Impact of a Massive Sandstone Channel on a 1500-Foot (457-Meter) Wide Longwall

Face – Mitigation and EvaluationDaniel W.H. Su, Sr. geomechanical engineer

Greg J. Hasenfus, Sr. geomechanical engineerLuke Stull, geologist

Jun Lu, geomechanical engineerMark Van Dyke, geologist

Stephen Morgan, geologistPaul Kelley, mine engineerDon Teter, project engineer

 

Outline

Introduction

Objective

Geology/Geologic Reconnaissance

Hydro Frac Hole Locations and Frac Process

Flac3D Models

Longwall Visual Analysis (LVA) Monitoring

Face Monitoring and Evaluation

Conclusions

Introduction

IntroductionSandstone Intrusion Encountered During Development

IntroductionSandstone Intrusion Encountered During Development

Base of Sandstone

Channel

Introduction

F20 Longwall Panel Problems

Delayed caving behind shield supports

Massive sandstone pot-outs in front of shields

Increased risk to personnelDelayed Production

Longwall production footage per week

344

24106

306

371

338

230

Objective

To evaluate the effectiveness of the hydraulic fracturing program and the validity of Longwall Visual Analysis (LVA) software to mitigate the impact of a 1, 000-foot (305-meter) wide massive sandstone channel on a 1,500-ft-wide (457-meter-wide) longwall face.

Geologic Reconnaissance

In-Mine Core Drilling

Stratascope Observations

In-Mine Mapping

Primary Stress Orientation

Rock Lab Testing

Average Axial Compressive Strength 8283 psi

Geologic Reconnaissance

Trough of Sandstone Channel at Wall # 29

Base of Sandstone

INBY OUTBYWALL #33

WALL #27

Drawslate

Pittsburgh Seam

5 Feet

Vertical Scale

Frac Hole Locations and Frac Stage Horizons

Frac ProcessPerforations were shot into the casing at the targeted horizons to pre-fracture the sandstone. The estimated shot penetration into the borehole surface was about 26 to 30 inches (0.66 to 0.76 meter).

Frac ProcessWater fracing was employed

Frac Process

Fracing resultInitial break

Shut-in

Outline

Introduction

Objective

Geology/Geologic Reconnaissance

Hydro Frac Hole Locations and Frac Process

Flac3D Models

Longwall Visual Analysis (LVA) Monitoring

Face Monitoring and Evaluation

Conclusions

FL AC3D 3 .10

Itasca Consulting G roup, Inc.M inneapolis , M N USA

©2006 Itasca Consulting G roup, Inc. Step 11503 M odel Perspec tive16:38:18 Thu Jul 26 2012

Center: X: 2.000e+000 Y: 3.860e+002 Z: 1.400e+001

Rotation: X: 0.000 Y: 0.000 Z: 90.000

Dist: 1.361e+003 M ag.: 18.2Ang.: 22.500

Job T itle : F -21 Sandstone F rac-Afte r

View T itle :

Z o n e E x tra 1 M agfac = 1.000e+000 Live m ech zones shown Gradient Calculation

1.9448e+002 to 5.0000e+002 5.0000e+002 to 1.0000e+003 1.0000e+003 to 1.5000e+003 1.5000e+003 to 2.0000e+003 2.0000e+003 to 2.5000e+003 2.5000e+003 to 3.0000e+003 3.0000e+003 to 3.5000e+003 3.5000e+003 to 4.0000e+003 4.0000e+003 to 4.3785e+003

Interval = 5.0e+002

FL AC3D 3.10

Itasca Consulting Group, Inc .M inneapolis , M N USA

©2006 Itasca Consulting G roup, Inc . Step 15221 M odel Perspec tive16:37:57 Thu Jul 26 2012

Center: X: 2.000e+000 Y: 2.138e+002 Z: 1.400e+001

Rotation: X: 0.000 Y: 0.000 Z: 90.000

Dis t: 1.361e+003 M ag.: 18.2Ang.: 22.500

Job T itle : F-21 Sandstone F rac-Befo re

View T itle :

Z o n e E x tra 1 M agfac = 1.000e+000 Live m ech zones shown G radient Calculation

1.4037e+002 to 5.0000e+002 5.0000e+002 to 1.0000e+003 1.0000e+003 to 1.5000e+003 1.5000e+003 to 2.0000e+003 2.0000e+003 to 2.5000e+003 2.5000e+003 to 3.0000e+003 3.0000e+003 to 3.5000e+003 3.5000e+003 to 4.0000e+003 4.0000e+003 to 4.3785e+003

Interval = 5.0e+002

Flac3D ModelWithout Frac

Massive Sandstone

Clayey Shale

Longwall face

FL AC3D 3.10

Itasca Consulting G roup, Inc.M inneapolis, M N USA

©2006 Itasca Consulting G roup, Inc . Step 15221 M odel Perspective14:55:06 Wed Jul 18 2012

Center: X: 1.585e+000 Y: 2.107e+002 Z: 8.023e+000

Rotation: X: 0.000 Y: 0.000 Z: 90.000

Dis t: 1.361e+003 M ag.: 18.2Ang.: 22.500

Job T itle : F -21 Sandstone Frac-Before

View T itle :

Z o n e E x tra 1 M agfac = 1.000e+000 Live m ech zones show n G radient Calculation

1.9448e+002 to 5.0000e+002 5.0000e+002 to 1.0000e+003 1.0000e+003 to 1.5000e+003 1.5000e+003 to 2.0000e+003 2.0000e+003 to 2.5000e+003 2.5000e+003 to 3.0000e+003 3.0000e+003 to 3.5000e+003 3.5000e+003 to 4.0000e+003 4.0000e+003 to 4.3785e+003

Interval = 5.0e+002

Massive Sandstone

Clayey Shale

Longwall face

Shear stress, psi

With Frac Frac horizon

15 ft

Longwall Visual Analysis (LVA)LVA was installed to track the face pressure and cavity formation index.

Cavity Risk Index (CRI)

Face Monitoring and Evaluation

To evaluate the effectiveness of the hydraulic fracturing program and the validity of LVA software, daily face monitoring over a 4-week period was conducted.

Based on the collected information, the correlations among the observed face conditions, the hydro frac hole locations and the LVA cavity formation prediction were analyzed.

Underground Observation

Hydraulic Fracturing

LongwallVisual

Analysis

Ming Direction

Dec. 20, 2011

Face Monitoring and Evaluation

Face Monitoring and Evaluation

Face Monitoring and EvaluationLongwall production footage per week

240

124

232

142

115

194

323

F21—SS fraced

344 24106

306

338

230

F20—SS not fraced

Conclusions

Successful application of hydraulic fracturing technique.

Successful application of LVA software.

Improve safety and increase productivity.

Thanks!Questions?