The Carpathians may play a significant role as a supplier of greenhouse gases to the atmosphere. Unfortunately, most of the discovered oil and gas deposits are recently only historical objects. An example is the Sękowa-Ropica Górna-Siary oil deposit located in the marginal part of the Magura Nappe where oil had been extracted in dug wells until the mid XX century. One of such extraction sites is the “Pusty Las” oilfield. In that area, 10 methane and carbon dioxide emission measurement sites were located, among which 4 in dried dug wells and 6 in dig wells still filled with oil and/or water. Dynamics of methane and carbon dioxide concentration changes were measured with the modified static chambers method. Gas samples were collected immediately after the installation of the chamber and again, after 5 and 10 minutes. In the case of reclaimed or dry dug wells, static chamber was installed directly at the ground surface. In wells still filled with oil and/or water the chamber was equipped with an “apron” mounted on special sticks. The dynamics of concentrations changes varied from -0.871 to 119.924 ppm∙min-1 for methane and from -0.005 to 0.053% obj∙min-1 for carbon dioxide. Average methane emission was 1.9 g∙m-2∙d-1 and that of carbon dioxide was 26.95 g∙-2∙d-1. The measurements revealed that an abandoned oil field supplies significant amounts of greenhouse gases to the atmosphere although the emission of methane is lower than that measured e.g. in mud volcanoes located in various parts of the world.
W pracy przedstawiono wstępną analizę statystyczną wyników powierzchniowych badań geochemicznych wykonanych „metodą gazu wolnego” w rejonie Krosno – Besko we wschodniej części Karpat Zewnętrznych. Badania wykonano wzdłuż 9 profili pomiarowych. Ogółem pobrano 984 próbki gazu wolnego. W analizowanych próbkach stężenia metanu, wyższych alkanów oraz gazowych alkenów dochodziły odpowiednio do 2100 ppm, 15,7 ppm i 8,1 ppm. Ogółem na analizowanym obszarze stwierdzono anomalne stężenia sumy alkanów C2-C5 (pow. 3σ) w 243 punktach pomiarowych, tworzących 55 stref o zasięgu od 200 m do kilku kilometrów. Strefy te, przedstawione na tle mapy geologicznej, wskazują na obecność głównie akumulacji ropnych i ropno-kondensatowych, położonych prawdopodobnie na różnych głębokościach. Poza tym badania potwierdziły obecność rozpoznanej akumulacji węglowodorów – złoża Iwonicz – Rymanów. Rozmieszczenie powierzchniowych anomalii geochemicznych jest również determinowane tektoniką obszaru.
EN
The paper presents the initial statistical analysis of surface geochemical surveys carried out using “free gas method” in Krosno – Besko area in the eastern part of the Outer Carpathians. The surveys were performed along 9 measurement profiles. A total of 984 samples of free gas were collected. In the analyzed samples, the concentrations of methane, higher alkanes and gaseous alkenes reached 2100 ppm, 15.7 ppm and 8.1 ppm, respectively. In total, in the analyzed area there were anomalous concentrations of total C2-C5 alkanes (area of 3s) in 243 measurement points, comprising 55 zones ranging from 200 m to a few km. These zones, presented against the geological map, indicate the presence of mainly oil and oil/condensate accumulations, probably located at different depths. In addition, the surveys confirmed the presence of recognized accumulation of hydrocarbons – Iwonicz – Rymanów deposits. The distribution of surface geochemical anomalies is also determined by tectonics of the area.
