GS&T has been conducting soil gas geochemical surveys since 1974 which
strongly support the association of both helium and hydrogen with tectonic
activity. Examples will be given over the San Andreas Fault in California,
the Duchesne Fault Zone in the Uinta Basin, and a thrust fault near Glacier
National Park in Montana. The largest helium anomaly observed was 1243
ppm near Glacier National Park while a maximum value of 350 ppm was observed
over the San Andreas Fault and 372 ppm over the Duchesne Fault Zone. Hydrogen
values are typically between twenty to several hundred ppm. Hydrogen anomalies
are also associated with petroleum deposits. Measurement of these gases
can be useful in interpretation of geochemical data.
GS&T has been involved in surface geochemical prospecting since the
inception of the earliest applications, around 1932 when A. J. Teplitz
and J. K. Rogers first tried to extract ethane from near-surface soils
(Figure 1). Great strides
have been made over the past 50 years, with results culminating in the
series of papers given here today. Most of our effort has been directed
toward exploration for oil and gas (Jones, 1980). Some of our initial
results were reported at the April 1979 annual AAPG meeting held in Houston,
Texas in a paper by Jones
and Drozd (1979) which indicated that the chemical compositions of
the light hydrocarbons measured in the near-surface soil gases could be
used to predict whether oil or gas was more likely to exist within the
surveyed area. This concept has been extended to the marine environment
by Williams and Mousseau, as described in the preceding paper. Incorporation
of both the surface and marine derived indicator parameters will be presented
in the next paper by Pazdersky, Drozd and Jones. The consistency of these
hydrocarbon seep parameters leaves little doubt of the validity of surface
geochemical prospecting as an adjunct to hydrocarbon exploration. This
paper will address two additional soil gas indicators, helium and hydrogen,
which have been found to be useful in soil gas prospecting, Figure
2, (Kartsev et al. 1959, Orchinnikov et al. 1972, Sokolov et al. 1971).
The results of this paper will be directed toward the demonstration that
soil gas helium and hydrogen anomalies show a clear association with deep
fault zones. Examples shown today will consist of soil gas profiles over
three different types of faults. The areas chosen are the San Andreas
fault which is probably the largest and most active fault in the US, the
Duchesne fault zone which is a major east-west fault zone in a less active
area; and the last is a very lose spaced geochemical profile over a proposed
thrust fault in the Disturbed Belt of the Rockies near Glacier National
Park in Montana.
In addition to demonstrating an empirical relationship between helium
and hydrogen soil gas anomalies and faults, I will briefly discuss the
possible sources of these gases and suggest applications for their use.
For example, helium and hydrogen appear to offer considerable promise
in structural mapping and prospecting for buried mineral deposits (Eremeev
et al. 1972). Because of the obvious relationship to tectonics, these
gases may even have promise for earthquake forecasting, although this
has not yet been demonstrated (Barsukov 1979, Borodzich 1979, Geothermal
Energy 1979, Geotimes 1981). In this regard GS&T donated one of our
helium-hydrogen chromatographs to Cal-Tech in 1980. It was installed on
their most recent earthquake monitoring station at Pacoima Dam in California.
Examinations of the published literature, coupled with extensive field
applications by GS&T scientists have indicated that large volumes
of diverse gases continually escape from the earth's crust into the atmosphere.
Areas of especially high activity appear to be related to zones of deep
tectonic fracturing and the accompanying jointing in which mineralization
is sometimes located (Figure
3). Typical deep gases are CO2, N2, CH4, H2, He, Ar, Rn, Hg, SO2,
COS and H2S. The major components are CO2, N2, CH4 and H2 with the remainder
of this list generally found as minor or trace components. The isotope
ratios of hydrogen, helium, carbon, oxygen and uranium have considerable
potential for helping to define the sources of these gases.
According to published literature, the magnitudes of deep gas anomalies
are governed strongly by tectonic and magmatic activity (Figure
4), thus stronger patterns are encountered in seismically active areas
of late orogenic activity. Accordingly, the weaker patterns are observed
in platform and shield areas that are relatively quiescent; that is in
consolidated blocks of the earth's crust.
That earthquakes may possibly be preceded or accompanied by deep mobile
gases appears to have first been observed in the USSR in 1966, Figure
5, (Fursov et al. 1968). Studies of this type were also undertaken
in China at about the same time (King 1980) and in Japan in 1973 (Wakita
et al. 1978). Chemical monitoring of earthquake activity was not widely
practiced in the US where most efforts were geophysical until about 1975,
when limited studies were initiated using Radon (Science News 1976). GS&T
also conducted our first measurements of helium and hydrogen in 1975.
