Direct Injection Of CO2 Research Articles

A numerical model for evaluating the long-term migration and phase transition behavior of foam-assisted injection of CO2 in saline aquifers

Geological Carbon Storage (GCS) is a rapidly developing technology with the potential to mitigate the environmental impact of excessive greenhouse gas emissions. Foam-assisted injection of CO2 can effectively alter fluid rheological properties, thereby enhancing sweep efficiency. In this paper, a numerical model to evaluate the long-term migration behavior of foam-assisted injected CO2 in saline aquifers is developed. It is found that foam-assisted injection improves storage efficiency and reduces the plume migration distance compared to direct CO2 injection. This creates higher demands on the injection pressure but minimizes the risk of leakage. The effects of injection strategy, volume fraction of foam, and reservoir heterogeneity were investigated. Modeling results show that the injection strategy with a high foam volume fraction enhances the sweep efficiency and improves the transition rate of injected CO2 to the dissolved state. This can effectively enhance the long-term security of the sequestration. Simulations of layered formations indicates that foams can potentially inhibit the rapid migration of plumes along high-permeability zones. Our study provides insights for foam-assisted injection to enhance reservoir storage efficiency and long-term safety for GCS.

Investigating the Potential of CO2 Nanobubble Systems for Enhanced Oil Recovery in Extra-Low-Permeability Reservoirs.

Carbon Capture, Utilization, and Storage (CCUS) stands as one of the effective means to reduce carbon emissions and serves as a crucial technical pillar for achieving experimental carbon neutrality. CO2-enhanced oil recovery (CO2-EOR) represents the foremost method for CO2 utilization. CO2-EOR represents a favorable technical means of efficiently developing extra-low-permeability reservoirs. Nevertheless, the process known as the direct injection of CO2 is highly susceptible to gas scrambling, which reduces the exposure time and contact area between CO2 and the extra-low-permeability oil matrix, making it challenging to utilize CO2 molecular diffusion effectively. In this paper, a comprehensive study involving the application of a CO2 nanobubble system in extra-low-permeability reservoirs is presented. A modified nano-SiO2 particle with pro-CO2 properties was designed using the Pickering emulsion template method and employed as a CO2 nanobubble stabilizer. The suitability of the CO2 nanobubbles for use in extra-low-permeability reservoirs was evaluated in terms of their temperature resistance, oil resistance, dimensional stability, interfacial properties, and wetting-reversal properties. The enhanced oil recovery (EOR) effect of the CO2 nanobubble system was evaluated through core experiments. The results indicate that the CO2 nanobubble system can suppress the phenomena of channeling and gravity overlap in the formation. Additionally, the system can alter the wettability, thereby improving interfacial activity. Furthermore, the system can reduce the interfacial tension, thus expanding the wave efficiency of the repellent phase fluids. The system can also improve the ability of CO2 to displace the crude oil or water in the pore space. The CO2 nanobubble system can take advantage of its size and high mass transfer efficiency, among other advantages. Injection of the gas into the extra-low-permeability reservoir can be used to block high-gas-capacity channels. The injected gas is forced to enter the low-permeability layer or matrix, with the results of core simulation experiments indicating a recovery rate of 66.28%. Nanobubble technology, the subject of this paper, has significant practical implications for enhancing the efficiency of CO2-EOR and geologic sequestration, as well as providing an environmentally friendly method as part of larger CCUS-EOR.

Remineralization of desalinated water: Duality roles of H2SO4 and CO2 injection during calco-carbonic equilibrium of osmosis water

In a desalination station, the remineralization step of osmosis water (OW) is essential to return to produced water its calco-carbonic equilibrium. For this, the use of calcite CaCO3 or lime Ca(OH)2 for water equilibrium in post-treatment processes needs the utilization of both CO2 and/or H2SO4 in osmosis water. For this reason, we describe here in detail, the effect of H2SO4 and CO2 on the remineralization process in a post-treatment desalination plant, especially with using hydrated lime Ca(OH)2 and calcite contactor (CaCO3)·In this paper, the different cases were discussed and investigated, by monitoring several indicator parameters such as pH, Ca2+ content, alkalinity, Langelier Index, etc. After the remineralization stage, we have shown that the efficiency of the remineralization process by CaCO3 or Ca(OH)2 depends on CO2 or H2SO4 content. Remineralization by CaCO3 (limestone) coupled with CO2 acidification is easy and more operator-friendly compared to the process using Ca(OH)2 (lime); it provides a clean environment for people working in the plant. In addition, the H2SO4 injection in the pretreatment stage followed by CaCO3 contact could lead to great results and correct calco-carbonic equilibrium. In the end, a comparative study of the investment cost in each process shows that the acidification of raw water with sulfuric acid (pretreatment) is the cheapest one, according to many studies. But on the other hand, the direct injection of CO2 is the easiest one to use for water balancing.