Methane emissions associated with the hydrocarbon-generation process occurring in sedimentary basins are considered to be one of two types of geologic sources of methane emissions to the atmosphere. Current methane emissions releasing from geological sources amount 45–60 Tg CH 4 yr –1. The measured values of flux migrating from soil into the atmosphere are influenced by a series of factors, e.g. porosity and permeability of overlying layers, occurrence of cracks and faults, atmospheric pressure, seasonal temperature fluctuations and presence of methanotrophic bacteria. The latter, as a result of methane consumption, may trigger negative flux values (Etiope 2015). Previously, the methane emission measurements in the Polish Outer Carpathians were carried out with a method of static chambers (Sechman & Dzieniewicz 2009). The studies presented in the paper consisted in initial methane emission measurements by flux meter. Their purpose was to examine distribution of methane fluxes on the land surface, as well as change in emission along with depth, omitting the ‘screening’ near-surface zone. The studies were carried out in a small area of the Carpathian petroleum oil region, nearby Rymanów, between October and December 2015. Measurement of the methane fluxes were performed with application of a portable flux meter (West System 2012). The device performs one measurement per second on average, recording concentration changes in time (ppm/s). Average measurement time was 360 seconds. When a high methane concentration was registered, gas samples were collected from the accumulation chamber and directed to a detailed chromatographic analysis (field sampling and analytical procedure – see Sechman & Dzieniewicz 2009). There were 137 measurements taken on 87 stands in total, recording emission from the land surface, and emission with application of 1-m deep holes – in order to omit the “screening” near-surface zone (Sechman & Dzieniewicz 2009). The emission was recorded along the 1000- m long profile, where samples of soil gas were collected previously, and around the drill holes covered with soil. Furthermore, during the process of drilling 4 boreholes, there were CH 4 test emission measurements taken examining change in methane flux with depth (to 10 m). In case of the KB-7 borehole, measurements were taken 1 and 22 days after the drilling. The natural emission was recorded on 70 measuring stations. The flux was identified only in 30% of the performed measurements. Negative emission was predominant within the examined area (68% of all measurements), with an average value of −3.8 mg∙m −2 ∙d −1. Average value of the positive flux reached 3 mg∙m −2 ∙d −1. Range of the measured flux values is comprised within the scope from −5.2 mg∙m −2 ∙d −1 to 14.9 mg∙m −2 ∙d −1. Emission measurements with the additional holes were carried out at 37 positions. Fluxes with positive values were identified in 6 of them, while the negative values were recorded in 4. Range of the measured flux values with the additional hole was from −6.4 mg∙m −2 ∙d −1 to 2 mg∙m −2 ∙d −1 ; average negative and positive flux values are as follows, respectively: −2.3 mg∙m −2 ∙d −1 and 1.3 mg∙m −2 ∙d −1. Within the examined area, methane emission from the land surface, and to the depth of 1 m, was identified only in 30% of measurements. The measurements are characterized by low values, from −6.4 mg∙m −2 ∙d −1 to 14.9 mg∙m −2 ∙d −1. Results of test emission measurements recorded in subsequently drilled depth intervals, performed for 4 drilling boreholes. For the KB-6, KB-7, KB-8 and KB-10 boreholes, average values of methane emission from subsequent depth intervals were as follows, respectively: 49.2, 68.6, 3.5 and 1.5 mg∙m −2 ∙d −1. These results are higher than values of natural emission measured on the land surface or with application of holes to 1 m. The highest emission values were recorded for the KB-7 borehole. A detailed distribution of CH 4 flux values was correlated with a lithology and molecular composition of gas collected from the accumulation chamber in three depth intervals (3.5 m, 5.5 m and 10 m). Results of the gas molecular analysis prove that the source of methane emission is characterized by both microbial and endogenous origin. It is assumed that occurrence of components heavier than methane in the samples, arises from their depth origin (Saunders et al. 1991). An increase of methane concentration in intervals related to occurrence of shales – may suggest its recent origin. It also needs to be noticed that C 1 /C 2 ratio values (from 207 to 807) increase along with depth, what may prove prevailing share of microbial methane. When 24 hours passed after drilling the KB-7 borehole, the emission value dropped to 0.6 mg∙m −2 ∙d −1, and after about three weeks, during an hourly emission measurement, a positive flux of 0.1 mg∙m −2 ∙d −1 was observed in time 0–470 second and a negative flux of −0.05 mg∙m −2 ∙d −1 was observed in time 480–2660 second. Furthermore, small concentrations of ethane (0.006 ppm) and ethylene (0.005 ppm) were identified in gas sample collected after 22 days. The emissions study conducted in the Rymanów area (Outer Carpathians) indicates the mixed source of methane. In order to determine the detailed methane source, it would be necessary to perform an analysis of the carbon isotopic composition in the samples taken. The low emission values measured on the land surface results from the fact that the emissions were suppressed by the sealing overburden layer. The measurements taken 1 day and then 22 days after drilling – in the KB-7 stabilized borehole, show a decline in emissions value. This may result from an insignificant inflow of hydrocarbons from the depth, bacterial oxidation of these hydrocarbons, and from the influx of air to the borehole.
