• Energy Research

This paper explores the concept of harnessing geothermal energy from heavy oil fields that have undergone steam flooding and so accumulated substantial heat from steam injection. Once the steam flooding process reaches economic cut-off resulting from high water cut and/or high steam-to-oil ratio, the reservoir would be abandoned, leaving behind stored energy in the form of heat. From this point, the reservoir could be regarded as an artificial geothermal system and its intrinsic heat from the steam flooding stage recovered by water circulation. This study shows the results of numerical reservoir simulations to quantify the energy that can be recovered by water injection after steam flooding. The results of the simulations, together with those of a sensitivity analyses on key reservoir parameters, suggest the feasibility of this concept. The results for the synthetic case used in this work show that the average produced energy rate during the water injection phase is approximately 11 MMBTU/day for 3,800 days, after which the operations stop. At that time, a cumulative net energy production of 3.02 × 10 4 MMBTU is recovered.

Sector coupling and energy sharing are key elements in effectively decarbonising the thermal grid. 5th Generation District Heating and Cooling (5GDHC) provides a system for combining heating and cooling via an ambient temperature network. A main design challenge for 5GDHC is establishing a control regime that allows flow bidirectionality and energy synergies between heating and cooling. This work develops and experimentally validates a 5GDHC system wide hydraulic design and two fitting control strategies on a small scale. One has fixed grid return temperatures (TGridFix) while the other free floating grid temperatures (TGridFloat). Both feature decentralised variable speed pumping and a centralised passive balancing unit aimed at alleviating control instabilities arising from pump hunting. Experiments showed that TGridFix demonstrates slightly higher electrical consumption for the booster heat pump (Seasonal Coefficient of Performance of 3.84 compared to 4.16 for 20 h of operation) due to a mismatch between the evaporator and the grid temperature difference. Overall, TGridFix can lead to low prosumer interaction and better system wide predictability. Further considerations on generalisability of findings and full-scale implementations are highlighted. This works presents a set of detailed and experimentally validated control philosophies for 5GDHC systems, elucidating a key system implementation challenge.

The decarbonisation of the energy sector can be a key contributor in the transition to a low-carbon economy. New low-CO2 energy production technologies are becoming available in the international market, contributing to building diversified portfolios of projects with very different features. Apart from technology-related features, the deployment of an energy production plant also depends on the availability of resources of the country/installation site, socio-economic implications, environmental impact and integration with the existing power grid. Decision makers should take all these factors into consideration when determining which project is more likely to move forward. Several studies have proposed the use of Key Performance Indicators (KPIs) to facilitate the decision-making process when selecting viable and sustainable energy projects. However, fewer studies exist that provide a detailed assessment of these KPIs. The scope of this paper is to critically review and investigate a set of multi-disciplinary KPIs, allowing a holistic comparison across different types of energy projects. The identified KPIs were classified as physical, economic, environmental and social. They were subsequently analysed to assess their limitations, determine inter-connections and identify the need for additional indicators to capture risks and opportunities within a mixed energy market. This paper can be the basis for the development of an integrated framework, allowing a fairer assessment of competing energy projects by relevant stakeholders.

In the subset of unconventional natural gases, shale gas, tight gas and coal bed methane are now being produced to some extent, whereas the biggest part of the unconventional resource is made up of gas hydrates which are still in the exploratory phase of development. It is recognised that the resource potential of gas hydrates existing in the Earth is twice the amount of the combined remaining resources of other fossil fuels (i.e. coal, oil and natural gas). So far, hydrates have been recovered using pressure coring carried out by vessels using conventional drilling methods. Original attempts to recover hydrates were based on upgrading underwater drill rigs with autoclaves. The present paper reviews the importance of pressure coring systems with the objective of assisting researchers and engineers in the development of technologies that will support the exploration of gas hydrates and to consider underwater drill rigs as novel drilling tools.

Geothermal is a renewable energy source that can be untapped through various subsurface technologies. Closed geothermal well solutions, such as deep geothermal heat exchangers (DBHEs), consist of circulating a working fluid to recover the available heat, with less dependency on the local geological settings than conventional geothermal systems. This paper emphasizes a double numerical method to strengthen the assessment of DBHE performances. A computational fluid dynamics (CFD) commercial software and the 1D coupled wellbore-reservoir geothermal simulator T2Well have been used to investigate the heat transfer and fluid flow in a vertical DBHE in high geothermal gradient environments. The use of constant water properties to investigate the energy produced from DBHEs can lead to underestimating the overall heat transfer at high temperature and low mass flow rate. 2D axisymmetric CFD modelling improves the understanding of the return flow at the bottom of the DBHE, readjusting and better estimating the pressures losses commonly obtained with 1D modelling. This paper highlights the existence of convective cells located at the bottom of the DBHE internal tubing, with no significant effects due to the increase of injected water flow. Both codes are shown to constrain the numerical limitations to access the true potential of geothermal heat extraction from DBHEs in high geothermal gradient environments and demonstrate that they can be used for geothermal energy engineering applications.

<p><strong>Abstract.</strong> The geothermal community lacks a universal definition of deep geothermal systems. A minimum depth of 400 m is often assumed, with a further sub-classification into middle-deep geothermal systems for reservoirs found between 400 and 1000 m. Yet, the simplistic use of a depth cut-off is insufficient to uniquely determine the type of resource and its associated potential. Different definitions and criteria have been proposed in the past to frame deep geothermal systems. However, although they have valid assumptions, these frameworks lack systematic integration of correlated factors. To further complicate matters, new definitions such as hot dry rock (HDR), enhanced or engineered geothermal systems (EGSs) or deep heat mining have been introduced over the years. A clear and transparent approach is needed to estimate the potential of deep geothermal systems and be capable of distinguishing between resources of a different nature. In order to overcome the ambiguity associated with some past definitions such as EGS, this paper proposes the return to a more rigorous petrothermal versus hydrothermal classification. This would be superimposed with numerical criteria for the following: depth and temperature; predominance of conduction, convection or advection; formation type; rock properties; heat source type; requirement for formation stimulation and corresponding efficiency; requirement to provide the carrier fluid; well productivity (or injectivity); production (or circulation) flow rate; and heat recharge mode. Using the results from data mining of past and present deep geothermal projects worldwide, a classification of the same, according to the aforementioned criteria is proposed.</p>

The concept of supply chain resilience continues to attract both industry and research experts in the field of energy. These stakeholders continue to tackle disruptions to supply chain systems through the introduction of strategy options for resilience. A better understanding of broader dimensions of potential disruptions to supply chains caused by uncertainties has become eminent, especially as currently experienced during the global COVID-19 pandemic. The effects of the outbreak in disrupting supply chains in the energy sector will, in the next decade, continue to be a likely concern for industry and research stakeholders. Balancing the increasing need for energy security to meet the continuous growth in energy demand through shortage reduction and increased uptime using optimization is the core of this research. This review paper provides an insight into recent studies in the field of natural gas supply chain resilience as a major player in the energy mix, and the continued disruption and subsequent shutdowns of plant nodes, which results in emission loss to the environment. This paper is motivated by the disparity between demand and supply triggered by the disruption of supply chain networks. Referenced in this paper are scientific work on supply chain resilience of biomass, water, power systems, and natural gas. Findings show that existing studies favor fewer system-based strategies in optimizing for resilience. This review concludes that an optimization is a useful tool to continuously achieve resilience in supply chain production, storage, and transportation activities.