Effects of calcium carbide slag on properties and carbon sequestration efficiency of cement pastes mixed under direct CO2 injection conditions

CO2-mixing by directly injecting CO2 into fresh cement-based materials is a burgeoning technology to produce low-carbon cement products. The objective of this study is to investigate the influence of the calcium carbide slag (CCS) content on the properties and carbon sequestration efficiency of cement pastes mixed under direct CO2 injection conditions. The results indicate that the addition of CCS reduced the fluidity of the cement pastes, accelerated the setting process, increased volume shrinkage, and reduced compressive strength. Following the injection of CO2 into the cement pastes, calcium hydroxide (CH) was carbonated to form calcium carbonate (CC) particles which fill the voids in the cement pastes, thereby reducing volume shrinkage and increasing compressive strength. A lower CO2 inflow rate (2 L/min) was more beneficial to the workability of the cement pastes, while a high inflow rate (6 L/min) can lead to insufficient hydration and affect the development of strength. However, a higher CO2 inflow rate was favorable for improving carbon sequestration efficiency. The highest amountof carbon sequestration can be reached at 6.93 %, when the CCS content is 10 % and the CO2 inflow rate is 6 L/min.

Investigating CO2–N2 phase behavior for enhanced hydrate-based CO2 sequestration

Storing CO2 in underwater sand sediments as hydrates offers vast capacity and minimal leakage risk. But direct CO2 injection can clog the surrounding area, reducing the flow. One solution is injecting CO2–N2 mixtures. This study investigated the movement and transformation of this gas mixture, with a focus on the formation rates and main factors of hydrate-based CO2 storage. Results revealed two distinct gas seepage-phase transition processes. In freshwater conditions, there was an initial temperature spike followed by localized hydrate formation, which then spread outward. In memory water, multiple hydrate formations occurred simultaneously. Freshwater conditions led to more blockages due to the concentration of hydrates, while the memory conditions maintained better flow due to more evenly distributed hydrates. Gas composition analysis showed that as CO2-rich hydrates formed, the CO2 level in the flowing gas dropped, which could stop further hydrate formation. This finding indicates that mixed gas injections could prevent excessive hydrate formations and maintain flow. The saturation of hydrates varied between 10 % and 50 %, with differences attributed to the unpredictable nature of initial hydrate formation. Overall, this research will guide efforts to optimize CO2 storage as hydrates and re-evaluate the viability and safety of this storage method using CO2–N2 mixtures.

Assessment of CO2 mineral storage potential in the terrestrial basalts of China

Basalts contain a lot of carbon-fixing minerals which can achieve the fast mineral trapping of CO2. Based on the CO2 mineral trapping mechanism, an evaluation method for CO2 storage capacity in basalts was established, which considers two injection scenarios including direct CO2 injection and carbonated water injection. Then the geological conditions of terrestrial basalts in China were assessed. The range of CO2 mineral storage capacity in basalts at different probabilities was calculated by Monte Carlo simulation. The results show that the total theoretical mineral storage capacity of CO2 in the terrestrial basalts of China is 39792.05–54325.44 Gt with an average of 46948.36 Gt (P50). The effective mineral storage capacities for direct CO2 injection and carbonated water injection are 607.79–1121.44 Gt (P50 = 847.95 Gt) and 201.13–303.85Gt (P50 = 249.50 Gt), respectively. The corresponding effective storage coefficients at P50 are 0.0181 and 5.31 × 10-3, respectively. Carbonated water injection is advised for prior use, which can achieve CO2 mineral trapping more rapidly. The effective storage capacity is usually much larger than the CO2 emissions in the same region except for the eastern region, but their distributions are not well matched, needing a comprehensive source-sink optimization. The screening and classification of basalts in China should also be strengthened in the future to promote the utilization of CO2 mineral storage capacity and the implementation of demonstration projects.

