Abstract
Soil gas measurements of radon (222Rn), CO2, and hydrocarbon concentrations, as well as gamma-ray spectrometry, were conducted at two separate locations to estimate the measurement results for known locations of hydrocarbon accumulations in the subsurface and oil seepage on the surface. The aim of the study was to confirm the applicability of the method for identifying migration pathways (e.g., faults) and to detect possible seepages of hydrocarbons to the surface as well as to investigate possible health issue potential about the soil gas analysis results. Site A investigations were performed with a large number of sampling points to provide sufficient spatial coverage to capture the influence of subsurface lithologic variability as well as the influence of the migration pathway on the measured parameters. For the investigation of site B, sampling points were positioned to reflect the situation between the area above producing hydrocarbon fields and areas with no confirmed accumulation. The results presented show that it is possible to distinguish the near-surface lithology (gamma-ray spectrometry), characterize the migration pathway, and indicate the area of oil seepage at the surface. Areas above the known hydrocarbon accumulations generally have elevated radon concentrations and detectable heavier hydrocarbons with sporadic methane in soil gas, which contrasts with the lower radon levels and lack of detectable heavier hydrocarbons in soil gas in the area with no confirmed hydrocarbon accumulation in the subsurface.
Highlights
Soil gas monitoring has numerous exploration applications, including soil contamination by anthropogenic factors [1,2], health risk from radon concentration in urban planning [3,4], earthquake prediction [4,5], and mineral and hydrocarbon resource exploration [6,7]
Monitoring the radon concentration in soil gas is mainly related to radiation risk in residential areas, since radon accounts for more than 50% of radiation dose coming from natural sources [8], probably due to gaseous form of its radioisotopes
All measurements have ECOPROBE 5 and gamma-ray spectrometry data, while additional radon and thoron levels were measured at 18 points
Summary
Soil gas monitoring has numerous exploration applications, including soil contamination by anthropogenic factors [1,2], health risk from radon concentration in urban planning [3,4], earthquake prediction [4,5], and mineral and hydrocarbon resource exploration [6,7]. Monitoring the radon concentration in soil gas is mainly related to radiation risk in residential areas, since radon accounts for more than 50% of radiation dose coming from natural sources [8], probably due to gaseous form of its radioisotopes. Mainly two radioisotopes of radon are present, 222 Rn and 220 Rn (thoron). 3.8 days, while thoron has half-life of 55.6 s [9]. Decay chain, while thoron is produced from radioactive decay of 224 Ra in thorium (232 Th) decay chain. Concentration of 222 Ra in soil is related to uranium mineralization of soils and concentration of 220 Ra is related to thorium concentration in soils
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