Enhanced Oil Recovery In Carbonate Reservoirs Research Articles

A critical review of carbon dioxide enhanced oil recovery in carbonate reservoirs

Carbon dioxide (CO2) enhanced oil recovery (EOR) in carbonate reservoirs is regarded as a promising EOR technology. However, the oil recovery factor of CO2 EOR is low due to the CO2 EOR mechanisms in carbonate reservoirs are not clear. In this study, the CO2 EOR in carbonate reservoirs is reviewed in detail. First, the carbonate reservoirs are characterized by strong heterogeneity, fractures and vugs with poor connectivity, complex fluid properties, leading to a variety of difficulties in drilling, acid fracturing and CO2 EOR. Second, CO2 EOR in carbonate reservoirs includes CO2 continuous injection, water-alternating-CO2 (WAG), carbonated water injection (CWI), CO2 foam and CO2 huff-n-puff. But the screening criterion for different CO2 injection schemes in carbonate reservoirs has not been established. Third, the mechanisms of the CO2 diffusion, CO2-oil interaction, and CO2-fluid-rock interaction are discussed. (1) The main experimental test method for CO2 diffusion coefficient is pressure decay, and the temperature of the CO2 diffusion coefficient test is 25–130 ℃, and the pressure is 0.772–34 MPa. But the matrix-fracture-vug system and CO2-fluid-rock interaction effects in the CO2 diffusion coefficient experiments, and the impure CO2 diffusion behavior and CO2 diffusion behavior in the oil–water mixture have not been studied. (2) The main mechanism of pure CO2 flooding for EOR has been studied, but the development of impure CO2 oil interaction and complex the matrix-fracture-vug system are unclear. (3) The CO2-fluid-rock interactions have great influences to CO2 EOR in the carbonate reservoirs. But CO2-fluid-rock interactions in-situ formation state is still unclear. Fourth, pilot test studies in carbonate reservoirsare discussed, and the challenges of CO2 EOR in carbonate reservoirs are pointed out. The findings of this study can help for better understanding of CO2 EOR mechanism in carbonate reservoirs, and it also proposes some future clues of CO2 EOR in carbonate reservoirs.

Performance evaluation and mechanism study of a functionalized silica nanofluid for enhanced oil recovery in carbonate reservoirs

In this investigation, a functionalized SiO2 nanofluid was developed by integrating sodium oleate to mercapto-terminated nano-SiO2 via the thiol-ene “click” reaction. The developed nanofluid in the presence of higher concentrations (> 40,000 ppm) of NaCl at 70 °C was confirmed to be more stable than the original SiO2 nanofluid based on the outcomes obtained from precipitate observation, particle dimension, and zeta potential measurements. Successful integration of sodium oleate on the target nanoparticles was corroborated by a series of characterization approaches. Furthermore, the viscosity, contact angle, and interfacial tension (IFT) determinations were conducted to investigate nanofluids' potential for enhanced oil recovery (EOR). The results indicated that the viscosity of the functionalized SiO2 nanofluid (labeled FF-4) accounted for 3.48 cp after adding 40,000 ppm NaCl, while that of the original SiO2 nanofluid (labeled OF-4) was 1.15 cp. From the contact angle values, the carbonate rock surface was transformed from oil-wet (135°) to water-wet (72° and 38°) after being treated with the OF-4 and FF-4. The wettability alteration was attributed to the formation of the wedge film in the contact line area between the rock and fluids (oil sample and nanofluid). The functionalized nano-SiO2 helped to reduce IFT because of the simultaneous presence of the alkane chain (oleophilic) and carboxylate group (oleophobic) on the particle surface, making the functionalized nano-SiO2 have an amphiphilic structure. However, the original nano-SiO2 hardly changed IFT. Micro-model experiments showed that the OF-4 had a prominent oil displacement effect by changing wettability to a water-wet state and reducing the viscous fingering phenomenon. Core flooding tests demonstrated that the oil recovery factor of the FF-4 was almost 2.5 times that of the OF-4. Viscosity improvement was considered as a new oil recovery mechanism after wettability alteration and IFT reduction. This paper revealed the important properties of the functionalized nano-SiO2 and provided a novel efficient nanofluid for EOR in carbonate reservoirs.

