RESERVOIR DYNAMICS-III

Fluid Displacement in the Reservoir

The macroscopic sweep efficiency is the fraction of total reservoir which is swept by water or by gas. The microscopic displacement efficiency is the fraction of the oil which is recovered in the swept of the reservoir.

Recovery factor= macroscopic sweep  X  microscopic displacement

At higher rates the macroscopic efficiency will be reduced thus optimum rate is often imposed to limit by passed oil and increase macroscopic sweep efficiency.

For microscopic efficiency the main thing is Darcy’s law. For clastic oil reservoir a good permeability is 100 mD while poor permeability in 10 mD. For gas reservoir reasonable permeability is 1 mD.

Production profile

Economic criteria are used which profile to use.

For depletion drive, the plateau of the production can only be done by drilling more wells.

Enhanced Oil Recovery

There are 3 types of techniques used for EOR.

  1.  Thermal Technique

  2. Chemical Technique

  3. Miscible Process

Thermal technique such as steam injection, in situ combustion is used where there is a thick oil.

Polymer flooding aims at reducing the amount of by passed oil by increasing the viscosity of the displacing fluid say water thereby improving the mobility ratio. Chemicals like poly saccharides are used for this purpose.

Surfactant flooding is targeted at reducing the amount of residual oil left in the pore spaces by reducing the interfacial tension between oil and water and allowing the oil droplets to break down into small enough droplets to be displaced through pore throats.

Miscible process is aimed at recovering oil which would normally be left behind as residual oil, by using a displacing fluid which actually mixes with oil. Hydrocarbon solvents, CO2, N2 and hydrocarbon gases are used for this purpose