Experimental Study of Chemical Enhanced Oil Recovery (EOR) Methods in Sandstone Core Samples: Effect of Salinity and Divalent Cations.

Chemical Enhanced Oil Recovery (CEOR) is defined as the injection of chemical slugs into the reservoir with the object to increase the oil recovery factor (RF). Optimal combinations of chemicals, alkali (A), surfactant (S) and polymer (P) for an ASP CEOR have shown being an effective recovery method. However, due to high salinity and hardness (defined as the concentration of divalent cations Ca2+ and Mg2+) existing in the brine of some reservoirs, numerous and complicated physicochemical interactions such as adsorption, retention, and formation of emulsions are triggered. This research project frames problems associated with the design of ASP CEOR for sandstone reservoirs under high salinity and hard brine. The fluid-fluid and fluid-rock interactions for the brine/oil, surfactant-brine/oil, alkali-surfactant-brine-oil, surfactant-polymer/oil, and alkali-surfactant-polymer/oil systems were evaluated at laboratory scale using Bentheimer sandstone core samples. Results from the study were aiming to understand the various mechanisms that favour the oil displacement efficiency of the ASP CEOR processes in sandstone. A sample of crude oil from the North Sea was used in this research and synthetic brines were prepared to reproduce the original brine composition. The first part of the research consisted of the study of the effect of brine salinity and hardness on the fluid-fluid and fluid-rock interactions for the brine/oil system. Further studies were required on the microemulsion formation using different surfactant formulations with alcohol alkoxy -sulfate (APS), alcohol ethoxy sulfate (AES), and internal olefin sulfonate (IOS) surfactants for the system surfactant-brine/oil. The effect of sodium hydroxide and sodium metaborate on the microemulsion formation for alkali-surfactant-brine-oil system and interactions with polyacrylamide based polymers in surfactant-polymer/oil and alkali-surfactant-polymer/oil systems were also investigated. Polymer viscosity exhibited shear thinning and Newtonian behaviour as a function of shear rate. The rheological behaviour was also associated with salinity, divalent cations, and the polymer size and structure in aqueous solution. These interactions were modelled adjusting experimental results to correlations proposed in the literature. A comparative study of the displacement efficiency of waterflooding, P, AS, SP and ASP CEOR methods under a salinity gradient was completed to understand the different chemicals interactions. It was found that the brine salinity and hardness affected the brine surface tension (ST) and the brine/oil interfacial tension (IFT). The brine ST and brine/oil IFT showed three well defined regions at different salinities. At low salinity (< 5,000 ppm TDS), the surface tension decreases with the salinity; between 5,000 ppm and 30,000 ppm TDS the ST and IFT slightly increase with salinity. In a third region the ST and IFT do not change with salinity exhibiting a plateau behaviour. Results from core-flooding tests showed that by creating a multicomponent salinity gradient that promotes the cationic exchange between divalent (Ca2+ and Mg2+) and monovalent (Na+) ions, an additional 5% of oil recovery was obtained. Alcohol alkoxy sulfate C13-14—7APS surfactant promotes microemulsion formation and tolerate divalent cations Ca2+ and Mg2+ at salinity higher than 28,000 ppm and lower than 48,000 ppm. Alcohol ethoxy sulfate C06-10-AES as co-surfactant moves the range of salinity for micoremulsion formation towards higher salinity (34,000 to 52,000 ppm) and enhance the stability of C13-14—7APS surfactant. While salinity restricts the use of surfactant alcohol ethoxylated (AEO) due to instability and precipitation formation, the combination of this surfactant with surfactant alcohol alkoxy sulfate (C13-14—7APS) increases its solubility and alsopromotes the microemulsion formation at salinity from 20,000 to 38,000 ppm. Surfactants reduce the surfactant-brine/oil IFT to ultra-low values and increase the oil displacement efficiency by 15% compared with waterflooding. Surfactant absorption increases with its concentration and with salinity; this effect is increased for brine with divalent ions. Co-surfactant alcohol ethoxy sulfate C06-10-AES reduces the adsorption of surfactant alcohol alkoxy sulfate C13-14—7APS. Divalent cations Ca2+ and Mg2+ react with alkali to form insoluble divalent hydroxides (Ca(OH)2 and Mg(OH)2); this effect limits the application of alkali for brines with divalent cations. However, the use of ethylene-diamine-tetracetic acid (EDTA) at controlled pH ≤ 9 prevents the precipitation of hydroxides by forming a complex between EDTA and divalent cations. The concentration of alkali should be controlled to reach a pH ≤ 9 in the formulation of alkali-surfactant slugs to prevent that a displacement reaction between the alkali in excess and divalent cations complexed with EDTA initiates. However, at pH ≤ 9 the formation of natural naphthenic surfactant from the oil is not favourable. The use of alkali-surfactant-brine increases the oil displacement efficiency by 12% compared with the use of surfactant. High salinity also affects the interactions between polymers molecules in aqueous solution and reduces the viscosity of polymers; the effect is more marked by the presence of divalent cations. Polymers reduce the mobility of the displacing fluid and mobility ratio by permeability reduction and viscosity augmentation. The effect is reflected in an increment of the displacement efficiency ED. Polymer CEOR increases the recovery factor by 25% for PHPA-6 and 16% for PHPAM-3. The addition of surfactants for SP CEOR adds 19% oil recovery in comparison with water flooding, whereas ASP CEOR adds 31% for blend of surfactant with sodium metaborate, and 33% for the blend of surfactant with sodium hydroxide/EDTA. The polymer HMPAM-3 is more effective in increasing the oil displacement efficiency than PHPA-6 polymer in formulations for SP and ASP CEOR. The advantages of the synergy of ASP CEOR were demonstrated on the displacement efficiency with an increase up to 33% for ASP using NaOH and EDTA. Stoichiometry calculations are required to complete desired equilibrium reactions involved in the process and avoid hydroxide precipitation. While the mechanism of polymer flooding is associated with mobility ratio, it was demonstrated that the predominant effect of IFT on the displacement efficiency of SP and ASP systems for CEOR, which indicates the mechanism is dominated by the changes in the capillary number Nc. It was found that the stability of chemicals is affected in a larger extent by the concentration of divalent ions Ca2+ and Mg2+ than by the total salinity. The surfactant stability in solution determines the optimal conditions for the microemulsion formation. Therefore, the selection of the surfactant formulation and controlling its stability are the main steps on the design of a successful ASP CEOR process. This research presents a detailed study of the fluid-fluid and fluid-rock interactions that affect the design of SP and ASP CEOR at a microscopic scale. The results from the study provide a systematic analysis of standalone methods and the synergy of combined methods on a fluid-fluid–rock system. Henceforward, the range of applicability and conditions of CEOR at laboratory scale for oilfield applications can be established