Two recent landmark publications in Science by Wakita et al. (1978, 1980),
Figure 6, have indicated
that both helium and hydrogen are observed in anomalous quantities along
active faults. In 1978 helium was observed to be as large as 350 ppm within
a nitrogen vent on the Matsushiro fault swarm. The authors proposed to
call these anomalous areas "Helium Spots" because the helium
leakage was not homogeneous throughout the fault zone. These unevenly
distributed helium spots were reported to occupy areas of about 30 x 50
meters. Extensive experience in soil gas prospecting by GS&T indicates
that all soil gas anomalies occur in such spots. This localization of
seeps occurs because the migration of gases are dominated by faults and
fractures, either on the macro or micro scale.
A second paper, published in October, 1980 in Science, reported 70 measurements
for hydrogen in the Yamasaki fault zone. These measurements, made in 0.5
to 1 meter deep holes reported hydrogen anomalies ranging from 2 to 30,000
ppm H2 in the fault zone, with ambient background values of 0.5 ppm observed
outside the influence of the fault. The authors postulated that the hydrogen
was formed by the reaction between groundwater and fresh rock surfaces
formed by fault movement.
Additional support for a deep H2 source has been advocated by Hebert Hawkes
(1972, 1980), Figure 7,
who has suggested that water at a depth of about 15 km (T~300ºC)
would react with minerals containing ferrous iron to yield hydrogen. Hawkes
calculations indicate that the contrast in the ratio of H2 to water between
a depth of 15 km and the surface is about a billion to one. Thus if this
deep water were to migrate upward from depth, then H2 gas would be continually
coming out of solution as bubbles. Considerable support for this deep
hydrogen mechanism can be obtained from Gold (1979), Levinson (1977) and
Hunt (1980). Both Levinson and Hunt have suggested additional study on
the mechanisms that could produce hydrogen. These would include hydrogen
generated near the surface by hydrogen-producing bacteria, maturation
of organic matter at various depths, magmatic sources and even from metamorphism
of graphite-containing rocks. In addition to the possibility of various
deep H2 Sources, we must also consider existing hydrocarbon reservoirs
and their source rocks as a viable alternative.
Hydrogen is a common constituent of all petroleum reservoirs, although
it is rarely reported at the lower levels of 0.1%, or less, because such
levels are considered to be insignificant for reservoir engineering purposes.
More recent analysis by GS&T have always found H2 to be present. In
western Siberia, Nechayeva (1968) found H2 in 15% of all reservoir samples
analyzed. As shown in Figure
8, peak hydrogen concentrations were 0.9% for gas fields, 6% for gas
condensate fields, and 11% for oil fields. The highest H2 concentrations
were observed in gases from organic-rich Jurassic sediments suggesting
that the H2 was related to thermal decomposition of the organic matter.
Additional confirmation for the presence of hydrogen in subsurface gases
was obtained at GS&T by putting a He-H2 detector on some of our wildcat
wells . Figure 9 shows
typical He-H2 values encountered on a gas log run by GS&T on a well
drilled at the research lab. The most important point as regards this
talk is to note that both helium and hydrogen occur with the three major
hydrocarbon shows observed during the drilling of this well, which initially
open flowed at ~1/MMCFPD. This gas contained 0.2% He and, 600 ppm H2.
Helium and H2 have proved to be useful gases to measure in well logging
because both gases appear together not only in reservoirs, but also in
more permeable zones such as faults. An additional positive element is
the fact that no contamination source exists for He and H2 in normal mud
Figure 10 shows the
location of soil gas surveys conducted in the US and Canada since 1972
(Jones and Drozd 1979).
The dots represent areas in which geochemical surveys were conducted.
This map contains about 120 surveys having more than 21,000 measurements
and covering 10,000 line miles of geochemical data. Data from this base
will be reported on here today.
A diagramatic representation of our soil gas sampling equipment is shown
on Figure 11. The soil
gas measurements are made in a shallow hole, at least 12 feet deep, which
is generally auger drilled with a 3-1/2 diameter auger. As shown, a packing
device which also serves as a soil gas probe is placed in this hole. The
packer is inflated to isolate the bottom of the hole from the atmosphere.
The soil gases are then pumped into a gas chromatograph for the determination
of light hydrocarbons (methane, ethane, ethylene, propane, propylene,
iso-butane, and normal-butane), helium, and hydrogen in our newer dual
gas chromatographs. There is a location in the input line where one can
connect an evacuated cylinder and collect a soil gas sample that can be
brought back to the Laboratory for additional gas analyses. This is currently
used for mass spectrogram and carbon isotope analysis of the soil gases.
