Page 437 - Enhanced Oil Recovery in Shale and Tight Reservoirs

Air injection 405

In a Greaves et al.’s (2000) LTO experiment (120 C), the oxygen, CO 2 ,

and CO concentrations were 2%, 8%, and 1.2% after 175 h of oxidation,
respectively. The experiment indicated that CO 2 and CO were produced
in an LTO process. It is believed that 12% CO 2 concentration in the
produced gas stream is a good indication of combustion (Montes et al.,
2010). A short time of pressure increased in Sarma et al.’s (2002) isothermal
aging ARC tests.

13.2.4 Ramped temperature oxidation (RTO)
A ramped temperature oxidation apparatus consists of two identical tubular
reactors mounted in a common heating block where both are simulta-
neously heated at a fixed rate. One is the active reactor packed with a
core saturated with oil and water, while the other one is the reference
reactor packed with a clean core only. Inert gas is flowed through the refer-
ence reactor, whereas an oxygen-containing gas is flowed through the active
reactor. The temperatures in the two reactors are compared to isolate
exothermic and endothermic events related to oxidation reactions. Apparent
atomic H/C ratio, apparent reacted oxygen/fuel ratio, and percentage of
reacted oxygen converted to carbon oxides from the active reactor are
reported (Moore et al., 1999).
Like TG or DSC tests, when the heating rate is higher than that caused
by oxidation reactions, an RTO test may not represent the oxidation
reactions that will occur in a reservoir (thermal hysteresis). This is because
when the heat generation rate in a reservoir is low, the subsequent higher
temperature oxidation may not be able to initiate because of the loss of
generated heat into overburden and underburden rocks.

13.2.5 Combustion tube test
The fundamental part of a combustion tube apparatus is the combustion
tube which is insulated and heated by a series of heaters. This is to reduce
the radial heat loss. However, the heaters should be adjusted so that they
do not drive the combustion. This is achieved by maintaining the temper-
ature in the middle of the test tube slightly higher than the wall temperature.
The tube is ignited at one end by using heaters. A combustion tube test (CT)
is designed to have artificial ignition; LTO is minimized; reaction kinetics
are not obtained from a combustion tube. The following data may be
obtained from a combustion tube test (Prasad and Slater, 1986):
• Atomic H/C ratio of the burned fuel
• Oxygen-fuel ratio