This article was submitted to Advanced Clean Fuel Technologies, a section of the journal Frontiers in Energy Research
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In this paper, a composite sample (VES and SiO2 nanoparticle) was used to overcome the deficiencies of polymer. The rheological character of the VES/nanoparticles hybrid and flow behavior in porous media were examined. It was found that SiO2 nanoparticles exhibited viscosifying action and improved the oil tolerance. In addition, the VES solution without nanoparticles showed a lower capacity to recover oil, which might be attributed to the fact that wormlike micelles would be destroyed in crude oil. On the contrary, an enhanced oil recovery of 9.68% was achieved in the composited experiment for the VES sample with nanoparticles which is relatively stable with oil.
Viscoelastic surfactant (VES) fluids, generally formed by wormlike micelles, have been utilized as completion or stimulation agents in the oil and gas industry (
Recent work has shown the advantageous use of nanoparticles in VES fluid systems, which included significantly increased thermal stability and fluid loss control properties in the fluid system (
For the majority of oil reservoirs, large amounts of oil are still left unrecovered after extensive water flooding. Chemical EOR technology is the most promising tertiary recovery technique to both improve sweep and displacement efficiency. The well-known process to improve sweep efficiency consists in injecting polymer solution. This process known as polymer flooding has been widely used at large scale especially at Daqing field in China (
Herein, a novel hybrid sample (VES and SiO2 nanoparticle) has been studied to overcome the deficiencies of HPAM. We investigated the effects of nano-SiO2 on the rheology of VES solutions and the influencing parameters, including surfactant concentrations, nanoparticle concentrations, particle diameters, and NaCl concentrations. We also compared the ability of the VES system in enhancing oil recovery in the presence and absence of nanoparticles. Our investigation may provide a new idea for the development of an oil recovery agent.
The VES solutions used during the experiments are composed of sodium dodecyl sulfate (chemical pure) and lauroylamidopropyl betaine (industrial product) purchased from Sinopharm. SiO2 nanoparticles with different particle diameters including 7nm, 12nm, and 22nm are those of Ludox SM, HS, and TM, were received as a gift from W. R. Grace. Sodium chloride (NaCl) was purchased from the Xilong Scientific Company. Deionized water with an electrical resistivity of 18.2MΩ·cm was used to prepare the solutions. Crude oil was obtained from the Shengli Oilfield in China, with a density and viscosity of 0.89g/cm3 and 80.1mPa⋅s, respectively, at 50°C. Component analysis results show that this oil is composed of 70.66wt% saturated hydrocarbons, 20.92wt% aromatic hydrocarbons, 5.83wt% resions, and 2.59wt% asphaltene.
Rheological experiments were performed using an Anton Paar MCR301 rotational rheometer. The sample temperature was adjusted using a Peltier thermostat (
The dynamic IFT values were measured using a Texas-500 spinning drop tensiometer (Temco, United States) (
Flooding experiments were performed at 50°C. A steel cylinder of 10 inches in height and 1 inch in inner diameter was filled with quartz sands of different sizes. The porosity of the porous sandpack was about 35.8%. The sandpack was initially saturated with synthetic brine, and then displaced by dehydrated crude oil. Water flooding was performed until the water proportion of the output fluid was higher than 98%. Afterward, the composite VES solution was injected. The difference between water flooding recovery and total recovery was calculated as the tertiary recovery increased by nanoparticle/surfactant composite flooding. The injection rate was maintained at 0.5ml/min (
The viscosity of injected solutions plays a significant role in displacing crude oil during oilfield development. Consequently, it is necessary to clarify the rheological behaviors of nanoparticle/surfactant solutions (
Effect of LAB percentage on apparent viscosity (
Effect of salinity on apparent viscosity (
The viscosity variation of the VES solution against surfactant concentration is shown in
Effect of surfactants concentration on apparent viscosity (LBA:SDS = 3:1, T = 50°C,
The curves of VES viscosity against the nanoparticle concentration at different salinities is shown in
Effect of SiO2 concentration on solution viscosity at different nanoparticle diameters (
Effect of SiO2 concentration on solution viscosity at different nanoparticle diameters (
Effect of SiO2 concentration on solution viscosity at different nanoparticle diameters (
The influence of silica particle concentration, salinity, surfactant concentration, and temperature on VES viscosity is shown in
Effect of SiO2 concentration on solution viscosity at different salinities (
Effect of SiO2 concentration on solution viscosity at different surfactant concentrations (LBA:SDS = 3:1, T = 50°C,
Effect of SiO2 concentration on solution viscosity at different temperatures (
Rheological evaluation of the viscoelastic nature of the surfactant fluids with and without nanoparticles was carried out.
