Page 107 - Enhanced Oil Recovery in Shale and Tight Reservoirs

94 Enhanced Oil Recovery in Shale and Tight Reservoirs

Because different gases or solvents produce different compositions, to
evaluate their performance, the total produced hydrocarbon at different
times should be compared. Such recovery factor (RF) is defined:

ðTotal hydrocarbons produced after primary total production of the injected fluidÞ in BOE
ðtotal hydrocrbons in place at the end of primary depletion in BOEÞ
Total hydrocarbons include methane, butane, heptane, and decane.
Note that the unit of barrels of oil equivalent (BOE) is used. The volumes

used for calculations are at the standard condition of 14.7 psi and 60 F. The
BOE volume at the end of primary depletion is taken as the base volume to
calculate the recovery factor. 1 BOE ¼ 5800 SCF gas.
Since no ethane and solvent is in the original fluid (Fluid A), the
produced compositions are from the injected fluid. For methane, the total
production volume of the injected methane is equal to the total injected
volume minus the additional methane volume in the core that is the remain-
ing volume in the core minus the methane volume in the core at the end of
primary depletion. The total hydrocarbon recovery factors from different
gases and solvent are shown in Fig. 4.15. Note that the time in the horizontal
axis is huff-n-puff time (excluding the primary depletion time). It shows that
ethane produces the highest recovery of the total hydrocarbon volume in
BOE based on the hydrocarbons in place at the end of primary depletion,

Figure 4.15 Total hydrocarbon recovery factors in different huff-n-puff time.