Three-Dimensional Simulations of Methane Injection

Transcription

1 Three-Dimensional Simulations of Methane Injection Preliminary Modeling Study Using MIN3P-Dusty 6 th Annual International Conference on Soil, Water, Energy, and Air March 1-4, 016 San Diego, California Parisa Jourabchi Ian Hers (Golder Associates Ltd.)

2 Background & Objectives Collaboration Dr. Nicholas de Sieyes & Dr. Douglas Mackay and team at UC Davis Controlled Release Experiments Densely monitored site-specific data input parameters Biodegradation and transport processes of methane in soil gas Process-Based Modeling: Data interpretation methane & carbon dioxide Efflux at ground surface Concentrations in soil gas Calibration and application to different scenarios Methane Distribution from Release of Ethanol-Blended Gasoline March 8, 016

3 Outline Site Description Key Factors & Focus of the Preliminary Modeling Effort Reactive Transport Model Description MIN3P-Dusty Model Simulations Scenarios - Dry & Wet season trials Model validation & comparison to measurements Summary & Next Steps March 8, 016 3

4 Site Description UC Davis controlled release field site Instrumentation for monitoring: Soil gas concentrations Gas effluxes to atmosphere Temperature Pressure Moisture content Soil microorganisms March 8, 016 4

5 Key Factors 1. Background CO efflux due to aerobic biodegradation of natural organic carbon of the soil;. Soil moisture content; 3. Methane oxidation kinetics; & 4. Soil temperature. Focus of the Preliminary Modeling Effort: Background CO efflux Dry soil conditions - October 014 Wet soil conditions - January 015 Methane oxidation: limited evaluation Assumption of constant soil temperature at 0 C March 8, 016 5

6 Reactive Transport Model MIN3P-Dusty Finite-volume, multi-component, reaction & transport Variably saturated porous media MIN3P 1 developed by Dr. Ulrich Mayer (UBC) + multi-species gas diffusion and gas advection = MIN3P-Dusty by Dr. Sergi Molins 1 Mayer, K. U., Frind, E. O. & Blowes, D. W. 00. Multicomponent reactive transport modeling in variably saturated porous media using a generalized formulation for kinetically controlled reactions. Water Resources Research, 38. Molins, S., and K.U. Mayer Coupling between Geochemical Reactions and Multicomponent Gas and Solute Transport in Unsaturated Media: A Reactive Transport Modeling Study. Water Resources Research, 43. March 8, 016 6

7 Soil Properties Dry & Wet Scenarios Porosity data ( ) particle density measurements bulk density measurements Water-filled porosity data Volumetric water content measurements Dry scenario: October 7 th, 014 ( ) Wet scenario: January 8 th, 015 ( ) Measurement data for 1 soil layers - maximum depth = 150 cm Relative permeability range x m Porosity and water-filled data Average hydraulic parameters for loam soil type March 8, 016 7

8 Soil Fraction of Organic Carbon Measurement Depth (cm) Organic Matter* (%) Organic Carbon** (%) Model Input Depth Range (cm) *Organic matter (OM) determined by loss on ignition method **Organic carbon calculated from OM assuming that OM contains 58% carbon March 8, 016 8

9 Background CO Efflux and Calibration of Background Respiration Rate Background respiration rate, assumed proportional to fraction organic carbon, : where, is the rate constant (mol/l (aq) /s) Assuming a 1:1 molar ratio for oxygen consumption and CO production Initial 1D simulations to estimate rate constant for natural soil respiration March 8, 016 9

10 Parameter Estimation, Chemical Components: natural organic carbon, CO, O, N, Ar Kinetic reaction: aerobic degradation of organic carbon One-dimensional simulation of a 3 m depth profile Scenario Simulation Time* (days) Degradation Rate Constant (mol/l/s) Predicted CO Efflux (µmol/m /s) Measured CO Efflux (µmol/m /s) Dry 70 3.E Wet E * Time to reach steady state conditions. March 8,

11 Degradation Rate Constant Literature Comparison Scenario Based on DeVaull (007)* for Moist Soils (mol/l/s) Predicted Based on CO Efflux Calibration (mol/l/s) Dry 1.0E-5 3.E-7 Wet 4.7E-6 3.4E-7 Λ, 1.69 *Assuming: average soil bulk density = 1.4 g/cm 3 average dry scenario water-filled porosity = average wet scenario water-filled porosity = 0.18 Key Point: Predicted rates 1 - orders of magnitude lower than literature values for moist soils. March 8,

12 Model Domain East-west bisect of the southern half -50 more frequently sampled arm Injection 1.0 m depth Gas Sampler Cluster Depths: 50 cm 100 cm 150 cm In addition, at the center: 3 cm 177 cm Y (cm) Collars Collars w/ Samplers X (cm) March 8, 016 1

13 Boundary Conditions 3D Model Setup Top boundary gas concentrations Component Dry Scenario Wet Scenario N (%) O (%) Ar (%) CO (ppm) CH 4 (ppm).1.4 CH 4 injection point free exit (ground surface) no flow 3.9 m 3 m no flow All boundaries are zero gradient or no flow except at ground surface. March 8,

14 Methane Source & Oxidation Rate Scenario Dry Wet Target (monitoring) Days October 4, 014 January 13 15, 015 Injection Rate (ml/day) Injection Makeup Modeled Injection Rate (ml/day) % CH % CH Dual Monod formulation _ _ Key Note: Methane oxidation in the aqueous phase proportional to moisture content. March 8,

