基于拉伸胶结强度的水泥环一界面完整性评价

Integrity Evaluation of the First Interface of Cement Sheath Based on Tensile Bonding Strength

油气井工作液密度降低或油气开采必将导致井筒内压降低,使水泥环一界面受到拉伸作用,造成水泥环与套管发生剥离,从而产生微环隙。过去由于没有拉伸胶结强度测量装置和方法,在进行水泥环封隔完整性研究和设计时,均采用水泥环一界面的剪切胶结强度或者水力胶结强度,导致在水泥浆体系优选和封隔完整性设计时存在不足。为此,根据水泥环工作时的受力过程,研制了水泥环一界面拉伸胶结强度测试装置并提出了相应的测量方法,基于该装置进行了水泥浆体系优选及一界面封隔完整性评价。通过对比水泥环一界面拉伸胶结强度和剪切胶结强度,发现前者约是后者的0.37~0.45,采用剪切胶结强度进行水泥浆体系优选或封隔完整性评价可能导致水泥环一界面封隔失效。实验发现,在高压养护条件下胶乳水泥浆体系一界面拉伸胶结强度大于膨胀增韧水泥浆体系和自愈合水泥浆体系一界面拉伸胶结强度。将水泥环一界面拉伸胶结强度作为油气井固井水泥浆实验设计、评价水泥环封隔完整性的重要依据之一,更能保证油气井安全生产运行。

The decrease of working fluid density in oil and gas wells or oil and gas exploitation will inevitably lead to a decrease in the internal pressure of the wellbore,causing the first interface of cement sheath to be stretched,causing the cement sheath and casing to peel off,resulting in micro-annular gaps.In the past,due to the lack of measuring device and method of the tensile bond strength,the shear bond strength or hydraulic bond strength of the first interface of cement sheath was used in the research and design of the sealing integrity of cement sheath,which resulted in deficiencies in the optimization of cement slurry system and the design of the sealing integrity of cement sheath.Therefore,according to the stress process of the cement sheath,a test device for the tensile bond sealing strength of the first interface of cement sheath is developed,and the corresponding measurement method is proposed.Based on the device,the cement slurry system is optimized and the integrity of the first interface is evaluated.By comparing the tensile bond strength and shear bond strength of the first interface of cement sheath,it is found that the former is about 0.37~0.45 of the latter.The use of shear bond strength to optimize the cement slurry system or evaluate the sealing integrity may lead to the first interface of cement sheath seal failure.It is found that the first interfacial tensile bond strength of latex cement slurry system is greater than that of expansion toughened cement slurry system and selfhealing cement slurry system under high pressure curing condition.Taking the tensile bond strength of the first interface of cement sheath as one of the important basis for the experimental design of cementing slurry and the evaluation of the sealing integrity of cement sheath can ensure the safe production and operation of oil and gas wells.