RU2772808C1 - Enhanced oil recovery method - Google Patents

Abstract

FIELD: oil industry.

SUBSTANCE: invention relates to the oil industry and can be used in the development and enhanced oil recovery of oil reservoirs by methods that include the stage of polymer flooding. The method for enhanced oil recovery includes the stage of polymer flooding by successively injecting at least two polymer rims with different polymer concentrations into the formation. The lower viscosity slug is injected after the higher viscosity slug. The polymer concentration, volume and injection time of the slug is determined using the following sequential steps. Obtaining the initial values ​​of the polymer concentration of the first injected polymer rim, and the total injection time of polymer rims and water, during which the leading edge of the first polymer rim should not be destroyed, and fixing n the number of polymer rims, while n is greater than or equal to 2. Determining of movement speeds the leading and trailing edges of the mixing zone at the boundary of the polymer rims, relative to the polymer injection rate, for each pair of polymer concentrations, taking into account polymer adsorption. Determining the injection time of each of the polymer rims, provided that the speed of the rear edge of the mixing zone of the slug with a higher polymer concentration is greater than or equal to the speed of the front edge of the mixing zone of the next slug. Obtaining the dependence of polymer concentration on injection time. Determining of the resulting dependence of the concentration values ​​for each of the n rims, except for the first polymer rim, at which the volume of the polymer has a minimum value. Determining of polymer volume and injection time values ​​corresponding to the polymer concentrations obtained in the previous step. Also claimed is a method for characterizing polymer rims for a method for enhanced oil recovery, a system for characterizing polymer rims, and a machine-readable medium for characterizing polymer rims.

EFFECT: increasing the efficiency of polymer flooding, saving polymer during injection, maintaining the efficiency of enhanced oil recovery.

42 cl, 15 tbl, 12 dwg

Description

The invention relates to the oil industry and can be used in the development and enhanced oil recovery of oil reservoirs by methods that include the stage of polymer flooding.

Of particular interest in recent years are various methods of increasing oil recovery, due to the relatively high values of the residual oil saturation of the fields. The reasons for the high proportion of oil remaining in the reservoir are, among other things, the action of capillary forces that do not allow oil to be displaced from the pores (capillary-jammed oil), low-permeability reservoir areas that are not covered by the displacing agent, or the formation of breakthroughs of injected water from the injection to the production well . One of the ways to eliminate these effects is the use of tertiary methods of enhanced oil recovery, including chemical ones.

In the process of field development using tertiary methods of enhanced oil recovery in order to save polymer, chemical agents are injected in rims: layers of a fixed volume and concentration that displace additional oil. The rims themselves are displaced by the water pumped in after them. Most often, the corresponding injection of chemistry is divided into stages, the last of which (and sometimes the only one) is the injection of a polymer slug. In this case, a “dangerous” jump in viscosity appears at the boundary of the polymer fringe and the water pushing it through. The danger of this jump is manifested in the formation of "viscous fingers" in the rims of a rapidly growing mixing zone, which reduces the efficiency of oil displacement in the event of a breakthrough. In order to save polymer and to reduce the risk of premature breakthrough, the slug is pumped in several thinner layers with gradually decreasing polymer concentration (sub-slug).

To avoid premature breakage of the fringe, it is necessary to reasonably calculate the required volume of the polymer and its viscosity, as well as to optimize the sizes and concentrations of the constituent fringes.

The efficiency of the displacement process is also influenced by the process of adsorption of the injected polymer solution in the reservoir, which leads to a decrease in the concentration of the polymer slug and a decrease in the efficiency of the enhanced oil recovery method.

A known method for increasing oil recovery using polymer flooding (application WO 2020030996, publ. 13.02.2020, IPC: E21B 43/16, CO9K 8/588), in which the determination of the concentration of polymer rims is carried out depending on the salinity of the water to reduce the effect of the adsorption process polymer in the reservoir. In this connection, according to the known method, the salinity and the corresponding concentration of the polymer in the first slug, the second salinity and the corresponding concentration of the polymer in the second slug are determined, the first slug is injected into the well and the second slug of the polymer is injected immediately after the first one.

Common features of the known and claimed methods is the determination of the concentration of the polymer in successively injected rims.

However, in the known method, it is proposed to determine the concentration of each slug depending on the salinity of the water used to reduce the adsorption of the polymer, but does not take into account the speed of movement of the mixing boundaries, which does not exclude the possibility of a breakthrough and will lead to a decrease in the efficiency of the method. In this case, the adsorption should decrease, but the residual adsorption of the polymer is not taken into account.

There is a known method for enhancing oil recovery (patent RU 2432455, publ. 27.10.2011, IPC: E21B 43/22), which includes pumping a slug of an aqueous polymer solution into injection wells, characterized in that the polymer concentration is selected from the transition condition of the filtration flow of the polymer solution in the formation into the regime of elastic turbulence when the inequality

D/U<10θ,

where U - linear speed of advancement of the slug in the inter-well space,

D is the average grain diameter of the porous medium,

θ - relaxation time of elastic stresses,

while θ is chosen from the previously obtained dependence of the relaxation time on the concentration of the selected polymer.

Common features of the known and claimed methods are the determination of the concentration of the polymer fringe, taking into account the speed of advancement of the fringe.

However, the known method does not take into account sequentially injected rims, which provide a gradual decrease in viscosity when determining the concentration of the polymer, which will lead to viscosity jumps at the mixing boundary and the possibility of breakthrough and, accordingly, to a decrease in the efficiency of polymer flooding. Also, in this case, no reduction in the volume of the polymer used for injection into the well is provided, and the adsorption of the polymer in the reservoir is not taken into account.

The closest analogue (prototype) is the method for determining polymer slug for use in the method of enhanced oil recovery using polymer flooding, disclosed in the preprint "Optimal polymer slug injection profiles" (F. Bakharev, A. Enin, K. Kalinin, Yu. Petrova, N. Rastegaev, S. Tikhomirov, https://arxiv.org/abs/2012.03114). The publication analyzes possible mathematical models for determining the amount, size and concentration of polymer rims, and their advantages.

Common features of the known and claimed methods are taking into account the speeds of movement of the front and rear edges of the mixing zone when determining the characteristics of the fringes, a similar mathematical apparatus for taking into account the growth rates of the mixing zone and for determining the size of the fringes.

However, in the known method, general approaches to the possibility of determining the characteristics of polymer rims are disclosed, but it is not disclosed how it is proposed to use these approaches to determine specific characteristics (size and concentrations of polymer rims), i.e. the sequence of stages at which the technical result will be achieved is also not reflected in the known method how the adsorption of the polymer that occurs in the reservoir during polymer flooding can be taken into account, i.e. the known method is not technically applicable.

The technical result is to increase the efficiency of polymer flooding, saving the polymer used during injection, while maintaining the efficiency of the enhanced oil recovery method, as well as the ability to take into account the adsorption of the polymer that occurs during polymer flooding.

EFFECT: technical result for the method of enhanced oil recovery, which includes the stage of polymer flooding by successive injection into the formation of at least two polymer slug with different polymer concentration, while the slug of lower viscosity is injected after the slug of higher viscosity, and the polymer concentration, volume and injection time of the slug are determined with using the following successive steps:

- obtaining the initial values of the polymer concentration of the first injected polymer rim, and the total injection time of polymer rims and water, during which the leading edge of the first polymer rim should not be destroyed, and fixing n the number of polymer rims, while n is greater than or equal to 2;

- determination of the velocities of the leading and trailing edges of the mixing zone at the boundary of the polymer rims, relative to the polymer injection rate, for each pair of polymer concentrations, taking into account polymer adsorption;

- determination of the injection time for each of the polymer rims, provided that the speed of the rear edge of the mixing zone of the rim with a higher polymer concentration is greater than or equal to the speed of the front edge of the mixing zone of the rim following it;

- obtaining the dependence of the polymer concentration on the injection time;

- determination of the obtained dependence of the concentration values for each of the n rims, except for the first polymer rim, at which the volume of the polymer has a minimum value;

- determination of the polymer volume and injection time values corresponding to the polymer concentration values obtained at the previous stage.

