Use of a Mechanistic Model To Forecast Cement-Sheath Integrity for CO2 Storage

Abstract

Implementation of CO2 storage in geological media requires a proper assessment of the risk of CO2 leakage from the storage sites. In particular, it is necessary to evaluate the risk that cement sheaths represent leakage pathways as this could occur if cement becomes damaged or when debonding exists at one of the interfaces of the cement sheaths. Tests performed in the laboratory have shown that there exist two types of mechanisms that could lead to cement-sheath loss of integrity: mechanical degradation, when cement is submitted to compressive or tensile loadings that are too high, or chemical degradation. The worst case is when both mechanisms occur at the same time or one after the other. For example, a cement sheath that is damaged before entering in contact with a degraded fluid will allow this fluid to penetrate deeper in the cement sheath, hence accelerating cement chemical-degradation. Hence, it is of paramount importance to understand the mechanisms that could lead to a cement-sheath loss of integrity before CO2 storage. This is with this objective, that we have been working on a mechanistic model that accounts for the various modes of cement-sheath loss of integrity after cement has been placed: a) cement volume-variations during hydration due to chemical shrinkage/expansion; b) cement volume-variations during hydration due to cement heat-production; c) contraction (dilation) of the casing due to a decrease (an increase) in mud density/temperature; d) cement volume-decrease due to pore collapse; e) thermal cycling. This paper has two objectives: presenting the mechanistic model and using this model to show that cement sheath loss of integrity not only depends on cement properties but also on the well architecture and well history.

Well integrity for CO2 injection from ships: Simulation of the effect of flow and material parameters on thermal stresses

“…The latter has been demonstrated to be a real problem in both laboratory and field studies (Carey et al, 2007;Crow et al, 2010;Kjøller et al, 2016), and is a major concern when it comes to CO 2 well integrity. The integrity of the interfaces between cement-casing and cement-rock is most severely threatened in situations where the well is exposed to strong temperature variations (Manceau et al, 2015;Nygaard et al, 2014;Bois et al, 2010). In this paper we seek to uncover when such critical situations can occur during CO 2 injection.…”

Characterization of Historical Methane Occurrence Frequencies from U.S. Underground Natural Gas Storage Facilities with Implications for Risk Management, Operations, and Regulatory Policy

“…By implication, frequencies based on the historical occurrence data could be incorporated into risk assessments and more sophisticated approaches such as Bayesian networks, in which probability density functions from the present analysis could become nodes within a network-scale analysis (Ayello, Jain, Sridhar, & Koch, 2014). Because forward analyses of occurrences from UGS facilities, such as mechanistic or decision-tree models for well integrity (e.g., Bois, Garnier, Galdiolo, & Laudet, 2010), may not be carried far enough out to predict failure occurrences, the historical data can provide a complementary view of postfailure occurrence mechanisms and severity magnitudes.…”

Identification of potential CO2 leakage pathways and mechanisms in oil reservoirs using fault tree analysis

“…Improper choice can deteriorate the interface connection and cause cracks. The cement body failure results from either the mechanical degradation when cement is under high loadings or chemical degradation when cement gets in contact with CO 2 ‐enriched water 67,68 . Poor cementing, compaction, tubular loading and thermal stress, casing eccentricity, wellbore inclination, and shrinkage in cement over time lead to de‐bonding at casing‐cement interfaces as well as cement‐formation interfaces, which transform into leakage pathways for CO 2 69 .…”