Page 135 - Fundamentals of Enhanced Oil and Gas Recovery

Miscible Gas Injection Processes 123

• Use of tubing and casing leak detection methods and repairing techniques, using
both resin and cement squeeze technologies as well as insertion of fiberglass and
steel liners,
• Formulation and implementation of criteria unique to siting wells in or near pop-
ulated areas incorporating: fencing, monitoring, and atmospheric dispersion moni-
toring elements to protect public safety.

4.8.2 Corrosion Control
Carbon steel casing is used for CO 2 EOR injection wells and as such, it is susceptible
to corrosion. To mitigate corrosion, several techniques are typically used as follows [88]:
• Correct cement placement. To minimize contact between carbonic acid and the steel
casing, great care is used to assure that the cement, used to bond casing to the for-
mation, is adequately distributed along its entire axis. This requires some treating
actions, including careful removal of residual drilling mud from the hole, use of
centralizers to center the casing string in the bore hole, and full circulation of the
cement returns to the surface. With a well-formed cement sheath in place, the rate
of permeation of corrosive material is greatly reduced.
• Placement of acid resistant cements in zones susceptible to cement carbonation. As appropri-
ate, operators will incorporate specialty cements or specialty slurry designs adjacent
to and above the CO 2 injection zone. These cements are more resistant to CO 2
attack and hence dramatically reduce the rate of CO 2 degradation.
• Cathodic protection of the casing string. Operators employ both impressed and passive
current techniques on the casing string to counteract naturally occurring galvanic
action, which leads to corrosion. Both methods are used widely in many industrial
applications.
• Corrosion inhibitor. After completing the well, a biocide/corrosion inhibitor-laden
fluid is placed in the annular space between the casing and tubing string to further
suppress any corrosive tendency.

4.9 DESIGN STANDARDS AND RECOMMENDED PRACTICES

Oil and gas wells have existed for almost 150 years, since the time of first efforts
in Pennsylvania in 1859. Hence, well technology has developed over these years, and
also professional organizations, such as American Petroleum Institute, American
Society of Mechanical Engineers, the National Association of Corrosion Engineers,
and others, have continued to evaluate the catalog and technical requirements and
contributed in designing the operational practices based on formal engineering