Full‐Life‐Cycle Analysis of Cement Sheath Integrity

Abstract

This paper addresses evaluating the evolution of stress inside the casing-cement sheath-formation system during the cement injection, setting, completion, and production stages of hydrocarbon recovery. This full-life-cycle analysis of cement sheath integrity gives rise to assessment of potential failure mode (i.e., tensile mode, shear mode, and microannulus) in different stages, and the prevention measures can be proposed accordingly. Considering the loading history, two regimes should be distinguished. Before the accomplishment of cementation, as the cement slurry can merely withstand its hydraulic pressure, the in situ stress and the wellbore pressure are withstood by the rock and the casing, respectively. Once the cementation process is completed, the stress increment (e.g., hydraulic fracturing pressure) is withstood by the casing-cement sheath-formation system. The autogenous shrinkage of cement adversely affects the resistance of the system to all types of failure, whereas a moderate swelling of cement is favorable to the cement sheath integrity. In addition, the cement sheath integrity is strongly influenced by the depth: the failure is encountered more easily at the shallow layer. Both the hydraulic fracturing pressure in the completion stage and the increase in casing temperature in the production stage may lead to tensile circumferential stress, and the hydraulic fracturing is the most critical stage for the integrity of cement sheath.

Simulation Model of Bottom Hole Dynamic Pressure and Reservoir Dynamic Stress in Hydraulic Fracturing with Pulse Injection

“…e bottom hole pressure calculated in the previous section is applied to the inner wall of wellbore as the internal boundary condition of the reservoir elastodynamic model. According to the maximum circumferential stress criterion, the circumferential stress distribution in the inner wall of wellbore has a significant influence on the location and time of hydraulic fracture initiation [23][24][25]. Figure 11 shows the results of circumferential stress distribution in the reservoir.…”

“…During the verification process, the maximum horizontal principal stress σ H is set to 79.5 MPa and the minimum horizontal principal stress σ h is set to 57.7 MPa. Only considering the effect of in situ stress, the circumferential stress distribution in the inner wall of the wellbore is solved by the analytical method [23,24] and the finite element method, respectively. e calculation results are shown in Figure 7.…”