Page 502 - Enhanced Oil Recovery in Shale and Tight Reservoirs

466 Enhanced Oil Recovery in Shale and Tight Reservoirs

Figure 14.4 Oil recovery from primary depletion and thermal stimulation with and
without kerogen (Egboga et al., 2017).

mechanism. At the end of heating, the temperature near the well increases,
but the viscosity due to this temperature increase is decreased from 0.3 to
0.23, indicating viscosity reduction is not an important mechanism.
Heating will accelerate kerogen decomposition into oil and gas, and the
decomposition will provide more pore space, resulting in an increase in
porosity and permeability. It is found that the porosity of the studied model
increases from 8% to 10%, and the permeability is increased from 0.0015 to
0.002 mD. From the absolute value increase in permeability, it seems that
the effect of stimulation by heating is not very significant. Note their model
does not include the mechanism of thermally driven fracturing. The ques-
tion is “Can such heating increase a local pressure higher than a fracturing
pressure?”
Fig. 14.4 shows the oil recovery for 7000 days for different recovery
schemes. It shows that the oil recovery from thermal stimulation when
the rock has 10% kerogen is 1% higher than that from the thermal stimula-
tion without kerogen, indicating that kerogen decomposition due to heat-
ing is not a dominant mechanism. It is because the thermal heating and the
resultant kerogen decomposition are concentrated locally near the heater.
This observation is consistent with the permeability data.
The simulation model shows the oil recovery is increased from 7.2% for
primary depletion to 11.5% for the depletion with 1000 days of heating. A
cost analysis shows that the energy cost is $26 to produce an additional barrel
of oil, which does not include the capital cost and implementation cost.