Pore matrix dissolution in carbonates: An in-situ experimental investigation of carbonated water injection

Carbonate rock dissolution during the reactive transport of carbon dioxide (CO2)-enriched brine has been studied extensively in the context of carbon storage in saline aquifers. However, there is limited knowledge of CO2-induced reactive transport in multiphase systems (containing oil and brine), which is more relevant to carbon sequestration in depleted oil reservoirs. In this work, we uncover the pore-scale dynamics of fluid flow and rock dissolution during carbonated water injection (CWI) in hydrophilic porous media containing two fluid phases (oil and brine). We combine novel core flooding and high-resolution imaging techniques to visualize and characterize changes in fluid occupancy and pore morphology. It is observed that the sequence of flow and transport in two-phase systems involves a pre-dissolution period, where CWI induces the displacement of waterflood-trapped oil, and a dissolution period typified by channel flow. Improved oil recovery during pre-dissolution emanates from an oil swelling mechanism that drives reconnection and mobilization of trapped oil globules. Additionally, CO2 is stored in both oil and carbonated water. Channel flow during dissolution results in the formation of wormholes with two distinct dissolution patterns. The first is a conical wormhole at lower injection rates where diffusion rates are significant. The second is a dominant wormhole at higher injection rates where advection dominates the transport of reactive species to the flow boundaries. We find that the oil displacement efficiency during dissolution is significantly lower than pre-dissolution levels and is dependent on the wormhole pattern, with dominant wormholes providing a high-permeability and high-velocity flow path for trapped oil movement. Therefore, unlike the injectivity losses that originate from salt precipitation during direct CO2 injection, CWI in depleted carbonate oil reservoirs enhances the injectivity of injection wells allowing for an energy efficient CO2 storage.

Effect of brine type and pH on the interfacial tension behavior of carbonated brine/crude oil

Although carbon dioxide (CO2) injection is an efficient tool to enhance the oil recovery, deposition of asphaltenes, extensive gas consumption, rapid breakthrough of CO2, etc. faced it with serious challenges. As a solution for these disadvantages, the injection of dissolved CO2 in water instead of direct CO2 injection is proposed during the past decade. Respect to this fact, in the current investigation, the dynamic interfacial tension (IFT) values of carbonated brines/acidic crude oil are measured to examine synergetic or antagonistic effect of CO2 and aqueous solution consisted of sulfate anions i.e. 15000 ppm of MgSO4 and Na2SO4 in a wide range of temperatures (30–80 °C) and pressures (500–4000 psi). The sulfate anion based salts are considered in the current investigation wince it has been well established that sulfate anion can introduce more profound effects on the dynamic IFT variation. Considering the obtained results and comparing them with the previously published studies, one can conclude that the variation of IFT of crude oil/carbonated brine as a function of temperature and pressure is completely different compared to IFT of crude oil/brine due to lower pH resulted regarding the dissolution of CO2 in aqueous phase, dominant effect of CO2 at higher pressures and more diffusivity of CO2 at higher temperatures.

Exploring sample size limits of AMS gas Ion Source 14C analysis at Cologneams

ABSTRACTIncreasing demands for small-scale radiocarbon (14C) analyses required the installation of a “SO-110 B” type ion source (HVE Europa B.V.) at our 6 MV Tandetron AMS (HVE) dedicated for the direct injection of CO2 using either the gas injection system (GIS) from Ionplus AG or a EuroVector EA 3000 elemental analyzer (EA). We tested both systems with multiple series of 14C-free and modern standards (2.5–50 µg C) combusted in quartz ampoules or EA containers and were able to quantify exogenous C introduced. In EA-GIS-AMS analysis exogenous C is mainly derived from the EA sample containers. Blank values for 50 µg C combusted in solvent-cleaned tin (Sn) vessels were 0.0127 ± 0.0012 F14C (boats) and 0.0090 ± 0.0010 F14C (capsules), while they were much higher for thermally cleaned silver (Ag) capsules. The processing of gas samples for GIS-AMS yields similar blank values corresponding to 0.30 ± 0.08 µg exogenous C with 0.93 ± 0.23 F14C consisting of 0.28 µg C modern and 0.02 µg C fossil C. The combustion of larger amounts of blank material (1 mg C) in a single quartz tube split into aliquots gives lower blanks (0.0064 ± 0.0008 F14C; 50 µg C). Thus, 14C analysis of small, gaseous samples is now possible at CologneAMS.