Multi-layer study of wave propagation in sunspots

We analyze the propagation of waves in sunspots from the photosphere to the chromosphere using time series of co-spatial Ca II H intensity spectra (including its line blends) and polarimetric spectra of Si I 10827 and the He I 10830 multiplet. From the Doppler shifts of these lines we retrieve the variation of the velocity along the line-of-sight at several heights. Phase spectra are used to obtain the relation between the oscillatory signals. Our analysis reveals standing waves at frequencies lower than 4 mHz and a continuous propagation of waves at higher frequencies, which steepen into shocks in the chromosphere when approaching the formation height of the Ca II H core. The observed non-linearities are weaker in Ca II H than in He I lines. Our analysis suggests that the Ca II H core forms at a lower height than the He I 10830 line: a time delay of about 20 s is measured between the Doppler signal detected at both wavelengths. We fit a model of linear slow magnetoacoustic wave propagation in a stratified atmosphere with radiative losses according to Newton's cooling law to the phase spectra and derive the difference in the formation height of the spectral lines. We show that the linear model describes well the wave propagation up to the formation height of Ca II H, where non-linearities start to become very important.Comment: Accepted by The Astrophysical Journa

Wave propagation and shock formation in different magnetic structures

Velocity oscillations "measured" simultaneously at the photosphere and the chromosphere -from time series of spectropolarimetric data in the 10830 A region- of different solar magnetic features allow us to study the properties of wave propagation as a function of the magnetic flux of the structure (i.e. two different-sized sunspots, a tiny pore and a facular region). While photospheric oscillations have similar characteristics everywhere, oscillations measured at chromospheric heights show different amplitudes, frequencies and stages of shock development depending on the observed magnetic feature. The analysis of the power and the phase spectra, together with simple theoretical modeling, lead to a series of results concerning wave propagation within the range of heights of this study. We find that, while the atmospheric cut-off frequency and the propagation properties of the different oscillating modes depend on the magnetic feature, in all the cases the power that reaches the high chromosphere above the atmospheric cut-off comes directly from the photosphere by means of linear vertical wave propagation rather than from non-linear interaction of modes.Comment: Accepted for publication in The Astrophysical Journal. 29 pages, 9 figures, 12pt, preprin

