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Collaborating Authors
Study on Heat Extraction Performance of 3D Enhanced Geothermal System with Faults Connected
Tang, Yijia (Engineering Technology Research Institute, PetroChina Southwest Oil & Gas Field Company / State Key Laboratory of Oil & Gas Reservoir Geology and Exploitation, Southwest Petroleum University) | Ma, Tianshou (State Key Laboratory of Oil & Gas Reservoir Geology and Exploitation, Southwest Petroleum University) | Guo, Jianhua (Engineering Technology Research Institute, PetroChina Southwest Oil & Gas Field Company) | Hu, Xihui (Engineering Technology Research Institute, PetroChina Southwest Oil & Gas Field Company) | Liu, Bo (Development Division, PetroChina Southwest Oil & Gas Field Company)
ABSTRACT: Enhanced geothermal system (EGS) is the major way to extract heat from impermeable hot dry rocks. As heat mining process in EGS is complex, effective numerical simulation method is required. Lots of EGS simulation models are proposed with different kinds of fracture system using discrete fracture network method or equivalent porous media method. However, the situation that EGS with faults connected have seldom investigated. Thus, a 3D geothermal heat extraction model connected with faults is established, and solved by the finite element method. The proposed numerical model is validated with single fracture heat extraction analytical model. The largest error between two models is 5.63%, which shows the efficiency of the proposed model. The effect of faults on heat extraction in EGS is studied. The results demonstrate that compared with the EGS disconnected with the fault, the EGS with fault get higher production temperature and poor production flow rate. The more faults there are, the more injected fluid is lost, resulting in lowest heat extraction performance. Thus, in hot dry rock heat mining engineering practice, hydraulic fracturing operations should avoid connect with faults to ensure much more injection fluid can be extracted. 1. INTRODUCTION With the energy crisis and environmental pollution problems more and more serious, increasing attention has been paid to the development of clean energy, especial for the hot dry rock (HDR) (Lund and Boyd, 2016). HDR is a kind of dense, high-thermal geothermal resource buried 3,000 meters underground. In China, the geothermal resource of HDR rock is about 7ร10 MWh, 2% of which can meet the requirement of energy consumption for 3,400 years (Zhu et al. 2015; Huang, 2014). Enhanced geothermal system (EGS) is developed to extract HDR geothermal resources. Typical EGS is composed of injection well, production well, and fracture network. The wells are connected through fracture network (Olasolo, 2016; Tang et al. 2020). The injected fluid extracts the heat though the fracture network and produces high thermal fluid from production well. The Fenton Hill EGS project in the United States was the worldโs first EGS site trial, proving the concept of EGS. France built the worldโs first EGS site for commercial application, namely the Soultz EGS site. The generation power reached 1.5MWe. Australia built the worldโs first EGS site from private company in Cooper Basin (Lu 2017). Other countries built EGS power stations after another. Unfortunately, most of them eventually shut down, because the fluid loss in the fracture network is dramatic, which is hard for commercial use (Kelkar et al. 2016). Therefore, it is very important to study the heat extraction mechanism of fluid in fracture network.
