Chemical Structure of Surfactant-Grafted Polyacrylamide Used in Oilfields

Surfactant-grafted Polyacrylamide (S-PAM) flooding is a new technique used in Daqiang Oil Field in China and also a novel way for improving the recovery efficiency of primary oil layer after polymer flooding. S-PAM flooding technology is perfected gradually with the proceeding of multiple polymer surfactant oil displacement tests. Test results showed that the S-PAM used in field was greatly different with conventional ones. Therefore, it is necessary to study the chemical structure of S-PAM. Aiming at making clear the chemical structure of S-PAM, this study characterized the two commonly used S-PAM in oil field through chemical analysis and Fourier infrared spectrometer detection and analyzed the main composition and chemical structure of the two S-PAM.


Introduction
Relevant data reveal that Surfactant-grafted Polyacrylamide (S-PAM) has a framework constituted by ordinary polyacrylamide hydrocarbon chains.By grafting and copolymerizing the functional monomers and functional group to the lateral groups of the molecular chains, the original polymer hydrocarbon chains can be converted into the hydrocarbon chains containing a large amount of surfactants.Therefore, the aqueous solution of S-PAM is provided with the physical and chemical properties of the polymer and surfactant, as well as the new properties which are absent in the two agents.Generally, surfactant reduces the interfacial tension between oil and water in oil-water two-phase system to improve oil displacement efficiency.The S-PAM disperses the nonpolar substances in non-water system (including crude oil, coal power, cement, pigment, and so on) into emulsion and thus overcomes the application limitations of conventional surfactants in non-aqueous system [1] [2].
As for unhydrous oil, the S-PAM can unify the phase viscosity, phase activity, thickening (water) ability, and solubilizing (oil) ability and reduced the tension of oil-water interface significantly in the aqueous solution with low molecular weight and concentration.The chemical agent of single component formed by special molecular design is called as multivariate graft polymer surfactants.Since the molecules contains hydrophilic and lipophilic groups (also known as hydrophobic group), such surfactants are known as parent molecule.
The molecular structures of polymer surfactants include random form, blocking form, and grafting form etc. This study investigated the Surfactant-grafted Polyacrylamide.Grafting surfactant is a kind of functional polymer compound with clear structure and also shows certain special effects in aspect of surface activity.According to the differences of the hydrophilic radicals in the molecules, the S-PAM can be generally classified into cationic surfactant, anionic surfactant, nonionic surfactant, and amphoteric surfactants.In broad sense, there are also surfactants composed of cationic and nonionic surfactants and those composed of anionic and nonionic surfactants.
The application performance of S-PAM greatly depends on the molecular structure and application condition.The molecular structure therein is the most fundamental factor and also the primary study aim for developing functional, efficient and new products.The molecular structure of S-PAM mainly includes the chemical composition of chains, the sequence distribution of chain structure, and the iconicity, charge density, and geometric structure (linear, branched, and cross linked) of molecular chains etc.It is of great significance of determining and characterizing the chemical structure of S-PAM for grasping the relationship between the chemical structure and performance of S-PAM, selecting S-PAM, optimizing usage mode and usage condition, improving synthesis methods and polymerization condition, as well as developing new S-PAM [3]- [8].
This study analyzed the composition and structure of Lianhua S-PAM and Haibo S-PAM using chemical analysis method (chemical surfactant group identification method) and instrument analysis method (infrared spectroscopy) etc.

Materials and Instruments
Two origins of S-PAM were used in this experiment: Daqing Refining & Chemical Company S-PAM (Lianhua type III), which is called Lianhua S-PAM ;Shanghai Haibo company S-PAM (Haibo type III), which is called Haibo S-PAM; polymer: polyacrylamide (the Fourth Oil Plant of Daqing Oilfield Company Limited, at molecular weight of 35,000,000); surfactants: cetyl trimethyl ammonium bromide(CTAB) (cationic surfacant), petroleum sulfonate surfactants (anionic surfactant, the Fourth Oil Production Plant); Main instrument: Btuker Ten-sor27 infrared spectroscopy.