During the early surveys reported on here, the helium and hydrogen analysis
was conducted at the GS&T labs using evacuated cylinders.
The first example is a soil gas survey over the San Andreas fault zone.
Figure 12 is a geologic
map of California (Jennings 1977) which shows the location of the soil
gas profile. The survey consists of a regional line which follows Highway
46 from Famosa to Paso Robles. The objectives of this survey were two
fold: (1) to cross the Lost Hills Oil Field and the San Andreas fault.
Figure 13 is a color
Landsat image on which one can clearly see the San Andreas fault. Vegetated
areas appear red on the color Landsat composite. As shown in these two
figures, the San Andreas fault is a giant shear zone that extends some
650 miles through Southern California and along the Coast Range of Central
California. This huge fissure has been instrumental in the development
of the topography all along its course, and has caused two of the largest
earthquakes in California's history (1857 and 1906), plus numerous smaller
Like all major faults, the San Andreas is not a single break in the rock,
but is a wide zone, made up of several lines of activity that are roughly
parallel. It is not of a single age, but includes the remnants of ancient
faults that have been quiet for countless centuries and other active breaks
that form the lines of most recent activity within the zone. The discontinuous
movement along the fault has given rise to a confused surface appearance
consisting of old features that have been heavily eroded, plus the fresher
results of movements of the past few thousand years.
Most California earthquakes originate at points about 10 miles deep, but
the San Andreas fault undoubtedly extends down through the earth's crust
(a distance of some 20 to 30 miles) to the East Pacific Rise, which is
one of the spreading centers associated with continental drift and plate
Within California, the San Andreas varies considerably in width. In places,
it may be less than 100 yards wide and made up of but a few entangled
lines of rupture. In most sections, however, it is several hundred yards
to a mile or more in width and is interlaced with any number of sub-parallel
fault lines. Its actual edges are indefinite because of the many old lines
of activity that are now hidden under recent gravel deposits or alluvium,
and because of the landsliding that has covered several miles at a stretch.
Figure 14 shows the
50 mile long traverse that was conducted along Highway 46 in 1975. As
shown on this profile, the Lost Hills anticline has a direct soil gas
anomaly which has a contrast of 5000 to 1 as compared to values observed
east or west of the field. Production ranges from 200 to 6000' in depth
and is Pleistocene to Miocene in age. Note that the west side of the basin
is clearly anomalous with respect to the east side. As shown, very low
hydrocarbon magnitudes are observed on the eastern side. This is particularly
significant since the western side of the basin contains most of the major
Helium and hydrogen are plotted on the uppermost profile. As illustrated,
hydrogen shows a strong correlation to the hydrocarbon anomalies and thus
appears to be a definite petroleum predictor. This data provides support
for the contention that helium is a deep fault, or tectonic indicator,
which is often independent of the oil and gas. Along this 50 mile long
line there are a couple of helium anomalies associated with the western
flank of the Lost Hills Field, and possibly with the cross faults. Another
cluster of helium values appear to be associated with this fault on the
east side. As shown, the helium anomalies do not occur randomly, but are
highly localized and appear to be concentrated near basement faults. The
most outstanding helium anomaly occurs directly over the San Andreas fault.
Figure 15 illustrates
the close-spaced geochemical profile along Highway 46 over the San Andreas
fault. As shown, values as high as 430 ppm helium were observed over this
deep fault. Adjacent sites ranged from 40 to 98 ppm within a distance
of 60 to 120 ft of the mapped location of the fault. Hydrogen is 50 ppm
on the fault and methane is 3.2 ppm. All three gases would be expected
on a deep crustal fault.
Figure 16 shows the
location of known active faults as of 1973 as compiled by C. W. Jennings
(1975). All Quaternary faults which have shown evidence of movement during
the past two million years are orange. Faults which have moved during
the past 200 years are shown in pink, along with the dates of their last
movements. At Cholame, where this profile is located, the fault moved
in 1857, 1906, 1922, and most recently in 1966.
Figure 17 shows two
pictures taken immediately after this last earthquake on July 22 when
the offset was only two inches, and again 12 days later, on August 4th,
when the highway offset has increased to five inches (Earthquake Country
Figure 18 is a picture
of our GS&T technician operating the portable auger drill which was
used for this survey. This picture was taken on Gold Hill, looking north.
The coverings shown are a USGS tiltmeter station.
