Permeability and meso-structure evolution of coking coal subjected to long-term exposure of triaxial stresses and high-pressure nitrogen

Feng, Zichao; Yang, Yifan; Niu, Wenxing; Zhao, Yangsheng; Wan, Zhijun; Yao, Yanbin

doi:10.1007/s40948-020-00167-9

Cited by 7 publications

(3 citation statements)

References 37 publications

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“…The metamorphic degree of the coal seam affects the coal matrix and its pore structure, which makes the elastic modulus and permeability of the coal seam change [36][37][38]. Different elastic moduli and permeability will show different fracturing results in hydraulic fracturing.…”

Section: Experimental Protocolmentioning

confidence: 99%

Numerical Simulation Study on the Evolution Law of Stress and Crack in Coal Seam Hydraulic Fracturing

Yang

Zhang

2023

Sustainability

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Hydraulic fracturing as a conventional reservoir permeability enhancement technique can effectively increase the production of coalbed methane, and it is important to study the stress and crack evolution law to evaluate the effect of coalbed fracturing and optimize the construction process. To accurately derive the evolution characteristics of stress and the propagation form of cracks during hydraulic fracturing of coal seams, a numerical model of hydraulic fracturing was established based on a three-point bending test of coal samples using the finite-discrete element method (FDEM). Based on a coal seam in a mining area in southwest China, a hydraulic fracturing model was established, and the reliability of the numerical model was verified by comparing the numerical simulation with the analytical expression. The model was used to study the evolution of stress and cracks with time during hydraulic fracturing, and the influence of elastic modulus and permeability on the evolution of stress and cracks was investigated. The results show that stress and cracks in the process of hydraulic fracturing belong to a mutual feeding mechanism during evolution, and the effective permeability range of fracturing is an ellipse with the crack as the long axis enclosed by the effective stress field. The greater the elastic modulus of the coal seam, the greater the crack initiation pressure and the shorter the crack initiation time, and a coal seam with a high elastic modulus is more likely to form complex cracks. The change in coal seam permeability has little effect on the initiation pressure and initiation time, but the crack propagation path is obviously different, and a coal seam with low permeability is more favorable to hydraulic fracturing.

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Section: Experimental Protocolmentioning

confidence: 99%

Numerical Simulation Study on the Evolution Law of Stress and Crack in Coal Seam Hydraulic Fracturing

Yang

Zhang

2023

Sustainability

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“…1 Schematic representation of early diagenesis in sedimentary basins. The sediments become consolidated after undergoing the weathering of pressure solution which involves non-hydrostatic dissolution over the inter-granular contact surface, diffusive transport into the pore water outside the contacts, and possible secondary mineral precipitation off after a long runtime (Moore et al 1994;Niemeijer et al 2002;Polak et al 2003;Yasuhara et al 2006Yasuhara et al , 2011Okamoto et al 2017;Cheng and Milsch 2020;Feng et al 2020). To remedy this issue, the cessation of pressure solution creep was attributed to a reduction of the non-hydrostatic stress to the point where it is no longer sufficient to supply the required activation energy (Stephenson et al 1992;Revil 1999;Yasuhara et al 2003;Van Noort et al 2008b;Taron and Elsworth 2010;Lu et al 2017Lu et al , 2018.…”

Section: Introductionmentioning

confidence: 99%

What process causes the slowdown of pressure solution creep

Cheng

Nagel

et al. 2021

Geomech. Geophys. Geo-energ. Geo-resour.

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The slowdown of pressure solution creep has been thought to be caused by stress redistribution. This study presents a fresh view towards this creep behaviour. Basically, two rate-limiting mechanisms come into play amid pressure solution creep: (1) stress redistribution across expanding inter-granular contacts and (2) solute accumulation in the water film. Because non-hydrostatic dissolution occurs under open system conditions, solute accumulation in the water film is constrained by the ensuing solute transport process. Relying on the matter exchange across the contact surface boundary, the active processes in the voids, e.g., solute migration and deposition, affect pressure solution creep. Based upon the above, we sum up two requirements that have to be met for achieving chemical compaction equilibrium: (1) the Gibbs free energy of reaction, i.e., the driving force of non-hydrostatic dissolution process, gets depleted and (2) the concentration gradient between the water film and surrounding pore water vanishes. Highlights The slowdown of pressure solution creep is a combined result of stress migration across contacts and solute accumulation in the water film. Matter exchange with the surroundings inhibits solute accumulation in the water film. This article identifies two prerequisites that need to be fulfilled for achieving chemical compaction equilibrium.

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“…Characterizing fluid flow behavior in the unconventional tight formations is of fundamental importance in geo‐engineering projects, such as gas exploration and production, 1‐3 CO 2 sequestration, 4‐6 radioactive waste isolation, 7,8 and geothermal energy recovery 9‐12 . Permeability of these formations must be measured effectively and accurately to understand and predict the fluid flow behavior in the reservoir 13,14 .…”

Section: Introductionmentioning

confidence: 99%

A simplified transient technique for porosity and permeability determination in tight formations: Numerical simulation and experimental validation

Feng

et al. 2020

Energy Science & Engineering

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A simplified pulse decay method (PDM) with only a single downstream reservoir is proposed to replicate the in situ conditions for reservoir fluid flow, where the pore pressure at any location declines as production continues. The proposed PDM also allows determining the effective porosity and permeability for the core sample under replicated in situ conditions. A mathematical model is firstly established to closely represent the experimental design and verify the feasibility of the method. The analytical solutions of the model are derived to calculate the effective sample porosity and permeability. A series of experiments are then conducted under triaxial stress condition, and a detailed comparison is also made between the PDMs with a single upstream reservoir and a single downstream reservoir. The experimental results showed that accurate measurements on effective sample porosity and permeability can be achieved by the single downstream reservoir PDM due to its capability of better replicating the in situ fluid flow behavior, which extends the application of the transient technique. It is also found that the pore pressure along the sample changes linearly, and its gradient varies with time, indicating the applicability of the single‐reservoir PDMs in permeability determination. This method also lays a foundation for studying flow behavior when a second fluid phase evolves during pressure decline, which occurs in many reservoirs.

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Permeability and meso-structure evolution of coking coal subjected to long-term exposure of triaxial stresses and high-pressure nitrogen

Cited by 7 publications

References 37 publications

Numerical Simulation Study on the Evolution Law of Stress and Crack in Coal Seam Hydraulic Fracturing

Numerical Simulation Study on the Evolution Law of Stress and Crack in Coal Seam Hydraulic Fracturing

What process causes the slowdown of pressure solution creep

A simplified transient technique for porosity and permeability determination in tight formations: Numerical simulation and experimental validation

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