Polymer flooding in high-temperature and high-salinity heterogeneous reservoir by using diutan gum

Abstract

Diutan gum, a biopolymer that has been widely used in cement and concrete industries, was introduced in this work to alleviate severe viscosity loss and the poor water solubility of polyacrylamide and its modified products in high-temperature and high-salinity reservoirs. Diutan gum is an exopolysaccharide secreted by sphingomonas. The rheological properties and capacity of diutan gum to enhance oil recovery in high-temperature and high-salinity heterogeneous reservoir (T = 130 °C, Total salinity = 223.07 g L−1, Vk = 0.93) was investigated and compared with those of two other kinds of biopolymer thickeners (xanthan and konjac gum), which are commonly used in oilfield development. The three biopolymers show pseudoplastic fluid properties in a steady-state rheological test: given the strong interactions in the double-helix structure of diutan gum, the number of the Newtonian zone and the shear rate of this zone are higher than the those of the two other biopolymers. The storage modulus (G′) of diutan gum are higher than its loss modulus (G″) in all the concentrations and frequencies measured through viscoelasticity tests. This result indicates that diutan gum exhibits remarkable elasticity in slow displacement speed while it seeping in porous media. The capability of establish flow resistance in high-permeability porous medium in high-temperature and high-salinity environment by three biopolymers was studied, and their viscosity and microscopic properties of injected and produced fluid were investigated to understand the reason why diutan gum can have good fluidity control ability. Oil displacement efficiency can be improved by the elasticity of the diutan gum even without an increase in displacement speed. The results of the oil displacement experiments in the heterogeneity model imply that diutan gum is more effective in improving the water injection profile of each layer than xanthan and konjac gum. The water channeling in the high-permeability layer is restrained, and the sweep ability of the displacement phase is improved. Furthermore, the effect of polymer flooding can be maintained for a long time. Under high-temperature, high-salinity and strong heterogeneity, diutan gum recovers 19.34% of original oil in place (OOIP). This value is higher than the values obtained with xanthan gum (14.15% OOIP) and konjac gum (8.60% OOIP). This finding implies that the diutan gum has great application potential in the development of high-temperature and high-salinity reservoirs with strong heterogeneity.