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.

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.

In this experimental work, three different types of nanofluids were evaluated for their stability using dynamic light scattering and particle morphological study using scanning electron microscopy. The nanofluids used in this study are zinc oxide (ZnO) nanoparticle in water and 5 wt% polyvinylpyrrolidone (PVP) as a dispersant, and ZnO with polyethylene glycol (PEG 600) and CuO with PEG 600 with 5 wt% PVP at different concentration of 0.1, 0.3 and 0.5 wt%. Thermal and electrical conductivities were determined by KD-2 Pro® and PC 700 Eutech®. The result shows better enhancement in the thermal and electrical conductivity in the ZnO+PVP+Water system, followed by the CuO+PVP+PEG and ZnO+PEG systems. The highest percentage enhancement in thermal conductivity found to be 35.5% of ZnO+ PVP+water systems. The thermal conductivity results were compared with a theoretical model and show good agreement with results predicted by the model. The proposed model of Nan et al. (1997) is based on a hypothesis regarding the physical mechanism in heat transfer for nanofluids. This study is expected to form the basis for the development of nanofluid-based technologies with PEG as the primary additive in the upstream oil and gas industry especially in gas hydrates and drilling technology.

The use of water-soluble polymers as natural gas hydrate inhibitors has gained interest in recent years. Variety of polymers have been studied for their kinetic performance in methane hydrate inhibition in the past; however, thermodynamic hydrate inhibition by water-soluble polymers is not fully understood and needs further investigation. This study investigates the effect of molecular weights and concentrations of aqueous solutions of various oilfield water soluble polymers on phase equilibrium of methane hydrate. Water-soluble polymers, such as polyacrylamide (PAM), xanthan gum (XG), and guar gum (GG) with two different molecular weights and varying concentrations, have been considered for the investigations. These are as follows: PAM (Mw: 1.1 × 10 6 g/mol, PAM-1 and 1.5 × 10 5 g/mol, PAM-2), XG (Mw: 6.4 × 10 5 g/mol, XG-1 and 2.4 × 10 5 g/mol, XG-2), and GG (Mw: 1.7 × 10 6 g/mol, GG-1 and 6 × 10 5 g/mol, GG-2), with varying concentrations of 100, 200, and 500 ppm each. These are referred to as high-molecular-weight polymers (PAM-1, XG-1, and GG-1) and relatively low-molecular-weight polymers (PAM-2, XG-2, and GG-2). The experiments have been conducted in the pressure and temperature range of 8.63-5.50 MPa and 284.6-279.8 K, respectively. The results indicate that the water-soluble polymers have shown thermodynamic hydrate inhibition with an average temperature depression ranging from 0.25 to 1.05 K. The molecular weight and the concentration of polymers have been shown to affect the hydrate inhibition tendency. We have also proposed a hypothesis for hydrate inhibition based on the mobility of the polymer chain in the solution with a desired functional group in relation to nonelectrolyte/electrolyte thermodynamic hydrate inhibitors. The presented study on methane hydrate phase stability in the presence of various oilfield polymers is vital for their use in the design and development of hydrate inhibitive drilling fluids for offshore wells, hydrate-bearing formations, and studies related to the recovery of methane from hydrate-bearing sediments using polymer injection.

Energy is an essential commodity for the survival and socioeconomic development of the human race. The energy supply sector primarily comprises of industrial, commercial, and domestic applications. The foremost challenges faced by the energy supply sector are growing consumption levels, limited accessibility, environmental concerns, viz-a-viz, climate change, and pollution of water and air resources. As conventional resources of energy have started to decline and are expected to get exhausted by 2040, the main focus has been shifted to unconventional sources [1]. In this category, natural gas resources such as gas hydrate, shale gas, coal bed methane will provide tremendous potential for meeting the demand. Gas hydrates are ice-like crystalline substance formed by a framework of water and natural gas molecules. Recent exploration programs by various agencies such as United States Geological Survey (USGS), National Gas Hydrate Program (India), Japanese Methane Gas Hydrate R&D have proved that massive amount of gas hydrate deposits lying across marine settings and permafrost environments. Hydrate deposits are currently estimated to be 5 × 1015 m3 of methane gas [2]. If this untapped resource of energy becomes feasible for the economic production, it could increase natural gas reserves to multifold. Moreover, this would be considerably greater than the total amount of all fossil fuels together. As reported by USGS, gas hydrates hold more than 50% of the entire world’s carbon. It has been estimated that commercial production of methane from 15% of natural gas hydrate can fulfill the energy requirement of the entire world for next 200 years [3]. Hence, natural gas hydrates are considered to be the vital sustainable energy resource. Many pilot production tests have been completed and are underway to recover methane from gas hydrate deposit across the world [4]. Preliminary studies and pilot tests have shown promising results in terms of methane recovery from natural gas hydrates by employing methods such as thermal stimulation, depressurization, inhibitor injection. Ongoing gas hydrate research programs throughout the world and advances in technology will certainly help to cater any technical challenges in order to potentially harness the huge amount of energy stored in the form of natural gas hydrates.

