Page 366 - Standard Handbook Petroleum Natural Gas Engineering VOLUME2

334 Reservoir Engineering

SurfactantlPolymsrr Flooding

Description. Surfactant/polymer flooding, also called micellar/polymer or
microremulsion f looding, consists of injecting a slug that contains water,
surfactant, electrolyte (salt), usually a cosolvent (alcohol), and possibly a hydro-
carbon (oil). The size of the slug is often 5%-15% PV for a high surfactant
concentration system and 15%-50% PV for low concentrations. The surfactant
slug is followed by polymer-thickened water. Concentrations of the polymer often
range from 500-2,000 mg/L; the volume of polymer solution injected may be
50% W, more or less, depending on the process design.

Mechanisms. Surfactant/polymer f boding recovers crude oil by:

Lowering the interfacial tension between oil and water
Solubilization of oil
Emulsification of oil and water
.Mobility enhancement

Technical Smeenirag Gui&s
cmrde oil
Gravity >25O API
Viscosity e30 cp
Composition Light intermediates are desirable
Reservoir
Oil saturation >30% PV
Type of formation Sandstones preferred
Net thickness >10 ft
Average permeability >20 md
Depth e about 8,000 ft (see temperatwe)
Temperature 475°F
Limitatlons.

An areal sweep of more than 50% on waterflood is desired.
Relatively homogeneous formation is preferred.
High amounts of anhydrite, gypsum, or clays are undesirable.
Available systems provide optimum behavior over a very narrow set of
conditions.
With commercially available surfactants, formation water chlorides should
be 80,000 ppm and divalent ions (Ca* and Mg”) 400 ppm.

Problems.
Complex and expensive system.
Possibility of chromatographic separation of chemicals.
High adsorption of surfactant.
Interactions between surfactant and polymer.
Degradation of chemicals at high temperature.
Polymer Flooding [386]

Descrlptlan. The objective of polymer flooding is to provide better displacement
and volumetric sweep efficiencies during a waterflood. Polymer augmented