|OVERVIEW OF GEOCHEMICAL EXPLORATION TECHNOLOGY - ABSTRACTS|
The following papers were either published in scientific journals or presented orally at national society meetings by Gulf Research scientists and Exploration Technologies, Inc. scientists under the direction of Dr.'s V.T. Jones and T.J. Weismann. They represent the state-of-the-art in surface geochemical exploration and provide the core information for this "Overview of Geochemical Exploration Technology."
1979 AAPG Meeting
1980 Tenth World Petroleum Congress
181st ACS National Meeting
1981 AAPG Meeting
183rd ACS National Meeting
57th Annual Fall Meeting of the Society of Petroleum
Engineers of AIME
186th ACS National Meeting
187th ACG National Meeting
International Symposium on Remote Sensing of Environment
Third Thematic Conference "Remote Sensing for Exploration Geology"
American Chemical Society
Proceedings of the International Symposium On Remote
Sensing of Environment Fourth Thematic Conference
AAPG Bulletin, Vol. 70, No. 7, July, 1986
Second Workshop on Remote Sensing/Lineament Applications
Fifth Thematic Conference on Remote Sensing for Exploration Geology, Reno, Nevada, October, 1986
"Remote Sensing and Surface Geochemical Study of Railroad Valley, Nye County, Nevada-Detailed Grid Study", S.G. Burtell and V.T. Jones.
19th Annual Offshore Technology Conference
Exploration for Precious Metals Symposium
"Mobile Mercury Applications in the Search for Gold," J.B. Maciolek and V.T. Jones
Sixth Thematic Conference on Remote Sensing for Exploration
"The use of Surface Geochemical Prospecting Techniques to Identify Sedimentary Gas Seepage Through Volcanic and Thrusted Formations" S.G. Burtell and V.T. Jones.
PREDICTIONS OF OIL OR GAS POTENTIAL BY NEAR-SURFACE GEOCHEMISTRY
Victor T. Jones
A near-surface hydrocarbon soil-gas technique developed by Gulf Research
& Development Co. has been shown to be capable of predicting whether
oil or gas is more likely to be discovered in the prospect area. These
predictions are made by using the percent compositions and ratios of methane
to ethane and propane. Typical average values are:
Intermediate values are expected for many hydrocarbon accumulations.
Extensive studies compiled and reported in the literature have clearly shown that reservoired hydrocarbons contain varying amounts of methane and heavier homologs. Frequency histograms of the sum or ratio of methane homologs illustrate that gas from gas deposits is quite distinguishable from that of oil deposits.
Gases from gas-condensate or combined oil and gas provinces plot intermediate between those of gas or oil only provinces as expected.
Light hydrocarbon ratios have been used successfully to predict the petroleum potential of a formation by monitoring C1-C5 hydrocarbons from a steam-still reflux gas sampling system during routine mud-logging operations (Pixler, 1973). Individual ratios of the C2-C5 light hydrocarbons with respect to methane have been demonstrated to provide discrete distributions which reflect the true natural variations of formation hydrocarbons between oil and gas deposits. Analyses of these same ratios for soil-gas hydrocarbons yield nearly the same limits for delineation of oil and gas potential. This correspondence with the actual formation gases shows that the upward migration of reservoired light hydrocarbons into near-surface soils represents a viable mechanism, allowing near-surface geochemical exploration techniques to be utilized for prospect evaluation.
Normalized histograms of composition data have been constructed which better represent the actual near-surface hydrocarbon populations. Correlations with known producing areas are presented in the Sacramento and San Joaquin Basins in California and from the Pineview and Ryckman Creek Fields in the Utah-Wyoming Overthrust Belt.
Abstract. This paper considers the exploration significance of developments in organic and other areas of geochemistry. The utility of geochemical criteria in early reconnaissance and developmental stages of exploration of sedimentary basins for crude oils and natural gases is discussed and illustrated with case histories. References to surface (land) and marine hydrocarbon survey technology, source bed determination, hydrocarbon maturation and migration phenomena, post-migration alteration and transformation, correlation processes and nonconventional hydrocarbon sources are made. Advances in spectroscopic techniques such as high resolution GC-mass spectrometry, nuclear and electron spin resonance, infrared and UV-fluorescence and their relevance in correlation of hydrocarbons with stratigraphic units and reservoirs are discussed. Results of an updated literature review on the theories of oil and gas formation will be presented. The role of stable isotopes of carbon, nitrogen, and sulphur in elucidating problems in evolution migration and alteration of petroleum is treated. Hydrocarbon gases, N, S, O organic compounds, and other elements as proximity indicators of petroleum reservoirs will be evaluated.