Enhanced oil recovery with nanofluids based on aluminum oxide and 1-dodecyl-3-methylimidazolium chloride ionic liquid

Surface-active ionic liquids (SAILs) have multiplied the possibilities of surfactant enhanced oil recovery (EOR) methods. Among their multiple promising features, the possibility of functionalization and their stability at harsh conditions should be highlighted for the application. They have been successfully applied to increase oil recovery by improving crucial parameters such as: formulation stability, reduction of water–oil interfacial tension, and wettability. Recently, nanoparticles have attracted attention for EOR applications due to their capacity to modify the properties of rock surfaces. However, to date no research has been conducted on the combination of SAILs with nanoparticles for EOR. In this work, the combination of the SAIL 1-dodecyl-3-methylimidazolium chloride, [C12mim]Cl, with Al2O3 nanoparticles is proposed for EOR. Stable dispersions in brine were achieved, using the polymer polyvinylpyrrolidone (PVP) as a stabilizing agent, and characterized through density and dynamic viscosity measurements. According to stability and interfacial tension studies, a nanofluid consisting of 0.05 wt% [C12mim]Cl, 0.05 wt% Al2O3 and 1.0 wt% PVP, in brine (5.0 wt% NaCl) was proposed for EOR in carbonate reservoirs. The presence of nanoparticles reduced the adsorption of the surfactant-polymer formulation on carbonate rocks and changed the aged rock wettability from oil-wet to water-wet. An additional oil recovery of 10.4 %OOIP was achieved with the surfactant-polymer formulation, in comparison with 14.8 %OOIP obtained with the nanofluid.

Emerging applications of TiO2/SiO2/poly(acrylamide) nanocomposites within the engineered water EOR in carbonate reservoirs

In this study, TiO2/SiO2/poly(acrylamide) nanocomposites (NCs) as a newly-developed-nano enhanced oil recovery (EOR) agent is proposed using a simple, green and economic method from the extract of pomegranate seeds. The ultraviolet–visible spectroscopy (UV–Vis), X-ray diffraction (XRD), Fourier-transform infrared spectroscopy (FT-IR), scanning electron microscopy (FE-SEM), transmission electron microscopy (TEM) and energy-dispersive X-ray spectroscopy (EDS) are applied to analyze the characterization of NCs. Nano-smart solutions are prepared from the dispersion of NCs within the smart water at three different concentrations (500, 1000 and 1500 ppm). The used smart water solutions are formulated from mixing the single and binary systems of the monovalent and divalent salts (NaCl, KCl, MgCl2, CaCl2, Na2SO4, MgSO4, K2SO4 and CaSO4) at different concentrations of 2500, 5000 and 10,000 ppm within the distilled water. In order to identify the effect of the prepared NCs in smart EOR applications, the interfacial tension (IFT) of crude-oil/smart-water and crude-oil/smart-nanofluid systems is measured using the pendant drop technique, the wettability behavior of carbonate rock is studied using the contact angle (CA) measurement, and recovery efficiency is determined by preforming the coreflooding test for eight core plugs. According to the obtained experimental results of IFT and CA, KCl-5000, K2SO4-5000, CaSO4 + CaCl2 (5000 + 5000) and K2SO4+ CaCL2 (2500 + 2500) are selected as the optimal smart solutions. Furthermore, the performance of the selected smart water solutions is influenced by 65% in IFT reduction, 32% in wettability alteration and 10.5% in oil recovery when the prepared NCs is added to the solutions. Nano-OSS3-5000 smart-nanofluid developed from mixing 1500 ppm of TiO2/SiO2/poly(acrylamide) NCs with 5000 ppm of CaSO4 and CaCl2 ions demonstrated the highest performance in increasing oil recovery from 36.0 to 46.53% original oil in place (OOIP).

