Marcellus Shale Gas Play Tetra Tech Capabilities

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1 Potential for Induced Seismicity From Injection Well Operations and Managing Related Risks The Shale Exchange GTI Dale E. Skoff, PG Tetra Tech, Inc. October 20-22, 2015 Pittsburgh, Pennsylvania Marcellus Shale Gas Play Tetra Tech Capabilities 1

2 Introduction Induced seismicity can be caused by a various human activities (e.g., dams, mining, injection wells) EPA estimates approximately 30,000 UIC Class IID wells (aka brine disposal wells and saltwater disposal wells ) in US Documented correlations between injection and significant seismicity are rare but noticeable seismicity has been related to injection (e.g., Youngstown, OH Northstar #1 well) The potential risk of induced seismicity in PA from injection activities will be reviewed considering likely injection intervals, geologic structure, etc. Approaches for managing induced seismicity risk as part of siting and during operations will be discussed. 2

3 Recent UIC Induced Seismicity Reports Pertaining to UIC Class IID Wells Potential Injection-Induced Seismicity Associated with Oil and Gas Development: A Primer on Technical and Regulatory Considerations Informing Risk Management and Mitigation Issued in 2015 by StatesFirst Induced Seismicity by Injection Work Group (ISWG) ; StatesFirst is an initiative of the Interstate Oil and Gas Compact Commission and the Ground Water Protection Council (GWPC) Minimizing and Managing Potential/Impacts of Injection- Induced Seismicity from Class II Disposal Wells: Practical Approaches Issued on Feb. 6, 2015 by EPA, National Underground Injection Control Technical Work Group (NTW) 3

4 Injection Wells and Induced Seismicity Source: GWPC 4

5 5 Source: Petersen et al

6 Youngstown, OH Earthquakes Scale Source: Missouri Department of Natural Resources 6

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8 Earthquake Epicenters In and Near PA 8 Source: PA DCNR

9 9 Brine Disposal Wells in PA

10 NTW Report on Induced Seismicity from Brine Disposal Wells Of the 30,000 Class IID wells very few disposal well sites have produced seismic events greater than M4.0. What conditions are necessary for significant injectioninduced seismicity? Sufficient pressure buildup from disposal activities Presence of Faults of Concern (i.e., critically stressed region, optimally oriented for movement, sufficient size, etc.) Pathway allowing increased pressure to communicate with fault Greatest risk associated with activating movement along basement faults A Seismicity Decision Model was developed for use by UIC Directors. 10

11 Epicenter Distribution Relative to Northstar #1 Injection Well Source: OH DNR 11

12 Generalized Cross-Section Eastern OH to Southwestern PA OH Injection Well Into Mt. Simon Sandstone PA Injection Well Into Oriskany Sandstone Base Figure Source: Geology.com 12

13 Mt. Simon Sandstone(and Equivalents) Drill Depth Youngstown Pittsburgh Source: MRCSP 13

14 Existing Injection Formations Upper Devonian Sandstones Typical extent of faulting in Appalachian Plateau Huntersville Chert Oriskany Sandstone Medina Tuscarora Sandstones Base of injection interval D&L Disp. Well _ Youngstown, OH 14 Depth to Precambrian Basement ranges from approx. 10,000 ft in NW PA to 20,000 ft+. In much of Marcellus Shale Play Area Source: Stratigraphic Column from PADCNR

15 Why Significant Induced Seismicity is Unlikely in PA USGS indicates very low earthquake risk for most of state Injection into intervals well above Precambrian basement Structural style in Appalachian Plateau typical fault not extending from injection interval (e.g., Oriskany) to basement Preference for injecting into depleted reservoirs which have lower pressures Relatively low injection rates (~500 to 2,000 bbls/d) USEPA permitted injection pressures below formation breakdown pressure No reported incidents to date from operating wells 15

16 UIC National Technical Workgroup (NTW) Injection-Induced Seismicity Decision Model 16 Source: Minimizing and Managing Potential Impacts of Injection-Induced Seismicity From Class II Disposal Wells: Practical Approaches (USEPA Nov. 2014)

17 Estimating Risk of Induced Seismicity from SWDW Operation 17

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19 Summary Although there are approximately 30,000 SWDWs in the US, there are relatively few cases of documented induced seismicity. Where induced seismicity has been correlated to injection well operation, earthquakes over Magnitude 4 are extremely rare. In general, potential for significant induced seismicity from SWDW operation in PA is very low. USEPA, GWPC and others have developed strategies for minimizing potential for induced seismicity and managing risk during operations. Research is ongoing and will likely improve upon these approaches. 19