Possible biogenic occurrences of C1-C4 light hydrocarbon gases have caused
concern in the interpretation of near-surface geochemical prospecting
data in both land and marine environments. It has long been known that
methane is produced in copious quantities by microbial activity in anaerobic
water flooded soils and marine muds, but the possible production of C2-C4
hydrocarbons has been less well defined and has not been proven conclusively
to occur.Recent studies conducted at Gulf Research & Development Co.
have investigated the anaerobic microbial evolution of C1-C4 hydrocarbons
upon decomposition of various organic substrates. Only methane was observed
in copious quantities with minor amounts of ethylene co-produced. Ethane,
propane, or the butanes were not evolved.
Dissolved methane and propane concentrations measured aboard Gulf's
exploration vessels, the R/V HOLLIS HEDBERG and the M/V GULFREX, on the
continental margins of North America are discussed. Propane concentrations
of less than 0.5 nanoliters/liter were observed in a majority of the samples
in many of the areas studied. This is in agreement with open ocean concentrations
reported by Swinnerton and Lamontagne.
ISOTOPE GEOCHEMISTRY OF SHALLOW
GROUNDWATER AS AN INDICATION OF ACTIVE GAS MIGRATION.
Carbonate cements with unusual carbon and oxygen isotopic compositions have been reported over hydrocarbon reservoirs. It has been suggested that the identification of such areas may have exploration utility. The unusual isotopic ratios are thought to be due to rapid migration of hydrocarbons from a reservoir and their possible oxidation. Isotopically distinct cements imply the prior existence of carbon dissolved in the groundwater. The identification of such cements indicates that hydrocarbon migration once occurred, but not that it is actively occurring. The detection of isotopically unusual carbon species in groundwater suggests ongoing hydrocarbon migration. This study involves the investigation of carbon and oxygen isotopes of dissolved carbon species, light hydrocarbon gas concentrations, and inorganic chemistry of shallow groundwater in areas of West Virginia and Kentucky.
Synchronous fluorimetry of the aromatic fraction of crude oils provides an additional correlation technique which can be applied with other chemical fingerprinting analyses for a genetic classification of oils within a sedimentary basin. It is estimated that greater than 90% of oil fluorescence is attributed to aromatic constituents with minor contributions from resin and asphaltene fractions. Fluorescence wavelengths and intensities are a direct function of the number of fused aromatic rings. Oils of high API gravity exhibit maximum fluorescence intensities at lower wavelengths due to an enrichment in 1- and 2-ring aromatic components. Although significant oil migration in a sedimentary basin may alter the proportion of aromatic constituents present in an oil, genetically related oils of slightly differing API gravities exhibit similar relative fluorescence intensities due to similar proportions of aromatic ring components. Oil correlations based upon fluorogram fingerprinting have generally agreed well with more detailed chemical fingerprinting of biodegraded and nondegraded oils.
The IFP-FINA "Rock-Eval" pyrolysis instrument has been utilized
for source rock correlation studies on several recent wells. The method
has been shown useful as a rapid means to determine petroleum generating
potential and degree of maturation of the source rock. The isolated soluble
hydrocarbon fractions have been analyzed also by the Rock-Eval technique
to determine the extent of overlap of the S1 (250-350ºC) and S2 (350-550ºC)
peaks. Our studies indicate an excellent correlation of the S1 peak and
saturated hydrocarbons while aromatic HC's tail into the S2 peak.
Chemical Instrumentation installed on modern petroleum exploration vessels
like Gulf Oil's R/V HOLLIS HEDBERG allows the explorationist to search
for seeps in the marine environment.
GS&T has been conducting helium and hydrogen geochemical surveys since 1974 which strongly support the association of both these elements 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.
USE OF COMPOSITIONAL INDICATORS IN PREDICTION
OF PETROLEUM PRODUCTION POTENTIAL
In soil gas geochemistry percent methane and ratios of methane to ethane and propane have been successfully used to predict production potential. Because these parameters are methane dependent, analyses are subject to an inherent bias which could lead to misinterpretation particularly where methane is derived from a bioqenic source. Since ethane is second in abundance to methane and is not subject to abundant biogenic generation, ratios using ethane should be more reliable. Ethane to propane and ethane to normal butane ratios provide alternate means to distinguish between oil, condensate and gas phases, and can confirm validity of methane dependent indicators. Application of these ratios is demonstrated with data from several soil gas studies and results are compared for land and marine data. Data sets predictive of oil condensate and gas in marine and soil gas analyses show similar compositional characteristics as would be expected if there were no fractionation in the seep process.
