Casing Burst Stresses in Particulate-Filled Annuli: Where's the Cement?

Journal of Natural Gas Science and Engineering

et al. 2015

Cement Sheath integrity has been gain more attention due to the increase of carbon sequestration activities in the recent years. Sealing ability of cement sheath can be lost because mechanical disruption in the CO 2 injection wells. Cement sheath mechanical failure can occur in the CO 2 injection wells. This paper proposes an analytical solution to address this issue. Cement sheath and formation rock stiffness are considered in the proposed model to simulate the cement sheath sealing ability on different depth of the formation. Both mechanical properties of cement and formations are evaluated and analyzed. Real field example is also provided. Young's modulus of cement sheath is identified as a major factor that affects the sealing ability of cement sheath. The sealing ability of cement sheath in shale formation is better than that in sandstone formation. Weak cement has better sealing ability than strong cement. The critical failure point lies at the top of sandstone formation. This model can also be used to design and optimize the cement system of new CO 2 injection wells in carbon sequestration projects.

Section: Analysis With Field Datamentioning

confidence: 99%

An analytical solution to simulate the effect of cement/formation stiffness on well integrity evaluation in carbon sequestration projects

Journal of Natural Gas Science and Engineering

et al. 2015

“…In recent years, severe casing damage in deep salt strata has been carefully followed and comprehensively studied by many scholars. Salt rock creep leads to open wellbore shrinkage and casing collapse [5][6][7][8], the well condition and casing performance are getting worse under high pressure and high temperature [1,9], and another cause of casing damage is cement sheath failures [4,10,11]. However, to simplify the calculation, prior work on casing damage in deep salt formation only considered the impact of a single factor, ignoring interaction between salt rock creep, defective cement, and HPHT, which has great deviations from actual situation.…”

Section: Introductionmentioning

confidence: 99%

Application of Multiphysics Coupling FEM on Open Wellbore Shrinkage and Casing Remaining Strength in an Incomplete Borehole in Deep Salt Formation

Tong

Mathematical Problems in Engineering

Zhu

2015

Drilling and completing wells in deep salt stratum are technically challenging and costing, as when serving in an incomplete borehole in deep salt formation, well casing runs a high risk of collapse. To quantitatively calculate casing remaining strength under this harsh condition, a three-dimensional mechanical model is developed; then a computational model coupled with interbed salt rock-defective cement-casing and HPHT (high pressure and high temperature) is established and analyzed using multiphysics coupling FEM (finite element method); furthermore, open wellbore shrinkage and casing remaining strength under varying differential conditions in deep salt formation are discussed. The result demonstrates that the most serious shrinkage occurs at the middle of salt rock, and the combination action of salt rock creep, cement defect, and HPHT substantially lessens casing remaining strength; meanwhile, cement defect level should be taken into consideration when designing casing strength in deep salt formation, and apart from the consideration of temperature on casing the effect of temperature on cement properties also cannot be ignored. This study not only provides a theoretical basis for revealing the failure mechanism of well casing in deep complicated salt formation, but also acts as a new perspective of novel engineering applications of the multiphysics coupling FEM.

“…In recent years, with more and more field data demonstrates that well casings designed by API bulletin 5C3 occur failure under salt creep conditions though their designed safety factors are greater than 1. 8,9 Some authors 3,8–13 begin to turn their sights on the cement and formation, which closely connected with the safety of well casings, in summary, their studies indicated that cement missing or deboning changes the stress distribution of the casing, resulting in well casings bearing nonuniform loading; the flowing of salt formation changes the existing local stress field and displacement field, resulting in the time-dependent nonuniform loading on well casings. Previous studies given us enlightenment that formation, cement and casing are an inextricably linked system when it comes to casing failure.…”

Section: Introductionmentioning

confidence: 99%

Research on a probabilistic assessment criterion of casing deformation in an incomplete borehole in deep salt formation

Tong

Proceedings of the Institution of Mechanical Engineers, Part E:

Zhu

2015

Drilling and completing wells through complex salt formation is technically challenging and costing. Field data demonstrates that well casings designed by traditional safety coefficient criterion occurring failure in deep salt formation though their safety factors are greater than 1. To reveal the failure mechanism, a probabilistic computational model coupled with salt formation, defective cement and worn casing is established and analyzed using Monte Carlo simulation method. On the basis of reliability theory, the results calculated by 5000 times simulations show that the traditional safety coefficient criterion has been unable to adapt to the safety assessment of well casings under salt creep conditions. To gain a sophisticated evaluation, a new assessment criterion is established and applied to assess the security of well casings under salt creep conditions. This study provides a new perspective for revealing the failure mechanism and solutions of evaluation on well casings under salt creep conditions, which may be an alternative method to study and predict the life of well casings in deep complicated formation.