Jitendra Sangwai

The upstream petroleum industry faces operational and technical problems due to increased deposition of waxes, aromatics and asphaltene from crude oil sludge in oil storage tanks in the form of tank-bottom sludge (TBS). This results in huge production losses, and threatens environmentally safe operation; therefore, safer solutions are needed. In this work, nine aromatic ionic liquids (ILs) are synthesized and tested for the dissolution of TBS with the aid of five solvents, namely, toluene, heptane, decane, ethyl acetate and hexane. The UV absorbance values of the standard solutions (TBS in solvent) are compared with the sample solutions (TBS in solvent + ILs). It is observed that ILs significantly improve the dissolution of TBS in solvents compared with neat solvent alone. Different weight ratios of TBS : ILs (1 : 1, 1 : 0.5 and 1 : 0.1) are considered in this study. Ionic liquids (ILs) based on an imidazolium cation and various anions, such as [Cl]-, [Br]-, [BF 4]-, [H2PO4]-, [HSO 4]-, and [PF6]-, are considered in this investigation. It is observed that the dissolution of TBS in heptane in the presence of [HMIM]+[Br]- is efficient to a maximum extent of 66% with other solvents showing similar increased solubility effect with various ILs. In the case of hexane, it should be noted that the efficiency of dissolution of TBS goes on decreasing with increasing concentration of TBS in hexane. A hold-time study is also performed with heptane containing ILs and heptanes without ILs to determine the maximum time required for efficient dissolution of TBS. It is observed that the efficiency is increased beyond 66% in the presence of ILs for the dissolution of TBS in heptane, provided that the mixture of solvent and ILs are in contact with the TBS for a prolonged period of 30 days, or even longer as required. FT-IR and 13C-NMR spectral analyses are also performed so as to understand the efficiency of the ILs in the dissolution of TBS in various solvents, and it was observed that there is a decrease in the intensity of the peaks in the spectra of treated TBS with solvents, which is further enhanced by the addition of ILs. This journal is © the Partner Organisations 2014.

Enhanced oil recovery is governed primarily by the role of interfacial tension between crude oil and water. Interfacial tension (IFT) of the crude oil-water system is one of the vital factors in the analysis of the capillary forces affecting trapped oil within the reservoir rocks. High salinity and temperature of the reservoirs tend to make researchers search for new surfactants to lower the interfacial tension in crude oil-water systems. The current study hopes to create a move toward solving the above problem through the use of aromatic ionic liquids (ILs) based on imidazolium as the cation and various anions such as [Cl]-, [Br]-, [BF4]-, [H2PO4]-, [HSO4]-, and [PF6]- in different concentrations. This work involves the study of the effect of concentration, temperature, time, and brine on the fate of surface tension (SFT) of water and interfacial tension of crude oil-water systems. The present study also addresses the trend in the electrical conductivity of ILs in water along with the effect of temperature and concentration of ILs. The study reveals that these ILs are effective in reducing the SFT and IFT of water and crude oil-water systems at high salinity and temperature conditions. In the IFT measurements, a linear decrement with increase in temperature is observed for crude oil-water in the presence of ILs. The interfacial tension of the various imidazolium-based ionic liquids with the crude oil-water system has been measured as a function of temperature by means of the Wilhelmy plate method. The influence of the nature of cation and anion of ionic liquids and of the chain length on the cationic head of the ILs on interfacial tension is also discussed in detail. At increased salinity conditions, unlike classical surfactants, these ILs are found to be more successful. Enhanced efficiency of the drop in IFT using NaCl and IL mixture has been confirmed by measuring the IFT between crude oil and the aqueous solution of IL. The synergism of salt and IL mixture on the reduction of IFT has been observed.

The deposition of crude oil in various production and surfaces facilities such as oil storage tanks in the form of tank-bottom sludge, pipeline deposition, skin formation at the near well-bore, deposition in the tubing leads to blockage which invites several operational challenges. These challenges, in turn bring about huge production losses, involvement of scarce human resources, and threatening the environmentally safe operation, thus needing safer solutions. An environmental-friendly method for the dissolution of heavy crude oil (HCO) with the use of ionic liquids (ILs) along with a paraffinic liquid hydrocarbon (organic solvent) is developed which is considered to be very helpful for easy pumping, reducing the risk of manual cleaning and time consumption. In this work, eleven ILs are selected from lactam, alkyl ammonium and hydroxyl ammonium families with various anions, such as, [HCOO]-, [CH3COO]-, [CF3COO]-, [C6H13COO]-. The results on the quantitative and qualitative dissolution of the HCO using organic solvents (with and without ionic liquids) are presented. Studies on the quantitative dissolution of crude oil are performed with the use of UV-vis spectrophotometer, while the qualitative information on the dissolution of HCO are carried out using FT-IR and 13C NMR techniques. In the case of sample system (HCO + solvent + ILs), the increase in solubility observed is up to a maximum of 80%. Time-hold study was conducted for a prolonged period of 30 days where the increase in solubility is improved in the range of 80-335% with the addition of ILs along with organic solvents, whereas standard system (without ILs), showed improvement in the range of 11-16% only. This method helps in increasing the efficacy of organic solvents, such as, the liquid hydrocarbons which would be suitable for upstream petroleum engineering application. Moreover, the used ionic liquids were recycled and can also be reused.

