Analysis of results of surface geochemical surveys in the transfrontier zone of the Polish and Ukrainian Carpathians

W pracy przedstawiono wyniki rozpoznawczych powierzchniowych badań geochemicznych wykonanych w latach 2007-2008 we wschodniej części polskich i zachodniej części ukraińskich Karpat Zewnętrznych, na północ od nasunięcia dukielskiego. Celem badań była ocena możliwości występowania wgłębnych akumulacji węglowodorów w obszarze cechującym się powszechnym występowaniem wycieków ropnych na wychodniach intensywnie sfałdowanych i głęboko rozciętych przez erozję warstw. Badania wykonano wzdłuż 11 profili przebiegających poprzecznie do rozciągłości fliszowych jednostek strukturalno-facjalnych. Ogółem pobrano 890 próbek gazu glebowego, w których określono stężenia węglowodorów gazowych i helu. Stężenia metanu, sumy wyższych alkanów, gazowych alkenów i helu dochodziły odpowiednio do 50% obj., 0.4% obj., 132 ppm i 52 ppm. Anomalne stężenia alkanów, przedstawione graficznie na tle głównych jednostek tektonicznych Karpat oraz udokumentowanych akumulacji złożowych, generalnie potwierdziły obecność tych ostatnich. Inne anomalie wskazują na możliwość występowania nieudokumentowanych dotąd, wgłębnych akumulacji węglowodorów.The paper presents results of reconnaissance surface geochemical surveys carried out in the years 2007 and 2008 in the eastern Polish Carpathians and western Ukrainian Carpathians between the Carpathian Foredeep and Dukla Overthrust. The surveys intended to assess the possibility of occurrence of subsurface hydrocarbon accumulations in the area characterized by common occurrence of oil seeps at outcrops of beds, which had been intensely folded and deeply dissected by erosion. The surveys were conducted along 11 profiles. The profiles were running transversally to the strike of flysch structural-facies units. The geochemical surveys consisted in taking 890 soil-gas samples, in which concentrations of gaseous hydrocarbons and helium were determined. Concentrations of methane, higher alkanes, gaseous alkenes and helium reached to nearly 50 vol.%, 0.4 vol.%, 132 ppm and 52 ppm, respectively. The anomalous alkanes concentrations, graphically presented against the background of major Carpathian tectonic units and documented hydrocarbon deposits, have confirmed, in general, the existence of the deposits, whereas some of the concentrations have indicated possible occurrence of other, still undocumented subsurface hydrocarbon accumulations

Methane emission measurements in selected areas of the Polish Outer Carpathians

W pracy przedstawiono wyniki pomiarów dynamiki stężeń metanu oraz jego emisji. Badania wykonano metodą komór statycznych na wybranych 16 stanowiskach położonych na obszarze polskich Karpat Zewnętrznych. Mierzono zmiany stężeń gazów węglowodorowych oraz dwutlenku węgla naturalnie uchodzących do atmosfery z powierzchni terenu, a także z głębokości 1 metra. Zmiany stężeń analizowano w różnych interwałach czasowych: od kilku minut do prawie 30 godzin. Stężenia metanu wahały się od ok. 1.6 ppm do prawie 8000 ppm. Dynamika zmian tych stężeń była najwyraźniejsza, kiedy metan wypływał z otworu o głębokości 1 m i zmieniała się w przedziale od -0.23 do 100.7 ppm x min-1. Obliczone wielkości emisji wahały się od -24.5 do 10 606.9 mg x m-2 x d-1, przy średniej 304.5 mg x m-2 x d-1 i medianie 0.21 mg x m-2 x d-1. Wyniki badań pozwoliły na zoptymalizowanie metodyki pomiarów terenowych, a także na szacunkową ocenę ilości metanu uwalnianego z jednostki powierzchni orogenu karpackiego w jednostce czasu.The paper presents measurement results of dynamics of methane concentrations and its emission. The investigations were carried out with application of the method of static chambers in 16 stations located in the Polish Outer Carpathians. The measurements included changes of concentrations of hydrocarbon gases and carbon dioxide, which naturally escape to the atmosphere from the land surface and flow from the depth of 1 m. The concentration changes were analyzed in various time intervals: from a few minutes up to almost 30 hours. Methane concentrations ranged from approximately 1.6 ppm up to nearly 8000 ppm. Dynamics of its concentrations was most distinct when it was flowing from the depth of 1 m and it was changing within the range of -0.23 to 100.7 ppm x min-1. The calculated emission quantities ranged from -24.5 to 10 606.9 mg x m-2 x d-1, with the mean value equal to 304.5 mg x m-2 x d-1 and median of 0.21 mg x m-2 x d-1. The results of the investigations enabled the authors to optimize the methodology of field measurements and to estimate the quantity of methane which escapes from an area unit of the Carpathian orogen during a time unit

