高压注水下套管蠕变损坏的机理研究

Analysis on Mechanism of Casing Failure Induced by Creep Deformation after High Pressure Water flooding and Its Precautions

油田注水开发以后,由于泥岩吸水蠕变,使非均匀地应力作用于水泥环和套管而导致水泥环和套管发生径向缩径变形。通过建立套管—水泥环—泥岩围岩蠕变力学模型,定量计算和分析了井壁泥岩蠕变载荷分布和变化规律,水泥环和套管外壁径向和环向载荷分布规律,揭示了套管外壁环向载荷分布规律是引起套管变形损坏的直接原因;套管外壁径向载荷与地应力分布规律、套管变形趋势相反说明水泥环在套管抵抗非均匀载荷时起到改变受力边界的作用。通过对套管损坏机理的研究,提出预防高压注水泥岩层的套管损坏主要从防止注入水窜入软弱的泥岩夹层和提高油层附近泥岩层段套管强度两方面入手,为后续套管损坏防治工作提供借鉴。

After high pressure water flooding in oilfield,absorbed mudstone begin to creep,which makes nonuniform ground stress act on cement mantle and casing.As a result,the cement mantle and casing string become deformed at radial direction.Established is the'casing-cement mantle-surrounding mudstone'creep mechanical model and conducted are quantitative calculation and analysis of creep load distribution and variation of mudstone.Analysis results show that radial and circumferential load distribution of outer wall of casing leads directly to casing deformation and damage and casing can change the stress boundary when it resists nonuniform load.Studied is the damage mechanism of casing and proposed are prevention measures of casing deformation and damage in high pressure water injection mudstone stratum,includingprevention ofwater penetratingsoft interbedded mudstone and strength improvement of the casing in mudstone stratum near oil layer,which will provide valuable reference for future prevention ofcasingdamage.