Carbon capture and storage is one way to reduce emissions of greenhouse gases in the atmosphere. Underground gas storage operations and CO2 sequestration in aquifers relay on both the proper wellbore construction and sealing properties of the cap rock. CO2 injection, candidates may be new wells or old wells. In both cases, the long-term wellbore integrity (up to 1. 000 years) is one of the key performance criteria in the geological storage Of CO2. The potential leakage paths are the migration CO2 along the wellbore due to poor cementation and flow through the cap rock. The permeability and integrity of the set cement will determine how effective it is in preventing the leakage. The integrity of the cap rock is assured by an adequate fracture gradient and by sufficient set cement around the casing across the cap rock and without a microannulus. CO2 storage in underground formations has revived the researc of long term, influence of the injected CO2 on Portland cements and methods for improving the long term efficiency of the wellbore sealant. Some researchers predicted that set cement will fail when exposed to CO2 leading to potential leakage to the atmosphere or into underground formations that may contain potable water. Other researchers show set cement samples from 30 to 50 year-old wells (CO2 EOR projects) that have maintained sealing integrity and prevented CO 2 leakage, in spite of some degree of carbonation, One of reasons for the discrepancy between, certain research lab tests and actual field performance measurements is the absence of standard protocol for CO2 resistance-testing devices, conditions, or procedures. This paper presents potential flow paths along the wellbore, CO2 behaviour under reservoir conditions, and geochemical alteration, of hydrated Portland cement due to supercritical. CO2 injection.
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