The technical result is achieved by pumping the polymer rim with several thin (several n) rims with a gradually decreasing concentration and, accordingly, the viscosity of the polymer rim. This reduces the risk caused by a sharp jump in viscosity between the water and the polymer slug and eliminates the premature breakthrough of "sticky fingers" that reduce the efficiency of displacement, and also allows you to reduce the volume of polymer used. At the same time, the exclusion of premature breakthrough is associated with a strict (accurate) assessment of the growth rates of the mixing zones and their accounting for sequential, in accordance with the claimed method, determination of the polymer concentration in the rims, as well as the injection time and size (volume) of the polymer rims.

When determining the characteristics of polymer rims, the condition of non-breaking of the rims is taken into account, which includes the values of the velocities of the front and rear edges of the mixing zone and the times of the beginning of injection of the rims. This eliminates the breakthrough of "viscous fingers".

The number of fringes can be chosen differently and their number can be chosen by experts or analytically. It is preferable to calculate the characteristics of the polymer rims for different numbers n and determine the number of rims (n) depending on the data on polymer savings that can be obtained, taking into account the technical possibilities for polymer injection and based on economic factors.

увеличивается в

раз по сравнению с аналогичным временем при полимерном заводнении без адсорбции. При этом следует иметь в виду, более высокого уровня вытеснения, также происходит и пересчет поровых объемов, на основании параметров функции Баклея-Леверетта (см. те же монографии). При этом учет адсорбции происходит не только при определении суммарного времени закачки полимерных оторочек и воды, но и при определении скоростей движения заднего и переднего края зоны смешивания, чтобы обеспечить сохранение условия непрорывания.When determining the pumping time of the polymer, it is necessary to take into account adsorption, namely the nature of adsorption of the polymer in the reservoir (see, for example, the monographs of Bedrikovetsky, Pavel, and Gren Rowan. Mathematical Theory of Oil and Gas Recovery: With Applications to Ex-USSR Oil and Gas Fields, 1993. https://doi.org/10.1007/978-94-017-2205-6., or Lake, Larry W., and Society of Petroleum Engineers of AIME, Fundamentals of enhanced oil recovery, Second edition, Richardson , Texas: Society of Petroleum Engineers, 2014.), which is understandable to a specialist. Polymer adsorption slows down the movement of the polymer front, for example, according to the general theory presented in these monographs, in the case of pure polymer flooding with adsorption time

increases in

times compared to the same time for polymer flooding without adsorption. At the same time, it should be borne in mind that a higher displacement level also occurs and the pore volumes are recalculated based on the parameters of the Buckley-Leverett function (see the same monographs). In this case, adsorption is taken into account not only when determining the total injection time of polymer rims and water, but also when determining the velocities of the rear and front edges of the mixing zone in order to maintain the non-breakthrough condition.

The technical result is achieved by using a method for determining the characteristics of polymer rims for the method of enhanced oil recovery, in which a slug of lower viscosity pushes a slug of higher viscosity, which includes the following steps: obtaining the initial values of the maximum injected polymer concentration, which must be set at the leading edge of the first polymer slug, and the total polymer slug injection time, during which the leading edge of the slug must not be destroyed, fixing n the number of polymer rims, while n is greater than or equal to 2, determining the speeds of the front and rear edges of the mixing zone, relative to the polymer injection rate, at the boundary polymer slug for each pair of polymer concentrations, determining the injection time of each of the polymer slug, provided that the speed of the rear edge of the mixing zone of the slug with a higher polymer concentration is greater than or equal to the speed of the leading edge of the zone mixing of the following slug, obtaining the dependence of the polymer concentration on the injection time, determining from the obtained dependence the concentration values for each of the n slug, except for the first polymer slug, at which the volume of the polymer has a minimum value, determining the corresponding volume values from the obtained values of the polymer concentration polymer and injection time.

The starting (maximum) polymer concentration of the first slug can be determined by comparing the mobilities of the polymer and the fluid displaced by it and the requirements for the stability of the displacing front, which is known to a person skilled in the art (see, for example, Hagoort, J., et al.: Displacement stability of water drives in water-wet connate-water-bearing reservoirs Soc Pet Eng J 14(1), 63 (1974)).

The total pumping time (injection) of the polymer can be determined based on the speed of the polymer and reservoir parameters. Time can be reduced to dimensionless or can be measured in pumped pore volumes.

(2)

(one)
The relative velocities of the leading and trailing edges of the mixing zone can be determined from laboratory experiments, field studies, or from numerical simulations. In one of the embodiments of the method, they can be evaluated analytically:

,

,

относительная скорость переднего края зоны смешивания,

relative speed of the leading edge of the mixing zone,

относительная скорость заднего края зоны смешивания,

relative speed of the trailing edge of the mixing zone,

зависимость вязкости от концентрации полимера,

dependence of viscosity on polymer concentration,

– концентрация в оторочке большей вязкости,

is the concentration in the slug of higher viscosity,

– концентрация в оторочке меньшей вязкости.

is the concentration in the slug of lower viscosity.

It is known to those skilled in the art that the polymer concentration in a higher viscosity slug is greater than the polymer concentration in a lower viscosity slug.

By analytically determining rates as a function of polymer viscosity, data can be obtained immediately for the entire concentration dependence of polymer viscosity values.

может быть проведено с использованием уравнения:
(3)
The determination of the rates takes into account the adsorption of the polymer, for example, by determining the normalized adsorption isotherm. Determination of the Normalized Polymer Adsorption Isotherm

can be done using the equation:

, где

, where

– изотерма адсорбции;

is the adsorption isotherm;

– плотность воды;

- density of water;

– плотность породы;

– rock density;

– пористость пласта.

– formation porosity.

When determining rates from laboratory experiments, polymer adsorption is also taken into account. Methods for determining polymer adsorption in the laboratory are known to those skilled in the art.

начала закачки каждой из n оторочек проводят, исходя из условия непрорывания оторочек, которое выражается неравенством 4:
(four)
Definition of time

the beginning of the injection of each of the n rims is carried out based on the condition of non-breaking of the rims, which is expressed by inequality 4:

                           

, гдеfor

, where

– концентрация в j-ой оторочке (

);

is the concentration in the j-th rim (

);

– время начала закачки (j+1)-ой оторочки с концентрацией

– start time of injection of (j+1)-th rim with concentration

– суммарное время прокачки всей полимерной оторочки, включая финальную закачку чистой воды, в течение которого передний фронт оторочки не должен быть разрушен зонами смешивания;

is the total pumping time of the entire polymer rim, including the final injection of clean water, during which the leading edge of the rim must not be destroyed by mixing zones;

– относительная скорость движения заднего края j-ой зоны смешивания между оторочками с концентрациями

;

is the relative velocity of the trailing edge of the j-th mixing zone between the rims with concentrations

;

– относительная скорость движения переднего края (j+1)-ой зоны смешивания между оторочками с концентрациями

;

is the relative speed of the leading edge of the (j + 1)th mixing zone between the rims with concentrations

;

– относительная скорость движения переднего фронта первой полимерной оторочки с

.wherein

is the relative velocity of the leading edge of the first polymer fringe with

.

The optimal design of n rims is distinguished by the fact that all inequalities (1) turn into equalities.

