PVA改性PLA纤维复合地热暂堵水泥的研制及性能表征

Development and performance characterization of PVA modified PLA fiber composite geothermal temporary sealing cement

摘要:

裂隙发育地层更易获得较好的地热水源补给，钻探中的严重漏失需要采用水泥进行封堵，但这容易造成储层损害问题。本文基于可降解纤维研制了地热暂堵水泥，该材料在钻井过程中渗透率较低，起到护壁堵漏作用，完井后部分降解为地热流体产出提供通道。在PVA覆膜PLA纤维（PVA-PLA）的制备、改性及表征的基础上，探究了改性纤维对水泥浆性能及高温热水浸泡前后固结水泥石性能的影响规律及机理。结果表明：通过覆膜、热处理和硅烷改性的方式，可实现对聚合物纤维降解性能的调控；PVA-PLA纤维水泥石的60℃抗压强度最大为19.8MPa、90℃浸泡后的孔隙率最高为28.88%，最符合低温堵漏、高温解堵的要求；60℃下PVA覆膜减少了PLA与水泥基质接触，90℃热水浸泡过程中PVA膜溶解、PLA暴露在水泥碱性环境下被水解消耗，从而在水泥石中形成较多>200nm的孔隙。低温下PVA-PLA纤维保持完整与水泥石共同堵漏，高温下纤维降解在水泥石内部形成通道而解堵，可在支撑破碎孔壁的同时，实现高温水热条件下对地热井的部分解堵。

Abstract:

Formations with developed fractures are more likely to receive better water supply, and severe leakage during drilling requires the use of cement for sealing, but this can easily cause reservoir damage problems. In this paper, a geothermal temporary plugging cement is developed based on degradable fibers, which has a low permeability during drilling, plays the role of wall protection and plugging, and partially degrades to provide a channel for the output of geothermal fluids after the completion of the well. Based on the preparation, modification and characterization of PVA-coated PLA fibers (PVA-PLA), the effects of the modified fibers on the performance of the cement paste and the performance of cemented cement stone before and after high-temperature hot-water immersion was investigated and the mechanism. The results showed that: the regulation of the degradation properties of polymer fibers can be achieved by coating, heat treatment and silane modification; the compressive strength of PVA-PLA fiber cementite at 60℃ was 19.8MPa at maximum, and the porosity was 28.88% at maximum after immersion at 90℃, which was most in line with the requirements of low-temperature plugging and high-temperature unplugging; the coating of PVA at 60℃ reduced the contact between PLA and cement matrix, and the PVA-PLA fiber cementite at 90℃ was more suitable to the requirements of low-temperature plugging and high-temperature unplugging. The PVA membrane dissolved and PLA exposed to cement alkaline environment was hydrolyzed and consumed during hot water immersion at 90℃, which resulted in the formation of more >200nm pores in the cement stone. The PVA-PLA fibers remain intact and plug with the cement stone at low temperature, and the fiber degradation at high temperature forms a channel inside the cement stone and unblocking, which can support the broken pore wall and at the same time, realize partial unblocking of geothermal wells under high temperature hydrothermal conditions.