Characteristics of remaining oil viscosity in water- and polymer-flooding reservoirs in Daqing Oilfield

Abstract

The experimental analysis of 21 crude oil samples shows a good correlation between high molecular-weight hydrocarbon components (C 40 + ) and viscosity. Forty-four remaining oil samples extracted from oil sands of oilfield development coring wells were analyzed by high-temperature gas chromatography (HTGC), for the relative abundance of C 21 − , C 21 -C 40 and C 40 + hydrocarbons. The relationship between viscosity of crude oil and C 40 + (%) hydrocarbons abundance is used to expect the viscosity of remaining oil. The mobility characteristics of remaining oil, the properties of remaining oil, and the next displacement methods in reservoirs either water-flooded or polymer-flooded are studied with rock permeability, oil saturation of coring wells, etc. The experimental results show that the hydrocarbons composition, viscosity, and mobility of remaining oil from both polymer-flooding and water-flooding reservoirs are heterogeneous, especially the former. Relative abundance of C 21 − and C 21 -C 40 hydrocarbons in polymer-flooding reservoirs is lower than that of water-flooding, but with more abundance of C 40 + hydrocarbons. It is then suggested that polymer flooding must have driven more C 40 − hydrocarbons out of reservoir, which resulted in relatively enriched C 40 + , more viscous oils, and poorer mobility. Remaining oil in water-flooding reservoirs is dominated by moderate viscosity oil with some low viscosity oil, while polymer-flooding mainly contained moderate viscosity oil with some high viscosity oil. In each oilfield and reservoir, displacement methods of remaining oil, viscosity, and concentration by polymer-solution can be adjusted by current viscosity of remaining oil and mobility ratio in a favorable range. A new basis and methods are suggested for the further development and enhanced oil recovery of remaining oil. remaining oil, viscosity, mobility ratio, water-flooding, polymer-flooding, heterogeneity, polymer-solution viscosity Citation: Xu Z S, Zhang J H, Feng Z H, et al. Characteristics of remaining oil viscosity in water-and polymer-flooding reservoirs in

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