Applied Mathematics and Mechanics (English Edition) ›› 2017, Vol. 38 ›› Issue (9): 1273-1294.doi: https://doi.org/10.1007/s10483-017-2237-8

• 论文 • 上一篇    下一篇

Analytical method for evaluating stress field in casing-cementformation system of oil/gas wells

Wei LIU, Baohua YU, Jingen DENG   

  1. State Key Laboratory of Petroleum Resources and Prospecting, China University of Petroleum, Beijing 102249, China
  • 收稿日期:2016-09-02 修回日期:2017-01-25 出版日期:2017-09-01 发布日期:2017-09-01
  • 通讯作者: Wei LIU,E-mail:liuwei@cup.edu.cn E-mail:liuwei@cup.edu.cn
  • 基金资助:

    Project supported by the National Natural Science Foundation of China (Nos.11502304 and 51521063) and the Science Foundation of China University of Petroleum (Nos.C201601 and 2462013YJRC023)

Analytical method for evaluating stress field in casing-cementformation system of oil/gas wells

Wei LIU, Baohua YU, Jingen DENG   

  1. State Key Laboratory of Petroleum Resources and Prospecting, China University of Petroleum, Beijing 102249, China
  • Received:2016-09-02 Revised:2017-01-25 Online:2017-09-01 Published:2017-09-01
  • Contact: Wei LIU E-mail:liuwei@cup.edu.cn
  • Supported by:

    Project supported by the National Natural Science Foundation of China (Nos.11502304 and 51521063) and the Science Foundation of China University of Petroleum (Nos.C201601 and 2462013YJRC023)

摘要:

In this paper, we present an analytical method for evaluating the stress field within a casing-cement-formation system of oil/gas wells under anisotropic in-situ stresses in the rock formation and uniform pressure within the casing. The present method treats the in-situ stresses in the formation as initial stresses since the in-situ stresses have already developed in the formation before placement of cement and casing into the well. It is demonstrated that, via this treatment, the present method excludes additional displacements within the formation predicted by the existing method, and gives more reasonable stress results. An actual tight-oil well is analyzed using the present and existing analytical methods, as well as the finite element method. Good agreement between the analytical results and the finite element analysis (FEA) results is obtained, validating the present method. It is also evident that, compared with the present method, the existing method overestimates the compressive stress level within the casing and the cement. Finally, the effects of elastic properties of the formation, cement, and inner pressure of casing on stresses within the casing and cement are illustrated with a series of sensitivity analyses.

关键词: matrix algebra, singular value decomposition, reanalysis, perturbation method, stress evaluation, anisotropic in-situ stress, near wellbore region, initial stress

Abstract:

In this paper, we present an analytical method for evaluating the stress field within a casing-cement-formation system of oil/gas wells under anisotropic in-situ stresses in the rock formation and uniform pressure within the casing. The present method treats the in-situ stresses in the formation as initial stresses since the in-situ stresses have already developed in the formation before placement of cement and casing into the well. It is demonstrated that, via this treatment, the present method excludes additional displacements within the formation predicted by the existing method, and gives more reasonable stress results. An actual tight-oil well is analyzed using the present and existing analytical methods, as well as the finite element method. Good agreement between the analytical results and the finite element analysis (FEA) results is obtained, validating the present method. It is also evident that, compared with the present method, the existing method overestimates the compressive stress level within the casing and the cement. Finally, the effects of elastic properties of the formation, cement, and inner pressure of casing on stresses within the casing and cement are illustrated with a series of sensitivity analyses.

Key words: matrix algebra, singular value decomposition, reanalysis, perturbation method, stress evaluation, initial stress, near wellbore region, anisotropic in-situ stress

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