C. The salinity of seawater used for injection was 42 g/L TDS. The polymer selection was based on a thorough rheology and filterability study. The coreflooding tests were performed on limestone outcrops with permeability in the range of 40 mD. Single-phase experiments were performed to evaluate the impact of a pre-shearing step and study the in-situ rheology. Secondary and tertiary oil recovery experiments were conducted using reservoir dead oil. In all experiments, the tracer method was used to determine dynamic adsorption. The rheology and filterability study identified the best candidate (SAV 10) among three different molecular weight polymers containing the same high-sulfonation level. The target viscosity for the desired mobility ratio was 3 cP at 120°C, achieved with a polymer concentration of 3500 ppm. The single-phase experiments suggested that pre-shearing the polymer reduced the apparent shear thickening at high velocities due to a reduction in viscoelastic properties. The best oil recovery performances were obtained in the secondary mode (polymer flood applied at Swi) with a 15% higher recovery when compared to the tertiary mode (after reaching Sorw). The results correlate with a later breakthrough for the earlier polymer flood case. In both cases the mobility ratio was comparable (0.18-0.20) and much lower than waterflooding (1.5). The polymer dynamic adsorption estimated with the tracer method was about 140 μg/g rock in brine saturated cores, decreasing to ~100 μg/g rock in the presence of residual oil saturation. The in-situ rheology evaluation after stable recovery was reached following polymer flooding (Sorp), evidenced less apparent shear thickening, which could be related to a change in the conformation of the pores in the presence of oil. Most studies reported on secondary and tertiary polymer flooding focused on the case of heavy-oil sandstone reservoirs. The present work introduces new insights on early implementation of polymer flooding to optimize oil production by maximizing the performance of the method in HT/HS carbonate reservoirs. Furthermore, our study provides new insights about sulfonated acrylamide-base copolymer rheology in porous media for low permeability carbonate cores.

Polymer flooding is a well-established EOR technique widely implemented in sandstone reservoirs. Sulfonated acrylamide-based copolymers recently proved their potential in harsh HT/HS carbonate reservoirs with pilot tests upcoming in the Middle East. While polymer flooding is often classified as a tertiary recovery method, the present study aims to evaluate EOR efficiencies in secondary and tertiary recovery scenarios. The polymer selection process and characterization in porous media are described in detail. The study was conducted on a lab-scale at a temperature of 120°C. The salinity of seawater used for injection was 42 g/L TDS. The polymer selection was based on a thorough rheology and filterability study. The coreflooding tests were performed on limestone outcrops with permeability in the range of 40 mD. Single-phase experiments were performed to evaluate the impact of a pre-shearing step and study the in-situ rheology. Secondary and tertiary oil recovery experiments were conducted using reservoir dead oil. In all experiments, the tracer method was used to determine dynamic adsorption. The rheology and filterability study identified the best candidate (SAV 10) among three different molecular weight polymers containing the same high-sulfonation level. The target viscosity for the desired mobility ratio was 3 cP at 120°C, achieved with a polymer concentration of 3500 ppm. The single-phase experiments suggested that pre-shearing the polymer reduced the apparent shear thickening at high velocities due to a reduction in viscoelastic properties. The best oil recovery performances were obtained in the secondary mode (polymer flood applied at Swi) with a 15% higher recovery when compared to the tertiary mode (after reaching Sorw). The results correlate with a later breakthrough for the earlier polymer flood case. In both cases the mobility ratio was comparable (0.18-0.20) and much lower than waterflooding (1.5). The polymer dynamic adsorption estimated with the tracer method was about 140 μg/g rock in brine saturated cores, decreasing to ∼100 μg/g rock in the presence of residual oil saturation. The in-situ rheology evaluation after stable recovery was reached following polymer flooding (Sorp), evidenced less apparent shear thickening, which could be related to a change in the conformation of the pores in the presence of oil. Most studies reported on secondary and tertiary polymer flooding focused on the case of heavy-oil sandstone reservoirs. The present work introduces new insights on early implementation of polymer flooding to optimize oil production by maximizing the performance of the method in HT/HS carbonate reservoirs. Furthermore, our study provides new insights about sulfonated acrylamide-base copolymer rheology in porous media for low permeability carbonate cores.