The oil accumulations discovered in the Skole Synclinorium (eastern part of Polish Outer Carpathians) are located in zones of pinch-out of the Kliva Sandstone. An example is the Wańkowa Oil Field, which contains the largest oil reserves in the region. As the seismic identification of this type of hydrocarbon trap is ambiguous, a surface geochemical survey was carried out in the vicinity of the Wańkowa Oil Field along an experimental line perpendicular to the fold axes. A traverse across the zones with anomalous seismic records indicated the presence of undiscovered lithological traps. During the surface geochemical survey, 94 samples of soil gas were collected from a depth of 1.2 m and then investigated chromatographically. The spacing of sampling sites was 100 m, which was reduced to 50 m in the Wańkowa Oil Field area. The maximum concentrations of CH4 and total alkanes C2-C5 detected in samples were: 4250.0 ppm (0.425 vol. %) and 0.43 ppm, respectively. The first of these was detected at measurement point no. 86, located over the Wańkowa Field and the second at point no. 59, about 1,300 m south of the Wańkowa Field. The chemical analyses also detected maximum values of total alkenes C2-C4, H2 and CO2: 0.147 ppm, 0.042 vol. % and 4.4 vol. %, respectively. The results of the surface geochemical survey were integrated with observations on subsurface geological structures, which were interpreted on the basis of seismic data. This procedure permitted the documentation of anomalous concentrations of alkanes in the near-surface zone and contributed to an understanding of the tectonics of the hydrocarbon reservoirs in depth. The pattern of geochemical anomalies here is controlled by anticlines made up of Early Oligocene–Paleocene sediments and by overthrusts that displace these structures. The hydrocarbons migrated from condensate and/or oil accumulations located at various depths. The character of the anomalous zone discovered over the Wańkowa Oil Field is related to the effective sealing of hydrocarbon traps and/or the relatively low pressure caused by the production of oil for 130 years. However, this anomaly also may be the result of hydrocarbon migration from deeper, as yet undiscovered gas or gas-condensate accumulations, hosted in older reservoirs forming the hinge of the Ropienka-Łodyna Mine Anticline. The most pronounced anomalies were detected over the Wańkowa Village - Bandrów and Grabownica-Załuż anticlines. The active hydrocarbon dispersion in this zone may have resulted from the presence of overthrusts displacing the structures. Moreover, these anomalies may indicate the presence of shallow, maybe poorly sealed hydrocarbon accumulations.
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Szeroko wykorzystywana w geochemii powierzchniowej „metoda gazu wolnego”, opiera się na analizie węglowodorów w próbce gazowej zassanej z gleby. Optymalna objętość próbki wynosząca 100 ml nie zawsze jest możliwa do pobrania z uwagi na zmienność utworów przypowierzchniowych. Bardzo często otrzymujemy dużo mniejsze objętości pobranych próbek. Zróżnicowana ich objętość może być parametrem wpływającym na wielkości rejestrowanych stężeń sumy węglowodorów. Tego typu pomiary wykonywane są w terenie z zastosowaniem przenośnego analizatora MicroFID. W związku z tym wykonano badania, których celem było określenie wpływu objętości próbki gazu, dozowanej do analizatora MicroFID na końcowy wynik pomierzonego stężenia metanu. Badania polegały na kilkukrotnym wykonaniu pomiarów stężeń metanu w próbkach gazu o objętościach: 50, 20, 10 i 5 ml pobieranych z worków tedlarowych i dozowanych do analizatora za pomocą strzykawki. Badania wykazały, że wartości stężeń pomierzone w próbkach dozowanych z worka tedlarowego są wyższe niż te pomierzone w próbkach dozowanych strzykawką. Główną przyczyną błędów jest mieszanie się próbki z powietrzem zasysanym z otoczenia. Dozując małe objętości gazu (np. 5 ml, 10 ml) popełniany błąd ma w przybliżeniu wartość stałą.
