低温晶核早强剂的制备与实验研究

Study on Properties and Mechanism of Cryogenic Nucleation Early Strength Agent

陕北部分区块浅油层井的井底温度低(小于40℃)导致水泥浆凝结时间长、早期强度低,严重影响固井质量。针对这些问题,文章研究合成了一种早强晶种,并通过多元复配获得一种复合型早强剂DW-45,其组成为早强晶种:Na_(2)SO_(4):Al_(2)(SO_(4))_(3):NaAlO_(2):Li_(2)CO_(3)=1:1:0.4:0.1:3。测试了DW-45对油井水泥抗压强度和稠化性能的影响,并利用XRD和SEM对早强剂作用下水泥水化产物的物相组成和形貌进行了分析。实验结果表明:在25、30、35、40、45℃养护条件下,3%的DW-45使水泥石6 h抗压强度分别增加为纯G级水泥的3.1、4.7、6.3、4.5、4.6倍;在35℃/15 MPa条件下,3%的DW-45的使水泥浆稠化时间缩短致63 min,稠化过渡时间为8 min,有利于油井的防窜。XRD和SEM结果表明,DW-45可加速水化保护膜破裂,促进C-S-H凝胶、Ca(OH)_(2)和钙矾石的生成,提高油井水泥中C_(3)S、C_(3)A的水化进程,同时提高了水泥石的密实度。DW-45有助于解决浅油层井固井所面临的早期强度低、凝结时间长等问题。

In view of the problems of long setting time and low strength at the early setting stage of cement slurry caused by low bottom hole temperature(<40℃)of shallow oil wells in some blocks in northern Shaanxi,a seed crystal early strength agent was synthesized,and a composite early strength agent DW-45 was obtained through multiple compounding.The effects of DW-45 on the compressive strength and thickening property of oil well cement at different temperatures and pressures were tested,and the phase composition and morphology of cement hydration products under the action of early strength agent were analyzed by XRD and SEM.The results show that the optimum content of this early strength agent is 3%of cement.At 25,30,35,40 and 45℃,the 6 h compressive strength of cement paste increased by 3%DW-45 to 3.1,4.7,6.3,4.5 and 4.6 times that of pure G grade cement.At 35℃/15 MPa,the thickening time of cement slurry with DW-45 is 63 min,and the thickening transition time is 8min.XRD showed that DW-45 promoted the formation of early Ca(OH)_(2) and ettringite,and then accelerated the hydration process of cement.When cured at 35℃for 6 h,DW-45 cement slurry system forms a large number of network type II C-S-H gel and fibrous type I C-S-H gel,which are closely overlapped among cement particles,and are packed tightly with the formed hexagonal plate type Ca(OH)_(2).DW-45 early strength agent can accelerate the rupture of hydration protective film,promote the formation of C-S-H gel,Ca(OH)_(2)and ettringite,improve the hydration process of C 3S and C 3A in oil well cement,and improve the compactness of cement paste.DW-45 is helpful to solve the problem of low strength at the early setting stage and long setting time for cementing shallow reservoirs.