Experimental Investigation of the Influence of Bedding Planes and Differential Stress on Microcrack Propagation in Shale Using X-Ray CT Scan

Gupta, Neel; Mishra, Brijes

doi:10.1007/s10706-020-01487-z

Cited by 8 publications

(4 citation statements)

References 49 publications

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“…Noting equation (12) in the form of separate volumetric and shear parts, and the relationships between the octahedral stresses and strains (19), (20), the material constants in the Burger's model can be relatively easily determined based on the estimation of non-linear parameters of the equation, using for example Statistica software (Statistica v 13.3, Tibco Software Inc., Palo Alto, CA, USA) [44].…”

Section: Theoretical Basics Of Rock Rheology In Triaxial Test Conditi...mentioning

confidence: 99%

“…Gas shales are specific heterogeneous rocks [8][9][10], with a larger or smaller anisotropy [11][12][13]. Their rheological features have been analyzed with regard to the selection of the creep model [14,15], the influence of the mineral composition on creep [16,17], and the possibility of applying micro-indentation [18][19][20] to determine the rheological properties in shales. Due to the relatively complex description and complexity of tests, anisotropic creep of shales has been rarely studied [21].…”

Section: Introductionmentioning

confidence: 99%

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Viscoelastic Strains of Palaeozoic Shales under the Burger’s Model Description

Wilczynski,

Cieslik,

Domonik

et al. 2023

Applied Sciences

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This article presents the results of creep studies of Palaeozoic shales from the Baltic Basin in which the exploitation of shale gas in Poland was planned. Knowledge of instantaneous and long-term properties investigated in triaxial stress conditions is important from the point of view of exploitation techniques related to hydraulic fracturing. Rheological phenomena also play an important role in the analysis of the initial stress in shales, the knowledge of which is indispensable in the hydraulic fracturing process. The tests were carried out on samples representing four siltstone–claystone lithostratigraphic units occurring in the Baltic Basin. The studies and analyses were aimed at determining the character of creep in shales, selection of the appropriate rheological model for the analyzed rocks, and determination of the threshold of the linear creep under triaxial compression conditions. An original approach together with analysis results are presented here, which enable the separation and monitoring of shear and volume creep effects, and on this basis, the determination of the significance of the contribution of volume creep in the entire creep process. A relatively simple methodology for determination of the parameters of the Burgers model using this division is presented. The original value of the article is also due to the test results themselves and the parameter values of the analyzed model for triaxial creep of shales, which are not numerous in the literature. The investigations were performed at various loading levels in relation to the triaxial strength of the shales. Depending on the load, at its low values up to 0.7 (σ1 − σ3)max, creep had a determined character and did not show features of progressive creep. The linear creep threshold was also analyzed in this range. The loading level of 0.7 (σ1 − σ3)max was the limit of linear creep. Exceeding this load resulted in the loss of the linear character of creep, which in consequence lead to the subsequent third creep phase ending with rock damage. Parameters of the Burger’s model for gas shales from the Baltic Basin (northern Poland) were identified. There are significant differences in the behavior of shales depending on the lithostratigraphic unit from which the samples were collected. The mineral composition of the shales also influenced their behavior.

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Section: Theoretical Basics Of Rock Rheology In Triaxial Test Conditi...mentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Viscoelastic Strains of Palaeozoic Shales under the Burger’s Model Description

Wilczynski,

Cieslik,

Domonik

et al. 2023

Applied Sciences

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“…The rapid development of technologies for enhanced petroleum production has led to the continuous need for and improvement of pore structure testing methods for shale reservoirs. Overall, shale pore structure testing methods can be divided into two categories, comprising direct observation methods, such as field emission-scanning electron microscopy (FE-SEM) [12,13], computed tomography (CT) [14,15], broad ion-beam scanning electron microscopy (BIB-SEM), and focused ion-beam SEM (FIB-SEM) techniques to analyze the pore networks [16,17], and fluid introduction techniques such as low-temperature gas (N 2 or CO 2 ) physisorption, mercury intrusion porosimetry (MIP) [18,19], nuclear magnetic resonance (NMR) [20], small-angle neutron scattering (SANS) [21,22], and synchrotronsourced small-angle X-ray scattering (SAXS) [23]. Each characterization method can obtain pore structure information within a specific size of scale, due to differences in its principles or data-interpretation models.…”

Section: Introductionmentioning

confidence: 99%

Experimental Studies on Pore Structure and the Gas Content Evolution Mechanisms of Shale Gas Reservoirs at Different Burial Depths in the Longmaxi Formation, Southern Sichuan Basin

