Thermoporoelastic Analysis of Artificially Fractured Geothermal Reservoirs: A Multiphysics Problem

2020 ◽  
Vol 142 (8) ◽  
Author(s):  
Arash Dahi Taleghani ◽  
Milad Ahmadi
Keyword(s):  
Fluid Flow ◽  
Heat Generation ◽  
Induced Seismicity ◽  
Closed Loop ◽  
Thermal Power ◽  
Surface Subsidence ◽  
Electricity Production ◽  
Working Fluid ◽  
Hydraulic Fractures ◽  
Geothermal Systems

Abstract Geothermal systems are identified as either open-loop system (OLGS) or closed-loop systems (CLGS). In OLGS, fluid is produced from the subsurface, while there might be a concurrent fluid injection into the reservoir. The loss of working fluid, surface subsidence, formation compaction, and induced seismicity are major challenges in OLGS. To address the indicated challenges, closed-loop geothermal systems can be considered as an alternative option. In this method, a working fluid with low-boiling point is circulated through the coaxial sealed pipes to harvest heat from the formation of rock and fluid. Induced seismicity is essentially caused by the drastic quick changes in pore pressure. Thereafter, seismic risk assessment is expected for any new geothermal technology before starting the field implementation phase. To improve the heat recovery from closed-loop wells, we suggest highly conductive hydraulic fractures for CLGS to improve the heat generation rate. In conventional hydraulic fracturing treatments, fractures facilitate fluid flow; however, in the proposed configuration, induced fractures enhance heat flux into the wellbore. Considering the multiphysics nature of CLGS, a comprehensive analysis of this problem requires simultaneous modeling of fluid flow, energy transfer (heat), and rock deformation. A thermoporoelastic model is developed in finite element methods to simulate this problem. The numerical results suggest that fractures significantly improve thermal power and cumulatively produced heat in CLGS. The thermal conductivity of the proppants is the key parameter enhancing heat generation. The level of surface subsidence in the proposed technique is negligible due to the lack of geofluid production from the reservoir. Significant numbers of abandoned oil or gas wells exist around the globe which can be converted into the geothermal wells to produce electricity. This study shows the feasibility of electricity production from CLGS with minimum environmental hazards.

scholarly journals Modelling an unconventional closed-loop deep borehole heat exchanger (DBHE): Sensitivity Analysis on the Newberry Volcanic Setting

2020 ◽  
Author(s):  
Hannah Rose Doran ◽  
Theo Renaud ◽  
Gioia Falcone ◽  
Lehua Pan ◽  
Patrick Verdin
Keyword(s):  
Sensitivity Analysis ◽  
Heat Exchanger ◽  
Closed Loop ◽  
Critical Conditions ◽  
Working Fluid ◽  
Enhanced Geothermal Systems ◽  
Geothermal Systems ◽  
Low Carbon ◽  
Deep Borehole ◽  
Geothermal Wells

Abstract Geothermal energy is a baseload resource that has the potential to contribute significantly to the transition to a low-carbon future. Alternative (unconventional) deep geothermal designs are thus needed to provide a secure and efficient energy supply. Current Enhanced Geothermal Systems (EGS) are under technical review as a result of the associated low recovery factors and risk of induced seismicity in connection with reservoir stimulation operations, and Supercritical EGS (SEGS) concepts are still under early research and development. The Newberry and Icelandic Deep Drilling Projects (NDDP and IDDP) aid these developments to drill deeper into very hot temperature zones. An in-depth sensitivity analysis was investigated considering a deep borehole closed-loop heat exchanger (DBHE) to overcome the current limitations of deep EGS. Using the DBHE, cold working fluid is pumped down in the outer annulus and rises to the surface via natural convection or is pumped up via an inner tubing. A T2Well/EOS1 model previously calibrated on an experimental DBHE in Hawaii was adapted to the current NWG 55-29 well at the Newberry volcano site in Central Oregon. A sensitivity analysis was carried out, including parameters such as: the working fluid mass flow rate, the casing and cement thermal properties and the wellbore radii dimensions. The results allow an assessment of key thermodynamics within the wellbore and provide an insight into how heat is lost/gained throughout the system. This analysis was performed under the assumption of sub-critical conditions. Requirements for further software development are briefly discussed, which would facilitate the modelling of unconventional geothermal wells in supercritical systems.

