Anisotropy characterization of the elasticity and energy flow of Longmaxi shale under uniaxial compression

He, Rui; Ren, Li; Zhang, Ru; Zhu, Zhixue; X, Sun

doi:10.1016/j.egyr.2021.12.050

Cited by 23 publications

(9 citation statements)

References 75 publications

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“…To overcome the limitations of the empirical crack initiation stress threshold, He et al [6] proposed an iterative method that synchronously determines the elastic parameters and the crack initiation stress, based on the work of [31]. The iterative method determines the elastic parameters and crack initiation stress step by step over a stress range from 0.01% of the lateral strain to a variable upper limit stress, and the detailed procedure is shown in Figure 2.…”

Section: (B) Iterative Methodsmentioning

confidence: 99%

“…Since shale reservoirs have extremely low porosity and permeability [4], hydraulic fracturing treatment has been widely used to produce stimulated reservoir volume (SRV) [5]. From a rock mechanics perspective, both deformation and failure of shale formations occur during SRV treatments, and one of the challenges to the effective implementation and evaluation of SRV treatments is the currently incomplete understanding of the mechanical behavior of shale [6]. Detailed mechanical characterization of shales is essential for hydraulic fracturing stimulation design; specifically, to better predict and mitigate fracture closure after stimulation [7,8].…”

Section: Introductionmentioning

confidence: 99%

“…Different experimental techniques have been applied in evaluating the characteristic stresses of shale gas reservoirs, including uniaxial and triaxial compressions. For example, He et al [6] performed several uniaxial compression experiments on Longmaxi shale samples with different bedding plane orientations, and the results showed that with an increase in the bedding plane angle, the crack initiation stress decreases and then increases. Concerning the in situ stress state, Li et al [25] performed triaxial tests on shale samples with seven different bedding plane orientations (0 • , 15 , 75 • and 90 • ).…”

Section: Introductionmentioning

confidence: 99%

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Elasticity and Characteristic Stress Thresholds of Shale under Deep In Situ Geological Conditions

Nie,

Fan,

Zhou

et al. 2023

Materials

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The mechanical properties of shale are generally influenced by in situ geological conditions. However, the understanding of the effects of in situ geological conditions on the mechanical properties of shale is still immature. To address this problem, this paper provides insight into the elasticity and characteristic stress thresholds (i.e., the crack closure stress σcc, crack initiation stress σci, and crack damage stress σcd) of shales with differently oriented bedding planes under deep in situ geological conditions. To accurately determine the elastic parameters and crack closure and initiation thresholds, a new method—i.e., the bidirectional iterative approximation (BIA) method—which iteratively approaches the upper and lower limit stresses of the linear elastic stress-strain regime, was proposed. Several triaxial compression experiments were performed on Longmaxi shale samples under coupled in situ stress and temperature conditions reflecting depths of 2000 and 4000 m in the study area. The results showed that the peak deviatoric stress (σp) of shale samples with the same bedding plane orientation increases as depth increases from 2000 m to 4000 m. In addition, the elastic modulus of the shale studied is more influenced by bedding plane orientation than by burial depth. However, the Poisson’s ratios of the studied shale samples are very similar, indicating that for the studied depth conditions, the Poisson’s ratio is not influenced by the geological conditions and bedding plane orientation. For the shale samples with the two typical bedding plane orientations tested (i.e., perpendicular and parallel to the axial loading direction) under 2000 and 4000 m geological conditions, the ratio of crack closure stress to peak deviatoric stress (σcc/σp) ranges from 24.83% to 25.16%, and the ratio of crack initiation stress to peak deviatoric stress (σci/σp) ranges from 34.78% to 38.23%, indicating that the σcc/σp and σci/σp ratios do not change much, and are less affected by the bedding plane orientation and depth conditions studied. Furthermore, as the in situ depth increases from 2000 m to 4000 m, the increase in σcd is significantly greater than that of σcc and σci, indicating that σcd is more sensitive to changes in depth, and that the increase in depth has an obvious inhibitory effect on crack extension. The expected experimental results will provide the background for further constitutive modeling and numerical analysis of the shale gas reservoirs.

