Introduction
This report focuses on collecting industry experience on the drilling, completion, regularity and interventions of CO2 wells. The aim for the report was to compare methodologies and techniques used for handling CO2 compared with those required for hydrocarbon extraction. This has allowed for a comparison to be made to the research already conducted on CO2 well integrity and monitoring techniques. The study will investigate whether conditions experienced during CO2 handling operations were predicted from modelling and experimental work and the effectiveness of linked risk assessments.
The differences between hydrocarbon and CO2 operations are driven by acidification of drilling muds, the high expansion factor of CO2 (going from liquid to gas phase), the effect of CO2 on elastomeric seals and finally the cooling behaviour of CO2 (which under uncontrolled depressurisation could chill equipment to temperatures below minus 70°C). Furthermore there is the potential to form CO2 hydrates if water is present. Also, temperature and pressure cycling due to phase-wise injection (e.g. if CO2 is delivered by boat) can strain the well equipment. Other wellbore integrity issues were also identified during a recent IEAGHG Modelling and Monitoring network meeting in July 2016. These included: timing and frequency of integrity log requirements; an improved understanding of cement pathways and a different (non-Darcy) approach to modelling flow in open wellbores. The choice of completion fluids could also be impacted by the presence of CO2 in the injection tubing and the potential of acidification of annular fluids should a tubing leak occur.
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Key Messages
The costs associated with CO2 EOR and CO2 storage projects are site and situation-specific. In general, oil prices have by far the larger impact on the economic viability of a CO2 EOR project, with the second largest impact being the cost of CO2. |
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