Page 312 - Challenges in Corrosion Costs Causes Consequences and Control(2015)

290 CORROSION CONTROL AND PREVENTION

cause corrosion damage. Solids such as formation sand can both erode the pipe inter-
nally and can cause underdeposit corrosion, if stagnant.
Oxygen is not found in oil reservoirs, and precautions are taken to prevent oxygen
entry into the production environment; however, in many cases a few parts per million
of oxygen enter the pipeline and enhance corrosion problems.
External corrosion problems in oil and gas production are similar to those in
pipelines, but the economic impact on the total cost of production is limited as the
lines are shorter and smaller in diameter. Atmospheric corrosion of structures and
vessels is a problem for offshore fields and those operating in marine environments.
The improved quality of the protective coatings for offshore environments resulted
in reduced frequency of repainting platforms and tanks.
A consequence of the use of advanced technology in oil production from a reser-
voir results in increase in the corrosivity of the oil production environment. The extent
of corrosion increases because: (i) oil, water, and gas are present in the field. Seawater
or fresh water is injected downhole to drive oil out of formation. As time passes, the
amount of water to the amount of oil increases and the degree of internal corrosion
increases. Water injection from seawater or fresh water sources causes “souring” of
oilfields with H S and increases in corrosion rate. These water sources require bio-
2
cide injection and deaeration to avoid the introduction of new corrosion pathways
into the existing system. Tertiary recovery techniques involve miscible and immisci-
ble gas floods that may contain as much as 100% CO . This leads to high corrosivity
2
of the fluids.
Because of the high cost of failure and inability to rehabilitate facilities in deep
water, offshore production in deep water requires the use of high alloy steels and
more exotic corrosion control measures. A similar need for advanced corrosion con-
trol measures is encountered when dealing with high-pressure and high-temperature
offshore oil and gas fields where conventional corrosion mitigation is not applicable.
Typical costs for various expenses for one large oilfield area are listed in Table 4.41.
Corrosion in oil and gas production varies from one location to another location.
Corrosion can be internal corrosion caused by the produced fluids and gases, external
corrosion because of exposure to groundwater or seawater, and atmospheric corrosion
caused by salt spray and weathering offshore. Of these, internal corrosion mitigation
is the most difficult and expensive to mitigate and inspect periodically.
The choice of corrosion control activity would vary greatly with the production
environment, area, and company philosophy; therefore, some oil fields will use very
little treatment chemicals, although the cost of alternatives such as alloys and plastic
liners will fill this void.

TABLE 4.41 Typical Costs for One Large Oilfield

Corrosion Expenses Cost ($× Thousand)
Inspection, monitoring, and staff costs 9625
Repairs 1350
Corrosion inhibitor 7200
Total $18.175 million