Measurement and Prediction of the Phase Behaviour of Carbon Dioxide, Alkane and Water Mixtures at Reservoir Conditions

Knowledge of the phase behaviour of mixtures of oil with carbon dioxide and water is essential for reservoir engineering, especially in the processes of enhanced oil recovery and geological storage of carbon dioxide. Both processes require versatile tools able to describe the global phase behaviour at reservoir conditions, which may include the critical region of the mixtures involved. For a comprehensive understanding however the study of simpler systems needs to be completed. In this work two ternary systems have been studied as models for (oil + carbon dioxide + water) mixtures. The first one consists of (n-decane + carbon dioxide + water); the second is a mixture of (propane + carbon dioxide + water). To measure phase equilibria at representative reservoir conditions, a new analytical apparatus has been designed with maximum operating temperature and pressure of 423K and 45MPa, respectively. The equipment relies on recirculation of two coexisting phases using a two-channel magnetically-operated micro-pump designed during this work, sampling and on-line compositional analysis by gas chromatography. The apparatus has been validated by comparison with published isothermal vapour-liquid equilibrium data for the binary system (n-decane + carbon dioxide). New experimental data have been measured for the systems (ndecane + carbon dioxide + water) and (propane + carbon dioxide + water) under conditions of three-phase equilibria. Data for the three coexisting phases in the mixture of (n-decane + carbon dioxide + water) have been obtained on five isotherms at temperatures from (323 to 413)K and at pressures up to the point at which two of the phases become critical. Similarly, for the mixture (propane + carbon dioxide + water), data for the three coexisting phases on four isotherms at temperatures from (311 to 353)K and pressures up to the same point are reported. The experimental work has been complemented here with a theoretical effort in which models for these molecules are developed within the framework of the statistical associating fluid theory for potentials of variable range (SAFT-VR). The phase behaviour of the three binary subsystems has been calculated using this theory and, where applicable, a modification of the Hudson and McCoubrey combining rules has been used to treat the systems predictively. The experimental data obtained for the ternary mixture are compared to the predictions of the theory. Furthermore, a detailed analysis of the ternary mixture is carried out based on comparison with available data for the constituent binary subsystems. In this way, the observed effects on the solubility when the third component is added are analysed. An accurate prediction of phase behaviour at conditions far and close to criticality cannot be accomplished by mean-field based theories, such as the SAFT-VR equation of state, that do not incorporate long-range density fluctuations. A treatment based on renormalisation-group (RG) theory as developed by White and co-workers has proven very successful in improving the predictions of the critical region with different equations of state. The basis of the method is an iterative procedure to account for contributions to the free energy of density fluctuations of increasing wavelengths. The RG method has been combined with a number of versions of the statistical associating fluid theory (SAFT), by implementing White’s earliest ideas with the improvements of Prausnitz and co-workers. Typically, this treatment involves two adjustable parameters: a cut-off wavelength L for density fluctuations and an average gradient of the wavelet function Φ. In this work, the SAFT-VR equation of state has been extended with a similar crossover treatment which however follows closer the most recent improvements introduced by White. The interpretation of White’s latter developments allows one to establish a straightforward method which enables Φ to be evaluated; only the cut-off wavelength L needs then be adjusted. The approach used here begins with an initial free energy incorporating only contributions from short-wavelength fluctuations, which are treated locally. The contribution from long-wavelength fluctuations is incorporated through an iterative procedure based on attractive interactions which incorporate the structure of the fluid following the ideas of perturbation theories and using a mapping that allows integration of the radial distribution function. Good agreement close and far from the critical region is obtained using a unique fitted parameter L that can be easily related to the range of the potential. In this way the thermodynamic properties of a square-well (SW) fluid are given by the same number of independent intermolecular model parameters as in the classical equation. Far from the critical region the approach provides the correct limiting behaviour reducing to the classical equation (SAFT-VR). In the critical region the β critical exponent is calculated and is found to take values close to the universal value. In SAFT-VR the free energy of an associating chain fluid is obtained following the thermodynamic perturbation theory of Wertheim from knowledge of the free energy and radial distribution function of a reference monomer fluid. By determining L for SW fluids of varying well width a unique equation of state is obtained for chain and associating systems without further adjustment of critical parameters. Computer simulation data of the phase behaviour of chain and associating SW fluids are used to test the accuracy of the new equation. Furthermore the treatment is here extended to model pure fluids and results are presented for a number of alkanes, carbon dioxide and water

Digitalization in Thermodynamics

Digitalization is about data and how they are used. This has always been a key topic in applied thermodynamics. In the present work, the influence of the current wave of digitalization on thermodynamics is analyzed. Thermodynamic modeling and simulation is changing as large amounts of data of different nature and quality become easily available. The power and complexity of thermodynamic models and simulation techniques is rapidly increasing, and new routes become viable to link them to the data. Machine learning opens new perspectives, when it is suitably combined with classical thermodynamic theory. Illustrated by examples, different aspects of digitalization in thermodynamics are discussed: strengths and weaknesses as well as opportunities and threats

