  We investigate the effect of a temperature gradient on oil recovery in a
two-dimensional pore-network model. The oil viscosity depends on temperature
as, $\mu_o=exp(B/T)$, where $B$ is a physico-chemical parameter depending on
the type of oil, and $T$ is the temperature. A temperature gradient is applied
across the medium in the flow direction. Initially, the porous medium is
saturated with oil and, then, another fluid is injected. We have considered two
cases representing different injection strategies. In the first case, the
invading fluid viscosity is constant (finite viscosity ratio) while in the
second one, the invading fluid is inviscid (infinite viscosity ratio). Our
results show that, for the case of finite viscosity ratio, recovery increases
with $\Delta T$ independently on strength or sign of the gradient. For an
infinite viscosity ratio, a positive temperature gradient is necessary to
enhance recovery. Moreover, we show that, for $\Delta T>0$, the percentage of
oil recovery generally decreases (increases) with $B$ for a finite (infinite)
viscosity ratio. Finally, we also extend our results for infinite viscosity
ratio to a three-dimensional porous media geometry.
