Abstract

The objective of the research presented in this paper was to examine direct evidence of well conditions to determine wellbore integrity factors and mitigation for oil and gas wells exposed to carbon dioxide (CO2) in the subsurface. This project involved identifying the nature and severity of well defects such as poor or permeable cement, microannulus occurrence, cracks, and mechanical defects, through a combination of sustained casing pressure testing and well history review. Two producing fields were used as case studies to explore wellbore integrity: a Michigan Basin site and an Appalachian Basin site. These sites contain wells that have been exposed to injected or naturally-occurring CO2 over several decades and are therefore good candidates for researching wellbore integrity and sustained casing pressure.

Gas sample analysis, field surveys of well conditions, cement bond logs, well records, and sustained casing pressure build-up tests were used to quantify wellbore integrity factors. This research improves understanding the viability of CO2 injection projects and safe, reliable, and environmentally responsible operations.

Growth in CO2-enhanced oil recovery (EOR) has led to an increased demand for information about operational safety and the integrity of wells that have been exposed to CO2 due to injection or natural sources. Addressing this concern requires knowledge of the wellbore construction and local geology in relation to potential for corrosion of wellbore materials and migration of CO2. These aspects factor into site characterization, field management, and well plugging, especially in the Midwest U.S. where many legacy oil and gas wells are located.

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