Enhancing vitamin C stability through liposomal encapsulation with optimised pressure and cycle conditions

Analysis of a recompression supercritical carbon dioxide power cycle with an integrated turbine design/optimization algorithm

Understanding the mechanisms of leakage-pathway formation are crucial for proper assessment, remediation, and in the end, prevention of leaking wells due to severe modern-day well stresses such as multistage hydraulic fracturing operations. Aiming to improve the understanding of the drivers behind fluid leakage from wells subject to modern-day well stresses, an experimental study of the cement sheath integrity under downhole stress conditions was conducted using a custom-designed and fabricated physical wellbore simulator. The physical wellbore simulator was designed and constructed to be capable of measuring the permeability (up to nanodarcy level) of the cemented annulus between two casings under cyclic temperature and pressure conditions (up to 43 MPa and 120°C). Permeability (nitrogen) of the casing-cement-casing system was measured under i-) non-cyclic temperature and pressure; ii-) non-cyclic temperature and cyclic pressure; iii-) cyclic temperature and non-cyclic pressure conditions. Potential leakage pathways were visually inspected after each experiment. The rough shear bonding strength between the inner casing and the cement sheath was also measured. Three factors were identified as having the most significant impacts on the permeability of the cemented annulus between two casings: i). Cement and/or casing shrinkage/expansion caused by the temperature change, ii). Casing shrinkage/expansion caused by the inner casing pressure change and, iii). Test duration time (time after curing and before each permeability measurement). The final permeability of the cemented annulus was controlled by the combined effects of these three factors. Overall, cement was extremely resilient to stresses, and slight increases in permeability were only observed after subjecting the cement sheath to significant stress. Once the debonding occurred at the cement/casing interface due to the initial change in pressure and/or temperature, applying cyclic pressure load did not significantly alter the permeability of the cemented wellbore section. The shear bonding strengths were on the high side, and the final permeabilities were below or around the critical permeability of 0.1 mD (Ozyurtkan et al. 2013). Through the development of the physical wellbore simulator the factors affecting the integrity of the cement-casing interfaces under representative real-world wellbore conditions of variable temperature and pressure conditions have been investigated. The improved understanding of the factors contributing to leakage-pathway formation are now being used to implement more reliable barrier technologies for effective mitigation of fugitive emissions.

Integrity of wellbores and near wellbore processes are crucial issues in geological carbon storage (GCS) projects as they both define the confinement and injectivity of CO2. For the proper confinement of CO2, any flow of CO2 along the wellbore trajectory must be prevented using engineered barriers. The effect of cyclic stimuli on wellbore integrity, especially in the context of GCS projects, has been given less attention. In this study, the effect of pressure- and temperature-cycling on two types of wellbore composites (i.e., casing-cement and cement-caprock) have been investigated experimentally in small- and large-scale laboratory setups. The experiments have been carried out by measuring the effective permeability of the composites under pressure and thermal cyclic conditions. Furthermore, the permeability of individual samples (API class G and HMR+ cement and caprock) was measured and compared to the permeability of the composites. The results indicate that the permeability of API class G cement when exposed to CO2 is in the order of 10−20 m2 (10−5 mD) as a result of the chemical reaction between the cement and CO2. In addition, the tightness of the composite cement–rock has been confirmed, while the permeability of the composite casing–cement falls within the acceptable range for tight cement and the CO2 flow was identified to occur through or close to the interface casing–cement. Results from thermal cycling within the range −9 to 14 °C revealed no significant effect on the integrity of the bond casing–cement. In contrast, pressure cycling experiments showed that the effective pressure has a larger influence on the permeability. The potential creation of micro-cracks under pressure variations may require some time for complete closing. In conclusion, the pressure and temperature cycling from this study did not violate the integrity of the casing–cement composite sample as the permeability remained low and within the acceptable range for wellbore cement.

