Poro-chemo-fracture-mechanics … bottom-up

This paper introduces a predictive model for the stress and pressure evolutions in a wellbore cement liner at early ages. A pressure state equation is derived that observes the coupling of the elastic changes of the solid matrix, the eigenstress developments in the solid and porespaces, and the mass consumption of water in course of the reaction. Here, the transient constitution of the solid volume necessitates advancing the mechanical state of the poroelastic cement skeleton incrementally and at constant hydration degree. Next, analytic function theory is employed to assess the localization of stresses along the steel-cement (SC) and rock-cement (RC) interfaces by placing the casing eccentrically with respect to the wellbore hole. Though the energy release rate due to complete debonding of either interface is only marginally influenced by the eccentricity, the risk of evolving a microcrack along the thick portion of the sheath is substantially increased. Additionally, it is observed that the risk of microannulus formation is principally affected by the pressure rebound, which is engendered by the slowing reaction rate and amplified for rock boundaries with low permeability.

Section: Matching the Boundary Argumentsmentioning

confidence: 99%

“…Hence, the out-ofequilibrium calculation of the mass growth is separated from the incremental loading of the solid (see Appendix of Ref. [5] for a more detailed thermodynamic reasoning).…”

Section: Stress and Pressure Evolutionsmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

See 1 more Smart Citation

Early-Age Stress and Pressure Developments in a Wellbore Cement Liner: Application to Eccentric Geometries

Petersen

Ulm

2016

Crack Tunneling in Cement Sheath of Hydrocarbon Well

Wang

Lou

Suo

2015

In a hydrocarbon well, cement fills the annular gap between two steel casings or between a steel casing and rock formation, forming a sheath that isolates fluids in different zones of the well. For a well as long as several kilometers, the cement sheath covers a large area and inevitably contains small cracks. The cement sheath fails when a small crack grows and tunnels through the length of the well. We calculate the energy release rate at a steady-state tunneling front as a function of the width of the tunnel. So long as the maximum energy release rate is below the fracture energy of the cement, tunnels of any width will not form. This failsafe condition requires no measurement of small cracks, but depends on material properties and loading conditions. We further show that the crit-ical load for tunneling reduces significantly if the cement/casing and cement/formation interfaces slide. [DOI: 10.1115/1.4031649

Fluid-Driven Cracks Tunneling in Cemented Hydrocarbon Wells

Wang

2022

Pressurized fluids may invade into the cement sheath of hydrocarbon wells during hydraulic fracturing and other construction operations in shale gas and oil exploitation. Excessive fluid pressure provides a driving force for small cracks to grow and tunnel through the length of the well, leading to the loss of zonal isolation and severe consequences. This work studies fluid-driven cracks tunneling in the bulk or along the interfaces of the cement sheath. We calculate the energy release rate of the tunneling crack as a function of the width of the tunnel. As long as the maximum energy release rate is below the fracture energy of the cement or the interfaces, no tunnels will form. This failsafe criterion predicts that the interfaces are much more vulnerable to tunneling cracks than the bulk of cement sheath. It is further shown that cement sheath with high Young's modulus and high Poisson's ratio can better resists fluid-driven cracks. The influence of casing pressure is also examined. Different loading conditions may have conflicting requirements on the properties of cement sheath. Compromises need to be made in engineering practice.