Barriers to the development of palliative care in Western Europe

The Eurobarometer Survey of the &lt;i&gt;EAPC Task Force on the Development of Palliative Care in Europe&lt;/i&gt; is part of a programme of work to produce comprehensive information on the provision of palliative care across Europe. Aim: To identify barriers to the development of palliative care in Western Europe. Method: A qualitative survey was undertaken amongst boards of national associations, eliciting opinions on opportunities for, and barriers to, palliative care development. By July 2006, 44/52 (85%) European countries had responded to the survey; we report here on the results from 22/25 (88%) countries in Western Europe. Analysis: Data from the Eurobarometer survey were analysed thematically by geographical region and by the degree of development of palliative care in each country. Results: From the data contained within the Eurobarometer, we identified six significant barriers to the development of palliative care in Western Europe: (i) Lack of palliative care education and training programmes (ii) Lack of awareness and recognition of palliative care (iii) Limited availability of/knowledge about opioid analgesics (iv) Limited funding (v) Lack of coordination amongst services (vi) Uneven palliative care coverage. Conclusion: Findings from the EAPC Eurobarometer survey suggest that barriers to the development of palliative care in Western Europe may differ substantially from each other in both their scope and context and that some may be considered to be of greater significance than others. A number of common barriers to the development of the discipline do exist and much work still remains to be done in the identified areas. This paper provides a road map of which barriers need to be addressed

Writing and Being Human

Truth is as moral as political in nature. This relation must be asserted more than ever, especially when seen against the background of today’s social media phenomenon, where people express their views about anything and anyone at an unprecedented speed and reach. Within the context of the academic world, the search for truth serves as the moral foundation of authorship and guides the practice of academic freedom. Teaching by writing affects the formation of fellow human beings for good or ill. Thus, every author must write only what is true, in view of communicating factual information, and not “fake news.” Before a deluge of information on social media, academics must always ask the critical question: Is this true

Network Connectivity in Epilepsy: Resting State fMRI and EEG-fMRI Contributions.

There is a growing body of evidence pointing toward large-scale networks underlying the core phenomena in epilepsy, from seizure generation to cognitive dysfunction or response to treatment. The investigation of networks in epilepsy has become a key concept to unlock a deeper understanding of the disease. Functional imaging can provide valuable information to characterize network dysfunction; in particular resting state fMRI (RS-fMRI), which is increasingly being applied to study brain networks in a number of diseases. In patients with epilepsy, network connectivity derived from RS-fMRI has found connectivity abnormalities in a number of networks; these include the epileptogenic, cognitive and sensory processing networks. However, in majority of these studies, the effect of epileptic transients in the connectivity of networks has been neglected. EEG-fMRI has frequently shown networks related to epileptic transients that in many cases are concordant with the abnormalities shown in RS studies. This points toward a relevant role of epileptic transients in the network abnormalities detected in RS-fMRI studies. In this review, we summarize the network abnormalities reported by these two techniques side by side, provide evidence of their overlapping findings, and discuss their significance in the context of the methodology of each technique. A number of clinically relevant factors that have been associated with connectivity changes are in turn associated with changes in the frequency of epileptic transients. These factors include different aspects of epilepsy ranging from treatment effects, cognitive processes, or transition between different alertness states (i.e., awake-sleep transition). For RS-fMRI to become a more effective tool to investigate clinically relevant aspects of epilepsy it is necessary to understand connectivity changes associated with epileptic transients, those associated with other clinically relevant factors and the interaction between them, which represents a gap in the current literature. We propose a framework for the investigation of network connectivity in patients with epilepsy that can integrate epileptic processes that occur across different time scales such as epileptic transients and disease duration and the implications of this approach are discussed

The Hanle and Zeeman Effects in Solar Spicules: A Novel Diagnostic Window on Chromospheric Magnetism

An attractive diagnostic tool for investigating the magnetism of the solar chromosphere is the observation and theoretical modeling of the Hanle and Zeeman effects in spicules, as shown in this letter for the first time. Here we report on spectropolarimetric observations of solar chromospheric spicules in the He I 10830 \AA multiplet and on their theoretical modeling accounting for radiative transfer effects. We find that the magnetic field in the observed (quiet Sun) spicular material at a height of about 2000 km above the visible solar surface has a strength of the order of 10 G and is inclined by approximately $35^{\circ}$ with respect to the local vertical direction. Our empirical finding based on full Stokes-vector spectropolarimetry should be taken into account in future magnetohydrodynamical simulations of spicules.Comment: 12 pages and 2 figure