как решение соответствующей системы линейных уравнений и выраженных формулой:
(5)
It is most preferable to determine the injection times

as a solution to the corresponding system of linear equations and expressed by the formula:

- суммарное время закачки полимерных оторочек, в течение которого передний фронт не должен быть разрушен.where

- total injection time of polymer rims, during which the leading edge should not be destroyed.

If the data on the speeds of movement are obtained analytically, the injection start times will also be an analytical dependence.

Taking into account the obtained (analytically or experimentally) data on the injection time, the dependence of the polymer concentration on the injection well on time is obtained, i.e. a polymer injection curve can be obtained. In the case of n fringes, this is a piecewise constant curve. The total amount of polymer will correspond to the area under the graph of this curve.

(6)
The volume of polymer for n number of rims can be determined, respectively, by the formula:

– концентрация оторочки с большей вязкостью;where

is the concentration of the slug with a higher viscosity;

– концентрация оторочки с меньшей вязкостью;

is the concentration of the slug with lower viscosity;

– время закачки оторочки с концентрацией

– injection time of the slug with concentration

In this case, when calculating the injection time, it is necessary to take into account the condition of non-breaking of the fringes.

In such an embodiment, the total volume of polymer to be injected can be analytically obtained. Next, the optimization problem of minimizing the total volume of the polymer over all possible sets of concentrations is solved.

This can be done either numerically or, in the case of an analytical specification of the viscosity curve, analytically using differential calculus. For example, the set of polymer concentrations for n rims at which the polymer volume is minimal can be defined as:

.

.

(7)
That is, taking into account the formula for determining the volume, the determination from the dependence of the concentration values for each of the n rims, except for the first polymer rim, at which the volume of the polymer has a minimum value, can have the form:

where c is the polymer concentration in n rims, starting from the second;

c _j is the concentration of the slug with a high viscosity value;

T _j is the start time of injection of a slug with concentration c _j+1 ;

c _j+1 is the concentration of the slug with a lower viscosity value.

является максимальной закачиваемой концентрацией полимера (c_max), которую надо задать на переднем крае первой полимерной оторочки, то данное значение не является искомым параметром, а задано априори, т.е. искомым аргументом служит набор

Because

is the maximum injected polymer concentration (c _max ), which must be set at the leading edge of the first polymer slug, then this value is not the desired parameter, but is set a priori, i.e. the desired argument is the set

Using the obtained concentration values, the corresponding injection start times and the volume (size) of the corresponding rims are determined.

(eight)
The slug injection times for each concentration can be determined by the formula:

,

,

- время начала закачки оторочки с концентрацией с_j+1;where

- start time of injection of a slug with concentration c _j+1 ;

- время начала закачки оторочки с концентрацией с_j.

- start time of injection of the slug with concentration c _j.

Wherein

That is, for example, for n = 2:

– время начала закачки оторочки с концентрацией

, а

– start time of injection of the slug with concentration

, a

– время начала закачки воды.

- start time of water injection.

(9)
The volume of polymer in each of the rims can be determined by the formula:

,

,

where q is the volumetric injection rate, determined based on the technological parameters of the oil reservoir.

In this case, examples of the possible definition of these characteristics are given. At the same time, the principles for determining, for example, the volume of polymer rims depending on concentration, injection time and reservoir parameters, are known to a specialist in this field of technology.

The choice of the number of rims is largely determined by organizational and economic factors. On the one hand, an increase in the number of rims gives a greater benefit in terms of the amount of polymer used, on the other hand, it requires more organizational costs.

In this connection, additionally, the determination of the characteristics of polymer rims may include repetition for different numbers n of stages: determining the velocities of the front and rear edges of the mixing zone, relative to the rate of injection of the polymer, at the boundary of the polymer rims for each pair of polymer concentrations, determining the injection time of each from polymer rims, provided that the velocity of the trailing edge of the mixing zone of the slug with a higher polymer concentration is greater than or equal to the velocity of the leading edge of the mixing zone of the rim following it, obtaining the dependence of the polymer concentration on the injection time, determining the concentration values for each of n from the obtained dependence rims, except for the first polymer rim, at which the polymer volume has a minimum value, determination of the corresponding values of the polymer volume and injection time from the obtained concentration values. Then calculate the total polymer volume for each value of n and the proportion of reduction in total polymer volume relative to the volume of polymer required to pump one slug and fix the value of n slug that achieves the optimal reduction in the proportion of polymer. Under the optimal reduction in the proportion of polymer in this case is understood as an increase in polymer savings of less than 1% with an increase in the number of slug. Those. it is possible to determine the number of rims at which polymer savings no longer occur with an increase in the number of rims, however, the injection of a large number of rims will require costs for technological processes and is not advisable (not optimal).

The technical result is also achieved when using in the methods a system (computer) for determining the characteristics of polymer rims, which contains at least one processor and a program code and is configured to be executed by the processor under the control of the program code: obtaining the initial values of the polymer concentration of the first injected polymer rim, and the total the injection time of polymer slug and water, during which the leading edge of the slug should not be destroyed; fixing n the number of polymer rims, while n is greater than or equal to 2; determination of the velocities of the leading and trailing edges of the mixing zone at the boundary of the polymer rims, relative to the polymer injection rate, for each pair of polymer concentrations, taking into account polymer adsorption; determining the injection time of each of the polymer rims, provided that the speed of the rear edge of the mixing zone of the slug with a higher polymer concentration is greater than or equal to the speed of the front edge of the mixing zone of the next slug; obtaining the dependence of the polymer concentration on the injection time; determining from the obtained dependence the concentration values for each of the n rims, except for the first polymer rim, at which the volume of the polymer has a minimum value; determining the values of the volume of the polymer and the time of injection, corresponding to the values of the polymer concentrations obtained in the previous stage.

The achievement of the technical result is also ensured when using in the methods a computer-readable medium for determining the characteristics of polymer rims, on which a computer program is stored that has a program code, when executed on a computer, the processor performs: obtaining the initial values of the polymer concentration of the first injected polymer rim, and the total injection time of the polymer fringes and water, during which the leading edge of the fringe must not be destroyed; fixing n the number of polymer rims, while n is greater than or equal to 2; determination of the velocities of the leading and trailing edges of the mixing zone at the boundary of the polymer rims, relative to the polymer injection rate, for each pair of polymer concentrations, taking into account polymer adsorption; determining the injection time of each of the polymer rims, provided that the speed of the rear edge of the mixing zone of the slug with a higher polymer concentration is greater than or equal to the speed of the front edge of the mixing zone of the slug following it; obtaining the dependence of the polymer concentration on the injection time; determining from the obtained dependence the concentration values for each of the n rims, except for the first polymer rim, at which the polymer volume has a minimum value; determination of polymer volume and injection time values corresponding to the values of polymer concentrations obtained at the previous stage.

To determine the velocities of the leading and trailing edges of the mixing zone, relative to the polymer injection rate, at the boundary of the polymer rims, for each pair of polymer concentrations, taking into account adsorption, analytical expressions can be used:

,

,

относительная скорость переднего края зоны смешивания,

relative speed of the leading edge of the mixing zone,

относительная скорость заднего края зоны смешивания,

relative speed of the trailing edge of the mixing zone,

зависимость вязкости от концентрации полимера,

dependence of viscosity on polymer concentration,

– концентрация в оторочке большей вязкости,

is the concentration in the slug of higher viscosity,

– концентрация в оторочке меньшей вязкости,

is the concentration in the slug of lower viscosity,

– адсорбция полимера при концентрации полимера в оторочке меньшей вязкости,

– adsorption of the polymer at a concentration of the polymer in the fringe of lower viscosity,

– адсорбция полимера при концентрации полимера в оторочке большей вязкости.

– polymer adsorption at polymer concentration in the slug of higher viscosity.

