RESERVOIR MODELING-BASED PREDICTION AND OPTIMIZATION OF VENTILATION REQUIREMENTS DURING 

DEVELOPMENT MINING IN UNDERGROUND COAL MINES 

C. Ö. Karacan, NIOSH, Pittsburgh, PA 

S. J. Schatzel, NIOSH, Pittsburgh, PA 

Abstract 

During development mining, ventilation capacity may decrease 

and the ventilation requirements may depart from initially planned 

values depending on the mining rate, increases in the methane 

emission rate, and changes in ventilation airway leakages. Insufficient 

ventilation air quantities and the occurrences of high methane liberation 

rates can overwhelm the existing quantity of ventilation air and result in 

elevated levels of methane gas during development mining. This 

condition can both limit the development of that section and increase 

the risk for an ignition that may lead to an explosion. Thus, the 

prediction of ventilation air requirements prior to mining can enhance 

worker safety by reducing the likelihood that explosive methane-air 

mixtures form. 

This study presents an approach for prediction of methane inflow 

rates using coalbed methane reservoir modeling. For this purpose, a 

two-phase coalbed reservoir model of a three-entry type roadway is 

developed. In the model, grids are dynamically controlled to simulate 

development of entries. Examples are given for methane inflow and 

ventilation air requirements as a function of mining rate, development 

section length, mining height, and the existence of degasification 

boreholes. This technology can be used to limit the methane 

concentrations occurring as a result of the influences of various 

coalbed and operational parameters. 

Introduction 

Ventilation planning is one of the most important elements for coal 

mining because of its impacts on productivity and safety. It is important 

to improve predictive and optimization methods to provide adequate 

ventilation airflow based on the coalbed and mining parameters. Entry 

length and the number of crosscuts (leakage) increase as development 

mining progresses, requiring additional airflow to adequately ventilate 

the working areas. In order to improve the safety of underground coal 

mines, it is important to have the predictive capabilities to estimate 

methane emission rates based on coalbed and mining parameters at a 

particular stage in mining and to be able to optimize the mine 

ventilation requirements. Furthermore, as development lengths 

increase, it may become increasingly difficult to keep methane levels 

under statutory limits by ventilation alone. One of the most effective 

approaches in this situation is to drill horizontal boreholes in the 

coalbed to drain excessive methane from the coalbed before mining 

starts and to shield entries from migrating methane. Horizontal drilling 

and its application to degasify coal seams are well-documented in the 

literature [1-4]. 

Over the years reservoir-modeling methods and simulators have 

been developed that can realistically represent the complex physics of 

reservoir flow mechanisms in coalbeds and gas production operations 

using diverse well designs [5]. These simulators have been 

successfully applied in various coal basins for coalbed gas recovery 

using both vertical and horizontal boreholes [6-8]. These models offer 

advanced predictive capabilities to simulate the development mining 

process and the prediction of methane inflow rates [9] as well as the 

subsequent determination of airflow requirements based on coalbed 

and mining parameters. However, as the number of independent 

variables increases, model solution and analysis become increasingly 

difficult. 

This paper applies coalbed reservoir simulation for improved 

prediction of methane inflow rates and optimization of ventilation 

requirements during development mining. The reservoir models were 

based on a typical three-entry Pittsburgh Coalbed mine operating in the 

Southwestern Pennsylvania section of the Northern Appalachian Basin. 

These models were developed using Computer Modeling Group’s [10] 

compositional reservoir simulator (GEM). The work evaluated the 

presence and lack of coal seam degasification and shielding against 

methane. The models were run “dynamically” to simulate advance of 

entry development using a “restart” approach [11-13]. The reservoir 

model predictions were compared with the in-mine monitoring data of 

air quality and flow rate obtained during tailgate and headgate entry 

development around a longwall panel. Various mining and 

degasification-related parameters were considered for parametric runs 

using this reservoir simulator. 

Reservoir Modeling of Development Mining 

The base model for development mining was a coalbed methane 

reservoir model created in cartesian coordinates. It simulated both 

entry development and fluid flows in the unmined sections of the 

coalbed and in the entries. A three-entry tailgate and headgate 

development, typical of coal mines operating in the Southwestern 

Pennsylvania section of the Northern Appalachian Basin, was 

analyzed. Figure 1 shows the layout of such a mine. 

