Characterization and Source Analysis of Suspended Solids in
Chemical Flooding Sewage
G L Liu
1,2, *
, X N Li
1,2
, F S Zhang
1,2
, Y Z Qu
3
, N Qi
4
, Y J Lu
1,2
and H M Su
1,2
1
Research Institute of Petroleum Exploration & Development, PetroChina, China
2
Key Laboratory of Oilfield Chemistry, CNPC, Beijing 100083, China
3
CNPC Drilling Research Institute, Beijing 102206, China
4
China University of Petroleum (East China), Qingdao 266580, China
Abstract. The oilfield sewage from chemical flooding was analysed in this paper. It showed
that the sewage contained high concentration of suspended solids, organic acrylamide
polymer, multivalent metal ions. IR and Electron microscope measurement showed the value
of suspended solids measured by membrane filtering method was much higher than the real
value due to polymer absorption and plugging on membrane. The suspended solids in filtered
sewage increased due to formation of fine inorganic scale and colloidal particles under certain
conditions. The zeta potential showed the sewage was much negatively charged. At pH value
3~4, the zeta potential of sewage shifted to -5.0mv quickly and much precipitate of polymer
gel appeared in sewage. Above all, the negatively charged polymer and high viscosity of
sewage played an important role in dispersing and stabilizing suspended solids.
1. Introduction
In recent years, various chemical flooding technologies have been developed to enhance oil recovery.
Polymer flooding technology has been applied successfully on an industrial scale in Daqing oilfield
and obtained satisfied stimulation effect[1-2]. On polymer flooding basis, Alkali-surfactant-polymer
(ASP) flooding pilot test has been performed in Daqing Oilfield. By using strong or weak alkali,
surfactant and polymer in the injected water, ASP flooding technology can improves recovery rate
dramatically. However, produced sewage from ASP flooding became more difficult to treat for it
contained much emulsified oil, suspended solids and residual chemicals[3-4]. In particular, the fine
suspended solids were very stable and difficult to remove. The effective treatment for ASP flooding
sewage became urgent and important for its industrial application.
Engineers and researchers are eager to know the Characterization, source and stability of
suspended solids (SS) in ASP flooding sewage[5]. In this paper, various measurement including Zeta
potential, Size distribution, IR and SEM were applied to suspended solids of ASP flooding sewage
from Daqing oilfield. The study would help understand the characteristics of suspended solids and
improve the treatment efficiency of ASP flooding sewage.
Liu, G., Li, X., Zhang, F., Qu, Y., Qi, N., Lu, Y. and Su, H.
Characterization and Source Analysis of Suspended Solids in Chemical Flooding Sewage.
In Proceedings of the International Workshop on Materials, Chemistry and Engineering (IWMCE 2018), pages 77-82
ISBN: 978-989-758-346-9
Copyright © 2018 by SCITEPRESS – Science and Technology Publications, Lda. All rights reserved
77

2. Experimental
2.1. Materials
JCXG-03 Suspended solids Measurement, Harbin Jin Boda Electrical Co., Ltd; X650 Scanning
Electron Microscope, Japan Hitachi Company; Nexus 670 Infrared Spectrophotometer, USA Nicolet
Company; EA940, The Thermo Orion; ICAP- 9000 Jarrel-ASH Company.
ASP flooding sewage was taken from wastewater treatment station in Daqing oilfield.
Microporous membrane (pore size 0.45μm, diameter 50mm) was purchased from Beijing Huada
Liming membrane material Co.; Hydrochloride and sodium hydroxide were all analytical grade and
supplied by Sinopharm Chemichal Reagent Beijing Co, Ltd; PAC was industrial grade.
2.2. Suspended solids content measurement and particle size analysis
Suspended solids content was measured with the microporous membrane filtration method
recommended by SY/T 5329-2012 standard. The particle size was analysized by Mastersizer 2000
laser particle sizer.
2.3. Zeta potential measurement
The zeta potential of suspended solids was measured by Nano Z zeta electric potential analyzer at
35°C .
2.4. SEM observation and elemental analysis
First, the blank membrane and membrane filtering sewage were dried at 60°C and sprayed platinum.
Then, the membrane was fixed on the SEM sampler for micro-morphology observation of retention
matter on membrane. Moreover elemental analysis was carried out by EDAX.
2.5. IR analysis
The dried retention matter on membrane filtering sewage was comminuted and ground with dried
KBr powder. The KBr disk was dried again and subjected to the IR spectrophotometer.
3. Results and discussion
3.1. Suspended solids content and particle size distribution
The sewage sample of ASP flooding was taken from Daqing oilfield. The water quality data
including suspended solids content, ions and chemicals was shown in Table 1.
Table 1. The water quality of ASP flooding sewage from Daqing oilfield (mg/L).
Item
Ca
2+
Mg
2+
Al
3+
Fe
3+
HCO
3
-
CO
3
2-
Data
36.8
27.51
0.94
0.68
920
32.5
Item
pH Value
Soluble silicon
Suspended solids
Total solid
HPAM
Surfactant
Data
8.6
32.1
123.5
6940
575
46.2
According to Table 1, the suspended solids content in ASP flooding sewage was above 120mg/L
measured with membrane filtering method. And there were much HCO3- and HPAM in sewage with
high pH value of 8.6. Meanwhile, there were multivalent metal ions such as Ca
2+
, Mg
2+
and soluble
silicon. Overall, the water quality of ASP flooding sewage was very complicated.
Figure 1 showed that the median grain diameter of suspended solids, namely D(0.5), was 2.2μm.
The D(0.1) and D(0.9)were0.085μm and 9.561μm respectively. According to the peaks of particles
size distribution, there were various size particles in ASP flooding sewage.
IWMCE 2018 - International Workshop on Materials, Chemistry and Engineering
78

