Over the past decade, low dosage hydrate inhibitors (LDHIs) which include anti-agglomerants (AA... more Over the past decade, low dosage hydrate inhibitors (LDHIs) which include anti-agglomerants (AAs) and kinetic hydrate inhibitors (KHIs) have seen increasing use as a cost effective technology for gas hydrate control in the oil and gas industry, offering significant CAPEX/OPEX advantages when compared with traditional thermodynamic inhibitors (e.g. methanol, glycols). While AAs prevent agglomeration/plugging, KHIs are primarily understood to be nucleation inhibitors, inducing an extended 'induction time' at a specific subcooled condition before hydrate nucleation can proceed to growth. The best known KHIs are water soluble poly-n-vinylamides such as poly-n-vinylcaprolactam (PVCap), poly-n-vinylpyrrolidone (PVP) and related polymers. As KHIs are seen primarily as 'nucleation delayers', evaluation is typically undertaken through measurement of induction times as a function of various parameters at the conditions of interest. However, as nucleation is stochastic by nature, obtaining repeatable/transferrable data is often highly problematic and time-consuming, making robust evaluation difficult. Here, we demonstrate that less well investigated aspect of KHI polymers their ability to inhibit crystal growth is considerably simpler to quantify than nucleation inhibition. Beginning at low aqueous concentrations (e.g. > 0.1 mass% aqueous), PVCap and other KHI polymers induce a number of highly repeatable, well-defined hydrate crystal growth inhibition (CGI) regions as a function of subcooling. Discernible by step changes in relative growth rates − commonly by an order of magnitude − CGI regions range from complete inhibition (even hydrate dissociation), through severely to moderately reduced growth rates, ultimately to final rapid/catastrophic growth as subcooling increases. Closely related to induction time data, CGI regions are readily measureable using conventional hydrate laboratory equipment, with subcooling extents − which it is speculated are polymer crystal surface absorption related phenomena providing a means to assess KHIs more rapidly and reliably, while giving a increased confidence in performance under worst case scenario (hydrate present) field conditions.
Low dosage Kinetic Hydrate Inhibitors (KHIs) have seen increasing use as a cost effective technol... more Low dosage Kinetic Hydrate Inhibitors (KHIs) have seen increasing use as a cost effective technology for gas hydrate control in the oil and gas industry, offering significant CAPEX/OPEX advantages over traditional thermodynamic inhibitors (e.g. methanol, glycols). As KHIs are traditionally considered 'nucleation inhibitors' i.e. they extend the induction (or 'hold') time, t i , at a specific subcooling before hydrate nucleation proceeds to growth evaluation is typically undertaken by measurement t i as a function of various parameters at the conditions of interest. However, as nucleation is stochastic by nature, obtaining repeatable/transferrable data is often highly problematic and time-consuming, making robust evaluation difficult. Likewise, the focus on nucleation, and associated belief that the appearance of hydrate crystals in a KHI inhibited system means the inhibitor has failed, lowers confidence in field use. Here, we discuss the application of a new crystal growth inhibition (CGI) based approach to evaluate a number of commercial formulations for a gas condensate system. As reported for simple gas−water−polymer systems in a companion paper, commercial KHI formulations similarly induce a number of highly repeatable, well-defined hydrate crystal growth inhibition regions as a function of subcooling, ranging from complete inhibition (even hydrate dissociation), through severely to moderately reduced growth rates, ultimately to final rapid/catastrophic growth as subcooling increases. Delineation of these regions provides a much more reliable and rapid means to evaluate the relative performance of KHIs under simulated worst case scenario conditions; i.e. hydrate already present. Furthermore, the ability of KHIs to completely or severely inhibit hydrate growth even when modest fractions of hydrate (e.g. 0.5% of water converted) are present gives greatly increased confidence in terms of real-world application. Significantly, while recommended by vendors for the systems under study, tested KHIs varied greatly in their ability to inhibit crystal growth, demonstrating the limitations of traditional t i based test methods in providing a suitably robust evaluation protocol.
Glycols are widely used in the oil and gas industry. Monoethylene glycol (MEG) is often used to a... more Glycols are widely used in the oil and gas industry. Monoethylene glycol (MEG) is often used to avoid hydrate formation and in many new developments, MEG is the preferred hydrate inhibitor over methanol. Another application where glycols are of importance is during the drying of natural gases. In this communication, we report new experimental solid-liquid equilibrium data for the monoethylene glycol (MEG) – water, propylene glycol (PG), diethyelene glycol (DEG) – water and triethylene (TEG) –water systems at temperatures down to -60°C. These new data were used to adjust a thermodynamic model in which the Cubic-Plus-Association equation of state is employed to model the phase equilibria. The new model has been tested with independent hydrate phase equilibrium data.
