Using abandoned gas wells as geothermal resources for energy production is an effective way to extract geothermal energy from geological formations. These abandoned wells have the potential to ...significantly contribute in the rising global demand for energy without requiring the land disruption resulting from deep drilling or digging, processes necessary for energy extraction from geological formations via more traditional methods. In this paper, a method to extract geothermal energy from abandoned gas wells is proposed. The method offers an efficient, economical, and environmentally-conscious way to generate electricity. A mathematical model of a thermal and hydraulic coupling process is constructed, and a 3D numerical model is generated to study the process of geothermal energy extraction by retrofitting an abandoned gas reservoir into a geothermal reservoir. Using the model, heat extraction and fluid flow are analyzed over a period of 50 years. The heat production, electricity generation, and thermal recovery over the lifetime of the reservoir indicate that a commercially viable geothermal dual well system can produce geothermal energy effectively. Dual-well systems contain at least one injection well and one production well. They are composed of a two-way flow system in which the fluid flows into the reservoir via an injection well and returns from the production well having absorbed thermal energy from the surrounding rocks. Sensitivity analysis of the main parameters controlling the average outlet temperature of the fluid from the sedimentary geothermal system reveals that abandoned gas wells are a suitable source of geothermal energy. This energy can be harvested via a method whose use of reservoir fluids differs from that of the traditional method of closed-loop circulation via a borehole heat exchanger. Here, it is demonstrated that abandoned oil and gas fields can be repurposed to be geothermal energy sources that provide low-cost electricity and are economically sustainable.
Almost 98% of methane hydrate is stored in the seawater environment, the study of microscopic mechanism for methane hydrate dissociation on the sea floor is of great significance to the development ...of hydrate production, involving a three-phase coexistence system of seawater (3.5% NaCl) + hydrate + methane gas. The molecular dynamics method is used to simulate the hydrate dissociation process. The dissociation of hydrate system depends on diffusion of methane molecules from partially open cages and a layer by layer breakdown of the closed cages. The presence of liquid or gas phases adjacent to the hydrate has an effect on the rate of hydrate dissociation. At the beginning of dissociation process, hydrate layers that are in contact with liquid phase dissociated faster than layers adjacent to the gas phase. As the dissociation continues, the thickness of water film near the hydrate-liquid interface became larger than the hydrate-gas interface giving more resistance to the hydrate dissociation. Dissociation rate of hydrate layers adjacent to gas phase gradually exceeds the dissociation rate of layers adjacent to the liquid phase. The difficulty of methane diffusion in the hydrate-liquid side also brings about change in dissociation rate.
Isolated fractures usually exist in fractured media systems, where the capillary pressure in the fracture is lower than that of the matrix, causing the discrepancy in oil recoveries between fractured ...and non-fractured porous media. Experiments, analytical solutions and conventional simulation methods based on the continuum model approach are incompetent or insufficient in describing media containing isolated fractures. In this paper, the simulation of the counter-current imbibition in fractured media is based on the discrete-fracture model (DFM). The interlocking or arrangement of matrix and fracture system within the model resembles the traditional discrete fracture network model and the hybrid-mixed-finite-element method is employed to solve the associated equations. The Behbahani experimental data validates our simulation solution for consistency. The simulation results of the fractured media show that the isolated-fractures affect the imbibition in the matrix block. Moreover, the isolated fracture parameters such as fracture length and fracture location influence the trend of the recovery curves. Thus, the counter-current imbibition behavior of media with isolated fractures can be predicted using this method based on the discrete-fracture model.
•Heat mining form deep hot dry rock beneath the current oilfield at bongor basin, chad.•Utilizing carbon dioxide from diesel power plants into deep geothermal reservoirs for heat mining and CO2 ...sequestration.•Utilizing oilfield geothermal water from high water-cut oil wells into geothermal wells for heat mining.•Using infrastructures and facilities of oilfield reduces the cost of geothermal project implementation.
In this paper, the feasibility of power generation from an enhanced geothermal system (EGS) located beneath an oilfield at the Bongor basin in Chad was examined through the analysis of numerical simulation parameters. A 3D geometric model is constructed to represent the proposed EGS and a thermo-hydro-mechanical (THM) coupled mathematical model was used in the simulation process to link all inter-dependent parameters of heat mining. Oilfield warm water is anticipated to be the circulating fluid of the thermal reservoir due to its ready availability from high water-cut oil wells. Chad depends heavily on a diesel power plant, thus this work further proposes the utilization of carbon dioxide (CO2) from the power plants to be used as heat mining fluid and likely CO2 sequestration into deep granite formation. The results indicate that the implementation of EGS beneath the current oilfield would have significant advantages both technically, environmentally, and economically. Oilfield produced water at warm temperatures improved heat mining efficiency and utilization of oilfield water in geothermal wells will reduce costs involved in water treatment and disposal. The geothermal gradient is sufficient to produce water at a higher temperature that can be utilized commercially by different binary power plants. Utilizing CO2 as heat extraction fluid showed significant heat extraction, higher than using oilfield produced water. Furthermore, substantial amount of CO2 can be deposited into the formation, thus reducing emission of greenhouse gasses to the atmosphere.
