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Abstract
CO2 emission is generally accepted to be one of the prime causes of global
warming and climate change issues. In order to combat this global warming by
reducing CO2 emissions, there are numerous pilot projects developed worldwide,
where injection of CO2 for sequestration/storage, and Enhanced Oil/Gas Recovery
(EOR/EGR) have been ongoing for many years. The well design and completion
consideration of such CO2 injected wells, especially pertaining to well
integrity, selection of downhole completion equipments, design of pressure
containment for high pressure and highly corrosive environment, differs in many
ways compared to typical injection wells in the oil field or natural gas
storage projects. There are various well integrity failures, which are reported
in the literature during drilling and completion of such wells either for EOR
or CO2 sequestration projects. The monitoring of CO2 migration within the wells
with time is also essential.
In this study, the principle mechanisms involving well integrity issues
including caprock and cementing integrity in CO2 injected wells are
investigated at various operating conditions, based on comprehensive review of
various field cases as published in the literature. The critical factors
associated with well design failures, pressure containment, corrosion issues,
tubing leakage, cementing problems, and selection of downhole equipments for
well completion etc are identified. Based on the study, precise screening
criteria are developed that enables the design and completion of CO2 injected
wells for EOR and CO2 sequestration; thereby minimizing the chance of integrity
failures.
Results for different conditions will be presented and discussed to provide
guide lines for mitigating the numbers of theses challenges with an emphasis to
the successful design and completion of such wells. The key factors concerning
monitoring of CO2 migration with time will be discussed.
Introduction
CO2 injection either for sequestration or Enhanced Oil Recovery (EOR) becomes
very popular and interested topic among the scientific communities, since it’s
believed to be provided douple benefits: (i) reduction of carbon emission in
order to combat the global climate change by capturing and injecting CO2 into
the underground storage (known as CO2 sequestration); and (ii) increasing the
recovery of proven reserve through EOR method to meet world energy demand by
injecting CO2 into depleted oil and gas reservoirs. The concept of CO2
injection as a means of EOR has been implemented in many different oil and gas
reservoir worldwide since early 1970’s (Haigh, 2009). The first large scale CO2
injection based EOR project SACROC (Scurry Area Canyon Reef Operators
Committee) field in West Texas has been in operation since 1972 (Seatman et al,
2009). The key success of long term storage in depleted reservoirs depends on
the integrity of both the formations (e.g fault seal capacity) and the
wellbores. The formation integrity issue is beyond the current study. This
study concentrated on wellbore integrity issues only.
The wellbore integrity issues have been identified in many studies as a key
risk factor to be considered while evaluating the applicability of CO2
sequestration (e.g., Metz et al., 2005; Bachu and Celia, 2007; Viswanathan et
al., 2008; Oldenburg et al., 2009).), and CO2 injection based EOR projects
especially for the abandoned wells that are exposed to CO2-rich environment for
a long period of time. Factors that influence the wellbore integrity are mainly
due to poor completion and abandonment of the wells; and the long-term
stability of wellbore materials in a CO2-rich environment. The long-term
stability of wellbores materials in a CO2-rich environment is a complex
function of material properties and reservoir properties, such as aquifer water
(brine), rock compositions, CO2 pressure, and formation pressure, temperature
gradients, and the rates of material reaction with CO2. Therefore the well
design and completion consideration of CO2 injected wells differs in many ways
compared to typical injection wells in the oil field or natural gas storage
projects.
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