Redistribution of fracturing fluid in shales and its impact on gas transport capacity
Redistribution of fracturing fluid in shales and its impact on gas transport capacity
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页岩中压裂液的重新分布及其对输气能力的影响
DOI：
10.1016/j.jngse.2020.103747
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发表时间：
2021-01-01
影响因子：
--
通讯作者：
Zhang, Ying
中科院分区：
文献类型：
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作者：
Chen, Mingjun;Bai, Jiajia;Zhang, Ying
压裂液的再分布对页岩气运移起着关键作用。本文通过专门设计的实验，包括压裂液吸留实验、电阻率实时测量实验和压力衰减实验，模拟了关井过程中压裂液的再分布行为。结果表明，泥页岩自吸可分为3个阶段：第一阶段（0-2 h），压裂液主要停留在大于15 μ m的微裂缝中;第二阶段（2-20 h），压裂液进入1-15 μ m的孔隙;第三阶段（20-48 h），压裂液进入小于1 μ m的孔隙。泥质电阻率的变化反映了压裂液的再分布，泥质电阻率的变化拐点表明压裂液再分布的结束。压力衰减测试结果表明，压裂液滞留量越大，渗透率损害程度越严重。同时，渗透率恢复率随停留时间的增加而降低。小于1 μ m的孔隙被压裂液充填时，渗透率损害率为99.09%，当压裂液重新分配完成时，渗透率仅恢复到初始渗透率的1.26%。考虑到压裂液滞留的缺点和潜在的优点，如果含水饱和度增加超过74%，则延长关井时间是没有意义的。本文还提供了一种替代的工作流程，用于评估流体分布及其对页岩中气体流动能力的影响。
The redistribution of retained fracturing fluid plays a key effect on shale gas transport. In this work, the fracturing fluid redistribution behavior during well shut-in is modeled through some specifically designed experiments, including fracturing fluid imbibition and retention experiments, real-time measurement of resistivity and pressure decay experiments. Results show that shale imbibition is categorized into three stages: stage I (0-2 h), where the fracturing fluid mainly stays in the microcracks greater than 15 mu m; stage II (2-20 h), where the fluid enters 1-15 mu m pores; stage III (20-48 h), where the fracturing fluid enters pores less than 1 mu m. Moreover, the change of shale resistivity reflects the redistribution of fracturing fluid, the inflection point of which indicates the end of fracturing fluid redistribution. Results obtained by the pressure decay measurement show that the more the retained fracturing fluid is, the more serious the damage degree of permeability is. Meanwhile, the permeability recovery rate decreases with the increase of retention time. When the pores less than 1 mu m are filled by fracturing fluid, the permeability damage rate is 99.09%; as well, only 1.26% of the initial permeability is recovered when the fluid redistribution is completed. Considering the disadvantages as well as the potential advantages of retained fracturing fluid, if the water saturation increases more than 74%, it is meaningless to prolong the shut-in time. This paper also provides an alternative workflow for evaluating fluid distribution and its influence on gas flow capacity in shales.