三维约束条件下MgO膨胀剂对油井水泥石早期性能的影响

Effect of MgO expanding agent on early performance of oil well cement under three dimensional constraint

为探讨三维约束条件下MgO膨胀剂对油井水泥石早期性能的影响,通过水泥石线膨胀率、抗压强度和孔结构的测定,结合XRD、DSC、SEM/EDS等微观分析手段,对掺入MgO膨胀剂油井水泥石的早期性能和MgO膨胀作用机制进行研究。结果表明:三维约束条件下,MgO水化产生的膨胀力有利于油井水泥石抗压强度和孔结构的优化,有望改善水泥环的胶结强度和防窜性能;MgO膨胀剂掺量为12%时,油井水泥石经80℃养护1 d和7 d的自由线膨胀率分别为0.034%和0.072%,水泥石三维约束膨胀经80℃养护3 d和7 d的抗压强度为27.5 MPa和31.6 MPa,较净浆油井水泥石提高了41.8%和49.1%,较自由膨胀水泥石提高了9.6%和16.2%;80℃养护7 d的三维约束膨胀水泥石孔隙率仅为22.7%,较净浆油井水泥石降低了30.8%,较自由膨胀油井水泥石降低了16.8%,且孔径尺寸向小孔(无害孔)方向移动;80℃养护7 d的油井水泥石试样出现了Mg(OH)2的衍射峰,DSC测试在365℃附近出现了Mg(OH)2的吸热峰,水泥石结构致密,且检测到Mg(OH)2晶体的存在,证实了MgO反应生成Mg(OH)2的过程。

In order to explore the effect of MgO expanding agent on the early performance of oil well cement under three-dimensional constraint,the early performance of oil well cement with the addition of MgO expanding agent and expansion mechanism of MgO were studied through the analysis of expansion rate,compressive strength,pore structure of cement and different methods of micro-analysis,such as XRD,DSC and SEM/EDS.The results show that under three-dimensional constraint the expansive force from MgO hydration can improve the compressive strength of oil well cement and porosity.The bonding strength and property for channeling prevention of cement sheath can also be enhanced.When the dosage of MgO expanding agent is 12％,the free-expansion rate of oil well cement curing at 80 ℃ for 1 days and 7 days are 0.034％ and 0.072％ respectively.Under three-dimensional constraint,compressive strength of cement with MgO curing at 80 ℃ for 3 days and 7 days were 27.5 MPa and 31.6 MPa,which increase by 41.8％ and 49.1％ compared with that of cement paste,and 9.6％ and 16.2％ compared with that of free-expansion cement paste,respectively.The porosity of cement with MgO under three-dimensional constraint,which is 22.7％,decreases by 30.8％ compared with that of cement paste and 16.8％ compared with that of free-expansion oil well cement,and the pore size tendes to be smaller （harmless pores）.A Mg（OH）2 diffraction peak exists in the XRD spectrum of oil well cement curing at 80 ℃ for 7 days.Endotherm peak of Mg（OH） 2 appears at 365 ℃ in DSC curves.The compactness of cement structure and existence of Mg（OH） 2 crystal proved the reaction behavior that MgO forms Mg（OH） 2.