Preparation Of Star Polyacrylamide Via Photopolymerization And Its Properties

As the regular oil displacement agent, the shear degradation resistance of linear poly acrylamide (PAM) is not good enough. The shear stability of PAM can be enhanced by change the molecular structure. In this paper, the star polyacrylamides (SxPAM) were synthesized by photopolymerization and the shear degradation resistance, some other properties and functional performance of these SxPAMs were investigated.Firstly, water-soluble thioxanthone-terminated poly(ehtylene imine)s (PEI600, PEI1800, PEI3000and PEI10000;600,1800,3000and10000are the weight-average molecular weights of the above PEIs, respectively) were synthesized to be as the macrophotoinitiators. These macrophotoinitiators were confirmed by elemental analysis,’H-NMR, FT-IR and UV spectra. Especially, the results of elemental analysis showed that there are4,12,22and67photoinitiated-agents (theioxanthone agent) in the four macrophotoinitiators, respectively.The effects of different reaction conditions on result of polymerization were studied. In order to meet the demand required by oilfield, the desired reaction condition was as follows:thioxanthone-terminated PEI10000was used as the initiator and its concentration was between0.015-0.020mmol/L; the mass fraction of comonomers was30%wt, the mol ratio of N,N-dimethyl-N-vinylnonadecan-1-ammonium chloride(C18DMAAC) to acrylamide was between0.3%and0.4%and the mass ratio of N-(2,4-dimethylpentan-2-yl) acrylamide to acrylamide was0.002%; the photopolymerization was carried out in a rectangular beaker by irradiating at30-35℃for40min; after the irradiation the mixture was put in the oven at40℃for2h and then was subject to hydrolysis at80℃for4h.In this paper, a new method to evaluate the shear stability of PAM was described. The flow-induced scission behaviour of different PAMs during planar elongational flow in a cross-slot flow cell was studied. The results showed that the shear stability of PAMs increased with the degree of branching of the PAMs and the shear stability of SxPAM decreased with the salt concentration in the solvent. However, at the same shear rate, the SPAMs exhibited superior shear stability in comparison to the linear PAMs in aqueous solutions.When the molecular mass of S67HPAM increases, its shear stability decreases at first then increasing molecular mass does not affect its shear strength. When the molecular mass of linear HP AM is between1.4×107and2.1×107, the increasing molecular mass also does not affect its shear stability. The shear stability of S67HPAM-0.3is mainly affected by its concentration and the content of C18DMAAC in polymer. Its shear stability first increases and then decreases along with increases of its concentration. In addition, its shear stability decreases with the content of C18DMAAC in S67HPAM-0.3.For PAM and HPAM, it was found that the reduction rate of relative viscosity exhibited an exponedntial dependence on shear rate, in which the coefficient C1can be used to quantitatively evaluate shear stability. The PAMs with better shear stability have smaller C1. For HPAM with C18DMAAC (hydrophobically modified acrylamide copolymer, HMPAM), the reduction rate of relative viscosity has a linear relationship with the shear rate and the coefficient K can be used to quantitatively evaluate shear stability.The HMPAMs with better shear stability also have smaller K. It can predict the reduction rate of relative viscosity of HPAMs and HMPAMs by using the C1and K, respectively. There are may be two reasons for the shear stability of SPAM is superior to LPAM. One is that the max shear stress endured by SPAM molecular is smaller than LPAM.The other is that the sacrificial scission of the branches can leads to only a minor decrease of molecular weight.Specific viscosity study showed that the conformation of PAM in water contracted with the increase of degree of branch of the PAM. The conformation of PAM with higher degree of branch was more spherical. The Schulz-Blaschke(S-B) more accurately describes the dilute solution properties of SxHPAM and star hydrophobically modified acrylamide copolymer. When the shear rate is between0.1and10000s-1, the apparent viscosity of HPAM solution in the distilled water increases with the degree of branch of the HMPAM. When the concentration of NaCl in the solvent is between0.1mol/L and lmol/L, the apparent viscosities of the HPAMs with different arms are closed to each other.The results of linear viscoelasticity test showed that when the frequency is0.05-1Hz, the elasticity and viscosity of the HPAM solution increases with its degree of branch firstly then decreases. Both the elasticity and viscosity of the SxPAM-0.3increase with its degree of branch. When1800mg/L S67PAM-y was dissolved in formation water at65℃, the polymer solution has a larger proportion of elastic component while the content of C18DMAAC is larger than0.2%. In the same condition, the elasticity of the S67PAM-0.3was much better than HAP. At50-80C, the solution time of S67PAM-0.3in brine (simulated formation water of SZ36-1oilfield) is between80-100min. When the concentration of S67PAM-0.3is1750mg/L, the apparent viscosities of the polymer solution before and after the stirring are more than50mpa.s and30mpa.s at65C. At the same time, at constant temperature of65℃and after aging test for90days, the apparent viscosity retention rate of the S67PAM-0.3solution is81.3. These results showed that the properties of S67PAM-0.3can meet the demand requested by oilfield completely.The result of core flow experiment showed that the resistance coefficient (RF) and residual resistance factor (RRF) of SHPAM are more than LHPAM. RF of S67PAM-0.3is smaller than regular hydrophobically modified acrylamide copolymer (HAP), but it can be injected easily and it’s RRF much larger than HAP. The oil displacement experiment showed that using the S67PAM-0.3can get incremental oil recovery factors of15%.