With the emerging focus of zonal isolation for underground storage projects, and the potential uncertainty of applicability of current barrier materials when exposed to a corrosive environment alongside added mechanical stressors a long-term exposure study was conducted. A base design known as a fit-for-purpose design for corrosive exposure was selected, with two additional permutations that would enhance the resistance towards the wellbore environmental risks. The study entailed a six-month long test schedule with intermittent sampling at one-three- and six-month intervals of the exposed plugs. Mechanical properties testing and complementary micro-CT scans were completed on the plugs in two separate laboratories and are detailed in this paper. Furthermore, the impact of constant pressure and temperature conditions in comparison to cyclic conditions was investigated. Aided by software simulations, a comparative discussion of the three designs was done to select the optimum design for a specific well scenario in the North Sea. Even though all considered cement systems showed an outstanding resistance towards CO2-saturated brines, minor differences based on the selection of additives could be observed. In addition, the choice of either static or cyclic test conditions also contributed to the degree of reaction during exposure. The realistic rather slow changes of the conditions given by the operational sequence for the well do not impose any impactful stress on the samples. Whereas the dominant factor appears to be the average partial pressure of CO2.

Comparative analysis on high-efficiency energy conversion system with different working mediums matched with small lead-cooled fast reactor

Experimental Investigation on Tensile Strength of Jurassic Red-Bed Sandstone under the Conditions of Water Pressures and Wet-Dry Cycles

Metamorphic Reaction Kinetics

In coalbed methane (CBM) exploitation, liquid nitrogen (LN2) fracturing has attracted much attention as a promising and effective means to enhance coal seam permeability. Considering the bituminous coal in the Xutuan coal mine of Anhui Province, China, the permeability characteristics of coal samples under different pressure and stress conditions, and a single LN2 treatment and cyclic fracturing conditions were studied. Additionally, an evaluation of the macroscopic cracking behavior of coal was carried out. LN2 treatment can be very effective in promoting the generation of macroscopic fissures in the coal, and the degree of damage increases with the number of fracturing cycles. The results of a single LN2 treatment showed that under a constant confining pressure, the permeability increased exponentially with the increase in gas pressure. The cyclic LN2 treatment showed that permeability first decreased and then increased with increasing gas pressure, which is consistent with the quadratic function distribution. The permeability of the coal sample increases exponentially with the number of cycles, but the growth rate gradually slows down. For the same absolute fracturing time, cyclic fracturing had a better fracturing effect than a single cycle, and the ratio of the permeability increment is 126.3%‐213.8%. The research results provide some guidance for the development of the LN2 freeze fracturing technology.

Chemical looping represents a promising technology with various applications ranging from clean power production to alternative syngas production. In this work, two oxygen carriers with different Ni loadings (4.3% wt. and 12% wt.) and similar Fe loadings (9.9% wt. and 8.5% wt.) are synthesized through a co-precipitation/impregnation route and tested in two thermogravimetric analyzers. Firstly, the effect of temperature (700–900 °C) on the oxygen transport capacity and reduction conversion of both materials is assessed at ambient pressure (0.5 nl/min with 20% H2/N2). The influence of material loading is also studied, and it is shown that higher Ni loadings provide a significant improvement in material activity. A complete reduction conversion is achieved at 900 °C and ambient pressure. At high pressure (10–20 bar), tests are carried out in a temperature range of 700–850 °C. The effect of flow rate (2 nl/min to 6 nl/min with 50% H2/N2) is first assessed to prevent external mass transfer limitations. Higher total pressures have a negative effect on reduction kinetics, while higher Ni loadings demonstrate increased final reduction conversion also at high pressure, reaching about 75% conversion after 20 min. The long-term cyclability of the material is also investigated both at low (100 cycles) and high pressure (80 cycles) conditions and a conversion gain is observed throughout the cycles in both cases. No changes in the material microstructure are observed after 80 high-pressure cycles.

Creep behavior and permeability evolution of red sandstone in three Gorges Reservoir area subjected to cyclic seepage pressure