Experimentally determined equilibrium phase relations are reported for the system H2-THF-H2O as a... more Experimentally determined equilibrium phase relations are reported for the system H2-THF-H2O as a function of aqueous tetrahydrofuran (THF) concentration from 260 to 290 K at pressures up to 45 MPa. Data are consistent with the formation of cubic structure-II (CS-II) binary H2-THF clathrate hydrates with a stoichiometric THF-to-water ratio of 1:17, which can incorporate modest volumes of molecular hydrogen at elevated pressures. Direct compositional analyses of the clathrate phase, at both low (0.20 mol %) and stoichiometric (5.56 mol %) initial THF aqueous concentrations, are consistent with observed phase behavior, suggesting full occupancy of large hexakaidecahedral (51264) clathrate cavities by THF, coupled with largely complete (80-90%) filling of small dodecahedral (512) cages by single H2 molecules at pressures of >30 MPa, giving a clathrate formula of (H2) < or =2.THF.17H2O. Results should help to resolve the current controversy over binary H2-THF hydrate hydrogen contents; data confirm recent reports that suggest a maximum of approximately 1 mass % H2, this contradicting values of up to 4 mass % previously claimed for comparable conditions.
Copyright 2011, Society of Petroleum Engineers This paper was prepared for presentation at the SP... more Copyright 2011, Society of Petroleum Engineers This paper was prepared for presentation at the SPE Offshore Europe Oil and Gas Conference and Exhibition held in Aberdeen, UK, 6–8 September 2011. This paper was selected for presentation by an SPE program committee ...
Copyright 2009, International Petroleum Technology Conference This paper was prepared for present... more Copyright 2009, International Petroleum Technology Conference This paper was prepared for presentation at the International Petroleum Technology Conference held in Doha, Qatar, 79 December 2009. This paper was selected for presentation by an IPTC Programme ...
Iranian Journal of Chemistry and Chemical Engineering, Apr 1, 2010
Asphaltene precipitation and deposition is a serious problem in many Iranian fields. The deposite... more Asphaltene precipitation and deposition is a serious problem in many Iranian fields. The deposited asphaltene results in partial or total blockage of the wellbore and wellstring reducing or completely seizing oil production. This paper studies the asphaltene problem and mitigation methods ...
The Gibbs-Thomson effect modifies the pressure and temperature at which clathrates occur, hence a... more The Gibbs-Thomson effect modifies the pressure and temperature at which clathrates occur, hence altering the depth at which they occur in the seabed. Nuclear magnetic resonance (NMR) measurements as a function of temperature are being conducted for water/ice/hydrate systems in a range of pore geometries, including templated SBA-15 silicas, controlled pore glasses and sol-gel silicas. Rotator-phase plastic ice is shown to be present in confined geometry, and bulk tetrahydrofuran hydrate is also shown to probably have a rotator phase. A novel NMR cryoporometry protocol, which probes both melting and freezing events while avoiding the usual problem of supercooling for the freezing event, has been developed. This enables a detailed probing of the system for a given pore size and geometry and the exploration of differences between hydrate formation and dissociation processes inside pores. These process differences have an important effect on the environment, as they impact on the ability of a marine hydrate system to re-form once warmed above a critical temperature. Ab initio quantum-mechanical molecular dynamics calculations are also being employed to probe the dynamics of liquids in pores at nanometric dimensions.
ABSTRACT Viscosity and density of a six-component synthetic fluid have been measured at 323, 373,... more ABSTRACT Viscosity and density of a six-component synthetic fluid have been measured at 323, 373, and 423 K, and pressures up to 140 MPa. The viscosity measurements have been made with a capillary-tube viscometer, incorporated into a high-pressure-high-temperature experimental facility. The fluid has been prepared gravimetrically and its dew-point pressure has also been measured at 323, 373, and 423 K.
... Maria Llamedo {dagger} , Ross Anderson and Bahman Tohidi * ... 1999; Henry et al. 1999). The ... more ... Maria Llamedo {dagger} , Ross Anderson and Bahman Tohidi * ... 1999; Henry et al. 1999). The melting and freezing behavior of organic and inorganic compounds confined to narrow pores is an extensively studied phenomenon (Christenson 2001). ...