может быть проведено с использованием уравнения:When determining the relative velocities of the leading and trailing edges of the mixing zone, the adsorption of the polymer can be taken into account by determining the normalized adsorption isotherm, while determining the normalized adsorption isotherm of the polymer

can be done using the equation:

, где

, where

- Изотерма адсорбции;

- Adsorption isotherm;

– плотность воды;

- density of water;

– плотность породы;

– rock density;

– пористость пласта.

– formation porosity.

The set of concentrations at which the volume of the polymer tends to a minimum can be determined by the formula:

where c is the polymer concentration in the fringes from the first to n;

c _j is the concentration in the slug of higher viscosity;

T _j is the start time of injection of a slug with concentration c _j+1 ;

c _j+1 – concentration in the slug of lower viscosity.

Start time of injection of each slug (T_j) maybe be determined by the formula:

where T _max is the total injection time of polymer rims, during which the leading edge must not be destroyed;

– относительная скорость заднего края зоны смешивания оторочки большей вязкости;

is the relative velocity of the trailing edge of the mixing zone of the slug with higher viscosity;

– относительная скорость переднего края зоны смешивания оторочки меньшей вязкости.

is the relative velocity of the leading edge of the mixing zone of the slug with lower viscosity.

The volume value for each of the obtained concentrations can be determined by the formula:

,

,

where q is the volumetric injection rate, determined based on the technological parameters of the oil reservoir.

The value of the injection times for each of the obtained concentration values can be determined by the formula:

- время начала закачки оторочки с концентрацией с_j+1 where

- start time of injection of a slug with a concentration of _{j + 1}

- время начала закачки оторочки с концентрацией с_j.

- start time of injection of the slug with concentration c _j.

The processor can additionally repeat the following steps for different numbers n: determining the velocities of the leading and trailing edges of the mixing zone, relative to the polymer injection rate, at the boundary of the polymer rims for each pair of polymer concentrations, determining the injection time of each of the polymer rims, provided that that the speed of movement of the rear edge of the mixing zone of the slug with a higher polymer concentration is greater than or equal to the speed of the front edge of the mixing zone of the slug that follows it, obtaining the dependence of the polymer concentration on the injection time, determining the concentration values for each of the n slug, except for the first polymer slug, from the obtained dependence , at which the polymer volume has a minimum value, determination of the corresponding values of the polymer volume and injection time from the obtained concentration values, calculation of the total polymer volume for each value of n and the share of the decrease in the total polymer volume relative to about the volume of polymer required to pump one slug and fixing the value of n slug, at which the optimal reduction in the proportion of polymer is achieved.

The processor can additionally determine the values of the maximum injected polymer concentration, which must be set at the leading edge of the first polymer slug, and the total injection time of the polymer slug, during which the leading edge of the slug must not be destroyed, when entering, in particular, the initial data on the previous main chemical rim and formation characteristics.

Figure 1 shows a diagram of the movement of the rims during oil displacement, where 1 is oil, 2 is the main chemical (for example, surfactant-polymer) rim, 3 is a polymer rim with a maximum concentration, 4 is a polymer rim with a lower viscosity (concentration), 5 is water, 6 - mixing zone, 7 - leading edge of the mixing zone, 8 - trailing edge of the mixing zone, the arrow (axis direction) indicates the direction of movement of the rims from the injection well to the production well.

The figure 2 shows 9 - the dependence of the viscosity of the polymer (polyacrylamide) on the concentration.

, 11 -

полиакриламида в зависимости от концентрации полимера в растворе.The figure 3 shows the adsorption curves 10 -

, eleven -

polyacrylamide depending on the concentration of the polymer in solution.

Figure 4 shows the general case of the dependence of the concentration of the polymer on the time of injection.

.The figure 5 shows the dependence of the relative velocity of the leading edge of the mixing zone between pairs of polymer rims with different polymer concentrations for the case of reversible adsorption

.

.The figure 6 shows the dependence of the relative velocity of the rear edge of the mixing zone between pairs of polymer rims with different polymer concentrations for the case of reversible adsorption

.

.The figure 7 shows the dependence of the relative velocity of the leading edge of the mixing zone between pairs of polymer rims with different polymer concentrations for the case of irreversible adsorption

.

.The figure 8 shows the dependence of the relative speed of movement of the rear edge of the mixing zone between pairs of polymer rims with different polymer concentrations for the case of irreversible adsorption

.

.The figure 9 shows the dependence of the relative velocity of the leading edge of the mixing zone between pairs of polymer rims with different polymer concentrations for the case of reversible adsorption

.

.The figure 10 shows the dependence of the relative velocity of the rear edge of the mixing zone between pairs of polymer rims with different polymer concentrations for the case of reversible adsorption

.

.The figure 11 shows the dependence of the relative velocity of the leading edge of the mixing zone between pairs of polymer rims with different polymer concentrations for the case of irreversible adsorption

.

.The figure 12 shows the dependence of the relative speed of movement of the rear edge of the mixing zone between pairs of polymer rims with different polymer concentrations for the case of irreversible adsorption

.

A method for enhancing oil recovery, which includes a stage of polymer flooding by successively injecting at least two polymer rims with different polymer concentrations into the formation. In this case, the slug of lower concentration 4 pushes the slug of higher concentration 3. To determine the polymer concentration of the slug, the initial values of the maximum injected polymer concentration are obtained, which must be set at the leading edge of the first polymer slug 3, and the total injection time of the polymer slug, during which the leading edge of the slug does not must be destroyed. Then fix the number of polymer fringes. The speed of movement of the front 7 and rear 8 edges of the mixing zone 6, relative to the polymer injection rate, is determined at the border of the polymer rims for each pair of polymer concentrations. The injection times for each of the polymer rims are determined, provided that the speed of the rear edge of the mixing zone of the slug with a higher polymer concentration is greater than or equal to the speed of the front edge of the mixing zone of the next slug. As a result, the dependence of the polymer concentration on the injection time is obtained and the concentration values are determined from the obtained dependence for each of the n rims, except for the first polymer rim, at which the polymer volume has a minimum value. According to the obtained values of the polymer concentrations, the corresponding values of the polymer volume and the injection time of each slug are determined.

Below is an example of the implementation of the method for determining the characteristics of the polymer for the method of enhanced oil recovery, which illustrates the claimed group of inventions, but does not limit.

In the example below, a generalized version of the method for characterizing polymer rims for polymer flooding is presented without specifying the characteristics of a particular formation, and therefore the characteristics were determined relative. When using data for a particular reservoir - taking into account the data presented, absolute values \u200b\u200bcan be determined.

The values of polymer concentration and injection time were determined analytically. At the same time, as mentioned above, data can also be obtained during laboratory studies, in particular, when determining the velocities of the leading and trailing edges of the mixing zone, relative to the polymer injection rate, at the border of polymer rims for each pair of polymer concentrations.

As data, data on the potential use of FLOPAAM AN125 polymer (polyacrylamide) in the context of chemical flooding for enhanced oil recovery at one of the fields in Eastern Siberia were used. The viscosity curve 9 of the polymer is plotted in FIG. 2.

= 0,0015 (массовая доля содержания полимера в первой оторочке) или 0,15%.The initial value of the polymer concentration of the first injected polymer slug was obtained based on the need to equalize the mobility of the polymer solution and the previous planned chemical cocktail slug, which is known to the specialist (Hagoort, J., et al.: Displacement stability of water drives in water-wet connate- water-bearing reservoirs Soc Pet Eng J 14(1), 63 (1974)). The initial injected polymer concentration of the first injected polymer slug was

= 0.0015 (mass fraction of the polymer content in the first slug) or 0.15%.

The total injection time of polymer rims and water, during which the leading edge of the polymer rim should not be destroyed, can be known and measured, for example, in the pore volume, or it can be dimensionless (relative), for example, taken as unity. For the given examples of the implementation of the method, a specific value of the total injection time of polymer rims and water was not used, which is determined depending on the injection rate of the polymer and reservoir parameters, but a variant of calculating relative values is given.

