Complex deformation of naturally fractured rocks

Mokhtari, Mehdi; Nath, Fatick; Hayatdavoudi, A.; Nizamutdinov, Rustam; Jiang, Shanhe; Rizvi, Hashim R.

doi:10.1016/j.petrol.2019.106410

Cited by 12 publications

(3 citation statements)

References 38 publications

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“…Renshaw et al [18] and Gu et al [19], respectively, established criteria for judging under what circumstances HFs could cross NFs on the basis of the stresses near a fracture tip in linear elastic fracture mechanics. In addition, test experiments for analyzing HF-NF interaction have also been extensively studied, including semi-circular bending (SCB) [20,21], central straight notched Brazilian discs (CSNBDs) [22] and Brazilian tests [23].…”

Section: Introductionmentioning

confidence: 99%

Experimental Investigation into the Process of Hydraulic Fracture Propagation and the Response of Acoustic Emissions in Fracture–Cavity Carbonate Reservoirs

Yang,

Wang,

et al. 2024

Processes

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Fracture–cavity carbonate reservoirs account for a considerable proportion of oil and gas resources. Because of the complicated relationships between cavities, fractures and pores in these reservoirs, which are defined as cavity clusters, fracturing technology is employed to enhance their hydrocarbon productivity. However, almost all previous studies have just considered the effect of a single natural cavity or fracture on the propagation of a hydraulic fracture; therefore, the mechanism by which a hydraulic fracture interacts with a cavity cluster needs to be clarified. In this study, cavity clusters with different distributions were accurately prefabricated in synthetically made samples, and large-scale simulation equipment was employed to systematically perform fracturing experiments considering different horizontal differential stress levels. Meanwhile, the hydraulic fracture propagation behaviors were comprehensively analyzed through fracture morphology, fracturing curves, the complexity of the fracture network and acoustic emission monitoring. It was found that a natural fracture with a smaller approach angle is favorable in guiding a hydraulic fracture to a cavity. The fracturing curves were divided into the following four types: frequent fluctuations with “step-like” shapes, great fluctuations with slightly lower closure pressure, fluctuations with obviously lower closure pressure, and little fluctuations with obviously lower closure pressure. And different cavity cluster distributions play a dominant role in the complexity of generated hydraulic fracture networks. In addition, AE energy was used to judge the ease of crossing the cavity. The above findings indicated that for the actual exploration and exploitation of carbonate reservoirs, the geological exploration of different fracture–cavity structures in reservoirs would be required, and targeted fracturing engineering designs need to be carried out for different fracture–cavity carbonate reservoirs.

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Section: Introductionmentioning

confidence: 99%

Experimental Investigation into the Process of Hydraulic Fracture Propagation and the Response of Acoustic Emissions in Fracture–Cavity Carbonate Reservoirs

Yang,

Wang,

et al. 2024

Processes

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“…Natural fractures in low-permeability sandstone reservoirs may significantly affect the propagation of hydraulic fractures (Mokhtari et al., 2019). Extra leak-off and a reduction in propped fracture length are avoided as far as possible in petroleum and coal-bed methane exploitation (Olajossy and Cieślik, 2019).…”

Section: Introductionmentioning

confidence: 99%

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

Shi

Zhang

et al. 2020

International Journal of Damage Mechanics

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Hydraulic fracture propagation is hard to predict due to natural joints and crustal stress. This process may lead to uncontrollable changes in hydrogeological conditions. Therefore, prediction and control of fracture propagation are paramount to permeability increase in ore-bearing reservoir. The coupled fluid-solid model was utilized to predict the hydraulic fracture propagation in low-permeability sandstone of a uranium mine. For this study, the model was modified to allow fractures to propagate randomly by using the cohesive zone method. The simulation was developed on a three-step process. First, geological data required to run the model, including crustal stress, strength and permeability, were assembled. Next, fracture propagation under different conditions of stress and injection volume were simulated. In the final step, experimental data required to validate the model were obtained. The simulation results indicate that the principal stress, distribution and orientation of natural fracture have vital influence on fracture propagation and induced complex fracture network. This work provides a theoretical basis for the application of hydraulic fracture in low-permeability sandstone reservoir and ensures the possibility to predict the generation of complex fracture network.

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“…Mokhtari et al [22] applied this method to characterize the fracture initiation and propagation on naturally fractured rock. Similarly, application of DIC was extended to characterize the deformation behaviors in sandstone and carbonates rocks [29,30], laminated shale [23,31], Buda limestone [32], and Mancos shale [33].…”

Section: Introductionmentioning

confidence: 99%

Analyzing the Validity of Brazilian Testing Using Digital Image Correlation and Numerical Simulation Techniques

et al. 2020

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Characterizing the mechanical behavior of rocks plays a crucial role to optimize the fracturing process in unconventional reservoirs. However, due to the intrinsic anisotropy and heterogeneity in unconventional resources, fracture process prediction remains the most significant challenge for sustainable and economic hydrocarbon production. During the deformation tracking under compression, deploying conventional methods (strain gauge, extensometer, etc.) is insufficient to measure the deformation since the physical attachment of the device is restricted to the size of the sample, monitoring limited point-wise deformation, producing difficulties in data retrieval, and a tendency to lose track in failure points, etc. Where conventional methods are limited, the application of digital image correlation (DIC) provides detailed and additional information of strain evolution and fracture patterns under loading. DIC is an image-based optical method that records an object with a camera and monitors the random contrast speckle pattern painted on the facing surface of the specimen. To overcome the existing limitations, this paper presents numerical modeling of Brazilian disc tests under quasi-static conditions to understand the full-field deformation behaviors and finally, it is validated by DIC. As the direct tensile test has limitations in sample preparation and test execution, the Brazilian testing principle is commonly used to evaluate indirectly the tensile strength of rocks. The two-dimensional numerical model was built to predict the stress distribution and full-field deformation on Brazilian disc under compression based on the assumptions of a homogenous, isotropic and linear elastic material. The uniaxial compression test was conducted using the DIC technique to determine the elastic properties of Spider Berea sandstone, which were used as inputs for the simulation model. The model was verified by the analytical solution and compared with the digital image correlation. The numerical simulation results showed that the solutions matched reasonably with the analytical solutions where the maximum deviation of stress distribution was obtained as 14.59%. The strain evolution (normal and shear strains) and displacements along the central horizontal and vertical planes were investigated in three distinguishable percentages of peak loads (20%, 40%, and 90%) to understand the deformation behaviors in rock. The simulation results demonstrated that the strain evolution contours consistently matched with DIC generated contours with a reasonable agreement. The changes in displacement along the central horizontal and vertical planes showed that numerical simulation and DIC generated experimental results were repeatable and matched closely. In terms of validation, Brazilian testing to measure the indirect tensile strength of rocks is still an issue of debate. The numerical model of fracture propagation supported by digital image correlation from this study can be used to explain the fracturing process in the homogeneous material and can be extended to non-homogeneous cases by incorporating heterogeneity, which is essential for rock mechanics field applications.

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Complex deformation of naturally fractured rocks

Cited by 12 publications

References 38 publications

Experimental Investigation into the Process of Hydraulic Fracture Propagation and the Response of Acoustic Emissions in Fracture–Cavity Carbonate Reservoirs

Experimental Investigation into the Process of Hydraulic Fracture Propagation and the Response of Acoustic Emissions in Fracture–Cavity Carbonate Reservoirs

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

Analyzing the Validity of Brazilian Testing Using Digital Image Correlation and Numerical Simulation Techniques

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