Gas hydrate blockages often cause impeded flow in transport pipelines of offshore gas and oil pro... more Gas hydrate blockages often cause impeded flow in transport pipelines of offshore gas and oil production, posing serious risks to facilities and personnel. The most common prevention measure of hydrate blockages is utilisation of various hydrate inhibitors. Typically, hydrate inhibitors are injected at the upstream of pipelines and the dosage of the deployed hydrate inhibitor is determined according to approximate assessment of the flowing conditions including the fluid temperature and pressure, water cut, and the hydrocarbon composition in the pipeline. Currently, it is a common case that the inhibitor is injected based on the worst temperature and pressure conditions, possibly high water cut as there are almost no means to monitor the actual degree of inhibition or to detect signs of early hydrate formation along the pipeline, resulting in unnecessarily high cost and severe impact on the environment. A joint industry project (JIP), called " Hydrate Monitoring and Early Warnin...
The main aim of this work was to establish whether the pertaining pressure and temperature condit... more The main aim of this work was to establish whether the pertaining pressure and temperature conditions and dissolved gas concentration in groundwater is conducive to gas hydrate formation using a modelling approach.
As nearly forty percent of fields lying untapped contain high concentrations of CO2 there is a re... more As nearly forty percent of fields lying untapped contain high concentrations of CO2 there is a requirement for accurate predictions of thermophysical properties essential for sound design of production facilities. For example, in some gas fields in South East-Asia, the CO2 content is higher than 70 mole%. The presence of such high concentrations of CO2 in the stream can lead to challenging flow assurance and processing issues. In this communication we present experimental techniques, equipment and thermodynamic modeling for investigating systems with high CO2 concentrations and discuss experimental results on the phase behavior and thermo-physical properties of a CO2-rich natural gas. The effect of high CO2 concentration on density and viscosity were experimentally and theoretically investigated over a range of temperature from -22 to 302°F and pressures up to 18,000 psia. A corresponding-state viscosity model was developed to predict the viscosity of the stream and a volume correct...
Proceedings of European Production Operations Conference and Exhibition, 1996
... Effect of Heavy Hydrate Formers on the Hydrate Free Zone of Real Fluids ... as L preaenlti, h... more ... Effect of Heavy Hydrate Formers on the Hydrate Free Zone of Real Fluids ... as L preaenlti, have not bean rewewed by Ihe SOW3ty of Petroleum ngmeers and are subject to Corrwtmn by the author(s). The materf al, as presentti, does nol nt?cessanly relled any pi?sthon of the ...
Over the past decade, low dosage hydrate inhibitors (LDHIs) which include anti-agglomerants (AA... more Over the past decade, low dosage hydrate inhibitors (LDHIs) which include anti-agglomerants (AAs) and kinetic hydrate inhibitors (KHIs) have seen increasing use as a cost effective technology for gas hydrate control in the oil and gas industry, offering significant CAPEX/OPEX advantages when compared with traditional thermodynamic inhibitors (e.g. methanol, glycols). While AAs prevent agglomeration/plugging, KHIs are primarily understood to be nucleation inhibitors, inducing an extended 'induction time' at a specific subcooled condition before hydrate nucleation can proceed to growth. The best known KHIs are water soluble poly-n-vinylamides such as poly-n-vinylcaprolactam (PVCap), poly-n-vinylpyrrolidone (PVP) and related polymers. As KHIs are seen primarily as 'nucleation delayers', evaluation is typically undertaken through measurement of induction times as a function of various parameters at the conditions of interest. However, as nucleation is stochastic by nature, obtaining repeatable/transferrable data is often highly problematic and time-consuming, making robust evaluation difficult. Here, we demonstrate that less well investigated aspect of KHI polymers their ability to inhibit crystal growth is considerably simpler to quantify than nucleation inhibition. Beginning at low aqueous concentrations (e.g. > 0.1 mass% aqueous), PVCap and other KHI polymers induce a number of highly repeatable, well-defined hydrate crystal growth inhibition (CGI) regions as a function of subcooling. Discernible by step changes in relative growth rates − commonly by an order of magnitude − CGI regions range from complete inhibition (even hydrate dissociation), through severely to moderately reduced growth rates, ultimately to final rapid/catastrophic growth as subcooling increases. Closely related to induction time data, CGI regions are readily measureable using conventional hydrate laboratory equipment, with subcooling extents − which it is speculated are polymer crystal surface absorption related phenomena providing a means to assess KHIs more rapidly and reliably, while giving a increased confidence in performance under worst case scenario (hydrate present) field conditions.
