Gelled polymer treatments are conducted to control fluid flow
in oil reservoirs.
After primary production in many oil reservoirs, additional
oil is recovered by injecting water to displace the oil through the
reservoir to production wells. Waterflooding success depends on the
volume of the reservoir contacted by the water. Rock layers with higher
permeabilities or fractures reduce the efficiency of the process by
providing low-resistance pathways for water to flow between injection
and production wells. Gelants are injected into these pathways from
either the injection and production wells and allowed to gel. The gel
provides high flow resistance, diverting injected water to oil-bearing
zones of the reservoir and increasing oil production.
A similar situation exists during primary recovery in natural
water-drive reservoirs such as those located in the Arbuckle formation
in Kansas. Wells in Arbuckle reservoirs are routinely completed in the
top few feet of the reservoir in order to delay excessive water
production that comes from the strong underlying aquifer. After these
production wells experience high water-to-oil ratios, gelled polymer
treatments can alter the fluid flow into the well, reducing water
production and increasing oil production.
Gelants are composed of a high molecular weight, water-soluble
polymers (usually partially-hydrolyzed polyacrylamide) and a
crosslinker (usually a chromium salt, chromium acetate). A typical
gelant contains about 0.5 wt.% polymer, 0.01 wt.% chromium and is mixed
in a brine solution. A polymer/brine solution is mixed inline with a
chromium solution to form the gelant that is injected into the well.
Typically, the injection is “bullheaded” or allowed
to flow unimpeded into the reservoir without zonal isolation or other
measures to direct the gelant at selected depths. The well is shut-in
for a time period to allow the solution to gel.
TORP has been conducting research
on gelled polymer treatments for over twenty years. Most of the work
has been fundamental and includes:
- Developing new gel systems
- Determining the effect of parameters, such as component
concentrations and pH, on the gelation behavior
- Conducting kinetic studies of the gelation reactions
- Mathematical modeling of the polymer crosslinking reactions
- Investigating the gelation behavior during flow in porous
media and fractures
- Examining the effect of fluid-rock interactions on gelation
behavior
- Mathematical modeling of gelant injection in porous media
(laboratory and field scales)
- Developing and validating a conceptual model of oil and
brine flow through gel-treated media