Surface geochemical survey in selected areas of the Polish and Ukrainian Flysch Carpathians

W pracy przedstawiono wyniki rozpoznawczych powierzchniowych badań geochemicznych wykonanych w wybranych strefach polskich i ukraińskich Karpat fliszowych. Ich celem była ocena możliwości występowania wgłębnych akumulacji węglowodorów. Badania wykonano wzdłuż ośmiu profili o łącznej długości ok. 150 km, przebiegających generalnie z NE na SW. Polegały one na poborze próbek gazu glebowego, w których określano stężenia węglowodorów gazowych i helu. Ogółem pobrano 315 próbek z punktów rozmieszczonych w odstępach ok. 500-metrowych. Stężenia metanu wahały się od 0.9 ppm do prawie 50% obj., stężenia wyższych alkanów dochodziły do ok. 0.4% obj., a stężenia gazowych alkenów do ok. 132 ppm. Stwierdzono również obecność helu o stężeniu dochodzącym do 52 ppm. Zmiany stężeń składników węglowodorowych przedstawione graficznie na tle istniejącego modelu geologiczno-złożowego potwierdzają dotychczasowe rozpoznanie złożowe, a także wskazują na możliwość występowania innych, nieudokumentowanych dotąd, akumulacji wgłębnych.The paper presents results of reconnaissance surface geochemical survey carried out in selected zones of the Polish and Ukrainian Flysch Carpathians. It intended to assess the possibility of occurrence of subsurface hydrocarbon accumulations. The survey was conducted along 8 profiles with total length of approximately 150 km, in general running from NE to SW, and consisted in taking samples of soil gas, in which concentrations of hydrocarbons and helium were determined. In sum, 315 samples were taken at points with the 500 m spacing. Concentrations of methane ranged from 0.9 ppm to almost 50 vol. %, concentrations of higher alkanes amounted to approximately 0.4 vol. % and concentrations of gaseous alkenes came up to approximately 132 ppm. Also presence of helium was recorded, its concentration amounting to 52 ppm. Variations in concentration of hydrocarbon constituents, graphically presented against the background of the existing geological and reservoir model, confirm the previous recognition of oil and gas fields and are indicative of opportunity of occurrence other, still undocumented subsurface accumulations

Surface geochemical survey at Starunia palaeontological site and vicinity (Carpathian region, Ukraine)

A surface geochemical survey was carried out in an abandoned ozokerite mine in Starunia, where remnants of a mammoth and three woolly rhinoceroses and one almost completely preserved rhinoceros carcass were found in 1907 and 1929. In total, 689 measurement sites were defined within the selected 300×350 m rectangle (ca. 10.5 ha). The analysed soil gases vary in their molecular and isotopic compositions. Several zones with anomalous methane concentrations over 10 vol% were identified in the study area. These anomalous concentrations correlate well with total C2-C5 alkane anomalies (over 1 vol%). The zones with carbon dioxide concentrations over 15 vol% are generally shifted SW of those, where the methane and the sum of C2-C5 alkanes anomalies were identified. High helium concentrations of crustal origin (over 0.001 vol%) are clustered near fault zones. In a majority of cases methane is of thermogenic origin, migrating to the near-surface zone from deep-seated accumulations. Microbial methane, or methane with a high microbial component, is genetically related to recent swamps. The high variability of concentrations of gaseous components together with the highly variable isotopic composition of individual gases in the soil, indicate their thermogenic and/or microbial origin, and point to the lithological diversity of Quaternary sediments in the study area. Several zones with thermogenic gaseous hydrocarbons and helium were delineated. It is likely that during the Pleistocene winters, under a thick ice and snow cover, the tundra lake and swamp zones around outflows of brines, oil, helium and thermogenic gases had a higher temperature, which resulted in melting and cracking of the ice cover. These sites would be more prospective for future search of well-preserved large vertebrates

Investigation of soil gas composition - examples of application in petroleum exploration and environment protection

The paper presents examples that confirm possibility of using the soil gas method. Soil gas method might be applied to petroleum exploration, to checking of well tightness and underground gas storage, to checking of underground gas pipelines and to prediction of gas hazard in the near-surface zone caused by coal mine closure in the Wałbrzych Coal District

