Wednesday, May 26, 2010

NETL Report - Degradation of Wellbore Cement Due to CO2 Injection

This NETL report may be found on the web -


The majority of locations that are being considered for carbon dioxide (CO2) injection

and sequestration are typically found in areas that have a history of oil, natural gas,

and/or coalbed methane production. This is due to value-added opportunities such

as enhanced oil recovery (EOR), enhanced gas recovery (EGR), and enhanced coal

bed methane (ECBM) recovery. There also exists a greater knowledge base for saline

formations that lie either above or below oil and gas reservoirs due to well logging

and exploration activities. As a result of human activity, these formations are typically

punctured by a significant number of wells from both exploration and production.

No matter how impermeable an overlying caprock is, the sealing integrity may be

compromised by the presence of wells. Well bores thus represent the most likely route

for leakage of CO2 from geologic carbon sequestration.

Abandoned wells are typically sealed with cement plugs intended to block vertical

migration of fluids. In addition, active wells are usually lined with steel casing,

with cement filling the outer annulus (Note: in oilfield terminology, an annulus is a

ring-shaped hole which extends the length of the well bore) in order to prevent

leakage between the casing and formation rock. The permeability and integrity of

the cement will determine how effective it is in preventing leakage.

After CO2 is injected into a saline formation, it may continue