Low dosage Kinetic Hydrate Inhibitors (KHIs) have seen increasing use as a cost effective technol... more Low dosage Kinetic Hydrate Inhibitors (KHIs) have seen increasing use as a cost effective technology for gas hydrate control in the oil and gas industry, offering significant CAPEX/OPEX advantages over traditional thermodynamic inhibitors (e.g. methanol, glycols). As KHIs are traditionally considered 'nucleation inhibitors' i.e. they extend the induction (or 'hold') time, t i , at a specific subcooling before hydrate nucleation proceeds to growth evaluation is typically undertaken by measurement t i as a function of various parameters at the conditions of interest. However, as nucleation is stochastic by nature, obtaining repeatable/transferrable data is often highly problematic and time-consuming, making robust evaluation difficult. Likewise, the focus on nucleation, and associated belief that the appearance of hydrate crystals in a KHI inhibited system means the inhibitor has failed, lowers confidence in field use. Here, we discuss the application of a new crystal growth inhibition (CGI) based approach to evaluate a number of commercial formulations for a gas condensate system. As reported for simple gas−water−polymer systems in a companion paper, commercial KHI formulations similarly induce a number of highly repeatable, well-defined hydrate crystal growth inhibition regions as a function of subcooling, ranging from complete inhibition (even hydrate dissociation), through severely to moderately reduced growth rates, ultimately to final rapid/catastrophic growth as subcooling increases. Delineation of these regions provides a much more reliable and rapid means to evaluate the relative performance of KHIs under simulated worst case scenario conditions; i.e. hydrate already present. Furthermore, the ability of KHIs to completely or severely inhibit hydrate growth even when modest fractions of hydrate (e.g. 0.5% of water converted) are present gives greatly increased confidence in terms of real-world application. Significantly, while recommended by vendors for the systems under study, tested KHIs varied greatly in their ability to inhibit crystal growth, demonstrating the limitations of traditional t i based test methods in providing a suitably robust evaluation protocol.
Glycols are widely used in the oil and gas industry. Monoethylene glycol (MEG) is often used to a... more Glycols are widely used in the oil and gas industry. Monoethylene glycol (MEG) is often used to avoid hydrate formation and in many new developments, MEG is the preferred hydrate inhibitor over methanol. Another application where glycols are of importance is during the drying of natural gases. In this communication, we report new experimental solid-liquid equilibrium data for the monoethylene glycol (MEG) – water, propylene glycol (PG), diethyelene glycol (DEG) – water and triethylene (TEG) –water systems at temperatures down to -60°C. These new data were used to adjust a thermodynamic model in which the Cubic-Plus-Association equation of state is employed to model the phase equilibria. The new model has been tested with independent hydrate phase equilibrium data.
Experimentally determined equilibrium phase relations are reported for the system H2-THF-H2O as a... more Experimentally determined equilibrium phase relations are reported for the system H2-THF-H2O as a function of aqueous tetrahydrofuran (THF) concentration from 260 to 290 K at pressures up to 45 MPa. Data are consistent with the formation of cubic structure-II (CS-II) binary H2-THF clathrate hydrates with a stoichiometric THF-to-water ratio of 1:17, which can incorporate modest volumes of molecular hydrogen at elevated pressures. Direct compositional analyses of the clathrate phase, at both low (0.20 mol %) and stoichiometric (5.56 mol %) initial THF aqueous concentrations, are consistent with observed phase behavior, suggesting full occupancy of large hexakaidecahedral (51264) clathrate cavities by THF, coupled with largely complete (80-90%) filling of small dodecahedral (512) cages by single H2 molecules at pressures of >30 MPa, giving a clathrate formula of (H2) < or =2.THF.17H2O. Results should help to resolve the current controversy over binary H2-THF hydrate hydrogen contents; data confirm recent reports that suggest a maximum of approximately 1 mass % H2, this contradicting values of up to 4 mass % previously claimed for comparable conditions.
Copyright 2011, Society of Petroleum Engineers This paper was prepared for presentation at the SP... more Copyright 2011, Society of Petroleum Engineers This paper was prepared for presentation at the SPE Offshore Europe Oil and Gas Conference and Exhibition held in Aberdeen, UK, 6–8 September 2011. This paper was selected for presentation by an SPE program committee ...
Copyright 2009, International Petroleum Technology Conference This paper was prepared for present... more Copyright 2009, International Petroleum Technology Conference This paper was prepared for presentation at the International Petroleum Technology Conference held in Doha, Qatar, 79 December 2009. This paper was selected for presentation by an IPTC Programme ...
Iranian Journal of Chemistry and Chemical Engineering, Apr 1, 2010
Asphaltene precipitation and deposition is a serious problem in many Iranian fields. The deposite... more Asphaltene precipitation and deposition is a serious problem in many Iranian fields. The deposited asphaltene results in partial or total blockage of the wellbore and wellstring reducing or completely seizing oil production. This paper studies the asphaltene problem and mitigation methods ...
