Polyacrylamide injection for enhanced oil recovery - CHINAFLOC
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Polyacrylamide injection for enhanced oil recovery
2015-04-03 09:09:11

In order to increase the percentage of oil that can be recovered in the oilfield, it has been implemented alternative techniques to improve the conditions of production and obtain higher ranks of recovery factors. The injection of polymers in the oilfield sweep efficiency improves increasing production in less time, which can be translated into lower costs for equipment use time surface, improving the economy of the process, provided that this is controlled under minimum standards of regularity. The properties of the polymers play a decisive role in the process efficiency.

Considering the factors favoring the polymer injection such as:

·Appropriate for water injection conditions.

·High movable oil saturation.

·High storage capacity.

Similarly, there are those factors considered unfavorable for the process.

·Extended fractures.

·Strong Push water.

·Layer gas.

·High permeability contrast.

·Highly saline formation water.

·Problem severe injectivity.

·High in swelling clays and calcium.

For the case study that can be conclude that theoretically factors are considered improved by injecting polymers and an increase in oil recovered 11.6% compared with the value obtained by water injection processes was obtained prior to the polymer injection project.

For the case study, it can be conclude the factors that theoretically are considered improved by injecting polymers and it was obtained an increase in the oil recovered 11.6% compared with the value obtained by water injection processes previous to the polymer injection project.

The mobility control is a generic term that describes any process that attempts to alter the relative rates to which injected and displaced fluids move through the oilfield. This is to improve volumetric sweep efficiency of the displacement process. Usually called in terms of proportion of mobility, M, and a displacement process that is considered to keep mobility control, if M ≤1.0. The volumetric sweep efficiency increases, if M is reduced.

Since it was unreliable change the properties of the fluid when this is displaced oil or rock permeability to fluid displaced, the most mobility control processes seek to add chemicals injected fluids. These chemicals increase the apparent viscosity of the injected fluid and / or reduce the effective permeability of the rock injected fluid. The chemicals used are primarily polymers injected when the fluid is water and lathering surfactants when the injected fluid is gas.

The sooner a project polymer, the better the performance will start.

Injection of polyacrylamide

The high molecular weight water-soluble polymers in dilute concentrations (ppm) significantly increase the viscosity of water by a factor of 10 to 50 and also reduces the relative permeability of the rock to the water, in other words decreases the rate of mobility of water to near unity or less. Thus, the volumetric sweep efficiency can be improved and can achieve a higher percentage of oil recovered a polymer injection process, however, the residual oil percentage remains constant for different viscosities, so that the improvement in oil recovery is that it is obtained earlier and with less water cut, therefore, in practice this translates into lower costs rising compared with water injection only.

In the polymer injection, higher polymer solution is injected into the oilfield with a previous injection of a pill low salinity brine (fresh water). The polymer is followed by other fresh water followed by water injection.

Since many times formation water adversely affects the polymer, the polymer solution (water salinity decreases the viscosity of the polymer solution) is often preceded by a solution of low salinity (preflush) as already mentioned. The solution is usually injected as a slug, followed by a water of low salinity and high salinity water used to move the water of low salinity. This procedure is performed to reduce mixing of the polymer solution with water of high salinity. To decrease the contrast of mobility between the polymer solution and the water behind it, the polymer concentration can be gradually reduced at the end of the slug.

The primary effect is to make dense polymer to water such that more efficient in displacing oil. The polymer injection probably not reduce residual oil saturation, but reduces the amount of water to be injected before reaching the residual saturation.

One of the important variables to consider concerns the pseudo plastic rheology liquid: To the water and oil in most cases, the viscosity is a constant value. However, polymer solutions for this is not the case. Viscosity is a function of the rate and shear stress, so it may vary from range since it depends on the geometry of flow and the flow rate which in turn is related to the distribution of the flow channels Rocks, yielding higher shear rates for grain distribution narrower and lower rates for more elongated grains.

Usually the higher permeability zones are invaded by water influx during secondary operations or natural power of water and in areas with lower permeability no injection so that oil is in these parts of the site. During polymer injection poor amount of efficiency of tilt can be improved, because the polymer solution first flows through the paths prepared by water and after due to their high viscosity tend to block these parts of the reservoir, so crude was still above starts flowing. The pressure gradient in the reservoir increases, especially in the area where the fluid was initially still increases by polymer injection process.

The polymer is injected not at a constant concentration, rather in a sequence of steps of reducing the concentration. The purpose of this sequence is to reduce the total amount of polymer used and prevent, or at least reduce, the viscous fingering low concentration fluid regions within higher concentrations. Viscous fingering each reduction occurs because the polymer concentration is accompanied by a reduction in the apparent viscosity of the solution.