15 Dry Scenario Methane Efflux at Ground Surface plan view plan view March 8,

16 Wet Scenario Methane Efflux at Ground Surface plan view plan view March 8,

17 Methane Efflux at Ground Surface Dry Scenario Wet Scenario Comparison of Results CH 4 Efflux (µmol/m /s) Comparison of Results CH 4 Efflux (µmol/m /s) Measured efflux -1.0E E-01 average = 1.8E-0 Measured efflux -5.1E E-0 average = 1.8E-03 3D model output with methane oxidation -7E-04 4E-0 3D model output with methane oxidation -9E-04 8E-04 3D model output without methane oxidation 3E-03 8E-0 3D model output without methane oxidation 4E-03 1E-01 Key Point: Methane oxidation overestimated methane efflux at ground surface underestimated. March 8,

18 Methane Injected, Transported, and Biodegraded Dry Scenario Key Point: Most of the injected methane biodegraded. Wet Scenario Key Point: complete biodegradation of injected methane -> influx of atmospheric CH 4 March 8,

19 Carbon Dioxide Efflux Dry Scenario Wet Scenario Comparison of Results CO Efflux (µmol/m /s) Comparison of Results CO Efflux (µmol/m /s) Measured efflux average = 0.43 Measured efflux average = 1.3 3D model output with methane oxidation D model output with methane oxidation D model output without methane oxidation 0.5 3D model output without methane oxidation 1.6 Background measured 0.53 Background measured 1.7 Background simulated (1D) 0.53 Background simulated (1D) 1.6 Key Points: CO efflux dominated by background Spatial variability in the measured CO efflux March 8,

20 Methane Gas Concentrations Dry Scenario (with methane oxidation) (4,16) CH 4 (%) Depth (m) Measured Model (0,0) Depth (m) CH 4 (%) Measured Model injection point (1,48) CH 4 (%) Depth (m) Measured Model 0.5 <1.6E-04 1E-4 1 <1.6E-04 6E <1.6E-04 4E-5 Key Point: Methane concentrations generally underestimated except at the injection point. (8,3) CH 4 (%) Dept h (m) Measured Model E-4 1 <1.6E-04 E <1.6E-04 E-4 March 8, 016 0

21 Methane Gas Concentrations Wet Scenario (with methane oxidation) (4,16) CH 4 (%) Depth (m) Measured Model E E E-4 (0,0) Depth (m) CH 4 (%) Measured Model injection point (1,48) CH 4 (%) Depth (m) Measured Model 0.5 <1.6E-04 4E-5 1 <1.6E-04 4E <1.7E-04 E-6 Key Point: Methane concentrations generally underestimated except at the injection point. (8,3) CH 4 (%) Dept h (m) Measured Model 0.5 <1.6E-04 4E-5 1 <1.6E-04 5E <1.6E-04 4E-6 March 8, 016 1

22 Methane Gas Concentrations Dry Scenario (without methane oxidation) (4,16) CH 4 (%) Depth (m) Measured Model (0,0) Depth (m) CH 4 (%) Measured Model injection point (1,48) CH 4 (%) Depth (m) Measured Model 0.5 <1.6E <1.6E <1.6E Key Point: Methane concentrations generally overestimated except near the injection point. (8,3) CH 4 (%) Dept h (m) Measured Model <1.6E <1.6E March 8, 016

23 Methane Gas Concentrations Wet Scenario (without methane oxidation) (4,16) CH 4 (%) Depth (m) Measured Model (0,0) Depth (m) CH 4 (%) Measured Model injection point (1,48) CH 4 (%) Depth (m) Measured Model 0.5 <1.6E <1.6E <1.7E Key Point: Methane concentrations generally overestimated except near the injection point. (8,3) CH 4 (%) Dept h (m) Measured Model 0.5 <1.6E <1.6E <1.6E March 8, 016 3

24 z(m) z(m) z(m) Predicted CO, O, N Distribution for Dry Scenario with methane oxidation without methane oxidation CO (%) - 0 O x(m) (%) N x(m) (%) x(m) z(m) z(m) z(m) CO (%) - 0 O x(m) (%) N x(m) (%) x(m) March 8, 016 4

25 z(m) z(m) z(m) Predicted CO, O, N Distribution for Wet Scenario with methane oxidation without methane oxidation CO (%) - 0 O x(m) (%) Nx(m) (%) x(m) z(m) z(m) z(m) CO (%) - 0 O x(m) (%) Nx(m) (%) x(m) March 8, 016 5

26 Overview of Model Results Model calibrated to account for aerobic respiration of soil organic carbon content background CO efflux Preliminary model setup based on measurements of soil properties in general consistent with field measurements of soil gas concentrations Simulated methane efflux and gas concentrations relatively small Methane oxidation rates overestimated; methane efflux underestimated Simulated and measured increase in CO efflux relatively small Soil gas advection not significant process Permeability Pressure increase March 8, 016 6

27 Next Steps Improved model calibration Transport processes: tracer gas (e.g., 1,1-difluoroethane) Methane oxidation kinetics: additional simulations; results of soil microcosm experiments; additional literature search Prediction of soil gas concentrations for what-if scenarios Application to ethanol or ethanol-blended gasoline release experiments Predicting methane generation and distribution from ethanol blended gasoline releases March 8, 016 7

28 Questions? Thank You 8