Structural Characterization and Hydraulic Fracturing Responses of Deep-Buried Geomaterials

Dear Colleagues,

After hundreds of years of exploitation, the more accessible shallow resources and energy are being depleted, and some have now been completely exhausted. This means that the economic exploitation of more of the earth’s deeper resources and energy is now required in order to meet society’s growing demand for resources and energy. In addition, due to the requirements of energy conservation and environmental protection, unconventional energy sources such as oil, gas, and geothermal in deep reservoirs have become the focus of current and future development and utilization. Deep reservoirs are mostly buried within 1500−4000 m, while some tight sandstone, shale, and hot dry rock reservoirs are buried over 5000 m or even nearly 10000 m. Deep geomaterials have the characteristics of deep burial, complex pore structure, and low porosity and permeability. Hydraulic fracturing technology is the main means to increase the permeability and productivity of low-permeability reservoirs. In the process of deep-hole hydraulic fracturing, the fracture mechanism of low-permeability rock mass is very complicated due to many factors, such as the properties and occurrence environment of the rock mass, the properties of fracture fluid, flow characteristics, the interaction between the rock mass and the fluid, and phase change. Moreover, the deep in situ stress state is very complex, and the lack of accurate and effective on-site monitoring means makes it impossible to directly observe the hydraulic fracturing effect in deep geomaterials. Hence, it is of great significance to clarify and master the structure characteristics and hydraulic fracturing responses of deep geological materials for hydraulic fracturing mining design, reservoir reconstruction, and improving the recovery ratio of resources and energy. This Special Issue aims to build a broad platform for global scholars to report, exchange, and discuss their ideas, conclusions, and insights regarding the structural characterization and hydraulic fracturing responses of deep geomaterials in engineering practice and Earth science research. We encourage the scholars to reveal and interpret the possible structure characteristics, mechanical properties, and hydraulic fracturing behaviors for deep geomaterials from macro-, meso-, and microscales. The characteristics include but are not limited to the pore structure characterization, permeability characteristics, crack initiation and propagation criteria, mathematical and mechanical models, in situ stress prediction methods, and electromagnetic–acoustic–optical characteristics for deep geomaterials are expected to be explored. Reviews, experimental and numerical work, as well as in situ research, are all welcome for consideration. Potential topics include but are not limited to the following themes:

• Structural characterization methods/techniques for deep geomaterials;
• Hydraulic fracturing tests of large-scale deep geomaterials under true triaxial conditions;
• Impacts of pressurization rate on the mechanical behaviors of deep geomaterials;
• Macroscopic and microscopic observations of hydraulic pressure crack initiation and propagation during hydraulic fracturing;
• Influences of high temperature and high pore pressure on the hydraulic fracturing process;
• Application of non-destructive inspections in failure prediction of deep geomaterials during hydraulic fracturing;
• Impacts of crustal stresses on fracture pressure and hydraulic fracture;
• Chemical reagent tracking in the hydraulic fracturing process;
• Failure criterion for hydraulic fracturing in deep geomaterials;
• Numerical simulation of internal structural changes in deep geomaterials during hydraulic fracturing;
• Numerical modeling for deep geomaterials during hydraulic fracturing;
• Fault reactivation and earthquake mechanisms induced by hydraulic fracturing;
• In situ stress prediction model of hydraulic fracturing in deep geomaterials;
• New development of hydraulic fracturing technique for in situ stress measurement at great depths;
• New theories and equipment for on-site hydraulic fracturing tests.

Dr. Peng Li
Dr. Zhengyang Song
Dr. Mostafa Gorjian
Topic Editors