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

Abstract

Summary For burst design, engineers routinely assume that the casing annular space is filled by a fluid equivalent. This assumption ignores mechanical resistance provided by solid cement. Some studies addressed this shortcoming by modeling the cement sheath as a solid with elastic failure criteria. Prior work used cement elastic modulus and Poisson's ratio to classify cement as "ductile" (soft) or "brittle" (hard). In the current study, numerical results from finite-element analysis (FEA) indicate that casing burst resistance is increased by the presence of the cement sheath. This study focuses solely on improvement offered by the cement sheath to casing burst resistance and ignores consequences of cement failure on overall well integrity. Comparisons are provided for casing burst resistance, assuming various backup profiles. These include fluid hydrostatics, solid cement matrix (both elastic and plastic response), and cement as "loose" particles. The fluid hydrostatics include mud weight in hole, cement-slurry density, mixed-water density; normal pressure (saltwater column), and actual pore pressure. Calculations show that these fluid profiles are conservative when used as burst-resistance backup. Original cement-slurry density is least conservative. Because well designers are familiar with fluid profile backup assumptions in casing burst design, recommendations are provided to approximate cement behavior as particles with a fluid profile. This allows ease of calculation and is consistent with current practice. Guidelines are provided to explicitly calculate the enhanced casing burst resistance caused by the particulate cement.

Reaction-driven casing expansion: potential for wellbore leakage mitigation

“…By comparison, preliminary calculations using Barlow's formula for the expansion of a cylindrical metal tube [7,124], plus typical casing tube dimensions and plastic yield data for conventional casing steels [56], suggest that expanding conventional wellbore casing via internal pressurisation would require effective internal stresses in the range of 100-300 MPa. Constraints from casing burst studies provide similar values [39,64]. As such, the stresses that could potentially be induced, if a wellbore would be plugged with low-porosity CaO aggregate, are more than sufficient to bring about casing expansion leading to mechanical closure of annuli and fractures similar to that seen in the experiments of Kupresan et al [74,75].…”

Casing structural integrity and failure modes in a range of well types - A review

“…As a result, both active and passive loading evolved on the casing, which exacerbate thermally induced strain based cyclic axial loading occurring in conjunction with net internal or external pressure differentials. Kalil and McSpadden (2012) study on casing burst stress in particulate annuli concluded that depending on the casing grade bonded annulus fill material provides more than 5% added support to the cemented casing's nominal burst rating.…”

Evaluating a Novel Fly Ash Resin-Reinforced Cement’s Interactions under Acidic, Basic, High-Salinity, and High-Temperature Conditions

“…Pollock, R. et al [ 17 ] emphasized the need for the improvement of cement in thermal stimulation wells due to excessive cement failures under extreme temperature conditions. Kalil, I. et al [ 18 ] used finite element analysis to investigate the casing burst effect when cement is present in the sheath. This was performed to overcome the limitations of previous models that assume that the casing annular space is filled by a fluid equivalent instead of cement.…”