A second traverse 5 miles north of Highway 46, on Gold Hill, has a very
similar signature as the first profile. Helium values at Gold Hill ranged
from 30 to 70 ppm, Figure
19. Sites 181 and 182 are located about 1/2 mile to the south of the
profile on Gold Hill. This data, leaves little doubt that helium and hydrogen
are associated with the San Andreas fault. Although CH4 appears to correlate
with helium on the fault, it is interesting to note that there were no
heavier hydrocarbons observed directly over the fault trace.
The second example was chosen to provide helium and hydrogen observations
over a less active, but deep basement fault. Figure
20 is a Landsat image of the Uinta Basin in northern Utah. The geologic
map is shown on Figure
21 (Stokes and Hintze 1963). The geochemical traverses are shown as
red lines and consist of four profiles. The Duchesne and Strawberry Rivers
are clearly shown in the image as are the snow-capped Uintah mountains
which are the only major east-west mountain range in the Rockies. The
most prominent fault in the southern half of the Uinta Basin is the Duchesne
fault zone which also runs east-west and lies just south of the Strawberry
and Duchesne Rivers. As shown in the Landsat image the Duchesne fracture
zone appears as a narrow lineament. Surface geological observations indicate
that there is an abrupt change in the direction and amount of regional
dip across this fracture. North of the zone the dip increases and becomes
more E-W, parallel to the zone.
The extreme length and linearity of the Duchesne fracture zone, which
can be traced for approximately 42 miles, suggest that it extends to great
depth, perhaps even to basement. The surface geometry also indicates that
the zone is essentially vertical, and this is certainly true where the
zone can be viewed through some 800' of stratigraphic section in the east
wall of Lake Canyon (Sec. 17, T4S, R6W). At its widest point the zone
is about two miles across. The Duchesne fracture zone consists of a main
line of normal faults which mark the south edge of the fracture zone proper.
This zone of maximum deformation has the general aspect of a slightly
asymmetric graben in that, although individual fault blocks within the
zone may be up or down relative to juxtaposed blocks, the general sense
of movement has been down relative to the terrain to the north and south.
In places, minor normal faults are found north of the main zone for another
quarter mile or so. Locally the individual surface faults may be offset
slightly en-echelon. The faults are all high angle and of small displacement,
maximum surface displacement of the bounding faults of the graben probably
being not more than 50-75 feet. Faults which are secondary to the main
faults appear to follow a regional trend of jointing. To the extent that
there has been continued activity along the Duchesne zone through the
Tertiary and probably also Cretaceous, it is possible that the graben
at the surface reflects a single fault at depth. Thus the en-echelon spatial
relations of the individual faults comprising the Duchesne fault zone
may extend to depth forming a complex structural system.
Traverses across the Duchesne fault indicate that the largest soil-gas
anomalies occur where a geochemical site is located on or immediately
adjacent to one of the faults of the zone. The faults may have similar
en-echelon spatial relations in section as well as in plain view so that,
as conduits for gas leakage, they can be expected to have abrupt discontinuities
both areally and at depth.
Duchesne Line 1 is a profile which extends from the town of Duchesne for
about 16 miles along Indian Canyon (Figure
22). The only break in helium occurs where the line crossed the Duchesne
fault zone at Sites 9 and 10. Hydrogen exhibits several anomalies in addition
to the large anomaly of 110 ppm over the Duchesne zone.
Duchesne Line 3 (Figure
23) runs down Highway 53 and crosses the fault zone between stations
80 to 84. Hydrogen values are high all across the fault, while helium
shows very little response.
Duchesne Line 2 extends along strike and follows the fault zone over its
entire length (Figure 24).
Two major helium anomalies of 681 and 470 ppm are noted. Hydrogen seems
to be greater than 20 ppm over most of the zone, with numerous values
over 150 ppm. The maximum hydrogen values range upwards of 3 to 5 thousand
The first three profiles were run during July, 1976. A second more detailed
traverse was conducted in December, 1976.
The detailed traverse, Figure
25, consists of 10 closely spaced sites which cross the northernmost
fault of the Duchesne zone that has a surface expression near the center
of Line 2. The traverse continues south to cross a second fault, which
is down to the north, as expressed in the topography, and forms a narrow
graben with the first fault.
Sites 10 and 11 are north of the surface expression of the fault but they
lie in small, shallow but topographically well-defined washes which are
tributaries to Cottonwood Canyon. As shown by the outstanding helium anomaly
of 372 ppm (Figure 26),
they could be near or on zones of fracturing associated with the fault
zone. Site 3 is definitely located on the surface expression of a fault.
