A Case Study of Shale Gas Well Casing Deformation in Longwall Chain Pillars Under Deep Cover

Details

• Journal Article:
  Rock Mechanics and Rock Engineering
• Personal Author:
  Zhang, Peter ; Su, Daniel W. H. ; Van Dyke, Mark ; Kim, Bo Hyun
• Description:
  Shale gas wells located in longwall chain pillars are subject to longwall-induced subsurface ground movements. Longwall mining on either side of the chain pillars can induce deformations in gas well casings. Excessive casing deformations could diminish casing integrity so that intrusive shale gas might leak into the longwall mine jeopardizing mine safety. This study investigated longwall-induced casing deformations of eight shale gas wells in the chain pillars between two adjacent longwall panels in the Pittsburgh coal seam under a cover depth of 314 m. The casing deformations were measured with a 56-arm caliper after each longwall face passed the gas well pad. Casing deformations were detected at ten locations below the surface after first panel mining, and the maximum casing deformation of 1.27 cm occurred at a 184-m depth. After second panel mining, the caliper survey showed that casing deformation locations remained the same, but generally the deformations increased slightly. The maximum deformation at the 184-m depth increased from 1.27 to 1.5 cm. The eight shale gas wells were also modeled by the FLAC3D modeling technique. The casing deformations predicted by the FLAC3D model were compared with the caliper survey results. The modeling predictions were in a good agreement with the caliper measurements in terms of deformation level and locations. The modeling results suggested that the gas well setback distance to the longwall gob would affect casing deformations, and that casing deformations can be minimized if gas wells are located around the center of the abutment pillar. The study showed that longwall-induced casing deformations occur at the same weak/strong rock interfaces after both first and second panel mining. The study also showed that, under deep cover, casing deformations above the coal seam horizon are smaller than those under shallow cover. Under deep cover, the production casing deformations evaluated in this study were demonstrated to be minimized by locating gas wells at the center of the chain pillars and by leaving the production casing uncemented from the surface to below the coal seam. Description provided by NIOSH
• Subjects:
  • Mining
  • Occupational Health
  • Safety
• Keywords:
  • Rock mechanics
  • Longwall mining
  • Pillar mechanics
  • Underground mines
  • Quantitative analysis
  • Analytical models
  • Geologic models
  • Author Keywords: Shale gas well
  • Longwall mining
  • Chain pillars
  More +
• ISSN:
  0723-2632
• Document Type:
  Text
• Genre:
  Journal Article
• Place as Subject:
  Pennsylvania ; Philadelphia Region OSHA ; San Francisco Region OSHA ; Washington
• CIO:
  National Institute for Occupational Safety and Health (NIOSH)
• Division:
  PMRD - Pittsburgh Mining Research Division ; SMRD - Spokane Mining Research Division
• Topic:
  Workplace Safety & Health
• Location:
  North America
• Pages in Document:
  17 pdf pages
• Volume:
  59
• Issue:
  5
• NIOSHTIC Number:
  nn:20071859
• Citation:
  Rock Mech Rock Eng 2026 May; 59(5):5665-5681
• Contact Point Address:
  Peter Zhang, Pittsburgh Mining Research Division, NIOSH, 626 Cochrans Mill Road, Pittsburgh, PA, 15236, USA
• Email:
  nmb2@cdc.gov
• Federal Fiscal Year:
  2026
• NORA Priority Area:
  Mining ; Oil and Gas Extraction
• Peer Reviewed:
  True
• Download URL:
  https://stacks.cdc.gov/view/cdc/260081/cdc_260081_DS1.pdf
• File Type:
  [PDF - 2.84 MB]
• Collection(s):
  National Institute for Occupational Safety and Health
• Main Document Checksum:
  urn:sha-512:60e3edc32b30ef1bf200a142536ff813c40bf14e0f07791ae05425ece81510581cd50d159f47f34596f0aab343c65c131beb6162e510d60756e50ed988dba5ad