Evolution of Hydraulic Conductivity of Unsaturated Compacted Na-Bentonite under Confined Condition—Including the Microstructure Effects

Compacted bentonite is envisaged as engineering buffer/backfill material in geological disposal for high-level radioactive waste. In particular, Na-bentonite is characterised by lower hydraulic conductivity and higher swelling competence and cation exchange capacity, compared with other clays. A solid understanding of the hydraulic behaviour of compacted bentonite remains challenging because of the microstructure expansion of the pore system over the confined wetting path. This work proposed a novel theoretical method of pore system evolution of compacted bentonite based on its stacked microstructure, including the dynamic transfer from micro to macro porosity. Furthermore, the Kozeny–Carman equation was revised to evaluate the saturated hydraulic conductivity of compacted bentonite, taking into account microstructure effects on key hydraulic parameters such as porosity, specific surface area and tortuosity. The results show that the prediction of the revised Kozeny–Carman model falls within the acceptable range of experimental saturated hydraulic conductivity. A new constitutive relationship of relative hydraulic conductivity was also developed by considering both the pore network evolution and suction. The proposed constitutive relationship well reveals that unsaturated hydraulic conductivity undergoes a decrease controlled by microstructure evolution before an increase dominated by dropping the gradient of suction during the wetting path, leading to a U-shaped relationship. The predictive outcomes of the new constitutive relationship show an excellent match with laboratory observation of unsaturated hydraulic conductivity for GMZ and MX80 bentonite over the entire wetting path, while the traditional approach overestimates the hydraulic conductivity without consideration of the microstructure effect.

Correlations for Melting Time and Melt Fraction for Bottom Charged Tube in Tube Phase Change Material Heat Exchanger

Multiple factors govern the Thermo-hydraulic behaviour of Latent heat storage devices. The correlation among these factors varies from case to case. In this work, a concentric tube in tube latent heat storage system is numerically modelled for the bottom charging case. Fixed grid enthalpy porosity approach is adopted to account for phase change. The numerical model’s independence is achieved by testing mesh size, time step, and maximum iterations per time step. The computational approach is validated against the experimental data. Non-dimensional parameters viz Rayleigh Number (3.04x105 to 65.75 x105), Stefan Number (0.2 to 1), Reynolds Number (600 to 3000), and L/D ratio (2 to 15) are varied in the respective ranges mentioned in parenthesis. Stefan number is found to have a major influence on the Melt Fraction and Melting time, compared to Rayleigh Number and Reynolds Number. Correlations are presented for quantifying the melt fraction and dimensionless melting time.

A Customized High Performance Water-Based Mud Solved the Challenge to Drill Reactive Shale Formation and Simplify the Logistic Challenge in an Exploration Well in Offshore East Kalimantan, Indonesia

Exploration drilling obviously requires a robust drilling fluid system to be a key factor in overcoming both the known and unexpected challenges of a structure that consists of reactive clay and lost circulation zones. Extra consideration has to be given to regulatory environmental requirements and complications resulting from regional politics. A High-Performance Water Based Mud (HPWBM) system was selected to address the aforementioned issues. The HPWBM was customized to respond to the subsurface conditions with the main requirement to provide maximum shale inhibition through a non-dispersed environment. Polyamine was utilized to stabilize all types of clay; an encapsulation polymer and a non-ionic polymer were included to prevent dispersion and to seal micro-fractures. A complete shale study was performed to determine the optimum concentration of the base fluid and each shale inhibitor. Then hydraulic behaviour of the mud was simulated with contractor proprietary software to understand the parameters for optimal hole cleaning as well as Equivalent Circulating Density (ECD) simulation. The HPWBM system successfully facilitated the execution of the exploration well and provided highly effective clay stabilization. No Non-Productive Time (NPT) was recorded as a result of reactive clay issues. The mud system also facilitated a good rate of penetration (ROP), formation stability, and lubricity. Waste cuttings transportation was not required. In addition, there is also no requirement for costly base oil including its associated transportation costs. The successful implementation of the HPWBM yielded an estimating saving of 25% compared to invert emulsion fluids, prior to considering costs associated with an expensive Liquid Mud Plant (LMP), environmental, and freight costs. Significant cost savings were achieved by eliminating the need for LMP rental, mobilization and demobilization. Another notable saving was realized from the reduced system maintenance of the HPWBM as less dilution was required compared to a regular Water Based Mud. Thinking outside of the box and embracing the departure from the default consideration of an invert system with a thorough risk assessment augmented value to wellbore construction. A smartly designed HPWBM system provided performance comparable to an invert emulsion system but with superior benefits with respect to environmental protection, simplified logistics and lower costs.

A Review of the Performance of Minewater Heating and Cooling Systems

As the decarbonisation of heating and cooling becomes a matter of critical importance, it has been shown that flooded mines can provide a reliable source of low-carbon thermal energy production and storage when coupled with appropriate demand via an appropriate heat transfer technology. This paper summarises the potential resource represented by a long legacy of mining operations, the means heat can be extracted from (or rejected to) flooded mine workings, and then considers the risks and challenges faced by minewater geothermal energy (MWG) schemes in the planning, construction, and operational phases. A combination of site visits, interviews and literature reviews has informed concise, updated accounts for many of the minewater geothermal energy systems installed across the world, including accounts of hitherto unpublished systems. The paper has found that a number of previously reported MWG schemes are now non-operational. Key risks encountered by MWG schemes (which in some cases have led to decommissioning) include clogging of system components with mineral precipitates (e.g., ochre), uncertainty in targeting open mine voids and their hydraulic behaviour, uncertainty regarding longevity of access to minewater resource, and accumulated ongoing monitoring and maintenance burdens.

Physical Modelling of Flow and Head along with Dead-end and Looped Manifolds

In this study, physical models were designed and fabricated to investigate the hydraulic behaviour of dead-end and looped PVC manifolds. The physical models consisted of a water supply tank with overflow, PVC manifolds, steel supports, collection tank, pump, pressure sensors and valves to allow flow control. Throughout the study, the water level in the supply tank was kept constant. The hydraulic behaviour of dead-end manifolds was investigated using different spacing, S between outlets (S= 3m, S=2.5m, S=2m, S=1.5m, and S=0.75m). The hydraulic behaviour of looped manifolds was investigated using a single outlet spacing of 1.5m. The comparison between the hydraulic behaviour of looped and dead-end manifolds was carried out using the data of the 1.5m outlet spacing. The value of uniformity, U for dead-end and looped manifolds was 82% and 92%, respectively. The value of friction ratio, fn/f1, was found to be 33 and 0.18 for dead-end and looped manifolds, respectively. The experimental data of this study were used to validate selected formulae for estimation of the friction correction factor (G Factor). The results showed that the equation proposed by Alazba et al. (2012) yielded the most satisfactory estimation. The performance of the selected formulae was tested using two statistical indices.

Simulation Studies of the Sodium Hydraulic Behaviour to Design a Mock-Up for ECFM Testing

The Eddy Current Flowmeter (ECFM) sensor plays an important part in the instrumentation of the future Sodium Fast Reactors (SFR), which will allows when located above the core to detect plugging (partial or total) of a sub assembly and when located on the primary pump to measure core pressure drop and core flowrate. This document describes the pre-design phase of a mock-up for ECFM tests and qualifications under sodium conditions for the detection of a partial or full plugging of a fuel sub-assembly. These tests will be the first of their kind, as the ECFM had never been qualified at nominal conditions of a reactor core outlet (sodium temperature, velocity and output flow).