Research On Sedimentary Facies And Distribution Of Oil & Gas In The Chang2-3 Oil & Gas Pools Of Triassic Yanchang Formation In Ansai Area

Ordos Basin is a polycyclic superposition basin as well as the largest sedimentary basin on land in China which possesses abundant oil & gas resources and has bright prospects in oil & gas exploration. It has been becoming one of the important tactical areas in oil & gas exploration and exploitation in China. The amount of oil & gas resources and the degree which it is proven will directly influence the development of China petroleum industry. Ansai oilfield is one important generative area of oil of Ordos basin. As two primary oil beds in Ansai oil field, Exploration and exploitation of Chang2-3 oil beds are significant. For the sake of deeply researching the rules of hydrocarbon accumulation and distribution, it is necessary to study sedimentary facies and distribution oil & gas in the Chang2-3 oil beds of Ansai oilfield.On the basis of the theories of sedimentary facies and petroleum geology, by means of geology investigations in the field and research indoors, combined with the data of geological background, lithological association, sedimentary structure, construction, geochemistry, reservoir, oil & gas testing and chemical analysis of organic compound, the paper research Chang2-3 oil beds rules of sedimentary subfacies, rules of distribution of stratum and sandstone, reservoir characteristics, shield of mud sediment, oil resources, the rules of accumulation and the distribution of oil and gas. The conclusions are listed as follows:Chang2 stratum is divided into 6 substratums. Chang3 stratum is divided into 4 substratums. The research systematically definite borderline between substratums and detailedly describe the characteristics of lithology and log displays of all substratums, which make divisions of substratums more rational and accurate establish the foundation for the studies of reservoir & waterflooding.Chang2 reservoir is braided river sediment and Chang3 reservoir is inner sediment in term of analytic result of plane configuration of sandstone, characteristics of lithology and log displays of all substratums, rate between sand and mud, the types of construction, sedimentary facies sequence of single well and granularity analysis. The characteristics of braided river sediment are that the watercouese sandbanks are main sediment. The ratio of thickness between sand and mud is beyond 1 in whole section, sometimes, even above 4. The characteristics of inner sediment are that floodplain sediment is correspondingly familiar, the ratio of thickness between sand and mud is close to 1.A majority of oil and gas of Chang2 reservoir come from the mudstone of Chang 1, not excluding the part from the mudstone of Chang4+5 and Chang7. The oil and gas of Chang3 reservoir come from the mudstone of Chang4+5 andChang7.The watercourse sand is dominating zones of hydrocarbon accumulation and distribution. The better combination between local construction and mud sediment in up-dip direction is the guarantee of oil and gas accumulation. The better the combination is, the higher the degree of enrichment is. The oil and gas resource has an effect on the degree of enrichment of oil and gas in Ansai area.The enrichment areas of oil and gas are predicted as follows: The advantaged areas of oil and gas accumulation in Chang3 reservoir locate the both sides of Sail53-Sai450, the western area which is confined by Sail75, Sail57 and Zhuan8, the southwest area of Yan51. The advantaged areas of oil and gas accumulation in Chang2 reservoir locate the south, the northeast and the north area of Sai413-Yan51, the east area of Sail50, the east area of Sail-Tannan411 and the inner area which is encircled by Sail59,Sail63 and Sail43.