2
gas well casing and cementing alternatives were demon-
strated to be one of the most important factors influencing
longwall-induced deformations and stresses in the produc-
tion casing (Su et al., 2023). This paper focuses on a recent
case study that revealed an anomalous shale gas well casing
deformation at a deep longwall mine.
CASE STUDY SITE AND STUDY SITE
GEOLOGY
Case Study Site
This case study was a coordinated effort by the coal and
gas industries, as well as by NIOSH and federal and state
regulatory agencies, to evaluate the effect of deep cover on
longwall-induced casing stresses and deformations. Figures
1 and 2 show the location of a gas well pad over a longwall
abutment pillar in a Pennsylvania coal mine with an over-
burden depth of 1,307 feet. The longwall panel employed
at this mine was 1,500-feet wide, and the average mining
height was 7 feet. The abutment pillar below the gas well pad
was 134 feet wide rib-to-rib. Five unconventional shale gas
wells were drilled over the longwall gate-road in late 2010,
although due to deviation, only three of the five wells were
located inside the abutment pillar (Figure 3). At the request
of NIOSH researchers, the gas operator purposely left the
4H well open for post-mining evaluation and plugged the
remaining four wells. The first longwall panel, located on
the north side of the well pad, mined past the well site in
May 2022, and the second longwall panel, located on the
south side of the well pad, mined past the well site in March
2023. Figure 4 shows the gas well casing construction and
cementing details at the study site, which indicates that all
casings are fully cemented.
FLAC3D MODELS AND STUDY SITE
INSTRUMENTATION
FLAC3D Models
Prior to the collection of post-mining field measurements,
a suite of FLAC3D finite difference simulations (Figure 5)
were constructed and analyzed to evaluate the effect of
longwall excavations on the induced stresses and deforma-
tions within the gate-road abutment pillar. Detailed over-
burden geology data, compiled from a nearby core hole
(1,500 feet away) and from an on-site gamma log, was
the primary model input. Prior to the first longwall exca-
vation, overburden geology from the core hole 1,500 feet
away was the primary input to the model. Upon detection
of the plastic casing deformation at the 1,284-foot hori-
zon, an on-site gamma log was conducted, which revealed
Figure 1. Location of a gas well pad over a longwall abutment pillar
gas well casing and cementing alternatives were demon-
strated to be one of the most important factors influencing
longwall-induced deformations and stresses in the produc-
tion casing (Su et al., 2023). This paper focuses on a recent
case study that revealed an anomalous shale gas well casing
deformation at a deep longwall mine.
CASE STUDY SITE AND STUDY SITE
GEOLOGY
Case Study Site
This case study was a coordinated effort by the coal and
gas industries, as well as by NIOSH and federal and state
regulatory agencies, to evaluate the effect of deep cover on
longwall-induced casing stresses and deformations. Figures
1 and 2 show the location of a gas well pad over a longwall
abutment pillar in a Pennsylvania coal mine with an over-
burden depth of 1,307 feet. The longwall panel employed
at this mine was 1,500-feet wide, and the average mining
height was 7 feet. The abutment pillar below the gas well pad
was 134 feet wide rib-to-rib. Five unconventional shale gas
wells were drilled over the longwall gate-road in late 2010,
although due to deviation, only three of the five wells were
located inside the abutment pillar (Figure 3). At the request
of NIOSH researchers, the gas operator purposely left the
4H well open for post-mining evaluation and plugged the
remaining four wells. The first longwall panel, located on
the north side of the well pad, mined past the well site in
May 2022, and the second longwall panel, located on the
south side of the well pad, mined past the well site in March
2023. Figure 4 shows the gas well casing construction and
cementing details at the study site, which indicates that all
casings are fully cemented.
FLAC3D MODELS AND STUDY SITE
INSTRUMENTATION
FLAC3D Models
Prior to the collection of post-mining field measurements,
a suite of FLAC3D finite difference simulations (Figure 5)
were constructed and analyzed to evaluate the effect of
longwall excavations on the induced stresses and deforma-
tions within the gate-road abutment pillar. Detailed over-
burden geology data, compiled from a nearby core hole
(1,500 feet away) and from an on-site gamma log, was
the primary model input. Prior to the first longwall exca-
vation, overburden geology from the core hole 1,500 feet
away was the primary input to the model. Upon detection
of the plastic casing deformation at the 1,284-foot hori-
zon, an on-site gamma log was conducted, which revealed
Figure 1. Location of a gas well pad over a longwall abutment pillar