• Energy Research

Abstract The impact of brine composition on rock wettability and oil recovery in carbonates has been an area of research in recent years. Many studies have reported contradictory results concerning the impact of water injection salinity and composition on oil recovery. The zeta potential, which is a measure of the electrical charge at the mineral surface, is highly variable in carbonates, depending on the ionic composition of the pore water. The zeta potential controls the magnitude and polarity of the electrostatic interactions between the mineral surface and polar species in the brine and oil; it also controls the magnitude and polarity of the streaming potential, an electrical potential which arises in response to pressure gradients across saturated rocks. Here we report the use of streaming potential measurements to characterize wettability and optimize injection brine composition during controlled salinity waterflooding (CSW) in carbonates. Crude oils, natural carbonate core samples and synthetic brines (equivalent to formation, seawater and modified seawater compositions) are used to evaluate wettability and CSW effect. We use the streaming potential measurements to determine the zeta potential, and correlate changes in zeta potential with changes in wettability and improved oil recovery. To predict the optimum brine composition for CSW requires knowledge of the zeta potential and how this responds to changes in brine composition. Such knowledge can be obtained using the streaming potential method reported here, which is much cheaper and quicker than conducting numerous multiphase coreflooding experiments and varying the brine composition on an ad-hoc basis.

The In-Situ Upgrading (ISU) of heavy oil and oil shale is investigated. We develop a mathematical model for the process and identify the full set of dimensionless numbers describing the model. We demonstrate that for a model with nf fluid components (gas and oil), ns solid components and k chemical reactions, the model was represented by 9 + k x (3 + nf + ns - 2) + 8nf + 2ns dimensionless numbers. We calculated a range of values for each dimensionless numbers from a literature study. Then, we perform a sensitivity analysis using Design of Experiments (DOE) and Response Surface Methodology (RSM) to identify the primary parameters controlling the production time and energy efficiency of the process. The Damkohler numbers, quantifying the ratio of chemical reaction rate to heat conduction rate for each reaction, are found to be the most important parameters of the study. They depend mostly on the activation energy of the reactions and of the heaters temperature. The reduced reaction enthalpies are also important parameters and should be evaluated accurately. We show that for the two test cases considered in this paper, the Damkohler numbers needed to be at least 10 for the process to be efficient. We demonstrate the existence of an optimal heater temperature for the process and obtain a correlation that can be used to estimate it using the minimum of the Damkohler numbers of all reactions.

Abstract Gravity-stable, miscible gas injection is a common oil recovery technique throughout the world. In homogeneous environments recovery efficiencies may be more than 90%. However the influence of heterogeneity on the sweep efficiency in these recovery schemes is not well understood. For example most clastic reservoirs contain ‘discontinuous’ shales that cannot be correlated between wells. Several numerical studies have suggested that these may cause significant bypassing of oil during waterflooding or gas injection. However flow experiments and detailed simulation of viscous dominated displacements, without gravity, indicate that very little oil is bypassed1. In this paper, we investigate flow patterns around discontinuous shales during vertical, gravity-influenced miscible gas injection in well-characterised bead-pack experiments at three flow-rates corresponding to unstable, partly stable and completely stable flow regimes. We examine the volume of oil bypassed and whether viscous fingering is reduced by gravity or altered by the presence of a discontinuous shale. The results are compared to the predictions of detailed simulation. We find that, during miscible displacements, an isolated shale causes negligible bypassing. However, during adverse mobility ratio displacements, the simulation program erroneously predicts significant bypassing of oil both upstream and downstream of the shale at high and intermediate flow-rates.

