Analysis of the External Pressure on Casings Induced by Salt-Gypsum Creep in Build-up Sections for Horizontal Wells
Analysis of the External Pressure on Casings Induced by Salt-Gypsum Creep in Build-up Sections for Horizontal Wells
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DOI：
10.1007/s00603-011-0162-5
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发表时间：
2011-06
影响因子：
6.2
通讯作者：
W. Ge;Mian Chen;Yan Jin;Fuxiang Zhang;Yunhu Lu;P. Yang;Ji-hui Ding;Hao Zeng
中科院分区：
文献类型：
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作者：
W. Ge;Mian Chen;Yan Jin;Fuxiang Zhang;Yunhu Lu;P. Yang;Ji-hui Ding;Hao Zeng
针对盐膏层蠕变耦合作用引起的套管挤毁问题，针对水平威尔斯井弯曲段，采用实验方法确定盐膏层的蠕变（粘弹性）特性，利用有限差分软件建立弯曲套管、井筒和盐膏层的蠕变模型。利用该模型分析了井眼曲率、钻井方向和套管厚度对套管外压的影响，模拟了非均匀地应力场下套管的变形。通过对盐膏层水平威尔斯井的分析，得出以下结论：沿着最小水平应力方向钻井时，套管更安全;（4）随着蠕变时间的增加，套管所受的外压迅速增大，直至达到最大值，并保持在最大值;（5）在非均匀地应力作用下，非均匀系数越大，套管所受的外压越大。该模型已成功地应用于西北某油田盐膏层水平威尔斯井造斜段弯曲套管外压力分析。该模型有助于改进套管设计，减少钻井停工时间，提高盐膏层井眼稳定性。
To alleviate the problems of casing collapse induced by the coupling effect of salt creep movement, as it relates to the curved sections of horizontal wells, an experimental approach was taken to determine the creep (visco-elastic) property of the salt-gypsum formation, using finite-difference software to establish a creep model with curved casing, wellbore and salt formation. With this model, the effects of borehole curvature, drilling direction and casing thickness on external pressure on casing were analyzed, and casing deformation in the non-uniform in situ stress field was simulated. For horizontal wells drilled through salt-gypsum formations, this analysis led to the following conclusions: (1) the casing tends to be much safer when drilling is undertaken along the direction of the minimum horizontal stress; (2) casing deformation occurs and stress increases as the borehole curvature increases; (3) for the same curvature and drilling direction, thicker casings are safer; (4) as the creep time increases, the external pressure on the casing rapidly increases until it reaches its maximum value, whereupon it stays at that value; (5) under the effect of non-uniform in situ stress, a larger non-uniform coefficient would result in greater external pressure on the casing. This model has been successfully applied to analyze the external pressure on curved casings in a build-up section for horizontal wells drilled through salt-gypsum formations in an oilfield in Northwest China. The model has helped to improve the casing design and reduce drilling downtime with greater wellbore stability in salt-gypsum formations.