my country provides favorable support for the development of the geothermal energy industry, so that the geothermal energy industry enters the fast lane of development. The two basic types of thermal storage in my country's deep geothermal development include traditional hydrothermal type and dry hot rock type. Traditional hydrothermal geothermal energy development related technologies have been mature. The current technical problem lies in the low natural recharge efficiency of sandstone thermal storage. Hot dry rock and natural gas hydrate are collectively referred to as important future energy sources. However, it is challenging to efficiently develop energy in hot dry rock. More than 30 demonstration projects have been carried out internationally, although hot dry rock heat has gradually accumulated However, due to the complexity and differences of geological conditions, the technical experience of a single project cannot be directly copied and applied to the next project, and the initial investment of the dry hot rock project is large, and the current economic efficiency is low , Resulting in slow progress in the development of hot dry rock.
Whether hot dry rock can be developed depends on the ability to build large-volume artificial heat storage (>1km3), which requires a large-scale fracture network to ensure a large-area heat exchange channel for long-term heat energy extraction and avoid heat recovery wells A premature thermal breakthrough has occurred and the heat recovery efficiency is reduced. The construction of a complex fracture network in deep wells (about >5000 meters), high temperature (>150°C) and high in-situ stress hard rock (ie granite) depends on the distribution of natural fractures in the formation before fracturing, ground temperature field, stress field and Rock physical properties and other characteristics and thermal storage excitation technology and excitation scheme.
The fracture system distribution and the reasonable characterization of the geothermal field in the dry hot rock reservoir before hydraulic fracturing will affect the propagation of fractures and the construction of fracture networks during thermal storage excitation. The Wuhan Institute of Rock and Soil Mechanics, Chinese Academy of Sciences combines multi-source data (including Seismic, logging, drilling, etc.) integrated geological modeling and parameter random inversion, and proposed a block-scale thermal storage prediction method with strong boundary constraints (Figure 1) to provide a geological model for the hydraulic fracturing of thermal storage.
In view of the fact that most of the existing hydraulic fracturing commercial software cannot realize the simulation of hydraulic fracture torsion, intersection and crossing in the presence of complex and different levels of natural fractures, based on the quasi-continuous medium theory, consider complex fracture network expansion, well-fracture-hole multiple For the physical processes of multiphase seepage of medium, heat and mass transfer, and heat-fluid-solid multi-field coupling response, researchers and Chongqing University have developed a three-dimensional numerical simulation of hydraulic fracture propagation based on the FLAC3D platform for multi-physical coupling of fractured rock masses The program can realize the numerical simulation of the torsion, intersection and crossing of hydraulic fractures in different levels of natural fractures and heterogeneous formations; the developed parallel computing program based on CPU and GPU heterogeneous, can realize the conditions of strong coupling of multi-physics The high-efficiency and accurate solution of numerical simulation calculation of the next million degrees of freedom has been applied to the two-dimensional and three-dimensional numerical simulation research of hydraulic fracturing reservoir reformation of hot dry rock and shale under the condition of complex natural fractures (Figure 2, Figure 3), to realize the simulation simulation of the rapid productivity evaluation of the hot dry rock hydraulic fracturing reservoir reconstruction effect (Figure 4).
In view of the difficulty of traditional single hydraulic fracturing technology to establish an effective fracture network in dry and hot rocks, the researchers proposed a combined thermal storage volume modification technology of alternating cold water thermal stimulation-matrix chemical stimulation-hydraulic fracturing, revealing the effects of thermal stimulation and chemical stimulation The damage mechanism of the microscopic damage of hot dry rock, thermal stimulation and matrix chemical stimulation can increase the permeability of hot dry rock by more than 5 orders of magnitude, and the mechanical strength has varying degrees of damage (Figure 5). In terms of the compound stimulation process, first alternately cyclically injected cold water to stimulate thermal fractures around the fracturing well section, inject soil acid at low temperature for acidification stimulation to expand the micro-rupture area, and then carry out high-pressure hydraulic fracturing to form main fractures and fractures. In the secondary fracture zone, further long-term low-pressure hydraulic fracturing is carried out to increase the stimulation fractures and micro-fracture channels. At present, the hot dry rock composite heat storage stimulation process is in the laboratory research and development stage, and the next step researchers will carry out experimental research on the site.
Related research results have been published in Geothermal Energy and Journal of Rock Mechanics and Geotechnical Engineering, etc. Liu Hejuan, associate researcher of Wuhan Institute of Geotechnical Engineering, is the first author of the paper.
Figure 1. Comparison of thermal simulation and measured data of thermal reservoirs with complex fractures at block scale under different bottom boundary constraints
Figure 2. Two-dimensional fracture network produced by different hydraulic fracturing methods in rock mass with natural fractures
Figure 3. The influence of the in-situ stress in the rock mass with natural fractures on the shape of the three-dimensional fracture network formed by hydraulic fracturing
Figure 4. Geothermal mining temperature field changes of the fracture network system formed by different hydraulic fracturing reforms
Figure 5. Characteristics of permeability change and mechanical strength damage of hot dry rock caused by thermal and chemical stimulation
Led Strip Lights,Led Phyto Lamp Strip Light,Led Plant Grow Strip Lights,Led Light Strips Non-Waterproof
Shenzhen You&My Electronic Technology Co., Ltd , https://www.szyoumy.com