Distribution and origin of gaseous hydrocarbons and carbon dioxide in the Quaternary sediments at Starunia palaeontological site and vicinity (Carpathian region, Ukraine)

Near-surface gases were investigated in Starunia, where remains of mammoth and woolly rhinoceroses were discovered at the beginning of the 20th century. Samples were collected at 30 measurement sites, from 0.8, 1.6, 2.4, 3.2 and 4.0 m depths and analysed for their molecular and isotopic compositions. Most of the methane and all higher gaseous hydrocarbons accumulated within the near-surface zone are of thermogenic origin. The distribution of thermogenic methane and higher gaseous hydrocarbons in Quaternary sediments is variable and, generally, increases with depth. Microbial methane or a mixture of microbial and thermogenic methane also occurs at the near-surface zone. The presence of hydrogen and alkenes in the near-surface gases also suggests a contribution from recent, microbial processes. Helium of crustal origin migrated through the Rinne Fault and other tectonic zones located in the study area, and was subsequently dispersed during migration through the lithologically diversified Pleistocene and Holocene sediments. The high variability of the carbon dioxide concentration and stable carbon isotope composition at various depths in the near-surface zone is caused by its polygenetic origin (thermogenic, microbial, and oxidation of hydrocarbons and Quaternary organic matter), and also by its dissolution in water and oil during migration through lithologically diversified Pleistocene and Holocene sediments. Zones of thermogenic methane occurrence within Pleistocene sediments, dominated by muds saturated with bitumen and brines, provide the most favourable environment for preservation of large extinct mammals. It is likely that during the Pleistocene winters, when thick ice and snow covered the tundra lake and swamp, zones of outflow of brines, oils, helium, and thermogenic gaseous hydrocarbons had a higher temperature, which could have resulted in melting and cracking of the ice cover and drowning of large mammals. The most favourable conditions for preservation of large, extinct mammals probably still exists in the vicinity of sampling probe sites Nos 21, 22, 23 and 36. Zones of dominance of microbial methane concentrations are less favourable sites for preservation of extinct mammals, because this methane was generated within recent swamps and also within recent descending meteoric waters which infiltrated into Pleistocene and Holocene sediments. Older Pleistocene microbial gases have already escaped to the atmosphere

Molecular and isotopic compositions of gases adsorbed to near surface sediments at Starunia palaeontological site and vicinity (Carpathian region, Ukraine)

The near-surface geochemical survey of gases desorbed from sediment samples was carried out in the area of an abandoned ozokerite mine in Starunia, where remnants of mammoth and three woolly rhinoceroses and one almost completely preserved rhinoceros carcass were discovered in 1907 and 1929. Numerous hydrocarbon seeps (gas and oil "eyes") occur on the surface of the study area. Analyses of molecular and stable carbon isotope compositions of adsorbed gases were carried out in two variants. The first included sampling of cuttings from 30 auger boreholes at depths of 4.8, 5.6 and 6.4 m. In total, 88 samples were collected. In the second variant core samples were collected from 17 selected boreholes. In total, 78 samples were taken from various depths to 12 m. The results of molecular composition analyses of desorbed gases indicated high saturation of near-surface sediments with the oil. The highest concentrations of alkanes were detected in Miocene strata. Hydrocarbon migration from deep accumulations to the surface was relatively fast and proceeded along the faults, fractures and cracks. In the near-surface zone hydrocarbons were subjected to oxidation and dehydrogenation, which resulted in generation of unsaturated hydrocarbons and hydrogen. These processes were most intensive in the Pleistocene sediments and in the mine dumps. Increased concentrations of hydrogen may also originate from water radiolysis in the presence of hydrocarbons. Concentrations of carbon dioxide in the adsorbed gases show the higher values in comparison with the analysed gaseous compounds. However, a slight increase in CO2 concentration was detected in the mine dump, which may indicate conditions more favourable for hydrocarbon oxidation. Carbon dioxide from the analysed adsorbed gases is of thermogenic origin. Occasionally, insignificant influence of secondary hydrocarbon oxidation and/or Quaternary organic matter can be observed. Concentrations of alkanes, alkenes and carbon dioxide in the gas derived from desorption of rock samples are lower and the concentration of hydrogen is higher than those measured in free gases. This indicates that additional effects from recent (e.g. microbial) processes are absent

Surface geochemical anomalies in the vicinity of the Wańkowa Oil Field (SE Polish Carpathians)

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

The results of geochemical survey in the vicinity of wells exploring and developing the unconventional gas deposits

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.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