scholarly journals Structural and Parametric Optimization of S-CO2 Thermal Power Plants with a Pulverized Coal-Fired Boiler Operating in Russia

Energies ◽  
2021 ◽  
Vol 14 (21) ◽  
pp. 7136
Author(s):  
Andrey Rogalev ◽  
Vladimir Kindra ◽  
Ivan Komarov ◽  
Sergey Osipov ◽  
Olga Zlyvko
Keyword(s):  
Power Plants ◽  
Thermal Power ◽  
Rankine Cycle ◽  
Combustion Products ◽  
Pulverized Coal ◽  
Electricity Production ◽  
Working Fluid ◽  
Inlet Temperature ◽  
Thermal Power Plants ◽  
Increase Energy Efficiency

The Rankine cycle is widely used for electricity production. Significant weight and size characteristics of the power equipment working on superheated steam are the main disadvantages of such power plants. The transition to supercritical carbon dioxide (S-CO2) working fluid is a promising way to achieve a significant reduction in equipment metal consumption and to increase energy efficiency. This paper presents the results of thermodynamic analysis of S-CO2 thermal power plants (TPPs) utilizing the heat of combustion products of an energy boiler. It was found that the net efficiency of the developed S-CO2 TPP with a pulverized coal-fired boiler reached 49.2% at an initial temperature of 780 °C, which was 2% higher compared to the efficiency level of steam turbine power plants (STPPs) at a similar turbine inlet temperature.

Investigation of injection-induced seismicity using a coupled fluid flow and rate/state friction model

Geophysics ◽  
2011 ◽  
Vol 76 (6) ◽  
pp. WC181-WC198 ◽  
Author(s):  
Mark W. McClure ◽  
Roland N. Horne
Keyword(s):  
Fluid Flow ◽  
Induced Seismicity ◽  
Large Scale ◽  
Injection Pressure ◽  
Friction Model ◽  
Enhanced Geothermal Systems ◽  
Geothermal Systems ◽  
Isolated Fracture ◽  
Lower Magnitude ◽  
Event Magnitude

We describe a numerical investigation of seismicity induced by injection into a single isolated fracture. Injection into a single isolated fracture is a simple analog for shear stimulation in enhanced geothermal systems (EGS) during which water is injected into fractured, low permeability rock, triggering slip on preexisting large scale fracture zones. A model was developed and used that couples (1) fluid flow, (2) rate and state friction, and (3) mechanical stress interaction between fracture elements. Based on the results of this model, we propose a mechanism to describe the process by which the stimulated region grows during shear stimulation, which we refer to as the sequential stimulation (SS) mechanism. If the SS mechanism is realistic, it would undermine assumptions that are made for the estimation of the minimum principal stress and unstimulated hydraulic diffusivity. We investigated the effect of injection pressure on induced seismicity. For injection at constant pressure, there was not a significant dependence of maximum event magnitude on injection pressure, but there were more relatively large events for higher injection pressure. Decreasing injection pressure over time significantly reduced the maximum event magnitude. Significant seismicity occurred after shut-in, which was consistent with observations from EGS stimulations. Production of fluid from the well immediately after injection inhibited shut-in seismic events. The results of the model in this study were found to be broadly consistent with results from prior work using a simpler treatment of friction that we refer to as static/dynamic. We investigated the effect of shear-induced pore volume dilation and the rate and state characteristic length scale, [Formula: see text]. Shear-induced pore dilation resulted in a larger number of lower magnitude events. A larger value of [Formula: see text] caused slip to occur aseismically.

scholarly journals The effect of the intermediate fluid flow rate on the system performance in the closed circuit applications of the solar collector