EN
‘The free gas method’, a widely applied method in surface geochemistry, is based on the analysis of hydrocarbons in a gas sample sucked from the soil. The optimal volume of the sample amounting for 100 ml is not always possible to collect due to the changeability of sub-soil creations. We very often receive much smaller volumes of the collected samples. Their varied volume might be the decisive parameter determining the credibility of the obtained results. It refers to the measurements of the total amount of hydrocarbons performed in the field by the means of MicroFID analyzer. Therefore, a study was conducted whose aim was to determine the influence of the volume of the gas sample, dosed to MicroFID analyzer, on the final result of the measured methane concentration. The study consisted in the performance of several measurements of methane concentration in gas samples whose volumes amounted for: 50, 20, 10 and 5 ml collected from tedlar bags and dosed to the analyzer with the syringe. The study has shown that the concentration values measured directly from the bag are higher than the ones measured in the samples dozed with the syringe. The main reasons for the errors is blending of the sample with the air sucked from the surroundings. By dosing small gas volumes (e.g. 5 ml, 10 ml) the error which is made is approximately of constant value.
W przypadku poszukiwania i eksploatacji gazu ziemnego ze złóż niekonwencjonalnych kontrowersję budzi możliwość pojawienia się zagrożeń dla środowiska. Jednym z nich może być niekontrolowana migracja gazu (głównie metanu) do strefy przypowierzchniowej i atmosfery na skutek np. nieszczelności odwiertu. W ocenie szczelności odwiertów najskuteczniejsze są powierzchniowe metody geochemiczne realizowane w wariancie gazu wolnego. Generalnie polegają one na zassaniu z niewielkiej głębokości mieszaniny gazu wypełniającego wolne przestrzenie w środowisku skalnym i określeniu w nich stężeń metanu i jego lekkich homologów, gazowych alkenów i dwutlenku węgla. W wybranych próbkach o podwyższonych stężeniach węglowodorów i dwutlenku węgla określono również skład izotopowy. W artykule przedstawiono wyniki powierzchniowych badań geochemicznych na obszarze jednego z zakładów prowadzących roboty geologiczne polegające na poszukiwaniu i rozpoznawaniu niekonwencjonalnych złóż węglowodorów metodą otworową z zastosowaniem szczelinowania hydraulicznego. Wyniki wykonanych badań wykazały obecność anomalnych stężeń metanu i dwutlenku węgla, a także podwyższonych stężeń wyższych od metanu alkanów i alkenów gazowych. Maksymalne stężenia metanu, sumy alkanów C2-C5, sumy alkenów C2-C4 i dwutlenku węgla wynosiły odpowiednio: 35,4 % obj., 99,4 ppm, 1,2 ppm i 19,7 % obj. Wyniki badań izotopowych wykazały, że metan i dwutlenek węgla są głównie pochodzenia mikrobialnego. Powstały one współcześnie podczas fermentacji mikrobialnej. Badania te wykazały, że na pewno nie jest to gaz termogeniczny związany z utworami syluru. Procesy fermentacji mikrobialnej mogą być intensyfikowane pod geomembraną izolującą środowisko gruntowo-wodne od atmosfery. Poza efektami współczesnych procesów mikrobialnych, w rejonie badań zarejestrowano w powietrzu gruntowym także naturalne podwyższone mikrostężenia alkanów C2-C5 świadczące o przenikaniu odzłożowym, prawdopodobnie z pokładów węgla w utworach górnego karbonu. Obecność tych gazów w strefie przypowierzchniowej może być rezultatem naruszenia, w czasie wiercenia, ciągłości utworów zawierających naturalne nagromadzenia węglowodorów w utworach karbonu. Geomembrana zaś powoduje zatrzymywanie migrujących składników alkanowych doprowadzając w konsekwencji do wzrostu ich stężeń.
