The Current Perspective of the Pennsylvania 1957 Gas Well Pillar Study and Its Implications for Longwall Gas Well Pillars

Details

• Personal Author:
  Mark C ; Rumbaugh G ; Su D ; Zhang P
• Description:
  Many states rely upon the Pennsylvania 1957 "Gas Well Pillar Study" to evaluate the coal barrier surrounding gas wells (Commonwealth of Pennsylvania, 1957). The study included 77 gas well failure cases that occurred in the Pittsburgh and Freeport coal seams over a 25-year span. At the time, coal was mined using the room-and-pillar mining method with full or partial pillar recovery, and square or rectangle pillars surrounding the gas wells were left to protect the wells. The study provided guidelines for pillar sizes under different overburden depths up to 700 ft. The 1957 study has also been used to determine gas well pillar sizes in longwall mines since longwall mining began in the 1970s. The original study was developed for room-and-pillar mining and could be applied to gas wells in longwall chain pillars under shallow cover. However, under deep cover, severe deformations in gas wells have occurred in longwall chain pillars. Presently, with a better understanding of coal pillar mechanics, new insight into subsidence movements induced by retreat mining, and advances in numerical modeling, it has become both critically important and feasible to evaluate the adequacy of the 1957 study for longwall gas well pillars. In this paper, the data from the 1957 study is analyzed from a new perspective by considering various factors, including overburden depth, failure location, failure time, pillar safety factor (SF), and floor pressure. The pillar SF and floor pressure are calculated by considering abutment pressure induced by full pillar recovery. A statistical analysis is performed to find correlations between various factors and helps identify the most significant factors for the stability of gas wells influenced by retreat mining. Through analyzing the data from the 1957 study, the guidelines for gas well pillars in the 1957 study are evaluated for their adequacy for room-and-pillar mining and their applicability to longwall mining. Numerical modeling is used to model the stability of gas wells by quantifying the mining-induced stresses in gas well casings. Results of this study indicate that the guidelines in the 1957 study may be appropriate for pillars protecting conventional gas wells in both room-and-pillar mining and longwall mining under overburden depths up to 700 ft but may not be sufficient for protective pillars under deep cover. The current evaluation of the 1957 study provides not only insights about potential gas well failures caused by retreat mining but also implications for what critical considerations should be considered to protect gas wells in longwall mining. [Description provided by NIOSH]
• Subjects:
  Mining Occupational Health Safety
• Keywords:
  Coal Mines Gases Ground Control Longwall Mining Pillar Design Room And Pillar Mining Underground Mines
• Series:
  Mining Publications
• ISBN:
  9780873354806
• Publisher:
  Society for Mining, Metallurgy & Exploration, Inc. (SME)
• Document Type:
  Text
• Genre:
  Proceedings
• Place as Subject:
  OSHA Region 3 ; Pennsylvania ; Virginia
• CIO:
  National Institute for Occupational Safety and Health (NIOSH)
• Division:
  PMRD - Pittsburgh Mining Research Division
• Topic:
  Workplace Safety & Health
• Location:
  North America
• Pages in Document:
  199-212
• NIOSHTIC Number:
  nn:20061170
• Citation:
  Proceedings of the 39th International Conference on Ground Control in Mining (ICGCM 2020), July 28-30, 2020, Canonsburg, Pennsylvania. Klemetti T, Mishra B, Lawson H, Murphy M, Perry K eds. Englewood, CO: Society for Mining, Metallurgy & Exploration, Inc. (SME), 2020 Jul; :199-212
• Editor(s):
  Klemetti T; Mishra B; Lawson H; Murphy M; Perry K
• Federal Fiscal Year:
  2020
• NORA Priority Area:
  Mining ; Oil and Gas Extraction
• Peer Reviewed:
  False
• Source Full Name:
  Proceedings of the 39th International Conference on Ground Control in Mining (ICGCM 2020), July 28-30, 2020, Canonsburg, Pennsylvania
• Collection(s):
  National Institute for Occupational Safety and Health
• Main Document Checksum:
  urn:sha-512:65f80ecb597f840730df2aa7fd5acf7b70cbec461b98e9aba32bb8479e8a5f13d544fdb319c8b9b4de08cc8d22b8ba47a655dff541c8386e5da40c37a090c0d1
• Download URL:
  https://stacks.cdc.gov/view/cdc/215332/cdc_215332_DS1.pdf
• File Type:
  [PDF - 561.46 KB ]