The number of polymer fringes n = 2 was fixed. Also, in accordance with an embodiment of the invention, according to which a different number of polymer fringes can be fixed to select the optimal value, the number of polymer fringes was changed in the range from 2 to 5 in order to determine the optimal number of fringes according to the value of the obtained polymer savings.

Characteristics of the polymer rims (concentration, volume and injection time) were determined according to the variant of the invention using the formulas given in the description. A script written in Phython can be used, or a program code can be created or used to perform these calculations. The characterization sequence is shown below.

The rates of movement of the leading and trailing edges of the mixing zone at the boundary of polymer rims are determined relative to the rate of polymer injection for each pair of polymer concentrations, taking into account polymer adsorption. The determination was carried out analytically by determining the normalized adsorption isotherm, taking into account the polymer viscosity versus concentration curve shown in FIG. 2.

Due to the fact that in all cases during polymer flooding, adsorption of the polymer in the reservoir takes place, the nature of which depends on the characteristics of the reservoir, below are examples of the implementation of the method for determining the characteristics of polymer rims for two different polymer adsorption curves shown in Figure 3.

The velocities were determined using the formulas:

,

,

,

,

скорость движения переднего края зоны смешивания

speed of movement of the leading edge of the mixing zone

скорость движения заднего края зоны смешивания

mixing zone trailing edge speed

зависимость вязкости от концентрации полимера (определяется по фиг.2)

dependence of viscosity on polymer concentration (determined from figure 2)

– концентрация оторочки с большим значением

is the concentration of the fringe with a large value

– концентрация оторочки с меньшим значением

is the concentration of the fringe with the lower value

– обратимая адсорбция, кривая 10 зависимости от концентрации полимера которой представлена на фиг.3.

- reversible adsorption, curve 10 depending on the concentration of the polymer which is shown in Fig.3.

The result of determining the values of the relative velocities of the front and rear edges of the mixing zones for different pairs of concentrations of polymer fringes are shown in figure 5 and figure 6, respectively.

Determining the injection time of each of the polymer rims, provided that the speed of the trailing edge of the mixing zone of the slug with a higher polymer concentration is greater than or equal to the speed of the leading edge of the mixing zone of the slug following it, is carried out using the obtained data on movement speeds. This action was based on the presented analytical expression:

As stated above, this expression includes the condition of non-breaking of the fringes.

The dependences of the polymer concentration on the injection time are obtained, i.e. the dependence of the polymer concentration on the injection well on time (curve of polymer injection), according to the obtained values of injection times of polymer rims (analytical dependence). From the polymer injection curve, the total amount of polymer can be determined.

(ten)
This dependence can be expressed by the formula:

where c _j is the concentration of the slug with a higher viscosity;

T _j, T _j-1 are the times of the beginning of injection of the corresponding rims.

A general view of such a dependence is shown in Figure 4.

, обратную к

Функция

может быть определена следующим образом:
(eleven)
In some cases it is convenient to consider the function

, inverse to

Function

can be defined like this:

where c _j is the concentration of the slug with a higher viscosity;

T _j is the start time of injection of the corresponding slug;

with _j+1 is the concentration of the slug with lower viscosity.

The volume of polymer for n number of rims is determined using the formula corresponding to this relationship:

(6)
where c is the polymer concentration in n rims;

c _j is the concentration of the fringe with a large value;

T _j is the start time of injection of the corresponding slug;

with _j+1 - the concentration of the fringe with a smaller value.

Based on the dependence obtained, the concentration values are determined for each of the n rims, except for the first polymer rim, at which the polymer volume has a minimum value.

The problem of minimizing the total volume of the polymer, which is determined by formula 6, over all possible sets of concentrations was solved using the formula below for different values of n:

.

.

Accordingly, for n = 2 there will be one argument for solving this optimization problem of minimizing the polymer volume. For n = 5, there will be 4 arguments.

Table 1 shows the results of solving this optimization problem for n from 2 to 5.

Table 1. Polymer concentrations for different amounts of polymer slug

The concentration of the first slug Values of concentrations of polymer rims at which the volume of polymer is minimal Number of fringes

0.0015 - - - -

0.0015 0.00046 - - -

0.0015 0.0011 0.00034 - -

0.0015 0.0012 0.00054 0.00021 -

0.0015 0.0012 0.00068 0.00036 0.00015

The values of polymer volume and injection time are determined corresponding to the polymer concentrations obtained in the previous step.

The value of the injection times for each of the obtained concentration values is determined by the formula:

- время начала закачки оторочки с концентрацией с_j+1 where

- start time of injection of a slug with a concentration of _{j + 1}

- время начала закачки оторочки с концентрацией с_j.

- start time of injection of the slug with concentration c _j.

Taking into account the obtained values of polymer concentrations, the values of the relative injection time for each of the n rims are determined in accordance with the equation:

).Table 2 shows the respective relative injection times (correlated with

).

Table 2. Injection time for different number of polymer rims

Time of injection of polymer slug Number of fringes

one - - - -

0.742 0.448 - - -

0.519 0.349 0.3515 - -

0.482 0.317 0.2385 0.220 -

0.464 0.299 0.175 0.180 0.1585

). Экономия полимера определялась как отношение (%) количества полимера, которое требуется при использовании нескольких оторочек, к количеству полимера, которое требуется при использовании одной оторочки. Результаты приведены в таблице 3. Due to the fact that in this example relative rather than absolute values of the injection time were determined, the polymer savings relative to the polymer volume for the case of one polymer slug were immediately determined from the relative values of the injection time and the obtained values of polymer concentrations (taking into account the relative injection times for several polymer rims correlated with time

). Resin savings was defined as the ratio (%) of the amount of polymer required when using multiple slug to the amount of polymer required when using a single slug. The results are shown in table 3.

также учитывается адсорбция, в результате которой значение увеличивается в

раз. At the same time, to determine the absolute values

adsorption is also taken into account, as a result of which the value increases in

once.

Table 3. Polymer Savings

Number of fringes

Saving - 12.1% 14.6% 15.6% 15.9%

Due to the fact that the savings in the amount of polymer with an increase in the number of rims from 4 to 5 did not exceed 1%, a further increase in the number of rims was not carried out.

For one of the fields, it was determined that the total injection time of polymer rims and water is 0.5 p.o. or 550 days. The injection times for each polymer slug for this case are shown in Table 4 and Table 5.

Table 4. Injection time for different number of polymer rims

Time of injection of polymer rims, p.o. Number of fringes

0.5 - - - -

0.371 0.224 - - -

0.2595 0.1745 0.1758 - -

0.241 0.1585 0.1193 0.110 -

0.232 0.1495 0.0875 0.09 0.0793

Table 5. Injection time for different number of polymer rims

Time of injection of polymer rims, days Number of fringes

550 - - - -

408 246 - - -

285 192 193 - -

265 174 131 121 -

255 164 96 99 87

(9)
The values of the volumes of the fringes are determined by the formula known to a person skilled in the art:

,

,

where q is the volumetric injection rate, determined based on the technological parameters of the oil reservoir.

The volume values in this case were calculated for an injection volume rate of 85 m ³ /day and are presented in Table 6.

Table 6. Volume of each polymer fringe

The volume of polymer rims, m ³ Number of fringes

70

52 9.6

36 eighteen 5.6

34 17 6.0 2.1

32.5 16.7 5.6 3.1 1.1

(кривая 10 на фиг.3), при условии, что в данном случае адсорбция является необратимой.Due to the fact that, depending on the characteristics of the reservoir, irreversible adsorption of the polymer may occur, the following is an example of characterizing polymer slug for the adsorption curve

(curve 10 in figure 3), provided that in this case the adsorption is irreversible.

