Impact of Impurities on Formation of CO2 Hydrates Prakash Kumar Nair & Dr Nejat Rahmanian University of Bradford, Uk

6th International conference on petroleum engineering 2017 Contents Introduction Objective of Study Methodology Results and Discussion Conclusions Acknowledgments 6th International conference on petroleum engineering 2017

6th International conference on petroleum engineering 2017 Introduction What is a hydrate? It is a crystalline compound, where a gas molecule is encaged in a water molecule cavitiy Formed at high pressures and low temperatures Source: MIDAS Source: Adewumi (2016) 6th International conference on petroleum engineering 2017

6th International conference on petroleum engineering 2017 Introduction Why consider impurities? The presence of impurities can causes the following issues: CO2 hydrate formation Impact on the vapour-liquid equilibrium (VLE) phase envelope Corrosion Carbon Dioxide hydrates? These will be observed in the transport of high-CO2 streams, e.g. Carbon Capture and Storage (CCS) Knowledge of how impurities affect high CO2 streams is essential for the combat against rising CO2 emissions Source: Li et al. (2011) 6th International conference on petroleum engineering 2017

Objective of this Study This has created a pathway for a study with the following objectives: To investigate the impact of impurities on the formation of CO2 hydrates through binary and tertiary analysis To determine the impurity/impurities effect on the vapour-liquid equilibrium (VLE) phase envelope To investigate two real-life case studies An aspect which has not been conducted before in literature is conducting this study through the eyes of an operator From conducting an in-depth literature survey, the major limitations discovered: Each study only considered certain impurities They fail to consider changing compositions to fully appreciate the impurities affect Little research has been conducted on how the impurities affect hydrate formation 6th International conference on petroleum engineering 2017

6th International conference on petroleum engineering 2017 Methodology Binary & Tertiary Analysis The uneven mole fractions for each impurity is problematic – 5% mole fraction was used Water will be included in each binary and tertiary system Source: Munkejord et al. (2016)   N2 O2 Ar SO2 H2S/COS NOx CO H2 CH4 H2O Amines NH3 𝒙 𝒎𝒊𝒏 (%) 0.02 0.04 0.005 <10-3 0.01 <0.002 0.06 0.7 𝒙 𝒎𝒂𝒙 (%) 10 5 3.5 1.5 0.3 0.2 4 6.5 3 6th International conference on petroleum engineering 2017

6th International conference on petroleum engineering 2017 Methodology Case Studies – Cortez pipeline (2) – Sheep Mountain Pipeline Sheep Mountain Pipeline Cortez Pipeline 808 km, 30” diameter, pipeline which transports CO2 from McElmo Dome natural source to the Wasson oil field located in Texas 656 km pipeline which begins at Sheep Mountain and ends in Seminole Cortez and Sheep Mountain pipeline accounted for 66% and 4%, respectively, of the total CO2 supply for enhanced oil recovery (EOR) in 2009 (Global CCS 2016) 6th International conference on petroleum engineering 2017

6th International conference on petroleum engineering 2017 Methodology Which specialist softwares were used? (1) – Aspen HYSYS® V9 (2) – HydraFLASH® V3.3 This is a gas hydrate and thermodynamic prediction software designed to predict phase equilibria and physical properties (Hydrafact 2017) Sophisticated workflow-orientated process simulation software used for various scenarios in the gas processing industries (Aspen Technology 2017) Which equation of state (EoS) to use? 6th International conference on petroleum engineering 2017

6th International conference on petroleum engineering 2017 Methodology Model Validation Peng-Robinson EoS is in excellent agreement to the literature data 6th International conference on petroleum engineering 2017

Results and Discussion Binary Analysis   Binary Mixture Hydrate Length (km) Difference in Hydrate Length (km) Hydrate Structure (1) 95% 𝐶𝑂 2 −5% 𝑁 2 58 23 Type I (2) 95% 𝐶𝑂 2 −5% 𝑂 2 100 65 (3) 95% 𝐶𝑂 2 −5%𝐴𝑟 (4) 95% 𝐶𝑂 2 −5% 𝑆𝑂 2 16 -19 (5) 95% 𝐶𝑂 2 −5% 𝐻 2 𝑆 (6) 95% 𝐶𝑂 2 −5%𝐶𝑂𝑆 15 -20 (7) 95% 𝐶𝑂 2 −5% 𝑁𝑂 2 17 -18 (8) 95% 𝐶𝑂 2 −5%𝐶𝑂 (9) 95% 𝐶𝑂 2 −5% 𝐻 2 18 -17 (10) 95% 𝐶𝑂 2 −5% 𝐶𝐻 4 (11) 95% 𝐶𝑂 2 −5% 𝑁𝐻 3 6th International conference on petroleum engineering 2017

Regulation for Single-Phase Flow 95% CO2 & 5%H2S 95% CO2 & 5%N2 Impurity % Increase Nitrogen 3.16 Oxygen 8.98 Argon 12.44 Hydrogen Sulfide 53.26 Methane 14.25 95% CO2 & 5% CH4 Impurity Regulation for Single-Phase Flow Temperature (⁰C) Pressure (kPa) Nitrogen 10-27 6500-8060 Oxygen 11-27 6500-7980 Argon 12-27 6500-7850 Hydrogen Sulfide 18-31 5500-7400 Methane 6000-7660 6th International conference on petroleum engineering 2017