Sites 4, 5 and 6 are within the graben. Station 5 is on the crest of a
little knoll and is located close to bedrock, while Site 6 is in the bottom
of a shallow wash and is probably very close to or on a main fault, as
indicated by the topography and subsidiary faults on the bluff to the
south. Sites 7 and 8 were placed so as to lie above the secondary normal
faults of slight displacement. These faults can be seen in the bluff east
of these stations (Figure
27). Of particular interest is the large helium anomaly of 227 ppm
at Site 7, which certainly indicates the possibility of a deep fault at
this station. It should be noted that all the sites between 2 and 7 were
observed to have considerable helium (50-100 ppm) associated with them.
Thus the entire fault zone can be said to contain anomalous helium values.
The presence of large hydrogen anomalies along this deep fault should
be viewed with caution because the anomalies could be merely indicating
the presence of excellent source rocks in, contact with the fault at depth.
The third, and final example is taken from an area of considerable structural
complexity. Figure 28
shows the location of the survey area in Montana and the major structural
features. The geochemical survey line is represented by the yellow line
which crosses the Lewis Thrust near Glacier National Park. Figure
29 shows the location of the survey line on the Montana Geological
Map (Ross 1958). The dot just NE of East Glacier marks the location of
a "hydrocarbon spot". This site was initially flagged by a very
high methane value of 108,500 ppm (10.8%). After this site was sampled,
it was noted by the GS&T operator that the hole had a positive flow
of about 30 cc/min. Detailed sampling on 5 foot centers indicated that
this seep had a width of 40 feet.
Figure 30 shows this
methane profile. Sampling was conducted at all marked sites on both sides
of the road. A scale of 1" = 2000 ppm methane was chosen because
of the very large magnitudes observed. The data clearly shows a NW-SE
trend suggesting fault control. Because no outcrops exist at this site,
it was not possible to map the suspected fault. This detail was finished
on October 14, 1977 on the day in which the park was closed in East Glacier.
This time limitation, coupled with the fact that this site is on the Indian
Reservation, made additional sampling impossible.
Interpretation was complicated by the fact that a gas pipeline crossed
the road about 150 feet to the northwest of this site. An analysis of
the pipeline gas shown Figure
31 clearly indicates that the seep gas is not related to the pipeline.
The seep gas appeared to be almost exclusively methane (75%) and ethane
(25%). The observation that isobutane is greater than normal butane may
suggest that this gas is an immature product of early maturation. The
carbon delta value for the isotopic ratio of 13C/12C was found to be -55.5,
again suggesting an early to middle stage of maturity, which the Kootenai
non-marine shale could fit.
The final geochemical information was obtained when the evacuated cylinder
was received at GS&T and found to contain 1243 ppm He, 27 ppm H2,
and 2.4% CO2. This is the largest helium value as yet observed from a
soil gas site.
The only fault and structural information available is contained in a
paper by Robert W. Weimer. As shown on Figure
32, Weimer interprets this area as having thin-skinned tectonics with
an upper plate which consists of a complex fault and drag-fold system
involving Mesozoic and Paleozoic rocks ranging in the thickness from a
few hundred feet at the eastern margin of the disturbed belt to 2 or 3
miles at the western margin. The lower plate is believed to be relatively
unfolded and to continue its normal regional west dip for at least 15
miles under the edge of the folded rocks. The Lewis thrust overrides the
younger sediments with pre-Cambrian aged rocks and is regarded as a third
structural element. Thus, the structural pattern exhibited by the surface
rocks in this area is principally one of west-dipping beds which have
been cut by numerous west-dipping thrust faults. The thrust faults occur
at intervals of one-half to one mile. The majority of the fault planes
appear to have a dip greater than 40 degrees, but this dip is thought
to decrease with depth. The throw is variable; on the majority of faults
it probably ranges between 1000 and 4000 feet. Just to the east of this
proposed thrust fault location is a zone of repeated Ellis, Kootenai and
lower Colorado (Blackleaf member) formations, with a width varying from
2 to 9 miles. The strike of the formations and faults in this zone averages
N 55º W., somewhat different from the strike of the formations further
east. This strike of N 55º W would appear to fit the strike of the
geochemical profile shown in the methane profile. Thus the assumption
that the gas leakage is associated with one of these thrust faults. This
last example illustrates the ability of these techniques to locate blind
faults or fractures. The magnitude, 1243 ppm, of this helium anomaly would
suggest either basement faulting or a very radioactive source in the near
surface rocks. If organic source and decay minerals can be ruled out,
then this data would have considerable impact on the interpretation of
thin-skinned tectonics. Thus geochemical data can sometimes lead to a
reevaluation of the geologic interpretations (Figure
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