Jitendra Sangwai

Asphaltenes are heavy and polar fractions present in crude oil. Literature survey reveals that studies underlying the effect of individual components of crude oil on hydrate formation are rare. In this work, asphaltene fractions were extracted from a vacuum residue of the crude oil according to method based on IP143/90 (AlHumaidan et al., 2017) and characterized by FTIR, element analysis, SEM and MALDI-TOF MS. Thereafter, the effect of asphaltenes was studied on the phase stability of pure methane hydrate system at 1000 ppm and 10000 ppm concentration. It has been observed that the asphaltene plays an important role in elucidating the phase stability of methane hydrate systems.

Natural gas hydrate is considered to be an attractive sustainable energy resource for the world. Hydrate as a technology can be of immense importance for various industrial processes, such as multicomponent natural gas separation, gas storage and transportation, and carbon dioxide capture from flue gases and sequestration. A variety of hydrate additives, which includes promoters (thermodynamics and kinetics) and porous media, are being researched to improve the hydrate formation kinetics. However, studies involving the combinations of these are rare in the open literature. In this work, the formation kinetics of methane hydrate/semiclathrate hydrate using tetra-n-butyl ammonium bromide (TBAB) and sodium dodecyl sulfate (SDS) aqueous solutions at various concentrations in a porous medium containing silica sand at initial hydrate formation pressures (7.5 and 5.5 MPa) and temperatures (273.65 and 276.15 K) have been investigated. All the experiments were conducted using 75% water saturation. Various kinetics parameters, such as gas uptake, gas-to-hydrate conversion, and induction time, have been reported. It was found that the combination of TBAB+ SDS showed favorable hydrate formation kinetics in porous media than the TBAB system. This work provides information for further studies involving semiclathrate hydrate applications for various industrial processes.

Increasing maturity of the crude oil reservoirs across the world have led to the production of waxy crude oil which need economical and efficient methods for enhanced oil recovery (EOR). The studies on the performance of bacteria in the presence of waxy crude oil is rare. In this study, experiments were performed to understand the efficacy of thermophillic microorganism Bacillus subtilis on the biodegradation of waxy crude oil for EOR applications. Bacterial growth, changes in crude oil composition, viscosity reduction, and surface and emulsification activity have been monitored to evaluate the oil degradation capabilities of the bacteria. This study also presents the effect of temperature, salinity, pH, and pressure on the stability of the produced biosurfactant for EOR applications. The biosurfactant produced by bacteria in the presence of crude oil was found to be stable up to 120°C, 10 MPa, 15% salinity, and wide range of pH, and thus favorable for reservoir environment. The crude oil composition before and after degradation at 75°C was determined using gas chromatography-mass spectroscopy and observed to be 60% in one day, while the maximum viscosity reduction was found to be 60% from initial values. Experimental results showed that the bacteria used in this work are capable of surviving at reservoir conditions, and are easy to grow on the waxy crude oil for enhanced oil recovery operations.

Conventional oil reserves are under production past several years, leaving the higher end hydrocarbons (paraffins/waxes) in the reservoir. The separation and deposition of these waxy components in the production and surface facilities are predominant when the system temperature reduces below the wax appearance temperature (WAT) during the flow of crude oil from a reservoir to the surface. It is, therefore, necessary to address various challenges posed by long chain paraffins using an economical, versatile, and eco-friendly technique. In the current scenario, microbial degradation of paraffins has gained considerable attention because of its environmentally friendly and operationally safer nature than other methods for sustainable development. In this study, the bio-surfactant producing microorganism Pseudomonas fluorescens, isolated from the marine port in Chennai, India, is used to degrade a wax sample, namely eicosane. The viscosity reduction and the delay in wax appearance temperature has been noticed. This study also analyzes the physico-chemical characteristics of the bio-surfactant produced by the microbe. The degradation of long chain paraffin to short chain molecule is confirmed by the gas chromatography-mass spectrometry (GCMS) result. From the GCMS results, it has been observed that 93% of the wax degraded in 10 days. The amount of bio-surfactant produced by the microbe is found to be as high as 9.5 g/L. The high surface tension reduction, production of higher amount of bio-surfactant, viscosity reduction and high rate of degradation indicates the potential of the microbe in flow assurance, oil-spill, enhanced oil recovery, etc.

