Study On High Resolution Sequence Stratigraphy And Prediction Of Low Resistivity Oil Reservoir In Minqiao Area

As the development of petroleum exploration gets further, the exploratary targets of many oilfields have turned from simple large-scale hydrocarbon reservoirs to multiple small-scale ones. Under these situation, the low resistivity reservoirs have become the main exploratary target of many oilfields, but due to middle and small scale of these sand bodies of fan delta front muitiple-layer are still not clear, which restrict the development of petroleum exploration.This thesis took the Third Member of Funning Formation in Minqiao area in Jinhu Depression as the study area which was typified with low resistivity reservoirs. Sedimentology tectonics and sequence statigraphy are applied in this paper. On basis of many data of drillings and observation wells, wo study the Third Member of Funning Formation by sequence strigraphy in Minqiao area in Jinhu Depression, the conclusions as follows:(1)The theory of high resolution sequence stratigraphy and classic stratigraphy of Vail′s is separately applied to divide the sequence stratigraphy in the study area. Comparison study of their advantage and disadvantage, we consider their difference is that the identification of sequence surface, the meaning on sediment of their basic stratigraphic cells and its reproducibility on large region, their fitting research object on sequence division and comparison. Through the comparison, we think that the theory of high resolution sequence stratigraphy is practicable to the oil and gas exploration of the study Area.(2)On basis of facies combination and facies-succesion, the identification model of base level with falling half cycle which is copmposed of shore-shallow muddy→delta front sand sheet→mouth bar→underwater distributary channel→interdistributary bay of delta front intrafacies, and the Third Member of Funning Formation of the study area is divided into three middle cycles of base level and then divided into twelve short cycles of base level. Based on these, the stratigraphic framework is built in the study area.(3)Based on short-term cycles, the paper discussed the distribution and evolution of the depositional facies in study area. Four types of depositional microfacies in the Third Member of Funing Formation of Min-qiao are recognized. They are underwater distributary channel, mouth bar, delta front sand sheet and interdistributary bay of delta front intrafacies. The vertical evolution of depositional microfacies has regularities, the underwater distributary channel and mouth bar were developed in the drop half cycle of MSC5 middle-term cycles and the transform interface of the middle-term cycles; the delta front sand sheet were developed in the drop half cycle of MSC4 middle-term cycles and the ascend half cycle of MSC5 and MSC6 middle-term cycles.(4)The reservoir of the Third Member of Funing Formation were mainly fine sandstone and siltstone, have high shale content. The pore is little throat size and mesoporosity. The reasons of low resistivity petroleum reservoir are small lithologic character, thin hydrocarbon reservoir and high bound water. Using the cross plot of acoustic logs and deep-induction resistivity, the criterion of recognition of low resistivity petroleum reservoir in Mingqiao area was established. The acoustic logs were more than 300μs/m, and the deep-induction resistivity distinguis from each other of the low resistivity reservoir in the study area.(5)After having analized the position of the discovered oil and gas in sequence stratigraphy, wo draw a conclusion comprehensively that underwater distributary channels and mouth bars are the most favvorable sandbody to the low resistivity reservoir exploration. The favorable members are in MSC5 with falling half cycle. Based on distribution disciline of reservoir sandbody and the recognition of low resistivity reservoir, wo propose four favorable exploration targets of low resistivity reservoir in the study area.