Summary
The rise in global temperature due to an unceasingly increase in non‐condensable gases (NCG) prompts more development of safe and economical CCUS (Carbon Capture Utilization and Storage) ...technologies. Carbon dioxide (CO2) sequestration with heat mining in deep enhanced geothermal systems (EGSs) is one of the promising methods to reduce CO2 emitted to the atmosphere. In this study, a cyclic alternation of pressures at the injection and production wells is applied in an EGS for heat mining together with CO2 deposit. Simultaneous alternation of the injection and production pressures can significantly increase the amount of CO2 sequestrated compared to applying a fixed pumping or withdrawing pressures at the injector and producer respectively. At the injection well, alternation in pumping pressures at high frequency (small interval of days) increased CO2 sequestration rate. Reducing the pumping frequency resulted in the lowering of the total amount of CO2 sequestrated, lesser than using a fixed pumping pressure. The alternation in pumping frequency has a direct relationship to the CO2 sequestration rate. The frequency of the injection and production pressures refers to the interval in days of the interchange in pressure between high to a low value and vice‐versa. Furthermore, simultaneous alternation of pressures at the injection and production wells respectively (double cyclic method) improved geothermal heat extraction efficiency, thus higher performance for both geothermal and CO2 sequestration projects.
This paper showed that pressure alternation at the injection and/or production well improves the cumulative amounts of CO2 sequestration and heat mining rate. The frequency of pressure variation affects the extent of CO2 deposit. Pressure alternation at higher frequency had more potential in depositing large volumes of CO2 into the geothermal reservoir. Therefore the frequency of pressure alternation at the injector or producer wells is proportional to CO2 sequestration rates.
Summary
Hydraulic‐fracturing treatments have become an essential technology for the development of deep hot dry rocks (HDRs). The deep rock formation often contains natural fractures (NFs) at micro ...and macroscales. In the presence of the NF, the hydraulic‐fracturing process may form a complex fracture network caused by the interaction between hydraulic fractures and NF. In this study, analysis of carbon dioxide (CO2)‐based enhanced geothermal system (EGS) and water‐based EGS in complex fracture network was performed based on the thermo‐hydro‐mechanical (THM) coupling method, with various rock constitutive models. The complexity of the fracture geometry influences the fluid flow path and heat transfer efficiency of the thermal reservoir. Compared with CO2‐based EGS, water‐based EGS had an earlier thermal breakthrough with a rapid decline in production temperature. CO2 can easily gain heat rising its temperature thus reducing the effect of a premature thermal breakthrough. Both CO2‐based EGS and water‐based EGS are affected by in‐situ stress; the increase in stress ratio improved the fracture permeability but resulted in an early cold thermal breakthrough. When the same injection rate is applied to water‐based EGS and CO2‐based EGS, water‐based EGS displayed higher injection pressure buildup. Water‐based EGS had higher reservoir deformation area than CO2‐based EGS, and thermoelastic constitutive model for water‐based EGS showed larger deformed area ratio than thermo‐poroelastic rock model. Furthermore, higher values of rock modulus accelerated the reservoir deformation for water‐based EGS. This study established a novel discussion investigating the performance of CO2‐based EGS and water‐based EGS in a complex fractured reservoir. The findings from this study will help in deepening the understanding of the mechanisms involved when using CO2 or water as a working fluid in EGS.
This paper showed that water‐ based enhanced geothermal system (EGS) had significant injection pressure buildup and higher reservoir deformation due to the flow behavior and properties of water in the thermal reservoir. CO2‐based EGS had a delayed thermal breakthrough than water‐based EGS, CO2 can easily gain heat thus reducing the effect of a premature thermal breakthrough. The thermoelastic or thermo‐poroelastic constitutive models influence the level of simulated results and they should be applied in accordance to the rock mineral constituents.
Hot Dry Rock (HDR) is considered as one of the most promising energy to increase the supply of local and renewable energy to alleviate energy crisis for sustainable development. Fractures and ...fracture networks of HDR are the dominate channel for working fluid to transfer mass and heat, so a detailed description of fracture is critical to numerical simulation. The coupled THM governing equations are formulated as the mathematical model, based on the local thermal non-equilibrium theory. A core-scale 3D numerical model with a single idealized rough fracture is created. The distributions of pressure, temperature, stress and deformation were discussed. Sensitivity analysis was conducted to evaluate the influence of fracture roughness and aperture on the outlet temperature of the model.
•Injecting cold water above the CO2 injector through annulus and tubing respectively improves injection efficiency in water dominant geothermal resources.•CO2 geological storage combined with ...geothermal water recovery increases the efficiency of CO2 storage.•Increase in power output from coupling of well-bore flow to power generation.•Water injection prevents CO2 bubble formation during initial stages.
Recently more attention has been paid to CO2 geological storage combined with geothermal water recovery (CO2-EWR). In this regard, the production performance of a geothermal site in Huizhou Sag was evaluated. In the process of evaluation, a new technology in which cold water is injected through the tubing and CO2 through the annulus is used and simulated. In this study, a conceptual model was established by coupling the wellbore and the geothermal reservoir according to the field exploration data. The power production performance was evaluated by using the output from the wellbore-reservoir coupled simulation. The numerical simulation outputs showed a temperature difference of approximately 5.5°C from well bottom to wellhead at the beginning. The 3D-visualization of CO2 distribution demonstrates two steps of migration, vertical migration and horizontal spreading. It was also found that injecting water above CO2 plays a significant role in preventing rising of CO2 “bubble” in the early stages of injection process. The results of thermodynamic simulations suggests the desired thermal production efficiency and gross power output could be obtained. In addition, the impact of various parameters on simulation results were investigated and analyzed, the analysis results provided a better understanding of CO2-EWR (CO2 geological storage enhanced with geothermal resources recovery) technology as well as practical perforation depth of the wells.
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