In the oil and gas industry, upstream and downstream hydrocyclones are used extensively to separate heavy or dense particles from the formation water/reservoir fluids. These hydrocyclones, after a long period of operation, can fail as a result of wear-initiated leakage, thereby needing maintenance or replacement. A detailed investigation of this failure was carried out using computational fluid dynamics (CFD). One-way and two-way coupling of a discrete phase model was used along with the Reynolds stress turbulence model (RSM). Experimental studies were conducted to understand the flow dynamics within the hydrocyclone and to validate the computational model. Key findings, such as bifurcation of the inlet flow, local acceleration of fluid within the hydrocyclone, the impact of the sand drain pipe on fractional efficiency, and the impact of multiple particle sizes and density interactions on the degree of particle entrapment, are discussed in detail. The approach and results presented in this work provide useful insights and a systematic basis for improving the service life and separation efficiency of the hydrocyclone.

Matured reservoirs are being targeted for enhanced oil recovery (EOR) operations in the hope to recover the residual oil that remains trapped within the porous media. Chemical enhanced oil recovery is one of the successful oil recovery methods which is being employed for the recovery of the residual oil. Many of the conventional chemicals fail to perform under high temperature and high saline reservoir conditions. These situations lead to the search for alternate flooding techniques which could efficiently produce the crude oil to the surface. The present work investigates a possible solution for the recovery of trapped crude oil using lactam and imidazolium based ionic liquids (ILs) specifically targeted towards recovery in high saline environment. Initially, the interfacial tension of the crude oil-water system has been investigated using various chemical agents, such as sodium dodecyl sulfate (SDS), and six different ILs at varying high saline concentrations as a function of temperature (283.15–353.15 K). Subsequently, flooding experiments with only polymer, only SDS, only IL, SDS + polymer and IL + polymer at zero and high saline conditions were performed. It was observed that the IL + polymer flood performed very well in both zero and high salinity conditions as compared to all other flooding systems. The present investigation also portrays an intuition on the evaluation of ILs based on their alkyl chain length.

Families of various quaternary ammonium salts (QAS) have been of great interest to gas hydrate based investigations. In this work, an attempt has been made to understand the effect of QAS of the bromide family with increasing alkyl chain length, such as tetra-methyl, tetra-ethyl, and tetra-butyl ammonium bromide (TMAB, TEAB, and TBAB) at two different concentrations (0.05 and 0.1 mass fraction) in an aqueous solution on the hydrate-liquid-vapor (H-L-V) phase equilibrium of the methane hydrate system. Various experiments were performed to capture phase equilibrium data in the equilibrium pressure range of 7.6-4.2 MPa and temperature range of 282.4-276.8 K. It has been observed that the addition of TMAB and TEAB shifts the phase equilibrium curve of methane hydrate to higher pressure and lower temperature conditions. TMAB and TEAB have shown thermodynamic inhibition unlike TBAB which has shown a promotion effect. The Clausius-Clapeyron equation is used to calculate the enthalpy of dissociation of methane hydrate in various QAS aqueous solutions to examine the effect of QAS on methane hydrate structural information. The electrical conductivity measurements were also made to correlate the hydrate inhibition effectiveness of QAS on methane hydrate system. In addition, a phase equilibrium model has been extended to predict the phase behavior of methane hydrate + (TMAB, TEAB, or TBAB) aqueous solutions for a total 91 experimental phase equilibrium data points obtained from this work and the literature. The absolute average relative deviation in equilibrium pressure (AARD/P (%)) observed from the proposed model with the experimental equilibrium pressure data produced in this work and from several sources in the literature have been observed to lie within ±3.2%, indicating the robustness of the model.

