Tracer and air acceptance characterization of a San Juan basin coal Page: 1 of 5
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TRACER AND AIR ACCEPTANCE CHARACTERIZATION
OF A SAN JUAN BASIN COAL
Frank L. Williams and H. E. Nuttall
The University of New Mexico
Albuquerque, NM 87131
Craig E. Tyner and R. D. Jacobson
Sandia National Laboratories
Albuquerque, NM 87185
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As part of an ongoing effort to develop and assess the feasibility of underground coal gasifica-
tion in New Mexico, a field study was performed to determine the natural flow characteristics of an
undisturbed coal seam. Dewatering, air injection, and tracer experiments were conducted on a two-
hole test pattern, spaced 30 ft apart, in a 15-ft-thick seam located about 500 ft below the surface.
This was the first field experiment in coal to utilize a newly developed downhole measuring system
designed and operated by Sandia National Laboratories. From the tracer flow logs and air acceptance
tests we found that the formation allows gas flow (100 SCFM at 250 psi) with low water production
(50 gpd). While some vertical variation in air flow and tracer residence time through the coal seam
was found, all of the coal sustained flow through a relatively low volume of active voids. Only 10
percent of the injected air was recovered and the recovery rate paralleled trends in the injection
Field tests at a potential Underground
Coal Gasification site in the San Juan Basin
of New Mexico are part of an ongoing effort
at The University of New Mexico to develop
UCG Technology. Since the site is only 5
miles east of the existing San Juan Power
Plant, the site lies within an area that is
being considered for commercial development
of UCG. Therefore, the field test results
have immediate application in planning the
development of coal use in the area.
Previous tests have documented the geol-
ogy and hydrology of the coal seam at the
test site (1,2). In this paper we report the
results of air acceptance and tracer studies
which define the gas flow characteristics
through the undisturbed formation.
As a result of previous testing, the
site consists of two holes, each cased to
the top of the coal with open hole comple-
tion through the coal and into the under-
burden. The two holes are 30 ft apart and
intersect about 15 ft of coal at 500 ft
depth. The smaller hole (GT-1) is nominally
4 in. diameter and intersects about 4 ft
more coal than the larger hole (GT-2) which
is nominally 6 in. diameter. The permeabil-
ity of the underburden and the overburden
was measured to be at least three orders of
magnitude less than the typical 3 to 5 md
found in the coal. The coal is saturated
with saline water and lies 330 ft below the
One week before this month long test
program began, both holes were reamed and
flushed to remove any debris that may have
accumulated due to sloughing or prior test-
The essential equipment for the air
acceptance tests consisted of a truck mounted
compressor (400 SCFM at 250 psi) and orifice
meters to measure the flow of air into and
out of the two holes. A downhole pump was
placed below the coal in GT-2 for dewatering.
The water production was measured by collec-
tion in a calibrated barrel. A schematic
diagram of the surface equipment is shown in
Fig. 1. The injection pressure was controlled
at the compressor by manually adjusting the
air bled to the atmosphere. In that way, the
Air Production Bun
Figure 1. Experimental equipment.
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Williams, F. L.; Nuttall, H. E.; Tyner, C. E. & Jacobson, R. D. Tracer and air acceptance characterization of a San Juan basin coal, article, January 1, 1980; United States. (digital.library.unt.edu/ark:/67531/metadc1067524/m1/1/: accessed November 14, 2018), University of North Texas Libraries, Digital Library, digital.library.unt.edu; crediting UNT Libraries Government Documents Department.