Heavy oil accounts for two-thirds of the world oil resources
but
contributes only one-seventh of the world oil production due to its
high oil viscosity and heavy distillates. Steam injection has been
widely used for heavy oil recovery by heating up the reservoir to
reduce oil viscosity. However, severe carbon loss to coking causes
low recovery efficiency and high energy consumption. Here, we report
supercritical water injection for heavy oil recovery. Supercritical
water is expected to be both a heat carrier and an organic solvent,
thereby not only reducing oil viscosity but also dissolving heavy
distillates to avoid coking. To test its feasibility, core experiments
were first conducted to simulate the recovery process. Results showed
that supercritical water flooding improved oil recovery by 17% and
reduced heat consumption by 34% versus classsical steam flooding.
Further, to clarify its recovery mechanism, a visualization technique
and a quantitative method were developed for regulating phase behaviors
and upgrading reactions between heavy oil and supercritical water.
Results showed that supercritical water has good miscibility with
heavy oil, and it is the key to both enhanced oil recovery and in
situ upgrading. High miscibility means formation of supercritical
water clusters around organic macromolecules, which makes asphaltene
difficult to aggregate and polymerize to form coke but easy to decompose
to form maltene and recover. Overall, supercritical water injection
has made great advances in enhanced oil recovery, energy saving, and
in situ upgrading for heavy oil recovery. The work provides a sound
basis for its application in oilfields.
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