Decellularised heart valve roots offer a promising option for heart valve replacement in young patients, having the potential to remodel and repair. Replacement heart valves have to undergo billions of opening and closing cycles throughout the patient’s lifetime. Therefore, understanding the effect of cyclic loading on decellularised heart valve roots is important prior to human implantation. The aim of this preliminary study was to investigate the influence of low concentration sodium dodecyl sulphate (SDS) decellularisation treatment on the in vitro real time mechanical fatigue of porcine aortic heart valve roots under physiological real time cyclic loading conditions. This required a specific real time in vitro method to be developed, since previous methods relied on accelerated testing, which is non-physiological, and not appropriate for valve replacement materials that exhibit time dependent characteristics. The effects of the real time fatigue on hydrodynamic function and mechanical properties of the heart valve roots were assessed. The mechanical fatigue of decellularised porcine aortic heart valve roots (n = 6) was assessed and compared to cellular porcine aortic heart valve roots (n = 6) in a modified Real time Wear Tester (RWT) at a physiological frequency and under cyclic pressure conditions for a maximum of 1.2 million cycles. Periodically, the heart valve roots were removed from the RWT to assess the influence of cyclic loading on valve competency (static leaflet closure). At the end of testing further hydrodynamic performance parameters were ascertained, along with determination of leaflet material properties. A real time mechanical fatigue assessment method was developed and applied; with two cellular and two decellularised porcine aortic leaflets in different heart valve roots showing tears in the belly region. The decellularised aortic heart valve roots exhibited comparative functionality to the cellular heart valve roots under in vitro static and pulsatile hydrodynamic conditions. However, the material properties of the decellularised aortic leaflets were significantly altered following cyclic fatigue assessment and showed increases in elastin and collagen phase slopes and ultimate tensile strength compared to the cellular porcine aortic leaflets in the circumferential direction. This preliminary study demonstrated that low concentration SDS decellularised porcine aortic heart valve roots can withstand physiological cyclic deformations up to 1.2 million cycles in a RWT whilst maintaining their overall hydrodynamic function and leaflet mechanical properties. This is the first full report of preclinical mechanical fatigue assessment of decellularised porcine aortic heart valve roots under physiological real time conditions.

Summary Minimum miscibility conditions of pressure and enrichment (MMP/MME) have been computed with an equation of state (EOS) for several reservoir-fluid systems exhibiting compositional gradients with depth owing to gravity/chemical equilibrium. MMP/MME conditions are calculated with a multicell algorithm developed by Aaron Zick, where the condensing/vaporizing (C/V) mechanism of developed miscibility is used as the true measure of minimum miscibility conditions when it exists. The Zick algorithm is verified by detailed one-dimensional (1D) slimtube simulations with elimination of numerical dispersion. The miscibility conditions based on the traditional vaporizing-gas-drive (VGD) mechanism are also given for the sake of comparison, where it is typically found that this mechanism overpredicts conditions of miscibility. Significant variations in MMP and MME with depth exist for reservoirs with typical compositional gradients, particularly for near-critical oil reservoirs and gas-condensate reservoirs where the C/V mechanism exists. An important practical implication of these results is that miscible displacement in gas-condensate reservoirs can be achieved far below the initial dewpoint pressure. The requirement is that the injection gas (slug) be enriched somewhat beyond a typical separator gas composition and that the C/V miscibility mechanism exist. This behavior results in many more gas-condensate reservoirs being viable candidates for miscible gas cycling than previously assumed, and at cycling conditions with lower cost requirements (i.e., lower pressures) and greater operational flexibility (e.g., cycling only during summer months).

Minimimum miscibility conditions of pressure and enrichment (MMP/MME) have been computed using an equation of state (EOS) for a number of reservoir fluid systems exhibiting a compositional gradient with depth due to gravity/chemical equilibrium. MMP/MME conditions are calculated using a multicell algorithm developed by Aaron Zick, where the condensing/vaporizing (C/V) mechanism of developed miscibility is used as the true measure of minimum miscibility conditions, when it exists. The Zick algorithm is verified by detailed 1D "slimtube" simulations with elimination of numerical dispersion. The miscibility conditions based on the traditional vaporizing gas drive (VGD) mechanism are also given for the sake of comparison, where it is typically found that this mechanism overpredicts conditions of miscibility. Significant variations in MMP and MME with depth exist for reservoirs with typical compositional gradients, and particularly for near-critical oil reservoirs and gas condensate reservoirs where the C/V mechanism exists. An important practical implication of these results is that miscibile displacement in gas condensate reservoirs can be achieved far below the initial dewpoint pressure. The requirement is that the injection gas (slug) be enriched somewhat beyond a typical separator gas composition and that the C/V miscibility mechanism exist. This behavior results in many more gas condensate reservoirs being viable candidates for miscible gas cycling than previously assumed, and at cycling conditions with lower cost requirements (i.e. lower pressures) and greater operational flexibility (e.g. cycling only during summer months).

Effects of surface texturing on the performance of biocompatible UHMWPE as a bearing material during in vitro lubricated sliding/rolling motion

CO2 hydrate heat cycle using a carbon fiber supported catalyst for gas hydrate formation processes