Effect of SiO2 concentration on solution viscosity at different shear rates. (
The G’ and G’’ viscous-elastic behavior between the VES fluids with and without nanoparticles at different shear stress and frequency are shown in
Effect of SiO2 concentration on the modulus with different shear stress. (
Effect of SiO2 concentration on the modulus at different frequencies. (
IFT between the VES solution and Zhuangxi crude oil.
Variations of recovery factors, water contents, and displacement pressures with injected volumes are plotted in
Recovery factor, water cut, and flooding pressure plotted as a function of injected volume of different samples (WF = water flooding; CW = chemical flooding; SWF = subsequent water flooding).
Sandpack parameters, displacement process, and the results of these oil displacement tests.
0.8% (LAB:SDS = 3:1) + 4% NaCl | 0.8% (LAB:SDS = 3:1) + 4% NaCl + 0.8% 7nm SiO2 | |||
---|---|---|---|---|
Permeability/mD | 500 | 1,500 | 400 | 1900 |
Initial oil saturation So/% | 88.56 | 88.16 | 89.90 | 88.45 |
Primary recovery efficiency Ro/% | 57.36 | 51.37 | 51.64 | 57.89 |
Secondary recovery factor Ro/% | 1.14 | 4.52 | 0.25 | 9.68 |
Overall recovery efficiency Ro/% | 58.50 | 55.89 | 51.89 | 67.57 |
Less than 5% oil recovery was achieved by the VES solution without particles (
Effect of oil ratio on apparent viscosity in different systems. (
It shows that oil has great influence on the apparent viscosity of the VES solution. Note that only 1% oil decreased the viscosity of the VES solution without nanoparticles by more than 97% which indicates the oil break of the structure of WLMs. But the presence of particles could weaken the influence of oil. The viscosity of the system with 0.8% SiO2 only decreased about 43% when mixed with 1% crude oil.
The poor oil recovery efficiency of the VES solution without particles may be attributed to the fact that VES micelles could be easily destructed while in residual crude oil. On the contrary, the structure of VES in the presence of nanoparticles could be significantly enhanced, and thus the water/oil mobility ratio could be improved, resulting in a higher oil recovery (
The rheological behaviors of the VES/SiO2 nanoparticle hybrid and sandpack flooding experiments were examined. It was found that the SiO2 nanoparticle exhibited viscosifying action and improved oil tolerance. In addition, the poor oil recovery efficiency of the solution without nanoparticles may be attributed to the destruction of the VES micelles upon contacting the residual oil. On the contrary, 9.68% of oil recovery was achieved from the VES and nanoparticle samples in the high permeability sandpack flooding test for the VES sample with nanoparticles which is relatively stable with oil in order to produce more oil. However, the nanoparticles bridging off the sandpack inlet restrict its use in a low permeability reservoir.
The original contributions presented in the study are included in the article/Supplementary Material, further inquiries can be directed to the corresponding author.
ZL, QW, and HC contributed to the conception and design of the work; QW, MG, and WL contributed to the acqusition and analysis of data for the work; QW, MG, and WL drafted the work; ZL and HC revise the work critically; All the five authors made the final approval of the version to be published; All the five authors made the agreement to be accountable for all aspects of the work in ensuring that questions related to the accuracy or integrity of any part of the work are appropriately investigated and resolved.
The authors declare that the research was conducted in the absence of any commercial or financial relationships that could be construed as a potential conflict of interest.
We acknowledge the Natural Science Foundation of China (51474234 and 51574266), the Natural Science Foundation of Shandong Province, China (ZR2014EZ002 and ZR2015EQ013), and the Fok Ying Tung Education Foundation (151049) for supporting this work.