Revisiting ocean carbon sequestration by direct injection: a global carbon budget perspective

Abstract. In this study we look beyond the previously studied effects of oceanic CO2 injections on atmospheric and oceanic reservoirs and also account for carbon cycle and climate feedbacks between the atmosphere and the terrestrial biosphere. Considering these additional feedbacks is important since backfluxes from the terrestrial biosphere to the atmosphere in response to reducing atmospheric CO2 can further offset the targeted reduction. To quantify these dynamics we use an Earth system model of intermediate complexity to simulate direct injection of CO2 into the deep ocean as a means of emissions mitigation during a high CO2 emission scenario. In three sets of experiments with different injection depths, we simulate a 100-year injection period of a total of 70 GtC and follow global carbon cycle dynamics over another 900 years. In additional parameter perturbation runs, we varied the default terrestrial photosynthesis CO2 fertilization parameterization by ±50 % in order to test the sensitivity of this uncertain carbon cycle feedback to the targeted atmospheric carbon reduction through direct CO2 injections. Simulated seawater chemistry changes and marine carbon storage effectiveness are similar to previous studies. As expected, by the end of the injection period avoided emissions fall short of the targeted 70 GtC by 16–30 % as a result of carbon cycle feedbacks and backfluxes in both land and ocean reservoirs. The target emissions reduction in the parameter perturbation simulations is about 0.2 and 2 % more at the end of the injection period and about 9 % less to 1 % more at the end of the simulations when compared to the unperturbed injection runs. An unexpected feature is the effect of the model's internal variability of deep-water formation in the Southern Ocean, which, in some model runs, causes additional oceanic carbon uptake after injection termination relative to a control run without injection and therefore with slightly different atmospheric CO2 and climate. These results of a model that has very low internal climate variability illustrate that the attribution of carbon fluxes and accounting for injected CO2 may be very challenging in the real climate system with its much larger internal variability.

Hollow Fibers Filtration and Cleaning Processes Under Ultrasound and Gas Bubbling Combination

AbstractFouling is one of the main obstacles to filtration process. In this study, the effects of gas bubbling by carbonated feed, gas bubbling by direct injection of CO2 (GB‐DI‐CO2) and N2 (GB‐DI‐N2) and ultrasound (US) were evaluated on flux enhancement during milk solution ultrafiltration and flux recovery during cleaning process of fouled hollow fibers membrane module. Results showed that the US and gas bubbling (GB) treatments significantly enhanced the performance of both ultrafiltration and cleaning processes, however, the effect of GB‐DI‐CO2 was not considerable. The best results were achieved when the GB‐DI‐N2 treatment was applied with US treatment in filtration and cleaning process, under this treatment, the permeation flux was remarkably enhanced up to 288.57% during ultrafiltration as well as the fouling percentage was reduced to 15.55% after cleaning the fouled membrane. Furthermore, the US was more effective than the GB during cleaning process.Practical ApplicationsFiltration process is faced to flux decline as a result of fouling. The ultrasound at low frequency and liquid–gas two phase flow can affect the concentration polarization and cake layer significantly. The combination of these techniques can be used as an effective methods to handle the fouling and flux decline. Also artificial neural networks model is able to predict the flux permeation of hollow‐fibers filtration under ultrasound and gas bubbling combination as a complex condition practically.

