EOR polymer for high temperature and high salinity oilfield
—The molecular design, synthesis and performance evaluation
Why do the research
Polymer flooding is the most common and effective means in EOR, but there is no suitable polymers for high temperature and high salinity reserviors
There is large amount of reserves in high temperature and high salinity reserviors in Sinopec which are suitable for polymer flooding but now the recovery ratio is low.
To resolve the water problems resulted from polymer flooding.
The basic requirements of the EOR polymer：completely dissolved in high salt
solution is less than 2 h, high apparent viscosity at high temperature and
good thermal stability
Ways to improve the polymer properties
The most commonly used method：
1.Increasing the molecular weight of polymers——Couldn’t improve the performance of temperature and salt resistance
2.Increasing the ratio of temperature and salt resistance monomer——
Will decrease the molecular weight and the solution apparent viscosity of the polymers
3.Introducing hydrophobic monomers to improve the interactions between molecular chains and then increase the solution apparent viscosity——will increase the earth absorption
4. 1+2，Increasing the ratio of temperature and salt resistance monomer and increasing the molecular weight——Difficult to achieve by the existing polymerization technology
Is there any possibility by changing the molecular microstructure to improve the polymers?
The significance of control the molecular microstructure
Means to get micro-block PAM——Template polymerization
Simple, moderate, environment-friendly, easy to operate
By using AMPS to increase the temperature and salt resistance ability of polymer
The introduce of AMPS decreased the hydrolysis rate of the molecular chains,
on the other hand it reduced the effect of Ca2+ and Mg2+ ions on the molecular
main chains, which could increase the tolerance of the polymer to the temperature
and salt.
Template polymerization of AM and AA
The template PDMC has strong interactions with ionized AA through
electrostatic interaction while has no interactions with AM.
The effect of template PDMC on the polymerization reaction rate
The reaction rate increased as the concentration of PDMC increased and reached the maxim at [PDMC]/[AA]=1.2 and then decreased which met the template polymerization mechanism I.
The template PDMC will significantly change the microstructure of the product.
The effect of PDMC on the reactivity ratio
Determined by Kelen-Tudos
The presence of PDMC significantly promoted the reactivity ratio of AM and AA especially AA’s , the reactivity ratio was greater than 1 which indicated that micro-block structure would be formed in the product.
The effect of template on the sequence distribution of the polymer
The three-sequence distribution determined by 13CNMR
1.Template polymerization significantly increased the contents of AAA and MMM three-sequence.
2. T/A was fixed, by changing the feed ratio of AM and AA MMM three-sequence could be changed.
3.The feed ratio of AM and AA was fixed, changing the feed ratio of T and AA the microstructure could be changed.
pH response of the polymer solution apparent viscosity
The solution viscosity of TP increased more significantly than that of CP as pH at the range 7～10(used pH range)
The results indicated that the polymer with micro-block microstructure has much greater solution viscosity than that with the common structure at the equivalent molecular weight .
The synthesis of the temperature and salt resistance polymer (PCK-2500 or LH-2500)
The characteristics of the temperature and salt resistance polymer for enhanced
oil recovery
1. Temperature and salt resistance——introduce temperature and salt resistance monomer
2. The apparent viscosity of the polymer solution(The decrease of molecular weight caused by the introduction of temperature and salt resistance monomers which reduced the apparent viscosity of the polymer solution) ——template polymerization
3. Solubility ——adjust the prescription and introduce some additives
The process of the polymerization
The typical increase of temperature with time
The polymerization was initiated at low temperature and polymerized in a adiabatic reactor.
The producing process was applied for Chinese patent: CN201261759
One Example of the properties of one LH-2500
Basic properties
Apparent viscosity in Sinopec Shengli oilfield produced water
Cation composition of the water, Na+ 11914.7 mg/L, Ca2+ 700.4 mg/L, Mg2+173.6 mg/L
The results indicated
LH-2500 has no hydrophobically associating behavior in aqueous solution
The order of the apparent viscosity of the solution at 1500mg/L and 85 ℃ is
LH-2500>hydrophobically associating PAM ＞ MO-4000
The simulated adsorption of the polymer by the earth at 25℃
The apparent viscosity of LH-2500 and MO-4000 has no change during the experiment while the hydrophobically associating PAM decreased rapidly which indicated that LH-2500 has no visible adsorption on the earth
Thermal stability
LH-2500 has higher thermal stability, could achieve the requirement of enhanced oil recovery
Compared with other temperature and salt resistance polymers used in Sinopec Shengli oilfield
The apparent viscosity performance of LH-2500 was better than all the polymers
currently in use, even increase the concentration by 20% of other polymers.
Summary of the characteristics of this LH-2500
LH-2500 has no hydrophobically associating behavior in aqueous solution, so the
adsorption by the earth was not obvious.
LH-2500 could be dissolved in oilfield produced water directly and the completely
dissolved time is less than two hours.
The performance of the solution viscosity and thermal stability was very good.
LH-2500 was the best temperature and salt resistance EOR polymer material up till now, it could fulfill the requirement of oilfield with high temperature (＞80 ℃) and high salt.
