Search

Light hydrocarbons migrate from the petroleum accumulations to the Earth’s surface through faults and fractures. The occurrence of these hydrocarbons in the near-surface zone forms the basis for the surface geochemical methods. The purpose of these methods is to record and analyze the distributions of micro-concentration of gaseous hydrocarbons. The paper presents the results of surface geochemical survey carried out in the “Kosina” hydrocarbon concession block in SE part of the Carpathian Foredeep. The surveys were conducted along 6 measurements profiles. A total of 270 soil gas samples were collected and analyzed for methane and higher gaseous hydrocarbons. The maximum concentrations of CH4, total alkanes C2-C5, total alkenes C2-C4 reached: 2.6 vol.%, 0.532 ppm and 8.25 ppm, respectively. These analytical results enabled us to calculate the geochemical indicators CH4/∑C2-C5 and C2H6/C3H8 which allowed to evaluate the character of deep hydrocarbon accumulations. The first indicator suggest that observed surface geochemical signature represents the hydrocarbon migration mostly from deep-seated petroleum accumulations. The values of CH4/∑C2-C5 varied from 6.02 – 141318.7 ppm with mean value – 845.7 ppm. Additionally, the statistical parameters and histogram distributions of C2H6/C3H8 indicator values suggest the dominance of condensate and condensate-gas accumulations at depths. Furthermore, normalized and filtered values of methane, total alkanes C2-C5 and total alkenes C2-C4 were placed on the structural map of the base of the Miocene strata. Small zones of anomalous concentrations of total alkanes C2-C5 are concentrated in the northern part of the area and occur above elevation of Miocene base as well as in the adjacent subsided zone. Measured concentrations and their normalized values plotted and then integrated with the seismic image. The results of study show the possibility of occurrence of relatively small accumulation of conventional gas trapped in Miocene compact structure, formed above the elevation of the Miocene strata. The condensate gas mostly migrated from deep-seated parts of the Miocene horizons. [ABSTRACT FROM AUTHOR]

The paper presents an attempt to integrate the results of surface geochemical survey (“free gas” method) and soil magnetic susceptibility carried out in "Brzesko-Wojnicz" area, the SE part of Poland. The measurement profile is located at the border of two regional tectonic units: the central part of the Carpathian Foredeep and the Outer Carpathians. . The purpose of the article was to find out a relationship between different indicators of hydrocarbon microseepage, which can provide useful information, especially in petroleum prospecting. A total of 38 soil and soil gas samples were collected from 1.2 m depth below the surface. Maximum concentrations of CH4, total alkanes C2-C5, total alkenes C2-C4 in soil gas samples reached: 36.1 ppm, 0.95 ppm and 0.23 ppm, respectively. Very low values of magnetic susceptibility of soil ranged between 0.8 and 12.9 10-8 m³ /kg. Moreover, the results of hydrocarbon concentrations and magnetic susceptibility measurements of soil gas samples were presented in a linear plot and then integrated with seismic image. The method presented in this paper is a complementary one and its results allow to better understanding of the complexity of hydrocarbon migration mechanisms in the studied area. [ABSTRACT FROM AUTHOR]

Methane and carbon dioxide are among the most active of greenhouse gases that contribute to climate change. Anthropogenic sources have a significant share of their emission into the atmosphere. One of the major sources of emissions of these gases can be exploration activity and operating oil&gas industry. It is associated with the possibility of uncontrolled migration of reservoir gases in the course of work consisting of geological exploration and recognition of hydrocarbon deposits by drilling. In connection with above-mentioned potential treats the paper presents measurements of methane and carbon dioxide emissions within one of the oil-rig conducting drilling aimed at exploring unconventional hydrocarbon deposits with the use of hydraulic fracturing. Emission measurements using the method of static chambers were conducted in three measurement sessions linked with drilling and hydraulic fracturing treatments carried out in horizontal boreholes. In total, the study was carried out in 14 measurements points with 56 gas samples collected from the static chambers. Measurements of methane emissions showed mostly negative values which are in the range of -2.02 to 2.25 [mgom-2od-1], indicating the microbial assimilation of hydrocarbons processes occurring in the soil. In contrast, measurements of carbon dioxide emissions have shown a significant increase in the value after the hydraulic fracturing. These values are in the range from 2.78 to 83.98 [gom-2od-1]. In the light of the performed studies it has to be said that in the case of recording anomalous concentration of methane and/or carbon dioxide, emission measurements are justified and should be carried out during drilling of the boreholes, after completion of the drilling and after hydraulic fracturing. [ABSTRACT FROM AUTHOR]