- Asia > China (1.00)
- North America > United States > New Mexico > Los Alamos County (0.24)
- North America > United States > Gulf of Mexico > Central GOM (0.24)
- Research Report > New Finding (0.34)
- Research Report > Experimental Study (0.34)
- Energy > Oil & Gas > Upstream (1.00)
- Energy > Renewable > Geothermal > Geothermal Resource > Hot Dry Rock (0.95)
- Energy > Renewable > Geothermal > Geothermal Resource for Power Generation > Enhanced Geothermal System (0.84)
- Oceania > Australia > South Australia > Cooper Basin (0.99)
- Oceania > Australia > Queensland > Cooper Basin (0.99)
- Asia > China > Sichuan > Sichuan Basin > Southwest Field > Longwangmiao Formation (0.99)
- Asia > China > Qinghai > Guide Basin (0.99)
ABSTRACT Geothermal process equipment is insulated to maximize energy extraction efficiency and to prevent heat loss to the environment. Insulated exterior metal surface may experience corrosion at elevated temperatures as a result of natural moisture ingress. Additionally, if brine leaks through valves, flanges or other connections, corrosion under insulation, CUI, may be exacerbated. Examples of CUI and corrosion mitigation efforts in the geothermal industry are provided. INTRODUCTION The primary purpose for using insulation in the geothermal industry is to mitigate heat losses in surface equipment and piping. A simplified schematic of a geothermal energy extraction facility is shown in Figure 1. After brine is separated from steam, it is injected back into the reservoir. The steam is then piped to the plant where it passes through a scrubber before entering the turbine, and is then condensed. Condensed steam is used in the cooling tower where roughly 75% of it evaporates, and the remainder is injected back into the reservoir. Geothermal water, brine and steam used at these facilities are often transported long distances in pipelines from wells to power plants. It is not uncommon for many kilometers of piping to be insulated at a geothermal field. For example, a Company geothermal field in Salak, Indonesia, with an installed capacity of 330 MWe and a land use area of 1.75 km2, uses more than 100 km of insulated piping and has about two dozen insulated vessels. In order to utilize steam efficiently and to prevent liquids from cooling so that scale deposits are minimized, piping, steam separation vessels, heat exchangers, steam scrubbers and other power plant equipment are typically insulated. Several types of insulation are employed at geothermal fields around the world, the most common being aluminum-clad perlite, aluminum-clad glass wool, cement-clad perlite, calcium silicate, glass wool and cements. Normally, internal corrosion is the major concern for the geothermal industry because of increasing fluid temperature and salinity. However, corrosion of external piping and vessels under insulation may also be significant at geothermal fields. The major culprits in external corrosion are moisture, temperature and leaking geothermal fluids. Although some geothermal fields are located in arid regions such as western North America, eastern Africa, and the Andes Mountains, the majority of fields are located in tropical regions or regions with significant amounts of rain and snowfall. The most common causes CUI in the geothermal industry include (1) moisture from rain or melting snow with inclusion of dissolved oxygen, (2) geothermal fluids migrating under or into insulation, and (3) damaged insulation and jacket materials. Moisture that penetrates or adsorbs through insulation can trigger external corrosion of steel substrate, especially when the source of moisture is brackish or briny geothermal fluids. Depending on the localized temperature, some geothermal piping may easily be corroded under wet insulation. Thermally insulated geothermal piping and vessels commonly have an operating temperature of 40ยฐC to 325ยฐC. At elevated temperatures, any moisture that penetrates or absorbs through insulation is usually vaporized before it reaches the steel surface. Note: This paper is specifically about CUI in the geothermal industry. For additional information about conditions that cause CUI in other industries and methods to mitigate this form of corrosion see a related article in Materials Performance.
- Geology > Structural Geology > Tectonics > Compressional Tectonics > Fold and Thrust Belt (0.54)
- Geology > Mineral (0.34)
Abstract Geothermal energy is the heat energy within the Earth, often manifested in geysers, hot springs and volcanoes. It offers an energy source that is far more efficient than fossil-fueled power generation, and it doesn't emit greenhouse gases into the air. Geothermal energy can therefore be very useful in generating electricity however; it currently plays a limited role in the electricity sector. Despite the many challenges to develop geothermal energy presently, future development can contribute significantly to a region's electricity portfolio, thereby decreasing customer costs of electricity, providing a potentially clean resource for power generation and creating a new resource economy. This paper evaluates the development opportunities for geothermal energy in the Caribbean with focus on main territories with potential geothermal resources. One of the main challenges to producing electricity from geothermal energy is the source of high temperature reservoirs near the Earth's surface. Such resources are rare since heat supply is normally encountered very deep in the earth's subsurface therefore resulting in many geothermal reservoirs being technologically or economically unfeasible to exploit. In the Caribbean, however there are high-temperature reservoirs that are located close enough to the Earth's surface, making them feasible to exploit and be potentially viable. The Lesser Antilles islands arc in the Caribbean have been largely built by volcanism above a subduction zone. As the Atlantic Plate is being sub-ducted under the Caribbean Plate, it gives rise to active volcanoes making for very attractive geothermal energy exploitation. The data from these estimated resources potential was used to determine development strategies for extracting thermal energy for power generation. The methodology can involve the use of technology from the oil and gas sector to explore for economically geothermal resources with sufficient high temperatures to warrant development. These include drilling exploration wells, development wells and evaluating reservoir potential. The analysis shows that development of geothermal energy in the Caribbean with a vast clean resource potential should clearly be considered given the future increases in demand for power generation in the region and the potential to become energy self-sufficient. The potentially lower cost of electricity generation from geothermal energy can mean significant savings for customers in the region. The various concepts, techniques, methods and technologies used in evaluating and drilling for hydrocarbon, can be successfully used in drilling exploration and development wells for producing thermal energy from the volcanic islands for electricity generation.