Monitoring points 

Tailgate entries 

Headgate entries 

Direction of development 

Start of monitoring End of monitoring W E 

N 

S 

Ventilation 

airflow 

direction 

Direction of development 

Bleeder 

Figure 1. The modeled longwall panel showing entry sections where 

mining and ventilation data was gathered during development mining 

The parameters and their average values in Table 1 were used. 

The pre-mining reservoir data for the particular mine site were gathered 

from previous NIOSH publications [14], external reports, personal 

communications with the operating mining company, and previous 

history matching studies [11-12]. 

Various factors impact ventilation requirements during 

development mining. Among these factors, coalbed parameters and 

mining parameters are probably the most important. Since ventilation 

requirements depend upon the quantity and rate of methane liberation 

into the entries, coalbed reservoir parameters such as pressure, 

methane content, adsorption parameters, and permeability have a 

direct impact on the methane emissions and thus on the ventilation 

design considerations. In this study, the average properties shown in 

Table 1 were used in the models. Thus, the variables originating from 

coalbed reservoir properties were mostly eliminated from parametric 

runs and subsequent analyses. The main areas of emphasis were 

mining parameters, the methane concentration level to be maintained, 
 

and the presence or absence of a degasification/shielding program to 

reduce methane inflow into the developed entries. 

Table 1. Values of some of the reservoir parameters of the coalbed 

used in the models. 

Parameter Value

Permeability-Face Cleat (milli-darcies) 4 

Permeability-Butt Cleat (milli-darcies) 1 

Effective Porosity (%) 4 

Effective Fracture (Cleat) Spacing (ft)/(m) 0.1/0.03 

Langmuir P. (psi) / (MPa) 326/2.2 

Langmuir Vol. (scf/ton) / (cc/g) 498/15.5 

Desorption Time (days) 20 

Initial Water Saturation (%) 60

Coal Density (lb/ft3) / (g/cc) 84.7/1.4 

Pressure (psi) / (MPa) 90/0.61 

For modeling advance of tailgate and headgate entries, a threeentry development model around a longwall panel was studied. Figure 

2 shows snapshots of mining advance, pillar layout, and ventilation 

scheme. The middle entry was modeled as the “track” or haulage 

entry, where intake air entered. In this entry, ventilation air injection 

and mine pressure assignments to the grids were performed using an 

injector well. The entry to the left of “track” was designated as the “belt” 

entry, where flow direction was out from the mine. The third entry was 

designated as the “return” entry carrying away majority (>90%) of the 

methane emissions and the methane-loaded ventilation air. 

During development mining, the entries and the cross cuts to be 

ventilated are continuously extended. The amount and rate of 

methane emission into the developed entries depend upon the extent 

of the continually created surfaces. As the continuous miner advances, 

new volumes are created that must be ventilated while new surfaces 

are created that liberate gas into that volume. In this study, the 

development of a three-entry continuous mining model, shown in 

Figure 2, was handled using “restart” model runs. These models were 

run sequentially with each characterizing an entry advance with a 

specified development rate where the assigned properties of the 

entries replaced the coalbed properties and ventilation-related features 

were built. All three entries were developed simultaneously to a 

specific distance in a predefined amount of time, allowing calculation of 

the rate of mining advance. For different mining rates, the times in the 

recurrent data set were changed. Thus, the rates reported in this study 

are not linear mining rates, but instead represent the rates of the mine 

section advance. Based on this approach, a 150 ft (45.7 m) section 

advance corresponds to 570 ft (173.7 m) of linear mining distance 

shown in Figure 1, including entries and cross cuts. 

As the entries were developed at the designated rates, the pillars 

and cross cuts were also developed at the same time. The pillars 

between the entries were 125 ft (38.1 m) in length and 75 ft (22.9 m) in 

width, and had the same properties as the coalbed. However, during 

the development of entries, the permeability was replaced with a high 

permeability in all three directions. Also, the coal-matrix pressures in 

the mined grids were assigned to atmospheric pressures to simulate 

the mining process. The development of cross cuts was modeled in 

the same way as the entries. However, during each simulation run 

only the last set of cross cuts was left fully open for ventilation airflow. 

During development of cross cuts, stoppings or block walls (between 

track-belt and track-return) were automatically created between the 

restart runs to force ventilation flow through the last open cross cuts at 

each section advance. A “curtain” resistance in the last section of the 

“track” diverted some of the intake air towards the “belt” entry to 

ventilate both belt and face. Figure 2 shows the progress of mining as 

well as the entries, cross cuts, pillars, ventilation airflow paths, and the 

locations of the curtains dynamically created during simulations. A 

permeability of 100 millidarcies was assigned to the stoppings to 

represent leakage, a common occurrence in underground mining. 

Time 

T1

T4

Advance of entry 

development 

Monitoring points 

Belt 

Intake 

Return 

Stopping Ventilation curtain Pillar 

T1 T2 T3 T4

Boreholes 

Pressure 

(psi) 

(Track) 

Figure 2. Snapshots of mining advance, pillar layout, and the 

ventilation scheme in the coalbed reservoir model. Locations where 

total methane inflow is monitored are also shown. The figures show 

the progress of mining in the coalbed at the end of first and fourth 

section advances. 

In this study, two different modeling approaches were undertaken 

to predict methane inflows and to estimate ventilation requirements 

during development mining. In the first approach, the methane inflows 

and the ventilation air requirements were determined based on the 

absence of any degasification wellbores around the entries to shield 

them from migrating methane. The variables of this model were mining 

rate, mining height (coalbed thickness), methane percentage in the 

ventilation air, and length of developed entries. In the second modeling 

approach, the presence of horizontal wellbores along the entries, as 

shown in Figure 2, was considered for their effects on degasification 

and shielding against methane inflow. The wellbores were 3 inches 

(7.6 cm) in diameter, with no wellbore skin, and operated with -0.2 psia 

(-1260 Pa) bottom-hole pressure to extract the methane. The lengths 

of the boreholes were equal to the lengths of the entries. 

Table 2. The parameters and their range of values changed in 

simulation runs. 

Parameter Range

Mining height (ft) / (m) 5-7 / 1.52-2.13 

Entry length (ft) / (m) 1000-12000 / 

305-3660 

Mining rate (ft/day) / (m/day) 25-175 / 7.6-53.3 

Methane concentration in mine air (%) 0.5-1.5 

Distance of shielding wells to entries (ft) /(m) 19-87 / 5.8-26.5 

Degas. duration before mining (days) 0-180 
During simulations, the proximity of the horizontal wellbores to the 

entries was changed between 19-87 ft (5.8-26.5 m) and the pre-mining 

degasification period was varied between 0-6 months. In all cases, the 

wellbores were operated during mining regardless of the duration of the 

pre-mining degasification period. The parameters and their ranges 

used in reservoir models are summarized in Table 2. 

Model Validation by Comparing Reservoir Model Prediction with 

In-Mine Monitoring Data 

The predictive performance of the reservoir model was compared 

with in-mine measurements of methane inflow, reported as monthly 

averages, during development of the tailgate and headgate entries. 

The reservoir models utilized mining parameters that were close in 

value to those obtained from recent field studies, i.e., 7 ft (2.1 m) 

mining height, 70 ft-110 ft (21.3 m-30.5 m) per day advance rate, and 

2000-12000 ft (610-3660 m) development length. Airflow rates were 

calculated to produce a constant 0.5% methane concentration based 

on methane inflow measurements. 

Figure 3 shows the simulator predictions and measured methane 

inflows into the headgate and tailgate entries. The solid markers and 

the trendlines show the simulator predictions for methane emissions at 

the two different mining rates as a function of entry length. Since the 

simulations use constant mining and coalbed parameters, the methane 

inflow results show a continuous increase with the length of mined 

entries, as opposed to the scattered increase in measured data. 

Nevertheless, the developed model closely predicts the range of 

measured data. 

0

100000

200000

300000

400000

500000

600000

700000

800000

900000

1000000

0 2000 4000 6000 8000 10000 12000 14000

Entry Length (ft)

Methane Inflow (scf/day)

Tailgate Entries - Measured

Headgate Entries - Measured

70 ft/day - 7 ft coal - Model

110 ft/day - 7 ft coal - Model

Average - Measured (Tailgate)

Average - Measured (Headgate)

Figure 3. Comparison of methane in-flows based on measurements of 

airflow rate and air quality and the simulator predictions at two different 

mining rates. 

The predicted airflow rates needed to maintain a constant 0.5% 

methane level in the ventilation air and the measured airflows that 

resulted in an average methane concentration of 0.5% are shown in 

Figure 4. This figure shows that, because of methane inflow increases, 

simulator predictions of airflows increase with entry length to keep the 

methane levels at 0.5%. Although the average predicted airflow is 

close to the average of the measured values, the measured values at 

the start and end of the mining are higher and lower than the predicted 

values, respectively. The model calculates the required amount of air 

based on simulated methane inflow. During gateroad development, 

the ventilation air rate was kept in a narrow range regardless of the 

length of the developed section or the mining rate. In fact, methane 

levels increased from 0.20% at the beginning of development to 0.85% 

at the end of development, indicating an abundance of ventilation air at 

the beginning and a lack of airflow at the end. This comparison 

suggests that adjusting airflow quantity based upon mining progress 

using a predictive method may be safer and more economical than 

supplying a fixed volume of air based on projected maximum demand. 

0

20000

40000

60000

80000

100000

120000

140000

0 2000 4000 6000 8000 10000 12000 14000

Entry Length (ft)

Air Flow Rate (cfm)

Tailgate Entries - Measured

Headgate Entries - Measured

70 ft/day - 7 ft coal - Model (0.5%)

110 ft/day - 7 ft coal - Model (0.5%)

Average - Measured (Tailgate)

Average - Measured (Headgate)

Figure 4. Comparison of airflow rate measured in the mine and the 

simulator calculations based on two different mining rates to maintain a 

constant methane level of 0.5%. 

Parametric Analysis of Reservoir Modeling Results 

The reservoir model generated parametric simulations to cover a 

range of values for the mining-related parameters shown in Table 2. 

Some of those results are presented in this section to show the 

relationships and the effects of different parameters on methane inflow 

into the entries. Once the methane inflow rate is known, the airflow 

requirements can be calculated to keep methane concentrations at a 

required level. 

Figure 5 shows the predicted methane inflow rates at 2000, 8000, 

and 12000 ft (610 m, 2440 m, and 3660 m) of roadway development in 

the 7-ft-high coalbed with different development rates. Results show 

that the methane inflow rate increases with the length of the 

development section because of the increase in surface area of the 

exposed coalbed. This increase is a strong function of the mining rate. 

However, the effect of the mining rate on methane inflow is less 

pronounced for shorter development distances than longer distances. 

For 2000 ft of roadway development, increasing the mining rate from 

25 ft/day (7.6 m/day) to 175 ft/day (53 m/day) increases the methane 

inflow rate from 109100 scf/day (3090 m3/day) to 214000 scf/day 

(6060 m3/day), which is approximately a two-fold increase. With an 

8000-ft entry development, increasing the mining rate from 25 ft/day to 

175 ft/day increases the methane inflow from 244300 scf/day (6920 

m3/day) to 700500 scf/day (19850 m3/day), a nearly three-fold 

increase. Similarly, increasing the mining rate from 25 ft/day to 175 

ft/day in developing 12000 ft of entries increases methane inflow rate 

from 309000 scf/day (8760 m3/day) to 991150 scf/day (28080 m3/day), 

over a three-fold increase. 

The methane inflow simulations performed for development 

mining can be used for evaluating and designing ventilation 

requirements. Figure 6 shows the calculated airflow requirements as a 

function of the mining rate to keep methane concentrations at 

predetermined concentrations during development of 2000- and 12000-

ft (610-m and 3660-m) entry sections. For these calculations, the 

methane inflow rates shown in Figure 5 were used. With shorter 

development distances, only minimal adjustments to ventilation airflow 

are needed to keep methane levels below 1%. Such adjustments 

appear to be independent of the mining rate. With longer development 

distances, more ventilation airflow is needed to keep methane levels 

constant, and the amount is more strongly affected by the mining rate. 