Polymer flooding has been one of the most promising methods used for enhanced oil recovery from matured crude oil reservoirs across the globe due to its distinct advantages over simple water flooding. However, the use of polymer flooding has not yet been investigated for methane recovery from hydrate reservoirs. In our earlier work, we have investigated the effect of various molecular weights and concentrations of polyethylene glycol (PEG) polymer on the phase stability and kinetics of methane hydrate. This information has been explored for successful use of PEG as a chemical agent for polymer flooding from hydrate reservoirs. In this work, detailed experimental investigations on methane production from hydrate bearing sediments have been carried out using PEG polymer flooding in a three-dimensional hydrate reactor. Initially, methane hydrate formation has been investigated using two silica sand porous beds (viz., 0.16 and 0.46 mm), and pure water at an initial hydrate formation pressure of 8 MPa and 277.15 K. Subsequently, hydrate dissociation studies have been carried out using polymer flooding at a final hydrate reservoir pressure of ∼4.3 MPa and 277.15 K. The effect of molecular weights (200 and 600 kg/kmol, viz., PEG-200 and PEG-600, respectively), concentrations (0.2 and 0.4 mass fractions), and injection rates (1 and 5 mL/min) of PEG aqueous solution has been analyzed for methane gas recovery. PEG-200 is observed to be an effective flooding agent as compared to PEG-600 and other inhibitor such as ethylene glycol used in the literature. In addition, studies on the total dissolved solids (TDS) and electrical conductivity of PEG aqueous solutions have also been investigated before and after flooding to check the efficacy of polymer flooding for methane production. PEG has a much lower freezing point (208.15 K, i.e., -65 °C) compared to ethylene glycol (260.25 K, i.e., -12.9 °C); therefore, polymer flooding is expected to be more beneficial for methane gas production from hydrate bearing zones with low reservoir temperatures.

The use of water-soluble polymers as natural gas hydrate inhibitors has gained interest in recent years. Variety of polymers have been studied for their kinetic performance in methane hydrate inhibition in the past; however, thermodynamic hydrate inhibition by water-soluble polymers is not fully understood and needs further investigation. This study investigates the effect of molecular weights and concentrations of aqueous solutions of various oilfield water soluble polymers on phase equilibrium of methane hydrate. Water-soluble polymers, such as polyacrylamide (PAM), xanthan gum (XG), and guar gum (GG) with two different molecular weights and varying concentrations, have been considered for the investigations. These are as follows: PAM (Mw: 1.1 × 106 g/mol, PAM-1 and 1.5 × 105 g/mol, PAM-2), XG (Mw: 6.4 × 105 g/mol, XG-1 and 2.4 × 105 g/mol, XG-2), and GG (Mw: 1.7 × 106 g/mol, GG-1 and 6 × 105 g/mol, GG-2), with varying concentrations of 100, 200, and 500 ppm each. These are referred to as high-molecular-weight polymers (PAM-1, XG-1, and GG-1) and relatively low-molecular-weight polymers (PAM-2, XG-2, and GG-2). The experiments have been conducted in the pressure and temperature range of 8.63-5.50 MPa and 284.6-279.8 K, respectively. The results indicate that the water-soluble polymers have shown thermodynamic hydrate inhibition with an average temperature depression ranging from 0.25 to 1.05 K. The molecular weight and the concentration of polymers have been shown to affect the hydrate inhibition tendency. We have also proposed a hypothesis for hydrate inhibition based on the mobility of the polymer chain in the solution with a desired functional group in relation to nonelectrolyte/electrolyte thermodynamic hydrate inhibitors. The presented study on methane hydrate phase stability in the presence of various oilfield polymers is vital for their use in the design and development of hydrate inhibitive drilling fluids for offshore wells, hydrate-bearing formations, and studies related to the recovery of methane from hydrate-bearing sediments using polymer injection.

This study investigates the kinetics of gas hydrate (methane gas) in the presence of Ionic Liquids (ILs) and organic Quaternary Ammonium Salts (QASs). Aqueous solutions of eight ILs (five aromatic ILs and three aliphatic ILs) and three QASs have been studied for the kinetics of methane hydrate formation. In this study, five aromatic-based ILs with cations, viz., 1-hexyl-3-methylimidazolium, 1-butyl-3-methylimidazolium, and 1-octyl-3-methylimidazolium, and anions such as [Br]−, [Cl]−, and [HSO4]− were selected. Three aliphatic ILs with cations, viz., diethylammonium, tripropylammonium, and tributylammonium, attached with the [HSO4]− anion were also selected. In the case of QASs, varying carbon chain lengths such as tetra-n-methyl-, tetra-n-ethyl-, and tetra-n-butylammonium bromide (TMAB, TEAB, TBAB) have been considered for the study. The kinetics of methane hydrate formation were investigated at a pressure of 7.5 MPa and a temperature of 276.15 K in the presence of aqueous solutions of QASs at 0.05 mf (mass fraction) and 0.1 mf concentrations and ILs at 0.01 mf. The results show that 0.05 mf of TBAB assists the methane hydrate to nucleate very rapidly and enhances the rate of growth. Hence, TBAB at 0.05 mf is observed to be most promising for gas storage and gas separation/processing among all investigated QASs. TMAB and TEAB have shown slow kinetics; therefore, their presence in a gas hydrate system may not aid in hydrate gas storage/gas separation applications; nevertheless, they could be used as an inhibitor for the prevention of hydrates in systems where other inhibitors may become unsuitable. The aqueous solution of aromatic-based ILs generally shows hydrate promotion, except for shorter chain lengths. The shorter chain length of ionic liquid with suitable anion (Cl-) behaved as a hydrate as the inhibitor and with Br- as the promoter. In general, a bigger cation acts as a good nucleating agent. The anion [HSO4]− is common in both the categories of ILs (aromatic and aliphatic), and it looks like the hydrate inhibition (no hydrate formation) may have occurred due to its presence. ILs offer more scope to understand the tunability of cations and anions to derive a better solution for gas hydrate inhibition and promotion, which have more applications in the ares of methane storage and transportation.

Methane is the smallest and cleanest burning fuel. It is found in the form of natural gas in which methane present in bulk but contains many impurities such as CO2, H2S which must be removed before being used by the consumer. In addition, it must be stored efficiently and transported economically. Gas hydrate is proposed to be one of the methods for storage, transportation and separation. A subclass of hydrate known as semiclathrate hydrate is capable of acting as a sieve for different sized gas molecules and have the capability to cohost smaller guest gases of specific size. Theses semiclathrate hydrate can be very useful for gas storage and multicomponent gas separation. In this work, a family of quaternary-ammonium salts such as tetra n-methyl/n-ethyl ammonium bromide (TMAB/TEAB) from the clan of tetra-alkyl ammonium bromide are examined at concentrations of 5wt% and 10 wt% for their phase stability along with the TBAB. Additionally, non-isothermal kinetics have been studied. Various experimental data have been obtained at different initial pressures of 8 MPa, 7.5 MPa, and 5.5 MPa to find out the influence of alkyl chain length on methane hydrate formation. It can be observed from experiential results that both TMAB and TEAB have shown thermodynamic inhibition as compared to TBAB. It can also be concluded from the phase stability curves that TBAB has more potential to aid in methane storage and separation than TMAB and TEAB at moderate pressure and temperature. An effect of carbon alkyl chain length is clearly seen on methane gas consumption. It has been witnessed that gas storage in hydrate increases with increase in the alkyl chain length of the salts. From this study, TBAB has found to be a more promising agent for gas processing and methane storage in the form of gas hydrate.

Recent production technologies to extract methane from mysterious hydrate reservoirs are not effective and need additional efforts to develop novel technologies to improve methane production. Chemical inhibitor injection is appraised as an effective method due to ease in operation, improved energy efficiency, and reduced threat of hydrate reformation. In the current study, several experiments on methane recovery have been performed in a simulated laboratory-based hydrate reservoir by injecting chemical inhibitors and combinations of aqueous chemical inhibitor/polymer systems. Different combinations of inhibitors and polymers, viz., chemical inhibitors such as methanol, ethylene glycol, methanol + polyacrylamide, and so forth, with varying concentrations, have been explored. Polyacrylamide has been used as in our previous study, it was shown that it can act as a better kinetic hydrate inhibitor, and also, the same polymer is often used for the enhanced oil recovery process in the upstream oil industry. In total, seven different simultaneous hydrate formation and dissociation experiments were performed. The inhibitor + polymer aqueous solution was injected to produce methane by dissociating the hydrate. The gas production ratio and the effectiveness of inhibitor aqueous solution and pure inhibitor in terms of methane recovery from hydrate-bearing sediments have been discussed and analyzed. This study provides a good insight into the use of some of the conventional hydrate inhibitors along with the oilfield polymer for methane recovery from hydrate-bearing sediments.