Experimental Study on Degradable PGA as Temporary Plugging Agent in Drill-in Fluids
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摘要: 聚乙醇酸（PGA）具有良好的环保特性，通过高温浸泡前后PGA力学性能、颗粒粒径、分子热稳定性和晶体致密度等参数分析，研究了PGA在水相及油相环境中的热稳定性，评价了PGA作钻完井液暂堵剂的应用潜力。结果表明PGA理化性质受钻井液液相环境和温度的影响较大。对水基钻井液而言，100 ℃高温水相环境下PGA分子受pH值影响降解生成低聚物，分子热稳定性降低、力学强度下降，表现为强酸（pH<5）及强碱（pH>9）环境加速降解，且强碱条件下降解快于强酸环境。高温油相环境导致PGA颗粒先溶胀后出现剥落、破碎现象，本体由塑性向脆性转变，抗拉及抗压强度出现一定程度下降，PPA封堵实验显示油相环境中8 d内具有良好的封堵效果。与水基钻井液相比，暂堵剂PGA更适合在油基钻井液中使用。Abstract: Polyglycolic acid (PGA) has good environment protection property. In laboratory study, the mechanical property, the particle sizes, the thermal stability of the PGA molecules and the crystal density of PGA before and after high temperature soaking are analyzed, the thermal stability of PGA in water and oil is studied, and the application potential of PGA as a temporary plugging agent for drill-in fluids is evaluated. It was found that the physiochemical properties of PGA are highly affected by the liquid environment of a drilling fluid and temperature. In water-based drilling fluids, PGA will degrade at 100 ℃ to oligomers because of the pH of the drilling fluid, and the thermal stability of the PGA molecules and the mechanical strength of PGA are all decreased as well. Strong acid (pH< 5) and strong base (pH< 9) both accelerate the degradation of PGA, and PGA degrades faster in strong base environment than in strong acid environment. In high temperature oil-based drilling fluids, the PGA particles first swell and then peel and break, and the main body of the PGA particles turns from plastic to brittle, resulting in a decrease in the tensional and compressive strengths of the particles to some extent. PPA plugging experiment shows that after 8 d of soaking in an oil environment, the PGA particles exhibit good plugging performance. These studies show that PGA is more suitable for use in oil-based drilling fluids than in water-based drilling fluids.
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Key words:
- Drill-in fluid /
- Degradable /
- Temporary plugging agent /
- Polyglycolic acid
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