Oil & Gas Geology ›› 2013, Vol. 34 ›› Issue (5): 631-639.doi: 10.11743/ogg20130508

• Petroleum Geology • Previous Articles     Next Articles

Accumulation conditions and characteristics of the Chang 7 tight oil reservoir of the the Yanchang Formation in Zhidan area,Ordos Basin

Bai Yubin1,2, Zhao Jingzhou1,2, Zhao Zilong1, Yin Yueyue1, Tong Jiangnan1   

  1. 1. School of Earth Sciences and Engineering, Xi'an Shiyou University, Xi'an, Shaanxi 710065, China;
    2. Key Laboratory of Shaanxi Province for Oil and Gas Accumulation Geology, Xi'an Shiyou University, Xi'an, Shaanxi 710065, China
  • Received:2013-03-31 Revised:2013-08-15 Online:2013-10-08 Published:2013-10-08

Abstract:

Through integration of geological and geochemical data,this paper comprehensively analyzed the conditions,main controlling factors and characteristics of oil accumulation in the Chang 7 tight oil reservoir from such aspects as the tight oil distribution,physical properties,geochemical features of the oil source,reservoir characteristics and heterogeneity,trap conditions,and oil and water distribution.The following results were obtained.The Chang 7 tight oil reservoirs own the geological conditions and characteristics for the formation of quasi-continuous oil and gas accumulation.The Chang 7 reservoir interval contains high-quality source rocks,of which the Zhangjiatan shale in the Chang 73 layer is the best one.The outer boundary of the tight oil reservoirs is controlled by the distribution of the source rocks.The favorable area of hydrocarbon accumulation occur in where the thickness of hydrocarbon source rocks is over 20 m.The Chang 7 tight oil accumulation has favorable source-reservoir-seal assemblages and the gravity flow sandbodies occur in the mudstone or source rocks mainly in lenticular or stripped shapes,thus are advantageous in trapping oil and gas.The importance of trapping conditions is relatively low for the accumulation of oil in the Chang 7 tight reservoir,as the main seals are lithological,physical property and diagenesis boundaries.Dynamic trap is also an important trap type.Oil enrichment in the Chang 7 tight reservoir has no direct relationship with the local tectonic background,instead is mainly controlled by reservoir distribution and their physical properties.The high intensity of hydrocarbon generation,expulsion and charging results in the relatively high original oil saturation in the Chang 7 reservoir.Due to the influences of the origin material composition and diagenetic intensity,the Chang 7 reservoir is of strong heterogeneity,resulting in the poor differentiation of oil,gas and water,and a complicated oil-water contact in the tight reservoir.

Key words: accumulation condition, accumulation characteristics, tight oil, Yanchang Formation, Zhidan area, Ordos Basin

CLC Number: