A RETROSPECTIVE ASSESSMENT OF GROUND CONTROL RESEARCH AND

SUCCESSFUL APPLICATIONS IN THE COAL INDUSTRY

DANIEL W.H. SUCONSOL ENERGY INC.

CANONSBURG, PA

OBJECTIVES•GROUND CONTROL RESEARCH ? -GROUND CONTROL ENGINEER? -WORTH ONE’S SALT ? -WORTH THE EFFORT ?•GROUND CONTROL RESEARCH AT CONSOL ENERGY•SUCCESSFUL APPLICATIONS TO CONSOL’S MINING OPERATIONS

GROUND CONTROL RESEARCH AT CONSOL ENERGY

COAL PILLAR DESIGN SURFACE SUBSIDENCE HORIZONTAL STRESS IMPACT FLOOR BEARING CAPACITY LONGWALL FACE SUPPORT DESIGN HYDRAULIC FRACTURING OF MASSIVE

SANDSTONE SANDSTONE STABILITY UNDER DEEP COVER ROOF GEOLOGY RECONNAISSANCE INNOVATIVE ROOF SUPPORT CONCEPTS

HORIZONTAL STRESS MEASUREMENTS AND IMPACT ANALYSIS

•STRESS MEASUREMENTS USING 3D BOREHOLE DEFORMATION GAGE•STRESS MEASUREMENTS USING MINIFRAC•STRESS MEASUREMENTS USING HYDRAULIC FRACTURING •IMPACT OF HIGH HORIZONTAL STRESS ON MINING OPERATIONS•HS CONCENTRATION – CSIRO HI CELL•PILLAR DESIGN MODIFICATION•RIGHT-HAND VS. LEFT-HAND LONGWALL

RESULTS OF STRESS MEASUREMENTS•POCAHONTAS #3 SEAM -MAX HORIZONTAL STRESS: 2970 PSI(N55E) -MIN HORIZONTAL STRESS : 2090 PSI•PITTSBURGH SEAM -MAX HORIZONTAL STRESS : 4300~5000 PSI(E-W) -MIN HORIZONTAL STRESS : 3400 PSI•ILLINOIS #6 SEAM -MAX HORIZONTAL STRESS : 2000 PSI(E-W) -MIN HORIZONTAL STRESS : 800 PSI

MEASUREMENTS OF HORIZONTAL STRESS CONCENTRATION AND ROOF DEFORMATION

-600 -500 -400 -300 -200 -100 0

-4000

-3000

-2000

-1000

0

1000

2000

LONGWALL INDUCED STRESS CONCENTRATION IN THE HEADGATE ROOF (3-RIGHT,100-FOOT HEADGATE PILLAR

CENTER)

Series1

Series3

Series5

DISTANCE FROM LONGWALL FACE TO STRESS SENSOR,FT

IND

UC

ED

RO

OF

ST

RE

SS

,PS

I

East-West

North-South

Vertical

-350 -300 -250 -200 -150 -100 -50 0 50

-3000

-2000

-1000

0

1000

2000

3000

4000

LONGWALL INDUCED STRESS CONCENTRATION IN THE HEADGATE ROOF(4-RIGHT,80-FOOT HEADGATE PILLAR

CENTER)

Series1

Series3

Series5

DISTANCE FROM LONGWALL FACE TO STRESS SENSOR,FT

IND

UC

ED

RO

OF

ST

RE

SS

,PS

I

East-West

North-South

Vertical

-140 -120 -100 -80 -60 -40 -20 0 20

-10000

-8000

-6000

-4000

-2000

0

2000

4000

6000

LONGWALL INDUCED STRESS CONCENTRATION IN THE HEADGATE ROOF(4-RIGHT,60-FOOT HEADGATE PILLAR CENTER)

Series1

Series3

Series5

DISTANCE FROM LONGWALL FACE TO STRESS SENSOR,FT

IND

UC

ED

RO

OF

ST

RE

SS

,PS

I

East-West

North-South

Vertical

ROOF GEOLOGY AND HORIZONTAL STRESS MAGNITUDE AND ORIENTATION

SUMMARY

•DETERMINE STRESS ORIENTATION AND MAGNITUDE•FORECAST ROOF CUTTER DEVELOPMENT•DEFINE RIGHT-HAND AND LEFT-HAND LONGWALL PANELS•PILLAR DESIGN MODIFICATION TO MITIGATE HORIZONTAL STRESS IMPACT•USE OF CABLE BOLTS AND INNOVATIVE STANDING SUPPORT TO MITIGATE HORIZONTAL STRESS IMPACT

HYDRAULIC FRACTURING

•TO PROMOTE CAVING OF THICK, MASSIVE SANDSTONE•TO IMPROVE FACE CONDITIONS•INDUCED HORIZONTAL FRACTURES•FACE MONITORING AND NUMERICAL MODELING CONFIRMED THE EFFECTIVENESS

Uniaxial Compressive Strength 10,000 psi

Indirect Tensile Strength 1,000 psi

Young's Modulus 2,000,000 psiPoisson's Ratio 0.25Internal Friction Angle 38 degrees

In-Situ Horizontal StressesMaximum Horizontal Stress

MagnitudeOrientation

5,200 psiEast-West

Minimum Horizontal StressMagnitude 3,500 psi

Depth of Cover 800' – 900'Vertical Stress

Magnitude 1,000 psi

Estimated Mechanical Properties of Pittsburgh Sandstone

BENDING STRESS,PSI

-9030

0

SANDSTONE

SHALE

BENDING STRESS DISTRIBUTION AT THE FACE WITHOUT FRACING

+420COAL

BENDING STRESS,PSI-9030

0

+420

SANDSTONE

SHALE

COAL

BENDING STRESS CONTOURS AT THE FACE WITH ONE FRAC

LongwallPanel

Total Time Lost Due to Bad Top

at the Face (Minutes)

Average Distance

of Longwall Advance/MS

(Feet)

B12 30,600 9.8

B13 3,655 16.6

B14 3,265 17.1

Comparison of Production Downtime and Average Face Advance for the B12, B13, and B14 Faces within the Sandstone Channel Interval

ROOF GEOLOGY RECONNAISSANCE

•INITIATED IN THE EARLY 90’S•CONDUCT ROOF SCOPING USING FIBERSCOPE, GAMMA LOGGER AND BOREHOLE CAMERA•GUIDE MINE PLANNING DECISION•GUIDE DAILY ROOF SUPPORT PRACTICES•IMPROVE ROOF STABILITY•MINIMIZE LONGWALL MOVE DELAYS•REDUCE ROOF FALL FREQUENCY UP TO 80%

CONCLUSIONS•SAFETY•COMPLIANCE•CONTINUOUS IMPROVEMENT•PRODUCTIVITY•COST•WORTH ONE’S SALT•WELL WORTH THE EFFORT

THANK YOUQUESTIONS ?