The response of abyssal organisms to low pH conditions during a series of CO2-release experiments simulating deep-sea carbon sequestration

The effects of low-pH, high-pCO2 conditions on deep-sea organisms were examined during four deep-sea CO2 release experiments simulating deep-ocean C sequestration by the direct injection of CO2 into the deep sea. We examined the survival of common deep-sea, benthic organisms (microbes; macrofauna, dominated by Polychaeta, Nematoda, Crustacea, Mollusca; megafauna, Echinodermata, Mollusca, Pisces) exposed to low-pH waters emanating as a dissolution plume from pools of liquid carbon dioxide released on the seabed during four abyssal CO2-release experiments. Microbial abundance in deep-sea sediments was unchanged in one experiment, but increased under environmental hypercapnia during another, where the microbial assemblage may have benefited indirectly from the negative impact of low-pH conditions on other taxa. Lower abyssal metazoans exhibited low survival rates near CO2 pools. No urchins or holothurians survived during 30–42 days of exposure to episodic, but severe environmental hypercapnia during one experiment (E1; pH reduced by as much as ca. 1.4 units). These large pH reductions also caused 75% mortality for the deep-sea amphipod, Haploops lodo, near CO2 pools. Survival under smaller pH reductions (ΔpH<0.4 units) in other experiments (E2, E3, E5) was higher for all taxa, including echinoderms. Gastropods, cephalopods, and fish were more tolerant than most other taxa. The gastropod Retimohnia sp. and octopus Benthoctopus sp. survived exposure to pH reductions that episodically reached −0.3pH units. Ninety percent of abyssal zoarcids (Pachycara bulbiceps) survived exposure to pH changes reaching ca. −0.3pH units during 30–42 day-long experiments.

Regulations on Ship Transport and On-board Direct Injection of CO2 into Sub-seabed Geological Formations

Ship based offshore CCS activities need to comply with international and national regulatory frameworks for carbon dioxide storage in sub-seabed geological formations. The 1996 London Protocol is an example of international framework, while the Marine Pollution Prevention Law covers the London Protocol obligations in Japan. They both set a series of guidelines to assess potential impacts to the surrounding marine environment in case of leakage from geological formations. Although both these guidelines are corresponding, there are some differences in specifications including purity of the CO2 stream and monitoring requirements for the operators.

Cargo Conditions of CO2 in Shuttle Transport by Ship

For shuttle transport of liquid CO2 in ship-based CCS, the cargo conditions were investigated in view of the pressure tank manufacturability, the cost of the tanks and the carrier vessel, the total energy efficiency of the CO2 flow, etc.In a CCS chain, since the critical path might be the injectivity of the well, the unit cargo of a carrier vessel is set to 3000 tonnes, which is equivalent to the Sleipner case, annual injection rate of ca. 1 million tonnes.The physical properties of CO2, specifically the vapor liquid equilibrium properties of CO2, are such that the design of a storage tank for the containment of liquid carbon dioxide is very similar to existing designs for intermediate pressure liquefied petroleum gas (LPG) containment systems. The design methodology for LPG cargo tanks is well understood and is regulated by international standards (specifically the “International Code for the Construction and Equipment of Ships Carrying Liquefied Gases in Bulk”; IGC code) and Classification Societion Societies (such as DNV, BV and LRS) The disign methodology employed in this study, which is for the marine transport of LCO2 is exactly the same as described by the IGC code and subject to Classification Society rules. These design rules are well proven with literally hundreds of LPG carriers operating worldwide in an industry that has an excellent safety record since the advent of LPG bulk marine transport in the early 1960s. The proposed ship design which installs two cargo tanks was as follows:-the volume of the tanks is about 1500m3 and design pressure and temperature are 3.10MPa and munus 10degC, respectively.-The shape of the tanks is a cylindrical bilobe with single cylinder radius of 3.50 m and 26.96m in lengthThe necessary facilities for LCO2 loading from land-based storage tanks are also examined, including CO2 buffer storage tanks, the loading pumps, the loading arms, and so on. The offshore delivery and injection system are investigated and the resultant design proposal was as follows: the temperature of the cargo LCO2 is raised to 5degC by on-board heat exchange system using the ambient seawater.The cost estimate of the proposed system will be also given in the presentation.The study is a part of the Preliminary Feasibility Study on CO2 Carrier for Ship-based CCS and its follow-up study sponsored by Global CCS Institute and conducted by Chiyoda Corporation. The other technical parts of the study are Ship-based offshore CCS featuring CO2 shuttle ships equipped with injection facilities by M Ozaki et al, “Offshore operational availability of onboard direct injection of CO2 into sub-seabed geological formations” by T Miyazaki et al, and “Onboard CO2 injection into subseabed geological formation via picked-up flexible pipe by N. Nakazawa et al.

