Characteristics and controlling factors of heavy oil distribution in Liaohe Depression, Bohai Bay Basin

Abstract

There are various types of crude oil in the Liaohe Depression, Bohai Bay Basin, among which heavy oil accounts for more than 50% of the oil and gas reserves and production. Therefore, it is of great significance for future exploration and development to study the main controlling factors of oil densification in the Liaohe Depression and to understand the distribution pattern of heavy oil. Based on the systematic understanding of heavy oil reservoir exploration and development in Liaohe oilfield for decades of years, and by aiming at the geological characteristics of heavy oil reservoirs such as "edge, shallow, unconsolidated, early, falling, loss, capping", this paper discusses the distribution and densification reasons of heavy oil from six aspects, including structural pattern, reservoir characteristics, reservoir burial depth, underground fluid, capping conditions, oxidation and biodegradation. The densification mechanism and controlling factors of heavy oil reservoirs in the Liaohe Depression are basically clarified. Through the study of heavy oil densification factors, it is found that structural pattern is the main factor controlling heavy oil distribution, geological conditions such as reservoir, burial depth, underground fluid and cap rocks are important factors controlling heavy oil densification, while biodegradation and oxidation are the keys for heavy oil densification. Oil and gas reservoirs accumulate around sags in the Liaohe Depression. There are three rings around the oil-generating sags from the inside to the outside. The inner zone is dominated by natural gas and condensate gas, and the buried depth is generally more than 3 500 m. The middle zone is dominated by light oil, partially enriched with natural gas and heavy oil, with a buried depth of 1 700-3 500 m. The outer zone is dominated by heavy oil, and the buried depth is generally less than 1 700 m.

Keywords

• heavy oil
• generation mechanism
• oil and gas distribution pattern
• controlling factors of densification
• oil and gas accumulate around depression
• liaohe depression
• bohai bay basin