- Geology > Geological Subdiscipline > Volcanology (1.00)
- Geology > Structural Geology > Tectonics > Plate Tectonics (0.68)
- Geology > Structural Geology > Tectonics > Compressional Tectonics (0.55)
- Energy > Renewable > Geothermal > Geothermal Resource (1.00)
- Energy > Oil & Gas (1.00)
Energy recovery by in-place boiling was studied with a laboratory to model, of a fracture-stimulated geothermal reservoir that can be heated to 500 deg. F and to a pressure of 800 psig. An analytical mode to evaluate rock-energy extraction was developed and agreement between predicted results and experimental results was satisfactory. Introduction Geothermal resources used for electric power generation are hydrothermal systems that exist either as vapor- or liquid-dominated reservoirs. Although the latter type is believed to be more abundant, the extent of hydrothermal resources is considered small compared with hot, igneous rock resources that. do not spontaneously produce steam or hot water because of a lack of permeability, porosity, and fluid storage. Economic development of geothermal resources will require advanced technologies for enhanced recovery of energy from hydrothermal reservoirs and the introduction of artificial circulation systems for extracting energy from hot, igneous rock. Several fracture-stimulation techniques have been proposed, such as explosive fracturing, hydraulic fracturing, and thermal stress cracking. Smith et al. described a large-scale hydraulic fracturing experiment in hot, igneous rock where a closed circulation loop of surface water under high pressure is used to extract the thermal energy by convective heat transfer. A variation of that extraction scheme using multiple fractures was proposed by Grinparten and Witherspoon . Stimulation of geothermal reservoir by nuclear explosive fracturing was proposed by Carlson and Kennedy. Nuclear explosive stimulation of natural gas reservoirs has been demonstrated successfully on an experimental basis . Explosive stimulation of hydrothermal systems was discussed by Ramey et al. They showed that the total energy in a hydrothermal system consists of tie thermal energy stored in the rock and the thermal energy stored in the geothermal fluids. The ratio of the magnitudes of these two components depends principally on the rock porosity. Ramey et (11. also demonstrated that the amount of energy extractable from a hydrothermal system can be enhanced by operating the system nonisothermally (for example, by pressure reduction) so that boiling (flashing) takes place within the rock formation. Nonisothermal heat-transfer processes in fractured rock systems have not been studied experimentally. However, several laboratory experiments on nonisothermal flow in porous media have been conducted. The studies described in this paper were designed to explore(1) conditions for optimum energy extraction, (2) rock heat-transfer characteristics, (3) moving flash fronts, (4) fluid-withdrawal reservoir pressure behavior. (5) effects of cool and hot fluid recharge, and (6) cyclic production/recharge operation of fracture-stimulated production/recharge operation of fracture-stimulated systems. The experiments were carried out in a laboratory model using rock loadings with characteristics that resemble the highly fractured region of a fracture-stimulated hydrothermal reservoir. Experiments were conducted with two rock loadings of different porosities and mean rock sizes at pressures and temperatures found in geothermal reservoirs. The extent of fluid recharge was limited so that energy addition by fluid recharge was less than the energy extracted from the rock. Preliminary evaluations of the results were reported by Hunsbedt et al. and detailed results were reported by Hunsbedt. This paper highlights these results. JPT P. 940
- Energy > Oil & Gas > Upstream (1.00)
- Energy > Renewable > Geothermal > Geothermal Resource (0.74)