Experimental study of combined microemulsion/brine flooding to EOR in carbonate reservoirs

The application of Enhanced Oil Recovery (EOR) methods is essential to promoting increase in the oil recovery where the conventional recovery methods unsuccessful. Numerous studies have demonstrated that microemulsion and surfactant systems injection can change the properties of fluids and increase the oil recovery. In this work, flooding tests were carried out combining brine and microemulsion in different proportions and schemes of injection. Microemulsion systems constituted by: Ultramine 200, n-butanol, kerosene and water were obtained and characterized by measurements of droplet diameter, surface tension, interfacial tension (IFT), and viscosity. The surfactant concentration in the microemulsion was evaluated on the oil recovery through flooding experiments. This study also evaluated how surface and interfacial tensions influence crude oil recovery (29° API). Results demonstrate that the oil recovery increases with the increase in surfactant concentration in the microemulsion. However, that increase is significant only up to 9 wt%, reaching an additional 21% oil recovery of the original oil in place (OOIP). This research recommends chemical method to EOR tests by combined injection from microemulsion and brine. The chemical action of microemulsion system results in a miscible phase, promotes oil mobilization, improve brine flooding, and increase the oil recovery.

A pH-Resolved Wettability Alteration: Implications for CO2-Assisted EOR in Carbonate Reservoirs

Wettability of an oil/brine/rock system is a critical petrophysical parameter, which governs subsurface multiphase flow behavior, thus hydrocarbon recovery. While the mechanisms of CO2-assisted enhanced oil recovery (EOR) techniques have been extensively investigated in carbonate reservoirs, few have been done to identify the controlling factor of CO2-induced wettability alteration, and fewer have looked beyond the implications for CO2-assisted EOR. We thus hypothesize that CO2-assisted EOR techniques cause a more hydrophilic system due to H+ adsorption on the interface of oil/brine and brine/carbonate as a result of CO2 dissolution. To test this hypothesis, we measured contact angles of two oils with different acid and base numbers in the presence of 1 M Na2SO4 at pH either 3 or 8. Moreover, we performed a geochemical study to identify the controlling factor of wettability alteration. Contact angle results support the hypothesis, showing that the oil/brine/rock system shifts toward more water-wet because...

Status of surfactant EOR technology

Abstract Surfactant enhanced oil recovery (EOR) includes surfactant flooding and surfactant stimulation. The main functions of surfactants are to reduce interfacial tension and wettability alteration. This paper is to review the EOR technology related to surfactant injection. The reviewed topics include the following: • Surfactant EOR mechanisms • Factors affecting interfacial tension • Trapping number • Screening criteria • Laboratory work • Numerical simulation work • Summary of pilot and large-scale applications • Surfactants used • Salinity gradient • Surfactant EOR in carbonate reservoirs • Surfactant EOR in shale reservoirs

Multi-scale Imaging and Simulation of Structure, Flow and Reactive Transport for CO2 Storage and EOR in Carbonate Reservoirs

As we continue to use fossil fuels for our energy supply, the concentration of CO2 in the Earth’s atmosphere is likely to continue to increase. It has been shown that this is correlated with an increase in the temperature of the atmosphere and potential associated climate change. To mitigate this problem, Carbon Capture and Storage (CCS) has been mooted over the past decade. In this chapter, we will focus on CO2 storage in downhole rock formations. Rock formations suitable for storage include saline aquifers and depleted oil and gas reservoirs. Also coal bed methane (CBM) reservoirs may be suitable for storage, but we will not consider these in the current chapter. In the case of saline aquifers, we consider only the storage of CO2. In the case of depleted oil/gas reservoirs, the storage of CO2 can be combined with Enhanced Oil Recovery (EOR). This may lead to a more favorable economic scenario and has recently been coined as CCUS (Carbon Capture and Utilized Storage). In particular we will focus in this chapter on carbonate reservoirs. Sandstone reservoirs have been relatively well studied. However, much less is known about the storage properties of carbonate rocks, which have very different petrophysical and flow properties. Moreover, carbonate rocks constitute a significant fraction of existing depleted hydrocarbon reservoirs. Our aim is to study the pore scale properties of carbonates and upscale these to the core and field scales. First, carbonates have a very different structure from sandstones, associated with their composition and diagenesis. Carbonates usually have a much broader pore size distribution (PSD) than sandstones with extensive microporosity (Cantrell and Hagerty 1999). In addition, carbonates are often naturally fractured (Ameen et al. 2010). This leads to a broad range of heterogeneity as a function of length scale, in comparison …