According to water quality standard in SY/T5329-2012(Water quality standard and practice for
analysis of oilfield injecting waters in clastic reservoirs), the suspended solids content of ASP sewage
was much higher than standard value about 10mg/L.
Figure1.Size distribution of suspended solids in ASP flooding sewage from Daqing oilfield.
3.2. Zeta potential studies of suspended solids
The suspended solids in sewage was always charged, which can be characterized with zeta electric
potential. Usually the stability of suspended solids increased with the increase of zeta potential
absolute value. Figure 2 and Figure 3 showed the influence of PAC flocculant or pH value on zeta
potential of suspended solids in sewage.
Figure 2. Influence of PAC on zeta potential. Figure 3. Influence of pH Value on zeta potential.
Figure 2 showed that the zeta potential of ASP flooding sewage was -23.8mv, indicating the
suspended solids was much negatively charged. The main reason for negative zeta potential was that
ASP flooding sewage contained much base, negatively charged HPAM and anionic surfactant, which
enhanced the stability of suspended solids. The zeta potential positively shifted when adding PAC
flocculant and keep -18.3mv finally, which showed that the PAC flocculant could decrease the
stability of suspended in ASP flooding sewage in some extent. The hydrolysate of PAC was
positively charge and changes the zeta potential of suspended solid by electric neutralization.
Figure 3 showed that pH value influenced zeta potential of sewage greatly. The zeta potential
positively shifted significantly with the increase of pH value with the maximum value of -32.7mv.
And the zeta potential positively shifted with the decrease of pH value. At pH value 3~4, the zeta
potential shifted to -5.0mv quickly and much precipitate appeared. Meanwhile the suspended solids
content decreased significantly to less than 20mg/L. At low pH values, negatively charged polymers
formed gels to improve the zeta potential of sewage. Although adding acid could make the suspended
Characterization and Source Analysis of Suspended Solids in Chemical Flooding Sewage
79

solids precipitation and decrease its content, it was not feasible considering economical and
technology factors for the precipitation pH value of suspended solids must be less than 4.
3.3. IR of the retention matter on microporous membrane
In order to determine the composition of suspended solids in ASP flooding sewage, the IR of
retention matter on microporous membrane was measured and analysized. The results were shown at
Figure 4.
Figure 4.IR of retention matter on membrane after filtering sewage.
The Figure 4 showed that the composition of retention matter on microporous membrane was
very complicated. The HPAM (hydrolyzedpolyacryamide) was evidenced by peaks at 3404cm-1,
1725 cm
-1
, 1663cm
-1
, 608cm
-1
. The -CH
3
and -CH
2
- functional groups were evidenced by peaks at
2922cm
-1
, 2851 cm
-1
, 1462 cm
-1
, 719 cm
-1
. The clay and inorganic salts were evidenced by peaks at
1560 cm
-1
, 1057cm
-1
,872cm
-1
.
The results showed that the retention matter on microporous membrane contained not only
suspended solids but also organic matters such as HPAM, hydrocarbons, etc.
3.4. SEM of the retention matter on microporous membrane
In order to study the composition and microstructure of suspended solids further, SEM measurement
and elemental analysis were carried on to retention matter on microporous membrane.
According to the SEM micrographs presented in Figure 5 (A), the blank membrane appeared as
network structure with multilayer connected by cellulose. Its pore diameter was 2~5μm and the main
elementals were C, O, Zr. As presented in Figure 5.(B) and Figure 5 (C), much fine particles(particle
size<1μm) with various shapes were intercepted and Na, Cl, Ca and Si elements content increased,
indicating existence of clay, inorganic salt or scale.
However, as presented in Figure 5 (D), there were much sticky and amorphous matters adsorbed
on membrane skeleton and the C content increased significantly, which also proved that the retention
matter on microporous membrane contained much organic matters such as HPAM in addition to
suspended solids.
The water-soluble HPAM shouldn’t be regarded as suspended solids according to the definition of
suspended solids in SY/T 5329-2012. However HPAM could make the value of suspended solids
measured by membrane filtering method much higher than the real value. The HPAM absorption on
membrane increased the mass of retention matter directly. On the other hand, HPAM absorption
resulted in the decrease of microporous membrane pore size, intercepting more suspended solids.
IWMCE 2018 - International Workshop on Materials, Chemistry and Engineering
80