If the ventilation rate cannot control methane levels, decreasing the 

mining rate can be considered as a desired control. 
 

0

200000

400000

600000

800000

1000000

1200000

0 50 100 150 200

Entry Development Rate (ft/day)

Methane Inflow (scf/day)

2000 ft Entry

8000 ft Entry

12000 ft Entry

Figure 5. The change of methane inflow rates predicted by the 

reservoir simulation as a function of the mining rate for different entry 

lengths. 

0

20000

40000

60000

80000

100000

120000

140000

160000

0 50 100 150 200

Entry Development Rate (ft/day)

Air Flow Rate (cfm)

2000 ft Entry-0.5% CH4

2000 ft Entry- 0.75% CH4

2000 ft Entry-1.0% CH4

12000 ft Entry-0.5% CH4

12000 ft Entry-0.75% CH4

12000 ft Entry-1.0% CH4

Figure 6. Calculated airflow rates required to maintain various

methane concentrations for different mining rates and entry lengths. 

Methane inflow during mining is also affected by the mining height 

of the developed entries. Figure 7 shows the simulated methane inflow 

rates for development lengths of 2000 and 12000 ft with advance rates 

of 25, 70, and 175 ft/day. This figure shows that the methane inflow 

rate is almost a linear function of the coalbed height for a given 

development length and mining rate. However, the effect of increasing 

coalbed height on methane inflow rate is less pronounced with shorter 

development distances than with longer distances, especially with high 

mining rates. Figure 7 suggests that if there are regional increases in 

the coalbed thickness in long development sections, decreasing mining 

rate may be a viable approach to avoid overloading the ventilation 

system with increased methane emissions. 

Using in-seam horizontal boreholes is an effective approach to 

shielding entries against methane inflow during development mining. 

To simulate the shielding effects of degasification wells and assess 

their impacts on the subsequent ventilation air requirements, 3-inch 

diameter (7.6-cm) horizontal boreholes with no wellbore skin were 

modeled and operated with -0.2 psi (-1360 Pa) bottom-hole pressure 

for pre-mining degasification periods of 0 months (i.e., no pre-mining 

degasification), 3 months, and 6 months. The boreholes were placed 

19-87 ft (5.8-26.5 m) away from the entries. In all cases, the wellbores 

were operated during mining regardless of the duration of pre-mining 

degasification. 

Figure 8 shows the variability of methane inflow rate with 

development length for horizontal boreholes located 19 ft (5.8 m) away 

from the intake and return entries and operated for various pre-mining 

durations. The data represent a 70 ft/day (21.4 m/day) development 

rate in a 7-ft (2.1-m) thick coalbed. Simulations show that the methane 

emissions are highest when shielding is not used against methane 

inflow before or during mining. Emission rates progressively decrease 

as a result of shielding and degasification duration. For instance, if the 

boreholes begin to operate when mining starts, the inflow rate 

decreases about 25% compared to the completely unshielded case. 

The methane inflow rates after longer pre-mining degasification times 

are less. 

0

200000

400000

600000

800000

1000000

1200000

4 4.5 5 5.5 6 6.5 7 7.5

Mining (Coalbed) Height (ft)

Methane Inflow (scf/day)

2000 ft Entry - 25ft/day

2000 ft Entry - 70 ft/day

2000 ft Entry - 175 ft/day

12000 ft Entry - 25 ft/day

12000 ft Entry - 70 ft/day

12000 ft Entry - 175 ft/day

Figure 7. The predicted methane inflow rates into the entries for 

different seam heights during mining of different entry lengths with 

various mining rates. 

0

100000

200000

300000

400000

500000

600000

700000

0 2000 4000 6000 8000 10000 12000 14000

Entry Length (ft)

Methane Inflow (scf/day)

No Degas.

0 mo. Pre-degas.

3 mo. Pre-degas.

6 mo. Pre-degas.