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Section: (B) Iterative Methodsmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

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Elasticity and Characteristic Stress Thresholds of Shale under Deep In Situ Geological Conditions

Nie,

Fan,

Zhou

et al. 2023

Materials

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“…To investigate the influence of hole size and crack length on f for the HDWS specimen, the inner hole size r of the circular ring was set to four levels, i.e., 2.5 mm, 5.0 mm, 7.5 mm, and 10 mm; and the crack length a was set to seven levels, i.e., 2.5 mm, 5.0. mm, 7.5 mm, 10.0 mm, 12.5 mm, 15.0 mm, and 17.5 mm. With reference to the elastic parameter tests of the Longmaxi shale by Rui He et al [33], the elastic parameters of the shale were set as follows: E = 24.91 GPa, v = 0.166, v = 0.253, and G = 6.21 GPa. The physical property parameters of rock vary across different areas or different depths [34,35].…”

Section: Procedures For the Numerical Calibration Of Fmentioning

confidence: 99%

“…The specimens tested in the experiment were collected from the Longmaxi shale outcrop in Chongqing, China, and have a density of 2.66 g/cm 3 . Through a series of uniaxial compression experiments, the five elastic parameters, E, E , G , v, and v , were measured to be 24.91 GPa, 20.87 GPa, 10.68 GPa, 0.166, and 0.212, respectively [33]. The shale was processed into HDWS specimens, each with an outer radius R of 25 mm, a hole radius r of 2.5 mm, prefabricated cracks of length a of 4 mm on both sides, and a height h of 100 mm.…”

Section: Hydraulic Fracturing Experiments Of Hdws Specimensmentioning

confidence: 99%

Fracture Toughness Testing of Brittle Laminated Geomaterials Using Hollow Double-Wing Slotted Specimens

Yao,

Fan,

Zhou

et al. 2023

Materials

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The fracture toughness of shale is a key parameter guiding hydraulic fracturing design and optimization. The hollow double-wing slotted (HDWS) specimen is a typical specimen configuration for measuring the mode I fracture toughness of rock. The calibration of the shape factor (f) is the basis for accurately obtaining the fracture toughness of rocks. In this study, the influences of crack length, hole size, and the anisotropy of elastic parameters on f for specimens with three typical bedding orientations—arrester (A), divider (D), and short-transverse (ST) orientations—are systematically investigated using finite element software. The numerical simulation results support the following findings. The mode I f increases monotonically with an increase in hole size. The influence of crack length on f varies depending on hole sizes. Under different bedding orientations, significant anisotropy in f was observed. In addition, the degree of anisotropy in Young’s modulus has a major impact on f, which is related to the bedding orientation of the specimen. The apparent shear modulus ratio has relatively little influence on f. As the hole size and crack length increase, the influence of the anisotropy of elastic parameters on f increases. Based on numerical calculations, hydraulic fracturing experiments were conducted on HDWS specimens of Longmaxi shale with three bedding orientations, and the results showed that the peak pressure and fracture toughness of the samples in the ST direction were the lowest, while those in the A direction were the highest.

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Progressive Failure Characterization of Sandstone from Yingjinshan Area in Qinghai-Tibet Plateau

et al. 2022

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Anisotropy characterization of the elasticity and energy flow of Longmaxi shale under uniaxial compression

Cited by 23 publications

References 75 publications

Elasticity and Characteristic Stress Thresholds of Shale under Deep In Situ Geological Conditions

Elasticity and Characteristic Stress Thresholds of Shale under Deep In Situ Geological Conditions

Fracture Toughness Testing of Brittle Laminated Geomaterials Using Hollow Double-Wing Slotted Specimens

Progressive Failure Characterization of Sandstone from Yingjinshan Area in Qinghai-Tibet Plateau

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