水泥石气密封性实验研究

Experimental study of air sealing of cement

固井水泥在各种复杂载荷的共同作用下,易发生气密封失效,针对该问题,本研究开展了不同加载方式下水泥石的力学特性分析实验,结合渗透率和声发射监测,对复杂载荷条件下水泥石损伤及渗透性变化进行研究,并分析了它们对水泥环气密封性的影响。研究发现,当水泥石所受应力低于其扩容屈服应力时,水泥石被压缩,渗透率降低,气密封性增强;当水泥石所受应力超过其扩容屈服应力时,水泥石损伤严重,渗透率增大,气密封性下降。循环加载过程中,水泥石损伤、裂缝的出现和发展主要发生在首次循环加卸载过程中。

Cement is prone to seal failure under complex load conditions. For oil and gas wells, such as hydraulic fracturing, steam injection or other operation, the stress situation of the cement sheath will change. The cement sheath and the casing and the formation in the stress-strain relation change, forming a micro ring gap, or cause internal damage in the cement to form micro cracks and increasing permeability, resulting in the loss of the sheath seal, which affects the safety and life of oil and gas wells. The failure of cement sheath seals not only increases the cost of subsequent drilling, completion and production increase, but also affects the period of well construction, the safe exploitation of oil and gas and the production capacity of the oil field, which may cause complete well rejection and even the loss of personnel and environmental damage. In order to deal with this problem, the industry has studied the failure of cement sheaths under various loads, and some mature theories have been obtained for the study of conventional cement. The damage of cement and the change of permeability under the condition of cement load are relatively rarely studied. Based on the experiments on the stress and strain relationship of cement under different loading methods, the failure mechanism of cement is explored and studied in combination with permeability and acoustic emission monitoring.