Drilling and Completion Report for
Thermal Gradient Wells Drilled in Southeast Idaho
John Welhan, Idaho Geological Survey
Final Report, prepared for
NGDS Supplemental Drilling Project
(DOE Project ID-EE0002850)
April 30, 2014
Summary
Four geothermal exploration borings were drilled within a 30 km (18 mile) radius of China Hat, near
Soda Springs, Idaho during the period September 28 - November 28, 2012. Three of these were
completed as temporary thermal gradient wells during the period October 19 - December 6, 2012 and
one was plugged and abandoned. Chip samples from the three completed wells were analyzed for
thermal conductivity, and these wells were thermally profiled in early April, 2013 and again in early July,
2013; they were plugged and abandoned in early October, 2013. In one well, a right-of-way was
obtained from the BLM to cement fiber optic cable into the casing during abandonment; the cable
termination was placed in a shallow enclosure to allow temperature-profile measurements to be made
in the future using DTS (distributed temperature sensing) pulsed-laser technology.
This report summarizes information on well construction, measurements, and well abandonment as
required by the Bureau of Land Management and Idaho Department of Water Resources in regard to
the conditions under which these wells were permitted. A companion report describes thermal data
obtained from these wells in greater detail and provides information on how heat flow estimates were
derived from these data and interpreted.
Site Location Information
The study area is in the Blackfoot volcanic field (BVF), a late-Quaternary volcanic field in southeast Idaho
that has considerable geothermal energy potential. The drilling sites are shown in Figure 1, indicating
five locations that were permitted for drilling, and Table 1 summarizes their location information. Due
to budgetary restrictions, site B5 was not drilled, and site B1’s borehole was plugged and abandoned
because it could not be completed as a viable thermal gradient well. Table 2 summarizes information
for the four holes that were drilled and the three that were completed. Additional information on well
locations is provided in the following sections, and well construction details and lithologic logs are
provided in Appendices 1 through 4.
Figure 1 – Locations of permitted drilling sites B1 through B5 (yellow squares) relative to
geologic / geothermal features of interest in the study area.
Table 1 – Site locations as permitted by BLM and IDWR (NAD 83 geographic coordinates).
Site
IDWR Permit Site description
T/R/S
Latitude
Longitude
B1
11-GD-2
On road easement
T08S R41E Sec 11
42 o 44' 58.7"N
-111 o 37' 45.4"W
B2
13-GD-2
Bear R. diversion area
T09S R41E Sec 31
42° 36' 06.2"N
-111° 42' 31.3"W
B3
27-GD-2
BLM right-of-way near
Old Oregon Trail route
T06S R44E Sec 02
42° 55' 51.0"N
-111° 16' 31.6"W
B4
27-GD-3
Disturbed ground, off
Government Dam Rd.
T05S R41E Sec 31
42° 56' 28.1"N
-111° 41' 32.9"W
B5
25-GD-3
Pull-out along Bone Rd.
T03S R40E Sec 26
43° 07' 39.5"N
-111° 44' 26.7"W
Table 2 – Drilled locations and well depths, with spud dates and abandonment dates.
Site
B1
IDWR Permit
11-GD-2
Latitude
42° 44' 33.2" N
Longitude
-111° 36' 48.6 "W
Elev.(ft)
5995
B2
13-GD-2
42° 36' 6.7 "N
-111° 42' 31.9 "W
B3
27-GD-2
42° 55' 57.6 "N
B4
27-GD-3
42° 56' 29.0 "N
B5
25-GD-3
Not drilled
TD (ft)
545
Spudded Plugged
09-28-12 10-18-12
5642
450
11-19-12 10-08-13
-111° 16' 28.6 "W
6815
350
10-19-12 10-04-13
-111° 41' 36.9 "W
6284
286
10-20-12 10-04-13
-
-
-
-
-
Borehole B1
This borehole was drilled 150 ft (45 m) ESE of the intersection of Government Dam Road and
Meadowville Road (Figure 2a). Anticipated subsurface geology is shown in Figure 2b and Figure 2c.
Basalt was encountered from 70 to 545 feet (TD). Because the basalt was far thicker than anticipated,
the borehole was plugged and abandoned as a thermal gradient measuring location because it did not
penetrate the highly permeable basalt aquifer in which rapid ground water flow obscures conductive
heat flow. Lithologies penetrated in the borehole and construction details are shown in Appendix 1.
Figure 2a – Location of abandoned borehole B1 (arrow), near the intersection of
Government Dam Road and Meadowville Road.
Figure 2b – Local geologic context and location of cross section through borehole site B1.
Figure 2c – Cross section through drill site B1 showing the anticipated geologic context and that actually
encountered in the vicinity of borehole B1. Based on Mansfield (1927) and Armstrong (1969).
