Browsing by Author "Liu, Xiaolei"

Now showing 1 - 7 of 7
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    Assessment of deep geothermal energy exploitation methods: The need for novel single-well solutions
    (Elsevier, 2018-06-28) Falcone, Gioia; Liu, Xiaolei; Radido Okech, Roy; Seyidov, Ferid; Teodoriu, Catalin
    Geothermal energy is a constant and independent form of renewable energy and plays a key role towards the world's future energy balance. In particular, deep geothermal resources are largely available across continents and can help countries become less dependent on energy imports and build a broader base in their future energy mix. However, despite its significant potential, the total contribution of the geothermal sector to global power generation remains relatively small. The International Energy Agency has recommended devising plans to address technology-specific challenges to achieve faster growth and improving policies tackling pre-development risks for geothermal energy. Reaching considerable depths is a requirement to exploit deep geothermal resources, but experience gained to date from the implementation of complex, engineered deep geothermal projects has unveiled technical and economic challenges, lower-than-expected performance and poor public image. There is therefore an urgent need for alternative, more sustainable well designs. This paper critically assesses conventional and unconventional deep geothermal well concepts, focusing on the basic Borehole Heat Exchanger (BHE) concept. The discussions are supported by numerical simulations of a BHE design that includes heat conductive fillers to enhance the heat exchange with the surrounding formation, while avoiding direct fluid interaction with the latter.
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    A comprehensive assessment of correlations for two-phase flow through Venturi tubes
    (Elsevier, 2020-04-17) Liu, Xiaolei; Lao, Liyun; Falcone, Gioia
    The objective of this study is to comprehensively evaluate established correlations for two-phase (gas-liquid) flow through Venturi tubes. Two-phase flow metering plays a critical role in the oil and gas industry and several commercial metering solutions incorporate a Venturi. However, despite its significance, there is no widely accepted standard for two-phase flow metering applications. In this paper, sixteen differential pressure correlations are critically assessed from literature and international standards, focusing on the Venturi tube. The discussions are supported by an independent dataset obtained from a two-phase flow test rig with an installed Venturi tube (following ISO 5167-4 2005) to assess correlations' performance within their own respective application range. The wide literature review and the obtained comparison results trended to inform that the homogeneous model performs better in most scenarios.
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    Liquid loading in gas wells: experimental investigation of back pressure effects on the near-wellbore reservoir
    (Elsevier, 2016-10-28) Liu, Xiaolei; Falcone, Gioia; Teodoriu, C.
    A large-scale core-flooding experimental setup was designed and constructed to investigate the back pressure effects on transient flow through porous medium, and so mimic the physical process of liquid loading and reservoir response. Between initial and final steady-state flowing conditions, where inlet pressure was maintained at a constant level while initiating a transient pressure build up at the core sample end, an “U-shaped” temporal distribution of pore fluid pressure within the medium itself was observed, which is in direct contrast to the conventional reservoir pressure profile.
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    Liquid loading in gas wells: From core-scale transient measurements to coupled field-scale simulations
    (Elsevier, 2017-08-12) Liu, Xiaolei; Falcone, Gioia; Teodoriu, Catalin
    Liquid loading is a major operational constraint in mature gas fields around the world. It manifests itself as an increasing back pressure on the reservoir due to a rising liquid column in the well, which initially decreases deliverability, then ultimately causes the gas well to cease production. Theoretically, every gas well will experience this debilitating phenomenon in the latter stages of its producing life. In this paper, both laboratory experiments and numerical simulations are presented to shed more light on the physical process of liquid loading, with a focus on reservoir responses. On the one hand, core-flooding experimental setups of different scales were designed and constructed to investigate back pressure effects on transient flow through the near-wellbore region of the reservoir. On the other hand, the modelling of a gas well undergoing controlled flow and shut-in cycles was performed to validate core-scale observations at reservoir scale, using commercial integrated numerical software that connects a transient wellbore model to a transient reservoir model. The simulated transient characteristics of short-term downhole dynamics (e.g. liquid re-injection and co-current/counter-current flows) supported the U-shaped concept observed in the experiments. The detected temporal distribution of pore fluid pressure within the reservoir medium itself (referred to as the U-shaped pressure profile) was observed both experimentally at the core-scale and numerically at the reservoir-scale. This pressure distribution can be used to explain re-injection of the denser phases into the near-wellbore region of the reservoir.
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    Prediction of two-phase flow patterns in upward inclined pipes via deep learning
    (Elsevier, 2020-08-15) Lin, Zi; Liu, Xiaolei; Lao, Liyun; Liu, Hengxu
    The industrial process involving gas liquid flows is one of the most frequently encountered phenomena in the energy sectors. However, traditional methods are practically unable to reliably identify flow patterns if additional independent variables/parameters are to be considered rather than gas and liquid superficial velocities. In this paper, we reported an approach to predict flow pattern along upward inclined pipes (0–90°) via deep learning neural networks, using accessible parameters as inputs, namely, superficial velocities of individual phase and inclination angles. The developed approach is equipped with deep learning neural network for flow pattern identification by experimental datasets that were reported in the literature. The predictive model was further validated by comparing its performance with well-established flow regime forecasting methods based on conventional flow regime maps. Besides, the intensity of key features in flow pattern prediction was identified by the deep learning algorithm, which is difficult to be captured by commonly used correlation approaches
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    Swept blade influence on aerodynamic performance of steam turbine nozzle cascades
    (Springer, 2018-04-12) Feng, Zi-Ming; Tan, Jingjing; Liu, Xiaolei; Wei, Cui
    To improve the aerodynamic performance of steam turbine nozzle cascades, it is significant to study the effect of swept blades to control the flow field within the cascade. Numerical simulations of three different sweep angle blades (−20°, +20° and 0°) were carried out, using CFD modelling. Simulation results showed that the aft-swept blade can effectively improve the corresponding flow characteristics and reduce the total pressure loss. Meanwhile, it has better aerodynamic performance than the straight blade and the fore-swept blade.
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    A systematic study of harnessing low-temperature geothermal energy from oil and gas reservoirs
    (Nature Publishing Group, 2017-10-23) Liu, Xiaolei; Falcone, Gioia; Alimonti, Claudio
    Mature hydrocarbon fields co-produce significant volumes of water. As the produced water increases over the life of the field, the project's operating costs increase (due to greater water management expenditure), while the oil revenues decrease. Typically, these waste streams of water have temperatures of 65–150 °C. The combination of moderate temperatures and large water volumes may be suitable for electricity generation and/or district heating. Being able to capture the geothermal energy from existing hydrocarbon fields could extend their lifespan by delaying their economic cut-off point. In this paper, mature oil and gas reservoirs worldwide are critically reviewed, where waste heat recovery has already been tested, or its potential identified. A roadmap of screening criteria based on geological, reservoir, production and economic parameters is then proposed, to assess how, where and when low-temperature waste heat recovery is feasible. The roadmap is tested against the Villafortuna–Trecate oil field in Italy, where the aquifer not only provides pressure support to the reservoir, but also represents a natural, in-situ hydrothermal resource. The results suggest that a single-well could recover approximately 25 GWh of electric power over a 10-year period, with an installed capacity of 500 kW.