Offshore Operational Availability of Onboard Direct Injection of CO2 into Sub-seabed Geological Formations

Offshore operational availability was investigated for the proposed handling system consisting of the carrier vessel equipped with dynamic positioning capability, on-board manual operation of picking-up the sea-surface float connected to the upstream end of the flexible riser pipe laid-dawn on sea floor.An offshore site was selected to collect the oceanographic off the southern part of Japan facing to the Pacific Ocean. The response amplitude operator of the proposed CO2 carrier vessel was calculated based on 3-D Singularity Distribution Method. Based on the result of the interview survey with captains of research vessels which showed that for offshore operations a vessel's pitch motion and service deck wetness are dominant factors which define a vessel's operational availability, the RAO of the pitch and relative wave elevation was evaluated.The hull motions and the relative wave elevation in unidirectional irregular waves and in multidirectional irregular waves were calculated by a conventional method based on the seakeeping theory using the RAOs, the wave spectrum and the directional wave spectrum.Under the assumption that the operational availability of the proposed CO2 carrier vessel is constrained by the pitch motion and the service deck wetness, the allowable upper limit values of the significant wave height were calculated by a conventional method based on the sea keeping theorem using the 1/10 maximum expected response value of pitch motion and the relative wave elevation evaluated in the above-mentioned calculation. The threshold value of operation availability was set at the pitch of 3.0 degrees and the relative wave elevation at the freeboard to the service deck, based on the result of the interview survey with captains of research vessels.Finally, the overall operational availability was estimated, on the assumption that the threshold value of operation availability was set at the pitch of 3.0 degrees and the relative wave elevation at the freeboard to the service deck.We concluded that the operational availability of the proposed CO2 carrier vessel reaches a target value of nearly 90% for both full year and four seasons in the case that freeboard of service deck for offshore buoy picking-up operations set greater than 2.3 m as a service platform.

Scoping analysis of brine extraction/re‐injection for enhanced CO2 storage

AbstractBrine extraction from the CO2 injection interval and re‐injection into overlying shallower aquifers have been described as an active management tool at sequestration sites. They improve injectivity and reduce risks, and are a potential cost‐saving measure. In this study, using analytical equations, we show that brine re‐injection from the deep aquifer into a shallower saline aquifer increases CO2 storage capacity relative to direct CO2 injection into the two saline aquifers as a result of the CO2 density change. Using generic models, we compare three different scenarios for CO2 injection: (i) injection of CO2 into the deep aquifer without the re‐injection program, (ii) injection of CO2 into both the shallow and deep aquifers, and (iii) injection of CO2 into the deep aquifer and extraction/re‐injection of the brine into the shallow aquifer. Volumetric calculations at different pressure and temperature conditions provide a simple analytical tool for studying CO2 storage capacity in stacked saline aquifers. Numerical compositional simulations confirm results of the analytical derivations and prior assumptions. Depending on the size and depth of the shallower aquifer, brine re‐injection can increase storage capacity by 30% or more, given a comparison of scenario 3 with scenario 1. However, when scenario 3 is compared with scenario 2, storage gain is generally less than 5%, although potential CO2 leakage risks are reduced. Results of a sensitivity analysis to shallow‐aquifer pore volume and geothermal‐temperature gradient are also presented. In addition, brine re‐injection from geopressured saline aquifers, when compared with that of normally pressured reservoirs, is twice as efficient. © 2012 Society of Chemical Industry and John Wiley &amp; Sons, Ltd

Development of a multi‐scale ocean model by using particle Laplacian method for anisotropic mass transfer

AbstractThe direct injection of CO2 into the deep ocean is one of the feasible ways for the mitigation of the global warming, although there is a concern about its environmental impact near the injection point. To minimize its biological impact, it is necessary to make CO2 disperse as quickly as possible, and it is said that injection with a pipe towed by a moving ship is effective for this purpose. Because the injection ship moves over a spatial scale of O(102km), a mesoscale model is necessary to analyse the dispersion of CO2. At the same time, since it is important to investigate high CO2 concentration near the injection point, a small‐scale model is also required. Therefore, in this study, a numerical model was developed to analyse CO2 dispersion in the deep ocean by using a fixed mesoscale and a moving small‐scale grid systems, the latter of which is nested and moves in the former along the trajectory of the moving ship. To overcome the artificial diffusion of mass concentration at the interface of the two different grid systems and to keep its spatial accuracy almost the same as that in the small‐scale, a particle Laplacian method was adopted and newly modified for anisotropic diffusion in the ocean. Copyright © 2010 John Wiley &amp; Sons, Ltd.