Figure 8. Methane inflow rate predictions for different development 

lengths and various pre-mining degasification durations. “No degas.” in 

the legend corresponds to a lack of degasification boreholes. 

Figure 9 shows the effects of mining rate and pre-mining 

degasification duration when developing entries with lengths of 2000 

and 12000 ft (610 m and 3660 m). The presence of methane shielding 

and the duration of pre-mining degasification are more important when 

development distances are long and mining rates are high. 

Figure 10 shows the effects of shielding well proximity and 

development length on methane inflow rates. The simulated data 

shown are for a 70-ft/day (21.4-m/day) development rate in a 7-ft (2.1-

m) thick coalbed after 6 months of pre-mining degasification. The nodegasification case does not include any shielding. This figure shows 

that those wellbores closest to the entries are most effective in 

reducing methane inflow rates during development mining about 50% 

at 12000 ft (3660 m) compared to no-shielding. Thus, positioning wells 

as close to the entries as practically possible is better for shielding 

purposes. However, local geology often dictates that shielding wells be 

positioned at least one hundred feet from the entries to avoid drawing 

excess gas toward these gateroads. 
 

0

200000

400000

600000

800000

1000000

1200000

-3 0 3 6

Pre-Mining Degasification Duration (month)

Methane Inflow (scf/day)

2000 ft Entry - 25ft/day

2000 ft Entry - 70 ft/day

2000 ft Entry - 175 ft/day

12000 ft Entry - 25 ft/day

12000 ft Entry - 70 ft/day

12000 ft Entry - 175 ft/day

No Degasification

Figure 9. Effect of degasification duration on methane inflow rate for 

various development lengths and rates. 

0

100000

200000

300000

400000

500000

600000

700000

0 2000 4000 6000 8000 10000 12000 14000

Entry Length (ft)

Methane Inflow (scf/day)

No Degas.

19 ft from Entry

62 ft from Entry

87 ft from Entry

Figure 10. Effect of proximity of shielding wells to the entries and the 

length of entries on methane inflow rate. 

Summary and Conclusions 

This study presented the development and application of 

“dynamic” reservoir models to predict and optimize ventilation airflow 

requirements to control methane inflows during gateroad development. 

The reservoir models were developed for a typical three-entry system 

and considered the presence or absence of shielding boreholes to limit 

methane inflow. Model simulations were performed by changing 

various mining and degasification parameters to predict methane 

inflows and airflow requirements. The reservoir model predictions were 

compared with the in-mine measurements available from the mining of 

tailgate and headgate entries around a longwall panel. 

This study made the following conclusions: 

1. Reservoir simulation can be used effectively for modeling 

development mining in underground coal mines. It can predict 

methane inflows into the entries based on various coalbed and 

operating parameters, from which the ventilation airflow requirements 

can be predicted to maintain a desired methane level. 

2. Methane inflow rate increases with entry length due to increases 

in the surface area of the coalbed exposed to the mine environment. 

However, the effect of the mining rate is less pronounced on methane 

inflow for shorter development distances compared to longer 

development distances. 

3. For shorter development distances, marginal adjustments in 

ventilation airflow may be adequate to keep methane levels under 1%. 

The model showed that this adjustment was generally independent of 

the mining rate. However, longer developments require significantly 

more ventilation air capacity to keep methane levels constant. This 

amount is a function of the mining rate. 

4. Methane inflow rate is a linear function of the coalbed height for a 

given development length and mining rate. However, the effect of 

increasing coalbed height on methane inflow rate is less when mining 

short, compared to long, entry developments, especially with high 

mining rates. 

5. Employing shielding boreholes to protect entries from methane 

migration during mining is an effective approach. Even if the boreholes 

cannot be operated for a long time prior to the start of mining, their 

presence during mining can reduce methane inflow rates (about 25%), 

especially during mining of longer sections. 

6. Positioning of the boreholes relative to the gateroad entries is 

important. These results show that positioning wellbores as close to 

the entries as practically possible is more effective, especially when 

mining long developments at higher mining rates. Although this is true 

in theory, practical considerations often limit the proximity of these 

boreholes to the entries to avoid drawing gas toward the gateroad 

developments. 

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