Influence of source-reservoir contact conditions on the enrichment of near-source tight oil: taking Chang 81 reservoir in the Longdong area of Ordos Basin as an example

Abstract

The geological characteristics of tight oil have been relatively well understood, but there are certain questions needed to be answered regarding the distribution of tight oil. With comprehensive analysis of core, well logging and physical properties, and by means of mathematical calculation, the effects of the source-reservoir contact conditions on the enrichment of near-source tight reservoir of the first section of the eighth member of Yanchang Formation (Chang 81) in the Longdong area of Ordos Basin were studied in this paper. Results show that the source-reservoir contact conditions can be classified as four types including direct contact, transitional contact, fracture connected, and mudstone barrier. Among them, the direct contact and fracture connected types are favorable for the migration and accumulation of tight oil, while the transitional contact and mudstone barrier types have an obvious barrier effect for the migration of tight oil. The oil wells in the Chang 81 member in the Longdong area are mainly located in regions with a thickness of mudstone barrier less than 4 m, while the water or dry wells are mainly located in regions with a mudstone barrier thickness greater than 4 m. Based on the above calculation, it can be concluded that the source-reservoir contact condition determines the enrichment and vertical migration distance of tight oil. For the exploration of near-source tight oil, not only the "sweet zone" of the reservoir is conducive, the type of the source-reservoir contact condition should also be considered as a key factor.

Keywords

• source-reservoir contact relationship
• enrichment mechanism
• tight oil
• yangchang formation
• triassic
• ordos basin