Technology Highlights
Theory of Abyssal Abiotic Petroleum Origin: Challenge for Petroleum Industry
Geological Evidences
There are a number of the geological data which don’t find a satisfactory explanation in the established biotic hypothesis of petroleum origin and which can only be explained by the theory of the abyssal abiotic petroleum origin. Let’s discuss the two most important of them.
Giant and super-giant petroleum deposits.
One of the main problems with the traditional biotic petroleum origin hypothesis is the determination of biotic sources for most of super-giant oil and gas fields. The estimated “in place” oil reserves of Saudi Arabia are 127⋅109 m3 (Worldwide, 2006). Areas within sedimentary basin where the kerogen is mature have been identified using an atomic H/C ratio between 0.8-1.3, and mapped (Ayres et al. 1982). Calculating the areas of mature organic source rock zones and multiplying this with the thickness of the zones give the volume of the petroleum source rocks as 5000 km3 approximately. It can be considered that the transformation ratio of kerogen into bitumen is around 15% and only 5-10% of this bitumen has been expelled from the petroleum source rocks. Therefore, we have enough data to calculate the volume of oil expelled from the source rock. The volume of petroleum source rock is equal to 5000 km3; volume of kerogen is 500 km3 (10 % of the petroleum source rocks volume); the volume of bitumen is 75 km3 (15 % transformation). If we accept that the migration coefficient is equal to 10 % the volume of migrated bitumen (i.e., oil) will be equal to 7.5⋅109 m3. Therefore, only 7.5⋅109 m3 of oil could migrate out of the petroleum source rocks, but this is less than 6 % of Saudi Arabia’s estimated “in place” oil reserves. Where did 94 % of Saudi Arabia’s recoverable oil come from? Something similar can be observed in the Bolivar Coastal oil field in Venezuela. According to Bockmeulen et al. (1983) the source rock here is the La Luna limestone of the Cretaceous age. Initial “in place” reserves of oil are equal to 32⋅1012 m3 of oil with a density of 820-1000 kg/m3. Kerogen transformation into bitumen here is about 10 % of volume, migration and accumulation capacity of the bitumen is about 5 % of the volume. In other words, 1 m3 of the oil-generating rock contains 2.5⋅10-2 m3 of kerogen which can generate 2.5⋅10-3 m3 bitumen, giving 1.25⋅10-4 m3 of oil within the accepted geochemical model of biotic petroleum origin. If this oil-generating potential and the 32⋅1012 m3 initial total oil reserves of the Bolivar Coastal field as a starting point, the necessary volume of oil source rock would be equal to 2.54⋅1014 m3. This is consistent with the oil-generating basin area of 570 km across if the oil source rock is 1,000 m thick. However, the average thickness of La Luna limestone is only 91 m (Bockmeulen et al. 1983) and so the diameter of the oil-generating basin would therefore be equal to 5,700 km. In this case the area of the oil-generating basin should be 28 times more than the territory of Venezuela.
A sufficient biotic source for the two previously mentioned areas is unknown. At the same time, it is well-known that the sedimentary basins of these areas are located on a crystalline basement which is dissected by a network of deep faults and cracks. It is also known that oils from these fields have a genetic relationship, i.e. the single common source. A presence of deep faults under giant and super-giant petroleum deposits, and a genetic relationship of petroleum from each area correspond to the basis of the theory of abyssal non-biotic petroleum origin: mantle fluids were migrated through deep faults and cracks in the crystalline basement, then penetrated into the sedimentary rocks and created giant and super-giant petroleum deposits.
Deep and ultra-deep petroleum deposits.
There are more than 1000 commercial petroleum fields producing oil and/or natural gas from sedimentary rocks at the depths of 4500-10,428 m. These fields were discovered in 50 sedimentary basins throughout the world.
The most important and significant achievements with ultra-deep petroleum exploration have been made in the deepwater portion of Gulf of Mexico, U.S.A. 20 ultra-deep oil and gas fields have been found there at the depth of 8000-10,428 m (Blackbeard, Caesar, Cascade, Chinook, Das Bamp, Genghis Khan, Jack, K-2 North, Llano, Mensa Deep, Notty Head, Ozona Deep, Pathfinder, Pony, S.Malo, Shenzi, Stones, Tahiti, Thunder Horse North, Thunder Horse South). Their petroleum reservoirs occur predominantly in the turbiditic sandstones of the Oligocene, Eocene, and Paleocene ages. The petroliferous area where the above-mentioned submarine fields were discovered is equal to 40⋅103 km3. Its recoverable reserves of oil is evaluated from 1430⋅106 to 2385⋅106 m3. This is 42-70 % of the total recent proven oil reserves in the U.S.A. (January 1, 2007). Data is taken from following sources: (Henderson 1998), (ChevronTexaco 2004), (Anadarko 2005).
Presence of deep and ultra-deep petroleum deposits at depths of more than 6 km does not correspond correctly with the biotic hypothesis. This hypothesis suggests that petroleum reserves should be significantly reduced with depth and increasing reservoir temperature due to the destruction of hydrocarbons and the reduction of the reservoir porosity. A presence of more than 1000 petroleum deposits at depths of 5-10 km over the world rejects this point of view and can be rigorously and unambiguously explained by the theory of abyssal non-biotic petroleum origin.