Page 353 - Standard Handbook Petroleum Natural Gas Engineering VOLUME2

320 Reservoir Engineering

Enhanced Oil Recovery
Chemical Oil Recovery or Chemical Flooding
Polymer-augmented waterflooding
Alkaline or caustic flooding
Surfactant flooding
-Low tension waterflooding
-Micellar/polymer (microemulsion) flooding
Hydyocarbon OT Gas Injection
Miscible solvent (LPG or propane)
Enriched gas drive
High-pressure gas drive
Carbon dioxide flooding
Flue gas
Inert gas (nitrogen)
Thmal Recovery
Steamflooding
In-situ combustion

These procedures are discussed in several texts on the subject [277,375-3791.
Two studies by the National Petroleum Council [SSO,SSl] and several papers
summarizing the later study are available [382-3851. The extensive literature on
enhanced recovery will not be cited, and the reader is referred to Reference 386
which provides numerous citations and is the basis of the following discussion.
Chemical Flooding

Chemical oil recovery methods include polymer, surfactant/polymer (variations
are called micellar-polymer, microemulsion, or low tension waterflooding), and
alkaline (or caustic) flooding. All of these methods involve mixing chemicals
(and sometimes other substances) in water prior to injection. Therefore, these
methods require conditions that are very favorable for water injection: low-to-
moderate oil viscosities, and moderate-to-high permeabilities. Hence, chemical
flooding is used for oils that are more viscous than those oils recovered by gas
injection methods but less viscous than oils that can be economically recovered
by thermal methods. Reservoir permeabilities for chemical flood conditions need
to be higher than for the gas injection methods, but not as high as for thermal
methods. Since lower mobility fluids are usually injected in chemical floods,
adequate injectivity is required. If previously waterflooded, the chemical flood
candidate should have responded favorably by developing an oil bank. Generally,
active waterdrive reservoirs should be avoided because of the potential for low
remaining oil saturations. Reservoirs with gas caps are ordinarily avoided since
mobilized oil might resaturate the gas cap. Formations with high clay contents
are undesirable since the clays increase adsorption of the injected chemicals.
In most cases, reservoir brines of moderate salinity with low amounts of divalent
ions are preferred since high concentrations interact unfavorably with the
chemicals that are injected.
Polymer-Augmented Waterfloodhg
High mobility ratios cause poor displacement and sweep efficiencies, and
result in early breakthrough of injected water. By reducing the mobility of water,
water breakthrough can be delayed by improving the displacement, areal, and
vertical sweep efficiencies; therefore more oil can be recovered at any given water