Unconventional oil and gas has become a major focus of development. However, after initial fracturing, the reservoir is not fully fractured, leading to rapid production decline and necessitating repeated fracturing to improve recovery. Refracturing in a new wellbore which reconstructed by solid expandable tubular is highly operable and has been successfully applied in both domestic and international oil fields. However, issues such as seal failure and the inability to seal old perforations hinder the potential for remaining production. Physical property testing and comparisons was used to determine the appropriate material constitutive model for expansion tube seals. Considering the original perforation burr as the primary cause of rubber failure, a finite element model was developed to analyze the impact of expansion tube-rubber-burr collisions on damage. Rubber failure criteria based on strain and stress were developed, the evolution of rubber failure was analyzed, and a method for normalizing damage volume was proposed. The rubber failure behavior under various factors was further analyzed. Finally, a relationship chart was established between the characteristic value of seal damage and its main controlling factors. Based on these findings, recommendations for expansion tube wellbore reconstruction operations were provided, focusing on two aspects: controlling the horizontal section string entry speed to ≥4 min/column and maintaining burr height below 3.0 mm.
如图2所示为实验应力-应变曲线与常见的几种超弹性材料本构拟合结果对比,分别附带了对应的拟合精度评价系数值。由图2可知,当工程应变较小时,每种模型均有良好的拟合精度,但van der Waals、Yeoh以及减缩多项式模型在名义应变为1~1.8内明显低估了材料的名义应力,拟合精度最好的是完全多项式模型(N=2)以及Ogden(N=2)模型,虽然在只有单轴拉伸测试数据下不建议使用Ogden模型,但考虑到该模型在大应变条件下表现出的更好适应性[23],最终选择其作为膨胀管橡胶密封件力学响应表征模型。该模型是基于连续介质的唯象理论模型,其应变能函数被表示为主伸长比的函数W,表达式为
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