Experimental Study of Pore-Scale Mechanisms of Carbonated Water Injection

Carbon dioxide (CO2) injection is a well-established method for increasing recovery from oil reservoirs. However, poor sweep efficiency has been reported in many CO2 injection projects due to the high mobility contrast between CO2 and oil and water. Various injection strategies including gravity stable, WAG and SWAG have been suggested and, to some extent, applied in the field to alleviate this problem. An alternative injection strategy is carbonated water injection (CWI). In CWI, CO2 is delivered to a much larger part of the reservoir compared to direct CO2 injection due to a much improved sweep efficiency. In CWI, CO2 is used efficiently and much less CO2 is required compared to conventional CO2 flooding, and hence the process is particularly attractive for reservoirs with limited access to large quantities of CO2 (offshore reservoirs or reservoirs far away from inexpensive natural CO2 resources). This article describes the results of a pore-scale study of the process of CWI by performing high-pressure visualisation flow experiments. The experimental results show that CWI, compared to unadulterated (conventional) water injection, improves oil recovery as both a secondary (before water flooding) and a tertiary (after water flooding) recovery method. The mechanisms of oil recovery by CWI include oil swelling, coalescence of the isolated oil ganglia and flow diversion due to flow restriction in some of the pores as a result of oil swelling and the resultant fluid redistribution. In this article the potential benefit of a subsequent depressurisation period on oil recovery after the CWI period is also investigated.

Physiological effects on fishes in a high‐CO2 world

Fish are important members of both freshwater and marine ecosystems and constitute a major protein source in many countries. Thus potential reduction of fish resources by high‐CO2 conditions due to the diffusion of atmospheric CO2 into the surface waters or direct CO2 injection into the deep sea can be considered as another potential threat to the future world population. Fish, and other water‐breathing animals, are more susceptible to a rise in environmental CO2 than terrestrial animals because the difference in CO2 partial pressure (PCO2) of the body fluid of water‐breathing animals and ambient medium is much smaller (only a few torr (1 torr = 0.1333 kPa = 1316 μatm)) than in terrestrial animals (typically 30–40 torr). A survey of the literature revealed that hypercapnia acutely affects vital physiological functions such as respiration, circulation, and metabolism, and changes in these functions are likely to reduce growth rate and population size through reproduction failure and change the distribution pattern due to avoidance of high‐CO2 waters or reduced swimming activities. This paper reviews the acute and chronic effects of CO2 on fish physiology and tries to clarify necessary areas of future research.

Numerical Simulation of Biological Impact Caused by Direct Injection of Carbon Dioxide in the Ocean

The direct injection of CO2 in the deep ocean is a promising way to mitigate global warming. One of the uncertainties in this method, however, is its impact on marine organisms in the near field before CO2 is diluted widely in the ocean. Since field experiments cost enormously, computational simulations are expected to show detailed information on the dilution process near injection points and its impact on marine organisms. In general, the LC50 concept is widely applied for testing the acute impact of a toxic agent on organisms. As a biological impact model we therefore consider mortality, which reflects recent laboratory experiments on zooplankton at various concentrations of CO2. Here we regard the sigmoid-transformed mortality as a linear function of time in the logarithmic scale, and not just of the concentration of CO2 in the logarithmic scale. This model was installed in a computational simulation code for the reconstruction of small-scale ocean turbulence. The results suggest that the biological effect is not significant when the ship speed is 4 knots and CO2 is injected at 0.1 ton/sec in the form of a spray through 100 nozzles provided vertically on a pipe at 10 m intervals. It is therefore considered that the moving-ship method is effective for direct CO2 injection.