Numerical model on predicting hydraulic fracture propagation in low-permeability sandstone

To study the influence of osmotic pressure on the uniaxial compression mechanical properties of limestone, uniaxial compression tests were carried out on limestone specimens under different osmotic water pressure. The test results show that with the increase of osmotic pressure, the closure strain, yield strain and peak strain of limestone gradually increase, while the closure stress, yield stress, peak stress and elastic modulus gradually decrease. To describe the stress-strain response of limestone during uniaxial compression failure, the concepts of compaction factor and osmotic pressure influencing factor were proposed, and a constitutive model of rock compaction stage was established by integrating the relationship between the compaction factor and osmotic pressure influencing factor and the tangent modulus of compaction section. On this basis, combining the continuum damage mechanics theory, and assuming that the rock micro-unit strength obeys the compound power function distribution, a constitutive model reflecting the uniaxial compression mechanical properties of rock under osmotic pressure was established by the statistical method. The rationality of the model was verified using the results of the uniaxial compression test of limestone under different osmotic pressures. The results show that the test results under different osmotic pressures are in good agreement with the theoretical curves, and the model in this paper can reflect the stress-strain response of limestone before its failure under different osmotic pressures.

Section: Test Results and Analysismentioning

confidence: 99%

Uniaxial compression mechanical properties and damage constitutive model of limestone under osmotic pressure

Song

Wang

et al. 2021

“…Additionally, there are some true triaxial fracturing experiments in laboratory experiments, which mainly study the propagation behaviour of hydraulic fractures (HFs) under different geological or engineering factors (Hou et al, 2014;Jia et al, 2021;Liang et al, 2015) and the interaction between HFs and weak planes such as bedding planes (BPs) or natural fractures (NFs) during HF propagation process (Guo et al, 2014;Norris et al, 2015;Shi et al, 2021). Guo et al (2014) carried out a hydraulic fracturing simulation experiment of a true triaxial horizontal well for a large-scale shale outcrop for the first time.…”

Section: Introductionmentioning

confidence: 99%

Numerical simulation on hydraulic fracture propagation in laminated shale based on thermo-hydro-mechanical-damage coupling model

Zhang

Guo

et al. 2023

The temperature of a deep shale reservoir may reach more than 100°C, and the effect of thermal shock on shale hydraulic fracturing has rarely not been considered in previous studies. Based on mesoscopic damage mechanics and the finite element method, a thermo-hydro-mechanical-damage (THMD) coupling model considering temperature, seepage, stress, and damage fields was constructed to investigate the effects of reservoir temperature, convective heat transfer coefficient ( h), in-situ stress difference and bedding plane angle ( αθ) on shale hydraulic fracturing. The results show that multiple hydraulic fractures (HFs) can occur under thermal shock and that HFs control the distribution of seepage, temperature, and stress fields. Reservoir temperature, in-situ stress difference and αθ are primary factors affecting hydraulic fracturing, whereas h is a secondary factor. When the reservoir temperature rises from 50°C to 150°C, the initiation and breakdown pressures decrease by 65.5% and 16.7%, respectively. HFs cross the bedding plane more easily, and fracture complexity is obviously enhanced. A higher h is favourable for slightly reducing the initiation and breakdown pressures, but it has little influence on the fracture complexity. Once the in-situ stress difference is low, there is a high fracture complexity, but HFs are more easily captured by bedding planes to limit the propagation of fracture height. When the in-situ stress difference is high, HFs are more likely to form bi-wing fractures. Whether αθ is too large or small, it is not conducive to improving the fracture complexity. In this study, when αθ is 30°, HFs and bedding planes intersect to form a fracture network. Essentially, thermal shock plays a key role in reducing the initiation pressure and forming multiple HFs during the fracturing process, and fracture propagation mainly depends on the injection pressure. The results can serve as reasonable suggestions for the optimization of shale hydraulic fracturing.

“…Wang et al (2013) investigated the evolution of permeability of intact coal samples under triaxial compression and proposed a process-based model for the instability of bursting underground coal seams. Some researchers have analyzed the effect of stress conditions on the hydrodynamic properties of different rocks uner triaxial compression tests (Liu et al, 2019;Shi et al, 2020;Wang et al, 2015). Xu et al (2018) investigated the permeability stress-sensitive behavior of sandstones and analyzed the relation of permeability and effective stress.…”

Section: Introductionmentioning

confidence: 99%

Hydro-mechanical coupling characteristics and damage constitutive model of low-permeability granite under triaxial compression

Zheng

Wang

et al. 2022

To investigate the effect of hydro-mechanical coupling characteristic in low-permeability hard rocks during the excavation of groundwater-sealed energy cavern and hydraulic engineering tunnels or chambers, triaxial compression tests were conducted on engineering granite under different confining and seepage pressures. The mechanical properties, such as the strength and deformation parameters, of granite under hydro-mechanical coupling condition were studied. The permeability of the granite under different stresses first decreases, then stabilizes, and then increases significantly until the final abrupt change, and the inflection point of the abrupt change in permeability tends to be in advance as the confining pressure increases or the seepage pressure decreases. Based on the statistical damage theory and test result, combined with the Mogi-Coulomb strength criterion, a hydro-mechanical coupling statistical damage constitutive model that considers the rock damage threshold and the initial compaction effect was proposed, and the proposed mechanical model was verified based on the test results under different confining and seepage pressures. The proposed mechanical model was further applied to predict permeability catastrophes during rock fracturing and achieves good results. This study provides a theoretical basis for the prevention and control of hydro-mechanical coupled disasters in rock engineering.