Page 89 - Principles of Catalyst Development

70 Principles of Applied Reservoir Simulation

pressure is not maintained above the minimum miscibility pressure (MMP) of
the system, the gasflood will be an immiscible gas injection process.
Immiscible gas can be used as the principal injection fluid in a secondary
displacement process, or it can be used as the injection fluid for a tertiary
process. Two improved recovery processes based on immiscible gas injection
are the double displacement process (DDP) and the second contact water
displacement (SCWD) process [Novakovic, 1999]. Both processes require the
injection of immiscible gas into reservoirs that have been previously waterflood-
ed. Oil remaining after waterflood can coalesce into a film when exposed to an
immiscible gas. The processes require favorable gas-oil and oil-water interfacial
tensions. The oil film can be mobilized and produced by down-dip gravity
drainage (the DDP) process or by water influx from either an aquifer or water
injection (SCWD) following the immiscible gas injection period.

Thermal
Thermal flooding methods include hot water injection, steam drive, steam
soak, and in situ combustion. The injection or generation of heat in a reservoir
is designed to reduce the viscosity of in situ oil and improve the mobility ratio
of the displacement process. Electrical methods can also be used to heat fluids
in relatively shallow reservoirs containing high-viscosity oil, but electrical
methods are not as common as hot-fluid injection methods. Steam injection
methods work by injecting steam into the reservoir, while in situ combustion
requires compressed air injection after in situ oil has been ignited. Steam and
hot water injection processes are the most common thermal methods because
of the relative ease of generating hot water and steam. The in situ combustion
process is more difficult to control than steam injection processes and it requires
an in situ oil that can be set on fire. Hot gases and heat advance through the
formation and displace the heated oil to production wells.

Microbial
Microbial EOR uses the injection of microorganisms and nutrients in a
carrier medium to increase oil recovery and/or reduce water production in
petroleum reservoirs. Dietrich, et al.[1996] summarized the results of five