Abstract Aquifer thermal energy storage (ATES) represents a promising solution for heating and cooling, offering lower greenhouse gas emissions and primary energy consumption than conventional technologies. Despite these benefits and the widespread availability of suitable aquifers, ATES has yet to see widespread utilisation, with uptake highly concentrated in select countries (Netherlands, Belgium, Sweden and Denmark). Beyond technical and hydrogeological feasibility, appropriate national policies are paramount in driving ATES deployment. This study provides an international comparison of ATES policies, highlighting best practices and revealing where measures are missing. It sources insights from a survey of experts across academia, industry and governmental bodies in 30 countries, complemented by semi-structured expert interviews. The study reveals significant differences in the existence and strength of supportive policy environments between countries with different ATES market maturity. A mere 33% of all survey respondents stated that there are policies designed to support ATES utilisation in their respective countries, while the existence of laws and regulations governing ATES was confirmed by 56% of the respondents. The interviews provide details on creating supportive environments (e.g. through facilitators like pre-existing groundwater technology use and building energy efficiency standards) and further barriers to ATES deployment. Ten recommendations for ATES policies are derived to address the following areas: legislative and regulatory issues, raising public awareness, ATES’ role in local energy transitions, and social engagement. This work aims to steer global policy towards better harnessing the potential of ATES to decarbonise buildings. Graphical abstract

The In-Situ Upgrading (ISU) of bitumen and oil shale is a very challenging process to model numerically because a large number of components need to be modelled using a system of equations that are both highly non-linear and strongly coupled. Operator splitting methods are one way of potentially improving computational performance. Each numerical operator in a process is modelled separately, allowing the best solution method to be used for the given numerical operator. A significant drawback to the approach is that decoupling the governing equations introduces an additional source of numerical error, known as splitting error. Obviously the best splitting method for modelling a given process is the one that minimises the splitting error whilst improving computational performance over that obtained from using a fully implicit approach. Although operator splitting has been widely used for the modelling of reactive-transport problems, it has not yet been applied to the modelling of ISU. One reason is that it is not clear which operator splitting technique to use. Numerous such techniques are described in the literature and each leads to a different splitting error. While this error has been extensively analysed for linear operators for a wide range of methods, the results observed cannot be extended to general non-linear systems. It is therefore not clear which of these techniques is most appropriate for the modelling of ISU. In this paper we investigate the application of various operator splitting techniques to the modelling of the ISU of bitumen and oil shale. The techniques were tested on a simplified model of the physical system in which a solid or heavy liquid component is decomposed by pyrolysis into lighter liquid and gas components. The operator splitting techniques examined include the Sequential Split Operator (SSO), the Strang-Marchuk split operator (SMSO) and the Iterative Split Operator (ISO). They were evaluated on various test cases by considering the evolution of the discretization error as a function of the size of the time-step compared with the results obtained from a fully implicit simulation. We observed that the error was minimum for a splitting scheme where the thermal conduction was performed first, followed by the chemical reaction step and finally the heat and mass convection operator (SSO-CKA). This method was then applied to a more realistic model of the ISU of bitumen with multiple components.

Aquifer Thermal Energy Storage (ATES) is an underground thermal energy storage technology that provides large capacity (of order MW𝑡ℎ to 10s MW𝑡ℎ), low carbon heating and cooling to large buildings and building complexes, or district heating/cooling networks. The technology operates through seasonal capture, storage and re-use of thermal energy in shallow aquifers. ATES could make a significant contribution to decarbonising UK heating and cooling, but uptake is currently very low: eleven low temperature (LT-ATES) systems currently operating in the UK meet <0.01% of the UK’s heating and <0.5% of cooling demand. The Wandsworth Riverside Quarter development in London is analysed as a successful UK case study. The UK has large potential for widespread deployment of LT-ATES, due to its seasonal climate and the wide availability of suitable aquifers co-located with urban centres of high heating and cooling demand. ATES could supply ca. 61% of UK heating demand, and ca. 79% of cooling demand with a 13%–41% reduction in carbon emissions for heating, and 70%–94% reduction for cooling, compared to equivalent ground- or air-sourced heat pump systems. However, problems with design and operation in some UK systems have caused sub-optimal performance. The UK can benefit from experience of both successful and unsuccessful deployments but these need to be more widely reported. Raising awareness, developing policies to encourage uptake, streamlining regulations and developing expertise are essential to unlock the potential of ATES technology in the UK, which requires engagement with policymakers, regulators, industry stakeholders and the general public.