Regulation for Single-Phase Flow 95% CO2 & 5%SO2 95% CO2 & 5%COS 95% CO2 & 5%NH3 95% CO2 & 5%H2 Impurity % Decrease Sulfur Dioxide 4.98 Carbonyl Sulfide 5.79 Nitrogen Dioxide 4.24 Carbon Monoxide 4.63 Hydrogen 1.23 Ammonia 5.22 Impurity Regulation for Single-Phase Flow Temperature (⁰C) Pressure (kPa) Sulfur Dioxide 10-40 4000-7980 Carbonyl Sulfide 11-35 4500-7490 Nitrogen Dioxide 10-43 4500-8340 Carbon Monoxide 12-27 7000-8000 Hydrogen 17 12,000 Ammonia 15-36 4500-7700 6th International conference on petroleum engineering 2017

Results and Discussion Tertiary Analysis 6th International conference on petroleum engineering 2017

Regulation for Single-Phase Flow 95% CO2 & 2.5% H2S & 2.5%O2 95% CO2 & 2.5% H2S & 2.5%Ar Impurity Mixture % Increase Hydrogen Sulfide + Oxygen 36.21 Hydrogen Sulfide + Argon 37.21 Hydrogen Sulfide + Methane 38.75 95% CO2 & 2.5% H2S & 2.5%CH4 Impurity Mixture Regulation for Single-Phase Flow Temperature (⁰C) Pressure (kPa) Hydrogen Sulfide + Oxygen 12-29 6000-7680 Hydrogen Sulfide + Argon 18-29 6000-7620 Hydrogen Sulfide + Methane 17-29 5500-7520 6th International conference on petroleum engineering 2017

Results and Discussion Case Studies Cortez Pipeline Sheep Mountain Pipeline Temperature (⁰C) 43.35 20 Pressure (MPa) 18.6 83 Capacity (MT/yr) 19 (1) – 6.3 (2) – 9.2 Pipe Length (km) 808 (1) – 296 (2) – 360 Pipe Diameter (inch) 30 (1) – 20 (2) – 24 CO2 Content 95% (minimum) 95-98% Source: Oosterkamp and Ramsen (2008) 6th International conference on petroleum engineering 2017

Impurity (Hydrate Zone Dampener) (1) – Cortez Pipeline To recap – COS, SO2 and NH3 were the ‘Hydrate Zone Dampeners’ which caused the most significant reduction in hydrate stability zone Oosterkamp and Ramsen (2008) stated a H2S limit of 0.002 mol% – no hydrates formed When 0.2 mol% H2S was incorporated within – hydrates were formed Impurity (Hydrate Zone Dampener) % Decrease Sulfur Dioxide 4.98 Carbonyl Sulfide 5.79 Nitrogen Dioxide 4.24 Carbon Monoxide 4.63 Hydrogen 1.23 Ammonia 5.22 Therefore, addition of any of these impurities could counteract H2S Base case simulation produced no hydrates. 6th International conference on petroleum engineering 2017

6th International conference on petroleum engineering 2017 Case 1 Case 2 Case 3 Inlet Outlet Cortez Pipeline 2% COS 2% COS 2% COS 2% SO2 2% SO2 2% NH3 COS COS SO2 COS SO2 NH3 6th International conference on petroleum engineering 2017

6th International conference on petroleum engineering 2017 Each system significantly increased the hydrate formation pressure thus counteracting H2S 6th International conference on petroleum engineering 2017

Regulation for Single-Phase Flow 2% COS 2% COS & SO2 2% COS & SO2 & NH3 Impurity Mixture Regulation for Single-Phase Flow Temperature (⁰C) Pressure (kPa) 2% COS 12-30 6200-7800 2% COS + SO2 10-33 6100-8000 2% COS + SO2 + NH3 12-35 6000-8200 6th International conference on petroleum engineering 2017

6th International conference on petroleum engineering 2017 (2) – Sheep Mountain Pipeline As it’s been proven ‘Hydrate Zone Dampeners’ can counteract H2S, purpose of this simulation is to discover which impurity is the most dominant out of COS, SO2 and NH3 No H2S limit was provided, so incorporating 1 mol% H2S Hydrate formation pressure significantly reduced to produce hydrates Base case simulation produced no hydrates 6th International conference on petroleum engineering 2017

6th International conference on petroleum engineering 2017 Case 1 Case 2 Case 3 Inlet Outlet Sheep Mountain Pipeline 2% NH3 2% COS 2% SO2 NH3 COS SO2 6th International conference on petroleum engineering 2017

6th International conference on petroleum engineering 2017 NH3 increases the hydrate formation pressure the furthest 5 mol% of each impurity is recommended to ensure no hydrate formation 6th International conference on petroleum engineering 2017

Regulation for Single-Phase Flow 5% NH3 5% COS Impurity Mixture Regulation for Single-Phase Flow Temperature (⁰C) Pressure (kPa) 5% NH3 11-33 5900-7900 5% COS 11-32 5500-7700 5% SO2 10-38 5900-8200 5% SO2 If operator does not want to add impurities into pipeline, a H2S limit of 0.5mol% is recommended 6th International conference on petroleum engineering 2017

6th International conference on petroleum engineering 2017 Conclusions The key findings from the present study can be summarised as follows: The presence of H2S causes a quicker onset of hydrate formation by expanding the hydrate stability zone (HSZ) and reducing the hydrate formation pressure The presence of COS, SO2, NH3 causes the opposite where they reduce the HSZ and increase the hydrate formation pressure H2 and N2 causes a significant expansion in the VLE phase envelope 6th International conference on petroleum engineering 2017

6th International conference on petroleum engineering 2017 Acknowledgements I would like to express my deepest gratitude towards Dr Nejat Rahmanian and the Chemical Engineering Division at the University of Bradford for their support during the course of this project. Special thanks go to everyone involved at the Petroleum Engineering 2017 conference for allowing me to present my work. 6th International conference on petroleum engineering 2017

Thank you for listening! Any Questions? 6th International conference on petroleum engineering 2017