Page 78 - Principles of Applied Reservoir Simulation 2E

Part I: Reservoir Engineering Primer 63

reservoir heterogeneity increases or mobility ratio increases, particularly for
mobility ratios greater than one. This makes sense physically if we recall the
definition of mobility ratio.
Mobility ratio is the mobility of the displacing fluid behind the front
divided by the mobility of the displaced fluid ahead of the front. If the mobility
of the displacing fluid is greater than the mobility of the displaced fluid, then
the mobility ratio is greater than one. On the other hand, if the mobility of the
displacing fluid is less than the mobility of the displaced fluid, then the mobility
ratio is less than one. Mobility ratios less than or equal to one are considered
favorable, while mobility ratios greater than one are considered unfavorable.
Unfavorable mobility ratios often occur when gas is displacing oil or water is
displacing high viscosity oil. An example of a flood with a favorable mobility
ratio is the displacement of a low-viscosity oil by water.

Exercises

Exercise 7.1 Core floods show that the waterflood of a core with 80% initial
oil saturation leaves a residual oil saturation of 30%. If the same core is
resaturated with oil and then flooded with carbon dioxide, the residual oil
saturation is 10%. What are the displacement efficiencies for the waterflood and
the carbon dioxide flood?

Exercise 7.2 Assuming a log-normal distribution, estimate the Dykstra-Parsons
coefficient for three sample permeabilities: k { = 35 md; k 2=48 md; k 3 -126 md.

Exercise 7.3 (A) Run EXAM6.DAT and record the time, pressure, oil rate, water
rate, gas rate, cumulative oil produced, and cumulative gas produced at the end
of the run. (B) What is the oil recovery efficiency at the end of the run? Hint:
original oil in place is output in the run output file WTEMP.ROF.