Study on remaining oil distribution after polymer flooding using logging data

Precise prediction of remaining oil distribution after polymer flooding is the key to explore the 40% remaining reserves in the post-polymer flooding reservoirs of Daqing Oilfield.In this paper,longitudinal production degree of single wells are calculated through using a lot of logging data that show the development status in late water flooding and polymer flooding separately.With signals representing different saturation intervals labeled on the diagram of sedimentary microfacies,probability distribution curves of remaining oil saturation of different microfacies are mapped to study the remaining oil distribution after polymer flooding.Results show that after polymer flooding the displacement in longitudinal direction tends to be more uniform but the remaining oil at upper parts of thick oil layers is relatively high in proportion.On the vertical,the remaining oil after polymer flooding changes little on the parts of oil layers of small thickness and low permeability.The remaining oil profile becomes more uniform at upper parts of oil layers of huge thickness where still a lot of remaining oil exists.In the horizontal,the polymer flooding efficiency of the channel sandstone microfacies is better than that of the non-channel sandstone microfacies.Remaining oil is mainly distributed in the isolated facies and the dividing location of two facies as well as the area where permeability gets worse and the injection rate is low.The research provides the base for the exploration of the 40% remaining reserves in the post-polymer flooding reservoirs of Daqing Oilfield.