Advances in Grid-Based Numerical Modeling Techniques for Improving Gas Management in Coal Mines

1. Advances in Grid-Based NumericalModeling Techniques forImproving Gas Management inCoal Mines C.Ö. Karacan NIOSH, Pittsburgh Research Laboratory TX. Ren, R. Balusu CSIRO Exploration and Mining

2. Mine ventilation and methane control systems: • Provide workable environment • Reduce or eliminate explosive mixtures • Use of simulation models is helpful in designs for: • Flexibility in making design decisions • Ability to run different scenarios Introduction

3. Network models: • MineVent • VNET • MFIRE • VUMA • and others…. Ventilation Models • Advantages: • Easier to built • Do not require detailed data • Best for network-like regions • Interface with AutoCAD • Disadvantages: • Original coding outdated • Steady state • Outputs are limited • Not applicable to regions such as gobs

4. Reservoir Models • CFD Models Grid-Based Models • Disadvantages: • Difficult to built • Requires more input data • Run times are longer • More expensive • Advantages: • Volume based • Steady and Unsteady state • Computes more parameters • Combines multi-mechanistic and multiphase flow • Powerful graphics • Make “unseen” and “inaccessible” parts of reservoir “accessible”

5. Introduce capabilities of grid-based models for • gas management in coal mines • Document recent advances in reservoir modeling • and CFD for ventilation and methane control • Overview of efforts of NIOSH and CSIRO Objective

6. 3280 ft 66 ft HG TG 656 ft TG Examples: Gas Flow Mechanicsin Gobs CSIRO developed CFD models to obtain a detailed understanding of the gas flow mechanics and distribution in the caved zone of longwall gobs

7. 656 ft Examples: Gas Flow Mechanicsin Gobs Oxygen %

8. 1850 ft 1250 ft 45 ft Gob (Caved Zone) Unmined Coalbed Longwall Face Entry Pillars Coalbed Layer Examples: Gas Flow Mechanicsin Gobs NIOSH developed “Reservoir Models” to obtain a detailed understanding of the gas flow distribution in the caved zone in the presence of gob gas ventholes

9. Concentration Gob gas venthole penetrating into the caved zone Bleeder fan Return Conveyor Gob (Caved Zone) Intake Tracer injection points Examples: Gas Flow Mechanicsin Gobs • Flow and distribution of an injected tracer in the gob area

10. Gob gas venthole Headgate Tailgate A Tailgate B Examples: Gas Flow Mechanicsin Gobs • Effect of a gob gas venthole accidently drilled in the upper gob

11. 656 ft TG HG Gob gas ventholes Examples: Locating Gob GasVentholes for Optimum Gas Management CFD was used by CSIRO in combination with field monitoring to optimize gob gas drainage design parameters

12. Panel start • Gob Gas Ventholes: • 300 ft from the tailgate • 7-inch diameter casing • 200-ft slotted casing 1-1 47 ft 1-2 35 ft 1-3 30 ft 1-4 40 ft 1-1 544 ft 1-2 2720 ft 1-3 5362 ft 1-4 8060 ft Examples: Locating Gob GasVentholes for Optimum Gas Management Reservoir models were used by NIOSH in combination with field monitoring to optimize gob gas venthole design and location parameters in a wider longwall face

13. The difference is 10 cfm increase in face emission Examples: Locating Gob GasVentholes for Optimum Gas Management • How many boreholes and which locations should be used to control excess methane • originating gob as a result of widening the longwall from 1250 ft to 1450 ft.

14. Examples: Gas Control in DevelopmentMining Ventilation airflow direction Direction of development Tailgate entries Monitoring points Headgate entries Start of monitoring End of monitoring Direction of development Reservoir models was used by NIOSH to control methane emissions into the entries during development mining. Bleeder (@ 656 ft behind face • In-mine measurements for tailgate and headgate were reported as monthly averages: • Air flow rate • Methane concentration

15. Examples: Gas Control in DevelopmentMining • Mining parameters have major impacts on methane inflow. • Two different modeling approaches were implemented. (@ 656 ft behind face

16. Examples: Gas Control in DevelopmentMining (@ 656 ft behind face Degasification boreholes

17. Examples: Gas Control in DevelopmentMining (@ 656 ft behind face

18. Examples: Gas Control in DevelopmentMining 0.5% 12000 ft 0.75% 1.0% 0.5% 2000 ft 0.75% 1.0% Ventilation Requirements for Different In-Mine Concentrations – No Degasification (@ 656 ft behind face

19. Examples: Gas Control in DevelopmentMining Degasification Borehole Proximity and Development Length on Methane Inflow (@ 656 ft behind face

20. Conclusions • The efforts of NIOSH and CSIRO are presented. • Advances in grid-based modeling techniques and their capabilities for ventilation • purposes were given. • These models may be suitable for ventilation problems and as alternative to • network models. At least, they can easily be complementary to each other. • Grid-based models help visualization of “unseen” parts of the reservoirs and • offer flexibility and alternative approaches to design engineers. • Grid-based models improve the fundamental understanding of gas flow • in underground coal mines and offer effective gas management techniques.