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rpsgroup.com
A NOVEL APPROACH TO SIMULATE THE COMPLEX DYNAMICS OF OIL SPILLS ON LAND
Jeremy Fontenault - RPSCo-Authors: Anusha Dissanayake, Tara Franey - RPS5/16/2019
Overview
• Need for spill modeling
• Traditional approach for modeling spills on land
• Drivers for more complex modeling
• Advanced Overland Modeling Approach: Particle-based model Advanced oil weathering Infiltration
2Complex Overland Modeling
Need for Oil Spill Modeling on Land
• High Consequence Area (HCA) Analysis
• Permitting
• Routing
• Engagement
• Response Planning
• Risk Management
• Environmental & Human Health Impact Assessments
Regulations:
Pipelines49 CFR part 195 (US)CSA Z662-11 (CAN)
Facilities40 CFR part 112
Rail49 CFR parts 107-174
3Complex Overland Modeling
Traditional Approach• Steepest downslope pathway
• Simplifying assumptions: Flow velocity Path width Static product density/viscosity Loss terms (adherence, evaporation, etc.)
4Complex Overland Modeling
Pros:• Fast simulations• Can run thousands of
simulations• Generally, a conservative
prediction
Cons:• Simplified overland pathway• Challenges with complex
terrain• Basic weathering of released
liquid
Drivers for More Complex Modeling
• Under a higher level of scrutiny
• More complex questions are being asked by regulators and stakeholders:
Could a release take multiple downslope flow paths?
How do the physical changes to the oil over time impact the potential trajectory, fate, and effects?
How could outcomes vary for the different products transported?
What is the potential for impact to ground water?
5Complex Overland Modeling
Source: inhabitat.com
Source: Ellen Schmidt, MPR News
New Approach for Advanced Overland Spill Modeling
Smooth Particle Hydrodynamics (SPH)
• Particle-based approach to simulate complex flow
Advanced Weathering• Accurate predictions of trajectory,
fates, and effects for the specific product released
Infiltration• Potential ground water impacts
6Complex Overland Modeling
Source: 350.org
Smooth Particle Hydrodynamics (SPH)• First developed in the field of astro-physics• Has been used to solve many flow problems:
7Complex Overland Modeling
• Each particle has its own: Volume, Mass, Physical properties, etc.
• Particle Movement Independent Contribution from neighboring particles using a kernel function
Lava Dam break
Waves Oil transport
• Liquid represented by discrete particles• No mesh/grid required
Source: Jan Bender and Dan Koschier, "Divergence-Free Smoothed Particle Hydrodynamics", In Proceedings of ACM SIGGRAPH / EUROGRAPHICS Symposium on Computer Animation (SCA), 2015
8
SPH Inputs
Complex Overland Modeling
Digital Elevation Model (DEM)• Derives slope and aspect• Define flow trajectory and gravity based velocity
Landcover• Estimate adherence to land surface• Define friction for overland flow velocity
SPH Example 1: Particle Transport
Release Scenario:• 1,500 bbl released• Released over 1.5 hours• Simulation shows the first 1.5 hours after the
release
Results:• Flow path is narrow in steeper terrain• Spreading in flatter terrain or in depressions
9Complex Overland Modeling
SPH Example 1: Time-Varying Grid Output
• Particles are summarized on a grid by model timestep
• Helps to assess fate of oil: Mass evaporated Thickness Volume
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SPH Example 1: End of Simulation Grid Output
11Complex Overland Modeling
• Grid summarized at the end of the model simulation
• Mass of oil evaporated at the end of the simulation
SPH Example 2: Complex Terrain
Release Scenario:• 2,000 bbl released• Released over 2 hours• 6 hour simulation
Results:• Two main flow paths• Lateral spreading
12Complex Overland Modeling
Advanced Weathering
13Complex Overland Modeling
Each line is adifferent chemical
Each chemical hasdifferent properties
Oil is a combination of 10’s-100’s of thousands of chemical compounds (e.g.