Measurement & Prediction of Phase Behaviour of Carbon Dioxide Mixtures

Acquiring a comprehensive understanding of the behaviour of carbon dioxide under reservoir conditions is essential for optimizing its usage in enhanced oil recovery (EOR) and for developing sequestration schemes. In order to obtain this understanding, it is necessary to study the physical properties and phase behaviour of mixtures of carbon dioxide with hydrocarbons and brines under conditions of high pressure. In this work we are addressing both the experimental and the theoretical aspects of this problem. A new apparatus, based on the static-analytical method, has been developed to measure phase equilibrium. The equipment comprises a high-pressure cell with sapphire windows for visual observation and phase sampling, with on-line gas chromatography analysis, for measuring the phase compositions. The experimental work is complemented with a theoretical modelling for these mixtures, using the statistical association fluid theory for potentials of variable range (SAFT-VR). As an example of the predictive capabilities of the equation, the fluid phase behaviour of the mixture (carbon dioxide + n-decane) is presented

Anxiety and Attentional Processes: The Role of Resting Heart Rate Variability

Individuals with high anxiety preferentially focus attention on emotional information. The autonomic nervous system (ANS) plays an important role in modulating both anxiety and attentional processes. Despite many studies having evaluated attentional bias in anxious people, few of them have investigated the change blindness phenomenon associated with the attentional response toward salient stimuli, considering the role of the ANS. This study aimed to examine the role of heart rate variability (HRV) in trait anxiety and top-down and bottom-up attentional processes toward emotional stimuli. Seventy-five healthy university students were divided into high (N = 39) and low (N = 36) trait anxiety groups and completed a change detection flicker task with neutral, positive, and negative stimuli. The results evidenced a different attentional pattern between people with high and low anxiety considering both the two attentional processes and the valence of the stimuli. Specifically, individuals with high anxiety showed a bias in elaborating emotional stimuli related to their salience (i.e., negative stimuli were faster elaborated than neutral and positive stimuli when top-down attentional mechanisms were involved, while slower performances were highlighted considering bottom-up attentional mechanisms in response to emotional stimuli compared to neutral stimuli). Moreover, an association between HRV, trait anxiety levels, and change blindness phenomenon was confirmed. These results underline the role of HRV as a possible predictor of the alteration of attentional mechanism in anxiety

Girls4STEM: Gender Diversity in STEM for a Sustainable Future

Science, Technology, Engineering, and Mathematics (STEM) are key disciplines towards tackling the challenges related to the Sustainable Development Goals. However, evidence shows that women are enrolling in these disciplines in a smaller percentage than men, especially in Engineering related fields. As stated by the United Nations Women section, increasing the number of women studying and working in STEM fields is fundamental towards achieving better solutions to the global challenges, since the potential for innovation is larger. In this paper, we present the Girls4STEM project, which started in 2019 at the Escola Tècnica Superior d’Enginyeria de la Universitat de València, Spain. This project works towards breaking the stereotypes linked to STEM fields, addressing both boys and girls aged from 6 to 18, but especially trying to open the range of career options for young girls through interaction with female STEM experts. The goal is to spark girls’ interest in STEM disciplines from childhood, so that they become more self-confident in these areas. To achieve this goal, the project is built over three main actions: the Girls4STEM Family Talks, where students, families, and teachers participate; the Girls4STEM Professional Talks, where the target is a general audience; and the Initial Training Seminars for teachers. Short-term results are here presented, showing that aspects related to self-perception and perception from others (family, teachers) play a significant role. Moreover, these results also indicate that there may not be a general understanding of which disciplines are included in STEM

Girls4STEM: gender diversity in STEM for a sustainable future

Science, Technology, Engineering, and Mathematics (STEM) are key disciplines towards tackling the challenges related to the Sustainable Development Goals. However, evidence shows that women are enrolling in these disciplines in a smaller percentage than men, especially in Engineering related fields. As stated by the United Nations Women section, increasing the number of women studying and working in STEM fields is fundamental towards achieving better solutions to the global challenges, since the potential for innovation is larger. In this paper, we present the Girls4STEM project, which started in 2019 at the Escola Tècnica Superior d'Enginyeria de la Universitat de València, Spain. This project works towards breaking the stereotypes linked to STEM fields, addressing both boys and girls aged from 6 to 18, but especially trying to open the range of career options for young girls through interaction with female STEM experts. The goal is to spark girls' interest in STEM disciplines from childhood, so that they become more self-confident in these areas. To achieve this goal, the project is built over three main actions: the Girls4STEM Family Talks, where students, families, and teachers participate; the Girls4STEM Professional Talks, where the target is a general audience; and the Initial Training Seminars for teachers. Short-term results are here presented, showing that aspects related to self-perception and perception from others (family, teachers) play a significant role. Moreover, these results also indicate that there may not be a general understanding of which disciplines are included in STEM