Well Engineering Aspects and Risk Analysis of Carbon Capture and Storage (CCS) Wells
Authors: Liu Zhengchun , Samuel Robello 
Published: August 2023

Abstract
Interest in strategies to reduce greenhouse gas emissions has increased as a result of rising awareness of international climate change target. On such technology in the roadmap is the carbon capture utilization and storage (CCUS). New and existing wells can be drilled or retro-fitted to serve the carbon dioxide (CO2) injection purpose; well engineering aspects of well construction will have to be adjusted to meet the functional specifications of injecting CO2 down the sub-surface to provide a life span of 25+ years from first CO2 injected, casing design will have to be tailored for the new load cases required for CO2 injection.
In this work, a methodology for well design in carbon capture and sequestration (CCS) projects is discussed. Utility wells, which are used to lower pressure by removing formation water, as well as observation or monitoring wells are included in the CCS wells in addition to CO2 injection wells. Our research took aim at Process Safety and Well Barriers, an area of Well Engineering that hasn't been developed to CCS Wells, our results proposed a comprehensive approach to well barrier diagrams for CCS Wells .A new risk assessment matrix and CCS Wells Risk Index has been developed for CCS Wells which introduces a qualitative and quantitative way to screen and rank CCS projects based on a holistic analysis of all well's related risk elements.
Based on CCS Well Risk Assessment, CCS Wells Risk Index and Detailed Engineering Design with Specific Mitigations for each risk identified, it is recommended to proceed throughout the well delivery process with the proposed CCS Well Prospect. Annular zonal isolation is critical for prevention of CO2 migration and cross flow in shallower reservoirs pass the water caprock (i.e., water table), to this end several research studies such as those e quoted in this paper confirm that Portland Cement Slurries are suitable to provide zonal isolation even in the presence of carbonation of a very small thickness near the injection layer interface for a period of 35 plus years, reduction of cement porosity will provide additional benefits via chemical products in the slurry as to further minimizing any CO2 migration through cement pores in the annular space. The detailed casing design carried out using Von Misses Triaxial equation confirmed that L80 casing will be more than enough for the intended most severe load cases with a DF of 1.84 &gt; 1.25 (Required).
The risk assessment conducted on this project prior to mitigation enabled an effective identification of critical risk elements and its mitigation; further implementation of the risk mitigation plan allows to reduce the likelihood and impact to ALARP levels (As-low-as-reasonably-practical).
The CCS Well Index calculated at 0.25 (25%) evidenced a low-risk project which should pass the concept select phase of the well delivery process and continue throughout the road map and mature to execution. The risk assessment conducted on this project prior to mitigation enabled an effective identification of critical risk elements and its mitigation; further implementation of the risk mitigation plan allows to reduce the likelihood and impact to ALARP levels (As-low-as-reasonably-practical).