1
24-064
NIOSH Gas Well Stability Research: Investigation into the
Causes of an Anomalous Shale Gas Well Casing Deformation at
a Deep Longwall Mine
Daniel Su and Peter Zhang
CDC/NIOSH/PMRD, Pittsburgh, PA
ABSTRACT
Following the first longwall excavation at a deep-cover gas
well site, the pre-mining modeling prediction of longwall-
induced casing deformations in the fully cemented produc-
tion casing were in excellent agreement with post-mining
Caliper survey results. However, after second panel min-
ing, the post-mining Caliper survey revealed a large plas-
tic deformation near the top of the Pittsburgh Seam. The
focus of this paper is to identify the possible cause of such
an anomalous deformation. Very high longwall-induced
casing stress near a thick claystone layer at 23 feet above
the Pittsburgh seam horizon was identified as the primary
cause. Leaving the production casing uncemented or using
softer cementing material between intermediate and pro-
duction casings is identified as the best practice.
INTRODUCTION
Since 2003, over 1,800 unconventional shale gas wells
have been drilled through active and future Pittsburgh
seam coal reserves in Pennsylvania, West Virginia, and
Ohio. These unconventional gas wells, whether tapped into
the Marcellus or Utica formations, contain very high gas
pressure and volume. Strata deformations associated with
underground longwall coal mining could induce stresses
and deformations in the shale gas well casings, which in cer-
tain situations could compromise the mechanical integrity
of the production, intermediate, and coal protection cas-
ings. Damaged well casings could potentially introduce
high-pressure, high-volume explosive gas into underground
mine workings to jeopardize underground miners’ safety
and health.
To provide critical scientific data to the stakeholders,
which includes the Mine Safety and Health Administration
(MSHA), the Pennsylvania Department of Environmental
Protection (PADEP), the West Virginia Department of
Mine Safety and Training (WVDOMS&T), the Ohio
Department of Natural Resources (OHDNR), coal
operators, and gas operators, the National Institute for
Occupational Safety and Health (NIOSH) initiated a
research program in 2016 to evaluate the effects of long-
wall-induced deformations on shale gas well casing sta-
bility under deep as well as shallow covers. The effects of
longwall-induced subsurface deformations on shale gas well
casing stability under deep cover, under medium cover, and
under shallow cover were published previously (Su et al.,
2018a and 2018b Su et al., 2019a and 2019b Su et al.,
2020 Zhang et al., 2020 Su and Zhang, 2021 Su et al.,
2021), which indicate that longwall-induced horizontal
displacements under shallow cover are one order of mag-
nitude higher than those under deep cover and longwall-
induced vertical stresses under deep cover are one order of
magnitude higher than those under shallow cover. Shale
24-064
NIOSH Gas Well Stability Research: Investigation into the
Causes of an Anomalous Shale Gas Well Casing Deformation at
a Deep Longwall Mine
Daniel Su and Peter Zhang
CDC/NIOSH/PMRD, Pittsburgh, PA
ABSTRACT
Following the first longwall excavation at a deep-cover gas
well site, the pre-mining modeling prediction of longwall-
induced casing deformations in the fully cemented produc-
tion casing were in excellent agreement with post-mining
Caliper survey results. However, after second panel min-
ing, the post-mining Caliper survey revealed a large plas-
tic deformation near the top of the Pittsburgh Seam. The
focus of this paper is to identify the possible cause of such
an anomalous deformation. Very high longwall-induced
casing stress near a thick claystone layer at 23 feet above
the Pittsburgh seam horizon was identified as the primary
cause. Leaving the production casing uncemented or using
softer cementing material between intermediate and pro-
duction casings is identified as the best practice.
INTRODUCTION
Since 2003, over 1,800 unconventional shale gas wells
have been drilled through active and future Pittsburgh
seam coal reserves in Pennsylvania, West Virginia, and
Ohio. These unconventional gas wells, whether tapped into
the Marcellus or Utica formations, contain very high gas
pressure and volume. Strata deformations associated with
underground longwall coal mining could induce stresses
and deformations in the shale gas well casings, which in cer-
tain situations could compromise the mechanical integrity
of the production, intermediate, and coal protection cas-
ings. Damaged well casings could potentially introduce
high-pressure, high-volume explosive gas into underground
mine workings to jeopardize underground miners’ safety
and health.
To provide critical scientific data to the stakeholders,
which includes the Mine Safety and Health Administration
(MSHA), the Pennsylvania Department of Environmental
Protection (PADEP), the West Virginia Department of
Mine Safety and Training (WVDOMS&T), the Ohio
Department of Natural Resources (OHDNR), coal
operators, and gas operators, the National Institute for
Occupational Safety and Health (NIOSH) initiated a
research program in 2016 to evaluate the effects of long-
wall-induced deformations on shale gas well casing sta-
bility under deep as well as shallow covers. The effects of
longwall-induced subsurface deformations on shale gas well
casing stability under deep cover, under medium cover, and
under shallow cover were published previously (Su et al.,
2018a and 2018b Su et al., 2019a and 2019b Su et al.,
2020 Zhang et al., 2020 Su and Zhang, 2021 Su et al.,
2021), which indicate that longwall-induced horizontal
displacements under shallow cover are one order of mag-
nitude higher than those under deep cover and longwall-
induced vertical stresses under deep cover are one order of
magnitude higher than those under shallow cover. Shale