Low thermal diffusivity of peat and soils overlying portions of the oil, and gas province of the eastern Magellan Basin has resulted in a small number of unusually shallow (<2m deep) relative heat flow determinations. The values are in agreement with the single published heat flow value for Tierra del Fuego of 2.3 HFU and with deep bottom-hole temperature measurements located in coincidence with the shallow determinations. They are furthermore consistent with local surface air temperature measurements obtained for a period of one year prior to the field work. Compared with that for similar tectonic provinces (post precambrian, non-orogenic) the heat flow in eastern Tierra del Fuego appears to be about 0.5 HFU greater than might be expected. Maturation level estimates based on burial history of sediments in the area suggest considerable lateral migration (~100 km) of hydrocarbons from deeper in the Magellan Basin. A model is explored whereby the same mechanism for transport of the hydrocarbons, namely, deep ground water movement can also explain the heat flow results. The dramatic 10 HFU decrease in relative surface heat flow observed across the southwestern edge of the San Sebastian oil and gas field is of similar magnitude as other thermal anomalies reported to be in close association with hydrocarbon accumulations.
Fluids migrate in sedimentary basins in response to forces such as compaction,
mineral dewatering, and gravity recharge. The water generally moves radially
outward from the center of the basin if sediments are currently being
deposited or inward from the basin edge if uplift and erosion have exposed
aquifers to recharging waters.
THE DETERMINATION OF MIGRATION
PATHWAYS USING CRUDE OIL AND EXTRACT CORRELATIONS.
Geochemical correlation between an extract from a source rock and reservoired
petroleum can be an extremely useful tool in determining migration pathways
in a basin. Such correlations depend upon the recognition of compositional
similarities between extracts remaining in the source rock and generated
products which have migrated from the source rock.
Systematic and Non-systematic rock fractures comprise effective avenues for both vertical and lateral migration of fluids under a variety of stress and geometric conditions. The systematic fracture network reflects elements of the regional tectonic framework and understanding the genetic aspects of this geometric association can provide clues to the mechanism and timing of fluid migration in the natural geologic environment.
Through the Geosat-NASA test case program, the usefulness of remote sensing data for petroleum/mineral exploration is being evaluated. The potential usefulness of this data as an aid to understanding, detecting, and mapping surface evidence of present and paleo fluid migration occurrences will be summarized. The ability to detect secondary mineral alteration haloes related to hydrothermal mineral emplacement by 1.6 and 2.2 um data will be demonstrated. This ability will be contrasted with similar attempts to understand fluid migration resulting in or related to uranium and/or petroleum accumulations. Emphasis will be placed on imaging systems but visible-near IR spectrometry data from laboratory and field devices as well as airborne line profiling information will be presented.
Analyses of 546 water wells by gas chromatography from the Eastern Snake
River Plain (ESRP) were conducted during the post recharge season in 1979.
Both light hydrocarbon and non hydrocarbon dissolved gas anomalies were
discovered after repeated surveys.
Geochemical data was collected on a semicontinuous basis from a concreted hot spring at Arrowhead springs from 12/8/81 to 12/1/82. The spring, which is located on a splay of the San Andreas fault releases significant quantities of free gas which has been analyzed for seven light hydrocarbons (methane, ethane, propane, iso-butane, normal butane, ethylene and propylene), helium, hydrogen and carbon dioxide. Although sample collection intervals were variable over this time period, systematic magnitude and compositional changes were recorded for the measured gases. Hydrocarbon magnitudes nearly doubles by July 1982 and remained fairly stable until sample collection termination on 12/1/82. This type of change may indicate a precursory signal related to potential earthquake activity on the locked southern section of the San Andreas fault. Additional geologic and geochemical studies are underway to further our understanding of the relationships between geochemical signatures and local geology.
