Theories explaining the origin of petroleum as ABIOTIC, however, ARE GENERALLY NOT WELL ACCEPTED by the SCIENTIFIC COMMUNITY,and are rejected by most researchers and scientific theories on the subject.
Some abiogenic hypotheses have proposed that OIL and GAS DID NOT ORIGINATE FROM FOSSIL DEPOSITS,but have INSTEAD ORIGINATED from DEEP CARBON DEPOSITS,present since the formation of the Earth
The abiogenic hypothesis regained some support in 2009when researchers at the Royal Institute of Technology (KTH) in Stockholm reported they believed they had proven that FOSSILS FROM ANIMALS and PLANTS ARE NOT NECESSARY for crude OIL and natural GAS to be generated.
The abiotic hypothesis is that the full suite of hydrocarbons found in petroleum can either be GENERATED in the MANTLE BY ABIOGENIC PROCESSES, OR BY BIOLOGICAL PROCESSING of THOSE ABIOGENIC HYDROCARBONS,and that the source-hydrocarbons of abiogenic origin can migrate out of the mantle into the crust until they escape to the surface or are trapped by impermeable strata, forming petroleum reservoirs.
Abiogenic hypotheses generally REJECT the SUPPOSITION that CERTAIN MOLECULES FOUND WITHIN PETROLEUM, KNOWN AS BIOMARKERS, are INDICATIVE of the BIOLOGICAL ORIGIN of PETROLEUM.
They contend that these molecules mostly come from microbes feeding on petroleum in its upward migration through the crust, that some of them are found in meteorites, which have presumably never contacted living material, and that some can be generated abiogenically by plausible reactions in petroleum
Thomas Gold’s work was focused on hydrocarbon deposits of primordial origin.
The thermodynamic CONDITIONS WITHIN THE MANTLEwould allow many hydrocarbon molecules to be at equilibrium under high pressure and high temperature. Although molecules in these conditions may disassociate, resulting fragments would be reformed due to the pressure.
CREATION WITHIN the MANTLE
Russian researchersconcluded that hydrocarbon mixeswould be created within the mantle. Experiments under high temperatures and pressures produced many hydrocarbons – including n-alkanes through C10H22– from iron oxide, calcium carbonate, and water.
Because such materials are in the mantle and in subducted crust, there is no requirement that all hydrocarbons be produced from primordial deposits.
Occurrences of abiotic petroleum in commercial amounts in the oil wells in offshore VIETNAMare sometimes cited, as well as in the Eugene Island block 330 oil field, and the Dnieper-Donets Basin.
HOWEVER, the origins of all these wells CAN ALSO BE EXPLAINED with the biotic theory.
Modern geologists think that commercially profitable deposits of abiotic petroleum COULD BE FOUND, BUT NO CURRENT DEPOSIT HAS CONVINCING EVIDENCE THAT IT ORIGINATED from ABIOTIC SOURCES.
The Soviet school of thought saw evidence of THEIR HYPOTHESIS in the FACT THAT SOME OIL RESERVOIRS EXIST IN NON-SEDIMENTARY ROCKS such as granite, metamorphic or porous volcanic rocks.
However, OPPONENTS noted that NON-SEDIMENTARY ROCKS SERVED AS RESERVOIRS FOR BIOLOGICALLY ORIGINATED OIL EXPELLED FROM NEARBY SEDIMENTARY SOURCE ROCK through common migration or re-migration mechanisms.
The following observations have been commonly used to argue FOR the abiogenic hypothesis, however each observation of actual petroleum can also be fully explained by biotic origin
Given the known occurrence of methane and the probable catalysis of methane into higher atomic weight hydrocarbon molecules, various abiogenic theories consider the following to be KEY OBSERVATIONS IN SUPPORTof abiogenic hypotheses:
- the serpentinite synthesis, graphite synthesis and spinel catalysation models prove the process is VIABLE
- the likelihood that abiogenic oil seeping up from the mantle is trapped beneath sediments which effectively SEAL mantle-tapping faults
- outdated[mass-balance calculations[ for supergiant oilfieldswhich argued that the calculated source rock could not have supplied the reservoir with the known accumulation of oil, implying deep recharge.
- the presence of hydrocarbons encapsulatedin diamonds
The PROPONENTSof abiogenic oil also use several arguments which draw on a variety of natural phenomena in order to support the hypothesis:
- the modelingof some researchers shows the Earth was accreted at relatively low temperature, thereby perhaps preserving primordial carbon deposits within the mantle, to drive abiogenic hydrocarbon production
- the presence of methanewithin the gases and fluids of mid-ocean ridge spreading center hydrothermal fields.
- the presence of diamond within kimberlites and lamproites which sample the mantle depths proposed as being the source region of mantle methane (by Gold et al.).
Oil deposits are not directly associated with tectonic structures.
ARGUMENTS AGAINST CHEMICAL REACTIONS, such as the serpentinite mechanism, being a source of hydrocarbon deposits within the crust include:
- the lack of available pore space within rocks as depth increases.
- this is CONTRADICTED by numerous studies which have documented the existence of hydrologic systems operating over a range of scales and at all depths in the continental crust.
- the lack of any hydrocarbon within the crystalline shield areas of the major cratons, especially around key deep-seated structures which are predicted to host oil by the abiogenic hypothesis. See Siljan Lake.
- LACK of CONCLUSIVE PROOF[THAT CARBON ISOTOPE FRACTIONATION OBSERVED in CRUSTAL METHANE SOURCES IS ENTIRELY of ABIOGENIC ORIGIN(Lollar et al. 2006)
- drilling of the Siljan Ring failed to find commercial quantities of oil, thus providing a counter example to Kudryavtsev’s Rule and failing to locate the predicted abiogenic oil.
- helium in the Siljan Gravberg-1 well was depleted in 3He and not consistent with a mantle origin
- Kudryavtsev’s Rule has been explained for oil and gas (not coal) – gas deposits which are below oil deposits can be created from that oil or its source rocks.
Because natural gas is less dense than oil, as kerogen and hydrocarbons are generating gas the gas fills the top of the available space. Oil is forced down, and can reach the spill point where oil leaks around the edge(s) of the formation and flows upward. If the original formation becomes completely filled with gas then all the oil will have leaked above the original location.
- ubiquitous diamondoids in natural hydrocarbons such as oil, gas and condensates are composed of carbon from biological sources, unlike the carbon found in normal diamonds.