Assessment of Leakage Pathways Along a Cemented Annulus

Abstract

Well integrity is one of the major concerns when assessing the containment of a geological CO 2 storage. Whereas defect-free cement sheaths provide reliable barriers that prevent vertical migration or leakage of the stored CO 2 , significant leakage can occur if pathways appear in the cement seal: the stored fluid can flow through and alter their initial properties. A simulator has been built to numerically investigate the leakage rate of CO 2 rich fluid through a pathway along a cemented annulus. Careful analysis of the physics and characteristic dimensions of the phenomena allows coupling of the flow, the mechanics of any defect and the chemical reactions that take place in the materials (fluid and cement). Results of the simulation, besides predicting the instantaneous flow rate and hydraulic conductivity of the defect, show different mechanisms of flow rates variation with time: in particular, coupling between flow along the defect and chemical reaction between cement and CO 2 can lead to the deposition of minerals within the defect space. This may lead to a total plugging of the pathway -a self-healing of the cement. Based on dimensional analysis and semi-analytical solution, a criterion is defined in order to assess the long-term stability of the pathway.

An Evidence-Based Approach to Well-Integrity Risk Management

“…Continuous leaks through steel thus tend to degrade within months, unlike long sections of cement. This is because any aging phenomenon in Portland cement [e.g., carbonation and leaching when exposed to carbon dioxide, requires very large leak volumes (of brine) and may lead to leak-pathway plugging anyway] (Deremble et al 2010). Besides cement, geologic barriers are also robust and, unlike cement, can heal when the cause of failure is removed.…”

“…Unfortunately, the presence of chlorides, hydrogen sulfide, sulfates, and important colonies of sulfate-reducing bacteria have resulted in corrosion rates of approximately 0.5 mm/a, which, in turn, have reduced interest for this resource-the last doublet system was installed in 1987. More recently, the Dogger aroused renewed interest as a possible carbon dioxide storage formation, with its proximity to emission sources and its well-understood hydrogeology (Grataloup et al 2009). Furthermore, the Dogger can also contain local hydrocarbon accumulations, which have been commercially produced, such as in the Malnoue field.…”

Analysis on inflowing of the injecting Water in faulted formation

“…There also exist speed-sensitivity, salt-sensitivity, acidsensitivity, stress sensitivity, and so on. [1][2][3] If injected fluid is ordinary water, most of the oil fields with low permeability will perform a strong stress sensitivity, which has already been confirmed in most oil fields at home and abroad. In the development of heterogeneous and low permeability reservoir, [4][5][6] the contradiction between interlayer and the inner layer is prominent, and injection-production process will lead to uneven distribution of pressure which will cause the difference of effective stress throughout reservoir; however, the reservoir's permeability can change when the effective stress varies; therefore, the permeability of reservoir is changing in the whole process of injection-production, and there is a strong non-linear relationship between them.…”