Electromagnetic waves-induced hydrophobic multiwalled carbon nanotubes for enhanced oil recovery
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Extracting the trapped oil into the pores is still a massive challenging. In this work, multiwalled carbon nanotubes were utilized to investigate the influence of the nanofluid’s flow rate on the oil recovery in enhanced oil recovery (EOR) stage. At the optimum conditions, comparative study was conducted to figure out the impact of EM waves on the recovery efficiency. The experimental study proved that 2 mL/min is the optimum flow rate for the utilized fluid. EM waves could enhance the recovered oil in EOR stage by 24.5% ROIP. The increment was ascribed to the extraordinary role of EM waves in increasing the viscosity of the nanofluid.
KeywordsMWCNT Dielectric properties Improve oil recovery Viscosity
Multiwalled carbon nanotubes
Enhanced oil recovery
Residual resistance factor
Residual oil in place
With the increase in the demand of crude oil and reduction in oil sources, extracting additional oil is becoming more challenging (Alnarabiji et al. 2014a, b, 2016, 2018; Shafie et al. 2014; Ahmed et al. 2018; Adil et al. 2018). Lately, nanosized materials have attracted wide attention due to their extraordinary characteristics (Ameen et al. 2019; Ghanem et al. 2018; Al-Swai et al. 2018; Alnarabiji et al. 2017, 2018; Ali et al. 2018; Chuah et al. 2016; Alqasem et al. 2017). Multiwalled carbon nanotube (MWCNT) as a type of nanomaterials has been implanted in enhanced oil recovery (EOR) and achieved remarkably high recovery (Alnarabiji et al. 2016). However, the previous study covered the influence of MWCNT concentration in the fluid on the recovery efficiency, whereas other parameters such as nanofluid flow rate as well as the effect of the electromagnetic (EM) waves on the recovery efficiency were not investigated.
In this work, the influence of the nanofluid’s flow rate on the oil recovery in EOR stage was investigated. At the optimum conditions, comparative study was conducted to figure out the impact of EM waves on the recovery efficiency.
MWCNT fluid preparation
Since MWCNT (obtained from Cambridge, UK) is in powder form, it was suspended in distilled water in order to be injected into a porous medium. The suspended MWCNT was subjected to two main stages. In the first stage, MWCNT was dispersed in distilled water as a base fluid and stirred for 15 min using magnetic stirrer on hotplate, whereas in the second stage agitation conducted to the prepared suspension in an ultrasonic bath for approximately 2 min at room temperature to enhance the homogenous dispersion of the powder in the base fluid.
Experimental setup and procedure
The combination between MWCNT and EM waves
The selected experiment of optimum flow rate in the absence of EM energy was considered as a reference experiment. Subsequently, the incremental recovery occurred from this experiment was considered as a baseline in the following experiment. The EM waves with 13.0 MHz square alternating current frequency was irradiated onto the studied porous medium in the EOR stage. The recovery efficiency and Rrf were computed and compared with the one in the absence of EM energy. Hence, Darcy’s equation was utilized to offer a better understanding of the recovery mechanism.
Results and discussion
On the other hand, previous studies proved that CNT with hydrophobic surface nature needs mechanical energy to form the emulsion (Wang and Hobbie 2003; Shen and Resasco 2009). It can be pustulated that EM waves provide the required mechanical energy to vibrate MWCNT. By increasing the pressure of the nanofluid injection, the viscosity of the formed emulsion can be remarkably higher than that of both water and oil. This might be attributed to the fact that the created emulsion exhibited non-Newtonian behavior (Schramm 1992). It is clear from Fig. 4 that the difference in the pressure in the presence of EM waves declines directly after injecting the brine into the medium. This is because brine possesses negative and positive ions attached to the surface of charged MWCNT to neutralize. In other words, even if electric dipoles are formed and charges are created on the surface of dielectric material, their effectiveness still depends on the ionic strength of the medium. For instance, brine ions are capable of neutralizing those polarized particles directly. Therefore, the neutralized particles will not be induced by the EM waves and no more emulsion will be formed under the influence of the vibration of dielectric nanoparticles induced by the frequency of EM waves. These results are in good agreement with previous study where it was found that the salinity of brine reduces emulsion stability (Zhang et al. 2009). It is clear from Fig. 4 that with the injection of brine into the porous medium, the pressure declines drastically to 6.2 psi and then gradually increases to 6.6 psi. The reason of this increment is that the salinity of brine works on increasing nanoparticles retention in the medium (Caldelas et al. 2011). This increment reached the maximum when 1 pore volume of brine was injected after the 2 pore volume of MWCNT fluid injected (Fig. 4). Later, the blockage was released gradually by injecting more pore volumes of brine till it stabilized at the end of the experiment.
It is expected that with increasing the concentration of MWCNT fluid, more number of nanoparticles will polarize under the impact of EM waves which will drive to create higher temporary viscosity and higher capillary number; as a result, MWCNT will contribute in forming stable emulsion (Zhang et al. 2009). However, this process might have negative impact on fluid mobility and recovery efficiency as a result. Therefore, further studies required to can be conducted to investigate the most suitable nanofluid conditions under EM field.
MWCNT has been utilized in EOR stage. It was found that 2 mL/min is the optimum flow rate of the prepared nanofluid. EM wave could enhance the recovery efficiency significantly where it was increased from 36.6 to 61.1% ROIP. The reason behind this increment was attributed to the increase in the MWCNT viscosity as well as the probable formation of emulsion.
The authors would like to acknowledge Universiti Teknologi PETRONAS for facilitating the work and ministry of education.
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