EN
The exploration for and production of natural gas from unconventional deposits raises many controversies concerning the environmental hazard. One of such threats can be an uncontrolled escape of gas (mostly methane) to the near-surface zone and to the atmosphere caused by e.g. leaking wells. In the evaluation of well tightness, the most effective are surface geochemical methods applying the free gas mode. The principle of these methods is the proper sampling of gases filling the open spaces in soils at shallow depths and determination of concentrations of methane and its gaseous homologues, gaseous alkenes and carbon dioxide. In samples showing increased concentrations of hydrocarbons and carbon dioxide, stable isotopes’ composition is analyzed, as well. The following paper presents the results of surface geochemical survey in the area where exploration for unconventional gas deposits is currently run with the fracking method. The results indicate the presence of anomalous concentrations of methane and carbon dioxide together with the increased contents of higher gaseous alkanes and alkenes. Maximum concentrations of the analyzed components are: methane – 35.4 vol.%, total alkanes C2-C5 – 99.4 ppm, total alkenes C2-C4 – 1.2 ppm and carbon dioxide – 19.7 vol.%. The results of stable isotope analyses reveal that methane and carbon dioxide were generated mostly during the recent microbial fermentation and preclude their thermogenic origin related to Silurian formations. Microbial fermentation can be intensified if it proceeds beneath a geomembrane, which isolates the soil and aquatic environment from the atmosphere. Apart from recent microbial reaction, the analyses indicate the increased microconcentrations of alkanes C2-C5, which documents the migration of gases from deep accumulations, presumably from coal seams hosted in Upper Carboniferous formations. The presence of these gases in the near-surface zone may result from the disruption of Carboniferous rocks hosting natural hydrocarbon accumulations during the drillings. The geomembrane restrains the migrating gaseous alkanes and raises their concentrations.
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In environmental protection and in petroleum prospecting, apart from the commonly applied geophysical methods, geochemical methods are becoming more common. They include gas methods (the most popular consists in the “free gas method”) as well as bacteriological, bitumen luminesce, hydrogeochemical, geobotanical methods and redox methods which are based on pH and Eh analyses.Geochemical research supported by geophysical research constitutes a very accurate tool in locating deep hydrocarbon deposits and in research conducted in relation to natural gas storage facilities. The geochemical research takes into account qualitative and quantitative measurement of parameters characterising the soil environment which includes the acidity and alkalinity of soil pH. The application of the method based on soil pH analysis in terms of exploring deep hydrocarbon pools became an area of interest for the Gas Chromatography Methods and Surface Geochemical AGH. Until now, the method based on soil pH analysis was not used in Poland in terms of exploring deep hydrocarbon pools. Such research was conducted only in the US (Reid 1992, Klusman 1993, Tedesco 1995) but this was done in varying environments and thus the results varied. Soil pH measurement may be performed in compliance with the Polish Standard (PN-ISO 10390:1997) by creating a soil solution however according to the manufacturer, the measurement tool in possession of the Laboratory is suited for taking measurement of solid substances such as cream or soil. Due to the fact that preparation of a soil solution is relatively time-consuming, the author of the work makes an effort of analysing the differences between the standard measurements taken on the solution and in situ measurements taken on the soil using the same device, the latter being a lot faster. Measurements were taken using 56 samples drawn in the area of one of the natural gas deposits in the Carpathian Foredeep Basin. Research has shown that the average values from taking in situ measurements and the collection of soil solution measurements are very similar and amount to 4.65 and 4.93 respectively. The graphical representation of the statistical parameters of both collections (box plot) shows that their distribution is similar. For both collections, the modal class on the performed histograms is between 4.5 and 5.0. Taking into account the variability of the soil centre and the impact of surface and weather conditions on the soil, the collections of values were normalized and filtered. Then, such data was subjected to directional correlation. It showed 85% of corresponding directions of changes. Furthermore, the correlations of measured values performed using the Cartesian coordinate system where the R2 coordinate equals to 0.64, show a relatively high correspondence. The conducted analyses and comparative correlations have shown that in order to characterise the researched area, an in situ test of samples using a mobile analyser may be sufficient to identify the variability of soil acidity in the researched area, thus allowing to save the valuable time and labour consumption to a large extent.