Carbon dioxide injection for methane replacement from hydrate reservoirs is considered as one of the effective techniques for both methane production and carbon dioxide sequestration. To understand the gas exchange process, a thermodynamic model based on the classical fugacity approach has been utilized to predict the phase behavior and the cage occupancies of both binary CH4+CO2 and ternary CH4+N2+CO2 mixed gas hydrate systems in three phase (L-H-V) equilibria. A total of 256 experimental phase equilibrium data points on binary CH4+CO2, and ternary CH4+N2+CO2 gas hydrate systems have been selected from various literatures. For the ternary system, various compositions of CH4+N2+CO2 gas mixtures with varying N2/CO2 gas ratio, i.e., 0.13, 0.19, 0.27, 0.33, 0.37, 0.5, 0.98, 2.6, and 4, and varying CH4 compositions, i.e., 20, 50, 60, 70, 80, and 90%, have been considered. The absolute average deviations (%AAD) in the predicted equilibrium pressures with the experimental results are observed to be within 2.9% and 6.4% for binary and ternary mixed hydrate systems, respectively. For CH4+CO2 mixed hydrate systems, the average distribution coefficient of methane has been found to be 2.06, which indicates that the CH4 molecules are selectively replaced by CO2 molecules preferentially from large cages. For the ternary CH4+N2+CO2 mixed hydrate system, the N2/CO2 ratio in small cages of the hydrate is found to be almost 20 times larger than that in the large cages revealing the capacity of N2 and CO2 molecules to replace most of the CH4 molecules from small and large cages of the hydrate, respectively. The N2/CO2 ratio in small and large cages is temperature independent at low N2/CO2 gas ratio, which becomes temperature dependent at higher ratios, i.e., 2.6 and 4. From this study, we conclude that the injection of N2/CO2 gas mixture having ∼1:3 ratio is a good choice for enhancing the production of methane gas and carbon dioxide sequestration deep into the hydrate reservoirs.

The experimental phase equilibrium data for methane (CH4) clathrate hydrates in the presence of polyethylene glycol (PEG) aqueous solutions with various number-average molecular weights of 200 kg/kmol (PEG-200), 400 kg/kmol (PEG-400), and 600 kg/kmol (PEG-600) for (0.077, 0.2, 0.4, 0.44 and 0.46) mass fractions at the temperature range (270.75 to 281.45) K and pressure range (4.60 to 7.05) MPa has been reported. The isochoric pressure-search method is used to generate the equilibrium data on the hydrate system. Comparative effects of PEG-200, PEG-400, and PEG-600 aqueous solutions at various concentrations (mass fraction and mole fraction basis) on the methane hydrate system have been studied. The inhibition effect using low molecular weight PEG-200 is observed to be more effective in suppressing the methane hydrate formation than PEG-400 and PEG-600 at the same mass fraction. On the mole fraction basis, at higher concentration, the inhibition effect of PEG-600 on the methane hydrate system at the same mole fraction is observed to be more than PEG-200. Surprisingly, at lower concentration (at the same mole fraction), PEG-200 is observed to inhibit the methane hydrate system more than PEG-600. The methane hydrate suppression temperature using PEG-200, PEG-400, and PEG-600 is also determined using Hammerschmidt's equation and are reported. The work also reports the values of enthalpy of dissociation determined using the Clausius-Clapeyron equation for a methane hydrate system in the presence of PEG-200, PEG-400, and PEG-600 aqueous solutions. The enthalpy of dissociation of methane hydrate is observed to increase with increasing molecular weight of PEG. The study shows the effectiveness of low molecular weight PEG in inhibiting methane hydrate as compared to higher molecular weight, thus indicating their possible use for effective design of drilling and completion fluids for hydrate bearing formation.

The overall oil production worldwide has declined due to the increase in maturity of the oil reservoirs. In developing countries like India, the oil production and demand plays a crucial role for the development of economy of the country. However, the domestic crude oil production is insufficient to meet the requirement for energy. Thus, there is a big challenge to minimize the gap between the demand and supply for crude oil. Several methods to enhance oil recovery have been developed to increase the production from matured reservoirs and are referred to as enhanced oil recovery (EOR) methods. This chapter discusses in detail about the various EOR methods, their applicability, and the screening criteria for various reservoir types. The EOR methods are further discussed in Indian contexts. This chapter also summarizes the details of various oilfields in India. The chapter will in general, help to understand the recent trends and the need of EOR for Indian oil reservoirs.