A computer based gas chromatograph control system has been developed for field use in soil gas monitoring. The system controls Gulf built Hydrogen-Helium and hydrocarbon chromatographs through a light pipe interface with a bubble memory based microcomputer. All computer hardware is housed in a single video terminal. Electrical isolation and a minimal number of moving parts help to insure reliable operation in the field. The system includes interactive software for gas chromatograph scan acquisition, calibration, and peak analysis. Also provided are programmable control of chromatograph operation and graphical data display, interactive graphics which allow examination of scan data with more than two orders of magnitude magnification, storage of scans on cartridge tape, and scan reanalysis including addition and averaging of multiple scans. Complete printed graphical reports are generated. Work is in progress to allow modem transmission of data over voice telephone lines from the field to a central laboratory. The system can be expanded to control multiple chromatographs and carry out complex analysis.
Regional soil gas investigations along the central part of the Utah Hingeline have measured anomalous seeps of carbon monoxide. These carbon monoxide microseeps averaging 210 ppm coincide with groundwater discharge areas along an arcuate geothermal zone. Typically, the interbasin groundwater flow is enhanced by cross cutting fracture zones, permitting artesian flow to be maintained. Relative high heat flow and active groundwater discharge combine to concentrate carbon monoxide levels in the overlying soils. Carbon monoxide anomalous sites appear to be associated with local "hot spots" and focus attention on prospective high permeability zones at depth.
A near-surface soil-gas geochemical survey was conducted in conjunction with the Phase II underground coal gasification experiment at the North Knobs GR&DC-DOE UCG facility. Soil gases were measured in 122 eighteen ft deep permanent sites over an extended time period from July 1981 to July 1982. Baseline values were established one month before the 600 ft deep retort was pressured and fired. Monitoring of leakage gases continued daily throughout the three months during the burn and for one month after in order to follow the relaxation of surface leakage. A final monitoring was conducted six months after in July 1982. The final report contains 57 contour maps which illustrate the surface leakage patterns over four times windows for the following retort components: methane, ethane, propane, iso butane, normal butane, ethylene, propylene, and hydrogen.
SHALLOW-WATER CHEMISTRY ABOVE OIL AND
GAS FIELDS OF TIERRA DEL FUEGO
Soil samples from depths less than 2 m were obtained as part of a thermal study of the oil and gas fields of Argentine Tierra del Fuego. Pore waters extracted from the samples were then analyzed for K, Mg, Ca, Na, Cl, SO4, NO3, and PO4. Results in the vicinity of the San Sebastian, La Sara, and San Luis Fields exhibit relatively high concentrations (up to several hundred ppm) of the cations and C1; however, with considerable variability. Crude sampling procedure of necessity may have affected the latter result. Regional samples along a 50 km line trending southwest from the San Luis Field, however, show a significant drop in concentration outside the hydrocarbon province. These observations could be the result of 1) discharge within the hydrocarbon province of waters from deeper in the Magellan Basin (this was one conclusion of the thermal study), 2) contamination of surface soils due to hydrocarbon production in the province or 3) an affect of increasing distance from the seacoast. Based on the geochemistry alone, it is difficult to reach an unequivocal conclusion.
The detection of visible hydrocarbon leakage at the surface has been
one of the most successful exploration techniques ever utilized. Although
most areas with macroseepage have been explored by the drill, there exist
many areas with microseepage that have potential production. Remote sensing
data has been shown to offer the potential to delineate some of these
microseepage areas under the right conditions.
During the summer of 1983, Gulf Research and Development conducted an extensive soil gas analysis at the NASA/Geosat Test Case Site at Lost River, WV. Results from this analysis have identified an order of magnitude methane and ethane soil gas anomaly precisely coincident with previously identified geobotanical anomalies at the site (anomalies noted on remote sensing images). A detailed discussion of root zone interactions with specific edaphic factors generated by methane microseepaqe will be presented. This discussion will provide a theoretical basis for interpretation of remotely sensed data sets acquired from heavily vegetated areas subjected to qeochemically-induced stress associated with hydrocarbon microseepage.
In the last year, multispectral remote sensing systems have become operational which provide significant new information for geological research and oil and gas exploration. These include both satellite (Landsat-4 Thematic Mapper, TM) and aircraft (Airborne Imaging Spectrometer, AIS, and Thermal Infrared Multispectral Scanner, TIMS) systems. In many cases these new data enable geologists to remotely identify and map the minerology of surface materials based on principles of visible short wavelength infrared (TM and AIS) and midinfrared (TIMS) spectroscopy. This talk will summarize these developments and provide examples of application of these new multispectral data to geologic mapping and oil and gas exploration in typical sedimentary basin environments.
