A New Framework for Quantifying the Risk of Hydrate Plug Formation

Zachary M. Aman, Bruce W. Norris, Michael L. Johns, Eric F. May

Australasian Oil & Gas Conference: New Trends in Flow Assurance

11 March 2015

Fluid Science & Resources

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Hydrate Plug Formation in Oil-Continuous Systems

2 Sloan and Koh (2007)

Fluid Science & Resources

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Motivation: Reduce Design Margins for Hydrate Management in Subsea Systems Increasing water depth

•  Enhanced driving force for hydrate formation •  Approach may create economic constraints

Increasing watercut leads to new behaviour •  Formation of free water phase •  Transition in flow regime

Foreign solids and chemicals •  Effect of asphaltene, wax, and sand •  Cross-interaction between chemical inhibitors

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Fluid Science & Resources

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Font: Lato LightHydrate Flow Assurance Simulation Tool (HyFAST)

•  Originally developed by Colorado School of Mines •  Employs the most advanced hydrate models •  Coupled with hydrodynamic relationships

Screening tool to select critical cases •  Identify high-risk cases for follow-up •  Designed for oil and water dominant systems

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HyFAST: Accessible Predictive Tool

5 km Flowline Solutions in ~ 5 Seconds

Output Dynamic Trendplots and Data

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Flowline, Loop & Autoclave Geometries

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Flash Module Enables Component Tracking Throughout Calculations

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Wellhead Pressure and Mean Velocity Specification

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Incorporates Dynamic THI Effects

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HyFAST 2 Incorporates Simple Transient Cases (Wellhead Operations)

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Base Case for Sensitivity and Behavioural Assessment

Flowline inlet: 2500 psi, 30 °C Geometry: 40 km, 25.4 cm I.D., 25 W/m2/K Fluids: 80% LL, 50% WC, Crude Oil

•  Hydrate kinetics •  Dynamic agglomeration •  Dynamic droplet sizes

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Region of Study

Base Case Shows Intermittent Hydrate Risk (1-6 hr)

‘Nucleation’: first timestep of hydrate formation •  Pipe initially uses unreacted components •  Steady-state reached within ~15 hours

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Decreasing Heat Transfer Coefficient Decreases Hydrate Growth

HyFAST groups wall layers and burial effects • Single heat transfer coefficient, manual entry • Does not incorporate thermal mass of wall 14

Dynamic Equilibrium Temperature Lookup for Systems with MEG

HyFAST tracks MEG fraction in aqueous phase • Enables combined assessment of required THI

fraction and insulation thickness 15

Flowloop Model Performance

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Validated against 26 oil and condensate experiments •  ExxonMobil flowloop

(Grasso et al., ICGH 8) •  1-3 m/s, 50-90% LL,

15-75% WC

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Quantitative Risk Assessment of Flowing Hydrate Slurries

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Qualitative

•  High risk: µrel > 100

•  Low risk: µrel < 10 *Zerpa et al., OTC, 2011 0  

20  

40  

60  

80  

100  

0   2   4   6   8   10   12  

Rela%v

e  Viscosity

 

Required  Sub-­‐Cooling  [K]  

Viscosity Profile

0  

0.1  

0.2  

0.3  

0.4  

0   2   4   6   8   10   12  

Prob

ability  Den

sity  

Required  Sub-­‐Cooling  [K]  

Probability Density Function

Translated ALTA Data

Quantitative •  Experimental data on

nucleation probability •  First approximation PDF,

validation ongoing •  Link risk (viscosity) through

system subcooling *May et al., Chem. Eng. Sci., 2013

High Risk

Low Risk

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0  

20  

40  

60  

80  

100  

0   10   20   30   40   50   60   70   80   90   100  

Rela%v

e  Viscosity

 

Cumula%ve  Probability  of  Observa%on  18

HyFAST Enables Risk Profile Plots

System Risk Profile

Worst Case (Unlikely)

Best Case (Unlikely)

High Risk

Low Risk

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0%  10%  20%  30%  40%  50%  60%  70%  80%  90%  100%  

0%  

20%  

40%  

60%  

80%  

100%  

0   10   20   30   40  Water  Cut  

Ope

ra%n

g  Re

gion

 Proba

bility  

Years  of  Opera%on  

Field Lifetime Risk Predictions

The effect of evolving reservoir conditions •  Based on Russian Romashkino Field •  Enhanced recovery by water injection pursued •  Led to an increase in water cut over time (1 to 85%)

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Low Risk

Intermediate Risk

High Risk

•  What we’ve done: 1.  Estimate WC

evolution 2.  At a given WC (time),

run simulations 3.  Determine sub-

cooling for µrel = 10 & 100

4.  Translate sub-cooling to probability

Water Cut

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Roadmap for Tool Development

Ongoing validation •  Flowloop plug formation •  Laboratory flash data •  Probabilistic nucleation models

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HyFAST 1.2 -  Flowloop & autoclave -  One control volume -  No flash -  Oil & water systems

HyFAST 2 -  Flowline geometry -  Integrated flash -  Oil & water systems -  Risk assessment

HyFAST 3 -  Gas-dominant cases -  Film growth and deposition module -  Momentum balance

2013 2014 2015

2016

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Conclusions

HyFAST 2 for hydrate formation in flowlines, flowloops and autoclaves

•  Direct validation for flowloop and autoclave •  On-going assessment of flowline accuracy

Features enable rapid case screening •  Robust flash module for component tracking •  Inhibitor (MEG) tracking with dynamic lookup •  Simple transient cases

HyFAST 2 made available through UWA •  Website: fsr.uwa.edu.au •  Includes user manual and technical documentation

THANK YOU Questions