Dependences of the speeds of movement of the front and rear edges of the mixing zone on the concentration of fringes are shown in figures 7 and 8, respectively.

Table 7 below lists the polymer concentrations for injection designs with no more than 5 slug counts, and Tables 8 and 9 show their respective injection times and polymer savings.

Table 7. Polymer concentrations for different amounts of polymer slug

The concentration of the first slug Values of concentrations of polymer rims at which the volume of polymer is minimal Number of fringes

0.0015 - - - -

0.0015 0.00046 - - -

0.0015 0.0011 0.00034 - -

0.0015 0.00117 0.00054 0.00021 -

0.0015 0.0012 0.00068 0.00036 0.00015

Table 8. Injection time for different number of polymer slug

Time of injection of polymer slug Number of fringes

one - - - -

0.794 0.357 - - -

0.616 0.278 0.280 - -

0.5865 0.253 0.190 0.1756 -

0.572 0.238 0.140 0.143 0.1265

Table 9. Polymer Savings

Number of fringes

Saving - 9.7% 11.6% 12.4% 12.7%

Determining specific injection times and polymer slug volumes are calculated as shown above when field specific data are available.

(кривая 11 на фиг.3).Below are the results of the implementation of the method for determining the characteristics of polymer rims for the adsorption curve

(curve 11 in figure 3).

The dependences of the speeds of movement of the front and rear edges of the mixing zone on the concentration of fringes for this example are shown in figures 9 and 10, respectively.

, в таблицах 11 и 12 представлены соответствующие им значения времен закачки и экономия полимера.Table 10 below shows the polymer concentrations for injection designs with the number of slug not exceeding 5, taking into account reversible adsorption

, Tables 11 and 12 present their respective injection times and polymer savings.

Table 10. Resin Concentrations for Different Numbers of Resin Slugs

The concentration of the first slug Values of concentrations of polymer rims at which the volume of polymer is minimal Number of fringes

0.0015 - - - -

0.0015 0.00046 - - -

0.0015 0.0011 0.00034 - -

0.0015 0.00117 0.00054 0.00021 -

0.0015 0.0012 0.00069 0.00036 0.00015

Table 11. Injection time for different number of polymer slug

Time of injection of polymer slug Number of fringes

one - - - -

0.653 0.603 - - -

0.352 0.469 0.473 - -

0.3025 0.4265 0.321 0.296 -

0.278 0.402 0.236 0.242 0.213

Table 12. Polymer Savings

Number of fringes

Saving - 16.3% 19.6% 21.0% 21.5%

Determining specific injection times and polymer slug volumes are calculated as shown above when field specific data are available.

, в таблицах 14 и 15 представлены соответствующие им значения времен закачки и экономия полимера.Table 13 below shows the polymer concentrations for injection designs with the number of slug not exceeding 5, taking into account irreversible adsorption

, Tables 14 and 15 present their respective injection times and polymer savings.

Dependences of the speeds of movement of the front and rear edges of the mixing zone on the concentration of fringes are shown in figures 11 and 12, respectively.

Table 13. Resin Concentrations for Different Numbers of Resin Slugs

The concentration of the first slug Values of concentrations of polymer rims at which the volume of polymer is minimal Number of fringes

0.0015 - - - -

0.0015 0.000457 - - -

0.0015 0.0011 0.00034 - -

0.0015 0.00117 0.00054 0.00021 -

0.0015 0.0012 0.00068 0.00036 0.00015

Table 14. Injection time for different number of polymer slug

Time of injection of polymer slug Number of fringes

one - - - -

0.90 0.17 - - -

0.81 0.13 0.135 - -

0.80 0.12 0.092 0.085 -

0.79 0.115 0.067 0.069 0.061

Table 15. Polymer Savings

Number of fringes

Saving - 4.7% 5.6% 6.0% 6.1%

Determining specific injection times and polymer slug volumes are calculated as shown above when field specific data are available.

The examples given illustrate the possibility of implementing a method for determining the characteristics of polymer rims for a method of enhanced oil recovery and confirm the achievement of a technical result for the claimed group of inventions, namely, saving the injected polymer, eliminating the "dangerous jump" in viscosity at the polymer-water interface, which is due to the fact that when determining characteristics of polymer rims, a non-breakthrough condition is introduced, an increase in the efficiency of the enhanced oil recovery method, and accounting for polymer adsorption in the reservoir.

Provided that the steps of the method can be carried out both in laboratory studies and analytically, the examples given confirm the achievement of a technical result when using a system for determining the characteristics of polymer fringes and a machine-readable medium for determining the characteristics of polymer fringes.

Claims (199)

1. A method for enhanced oil recovery, which includes the stage of polymer flooding by successively injecting into the reservoir at least two polymer slug with different polymer concentration, while the lower viscosity slug is injected after the higher viscosity slug, and the polymer concentration, volume and injection time of the slug are determined using the following successive stages: - obtaining the initial values of the polymer concentration of the first injected polymer rim, and the total injection time of polymer rims and water, during which the leading edge of the first polymer rim should not be destroyed, and fixing n the number of polymer rims, while n is greater than or equal to 2; - determination of the velocities of the leading and trailing edges of the mixing zone at the boundary of the polymer rims, relative to the polymer injection rate, for each pair of polymer concentrations, taking into account polymer adsorption; - determination of the injection time for each of the polymer rims, provided that the speed of the rear edge of the mixing zone of the rim with a higher polymer concentration is greater than or equal to the speed of the front edge of the mixing zone of the rim following it; - obtaining the dependence of the polymer concentration on the injection time; - determination of the obtained dependence of the concentration values for each of the n rims, except for the first polymer rim, at which the volume of the polymer has a minimum value; - determination of the polymer volume and injection time values corresponding to the polymer concentration values obtained at the previous stage. 2. The method of enhanced oil recovery according to claim 1, in which the concentration of the polymer of the first injected polymer slug is determined by comparing the target mobility of the polymer and the fluid expelled by it and the requirements for the stability of the displacement front of the main chemical slug. 3. The method of enhanced oil recovery according to claim 1, in which the total injection time of polymer rims and water is determined by the speed of the polymer and reservoir parameters. 4. The method of increasing oil recovery according to claim 1, in which the relative velocities of the front and rear edges of the mixing zones are determined analytically:

where

,

- relative speed of the leading edge of the mixing zone,

- relative speed of the trailing edge of the mixing zone, μ(s) - dependence of viscosity on polymer concentration, c _j - concentration in the slug of higher viscosity, c _j+1 - concentration in the slug of lower viscosity. 5. The method of enhanced oil recovery according to claim 1, in which, when determining the relative velocities of the front and rear edges of the mixing zone, the adsorption of the polymer is taken into account by determining the normalized adsorption isotherm. 6. The method of enhanced oil recovery according to claim 5, in which the determination of the normalized polymer adsorption isotherm a (c) is carried out using the equation:

where Г(с) - adsorption isotherm; ρ _w is the density of water; ρ _s - rock density; ϕ - formation porosity. 7. The method of increasing oil recovery of claim 1, in which, when determining the total injection time of polymer rims and water, adsorption of the polymer in the reservoir is additionally taken into account. 8. The method of enhanced oil recovery according to claim 1, in which the set of concentrations at which the volume of the polymer tends to a minimum is determined by the formula:

where c is the concentration of the polymer in the fringes from the first to n; c _j - concentration in the slug of higher viscosity; T _j - start time of injection of the slug with concentration c _j+1 ; c _j+1 - concentration in the slug of lower viscosity. 9. The method of enhanced oil recovery according to claim 1 or 8, in which the start time of injection of each slug (T _j ) is determined by the formula:

for j=1,…,n, where T _max is the total injection time of polymer rims, during which the leading edge must not be destroyed;