Therefore, measurement method of suspended solids content suitable for ASP flooding sewage
should be established to decrease the effect of HPAM to measurement result.
(A) (B)
(C) (D)
Figure 5.SEM images of the blank membrane (A); Membrane after filtering sewage(B);Membrane
after filtering sewage and solvent extraction(C); Membrane after filtering sewage, solvent extraction
and removing surface layer(D).
3.5. Suspended solids increase of filtered sewage with scale formation
It was found that the sewage of removing suspended solids through microporous membrane filtration
gradually became cloudy when keeping at 45°C of reservoir formation temperature. The turbid
matter could react with hydrochloric acid and release bubbles, which indicated that it contained much
carbonate scale. From Figure 6, the SS content of sewage increased from 82mg/L to 160mg/L after
24hat 45°C because of scale formation.
During ASP flooding process, the scale of calcium carbonate and hydroxide and silicate scale was
formed as followed:
Ca
2+
+ CO
3
2-
→CaCO
3
↓+CO
2
↑+H
2
O
Ca
2+
+ HCO
3
-
→CaCO
3
↓+CO
2
↑+H
2
O
Ca
2+
+ SiO
3
2-
→CaSiO
3
↓
SiO
3
2-
+H
2
O→H
m
SiO
4
m-4
→Polysilicic acid→Silicic acid gel→SiO
2
Because of the reaction between strong alkali in the ASP flooding system with formation fluid
and minerals, the produced sewage contained OH-, HCO
3
-
, CO
3
2-
, Ca
2+
, SiO
3
2-
and other scaling ions.
Under certain conditions, there would be various inorganic carbonate scales and silicon colloidal
particles. On the other hand, a large number of negatively charged HPAM adsorbed on the scale of
sewage would play a role in dispersing and stabilizing scale and particulate matters. The high
viscosity of sewage made the particles deposition very slow and suspended in water.
5.00μm
5.00μm
4.00μm
5.00μm
(1)
(2)
(3)
(4)
Characterization and Source Analysis of Suspended Solids in Chemical Flooding Sewage
81

Figure 6.Scaling and suspended solids (SS) content variation(45°C ) for ASP flooding sewage after
membrane filtration
4. Conclusions
(1) The ASP flooding sewage contained high concentration of suspended solids and much HCO
3
-
,
HPAM, multivalent metal ions such as Ca
2+
, Mg
2+
and soluble silicon. And there were various
size particles in ASP flooding sewage.
(2) The zeta potential showed suspended solids in ASP flooding sewage was much negatively
charged due to negatively charged HPAM. PAC could make the zeta potential positively shifted
with a finite limit. But the pH value influenced zeta potential of sewage greatly because HPAM
changed to gel and precipitate at pH value 3~4.
(3) IR and SEM measurement showed that the HPAM influenced the measurement and stability of
suspended solids greatly. This was different from usual suspended solids, such as clay and
corrosion products. It is necessary to eliminate the influence of polymers by means of
degradation and other measures.
(4) The suspended solids in filtered sewage increased due to formation of inorganic scale and silicon
colloidal particles under certain conditions. Scaling prevention are needed to avoid the formation
of suspended solids again.
Acknowledgement
The authors thank the financial support of PetroChina Ministry of science and technology and
Research Institute of Petroleum Exploration and Development. This work is also supported by
Daqing Oilfield Engineering Co., Ltd. and Testing Center of USTB Co.,Ltd.
References
[1] Guo H, Li Y Q and Wang F Y 2017ASP Flooding: Theory and Practice Progress in China.
Journal of Chemistry 10 1-18
[2] Cheng J C, Liao G Z and Yang Z Y 2001 Pilot Test of ASP Flooding in Daqing Oilfield.
Petroleum Geology & Oilfield Development in Daqing 20 46-49
[3] Zhang F S, Zhang Y Q and Cheng J C 2008 Relation between composition of the crude oil and
demulsifation of the liquid produced by ASP flooding and polymer flooding Acta Petrolei
Sinica (Petroleum Processing Section) 24 117-120
[4] Jing G L 2012 The Asp Flooding Scaling Mechanism in Daqing Oilfield. Advanced Materials
Research 460 48-52
[5] Deng S B 2009 Characterization of suspended solids in produced water in Daqing oilfield
Colloids & Surfaces A Physicochemical & Engineering Aspects 332 63-69
IWMCE 2018 - International Workshop on Materials, Chemistry and Engineering
82