Chemical and mechanical properties of carbonated wellbore cement using a multi-analytical approach Page: 4 of 29
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22
23 INTRODUCTION
24 Successful implementation of geologic CO2 storage in deep saline and depleted oil
25 reservoirs hinges on the long-term integrity of wellbore cements used to isolate gas and fluid
26 flow between geologic strata, because these wells are potential sources for leakage out of the
27 storage reservoir.' Cement is highly reactive in carbon sequestration environments in which pH
28 and chemical gradients develop across the cement sample creating distinct reaction fronts. 2-4 It is
29 unclear what the impact of the alteration is on the long-term integrity of the cement in the
30 wellbore environment. Alteration of the cement does not necessarily lead to enhanced
31 permeability and leakage. A recent experimental study shows a mixed response of permeability
32 over time when reacted with acidic fluids.5 The apparent reduction in permeability due to cement
33 carbonation has also been seen in the field. Detailed analysis of wellbore cement from a CO2
34 enhanced oil recovery field indicated some leakage along surfaces adjacent to caprock and
35 casing, but the overall performance of the cement to isolate reservoir fluids was not
36 compromised.6 These observations suggest a strong interplay between cement carbonation and
37 its mechanical response to in situ stress within the wellbore environment. Alteration of Portland
38 cement by acids (used to accelerate degradation at ambient conditions) can significantly reduce
39 the effective moduli making the reacted material significantly more compressible.' a It is likely
40 that cement carbonation and the development of distinct reaction zones will also induce
41 structural and mechanical changes that will impact transport of gas and fluid. Ultimately, long-
42 term assessment of wellbore performance to isolate CO2 reservoir fluids will use advanced
43 models that couple chemical, mechanical and transport processes to represent the range of2
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Mason, H E; DuFrane, W L; Dai, Z; Charnvanichborikarn, S & Carroll, S A. Chemical and mechanical properties of carbonated wellbore cement using a multi-analytical approach, article, October 1, 2012; Livermore, California. (https://digital.library.unt.edu/ark:/67531/metadc840903/m1/4/: accessed April 25, 2024), University of North Texas Libraries, UNT Digital Library, https://digital.library.unt.edu; crediting UNT Libraries Government Documents Department.