Technology Focus: EOR Performance and Modeling (January 2012)

Technology Focus In spite of continued investment and advances in exploiting alternative-energy sources, oil and natural gas will continue to be a significant portion of US and global energy portfolios for decades. Enhanced oil recovery (EOR) uses unconventional hydrocarbon-recovery methods that target the approximately two-thirds of the oil volume remaining in reservoirs after conventional-recovery methods have been exhausted. Though limited by high capital and operating costs, EOR techniques will have a substantial effect on the future supply of oil. In 2011, SPE hosted an EOR conference in Kuala Lumpur, and three workshops to address EOR technologies in Malaysia, Kuwait, and the Syrian Arab Republic. The Malaysia workshop focused on chemical-EOR methods, the Kuwait workshop addressed opportunities and for challenges of EOR methods in the Middle East, and the Syrian Arab Republic workshop discussed EOR in carbonate reservoirs. More than 300 EOR papers were published in SPE conferences, with many additional presentations in EOR workshops. These papers address important issues related to practical application of conventional EOR methods and the development of novel EOR technologies. The topics cover experience with, opportunities for, and challenges of EOR technologies; fundamental study of EOR mechanisms for different methods; feasibility study and improvement of an EOR method for a specific reservoir; EOR-screening criteria; reservoir surveillance, monitoring, and evaluation technologies; reservoir simulation and modeling; lessons learned from EOR pilot and field trials; and some novel EOR methods. Polymer flooding has been proved the most cost-effective chemical-EOR method in the laboratory and in the field. A recent focus on polymer flooding evaluated associative polymers because of their advantage over traditional hydrolyzed polyacrylamide (HPAM) polymers; thus, one paper about comparing the flow behavior of associative polymer and HPAM in porous media was selected for this feature. CO2 injection is a win/win strategy because it can enhance oil recovery and be used for CO2 storage in reservoirs to reduce greenhouse-gas levels in the atmosphere. However, CO2 EOR targets maximum oil recovery while CO2 sequestration targets maximum storage capacity without leakage. One paper featured here provides some guidance to balance the two technologies. Steamflooding has been applied successfully in heavy-oil reservoirs. However, one paper synopsized in this feature will describe successful steamflooding in a light-oil reservoir. Recommended additional reading at OnePetro: www.onepetro.org. SPE 142668 Enhanced Waterflood for Middle East Carbonate Cores—Impact of Injection-Water Composition. By Robin Gupta, ExxonMobil Upstream Research, et al. SPE 142105 A Simplified Model for Simulations of Alkaline/Surfactant/Polymer Floods. By Mojdeh Delshad, SPE, University of Texas at Austin, et al. SPE 144294 Large-Scale High-Viscous-Elastic-Fluid Flooding in the Field Achieves High Recoveries. By Wang Demin, SPE, Daqing Oil Company, et al. \ SPE 144599 A Combined Experimental and Simulation Workflow To Improve Predictability of In-Situ Combustion. By M. Bazargan, Stanford University, et al. SPE 147858 In-situ Combustion Using Sugar Dust, ‘Sweet Reservoirs’—A Smart and Better Alternative by Panchamlal, SPE, Maharashtra Institute of Technology, et al. SPE 147999 Lessons Learned From Nine Years of Immiscible-Gas-Injection Performance and Sector-Modeling Study of Two Pilots in a Heterogeneous Carbonate Reservoir by Lakshi Konwar, SPE, Zakum Development Company, et al.