hydrocarbons)
Each oil has adifferent composition
ASA Offices
Example Composition of a Light Crude Oil
LowMW
“Light”
HighMW
“Heavy”
Low % High %
Simplify each oil by grouping like-compounds (pseudo-component approach):
Advanced Weathering• For each “particle” of the SPH Model: Composition tracked by 4 pseudo-component groups Each group weathers independently
• Weathering also factors in: Surface area exposed to the air Wind speed Air temperature
• Additional weathering processes: Changes in density Changes in viscosity
14Complex Overland Modeling
Source: lcengineering.com
SPH Example 3: Comparing Oil Products
Release Scenario:• 2,000 bbl released• Released over 2 hours• 6 hour simulation
Results:• Lighter oil travels
further and moves faster
15Complex Overland Modeling
Heavy Crude Light Crude
InfiltrationDetermine:
• Maximum infiltration depth• Infiltration rate
Can be used to assess:• Loss of oil form the land surface• Potential impacts to ground water• Potential clean-up costs
Fast prediction• Conservative approach – does not
include horizontal migration• Short-term period after a release
16Complex Overland Modeling
Source: Shahar Ischarov/Israeli Environmental Protection Ministry
Infiltration: Maximum DepthDetermines:
• Impact to ground water
Factors:• Volume of oil on the surface• Surface area of the oil pool• Retention Capacity of the soil (𝑅𝑅) Smaller particles → smaller pore size → more liquid
retained in the pores• Viscosity (𝜉𝜉) Higher viscosity = more retention
17Complex Overland Modeling
𝑀𝑀𝑀𝑀𝑀𝑀 𝐼𝐼𝐼𝐼𝐼𝐼𝐼𝐼𝐼𝐼𝐼𝐼𝐼𝐼𝑀𝑀𝐼𝐼𝐼𝐼𝐼𝐼𝐼𝐼 𝐷𝐷𝐷𝐷𝐷𝐷𝐼𝐼𝐷 =𝑉𝑉𝐼𝐼𝐼𝐼𝑉𝑉𝑉𝑉𝐷𝐷 𝐼𝐼𝐼𝐼 𝐼𝐼𝐼𝐼𝐼𝐼 𝐼𝐼𝐼𝐼 𝑃𝑃𝐼𝐼𝐼𝐼𝐼𝐼𝐴𝐴𝐼𝐼𝐷𝐷𝑀𝑀 𝐼𝐼𝐼𝐼 𝑃𝑃𝐼𝐼𝐼𝐼𝐼𝐼 × 𝑅𝑅 × 𝜉𝜉
Source: USDA, Lindsey Benne
Infiltration: RateDetermines:
• Time to maximum depth or ground water impact
Factors:• Relative permeability (𝑘𝑘𝑟𝑟−𝑁𝑁𝑁𝑁𝑁𝑁𝑁𝑁) Based on assumed level of water saturation
• Hydraulic conductivity (𝐾𝐾)• Water viscosity (𝜈𝜈𝑤𝑤) vs. Oil viscosity (𝜈𝜈𝑜𝑜𝑜𝑜𝑜𝑜)• Soil porosity (𝜃𝜃𝑠𝑠)• Retention Capacity of the soil (𝑅𝑅)
18Complex Overland Modeling
𝑃𝑃𝐷𝐷𝐼𝐼𝐷𝐷𝐼𝐼𝐼𝐼𝑀𝑀𝐼𝐼𝐼𝐼𝐼𝐼𝐼𝐼 𝑉𝑉𝐷𝐷𝐼𝐼𝐼𝐼𝑉𝑉𝐼𝐼𝐼𝐼𝑉𝑉 =𝑘𝑘𝑟𝑟−𝑁𝑁𝑁𝑁𝑁𝑁𝑁𝑁 𝐾𝐾𝜃𝜃𝑠𝑠 − 𝑅𝑅
𝜈𝜈𝑤𝑤𝜈𝜈𝑜𝑜𝑜𝑜𝑜𝑜
Infiltration: InputsSoil Data – SSURGO
19Complex Overland Modeling
Groundwater data• Depth to water table• Porosity
• Hydraulic Conductivity• Retention• Infiltration barriers
Infiltration: Overland Plume Pooling
• Starts with outputs from an overland plume model
• Identify locations of “pools”
Depression in the land surface that traps larger volumes of oil
Summarize volume of oil in each
Combined surface area of each
20Complex Overland Modeling
Pools
Infiltration: Results
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Infiltration: Additional Considerations
• Horizontal migration
• Interaction with water table
• Long-term transport and fate in the subsurface
22Complex Overland Modeling
Jeremy Fontenaultjeremy.fontenault@rpsgroup.com
23Complex Overland Modeling
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