Abstract This work is intended to present an in-house coupled geomechanics and fluid-heat flow model and investigate the circulation performance when injecting cold water into a geothermal reservoir. To understand the dominant role of fractures with extremely high conductivities, played in heat energy extraction from geothermal reservoirs, the embedded discrete fracture model (EDFM) is employed to explicitly tackle these fractures. The matrix part is treated as elastic porous media, in which the fluid-heat flow and rock deformation are solved by a mixed finite volume and finite element method. This numerical approach is presented at length and is verified by an analytical solution. Subsequently, we investigate the performance of heat extraction via water circulation within a synthetic, connected fracture network. Numerical results demonstrate that for a prescribed fracture area, the injection rate should be chosen carefully to delay the breakthrough time and to better the performance of geothermal reservoirs. 1 Instruction To tap enormous heat stored in low permeability hot dry rocks (HDR), rock-fracturing technologies, e.g., hydraulic fracturing, were put forward to generate a fracture network, linking injection wells to production wells. This technology could artificially create geothermal reservoirs, i.e., enhanced geothermal systems (EGS). As a result, heat energy can be extracted from HDR through a circulation of a certain working fluid between injection wells (cold fluid) and production wells (hot fluid). How to improve the efficiency of heat development from EGS for power generation has become a great concern of engineers, managers, and stake holders of geothermal reservoirs. Numerical simulation could serve as a useful tool for evaluating the efficiency of different development schemes, so as to suggest an optimal one. Extraction of heat energy from EGS involves fluid flow, heat conduction and heat advection through fractures and porous rock matrix, and the deformation of fractures and matrix. Thus, simulation of fluid/heat circulation in EGS with fractured porous medium requires a coupled geomechanis and fluid-heat flow model, considering both fractures and matrix. The greatest challenge here lies in how to properly handle embedded fractures in hydraulic and mechanical aspects since they are featured as extremely high conductivity but very small thickness. A common scheme is the equivalent continuum approach [Li et al., 2016; Oda, 1986], in which the fractured rock is homogenized as an anisotropic, elastic porous medium with the equivalent elastic compliance and permeability tensors. This approach honors its simplicity and completeness in theory. However, high resolution grid must be utilized to capture certain sharp interface (e.g., the contaminant halo front of groundwater, and the chemical reaction front associated with acid fracturing, and the cooling front related to EGS), which can be computationally expensive. Multiscale methods are proposed to save simulation time, in which multiscale basis functions solved at a local scale are used to construct the missing degrees of freedom at an overall scale [Hou and Wu, 1997]. Dual-/multiple-continuum approach. An alternative is to treat fractures as lower-dimensional surfaces [Karimi-Fard et al., 2003]. Natural/hydraulic fractures are represented by embedded surfaces, either residing on borders of pre-existing matrix grids, e.g., discrete element model (DEM), or arbitrarily cutting those matrix blocks, i.e., embedded discrete fracture model (EDFM). The latter has become popular in petroleum engineering since it remains relatively high accuracy even with coarse grids. The EDFM is a generalized dual-permeability, dual-porosity model, in which three types of connections, i.e., fracture-fracture, fracture-matrix, and matrix-matrix connections, are built to characterize the fluid-heat exchange between fractures and matrix, allowing for irregular fracture-matrix contact and ununiform fracture distributions.
- Energy > Oil & Gas > Upstream (1.00)
- Energy > Renewable > Geothermal > Geothermal Resource (0.68)