Methods
The structure and composition of the S-PAM were firstly studied using chemical analysis method to analyze the surfactant types in the two S-PAM on whole and accurately determine the group type in the following infrared spectrum test.
Determination of cationic surfactants: we took a certain volume of S-PAM solution and adjust the pH value to 7. Then we added 10 ml bromophenol blue reagent into the solution.In case of cationic surfactant, the solution shows blue color.
Determination of anionic and nonionic surfactants: we took a certain volume of S-PAM solution and added 10 mL methylene blue solution and 5 mL chloroform into the solution.The solution obtained was violently oscillated for 2 -3 s and then stayed for layering.The colors of the two layers were observed.In case of cationic surfactant, the chloroform layer was blue.Then we added surfactant solution again and repeated the operations above.The chloroform layer then turned dark blue.In case of nonionic surfactants, the solution was milky solution or the two layers present the same color.
To further determine the group types in the surfactants produced by Daqing and Shanghai, instruments were used for analysis.In S-PAM analysis field, infrared spectra were mainly used for quantitative analysis, especially for the quantitative analysis of the functional groups of S-PAM.According to the characteristic absorption of compounds, it was aware of the functional groups in the compounds, which were conductive to determine and verify the types of related compounds.This section used the infrared spectrum analysis method to analyze the compositions of the two surfactants.The experiments preliminarily showed that there was no cationic surfactant involved in above two S-PAM.

Determination of Anionic and Nonionic Surfactants
As shown in

Identification of the Anions in S-PAM Solution
The anions were primarily examined to obtain the grafting groups in S-PAM solution.The primary examination results showed that the anions included sulfate radical ions ( 2 4 SO − ) and chloride ions Cl − .The barium chloride and silver nitrate at certain concentrations were mixed with S-PAM solutions at certain concentration.The reaction phenomena were observed.In case of white precipitate and the precipitate that were insoluble after the hydrochloric acid and barium chloride were added in, it was proved that there were 2 4 SO − and Cl − .Table 1 shows the test results:

Infrared Characterization
The compositions of the two S-PAM were analyzed using infrared spectrum in this section.Figure 3 and Figure 4 show the infrared spectra of the two S-PAM (Table 2 and Table 3).Amino acid hydrochloride , cationic Analysis above showed that Lianhua S-PAM refining factory polymerized the nonionic and cationic surfactants, while that Haibo S-PAM polymerized the nonionic surfactants on the main chain of polyacrylamide.Moreover, the functional groups of the two S-PAM are different.

Conclusion
Analysis on the compositions of S-PAM implied that, Lianhua S-PAM polymerized the nonionic and cationic surfactants, while Haibo S-PAM polymerized the nonionic surfactants on the main chain of polyacrylamide.Moreover, the functional groups of the two polymer surfactants were different.

3. 1 .
The Compositions and Structure of S-PAM 3.1.1.Determination of Cationic Surfactant The solutions in Figure 1 are distilled water blank control, Lianhua S-PAM, Haibo S-PAM, polyacrylamide (used by the Fourth Oil Plant of Daqing Oilfield Company Limited, at molecular weight of 35,000,000), CTAB (cationic surfactant) in turn from left to right.

Figure 2 ,
the solutions are distilled water blank control, Lianhua S-PAM, Haibo S-PAM, polyacrylamide (used by the Fourth Oil Plant of Daqing Oilfield Company Limited, at molecular weight of 35,000,000), CTAB (cationic surfactant) in turn from left to right.As shown in this figure, Lianhua S-PAM contains nonionic surfactant and possibly contains cationic surfactant; Haibo S-PAM contains both nonionic surfactant and cationic surfactant.

Figure 4 .
Figure 4.The infrared spectrum of Haibo S-PAM.

Table 1 .
Primary determination results on anions.

Table 2 .
The analysis result on the infrared spectra of Lianhua S-PAM.

Table 3 .
The analysis results on the infrared spectra of Haibo S-PAM.

. The Structure and Composition of S-PAM
By means of chemical analysis, IR spectra analysis, as well as related data concerning S-PAM synthesis, the chemical structures of two S-PAM are indicated as follows:The structure and compositions of Lianhua S-PAM: