Geological Structure Map
A: First of all, there were relatively few species and numbers of organisms in the Ordovician period. At that time, most of the oceans were on the surface of the land. After the organisms died, they were easy to be oxidized and difficult to form the organic matter needed for oil generation.
Secondly, the Ordovician strata are old, experienced many geological events, and been damaged seriously.
2) Throughout the world, Ordovician oil and gas resources are mainly gas, but why can oil be found in the Ordovician of Tarim Basin?
A: The Ordovician is relatively ancient and deeply buried. After the reservoir is deeply buried, the temperature is high, the organic matter evolution is high, and it is easy to become gas. However, Tarim Basin is a "Cold Basin", that is, the increasing degree of geotemperature is low, and the evolution degree of source rock is not high.
3) Has there ever been a large oil and gas reservoir (field) in Silurian of Tarim Basin?
A: Yes, the Silurian System in the Tarim Basin once had the formation of large oil and gas reservoirs (fields), as evidenced by the large-scale distribution of asphalt found in the Silurian System by drilling. However, the large oil and gas reservoirs (fields) formed in the early stage were later uplifted from the ground due to intense crustal movement, such as strong structural compression, and at the same time, the surface fractures occurred. After contacting with the atmosphere and fresh water, the oil layer is biodegraded and destroyed.
4) At present, 50% of the natural gas production in Sichuan Basin comes from Carboniferous. Are these gases of Carboniferous origin?
A: There are at least 2 sets of regional source rocks of Cambrian and Silurian under Carboniferous in Sichuan Basin. These 2 sets of source rocks have produced a lot of natural gas. However, due to the lack of reservoirs in the source rock series, i.e. the lack of oil storage places, the gas is sent to the "warehouse" of the Carboniferous system just like there is no warehouse in the factory. Therefore, most of the natural gas from Carboniferous is actually contributed by Silurian or Cambrian. In addition, the Cambrian and Silurian have good air drying conditions, and some gas remains, that is, Shale Gas, our key exploration object in Sichuan today.
5) From a geological point of view, why does the Triassic System in Ordos Basin appear the phenomenon of "Well see oil, well do not flow"?
A: some scholars have shown that the Ordos Basin reached the maximum burial depth in the early Cretaceous, during which a large number of oil and gas resources were formed and discharged into the Triassic Strata. Therefore, the Triassic oil and gas resources in the Ordos Basin are considerable, thus forming the scene of "Oil from Wells". However, after the formation of oil and gas resources, Iron Carbonate Cement and so on led to the densification of the Triassic Reservoir, resulting in the inability of oil and gas to flow in the reservoir, so there was a phenomenon of "No flow of wells and wells".
6) Jurassic is not only rich in oil and gas resources, but also the main coal forming period. Are coal and oil and gas "Close Relatives"?
A: There are countless connections between coal and oil and gas. For example, the coalbed methane in unconventional oil and gas resources is the natural gas generated and stored in the coalbed. Coal formed oil and gas resources in many basins in China are also evolved from coal. Therefore, coal itself can partly generate oil and gas to a certain extent. However, there are essential differences between them. The material sources of oil and gas are mainly microorganisms and algae, while the material sources of coal are mainly terrestrial plants.
7) The Middle East is rich in Jurassic oil and gas resources, but the Turpan Hami Basin is not rich in China. Why is the distribution of Jurassic oil and gas resources "Uneven between the rich and the poor"?
A: The Jurassic in the Middle East is mainly Marine Sedimentation, with relatively simple geological conditions, less intense crustal activity, good porosity and permeability of reservoir, and rich oil and gas resources. The Turpan Hami Basin is a Continental Sedimentation with complex geological conditions, strong tectonic activity and relatively poor oil and gas resources.
8) The Cretaceous System is the main source oil layer of large-scale oil fields. It has not only produced marine oil fields in the Middle East and other regions, but also produced continental oil fields such as Daqing in China. Why is the Middle East Marine and the East China Continental?
A: In the Cretaceous, the Middle East was still a vast ocean, while in the Eastern part of China, the sea had risen and retreated, leaving only some lakes and rivers. Therefore, the Middle East is Marine Sedimentation, while China is Continental Sedimentation.
9) Why does Cretaceous Generate more oil than natural gas in China?
A: The Cretaceous source rocks in China are relatively shallow, and the maturity of organic matter is not high, just in the stage of a large number of oil generation. Therefore, a large amount of oil is formed in this period, while natural gas will be generated in a relatively high maturity period of organic matter.
10) Why the Bohai Bay Basin is not rich in Jurassic and Cretaceous oil and gas, but in Tertiary oil and gas resources?
A: the Bohai Bay area was uplifted by the subduction of the Pacific plate in the Jurassic and Cretaceous, and suffered from denudation. In Jurassic and Cretaceous, the Bohai Bay area did not form effective source rocks due to the lack of deposition. In the tertiary, the Bohai Bay area entered an important basin forming period, formed effective source rocks and formed effective traps in the tertiary, so the tertiary oil and gas resources of the Bohai Bay Basin are rich.
This article is excerpted from the Internet.
If you have any questions, please contact the editor.