Discrete Element Numerical Simulation Method for Permeability Stress Sensitivity of Persistent Fractured Coal Samples

Zhang, Cun; Ren, Zhaopeng

doi:10.1007/s10706-019-01114-6

Cited by 5 publications

(8 citation statements)

References 27 publications

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“…It has been reported that the reservoir permeability and production rate decrease with the stress sensitivity coefficient for both coal seams and shale reservoirs, and the stress sensitivity coefficient reduces with the increasing effective stress. ,,, In other words, the increase of effective stress results in compaction of cleats, making cleats more resistant to compaction force, and the stress sensitivity coefficient drops, as proven by a number of experimental data (e.g., Figure ). ,− Studies have also revealed that (i) temperature and moisture content can enhance the stress sensitivity, (ii) the stress sensitivity decreases with the pore/fracture aperture and can be affected by fracture morphology, ,− and (iii) the stress sensitivity coefficient show strong anisotropy with a higher value typically in the horizontal direction. ,, Zhang et al proposed that the new fractures generated from shear and tensile failure in coal exert an evident impact on stress sensitivity, which matched with the results obtained by Tan and Konietzky . It is clear that the stress sensitivity coefficient constantly varies during production, so it is vital to quantify its variation to reliably estimate coal permeability evolution during the dewatering as well as gas production stages.…”

Section: Affecting Factors Of Dewatering Rate Optimizationmentioning

confidence: 56%

Dewatering Optimization of Coal Seam Gas Production Wells: A Review and Future Perspectives

et al. 2022

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Coal seam gas (CSG), as a type of unconventional gas resource, is playing an increasingly important role in energy generation and transition to renewables, as the world takes action to meet the climate change challenge. To produce CSG, the reservoir first needs to be dewatered, but unreasonable dewatering rates can lead to various unfavorable outcomes, such as a reduction in productivity, capillary trapping, borehole instability, excessive coal fines generation, and frequent production well workovers due to particle-induced damage to pumps. Determining the optimum dewatering strategy is currently in a very primitive stage of development, and CSG operators rely on empirical and instinctive approaches to deal with this problem. This paper conducts a comprehensive literature review to (i) explain why dewatering rate optimization remains a great challenge for the CSG industry, (ii) illustrate the complexity and nature of the issue through a conceptual model, and (iii) investigate four key factors that dominate the dewatering optimization design, borehole stability, stress-dependent permeability, gas–water two-phase flow, and generation of coal fines. A detailed summary of current dewatering optimization practices in CSG reservoirs is then presented, focusing on the employed theories, methodology, key learnings, and limitations of each practice. Finally, the remaining knowledge gaps are highlighted, and recommendations for further future work are provided.

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Section: Affecting Factors Of Dewatering Rate Optimizationmentioning

confidence: 56%

Dewatering Optimization of Coal Seam Gas Production Wells: A Review and Future Perspectives

et al. 2022

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“…However, the penetrating fractures used in these experiments were all vertical or horizontal, and the effect of the fracture dip angle on the stress sensitivity of permeability was not considered. The sensitivity of inclined fractures to confining and axial stress is related to the fracture dip angle 14,17‐19 . If there are different inclined segments in penetrating fractures, their sensitivities to axial and confining stress are bound to be different from those of single vertical and horizontal fractures.…”

Section: Introductionmentioning

confidence: 99%

“…However, the flow channel actually contains horizontal, vertical, and inclined fractures (see Figure 4). The flow rate in these channels depends on the relatively small aperture of the fracture groups 18 . If the JSFM is adopted, it is difficult to describe the actual flow situation under a changing stress environment.…”

Section: Introductionmentioning

confidence: 99%

“…The flow rate in these channels depends on the relatively small aperture of the fracture groups. 18 If the JSFM is adopted, it is difficult to describe the actual flow situation under a changing stress environment.…”

Section: Introductionmentioning

confidence: 99%

“…The sensitivity of inclined fractures to confining and axial stress is related to the fracture dip angle. 14,[17][18][19] If there are different inclined segments in penetrating fractures, their sensitivities to axial and confining stress are bound to be different from those of single vertical and horizontal fractures. Many studies have concluded that, during pressure-relief mining and hydraulic fracturing in deep coal seams, the induced stresses vary differently, and the fracture morphology has an important effect on the stress sensitivity of the fractured coal seams.…”

Section: Introductionmentioning

confidence: 99%

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Efficient and simple simulation method for matching stress‐permeability test results

Zhang

Chen

Song

2022

Energy Science & Engineering

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In the process of pressure-relief mining in high gas coal seams and hydraulic fracturing of deep coalbed methane, a large number of irregular fractures are generated inside the coal, which becomes the main path for gas migration. The stress sensitivity of fractures directly affects the gas migration characteristics in the coal. For better matching stress-permeability test results, a fluid-solid coupling simulation method with the joint stiffness changing method (JSCM), which accommodates fracture (or joint) stiffness through the stress acting on the fracture, is proposed. The stress sensitivity of permeability under different stress states was matched in a simulation and compared with a laboratory experiment. This method has the following advantages compared with the traditional joint stiffness fixing method (JSFM). (1) The JSCM does not need to set the residual joint aperture, which can match a wider range of stresses, so there is no upper limit in principle. (2) The JSCM can match the laboratory test results better than the JSFM. A parameter-determining method for the JSCM is given for the flow test results. Based on the JSCM, the flow in an irregular fracture under different confining and axial stresses was determined. The results show that the occurrence of segmental fractures with different dip angles in persistent fractures determines the stress sensitivity of the fracture flow. With the increase in axial stress, the fracture aperture of the horizontal section is reduced, causing the decrease in horizontal section seepage capacity. It determines the whole flow of the persistent fracture. While with the increase in confining stress, the fracture aperture of vertical section is greatly reduced and causing flow rate of the whole fracture reducing greatly.

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Using discrete element numerical simulation to determine effect of persistent fracture morphology on permeability stress sensitivity

Wang

Zhang

et al. 2022

Num Anal Meth Geomechanics

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The stress sensitivity of coal seams with different fracture structures affects gas migration characteristics in the fracture zone. In this study, permeability stress experiments for intact and persistent fracture coal samples are carried out. A discrete element method numerical simulation that adopts the changing joint stiffness method is proposed. Based on the experimental data, the corresponding parameters of persistent fractures and elastic joints for fluid-solid coupling simulations are determined. Subsequently, the internal influence mechanisms of fracture morphology on axial and confining stress sensitivities are determined. The simulation results show that sectional fractures with different dip angles in the persistent fracture control the sensitivity to axial and confining stresses. The horizontal segment fracture aperture decreases with an increase in axial stress, which reduces its flow capacity. This results in a decrease in the flow rates in the persistent fracture. When the confining stress increases, the vertical fracture aperture is significantly reduced, considerably reducing the flow rate in the persistent fracture.

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Discrete Element Numerical Simulation Method for Permeability Stress Sensitivity of Persistent Fractured Coal Samples

Cited by 5 publications

References 27 publications

Dewatering Optimization of Coal Seam Gas Production Wells: A Review and Future Perspectives

Dewatering Optimization of Coal Seam Gas Production Wells: A Review and Future Perspectives

Efficient and simple simulation method for matching stress‐permeability test results

Using discrete element numerical simulation to determine effect of persistent fracture morphology on permeability stress sensitivity

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