The Gibbs-Thomson effect modifies the pressure and temperature at which clathrates occur, hence a... more The Gibbs-Thomson effect modifies the pressure and temperature at which clathrates occur, hence altering the depth at which they occur in the seabed. Nuclear magnetic resonance (NMR) measurements as a function of temperature are being conducted for water/ice/hydrate systems in a range of pore geometries, including templated SBA-15 silicas, controlled pore glasses and sol-gel silicas. Rotator-phase plastic ice is shown to be present in confined geometry, and bulk tetrahydrofuran hydrate is also shown to probably have a rotator phase. A novel NMR cryoporometry protocol, which probes both melting and freezing events while avoiding the usual problem of supercooling for the freezing event, has been developed. This enables a detailed probing of the system for a given pore size and geometry and the exploration of differences between hydrate formation and dissociation processes inside pores. These process differences have an important effect on the environment, as they impact on the ability of a marine hydrate system to re-form once warmed above a critical temperature. Ab initio quantum-mechanical molecular dynamics calculations are also being employed to probe the dynamics of liquids in pores at nanometric dimensions.
ABSTRACT Viscosity and density of a six-component synthetic fluid have been measured at 323, 373,... more ABSTRACT Viscosity and density of a six-component synthetic fluid have been measured at 323, 373, and 423 K, and pressures up to 140 MPa. The viscosity measurements have been made with a capillary-tube viscometer, incorporated into a high-pressure-high-temperature experimental facility. The fluid has been prepared gravimetrically and its dew-point pressure has also been measured at 323, 373, and 423 K.
... Maria Llamedo {dagger} , Ross Anderson and Bahman Tohidi * ... 1999; Henry et al. 1999). The ... more ... Maria Llamedo {dagger} , Ross Anderson and Bahman Tohidi * ... 1999; Henry et al. 1999). The melting and freezing behavior of organic and inorganic compounds confined to narrow pores is an extensively studied phenomenon (Christenson 2001). ...
Gas hydrate blockages often cause impeded flow in transport pipelines of offshore gas and oil pro... more Gas hydrate blockages often cause impeded flow in transport pipelines of offshore gas and oil production, posing serious risks to facilities and personnel. The most common prevention measure of hydrate blockages is utilisation of various hydrate inhibitors. Typically, hydrate inhibitors are injected at the upstream of pipelines and the dosage of the deployed hydrate inhibitor is determined according to approximate assessment of the flowing conditions including the fluid temperature and pressure, water cut, and the hydrocarbon composition in the pipeline. Currently, it is a common case that the inhibitor is injected based on the worst temperature and pressure conditions, possibly high water cut as there are almost no means to monitor the actual degree of inhibition or to detect signs of early hydrate formation along the pipeline, resulting in unnecessarily high cost and severe impact on the environment. A joint industry project (JIP), called " Hydrate Monitoring and Early Warnin...
The main aim of this work was to establish whether the pertaining pressure and temperature condit... more The main aim of this work was to establish whether the pertaining pressure and temperature conditions and dissolved gas concentration in groundwater is conducive to gas hydrate formation using a modelling approach.
As nearly forty percent of fields lying untapped contain high concentrations of CO2 there is a re... more As nearly forty percent of fields lying untapped contain high concentrations of CO2 there is a requirement for accurate predictions of thermophysical properties essential for sound design of production facilities. For example, in some gas fields in South East-Asia, the CO2 content is higher than 70 mole%. The presence of such high concentrations of CO2 in the stream can lead to challenging flow assurance and processing issues. In this communication we present experimental techniques, equipment and thermodynamic modeling for investigating systems with high CO2 concentrations and discuss experimental results on the phase behavior and thermo-physical properties of a CO2-rich natural gas. The effect of high CO2 concentration on density and viscosity were experimentally and theoretically investigated over a range of temperature from -22 to 302°F and pressures up to 18,000 psia. A corresponding-state viscosity model was developed to predict the viscosity of the stream and a volume correct...
Proceedings of European Production Operations Conference and Exhibition, 1996
... Effect of Heavy Hydrate Formers on the Hydrate Free Zone of Real Fluids ... as L preaenlti, h... more ... Effect of Heavy Hydrate Formers on the Hydrate Free Zone of Real Fluids ... as L preaenlti, have not bean rewewed by Ihe SOW3ty of Petroleum ngmeers and are subject to Corrwtmn by the author(s). The materf al, as presentti, does nol nt?cessanly relled any pi?sthon of the ...
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