I
n EOR, polymer drive has produced significant results in increasing oil production and decreasing water cut. However, a problem can occur from
polymer channels thru the high-perm zone and large pores between producers and injectors, causing premature polymer break through in the producers. Thus large quantity of polymer is produced from the producers without acting as driving agent, and in the early stages of polymer drive, polymer content is quite high in the produced fluids. This means a big waste of the polymer, disposal problems, and subsequent high oil production costs. So, the kind of technology to be used to solve this "channeling" problem and to make full use of the injected polymer, is a difficult task to be urgently tackled in EOR. Our company put emphasis on this subject to be technically tackled and developed. Through a large number of tests, it was found that two methods are quite effective in controlling polymer "channeling": one is delayed gel-forming, that is to use gel in deep-penetration profile modification. This technology is already explained in "Product Introduction" of our company. The other is crosslinking and precipitating technology in the formation by anionic and cationic polymer, that is an anti-channeling agent" in the EOR of oilfields.

Prior to injecting as oil driving agent, a certain amount of cationic polymer, which can be strongly adsorbed, is first injected into the oil producer or water injector. Such cationic polymer is what we call "anti-channeling agent". Its trade name and characteristics are shown below:

Trade Names and Characteristics of Anti-Channeling Agent

Trade Name
Cationicity(%)
Molecular Weight(x106)
Appearance
Solid Content(%)
Residual Monomer(%)
FC-1
100
3
White powder
90
0
FC-2
80
5
White powder
90
<0.01
FC-3
60
8
White powder
90
<0.03

Note: Product is packaged in 25kg dual-wall bags. Inner liner is sheet plastic and outer cover is woven plastic.

Normal injected concentration of anti-channeling agent is~0.1-0.2%, which can be determined according to the concentration and viscosity of the injected anionic polymer oil-driving agent. Since the viscosity of the anti-channeling agent solution is high, the anti-channeling agent will selectively penetrate the high-perm zone to a large degree, and will be adsorbed onto the rock surface in the high-perm zone. When the subsequently injected anionic polymeric oil-driving agent begins to channel along this high-perm zone, it will meet the already-adsorbed cationic polymer, and a crosslinking reaction will occur between anionic and cationic polymer to form a three-dimensional, network-like structure. The resulting gel has a very high viscosity and occupies the big pores, thus greatly reducing the effective porosity of this high-perm zone. Consequently, the following injected oil-driving agent is forced to bypass the blocked zone, and directs its flow towards medium-and low-perm zones. As the reaction between anionic and cationic proceeds, a large amount of precipitate will occur which mainly acts as a physical blocking agent in the big pores. This will enlarge the covered volume of the polymer flood. The features of the antichanneling agent system enables it to minimize the cost of a polymer drive.

 

 
 

 


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