Igrenes Metan
Igrene har en metanfyndighet utanför Mora. Metanet strömmar upp ur ett borrhål under tryck. Den gas som kommer upp består av 97% metan, och 3% andra ämnen (kväve, och mindre mängder av etan, helium, och koldioxid). Sammantaget brukar man kalla en sådan sammansättning för ”naturgas”.
Men naturgas är inget homogent ämne, och kan ha olika ursprung. Oftast handlar det om metan som bildats av biologiskt material som bryts ner i frånvaro av syre, under stort tryck och i varma förhållanden. Detta gäller t ex den naturgas som produceras i Nordsjön, eller i Ryssland. Metanhalten är ofta lägre och förekomsten av andra ämnen högre än i vårt fall.
Även biogas är en form av naturgas. I detta fall handlar det om bildning av metan i en rötningsprocess. Det bildade metanet måste renas och koncentreras innan det kan användas. Men i grund och botten är det samma molekyl som är energibärare – metanmolekylen.
Igrene har låtit analysera gasen som kommer upp ur våra borrhål av renommerade forskningsinstitut. Samtliga fastslår att ursprunget i vårt fall är icke-fossilt. Det vill säga att metanet har bildats på annat sätt än av nedbrutet biologiskt material. Inte heller handlar det om rötning. Man talar i detta fall om abiotisk naturgas (naturgas av icke-biologiskt ursprung), eller om biogen naturgas (naturgas som bildats av bakterier som producerar metan långt ner i jordskorpan). I båda fall handlar det om pågående processer, det vill säga metanet nybildas i jordens inre hela tiden.
Igrenes naturgas är alltså icke-fossil.
Vi har sammanställt några nyckelcitat ur forskningsrapporterna nedan. Samtliga rapporter finns tillgängliga i pdf nedan för den som är intresserad.
Geochemical Analysis of One Gas Sample, Well VM-5, Siljan Ring; Applied Petroleum Technology
“Gas composition and isotope ratio analyses of one gas sample from well VM-5, drilled in the Siljan Ring, have been carried out on behalf of AB Igrene. The results have been compared with previous composition analyses of three VM-5 gas samples, and composition and isotope ratio analyses of four gas and two water samples from well VM-2 and three gas samples from well PT17. All samples have similar gas compositions and isotope ratios. Gaseous hydrocarbons are dominated by C1 with low C2 and trace amounts of C3+. Dry gas compositions and light δ13C(C1) values indicate mainly biogenic gas. Relatively heavy δ13C(C2) values suggest a minor thermogenic gas generated from a gas mature source rock. The proportion of thermogenic gas is estimated to be less than about 5%. Biodegradative alteration of the thermogenic gas is indicated by high i-C4/n-C4, C2/C3 and neo-C5/i-C5 molecular ratios, and unusually heavy δ13C(C3) values. All samples have significant CO2 contents, much higher than could be possible due to atmospheric contamination alone. The δ13C(CO2) values are relatively heavy, probably related biodegradation of the C2+ gaseous hydrocarbons. Concentrations of N2 and O2+Ar are probably atmospheric air.”
Biosignatures of ancient microbial life are present across the igneous crust of the Fennoscandian shield
“Earth’s crust contains a substantial proportion of global biomass, hosting microbial life up to several kilometers depth. Yet, knowledge of the evolution and extent of life in this environment remains elusive and patchy. Here we present isotopic, molecular and morphological signatures for deep ancient life in vein mineral specimens from mines distributed across the Precambrian Fennoscandian shield. Stable carbon isotopic signatures of calcite indicate microbial methanogenesis. In addition, sulfur isotope variability in pyrite, supported by stable carbon isotopic signatures of methyl-branched fatty acids, suggest subsequent bacterial sulfate reduction. Carbonate geochronology constrains the timing of these processes to the Cenozoic. We suggest that signatures of an ancient deep biosphere and long-term microbial activity are present throughout this shield. We suggest that microbes may have been active in the continental igneous crust over geological timescales, and that subsurface investigations may be valuable in the search for extra-terrestrial life.”
Timing and origin of natural gas accumulation in the Siljan impact structure, Sweden
“Fractured rocks of impact craters may be suitable hosts for deep microbial communities on Earth and potentially other terrestrial planets, yet direct evidence remains elusive. Here, we present a study of the largest crater of Europe, the Devonian Siljan structure, showing that impact structures can be important unexplored hosts for long-term deep microbial activity. Secondary carbonate minerals dated to 80 ± 5 to 22 ± 3 million years, and thus postdating the impact by more than 300 million years, have isotopic signatures revealing both microbial methanogenesis and anaerobic oxidation of methane in the bedrock. Hydrocarbons mobilized from matured shale source rocks were utilized by subsurface microorganisms, leading to accumulation of microbial methane mixed with a thermogenic and possibly a minor abiotic gas fraction beneath a sedimentary cap rock at the crater rim. These new insights into crater hosted gas accumulation and microbial activity have implications for understanding the astrobiological consequences of impacts.”
Survey of the methane-rich aquifers, Siljan Crater, Mora, Sweden
“The Bernard Diagram [..] allows to distinguish between bacterial, thermogenic and inorganic gases using molecular ratio of the lighter hydrocarbons and the isotopic ratio of methane carbon. The Mora well gas samples plot in the mixing trend between bacterial and thermogenic origins, similarly to Wilson well gas. [..] Comparing the isotopic ratio of CO2 and CH4 carbon (Figure 11), the values for the Mora gases indicate a mixed origin of the CO2 and methane from methyl fermentation to CH4 oxidation. Indeed, the low concentration of CO2 in gases is probably the result of subsurface oxidation of CH4 by micro-organisms. In the light of these results, we can conclude that the process by which methane was generated is bacterial, with a potential minor contribution from a thermogenic gas source (ethane?).