煤粉运移与沉积对支撑裂缝渗透率动态影响规律
Dynamic influence law of coal powder migration and deposition on propped fracture permeability
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摘要: 煤粉沉积导致的支撑裂缝渗透率的伤害是影响煤层气排采效果的重要因素之一。基于毛细管束模型，结合Carman-Kozeny公式建立了考虑煤粉运移与沉积的支撑裂缝渗透率演化模型，并利用煤岩导流性能测试系统进行了不同条件下的煤粉侵入支撑裂缝实验，验证了模型的正确性，探讨了煤粉沉积特性对支撑裂缝内煤粉分布规律及渗透率时空演化的影响。研究结果表明:沿煤粉运移方向，支撑裂缝内沉积煤粉浓度逐渐减小，大量煤粉沉积在裂缝入口端，导致裂缝入口端孔隙堵塞程度较大，裂缝内孔隙堵塞程度较小，支撑裂缝渗透率沿煤粉运移方向减小，且随着煤粉运移时间增加，支撑裂缝内悬浮煤粉浓度先快速上升到峰值，随后保持不变，沉积煤粉浓度不断增大，支撑裂缝内孔隙的堵塞程度增大，支撑裂缝的渗透率不断减小。煤粉沉积系数与弥散系数是影响支撑裂缝内煤粉分布规律及渗透率的重要因素，且随着煤粉沉积系数增大，煤粉运移越困难，支撑裂缝入口端沉积煤粉量增大，运移至支撑裂缝内的煤粉量减小，支撑裂缝内悬浮煤粉与沉积煤粉浓度减小，煤粉占据孔隙体积变小，支撑裂缝渗透率增大;而煤粉弥散系数越大，煤粉越容易运移，运移至支撑裂缝内的煤粉量越大，支撑裂缝内悬浮煤粉质量浓度与沉积煤粉体积分数越大，煤粉占据孔隙体积越大，支撑裂缝渗透率越小。Abstract: The permeability damage of propped fracture caused by coal powder deposition is one of the important factors that affect the effect of coalbed methane drainage.Based on capillary tube bundle model and Carman-Kozeny formula,the permeability evolution model of propped fracture considering coal powder migration and deposition is established,and the coal rock conductivity test system is used to test the penetration of coal powder into propped fracture under different conditions,and the model is verified.The influence of coal powder deposition characteristics on the distribution of coal powder and permeability spatio-temporal evolution in the propped fracture are investigated in this study.The results show that along the migration direction of coal powder,the concentration of deposited coal powder in the propped fracture gradually decreases,and a large number of coal powder deposited in the entrance end of the fracture,leading to a greater degree of pore plugging at the entrance end of the fracture and a smaller degree of pore plugging in the fracture,and the permeability of the propped fracture decreases along the migration direction of coal powder.And with the increase of coal migration time,the concentration of suspended coal powder in the propped fracture first rises to the peak value,and then remains unchanged,the concentration of deposited coal powder continues to increase,the plugging degree of pores in the propped fracture increases and the permeability of the propped fracture decreases.With the increase of deposition rate coefficient of coal powder,it is more difficult to transport coal powder into the powder fracture,and the amount of deposited coal powder at the entrance of the propped fracture increases,the amount of coal powder entering into the propped fracture decreases,the concentration of suspended coal powder and deposited coal powder in the propped fracture decreases,the pore volume occupied by coal powder becomes smaller,and the permeability of propped fracture increases;as the dispersion coefficient increases,the coal powder is easier to migrate,and the amount of coal powder entering the propped fracture increases,the concentration of suspended coal powder and deposited coal powder in the propped fracture become higher,the pore volume occupied by coal powder becomes larger,and the permeability of propped fracture becomes smaller.
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Keywords:
- coal powder /
- migration /
- deposition /
- permeability /
- propped fracture
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