The Effect of Sustained Casing Pressure on the Mechanical Integrity of#br# Cement Sheath in Gas Wells

doi:10.11885/j.issn.1674-5086.2014.02.13.01

Abstract

Abstract:

Sustained casing pressure（SCP），resulted from downhole operations，the leakage of casing and oil tube or packer
poses great challenges to the sealing integrity of cement sheath in HTHP gas wells. Thus，we estasblished the failure calculation
model and the stresses of cement sheath，and studied the influences of SCP on the stresses and failure of cement sheath，based on
the multi-layer thick wall cylinder theory of elastic mechanics and Mohr-Coulomb failure criterion. Results show that the SCP
problem will make cement sheath sustain overlarge tangential tensile stress which is the principal factor for its failure. Besides，
the tangential tensile stress that is resulted from the increasing temperature in wellbore will increase the risk of the failure of
cement sheath. The larger the SCP value，the lower the safety factor of cement sheath，and the influence of temperature effect on
the safety factor is not clear. For high temperature and high pressure gas wells，a safety factor diagram of cement sheath can be
drawn according to parameters of well construction（formation-cement sheath-casing），which gives the basis for determining
proper allowable maximum SCP value and is of great guiding significance to increase the wellbore safety and to extend the
working life of gas well production.

Key words: gas well, HTHP, cement sheath, analytical model, sustained casing pressure, stress, failure

CLC Number:

TE256

ZHANG Zhi1*, XU Honglin2, LIU Zhiwei1, LI Wei3, SHI Taihe1. The Effect of Sustained Casing Pressure on the Mechanical Integrity of#br# Cement Sheath in Gas Wells[J]. 西南石油大学学报(自然科学版), DOI: 10.11885/j.issn.1674-5086.2014.02.13.01.

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