Well B2
This well was drilled and completed about 150 feet east of Last Chance Road and 40 feet south of
Pacificorp’s property line that bounds the north side of BLM’s parcel. Anticipated subsurface geology is
shown in Figure 3b and Figure 3c. The well is located within 200 feet of the footwall of thw Quaternary
East Gem Valley fault. A 2-inch steel casing capped at the bottom was sealed in place with cement grout
and bentonite according to the construction and lithologic details provided in Appendix 2. A prolific
series of water-bearing lithologies was encountered from about 205 – 450 feet bls (TD), including an
artesian zone below 230 feet.
Figure 3a – Drill site B2, located near the east Gem Valley fault scarp off Last Chance Road.
Well B3
This well was drilled and completed 250 feet (76 m) SE of the section corner post on Flat Valley Road
(Figure 4a). Anticipated subsurface geology is shown in Figure 4b and Figure 4c. The site is located
within ca. 300 feet of the footwall of the Meade thrust fault’s mapped trace. No significant waterbearing lithologies were encountered to 350 feet bls (TD). The well was completed with a 2-inch steel
casing capped at the bottom and sealed in place with cement grout and bentonite according to the
construction and lithologic details provided in Appendix 3.
Figure 3b – Local geologic context and location of cross section through borehole site B2.
Figure 3c – Cross section through drill site B2 showing the anticipated geologic context and that actually
encountered in the vicinity of borehole B2. Based on Armstrong (1969).
Figure 4a – Location of completed thermal gradient well B3 (arrow).
Figure 4b – Local geologic context and location of cross section through borehole site B3.
Figure 4c – Cross section through drill site B3 showing the anticipated geologic context and that actually
encountered in the vicinity of borehole B3. Based on Mansfield (1927).
Well B4
This well was drilled and completed 1900 feet SW of Government Dam Road at the end of a cattle road
near the north end of Reservoir Mountain (Figure 5). First water was encountered at ca. 80 feet bls,
but no significant water-bearing zones were identified between 80 and 286 feet bls (TD). The well was
completed with a 2-inch steel casing capped at the bottom and sealed in place with cement grout and
bentonite according to the construction and lithologic details provided in Appendix 4.
Figure 5a – Location of completed thermal gradient well B4 (arrow).
Figure 5b – Local geologic context and location of cross section through borehole site B4.
Figure 5c – Cross section through drill site B4 showing the anticipated geologic context and that actually
encountered in the vicinity of borehole B4. Based on Mansfield (1927).
Drilling Results
Lithologic and well construction information for each borehole is summarized in Appendices 1 to 4,
including information collected during drilling (water depths, air/mud return temperatures) and
completion details (casing, sealing method). Detailed lithologic logs were constructed in spreadsheet
form.
Borehole B1
The scientific objective at this site was to penetrate the late Quaternary basalt and complete a thermal
gradient well in the underlying Salt Lake Formation where an accurate measurement of conductive heat
flow could be obtained. Unfortunately, due to cost overruns from the severity of lost circulation, the
borehole had to be abandoned at a total depth of 550 feet and plugged and abandoned prior to
penetrating the basalt. Maximum mud return temperature observed during drilling was 45 oF. The
disturbed area of the site was reclaimed by bringing in topsoil, followed by grading and reseeding with a
BLM-approved seed mix.
Well B2
Following the difficulties encountered with basalt at site B1, the primary drilling firm subcontracted with
High Plains Drilling of Rexburg, Idaho to drill and complete well B2. It was drilled to a depth of 450 feet;
maximum temperature of returned water during drilling was 54 oF, although, to some extent, this
reflects the temperature of compressed air used as a drilling fluid. The well was completed with 2-inch
steel casing which was capped at the bottom and filled with fresh water for thermal profiling. Following
drilling, the disturbed area at the site was raked level and reseeded.
Well B3
This well was drilled to a depth of 350 feet and completed as a thermal gradient well in the same
manner as well B2. Maximum mud-return temperature recorded during drilling was 54 oF. The site was
raked level and reseeded following drilling.
Well B4
This borehole was advanced to 286 feet before circulation was lost in porous limestone, at which point
the well was completed in the same manner as wells B2 and B3. The site was raked level and reseeded
following drilling.
Heat Flow Results
A total of 102 chip samples from Wells B2, B3 and B4 were analyzed for thermal conductivity at the
University of Utah and are summarized here. Temperature logging was conducted by the Utah
Geological Survey on July 1 and July 2, 2013. The thermal conductivity and temperature logging data are
summarized in Figure 6. Calculated heat flows as calculated in the companion report ranged from a low
of 45 mW/m2 at site B4 to a high of 106 mW/m2 at site B2. Well B2’s calculated heat flow is not
representative of regional conductive heat flow in Gem Valley, however, because its thermal profile
reflects advective overprinting by warm water infiltrating from the nearby Bear River or that upwells
along the East Gem Valley fault.
