The Urengoy oil, gas and condensate field located in the West Siberian basin is ranked among the top three largest onshore fields in the world. Its total geological reserves are estimated in the amount of 16 trillion cubic meters of natural gas. The field was discovered in 1966 and its development started in 1977. Gas production started in 1978. The work of gas workers is complicated by harsh natural and climatic conditions such as permafrost, freezing weather, tundra and the fragile ecosystem.
The Urengoy field extends from north to south for more than 230 km. It is 30 to 60 km wide and covers an area of about 6000 square km. Most of the field is located beyond the Arctic Circle. The currently developed sandstones are mainly related to the Upper Cretaceous period. They were formed 90 million years ago and lie at a depth of more than 1200 m. To minimize the impact on a sensitive ecosystem, the so-called pad drilling is used. One pad usually contains from two to seven wells.
The Urengoy Field includes three main horizons containing hydrocarbons: Cenomanian, Valanginian and Achimov.
Cenomanian deposits are located at a depth of 1,000-1,700 m. They are located below the Turonian deposits. They differ from the Valanginian deposits with a significantly lower content of ethane, propane and gas condensate. Cenomanian gas mainly consists of methane. It is the most easily extractable gas and requires minimum processing costs. In the development of Cenomanian deposits less deep wells and larger diameter tubing are used, as compared to the Valanginian deposits.
Valanginian (Neocomian) hydrocarbon deposits occur at a depth of 1,700-3,200 m. They differ from Cenomanian deposits with a significant content of ethane, propane and gas condensate. Valanginian deposits formed during the Neocomian period just like Berriasian, Hauterivian and Barremian deposits. The Berriasian deposit is often viewed as the bottom level of Valanginian deposits. The methods of gas and condensate production used at such deep occurrence require special well design (gas flow-line should also meet special requirements) and innovative technologies at gas treatment plants.
This gas contains heavy hydrocarbons; therefore, it has higher gas hydrate formation point. Gas extracted from these fields must be separated from water, mechanical impurities and its temperature needs to be reduced to 30 Сº below zero to obtain a final product of required condition. In the development of Valanginian deposits deeper wells and smaller diameter tubing are used, as compared to the development of the Cenomanian deposits. Gas flow-lines are designed to operate at a higher pressure.
The Achimov deposits occur at a depth of approximately 3,500-4,000 m and have much more complex geological structure, as compared to the Cenomanian (occurring at a depth of 1,100-1,700 m) and Valanginian (1,700-3,200 m) deposits. Other gas-bearing beds occur at a depth of more than 3,500 m. This relates to the Early Cretaceous Achimov deposits formed about 140 million years ago. Achim sandstones have medium porosity and quite low permeability. These deposits bear oil and gas and are widespread in Western Siberia and found in many fields.
AO Achimgaz is one of the active field operators. Licensed block 1А, with an area of 354,689 sq. km, where the company carries out its activity, is located in the south-eastern part of Urengoy oil, gas and condensate field, south of the Arctic Circle.