可降解钻井液对煤岩渗透率的影响评价

在煤矿瓦斯（煤层气）抽采过程中，要求钻井液既能有效地保持孔壁稳定，又尽可能降低对煤层的伤害。笔者分别以原状煤样（模拟较致密的煤岩）和人工煤样（模拟较松散或大裂隙煤岩）为实验对象，通过比较不同阶段（污染前、污染后、生物酶解堵和酸化解堵）煤岩渗透率的变化，评价了可降解钻井液对煤岩的暂堵与解堵效果，并探讨了其现场实施工艺。通过实验发现：可降解钻井液能满足钻进煤层时的护孔要求；采用“生物酶＋稀盐酸”浸泡解堵工艺可清除聚合物和碳酸盐岩类矿物带来的伤害，而单独使用其中一种工艺均会降低解堵效果；稀盐酸解堵的效果取决于煤岩和可降解钻井液中碳酸盐岩类矿物的含量；对煤岩进行加热处理可以提高其气测渗透率；可降解钻井液的现场实施工艺方便，应择机在煤层气钻井领域进行现场试验。

Effect appraisal of degradable drilling fluid on coal rock permeability

In the abstracting and exploitation process of coalmine gas(coalbed methane)，the drilling fluid should maintain the borehole stability and lower the damage to coal reservoir simultaneously.Using original coal rock(simulating compact coal rock) and man made coal rock(simulating incompact coal rock or coal rock with big crack)，authors appraised the temporally plugging and unplugging performances of degradable drilling fluid to coal rock during the sequent stages such as the initial stage，polluted stage，unplugging stage by enzyme and unplugging stage by low concentration HCl.The onsite implement technology was also discussed.The results show that firstly degradable drilling fluid can maintain borehole stability during coal drilling.Then，the technologies of soaking enzyme and low concentration HCl successively can remove the damage caused by polymers and carbonate rocks.Furthermore，absence of enzyme or HCl will lead a lower unplugging performance.Thirdly，the concentration of carbonate rocks in the coal rock and degradable drilling fluid determines the unplugging performance of low concentration HCl.Fourthly，the gas permeability of coal rock can be improved by heat treatment.Finally，the onsite implement technology is feasible and field trial should be carried out in coalbed methane drilling.