Study of the Mechanism of Polymer Solution With Visco-Elastic Behavior Increasing Microscopic Oil Displacement Efficiency and the Forming of Steady "Oil Thread" Flow Channels

Abstract

In this paper, the visco-elastic characteristics of polyacrylamide solution have been studied experimentally. The mechanisms of the effect of polymer solution with visco-elastic characteristic on each type of residual oil after water flooding are analyzed and the mechanisms of polymer solution with visco-elastic characteristic increasing microscopic oil displacement efficiency are studied. By the analysis of microscopic experiments of percolating flow, corresponding relationships between the characteristic parameter describing the visco-elastic behavior of polymer solution and displacement efficiency of residual oil in "dead ends" are given. It is shown that the larger the visco-elastic behavior of polymer solution, the higher the displacement efficiency of residual oil in "dead ends". A phenomenon that is not seen during water flooding is observed during polyacrylamide solution flooding in the microscopic experiment of percolating flow, that is, residual oil can be pulled into "oil threads" by the polyacrylamide solution. So a new type of oil flow channel, i.e. "oil thread" channel, can be formed and residual oil flows downstream through the "oil thread" channel. The probability of forming a steady "oil thread" flow channel in polymer flooding is also analyzed theoretically and proved. The research indicates that the mechanism of polymer solution microscopically increasing oil recovery is due to the visco-elastic characteristic of the polymer solution, the sweeping force acting on the residual oil for the visco-elastic polymer solution is larger than that of water. The residual oil is not pushed out by the polymer solution but pulled out by the polymer solution. It is also found that every type of residual oil after water flooding can be decreased by visco-elastic polymer solution, and the larger the visco-elastic property, the stronger the capability of the polymer solution to "sweep out" the residual oil. In brief, the results indicate that polymer flooding can not only macroscopically increase the sweep efficiency but also microscopically increase the oil displacement efficiency and a new type of flow channel, "oil thread", can also be formed. Besides new understanding on the mechanism of the flow of fluid through porous media and the displacement of residual oil, the above results should be beneficial to designing new EOR methods to further increase the recovery of oil fields. Introduction In the field of petroleum engineering, it has long been believed that the mechanism of polymer flooding in EOR is to improve the mobility ratio and macroscopically enhance sweep efficiency. However, the knowledge about the microscopic oil displacement mechanism of polymer solution is insufficient. Concerning the mechanism of polymer flooding, there are many different views. One is that injecting water with a certain viscosity has the same ultimate residual oil saturation as conventional water flooding, polymer flooding can not decrease the residual oil saturation within the sweeped area, and another is that the mechanism of polymer enhancing oil recovery is rather complex, and not yet understood completely so far[1]. In fact, the researches are far from perfect about the percolation flow behavior of polymer solutions in porous media, especially its microscopic physicochemical filtration flow rule. So it is necessary to further study the mechanism of polymer solution increasing the microscopic oil displacement efficiency.

A review on applications of nanotechnology in the enhanced oil recovery part A: effects of nanoparticles on interfacial tension

“…Currently, polymer flooding is considered as one of the most promising technologies in EOR process because of its technical and commercial feasibility. Particularly, the interest on polymer flooding applications worldwide has been stimulated by the outstanding results reported from the large-scale polymer flooding application in the Daqing oil field in China, with incremental oil productions of up to 300,000 barrels per day [47].…”

Use of Polymers to Recover Viscous Oil From Unconventional Reservoirs

“…However, for conditions associated with the Daqing reservoir, researchers (Wang et al 2000, 2001a, 2001b, Xia et al 2004, Wu et al 2007) argued that HPAM solutions reduced S or by 6 to 15 saturation percentage points, even with waterfloods and polymer floods conducted at the same constant capillary number. Notably, Wu et al (2007) observed that HPAM polymers reduced the waterflood S or by up to 15 saturation percentage points (i.e., a S or of 36.8% with waterflooding versus 21.75% for polymer flooding) using a constant capillary number of 5x10 -5…”

Aperture-Tolerant, Chemical-Based Methods to Reduce Channeling

“…138 Furthermore, they impart greater solution viscoelasticity, which provides higher oil recoveries and lower residual oil saturations under Daqing conditions. 139 From the two pilot tests 140 at Daqing (specifically, at areas called "West of Center" and "4-4# Station of the Northwest in Lamadian"), the following observations were noted: (1) Water intake profile was improved after injecting higher polymer concentrations. (2) During polymer flooding, the period of relatively low water cuts can be prolonged by injecting higher polymer concentrations.…”