Electronic and vibrational transitions occurring in the visible near infrared (400-250 nm) spectral region produce unique reflectance spectral signatures for many rock forming constituents. Electronic transitions, including charge transfer and crystal field effects, have been utilized to identify transition metals, the crystal sites they occupy, and their oxidation state. This has been extended to the detection of rare earth elements in phosphate minerals. Vibrational absorptions which occur in the near infrared are due to combinations and overtones produced in hydroxyl and carbonate bearing minerals. The detection and identification of vibrational signatures has shown many clay minerals to have unique sets of spectral features. Several problems were encountered during attempts to interpret these data quantitatively. However, it was found that the concentration of alunite and kaolinite in synthetic samples could be determined to within 5 percent.
Efficient and inexpensive methods for measuring free and occluded mercury in near surface soils have been developed. Occluded mercury gives excellent results as a pathfinder over gold and silver deposits, and appears to offer greater contrast between background and anomaly thresholds as compared to free or total mercury. The techniques developed are based on the precollection of mercury and utilize the property of gold to amalgamate mercury at relatively low temperatures. Adsorption of occluded mercury by gold takes place on the inside of gilded quartz vials at a fixed temperature in the range of 130ºC to 220ºC. Adsorption of mercury vapor from soil gas is achieved by flowing a predetermined aliquot of soil gas through a collector containing gold coated, purified quartz sand. Field tests determined the best time and temperature of amalgamation, the optimal depth of sampling, the reproducibility of the method and the effect of climatic variations on soil gas mercury content. Occluded mercury anomalies have been demonstrated to correlate reasonably well with free soil gas mercury, however, they are more repeatable and reproducible, and are not affected by climatic variations.
The geosat oil and gas test site program stimulated interest in the potential
interaction between surface hydrocarbon concentration and interpretation
of remote sensing data. The test case results suggested that lineaments
correspond to avenues of preferential hydrocarbon seepage and that this
seepage effects vegetation health and populations at Patrick Draw field
in Wyoming and potentially at Lost River field, West Virginia. These two
areas were selected for extensive surface hydrocarbon surveys in order
to test these hypotheses.
The conclusion that preferential pathways of hydrocarbon leakage can be recognized in spectral and textural analysis of remote sensing data will be supported by other studies and integrated into a suggested exploration/hydrocarbon migration model.
A variety of commonly applied surface soil-gas techniques used in evaluating
an area's hydrocarbon potential are compared. These techniques include
a thermal-mechanical disaggregation technique, a commercial acid-extraction
technique (Horvitz), a shallow probe (4 ft.) free soil-gas technique,
and a deep (12 ft.) packer free soil-gas technique. Data collected from
a variety of areas with known or implied potential have been studied.
Results show that at least one to several of the methods applied correctly
identify the potential (i.e., oil, mixed oil-gas/condensate, or dry gas
prone) of the areas.
Fluorescence spectroscopic analysis of geochemical samples has been used
with increasing frequency to provide information on the composition and
quantity of aromatic hydrocarbons in oils, source rocks and recent sediments.
In this paper we present analytical methods for optimizing fluorescence
measurements on recent sediments. Wet and dry extraction techniques are
compared with each other for quantitative and qualitative analysis. Specific
pitfalls are also discussed which can be traced to contamination and nonlinear
A Lear Siegler SM-400 derivative spectrometer was used to identify and quantify benzene and toluene in drilling returns in a well in the western United States. Excellent correlations were noted between these gases and all macro oil shows encountered, improving the geochemical recognition of potential oil producing zones. The largest benzene and toluene magnitude anomalies are coincident with the well's only current producing zone. Subsequent to these measurements, a new spectrometer was designed and built which is capable of simultaneous determination of benzene and toluene in wellsite applications.
The principal method practiced to release adsorbed or chemisorbed hydrocarbons
from soil or sediment samples involves acidification in the presence of
copper sulphate. Experience in a number of surveys indicates that the
method yields excellent results in some areas and equivocal results in
others. In our study, measurements of the incremental release of C1-C4
hydrocarbons with decreasing pH indicated a release threshold at about
4.5. Samples from three areas were titrated with acid and the evolved
gases and pH were monitored. Copper sulphate increased the amount of gas
released but did not alter the pH dependence.
