Wednesday, May 26, 2010
I consider this a must read document -
This NETL report may be found on the web -http://www.netl.doe.gov/publications/factsheets/rd/R%26D044.pdf
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