Influences of hydraulic fracturing on microfractures of high-rank coal under different in-situ stress conditions

Mou, Pengwei; Pan, Jienan; Wang, Kai; Jiang, Wei; Yang, Yanhui; Wang, Xianglong

doi:10.1016/j.fuel.2020.119566

Cited by 85 publications

(37 citation statements)

References 45 publications

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“…With the intensification of the energy crisis and global greenhouse effect, the developments of clean resources and CO 2 sequestration have attracted extensive attention. 1 As a clean resource, coalbed methane (CBM) is a type of hydrocarbon gas that exists in the coal seam and its surrounding rock, which mainly consists of methane. In addition, it has been reported that carbon capture and sequestration technology can effectively reduce the CO 2 content in the atmosphere.…”

Section: Introductionmentioning

confidence: 99%

Coal Pores: Methods, Types, and Characteristics

et al. 2021

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Coal pores are the locations of coalbed methane occurrence and enrichment and the main storage space targeted in CO2 sequestration. The systematic investigation of the coal pore structure and its development is of great significance to provide insights into coalbed methane generation, coal mine gas outburst mechanisms, and coal seam CO2 sequestration. In this study, coal pore testing technologies and methods, pore classification methods, and coal pore structure characteristics and their main control factors were systematically investigated and summarized. The results show that direct test methods, indirect fluid injection test methods, and X-ray and spectroscopic methods have been used for the quantitative characterization of the pore structure. However, each testing method has limitations. Therefore, a comprehensive method for the quantitative characterization of the full-scale pore structure must be developed, especially for the accurate quantitative characterization of closed pores in coal. The in situ measurement of pores in coal is one of the future research trends. Classification methods of pores in coal mainly include the classification of the genetic pore type, pore size, and pore morphology. Metamorphism, tectonic deformation, and macerals are the main internal factors affecting the pore distribution in coal. The effect of tectonic deformation on the macromolecular structure and micro- and ultramicropores of coal must be further studied. In addition, molecular mechanics simulations, molecular dynamics simulations, and quantum chemistry calculations of the dynamic response of the macromolecular structure and micro- and ultramicropores during gas adsorption and desorption must be carried out.

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Section: Introductionmentioning

confidence: 99%

Coal Pores: Methods, Types, and Characteristics

et al. 2021

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“…Figure shows that in the initial stage of the laboratory HF experiment (AB), the water pressure approximates to zero constantly. Generally, cylindrical (ϕ × H : 50 mm × 100 mm) and cubic (100 mm × 100 mm × 100 mm or 300 mm × 300 mm × 300 mm) coal or rock specimens are used in laboratory HF tests, having water injection borehole diameters of about 10–20 mm and depth of about 50–75 mm. ,, Hence, the volume of the water injection borehole is relatively large compared with the volume of the specimen; in other words, the influence of the borehole size on coal or rock samples is huge and cannot be ignored. Therefore, water needs some time to fill the injection borehole in the laboratory HF experiment, and so the pressure that coal or rock samples experienced is near zero for a short period of time during the initial stage, as seen in Figure .…”

Section: Discussionmentioning

confidence: 99%

Response Characteristics of Coal Measure Strata Subjected to Hydraulic Fracturing: Insights from a Field Test

et al. 2021

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Hydraulic fracturing (HF) is an effective method to improve the permeability of coal seams and enhance coalbed methane recovery in underground coal reservoirs. However, the induced stress and strain evolution behaviors triggered by HF engineering practice remain unclear, which hinders our perception and field applications on HF technology. In this work, an HF field experiment was conducted in a deep buried coal mine, and a hollow inclusion cell (HI cell) was proposed to investigate the induced strain and stress evolution behaviors of HF. In addition, the HF complete evolution process was sectioned and comprehensively studied. The results showed that the influence range of this HF field test exceeds 44 m, and the induced strain primarily experiences three stages when subjected to HF: initial constancy, strain fluctuation, and later, stability. The induced stress experiences intense variations when subjected to HF, with the minimum principal stress increment being the greatest. Principal stress tends to recover to the initial stress state after HF, but the recovery speed declines with time. Further, azimuth and dip angle experience intense changes under HF. The change law is irregular, but they all tend to return to the primary state. Moreover, combining water flow and pressure, the HF evolution process can be divided into five stages: prehydraulic fracturing, unstable crack propagation, stable crack propagation, posthydraulic fracturing, and pump off stage, which can reflect the real evolution behaviors accurately. The research results have profound implications for coalbed methane recovery and coal mine gas governance.

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“…In order to quantitatively evaluate the difference of stress in different directions of coal reservoir, the concept of in situ stress anisotropy is introduced, 34,35 and the formula is as follows:…”

Section: In Situ Stress Anisotropymentioning

confidence: 99%