How are gas deposits classified

Natural resources, which have enabled rapid development of modern civilization, were formed in the Cretaceous period of the Mesozoic Era. The process started between 145 and 146 million years ago and ended 65 million years ago. At the global scale, it is a very short period of time, because according to current scientific data, the Earth is between 4.5 and 4.6 billion years old.

The mankind is about 200 thousand years old. Gas production started only in the last century.

Mesozoic Era (251–65 million years ago)
145–65 million years ago

Cretaceous period

It was during the Cretaceous period, which lasted 80 million years, when the largest animals in the history of the Earth – dinosaurs – lived. We also know that the largest extinction of these animals occurred at the end of the Cretaceous period. Scientists are still arguing why it happened. Meanwhile, one of the leading theories now is the biogenic theory of fossil fuel formation.


Biogenic theory

As to the origin of natural gas (as well as oil), there is still no consensus among scientists. Two main concepts – biogenic and mineral – claim various reasons for fossil fuel formation in the Earth’s interior.

По мнению ученых, According to scientists holding to the biogenic theory of oil and gas formation, living organisms, dead and sank to the bottom of water bodies, decomposed in vacuum. Sinking deeper and deeper because of geological movements, the remains of decomposed organisms under heat and pressure turned into a fossil fuel, particularly natural gas.

Stages and substages

Knowing with what rock we are dealing with, we can assume what natural resources, in what quantities and conditions it contains. Gas deposits (stages and substages) are named according to the intervals of the Cretaceous period.

Cretaceous period:

  • Maastrichtian
  • Campanian
  • Santonian
  • Coniacian
  • Turonian
  • Cenomanian
  • Albian
  • Aptian
  • Barremian
  • Hauterivian
  • Valanginian
  • Berriasian

Stages of the Cretaceous period were named after the settlements and castles, near which the deposits were found – mainly in France and neighboring Switzerland, the Netherlands and Denmark. In particular, the Coniacian stage is located above the Turonian deposits, just above – the Campanian stage (from the name of the Champagne province) – these names are known mainly due to alcoholic drinks traditionally produced in the area (cognac and champagne). It is an attractive possibility – to produce, for example, cognac gas, isn’t it?

Lithology is the science of sedimentary rocks and modern geological settlings, their material composition, structure, behavior, conditions of formation and change.

Turonian gas

Turonian gas is the youngest one – according to the age of occurrence and the production start in Russia. The Turonian stage (from the ancient name of the French city of Tours) is located at a depth of about 800 meters. These deposits feature heterogeneity and variability in lithology and in low permeability of reservoirs.

The main difficulty in their development is work at temperatures close to subzero. In Russia Turonian gas production started only in 2011.

Cenomanian gas

The Cenomanian gas deposits located below the Turonian ones are unique in size and are the easiest to extract. The Cenomanian stage got its name from the Latin name of the French city of Le Mans (Senomanum). Cenomanian gas deposits, located at the depth of 1,000 to 1,700 meters, are mainly the accumulation of methane and, therefore, do not require processing costs. The history of Russian gas production is primarily based on the Cenomanian gas.

‘Neuchatel’ can be translated from French as a ‘new castle’

Valanginian gas

Much lower, some stages after Cenomanian gas, which reserves are gradually being depleted, there is the Valanginian stage. It received the name after a Swiss castle. Valanginian gas located at the depth of 1,700 to 3,200 meters features a high content of ethane, propane and gas condensate. The Valanginian stage is part of the Neocomian superstage, which also includes Berriasian, Hauterivian and Barremian stages. The Neocomian stage has the Latin name of the Swiss canton of Neuchatel. The Berriasian stage is often regarded as the lower substage of the Valanginian stage. Then there are stages of the Jurassic period.

Achimov deposits

The Achimov deposits with significant gas reserves are still being explored. Achimov deposits are generally considered among the lower stages of the Neocomian period and even to the Jurassic period.

The Neocomian superstage (from Neocomium – the Latin name of the Canton of Neuch?tel, Switzerland), a division of the lower part of the Cretaceous period, initially deemed a lower stage of the Cretaceous system. After distinguishing the Berriasian, Valanginian, Hauterivian and Barremian stages from it, it is usually understood as a combining unit with the rank of superstage.

Achimov gas is contained in the formation with some 4,000 meter depth, more complex geological structure, abnormally high formation pressure and high content of heavy paraffins.