机械振动对弃置井水泥塞性能影响的试验研究

Experimental Study on Influence of Mechanical Vibration on Performance of Cement Plug in Abandoned Wells

弃置井筒的高质量封堵是油气井弃置技术体系中重要的技术环节。为此提出了一种主动机械激振提高井筒封堵质量的方法,搭建了一套室内试验测试平台,研究不同振动频率、振动时间及振动幅度等参数组合对井筒封堵水泥材料力学性能的影响。通过设计正交试验,得到了最佳振动参数组合,并在此基础上进一步研究了单一因素对水泥石性能的影响规律。研究结果表明:当振动频率为15 Hz、振动时间为6 min及振动幅度为3 mm时,为最佳激振参数组合;相对于无振动工况,井筒封堵水泥塞的胶结强度最大提高51%、抗压强度提高38%、抗拉强度提高20%;水泥石胶结强度随参数变化影响最大,在达到最佳振动参数前,水泥石强度都随之提高,继续增大参数反而会有不利影响。分析了水泥石振动前、后的渗透率,发现振动后渗透率明显减小。通过扫描电镜观察水泥石微观结构,发现机械振动能有效消除水泥石内气孔,减少裂纹,使水泥石更加致密。所得结果可为水泥塞封堵作业提供基础数据,具有工程指导意义。

High-quality plugging of abandoned wellbore is an important part in the abandonment technology system of oil and gas wells.In this paper,a method of improving the wellbore plugging quality by active mechanical vibration was proposed,and a laboratory test platform was built to analyze the effects of vibration parameter(frequency,time and amplitude)combinations on the mechanical properties of wellbore plugging cement materials.By means of designing orthogonal test,the optimal vibration parameter combination was obtained.On this basis,the influence of single factor on the performance of hardened cement was further investigated.The study results show that the vibration frequency of 15 Hz,the vibration time of 6 min and the vibration amplitude of 3 mm constitute the optimal vibration parameter combination.Compared with the vibration-free condition,the cementing strength of the shut-off plug in wellbore is increased by 51%,the compressive strength is increased by 38%,and the tensile strength is increased by 20%.The parameter variation has the greatest influence on the cementing strength of hardened cement.Before reaching the optimal vibration parameter combination,the cement strength increases,but the continuous increase of the parameters has adverse effects.The permeability of hardened cement apparently decreases after vibration.The observation of microstructure of hardened cement under SEM shows that the mechanical vibration can effectively eliminate pores in hardened cement,reduce cracks and make hardened cement denser.The study results provide basic data for the cement plugging operation and have engineering guiding significance.