The Development And Distribution Of The Reservoir Sandstones In The Chang 4+5 And Chang 6 Oil-bearing Beds In The Tayagou Oil Field, Zichang, Shanbei

Tayagou area is located in the middle east of Shanbei slope of Ordos Basin. The Chang 4+5 and Chang 6 oil-bearing beds of the Upper Triassic Yanchang formation are the main oil producing bed in the Tayagou oil field. According to the characters of lithology, electricity and oilness, the Chang 4+5 and Chang 6 oil-bearing beds are subdivided into Chang 4+5~1, Chang 4+5~2, Chang 6~1,Chang 6~2 and Chang 6~3. And in sequence stratigraphic unit was subdivided according to the temporal rock marks.According to the analysis of the facies marks, such as lithology, sedimentary structure, fossils, logging facies and other marks in the study area, the analysis of the facies shows that the Chang 4+5 and Chang 6 oil-bearing beds are a delta sedimentary system, including front-delta and delta plain and the main sedimentary facies is front-delta. The sedimentary microfacies include distributary channel, interdistributary despoits and distributary mouthbar and so on, and the main sedimentary microfacies are distributary channel and interdistributary despoits.On the basis of the former data, by Sequence stratigraphy , Yanchang formation in the study area is identified 4 kinds of sequence boundaries. And on the basis of the dividing sequence boundary, it is identified 3 kinds of different base-level cycles. They are 22 short-term cycles, 4 medium-term cycles and 2 long-term cycles. The development and distribution of the reservoir sandstones in these cycles are different.The study show that: feldspathic sandstones is the mainly reservoir sandstone of Chang 4+5 and Chang 6 oil-bearing beds in the study area. Generally speaking, the reservoir is the one with low porosity and low permeability. The porosity is mainly the kind of intergranular pore and intragranular dissolved pore. The pore structure types are fine throat-small pore and micro-fine throat-small pore. The reservoir shows stronger unhomogeneity in the study area. Analyzing the controlling factors to reservoir, the result shoes that sedimentary microfacies and diagenesis are the main factors of controlling and affecting distribution of reservoir in the study area.