Comparison of Measured and Modeled Casing Deformation of a Test Well in a Longwall Abutment Pillar

Details

• Personal Author:
  Zhang, Peter ; Su, Daniel W. H. ; Kim, Bo Hyun ; Midler, Evan
• Description:
  Shale gas wells in longwall pillars are subjected to longwall-induced subsurface ground movements, and their stability has been a safety concern for both mining and gas operators. To understand the impact of longwall mining on gas wells in longwall chain pillars, a test well was drilled through an abutment pillar between two adjacent longwall panels to measure the casing deformations after each panel was mined. The longwall panels extracted the Pittsburgh Coal Seam under a depth of 177 m and were developed with a 3-entry system with 52-m-wide chain pillars and 366-m-wide panels. Casing deformations were measured with a 60-arm caliper and were observed with a downhole camera. Casing deformations were detected at ten locations with the maximum deformation being 8.2 cm at a 51-m depth after second panel mining. A FLAC3D model was set up to predict longwall-induced stresses and deformations in the test well casing. The model was validated with measured surface subsidence and longwall-induced pillar pressure. Both measurements and numerical modeling showed that the casing deformed because of relative horizontal displacements along distinct weak rock interfaces, and most of the casing deformations occurred after first panel mining. The casing deformations at the weak claystone interfaces were found to be confined within the thickness of the claystone layers. The knowledge of longwall-induced casing deformations gained from the test well was used to plan a mine-by case with five shale gas wells in chain pillars. These gas wells had production casings uncemented. The established FLAC3D model from the test well was used to predict intermediate casing deformations in the shale gas wells at the mine-by site. The predictions showed that the production casings were unaffected by longwall mining as the deformations in the intermediate casings were less than the open annulus between production and intermediate casing. The study of the test well led to a successful mine-by in which five shale gas wells in chain pillars were unaffected by the passing of the longwall faces and resumed production after being interrupted during the period of mine-by. The post-mining caliper survey showed no casing deformations in the uncemented production casings, and all the production casings passed pressure test. The FLAC3D model proved to be capable of predicting longwall-induced casing deformations with reasonable accuracy.
• Subjects:
  Mining Occupational Health Safety
• Keywords:
  Author Keywords: Test Well; Shale Gas Well; Longwall Mining; Chain Pillars; Casing Deformations Rock Mechanics; Pillar Mechanics; Ground Control; Longwall Mining; Gases; Three Dimensional; 3D; Geologic Models;
• Series:
  Mining Publications
• ISSN:
  0723-2632
• Document Type:
  Text
• Genre:
  Journal Article
• Place as Subject:
  Pennsylvania ; West Virginia ; Washington ; Philadelphia Region [OSHA] ; San Francisco Region [OSHA]
• 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:
  18 pdf pages
• NIOSHTIC Number:
  nn:20071184
• Citation:
  Rock Mech Rock Eng 2025 Dec; :[Epub ahead of print]
• Email:
  nmb2@cdc.gov
• Federal Fiscal Year:
  2026
• Peer Reviewed:
  True
• Source Full Name:
  Rock Mechanics and Rock Engineering
• Collection(s):
  National Institute for Occupational Safety and Health
• Main Document Checksum:
  urn:sha-512:beffd86fdb9bef61b02c7ac2a6e94df3f3ba66f2f4095d42b1ed2c718dca1632e50640be9a5ba7b995a82da5d3124b06452c98be2cd435d3cda58589733aa897
• Download URL:
  https://stacks.cdc.gov/view/cdc/257946/cdc_257946_DS1.pdf
• File Type:
  [PDF - 2.60 MB ]