The need for development of better surface active agents for upstream oil and gas industry which can survive harsh condition of salinity are in great demand, particularly for the applications related to improved/enhanced oil recovery, flow assurance and oil and gas production operations keeping in mind the environmental constraints. The technical difficulties which need to be considered are those involving the surface forces such as surface tension (SFT) and interfacial tension (IFT) acting between the formation water and the low waxy crude oil. In this study, we have employed the use of eight aliphatic ionic liquids (ILs), based on di- and tri-alkyl ammonium as cations and with various anions such as [CH3COO]-, [BF4]-, [H2PO4]- and [HSO4]- for the investigation of the surface phenomenon of crude oil-water system. The synergistic effect of NaCl along with the ILs is investigated in detail. It is observed that there is a significant reduction in the surface tension of water and the interfacial tension of crude oil-water system in the presence of salt, particularly at higher concentration of NaCl (200,000ppm). Effect of temperature, time, alkyl chain length of the cationic part of the ILs, nature of anions of ILs and the concentration of ILs is also discussed. The trend in the electrical conductivity of aqueous IL solutions with various concentrations at three different temperatures 298.15-318.15K is also presented along with critical aggregation concentration. The study on the effect of ILs on the SFT/IFT of water and low waxy crude oil-water system reveal that the ILs are successful in minimizing the effect of the surface forces in the presence of salt and thereby, could pave the way for efficient enhanced oil recovery operations.

Chemical treatment of aromatic heavier hydrocarbons are traditionally done by using cyclic aromatic nonpolar solvents, such as benzene, xylene, and toluene, which have the capability to dissolve asphaltenes. However, these aromatic solvents are volatile and hazardous and hence not advisable to use. Alternatively, lighter hydrocarbons, such as heptane, hexane, etc., show lesser solubility. It is, therefore, crucial that these problems require intelligent, cost-effective, and innovative solutions. The present work investigates the possible solution for the dissolution of heavy crude oil using the application of eight aliphatic ionic liquids (ILs) along with five solvents, namely, toluene, heptane, decane, ethyl acetate, and hexane. Ionic liquids (ILs) based on [CH3COO]-, [BF4]-, [H2PO4]-, and [HSO4]- as anions and with various cations, such as di- and tri-alkyl ammonium, are considered. The enhancement in the solubility of heavy crude oil in solvent + ILs mixture is investigated using Ultraviolet - visible (UV - vis) spectrophotometry, Fourier transform-infrared spectroscopy (FT-IR), and 13C-nuclear magnetic resonance (NMR) spectroscopic techniques. The absorbance of the sample solution (heavy crude oil + solvent + IL) is compared with the standard solution (heavy crude oil in neat solvent alone). It is observed that the dissolution of heavy crude oil is more in the solution with IL than with the solvent alone. Solubility of heavy crude oil in solvents increases to about 70% in the presence of ILs. Hold-time study is also performed to understand the maximum time required for efficient dissolution of heavy crude oil. The hold-time study reveals that solubility of heavy crude oil in heptane increased to about 61-222% in the presence of ILs, as compared to 11-16% in the case of standard solution for a prolonged period of 30 days.

Enormous production losses have ascended in diverse operational and technical issues due to deposition of heavy crude oil (HCO) in various production components like tubing, near well bore (skin formation), surface storage tank, pipeline blockage, etc. Existing methods employed for the dissolution of HCO are either cumbersome or use organic solvents, which are hazardous to the environment. This study presents findings on the enhanced dissolution of HCO using low waxy crude oil (LWC) in the presence of ionic liquid (IL). The use of ILs is found to be compatible with the polar moieties in heavy crude oil, such as resins, aromatics, and asphaltenes, enhancing its dissolution. Twelve ionic liquids were tested for the dissolution of HCO using LWC. The dissolution of HCO was performed and confirmed using gravimetric analyses, ultraviolet-visible (UV-vis) spectrophotometry, Fourier transform-infrared spectroscopy (FT-IR), ¹³C-nuclear magnetic resonance (¹³C NMR), and the interfacial tension (IFT) measurements. The total percentage of dissolution of HCO in LWC (2:3 wt/wt) with 100 ppm of ionic liquid is found to be increased by a magnitude of 30% (71% from 41%) of the standard HCO+LWC alone. The increase in solubility (%) of HCO+ LWC with organic solvent (used for dilution in UV-vis) in the presence of ILs is observed to be a maximum of 38%. The results are further confirmed qualitatively through the use of FT-IR and ¹³C NMR spectroscopy. These findings are further supported by the determination of IFT substantiating the fact that the ILs possess the tendency to dissolve and recover residual oil from production systems and reservoirs. In all of the above experiments, the efficiency of the ILs with a longer alkyl chain and a larger ring size is very convincing as compared with the rest of the studied ILs.

Crude oil recovery from matured reservoir still pose challenges due to the low efficiency of the existing enhanced oil recovery (EOR) methods. The chemical enhanced oil recovery technique is one of the potential EOR technique being used to produce trapped oil from mature reservoirs. One of the key challenge for chemical-EOR process is that the conventional surfactants does not show efficacy toward reduction in interfacial tension and oil recovery under high saline and high temperature conditions. Ionic liquids (ILs) can be one of the potential alternative for possible application in chemical-EOR due to their enhanced stability under high saline and thermal conditions. In this investigation, six different alkyl ammonium ILs and sodium dodecyl sulfate (SDS) have been investigated for their effect on the interfacial tension (IFT) of low waxy crude oil-water system (with and without salt) as a function of temperature (283.15-353.15 K) and for EOR-flooding process. Water-soluble polymer (polyacrylamide) was used as a polymer flood after SDS/ILs flood in EOR study. This combined flood is referred to as SDS/IL + polymer EOR flooding process. Several EOR flooding experiments such as, only polymer, only SDS, only IL, and SDS/ILS + polymer have been carried out. Also, the evaluation of ILs and SDS for EOR has been investigated under zero and high salinity (100000 ppm) reservoir conditions and compared. The study also provides an insight into the effects of different cations and anions (alkyl chain length) of the ILs on the IFT of crude oil-water system and for the enhanced oil recovery operation.