Fu,

Zhang,

Jiang

et al. 2023

Applied Sciences

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Micro- and nano-scale pores develop in shale reservoirs, and the associated pore structure controls the occurrence state, gas content, seepage capacity, and micro-migration and accumulation mechanisms of shale gas. For this study, we mainly conducted tests, using field emission-scanning electron microscopy, of the isothermal methane adsorption of powder-sized samples under high temperatures (60–130 °C) and pressures (0–45 MPa), along with methane-saturated nuclear magnetic resonance tests of plug-sized samples under different temperatures (60–100 °C) and pressures (0–35 MPa). These samples were from Longmaxi shale cores from strata at different burial depths from the Zhaotong, Weiyuan, and Luzhou areas. As the burial depth increases, organic pores transform from complex networks to relatively isolated and circular pore-like structures, and the proportion of organic matter-hosted pores increases from 25.0% to 61.2%. The pore size is influenced by the pressure difference inside and outside the pores, as well as the surface tension of organic matter in situ. As the burial depth increases to 4200 m, the main peak of the pore size first increases from 5–30 nm to 200–400 nm and then decreases to 50–200 nm. This work establishes an NMR method of saturated methane on plug-sized samples to test the free gas content and develop a prediction model of shale reservoirs at different burial depths. The gas content of a shale reservoir is influenced by both burial depths and pore structure. When the burial depth of the shale gas reservoir is less than 2000 m, inorganic pores and microfractures develop, and the self-sealing ability of the reservoir in terms of retaining shale gas is weak, resulting in low gas content. However, due to the small pore size of organic pores and the low formation temperature, the content of adsorbed gas increases, accounting for up to 60%. As the burial depth increases, the free gas and total gas content increase; at 4500 m, the total gas content of shale reservoirs is 18.9 m3/t, and the proportion of free gas can be as high as 80%. The total gas content predicted by our method is consistent with the results of the pressure-holding coring technique, which is about twice our original understanding of gas content, greatly enhancing our confidence in the possibility of accelerating the exploration and development of deep shale gas.

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“…The results demonstrate a strong correlation between the stress-strain curve, permeability-axial strain curve, and the acoustic emission activity mode under unloading conditions. Gupta et al [19] examined shale deformation using various stress paths, highlighting the significant influence of stress level and bedding plane orientation on microcrack geometry. Additionally, Dai and Zhang et al [20,21] showed that the strain increment is significantly influenced by the unloading path, whereas the unloading rate of the confining pressure is comparatively less affected.…”

Section: Introductionmentioning

confidence: 99%

Study on the Strength and Failure Characteristics of Silty Mudstone Using Different Unloading Paths

Wang

Zhang

et al. 2023

Materials

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To investigate the strength and failure characteristics of silty mudstone using different stress paths, silt-like mudstone specimens were subjected to triaxial unloading tests. The results indicate the following. (1) When subjected to equivalent initial deviator stress levels and differing confining pressures, the peak stress, residual stress, and elastic modulus, exhibited during unloading, increased concordantly with greater initial confining pressure. Both the peak strain and residual strain increased with rising initial confining pressure. The increase in peak strain and residual strain initially decelerated, then noticeably increased, before ultimately decreasing again. Additionally, the unloading failure time and strain rate demonstrated a negative correlation as the confining pressure increased. (2) Under different initial deviatoric stress conditions, the peak stress, residual stress, and residual strain, under unloading confining pressure conditions, decreased as the initial deviatoric stress levels elevated. Conversely, the peak strain and elastic modulus initially increased, then decreased under increasing initial deviatoric stress conditions. The unloading failure time and strain rate were both observed to decrease as the initial deviatoric stress levels increased. (3) Utilizing the Mohr stress circle enabled the characterization of the shear strength variation in the specimens during the unloading process. The cohesion and internal friction angle remained relatively consistent across the different unloading stress paths appraised, with cohesion being greater in path I versus path II, whereas the internal friction angle exhibited an inverse relationship. (4) The specimen failed during unloading due to lateral expansion caused by unloading confining pressure and collapse failure. The failure fracture surfaces predominantly manifested shear failure morphologies.

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Experimental Investigation of the Influence of Bedding Planes and Differential Stress on Microcrack Propagation in Shale Using X-Ray CT Scan

Cited by 8 publications

References 49 publications

Viscoelastic Strains of Palaeozoic Shales under the Burger’s Model Description

Viscoelastic Strains of Palaeozoic Shales under the Burger’s Model Description

Experimental Studies on Pore Structure and the Gas Content Evolution Mechanisms of Shale Gas Reservoirs at Different Burial Depths in the Longmaxi Formation, Southern Sichuan Basin

Study on the Strength and Failure Characteristics of Silty Mudstone Using Different Unloading Paths

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