TY - THES

T1 - Enhanced Research on the Carbonation Resistance of Wellbore Cement under In-situ Downhole Conditions

AU - Lebwohl, Stefan

N1 - embargoed until 20-03-2028

PY - 2023

Y1 - 2023

N2 - Carbonation of Portland-based cement systems poses a significant risk to well integrity in the harsh environment of CO2 injection wells. Due to the corrosion potential of CO2 in conjunction with water, the cement matrix is attacked, resulting in cement degradation. Therefore, a fundamental knowledge of the ongoing changes in physical, mineralogical, and mechanical properties within the cement matrix and the propagation rate of the carbonation front has the highest priority to ensure well safety throughout its entire life cycle. In this thesis, an innovative, in-situ, computed tomography (CT) -scannable test cell will be presented, enabling unprecedented research on the carbonation propagation over time. Furthermore, with this pressure cell, a system permeability indication, real-time monitoring, and cement curing within the cell under simulated downhole conditions were realized. The carbonation resistance of the specially designed cement was additionally investigated by an autoclave experiment, where the cement samples were exposed to a supercritical CO2 environment for 28 days. Mineralogical investigations, such as optical microscopy, scanning electron microscopy (SEM), element mapping, and X-ray diffraction (XRD) analysis provided insights into the cement matrix alteration and the distribution of cement phases. Compressive strength tests were conducted on the untreated and CO2-exposed samples to evaluate the cement¿s strength alteration. The results of the mineralogical investigation show that the cement matrix was significantly chemically restructured by the influence of CO2. Both the autoclave and in-situ test cell experiment verified a self-healing effect due to calcium carbonate precipitation. Impressive results were obtained by the CT-scan analysis. These show that the propagation rate of the carbonation front reached a maximum after CO2 injection and declined steadily with time since a protective layer was formed.

AB - Carbonation of Portland-based cement systems poses a significant risk to well integrity in the harsh environment of CO2 injection wells. Due to the corrosion potential of CO2 in conjunction with water, the cement matrix is attacked, resulting in cement degradation. Therefore, a fundamental knowledge of the ongoing changes in physical, mineralogical, and mechanical properties within the cement matrix and the propagation rate of the carbonation front has the highest priority to ensure well safety throughout its entire life cycle. In this thesis, an innovative, in-situ, computed tomography (CT) -scannable test cell will be presented, enabling unprecedented research on the carbonation propagation over time. Furthermore, with this pressure cell, a system permeability indication, real-time monitoring, and cement curing within the cell under simulated downhole conditions were realized. The carbonation resistance of the specially designed cement was additionally investigated by an autoclave experiment, where the cement samples were exposed to a supercritical CO2 environment for 28 days. Mineralogical investigations, such as optical microscopy, scanning electron microscopy (SEM), element mapping, and X-ray diffraction (XRD) analysis provided insights into the cement matrix alteration and the distribution of cement phases. Compressive strength tests were conducted on the untreated and CO2-exposed samples to evaluate the cement¿s strength alteration. The results of the mineralogical investigation show that the cement matrix was significantly chemically restructured by the influence of CO2. Both the autoclave and in-situ test cell experiment verified a self-healing effect due to calcium carbonate precipitation. Impressive results were obtained by the CT-scan analysis. These show that the propagation rate of the carbonation front reached a maximum after CO2 injection and declined steadily with time since a protective layer was formed.

KW - Bohrlochintegrität

KW - CCS

KW - Karbonatisierung von Bohrlochzement

KW - innovatives Testequipment

KW - CT-Scan Analyse

KW - In-Situ Test

KW - Well Integrity

KW - CCS

KW - carbonation of wellbore cement

KW - innovative testing equipment

KW - CT scan analysis

KW - in-situ testing

U2 - 10.34901/mul.pub.2023.42

DO - 10.34901/mul.pub.2023.42

M3 - Master's Thesis

ER -