The performance evaluation of simulated enhance oil recovery by double-tube model
Double-tube model: there have two tubes and are filled with sand,
the permeability of each tube is different to simulate the diversity of the reservoir.
Tube：L：60 cm，D：3.8 cm，A：11.3 cm2，V：680 ml
Filled sand：the produced sand of Shengli oilfield
Permeability of hypertonic tube：～2500mdc
Permeability of hypotonic tube ：～400mdc
Pressure measurement points：a total pressure measurement point ahead the
tubes and two pressure measurement points along each tube
Temperature：85℃
The viscosity of the crude oil：85℃，60mPa.s
The concentration of PAM：1.5g/L solved in the simulated Shengli oilfield
produced water
The injection volume of PAM：0.4PV
The injection rate：0.5ml/min
Without the presence of surfactant only PAM
The apparent viscosity of the PAM solution
The changing of the pressure at each pressure measurement point
The pressure increased more significantly after the injection of LH-2500 than the injection of
MO-4000, after changing to inject the water, the residual pressure is much higher, which indicated that LH-2500 has higher core drag coefficient and residual drag coefficient.
The effect of inject volume (PV) on the recovery ratio
After the injection of PAM and changing to water, the recovery ratio of the two tubes
both increased significantly
The result of the recovery—— MO-4000
The result of the recovery—— LH-2500
Even though the recovery ratio is higher in the process of water flooding, the average recovery ratio of LH-2500 is still much higher than that of MO-4000.
The enhanced recovery by LH-2500+PS
LH-2500 and petroleum sulfonate have a good synergy, the recovery ratio of hypertonic tube was promoted up to 50%.
The permeability of the tubes are changed to about 1000mdc and 5000mdc
Increase the permeability, the recovery ratio of the two tubes decreased slightly, especially the hypotonic tube, but the recovery ratio of the hypertonic tube was still significantly higher than that of the one used PAM alone.
Summary of the simulated enhanced oil recovery
Compared with MO-4000, LH-2500 has higher core resistance efficiency and
residual resistance efficiency which indicated that LH-2500 has the ability to
promote the sweep efficiency and the sweep range.
For the recovery ratio of the hypertonic tube LH-2500 and MO-4000 was almost
the same, but in the hypotonic tube the recovery ratio of LH-2500 was much
higher than that of MO-4000 due to the higher ability to increase the sweep
efficiency and the sweep range.
LH-2500 has a good synergy with PS, the injection of LH-2500 and PS
further increased the recovery ratio
Determination of the molecular weight and root mean square radius
Instrument: Wyatt DAWN EOS multi-angle (eighteen) laser light detector
The calculating formula
Kc=4π2n2（dn/dc）2（NAλ04） q=（4π n /λ0）sin（θ/2）
The determination of refractive index increment dn/dc
The molecular weight determination of LH-2500
The molecular weight determination of MO-4000
The Mw and ＜R2g＞1/2 of LH-2500 were much higher than those of MO-4000
Root mean square radius ＜R2g＞1/2 at different NaCl concentration
The root mean square radius decreased as the NaCl concentration increased.
But the ＜R2g＞1/2 of LH-2500 was greater than that of MO-4000 at any
conditions which indicated that the performance of salt resistance of LH-2500
was stronger and the branch degree was lower.
The size distribution of the synthesize PAM at different NaCl concentration
The interaction of LH-2500 with surfactant
Why do the research
The actual results proved that PAM used with petroleum sulfonate
surfactant could increase the flooding efficiency.
So it is necessary to study the interactions between the PAM and
sulfonate surfactant. The focus is on the viscosity behavior of the
PAM solution caused by the presence of the surfactant.
The interaction between LH-2500 and Sodium dodecyl benzene sulfonate(SDBS) in the presence of NaCl
The micro-morphology of the complex formed by LH-2500 and SDBS
The increase of the apparent viscosity was due to the formation of
cross-linked complex between the PAM and SDBS
The size distribution of the complex
The effect of the temperature on the solution apparent viscosity of PAM and SDBS
The transmittance of the solution increased rapidly as the temperature reached
40℃, while the viscosity also increased slightly.
The interaction between LH-2500 and petroleum sulfonate(PS) in the presence of NaCl
The effect of the temperature on the solution apparent viscosity of PAM and PS
In the presence of PS as the temperature increased the viscosity decreased
overall, but at 60-70℃ the viscosity increased slightly
The interaction between LH-2500 and PS in simulated Shengli oilfield produced water
Summary of the interactions between LH-2500 and surfactant
In the presence of salt LH-2500 has strong interactions with surfactants such as
SDBS and PS, when the concentration of the surfactants exceeds the critical
overlap concentration, the complex with the cross-linked structure is formed
which induce the rapid increase of the apparent viscosity of the solution.
The shielding of the carboxyl acid by the metal cations of the salt could increase
the hydrophobicity of the PAM and then increase the interactions bwtween the
PAM and surfactant.
The increase of temperature could induce the dissociation of the complex formed
by PAM and surfactant.