- relative speed of the trailing edge of the mixing zone of the slug of higher viscosity;

- relative speed of the leading edge of the mixing zone of the slug of lower viscosity. 10. The method of increasing oil recovery according to claim 1, in which the value of the volume for each of the obtained concentrations is determined by the formula: V _j \u003d c _j (T _j -T _j-1 )V, where V is the volume of water injected into the reservoir during the time T _max equal to T _max q, where q is the volumetric injection rate determined based on the technological parameters of the oil reservoir. 11. The method of increasing oil recovery according to claim 1, in which the value of injection times for each of the obtained concentration values is determined by the formula: t _j \u003d T _j -T _j-1 , where T _j - start time of injection of the slug with concentration c _j+1 , T _j-1 - start time of injection of the slug with concentration c _j . 12. The method of enhanced oil recovery according to claim 1, which further includes repeating the following steps for different numbers n: - determination of the velocities of the leading and trailing edges of the mixing zone at the boundary of the polymer rims, relative to the polymer injection rate, for each pair of polymer concentrations, taking into account polymer adsorption, - determination of the injection time for each of the polymer rims, provided that the speed of the rear edge of the mixing zone of the slug with a higher polymer concentration is greater than or equal to the speed of the front edge of the mixing zone of the rim following it, - obtaining the dependence of the polymer concentration on the injection time, - determination of the obtained dependence of the concentration values for each of the n rims, except for the first polymer rim, at which the volume of the polymer has a minimum value, - determination of the obtained values of the concentrations of the corresponding values of the polymer volume and injection time; calculating the total polymer volume for each value of n and the share of reduction in the total polymer volume relative to the volume of polymer required to pump one slug, and fixing the value of n slug at which the optimal reduction in the polymer share is achieved. 13. A method for characterizing polymer slug for an enhanced oil recovery process in which a slug of lower viscosity pushes a slug of higher viscosity, which includes the following steps: - obtaining the initial values of the polymer concentration of the first injected polymer rim and the total injection time of polymer rims and water, during which the leading edge of the first polymer rim should not be destroyed, and fixing n the number of polymer rims, while n is greater than or equal to 2; - determination of the velocities of the leading and trailing edges of the mixing zone at the boundary of the polymer rims, relative to the polymer injection rate, for each pair of polymer concentrations, taking into account polymer adsorption; - determination of the injection time for each of the polymer rims, provided that the speed of the rear edge of the mixing zone of the rim with a higher polymer concentration is greater than or equal to the speed of the front edge of the mixing zone of the rim following it; - obtaining the dependence of the polymer concentration on the injection time; - determination of the obtained dependence of the concentration values for each of the n rims, except for the first polymer rim, at which the volume of the polymer has a minimum value; - determination of the polymer volume and injection time values corresponding to the polymer concentration values obtained at the previous stage. 14. The polymer slug characterization method of claim 13, wherein the polymer concentration value of the first injected polymer slug is determined by comparing the target mobility of the polymer and the fluid expelled by it and the drive front stability requirements of the main chemical slug. 15. The method for determining the characteristics of polymer rims according to claim 13, in which the total injection time of polymer rims and water is determined by the speed of the polymer and reservoir parameters. 16. The method for determining the characteristics of polymer rims according to claim 13, in which the relative velocities of the front and rear edges of the mixing zones are determined analytically:

where

,

- relative speed of the leading edge of the mixing zone,

- relative speed of the trailing edge of the mixing zone, μ(s) - dependence of viscosity on polymer concentration, c _j - concentration in the slug of higher viscosity, c _j+1 - concentration in the slug of lower viscosity. 17. The method for determining the characteristics of polymer rims according to claim 13, in which, when determining the relative speeds of movement of the front and rear edges of the mixing zone, the adsorption of the polymer is additionally taken into account by determining the normalized adsorption isotherm. 18. The method for determining the characteristics of polymer rims according to claim 17, in which the determination of the normalized polymer adsorption isotherm a (c) is carried out using the equation:

where Г(с) - adsorption isotherm; ρ _w is the density of water; ρ _s - rock density; ϕ - formation porosity. 19. The method for determining the characteristics of polymer rims according to claim 13, in which, when determining the total injection time of polymer rims and water (T _max ), adsorption of the polymer in the reservoir is additionally taken into account. 20. The method for determining the characteristics of polymer rims according to claim 13, in which the set of concentrations at which the volume of the polymer tends to a minimum is determined by the formula:

where c is the concentration of the polymer in the fringes from the first to n; c _j - concentration in the slug of higher viscosity; T _j - start time of injection of the slug with concentration c _j+1 ; c _j+1 - concentration in the slug of lower viscosity. 21. The method for determining the characteristics of polymer rims according to claim 13 or 20, in which the injection start time of each rim (T _j ) is determined by the formula:

for j=1,…,n, where T _max is the total injection time of polymer rims, during which the leading edge must not be destroyed;

- relative speed of the trailing edge of the mixing zone of the slug of higher viscosity;

- relative speed of the leading edge of the mixing zone of the slug of lower viscosity. 22. The method for determining the characteristics of polymer rims according to claim 13, in which the volume value for each of the obtained concentrations is determined by the formula: V _j \u003d c _j (T _j -T _j-1 )V, where V is the volume of water injected into the reservoir during the time T _max equal to T _max q, where q is the volumetric injection rate determined based on the technological parameters of the oil reservoir 23. The method for determining the characteristics of polymer rims according to claim 13, in which the value of injection times for each of the obtained concentration values is determined by the formula: t _j \u003d T _j -T _j-1 , where T _j - start time of injection of the slug with concentration c _j+1 , T _j-1 - start time of injection of the slug with concentration c _j . 24. The method for characterizing polymer rims according to claim 13, which further includes repeating the following steps for different numbers n: - determination of the velocities of the leading and trailing edges of the mixing zone at the boundary of the polymer rims, relative to the polymer injection rate, for each pair of polymer concentrations, taking into account polymer adsorption, - determination of the injection time for each of the polymer rims, provided that the speed of the rear edge of the mixing zone of the slug with a higher polymer concentration is greater than or equal to the speed of the front edge of the mixing zone of the rim following it, - obtaining the dependence of the polymer concentration on the injection time, - determination of the obtained dependence of the concentration values for each of the n rims, except for the first polymer rim, at which the volume of the polymer has a minimum value, - determination of the obtained values of the concentrations of the corresponding values of the polymer volume and injection time; calculating the total polymer volume for each value of n and the share of reduction in the total polymer volume relative to the volume of polymer required to pump one slug, and fixing the value of n slug at which the optimal reduction in the polymer share is achieved. 25. The system for determining the characteristics of polymer fringes, which contains at least one processor and a program code and is configured to be executed by the processor under the control of the program code: - obtaining the initial values of the polymer concentration of the first injected polymer rim and the total injection time of polymer rims and water, during which the leading edge of the rim should not be destroyed; - fixing n the number of polymer rims, while n is greater than or equal to 2; - determination of the velocities of the leading and trailing edges of the mixing zone at the boundary of the polymer rims, relative to the polymer injection rate, for each pair of polymer concentrations, taking into account polymer adsorption; - determining the injection time for each of the polymer rims, provided that the speed of the rear edge of the mixing zone of the slug with a higher polymer concentration is greater than or equal to the speed of the front edge of the mixing zone of the next slug; - obtaining the dependence of the polymer concentration on the injection time; - determination of the obtained dependence of the concentration values for each of the n rims, except for the first polymer rim, at which the volume of the polymer has a minimum value; - determining the values of the volume of the polymer and the injection time, corresponding to the values of the polymer concentrations obtained at the previous stage. 26. The system for determining the characteristics of polymer rims according to claim 25, in which analytical expressions are used to determine the velocities of the leading and trailing edges of the mixing zone, relative to the polymer injection rate, at the boundary of the polymer rims for each pair of polymer concentrations:

where

,

- relative speed of the leading edge of the mixing zone,

- relative speed of the trailing edge of the mixing zone, μ(s) - dependence of viscosity on polymer concentration, c _j - concentration in the slug of higher viscosity, c _j+1 - concentration in the slug of lower viscosity. 27. The system for determining the characteristics of polymer rims according to claim 25, in which, when determining the relative velocities of the front and rear edges of the mixing zone, the adsorption of the polymer is additionally taken into account by determining the normalized adsorption isotherm. 28. The system for determining the characteristics of polymer rims according to claim 27, in which the determination of the normalized polymer adsorption isotherm a (c) is carried out using the equation:

where Г(с) - adsorption isotherm; ρ _w is the density of water; ρ _s - rock density; ϕ - formation porosity. 29. The system for characterizing polymer rims according to claim 25, in which the set of concentrations at which the volume of polymer tends to a minimum is determined by the formula:

where c is the concentration of the polymer in the fringes from the first to n; c _j - concentration in the slug of higher viscosity; T _j - start time of injection of the slug with concentration c _j+1 ; c _j+1 - concentration in the slug of lower viscosity. 30. The system for characterizing polymer rims according to claim 25 or 29, in which the start time of injection of each rim (T _j ) is determined by the formula:

for j=1,…,n, where T _max is the total injection time of polymer rims, during which the leading edge must not be destroyed;

- relative speed of the trailing edge of the mixing zone of the slug of higher viscosity;

- relative speed of the leading edge of the mixing zone of the slug of lower viscosity. 31. The system for determining the characteristics of polymer rims according to claim 25, in which the volume value for each of the obtained concentrations is determined by the formula: V _j \u003d c _j (T _j -T _j-1 )V, where V is the volume of water injected into the reservoir during the time T _max equal to T _max q, where q is the volumetric injection rate determined based on the technological parameters of the oil reservoir. 32. The system for characterizing polymer rims according to claim 25, in which the value of injection times for each of the obtained concentration values is determined by the formula: t _j \u003d T _j -T _j-1 , where T _j - start time of injection of the slug with concentration c _j+1 , T _j-1 - start time of injection of the slug with concentration c _j . 33. The system for determining the characteristics of polymer rims according to claim 25, in which the processor additionally repeats the following stages for different numbers n: - determination of the velocities of the leading and trailing edges of the mixing zone at the boundary of the polymer rims, relative to the polymer injection rate, for each pair of polymer concentrations, taking into account polymer adsorption, - determination of the injection time for each of the polymer rims, provided that the speed of the rear edge of the mixing zone of the slug with a higher polymer concentration is greater than or equal to the speed of the front edge of the mixing zone of the rim following it, - obtaining the dependence of the polymer concentration on the injection time, - determination of the obtained dependence of the concentration values for each of the n rims, except for the first polymer rim, at which the volume of the polymer has a minimum value, - determination of the obtained values of the concentrations of the corresponding values of the polymer volume and injection time; calculating the total polymer volume for each value of n and the proportion of reduction in total polymer volume relative to the volume of polymer required to pump one slug, and fixing the value of n slug that achieves the optimal reduction in the proportion of polymer. 34. A machine-readable medium for determining the characteristics of polymer fringes, on which a computer program is stored that has a program code, when executed on a computer, the processor performs: - obtaining the initial values of the polymer concentration of the first injected polymer rim and the total injection time of polymer rims and water, during which the leading edge of the rim should not be destroyed; - fixing n the number of polymer rims, while n is greater than or equal to 2; - determination of the velocities of the leading and trailing edges of the mixing zone at the boundary of the polymer rims, relative to the polymer injection rate, for each pair of polymer concentrations, taking into account polymer adsorption; - determination of the injection time for each of the polymer rims, provided that the speed of the rear edge of the mixing zone of the rim with a higher polymer concentration is greater than or equal to the speed of the front edge of the mixing zone of the next rim; - obtaining the dependence of the polymer concentration on the injection time; - determination of the obtained dependence of the concentration values for each of the n rims, except for the first polymer rim, at which the volume of the polymer has a minimum value; - determination of polymer volume and injection time values corresponding to the values of polymer concentrations obtained at the previous stage. 35. A computer-readable medium for characterizing polymer rims according to claim 34, in which analytical expressions are used to determine the speeds of the leading and trailing edges of the mixing zone, relative to the polymer injection rate, at the boundary of the polymer rims for each pair of polymer concentrations:

where

- relative speed of the leading edge of the mixing zone,

- relative speed of the trailing edge of the mixing zone, μ(s) - dependence of viscosity on polymer concentration, c _j - concentration in the slug of higher viscosity, c _j+1 - concentration in the slug of lower viscosity. 36. A computer-readable medium for characterizing polymer rims according to claim 34, in which, when determining the relative velocities of the leading and trailing edges of the mixing zone, adsorption of the polymer is additionally taken into account by determining the normalized adsorption isotherm. 37. A computer-readable medium for characterizing polymer rims according to claim 34, in which the determination of the normalized polymer adsorption isotherm a (c) is carried out using the equation:

where Г(с) - adsorption isotherm; ρ _w is the density of water; ρ _s - rock density; ϕ - formation porosity. 38. A computer-readable medium for characterizing polymer rims according to claim 34, in which the set of concentrations at which the volume of polymer tends to a minimum is determined by the formula:

where c is the polymer concentration in the fringes from the first to n; c _j - concentration in the slug of higher viscosity; T _j - start time of injection of the slug with concentration c _j+1 ; c _j+1 - concentration in the slug of lower viscosity. 39. A computer-readable medium for characterizing polymer slug according to claim 34 or 38, wherein the injection start time of each slug (T _j ) is determined by the formula:

for j=1,…,n, where T _max is the total injection time of polymer rims, during which the leading edge must not be destroyed;

- relative speed of the trailing edge of the mixing zone of the slug of higher viscosity;

- relative speed of the leading edge of the mixing zone of the slug of lower viscosity. 40. A computer-readable medium for characterizing polymeric rims according to claim 34, in which the volume value for each of the obtained concentrations is determined by the formula: V _j \u003d c _j (T _j -T _j-1 )V, where V is the volume of water injected into the reservoir during the time T _max equal to T _max q, where q is the volumetric injection rate determined based on the technological parameters of the oil reservoir. 41. A computer-readable medium for characterizing polymeric rims according to claim 34, in which the value of injection times for each of the obtained concentration values is determined by the formula: t _j \u003d T _j -T _j-1 , where T _j - start time of injection of the slug with concentration c _j+1 , T _j-1 - start time of injection of the slug with concentration c _j . 42. The computer-readable media for characterizing the polymer slug of claim 34, wherein the processor further repeats the following steps for different numbers n: - determination of the velocities of the leading and trailing edges of the mixing zone at the boundary of the polymer rims, relative to the polymer injection rate, for each pair of polymer concentrations, taking into account polymer adsorption, - determination of the injection time for each of the polymer rims, provided that the speed of the rear edge of the mixing zone of the rim with a higher polymer concentration is greater than or equal to the speed of the front edge of the mixing zone of the next rim, - obtaining the dependence of the polymer concentration on the injection time, - determination of the obtained dependence of the concentration values for each of the n rims, except for the first polymer rim, at which the volume of the polymer has a minimum value, - determination of the obtained values of the concentrations of the corresponding values of the polymer volume and injection time; calculating the total polymer volume for each value of n and the proportion of reduction in total polymer volume relative to the volume of polymer required to pump one slug, and fixing the value of n slug that achieves the optimal reduction in the proportion of polymer.

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