The Tyrone-Mt. Union lineament of central Pennsylvania is one of many
lineaments recognized in the Appalachian Valley and ridge province. This
feature has been projected into the Plateau province where it defines
a cross-stride structural discontinuity. Geomorphic evidence of the lineament
is recorded in Mississippian and older rocks. Near-surface hydrocarbon
measurements, reservoir gas analysis, fracture measurements, borehole
surveys, and very low-frequency electromagnetic data indicate that these
lineaments are zones of increased fracture permeability with enhanced
hydrocarbon and fluid migration. In one gas field, wells drilled along
the lineament had significant gas shows in organic-rich Devonian shales.
Near-surface hydrocarbons, C1-C4, have been measured around a leaking
production well, around a leaking storage cavern, over known crude oil
and diesel oil spills, and over a leaking pipeline. Aerial and depth profiles
of hydrocarbon magnitudes together with hydrocarbon composition in hydrocarbon
contamination in the near-surface.
Cretaceous inliers in north-central Oregon represent isolated exposures
of potential source rocks in the region.
Carbon Monoxide (CO) was measured in soils over a Known Geothermal Resource Area (KGRA), located in west-central Utah. Attendant sampling of carbon dioxide (CO2) soil-gas was undertaken to compare with the spatial distribution of carbon monoxide anomalies. Anomalous CO data ranging up to 940 ppm are singularly grouped south of Devils Kitchen fault or rift in the vicinity of the KGRA. In contrast, the CO2 anomaly ranges up to 2.3 percent and is broader, forming a band extending northeastward in Pavant Valley. An active shallow groundwater regime apparently influences the upward migration of these gases into the soil horizon, resulting in sharply defined anomalies. It is suggested that CO is highlighting a local geothermal system with greater resolution than CO2 and should be more widely employed in geothermal investigations.
A remote sensing and soil gas geochemical survey has been completed in
Railroad Valley, Nevada fot Japex Geoscience Institute, Inc., Tokyo Japan.
The initial survey was designed around an existing structural model published
by Foster and Dolly (1979). This study provides a test of this model with
remote sensing and geochemical information. Combined interpretation, using
SAR, TM and TM enhanced images has suggested a series of major fracture
lines which define regional fault and fracture systems. Many fracture
lines cross the valley graben and may reflect structural subdivisions
within the qraben blocks, some of these confirm structural divisions identified
by Foster and Dolly.
The adsorbed mercury content of surface soils has been measured along
10 traverses across the San Andreas Fault from the San Gorgonio Mountains
to Chalome in Southern California. The results of these analyses indicate
that anomalous mercury values are associated with the strike of the fault
in some areas which are not affected by seasonal sediment influx.
The focus of this paper is to compare some of the published techniques used in compositional classifications to the method initiated by the current authors. The authors have previously presented findings that suggest a spatial and compositional correlation of hydrocarbon reservoirs in various basins. Clustering of the data based on chemical analyses, generally correlate with a similar set of spatial clusterings of proven producing wells. In order to define a more consistent set of boundary conditions for compositional classifications, mathematical means (i.e., frequency plots), based on compositional data will be investigated; published well data of various North American basins will be studied.
Previous publications (Jones & Drozd, AAPG Bull. 1983) and ACS presentations (Williams et al, 1981 and Pardensky, Drozd, and Jones 1981) have proposed the use of several methane through butane light hydrocarbon ratios and cross-plot schemes for identification of surface and marine hydrocarbon seeps. The marine crossplots presented by Williams et al were based on Gulf of Mexico well analysis data published by Rice et al in a USGS open file report. Further tests of this crossplot model are provided by additional plots of published U.S. Bureau of Mines gas analysis data. Examination of onshore Sacramento and San Joaquin Basin Wells proves the validity of the concept and suggests that considerable information concerning source rocks and potential migration pathways are contained within such plots, in addition to their value for predicting the types of hydrocarbon reservoirs associated with near-surface seepage anomalies.
THE 1983 LANDSAT SOIL-GAS GEOCHEMICAL
SURVEY OF PATRICK DRAW AREA, SWEETWATER COUNTY, WYOMING
Remote sensing and surface geochemical prospecting are excellent tools
for providing the initial evaluation of any frontier basin. Examples will
be shown that demonstrate the natural utility of surface geochemistry
to distinguish between potentially productive and non-productive basins
and as a method of predicting oil versus gas potential of productive reservoirs.
