Development of a Novel Method To Evaluate Well Integrity During CO2 Underground Storage

Abstract

A safe and ecologic underground storage of carbon dioxide (CO 2 ) requires long-term integrity of the wells affected by the injected CO 2 , including both active wells and abandoned wells. In line with other investigators, technical integrity is assumed if there is no significant leak in the subsurface system from the storage reservoir. The evaluation of integrity of abandoned wells over a long time frame during CO 2 underground storage can only be performed indirectly and requires a comprehensive understanding of relevant thermal/hydraulic/mechanical/chemical processes affecting well integrity. This paper presents an integrated approach coupling qualitative features, events, and processes (FEPs) and scenario analysis with quantitative-model development and consequence analysis. The qualitative analysis provides a solid and comprehensive study on all the FEPs that affect well integrity. The mechanical model presents the stress distribution of the casing/cement/rock composite system and provides a quantification of the defect dimension caused by different load conditions. The defect dimension can be used to compute equivalent permeability of the cement sheath by use of empirical correlations, which is an important input parameter for the following CO 2 -leakage simulation, provided it is considered that CO 2 can only migrate through the defects instead of the cement matrix. When integrity is compromised, the storage reservoir will leak CO 2 . For this leakage, a numerical model is presented to simulate the flow of CO 2 along abandoned wellbores during the storage period, such as 1,000 years. It is found from the FEP analysis that the most-critical system components are caprock, casing/cement/rock composite system, and abandonment elements. By building a geomechanical model and a leakage model, it is also found that in the simulated scenarios the CO 2 -leakage rate is very small except for when using cement sheaths of very poor quality, which can lead to a leakage rate exceeding the maximum-allowable value. The sensitivity analysis shows that the vertical permeability of the cement sheath plays the most critical role. In comparison with previous studies, this method is comprehensive and easy to implement.

Risk assessment of abandoned wells affected by CO2

“…It can be seen as a reference book or an initial help in the early phase of a storage project and provides the basis for modeling (Bai et al 2014d). Performance and risk (PR TM ) method A performance and risk (PR TM ) method was developed by the company Oxand S.A. and Schlumberger (Bai et al 2014b;Le Guen et al 2009). Different from FEPs analysis, the PR TM method is a quantitative tool to evaluate well integrity.…”

Review on Carbon Capture, Utilization, and Storage for Enhancing Gas Recovery

“…As shown in Figure , these leakage paths may occur via or near old wells, as well as in presently active wells that do not meet the necessary construction criteria. Wells that have not been properly sealed after being abandoned are likely to be major pathways for CO 2 movement, particularly when CO 2 is being injected and natural gas is being produced simultaneously. , This situation highlights the need to strictly follow well construction and abandonment standards to reduce the possibility of CO 2 leakage in CO 2 -EGR projects. Monitoring and analyzing geotechnical responses is a significant challenge in implementing field-scale carbon dioxide (CO 2 ) storage projects.…”

“…Wells that have not been properly sealed after being abandoned are likely to be major pathways for CO 2 movement, particularly when CO 2 is being injected and natural gas is being produced simultaneously. 239,240 This situation highlights the need to strictly follow well construction and abandonment standards to reduce the possibility of CO 2 leakage in CO 2 -EGR projects.…”

Worldwide Status of CCUS Technologies and Their Development and Challenges in China

“…The stages of a CCS project can be divided into (1) CO 2 capture, (2) CO 2 transportation, (3) CO 2 injection, and (4) postinjection of CO 2 [12][13][14][15][16][17][18][19].…”