Figure 6 – Summary of lithologies, thermal conductivities and temperature logs for (A) well B2 on the
East Gem Valley fault (heat flow = 106 mW/m2 estimated in the 22-30 m depth interval), (B) well B3 near
Meade thrust fault (heat flow = 86 mW/m2), and (C) well B4 near the north end of Reservoir Mountain
(heat flow = 46 mW/m2). Lithologic legend: Qb – Quaternary basalt of Gem Valley; Qg – gravel,
alluvium; Ql – loess; Tmc – Main Canyon lake sediments; Kw – Wayan Formation; Tsl – Salt lake
Formation; Trt – Thaynes Formation; Cb – Bloomington Limestone; Cnl – Nounan Limestone. See
Appendices 1 -4 and spreadsheet for detailed lithologic logs, as well as spreadsheets for thermal
conductivity and thermal logging data.
Well Abandonment
All wells were abandoned according to IDWR’s stipulations (C. Hersley, pers. comm., 2012; 2013) which
also meet BLM requirements (R. Lange, pers. comm., 2012). Abandonment operations were performed
by High Plains Drilling, Rexburg, Idaho on October 4, 2013 (wells B3, B4) and on October 8 (well B2)
according to the plan specified in our Notice of Intent (Figure 11 of supplemental documentation) of
2012. A small, trailer-mounted water tank with grout pump and mixing tank was used to mix sufficient
cement on site to fill the 2-inch well casing. The casing was then excavated to a depth of 12 inches
below land surface, cut off at that depth, and the cement mixture pumped via tremmie pipe to fill it
from the bottom up. Following plugging, the hole was covered with local soil, raked level and re-seeded.
Well B2 was abandoned in the same manner but with the modification of a fiber optic cable that was
installed to TD and cemented in place during the plugging operation (Figure 7). This modified
abandonment plan follows that described in our BLM Sundry Notice of September 26, 2012 and for
which we filed a right-of-way application on July 10, 2013 to install a shallow trench and buried
enclosure to house the fiber-optic cable’s termination at the surface so it could be accessed in the future
to collect additional temperature profile data and monitor possible transient thermal characteristics at
this site. As installed, the buried enclosure is situated approximately five feet from the wellhead and 6
inches below land surface with a locking top that can be removed to access the cable coiled inside. The
total length of cable from the wellhead to the first 30-foot reference coil in the enclosure is
approximately 27 feet and the second 30-foot reference coil is separated from the first by 4.5 feet of
cable length.
To make measurements, the soil over the enclosure will be scraped aside and the reference coils placed
in an ice-water bath and the other in an ambient temperature bath to provide calibration reference
information for the DTS readings. Once the data have been collected, the coils will be returned to the
enclosure and it will be covered over again with soil.
Figure 7 – Completed installation at site B2, showing approximate locations and dimensions
of trench and buried enclosure.
Site Reclamation
As described in the preceding sections, site reclamation was performed in two stages: once following
drilling and well installation and again following well abandonment. In the first stage, the area of
disturbed ground at the drilling site was raked level (after topsoil brought, in at site B1) and seeded with
a BLM-approved seed mixture. This had the effect of returning the sites to near their initial undisturbed
condition by the following summer, with vigorous wildflower growth and grass cover.
In comparison, the second stage of reclamation was relatively minor, involving the immediate ca. 10
sq.ft. area around the wellhead in the case of wels B3 and B4 or the ca. 20 sq.ft. trenched area adjacent
to well B2; in that case, the disturbed area around each abandoned well was raked level and re-seeded
again to promote vegetation growth. Bryce Anderson of Pocatello’s BLM field office inspected sites B1
through B4 on October 22, 2013 when this was done and also assisted with further raking and leveling of
cuttings and topsoil at site B1 to promote its recovery to initial conditions.
References
Armstrong, F.C., 1969, Geologic map of the Soda Springs Quadrangle, southeastern Idaho: U.S.
Geological Survey Misc. Geologic Investigations Map I-557, scale 1:48,000, 2 sheets.
http://pubs.er.usgs.gov/publication/i557
Mansfield, G.R., 1927, Geography, geology, and mineral resources of part of southeastern Idaho: U.S.
Geological Survey Professional Paper 152, 454 p., 7 sheets, scale 1:62,500 (one .compilation sheet scale
1:250,000).
APPENDIX 1 – Drilling and completion log of Well B1
APPENDIX 2 – Drilling and completion log of Well B2
APPENDIX 3 – Drilling and completion log of Well B3
APPENDIX 4 – Drilling and completion log of Well B4