Remote sensing techniques greatly increase the cost effectiveness of geochemical
prospecting by highlighting areas most likely to have enhanced fracture
permeability to aid regional geochemical survey design. The proper application
of these two tools applied in concert provides a very cost-effective method
for a preliminary evaluation of the hydrocarbon potential of any frontier
Helium analysis in soil gas has been used as a complimentary geochemical technique for geothermal, uranium and hydrocarbon exploration for over 10 years. In this paper we report an analytical method which can be used at sea in near-surface marine sediments for sensitive and reproducible analysis of helium. This technique utilizes a helium leak detector (mass spectrometer) with the same inlet configuration described by the USGS. Samples of marine sediment are sealed in metal cans using specially prepared brine and an air headspace, heated at 60º for 16 hours and then shaken on a high speed mixer to partition helium out of the pore fluids and sediment matrix into the headspace. Subsamples are injected into the helium analyzer and compared to helium concentration in air. Values for helium in marine sediments range from 0 to 2 ppm. This indicates that some sediments contain less than sea water helium concentrations. Equilibration experiment onboard ship demonstrate that helium concentrations reach equilibrium after 16 hours. Helium determined prior to this period show erratic and low concentrations. After the equilibration period results are reproducible to within 5% with + sensitivities of 0.03 ppm relative to air. This method of helium + analysis has been used effectively to analyze over 5000 samples offshore. The results provide reproducible and meaningful information which compliments organic geochemical data and provide inorganic confirmation for the migration of thermally derived hydrocarbons in the surface ocean sediments.
DETECTION OF HYDROCARBON MICROSEEPS AND RELATED GEOBOTANICAL ANOMALIES
USING MULTI-DATE IMAGE SUBTRACTION, RAILROAD VALLEY, NEVADA
Railroad Valley, Nye County, Nevada is a N.N.W. trending closed basin
70 miles long and 20 miles wide which shows substantial hydrocarbon microseepage.
The distribution of the dominant vegetation types is influenced by the
microseepage. A technique utilizing subtraction of two dates of registered,
atmospherically corrected imagery was developed to test the utility of
remote sensing as a means of locating vegetation growing on the microseeps
through phenological differences on and off the microseeps.
THE ROLE OF NATURAL FRACTURE SYSTEMS IN NEAR SURFACE GEOCHEMICAL PROSPECTING
A remote sensing and soil gas geochemical survey has been completed in
railroad valley, Nevada for Japex Geoscience Institute, Inc., Tokyo, Japan.
The initial survey was designed around an existing structural model published
by Foster and Dolly (1979). This study provides a test of their model
via remote sensing and geochemical information. Combined information from
SARI TM and TM-enhanced images has suqgested a series of major fracture
lines which define regional fault and fracture systems.
Radon prospecting for hydrocarbon deposits provides an additional correlation
method which can be used with other geochemical surveys in order to support
the genetic association between soil gas hydrocarbon fingerprints at the
surface and bed rock sources at depth.
NEW CRITERIA FOR DISTINGUISHING ACTIVE MICROSEEPS FROM BACKGROUND
A statistical comparison of soil-gas samples over production with samples
off production in eight geochemical surveys found as a general rule that:
1) large magnitude samples were twice as common over production, 2) large
alkane/alkene ratio samples were twice as common over production, and
3) large magnitude samples with large alkane/alkene ratios were six times
more common over production. A comparison of samples over fracture zones
with samples off fracture zones found even greater correlation.
GEOCHEMICAL PROSPECTING OVER THE ROSE HILL OIL FIELD LEE COUNTY, VIRGINIA,
USING A SHALLOW PROBE TECHNIQUE
Soil gases were recovered using a shallow probe technique over the Rose
Hill oil field in Lee County, Va. The gases were analyzed for light hydrocarbons,
C1-C4, plus hydrogen and helium using a custom built chromatograph.
A global correlation between known hydrocarbon production and high heat
flow can be explained by convective heat transport.
A direct method of detecting leaks in submarine pipelines using established geochemical technology is discussed, including the theoretical basis and available equipment. An operational plan for location and pinpointing of a leak is outlined. This technology offers a superior solution for environmental monitoring for potential leakage, and a systematic means of locating the leaks that actually occur before any significant environmental damage is done.
A near surface soil gas geochemical survey was executed in conjunction
with the Phase II experiment at the North Knobs, Wyoming, GR&DC-DOE-UCG
facility from July 22, 1981, through December 12, 1981.