2019 ◽  
pp. 472-472 ◽  
Author(s):  
Hasan Yildizhan ◽  
Taqi Cheema ◽  
Mecit Sivrioğlu
Keyword(s):  
Heat Transfer ◽  
Fluid Flow ◽  
Flow Rate ◽  
Solar Collector ◽  
Closed Loop ◽  
Closed Circuit ◽  
Working Fluid ◽  
Solar Collectors ◽  
Flow Rates ◽  
Energy And Exergy

Solar collector water heating system use solar thermal energy to provide hot water for domestic and industrial use. These systems are operated either as open-loop or closed-loop flow circuit. The former loop systems are not recommended for the cold climates having water freezing problem. Although previous studies on solar collectors have used closed-loop operation with water as the working fluid; however, it must have high boiling and low freezing points for the colder regions and thus arises the need for antifreeze mixtures of water. Another solution to the same problem is the use of heat transfer oil as intermediate working fluids. In the present study, the energy and exergy analysis of a boiler supported vacuum tube solar collector system working with closed-loop in different working fluid flow rates have been performed and evaluated. Heat transfer oil has been used as an intermediate working fluid in the closed loop system at different flow rates of 0.277 kg/s, 0.383 kg/s, 0.494 kg/s. The results show that the collector temperature difference as well as the outlet temperature decrease; however, the collector inlet temperature increases by increasing the flow rate. Moreover, with the increase in flow rate, it was ascertained that the energy and exergy efficiency of the system and the collectors increase. The main finding of the present study is that the intermediate fluid used in the closed-circuit operation of the solar collectors has a direct effect on the energy and exergy efficiency of the system.

scholarly journals Modelling an unconventional closed-loop deep borehole heat exchanger (DBHE): sensitivity analysis on the Newberry volcanic setting

2021 ◽  
Vol 9 (1) ◽  
Author(s):  
Hannah R. Doran ◽  
Theo Renaud ◽  
Gioia Falcone ◽  
Lehua Pan ◽  
Patrick G. Verdin
Keyword(s):  
Sensitivity Analysis ◽  
Heat Exchanger ◽  
Mass Flow Rate ◽  
Mass Flow ◽  
Flow Rate ◽  
Energy Flow ◽  
Closed Loop ◽  
Working Fluid ◽  
Valuable Insight ◽  
Deep Borehole

AbstractAlternative (unconventional) deep geothermal designs are needed to provide a secure and efficient geothermal energy supply. An in-depth sensitivity analysis was investigated considering a deep borehole closed-loop heat exchanger (DBHE) to overcome the current limitations of deep EGS. A T2Well/EOS1 model previously calibrated on an experimental DBHE in Hawaii was adapted to the current NWG 55-29 well at the Newberry volcano site in Central Oregon. A sensitivity analysis was carried out, including parameters such as the working fluid mass flow rate, the casing and cement thermal properties, and the wellbore radii dimensions. The results conclude the highest energy flow rate to be 1.5 MW, after an annulus radii increase and an imposed mass flow rate of 5 kg/s. At 3 kg/s, the DBHE yielded an energy flow rate a factor of 3.5 lower than the NWG 55-29 conventional design. Despite this loss, the sensitivity analysis allows an assessment of the key thermodynamics within the wellbore and provides a valuable insight into how heat is lost/gained throughout the system. This analysis was performed under the assumption of subcritical conditions, and could aid the development of unconventional designs within future EGS work like the Newberry Deep Drilling Project (NDDP). Requirements for further software development are briefly discussed, which would facilitate the modelling of unconventional geothermal wells in supercritical systems to support EGS projects that could extend to deeper depths.

scholarly journals Influence of Nozzle Jet Flushing on Working Fluid Flow and Wire Electrode in Trim-cut WEDM

Procedia CIRP ◽  
2020 ◽  
Vol 95 ◽  
pp. 250-254
Author(s):  
Hiroki Iwai ◽  
Tomonori Ebisu ◽  
Akira Okada ◽  
Haruya Kurihara
Keyword(s):  
Fluid Flow ◽  
Working Fluid ◽  
Wire Electrode ◽  
Trim Cut
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