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Powierzchniowe badania geochemiczne poza prospekcyjnym zastosowaniem są również wykorzystywane w badaniach środowiskowych (np. do oceny szczelności podziemnych magazynów gazu). W przypadku, gdy konieczna jest szybka analiza pobranych w terenie próbek, korzysta się często z przenośnych analizatorów. W pracy przedstawiono statystyczną analizę porównawczą zbiorów stężeń sumy węglowodorów gazowych pomierzonych w terenie za pomocy przenośnego analizatora MicroFID oraz oznaczonych w laboratorium przy pomocy stacjonarnego chromatografu gazowego. Wyjściowy materiał analityczny stanowiły wyniki oznaczeń sumy węglowodorów w 314 próbkach gazu glebowego. Parametry statystyczne zbiorów stężeń pomierzonych przy pomocy stacjonarnego chromatografu gazowego oraz przenośnego analizatora MicroFID znacząco się różnią. Największe rozbieżności dotyczą stężeń powyżej 2000 ppm (0,2% obj.). Wynika to z technicznych ograniczeń analizatora MicroFID, który umożliwia oznaczenie stężeń węglowodorów w zakresie do 5% obj., przy zawartości tlenu powyżej 12% obj. Inną przyczyną rozbieżności mógł być sposób zastosowanej procedury kalibracyjnej, determinowany ograniczoną objętością próbki gazu glebowego i metodą jej dozowania. Natomiast analiza statystyczna zbiorów stężeń sumy węglowodorów nieprzekraczających 2000 ppm wykazała generalnie wysoką zgodność wyników uzyskanych stacjonarnym chromatografem gazowym i analizatorem MicroFID. Zmiany stężeń sumy węglowodorów, pomierzonych przenośnym analizatorem i chromatografem, cechują się wysoką jakościową i ilościową zgodnością korelacyjną danych. W tym świetle zastosowanie przenośnego analizatora MicroFID w badaniach terenowych jest uzasadnione na etapie wstępnego rozpoznania geochemicznego. Zaletami analizatora MicroFID są: łatwość obsługi w terenie oraz możliwość szybkiego pomiaru dużej liczby próbek. Jakkolwiek urządzenie to nie jest w stanie zastąpić stacjonarnego chromatografu gazowego, to jednak może być pomocne w prowadzeniu tego typu badań.
EN
Surface geochemical surveys are used not only for the purpose of prospecting but also for the purpose of environmental research (for example to assess the tightness of underground gas storages). Portable analyzers are used frequently whenever there is a need for conducting a fast analysis of samples on the spot. The paper presents a comparative statistical analysis of collections of hydrocarbon gases concentrations measured in the field using a MicroFID portable analyzer against the concentrations marked in a laboratory using a stationary gas chromatograph. The initial material was a concentration of total hydrocarbons determined in 314 samples of soil gas. There is a significant difference between the statistical parameters of concentrations collections measured using the stationary gas chromatograph and those measured using the MicroFID portable analyzer. The biggest discrepancies concern the concentrations exceeding 2000 ppm. They are caused by technical limitations of the MicroFID analyzer which allows determining the hydrocarbons concentrations in the range of up to 5 vol.% at an oxygen content above 12 vol.% Another cause for the above mentioned discrepancies may be the applied method of calibration procedure which was determined by the limited volume of soil gas sample and the method of its dosage. The statistical analysis of collections of hydrocarbon gases concentrations not exceeding 2000 ppm showed in general a high accuracy of the results obtained both by the stationary gas chromatograph and by the MicroFID analyzer. The changes in hydrocarbon gases concentrations measured both by the portable analyzer and by the gas chromatograph are characterized by a high correlation compliance of qualitative and quantitative data. Based on these changes, it can be stated that the use of the MicroFID portable analyzer in field surveys is justified at the stage of initial geochemical identification. The MicroFID portable analyzer is easy to use while being in the field and allows for fast analysis of large amounts of samples, and that constitutes its major advantages. Although the device is helpful during conducting a research, it cannot replace the stationary gas chromatograph.
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