Oil recovery mechanism

Yang, P.-H., et al., 1992. Oil recovery mechanisms of alkaline/polymer flooding. Paper presented at the Second and Tertiary Recovery Symposium, Chengdu. 

Some of this mobility control and improvement in sweep could be due to the emulsions formed diich exhibit a higher bulk viscosity. Some work by Wasan et al (32) has shown that the sodium silicates will result in emulsions with lower shear or interfacial viscosities than sodium hydroxide. These lower interfacial viscosities at the micro-level help promote oil coalescence so that oil banking can occur and oil droplets are not retrapped and left behind. The oil banking and rapid emulsification on the macro-level or in the bulk help to give good mobility control. Also some recent work by Wasan has indicated that the silicates tend to keep the surfaces more water-wet, thereby inproving recovery. It has been noted that the thickness of the water film on quartz surfaces is thicker when silicates are present. Further work in these areas is currently being done to determine the limits and effects on the oil recovery mechanisms. 

Alkaline flooding (AF) is a chemical process used in the Petroleum Industry to remove oil from pore walls and to mobilize the mechanically entrapped oil globules or ganglia in porous media. Among all the enhanced oil recovery (EOR) processes, the AF is one of the most complicated and least understood due to its complex oil recovery mechanisms. 

The reactions between the alkaline solution and reservoir oil generate the complex oil recovery mechanisms of AF postulated to date (1) in-situ surfactant generation by neutralization (saponification), (2) reduction of the interfacial tension (IFT) at the oil-water interface, (3) temporary wettability alteration, (4) emulsification with entrainment, (5) emulsification with entrapment, (6) emulsification with coalescence, (7) oil phase swelling, and (8) breaking out the rigid films. Thus, the consumption of alkalinity through the reactions of alkaline solution with reservoir waters and rock constituents has been accepted as the most important disadvantage of the AF process. ... 

FIG 4 OIL RECOVERY MECHANISM FOR POLYMER FLOODING OF HETEROGENEOUS SYSTEMS... 

Ahmed, T. 2010. Reservoir Engineering Elandbook, 4th ed. Boston Gulf Professional Publishers. This book explains the fundamentals of reservoir engineering and their practical applications in conducting a comprehensive field study (from Preface, p. xv). Divided into 17 chapters., the coverage includes reservoir fluid behavior and properties, fundamentals of reservoir fluid flow, oil and gas well performance, oil recovery mechanisms, and methods for the prediction of oil reservoir performance. 

Central to all polymer oil recovery mechanisms, however, is the idea of mobility ratio, M, defined as ... 

Here the mathematical and experimental aspects of linear flooding will be considered. In this case, the only polymer flooding mechanism that may operate is the improved microscopic displacement that is possible when a lower viscosity drive water displaces a more viscous oil. First a simple mathematical fractional flow approach to analysing the improved oil recovery mechanism will be examined. Results from corresponding 1-D oil displacement experiments using water and polymer flooding are then presented in order to illustrate some of the points that arise. 

However, the cross-flow of oil accounts for only a small fraction of the total incremental oil production, so that the overall profile for kjk = 0.1 is similar to the case of kjk = 0.001. It appears that the vertical permeability has to be extremely low (k < 0.001 kj in order to eliminate effectively the oil recovery mechanism. 

In order to make pore blocking an effective oil recovery mechanism, the residual resistance factors must be greater in the high-permeability zone than those estimated for the biopolymer. However, if the residual resistance factors... 

Thus, when considering the required stability limits of a polymer for field application, the actual timescale of operation of the polymer oil recovery mechanism must also be examined. Obviously, this is also related to the physical size of the reservoir system and the planned injection/production rates. However, it should again be stressed that a careful analysis of the recovery mechanism may assist in the polymer design tolerances associated with chemical degradation. As a final practical comment on this matter, it is still recommended that, in field applications, the most stable available polymers should be used which can also achieve other design specifications. 

For a heterogeneity control polymer flood, since the recovery mechanism is 2-D in nature (cross-flow), it is simply not present in an oil displacement experiment in a 1-D reservoir core. Therefore, nothing can be learned from polymer flooding field cores if this is the proposed oil recovery mechanism in the pilot flood. Indeed, this could be positively misleading, since the local (linear) mobility ratio in the system could be close to unity and a waterflood... 

The polymer concentration and salt content in the produced fluid have the function of tracers and are capable of describing the displacement and other oil recovery mechanisms. 

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