气孔对发气膨胀固井水泥石强度影响

发气膨胀剂产生的气孔具有补偿水泥石体积收缩及改善水泥石韧性的双重作用,对不同气孔体积比率的固井水泥石的抗压强度及水泥-套管界面胶结强度进行测试,并结合气孔结构显微观察对试验结果进行理论分析。结果表明:随着气孔体积比率增加,水泥石抗压强度及界面胶结强度先升高然后下降,进而又升高;气孔直径越均一,越利于提高水泥石强度;表面收缩压使半径不同的气孔内压力不同,小气孔内压力大于大气孔内压力;气孔间压力差增加了气孔边界骨架错位的可能性及小气孔沿着界面窜入大气孔内的趋势,从而降低水泥石的抗压强度和界面胶结强度;气孔通过影响水泥石的自应力、骨架应力和胶结面积,进而影响水泥石的抗压强度和界面胶结强度。

Effects of gas pores on strength of oil well cement using gas swelling agents

Gas pores can be generated during gas expansion when using gas swelling agent in the cementing process of an oil well, which can compensate for volume shrinkage and improve the ductility of the cement. The compressive strength of cement and the bonding strength between cement and casing were measured, and the gas pore structure was examined using a microscope. The influence of gas volume on the strength of the cement was investigated and analyzed. The experimental results show that, with the increase of the ratio of gas volume to the total volume of the cement matrix, its compressive strength and interfacial bonding strength increase first and then decrease. The strength of the cement can be increased when the pore sizes are uniformly distributed. The pressure in small pores is greater than that in large pores due to the effect of surface contract pressure. This pressure difference among different gas pores may cause collapses of pore boundaries that can make small pores merge with large ones, which can reduce the strength of the cement. The effects of gas pores on the strength of the cement can be attributed to the intrinsic stress, matrix stress and bonding area inside the cement body.