Title: Influence of effective stress and transport on mechanical and chemical alteration processes at the Cement-Caprock interface

Abstract

Fractures along interfaces between host rock and wellbore cement have long been identified as potential CO₂ leakage pathways from subsurface CO₂ storage sites. As a consequence, cement alteration due to exposure to CO₂ has been studied extensively to assess wellbore integrity. Previous studies have focused on the changes to either chemical or mechanical properties of cement upon exposure to CO₂-enriched brine, but not on the effects of loading conditions. This paper aims to correct this deficit by considering the combined effects of the fracture pathway and changing effective stress on chemical and mechanical degradation at conditions relevant to geologic carbon storage. Flow-through experiments on fractured cores composed of cement and tight sandstone caprock halves were conducted to study the alteration of cement due to exposure to CO₂-enriched brine at 3, 7, 9, and 12 MPa effective stress. We characterized relevant reactions via solution chemistry; fracture permeability via changes to differential pressure; mechanical changes via micro-hardness testing, and pore structure changes via x-ray tomography. This study showed that the nature and the rates of the chemical reactions between cement and CO₂ were not affected by the effective stress. The differences in the permeability responses of the fractures were attributed to interactionsmore » among the geometry of the flow path, the porosity increase of the reacted cement, and the mechanical deformation of reacted asperities. The suite of observed chemical reactions contributed to change in cement mechanical properties. Compared to the unreacted cement, the average hardness of the amorphous silica and depleted layers was decreased while the hardness of the calcite layer was increased. Tomographic imaging showed that preferential flow paths formed in some of the core-flood experiments, which had a significant impact on the permeability response of the fractured samples. We interpreted the observed permeability responses in terms of competition between dissolution of cement phases (leading to enhanced permeability) and mechanical deformation of reacted regions (leading to reduced permeability).« less

Authors:

Rhino, K. ;

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Iyer, J.; Walsh, S. D. C.; Carroll, S. A.; Smith, M. M.

Publication Date:

Thu Jul 01 00:00:00 EDT 2021

Research Org.:

Lawrence Livermore National Lab. (LLNL), Livermore, CA (United States)

Sponsoring Org.:

USDOE National Nuclear Security Administration (NNSA)

OSTI Identifier:

1780405

Alternate Identifier(s):

OSTI ID: 1807763

Report Number(s):

LLNL-JRNL-815337
Journal ID: ISSN 1750-5836; S175058362100092X; 103340; PII: S175058362100092X

Grant/Contract Number:  

AC52-07NA27344; AC02-05CH11231; FEW0208

Resource Type:

Published Article

Journal Name:

International Journal of Greenhouse Gas Control

Additional Journal Information:

Journal Name: International Journal of Greenhouse Gas Control Journal Volume: 109 Journal Issue: C; Journal ID: ISSN 1750-5836

Publisher:

Elsevier

Country of Publication:

Netherlands

Language:

English

Subject:

58 GEOSCIENCES; geosciences; environmental sciences; chemistry; carbon dioxide; geological carbon storage; Wellbore integrity; cement; caprock; water-rock interaction