In the zones of boreholes drilled to explore and extract hydrocarbons uncontrolled migration of gas to soil environment and therefore to atmosphere may occur. Such phenomena may be related to insufficient tightness of the rock mass or poor technical condition of the borehole. Due to the occurrence of potential risks to the environment and human health and life, a set of constant monitoring probes was designed and tested. Location of six permanent monitoring probes were based on the results of surface geochemical surveys carried out in three cycles of measurements in 2014, before the drilling of planned wells. Measured concentrations of methane, total alkanes C2-C5 and total alkenes C2-C4 in all measuring sessions reach up to 11.99, 0.367 and 0.918 ppm, respectively. Conducted periodical studies show an increase in the average value of methane and total alkanes C2-C5 concentrations after drilling and hydraulic fracturing. This may suggest a negligible impact of performed drilling works, the effect of which is microseepage of hydrocarbons from the borehole to the soil. The proposed monitoring procedures of near to borehole zone proved to be justified and should be carried out during drilling of wells related to exploration of oil and gas. [ABSTRACT FROM AUTHOR]

Surface geochemical method is an important technique in petroleum exploration. The purpose of this method is to record and analyze the distribution of micro-concentration of gaseous hydrocarbons, which migrate from subsurface accumulations to the nearsurface zone. The paper presents the results of surface geochemical survey carried out in the area of the Mołodycz gas deposit of the Carpathian Foredeep. A soil-gas geochemical survey was carried out along the six sampling lines corresponding to the seismic section. A total of 192 soil gas samples were collected from 1.2 m depth below the surface and then analyzed chromatographically. The maximum concentration of CH4, total alkanes C2-C4, total alkenes C2-C4 reached: 369.1 ppm, 3.5 ppm and 4.6 ppm, respectively. Based on the concentrations measured in the soil gas the C2H6/C3H8 (C2/C3) ratio was calculated, which allowed to evaluate the character of deep hydrocarbon accumulations. The statistical parameters, histogram distribution and scatter-plots of ethane versus propane concentrations shown dominance signals characteristic for gas-condensate accumulations. Moreover, normalized and filtered values of the total alkanes C2-C4 concentrations were drawn against structural map of the gas horizon of the Miocene strata. Anomalous concentrations of total alkanes C2-C5 were found in 11 zones. These zones were the effect of the migration from sources located at various depths. Such a comparison demonstrated also that hydrocarbon accumulations can be expected outside the known contours of the gas deposit. Results of surface geochemical survey combined with the geological studies and geophysical surveys provide a valuable source of comprehensive information about the explored area and can be a new perspective for exploration in a hydrocarbon provinces. [ABSTRACT FROM AUTHOR]

The paper presents the results of surface geochemical surveys carried out using "free gas method" in "Brzesko-Wojnicz" area in the SE part of the Poland. The surveys were conducted along 2 measurement profiles. A total of 341 soil gas samples were collected from 1.2 m depth below the surface. Maximum concentrations of CH4, total alkanes C2- C5, total alkenes C2-C4 reached: 27,1 vol.%., 45,3 ppm and 0,174 ppm, respectively. In total, in the analyzed area there are anomalous concentration of total C2-C5 alkanes (over 3σ above calculated background mean) in 121 measurement points, comprising 9 zones ranging from 200 m to a 2 kilometres. Calculated hydrocarbon ratios CH4/ΣC2-C5 (C1/ΣC2-C5) and C2H6/C3H8 (C2/C3) allow to define the presence of compositionally diversified, deep hydrocarbon accumulations. The statistical parameters and histogram distributions of the above-mentioned ratios show dominance of condensate-oil character of deep-seated sources with the presence, in some samples, of the effects of current biochemical processes. The highest number of anomalies of total alkanes C2-C5 was determined over the Wojnicz thrust slice, particularly in the area of significant increase in thickness of autochthonous miocene sediments. The Wojnicz thrust slice is bordered to the south by the Dębno thrust slice, over where a decay of anomalous indications of total alkanes C2-C5 was observed. Besides, the thrust fault zone of this thrust slice collectively with the marginal part of the Outer Carpathian may create barriers to the potential migration and microseepage of hydrocarbons from deeper miocene horizons and from flysch sediments. The conducted analysis indicates that the number and distribution of surface geochemical anomalies point to the possibility of the occurrence of deep-seated accumulations, but the penetration of gas ingredients to the surface is determined predominantly by the tectonics of the area. [ABSTRACT FROM AUTHOR]