Research on the Reservoir Adaptability and Oil Displacement Mechanism of a New Soft Microgel Particle Dispersion System
Authors: Sun Zhe , Kang Xiaodong , Na Risu , Zhou Jun 
Published: September 2020

Abstract
Heterogeneity is the basic characteristic of reservoir, which seriously affects the overall development effect of oilfield. In order to solve this problem, a new flooding system, soft microgel, has been developed in recent years. Its field test has obtained obvious effect of increasing oil and decreasing water. However, the research on its reservoir adaptability and displacement mechanism are still in the initial stage. Therefore, this paper has carried out relevant research work and introduced the field test results.
Soft microgel particle dispersion is a heterogeneous system, composing of microgel particles and carrier fluid. In this paper, the microfluidic technology was used to simulate the particle separation phenomenon in the migration process of soft microgels. Guided by the theory of red blood cells in biological fluid mechanics, a mathematical model of concentration distribution of soft microgels in different channels was established. Furthermore, in order to explore its oil displacement mechanism and performance, micro and macro physical simulation experiments were carried out. Finally, its typical field application is introduced.
Results show that, the separation phenomenon between soft microgel particles and carrier fluid occurs when injecting into the core. That is, soft microgel particles first enter the larger channel with low seepage resistance, while fluid turns into the smaller channel to displace oil. Therefore, by the cooperation between microgel particles and carrier fluid, soft microgel particle dispersion can effectively expand sweep volume. Furthermore, soft microgel particles can migrate, be trapped, deform in the porous medium. Based on the resistance coefficient, residual resistance coefficient and plugging rate, the migration and plugging modes of soft microgels can be divided into 3 modes: efficient plugging, normal plugging and low efficiency plugging. In the normal plugging mode, soft microgels can not only adjust the profile effectively in the early stage of injection, but also migrate to the deep reservoir and improve the injection pressure. Also, 3D macroscopic physical simulation experiments show that soft microgels can moderately plug the high permeability layer and improve the displacement effect of low permeability layer, which finally achieve the goal of enhanced oil recovery. Furthermore, soft microgel particle dispersion has been applied in 8 different reservoirs, and has achieved remarkable effect of increasing oil. Taking JX6ZD as an example, the daily oil production in the pilot test area increased from 25t/d to 75t/d, and the water content decreased by 38%. Therefore, through the lab physical simulation and field tests, the progressiveness of soft microgel particle dispersion can be proved.
In this paper, the mechanism and performance of soft microgel particle dispersion are studied by a multidisciplinary approach. On this basis, the field test results are analyzed. The above research results provide theoretical basis and technical support for the popularization and application of soft microgel particle dispersion system.