CN114136838A - Method for determining viscosity limit of water injection flooding crude oil at different water-containing stages of offshore heavy oil - Google Patents

Abstract

The invention discloses a method for determining the viscosity limit of water injection water flooding crude oil at different water-containing stages of offshore heavy oil, which comprises the following steps: determining the maximum temperature Tmax of a hot water flooding at the bottom of a well according to the temperature resistance limits of a well completion pipe column and a tool; secondly, determining the viscosity mu of the degassed crude oil_odA relation with temperature T; thirdly, determining the crude oil viscosity mu under the formation condition_oA relation with temperature T; fourthly, determining the relative permeability ratio K of oil and water_ro/K_rwCalculating the water content of different water saturation degrees according to a relational expression of the water saturation degrees; fifthly, calculating the pseudo-fluidity ratio M values of different temperatures; sixthly, calculating the quasi-fluidity value ratio M and the area sweep coefficient E of different temperatures_VAnd determining the spread systemNumber E_VInflection point value E of_{V inflection point}(ii) a Seventhly, calculating the inflection point E of the sweep coefficient reversely_{V inflection point}Corresponding pseudo-flow ratio M_{Inflection point}(ii) a Eighthly, the calculation reaches M_{Inflection point}Hot water drive viscosity inflection point value mu_{Inflection point}And will mu_{Inflection point}The crude oil viscosity limit value mu is obtained by reverse calculation under the condition of oil reservoir temperature_omax. The invention solves the problem of determining the viscosity limit of the hot water flooding crude oil in the current industry.

Description

Method for determining viscosity limit of water injection flooding crude oil at different water-containing stages of offshore heavy oil

Technical Field

The invention relates to the field of analysis of viscosity of crude oil of offshore heavy oil injection water flooding, in particular to a method for determining viscosity limit of crude oil of offshore heavy oil injection water flooding at different water-containing stages of conventional water flooding.

Background

The scale of the thick oil in the Bohai sea is large, and for the thick oil reservoir with crude oil viscosity of about 400 mPa.s under stratum conditions, the current development modes include cold production development of natural energy, conventional water injection flooding, activated water flooding and the like, and thermal production development of multi-element hot fluid injection huff and puff, hot water injection flooding and the like. For the cold recovery and heavy oil reservoir development, the conventional water drive has the problems of large oil-water fluidity ratio due to large crude oil viscosity and low oil displacement efficiency and sweep efficiency due to the fact that injected water enters suddenly, so that a pilot test for improving the recovery ratio by converting the conventional water drive of heavy oil into hot water drive is currently carried out in Bohai sea. The conventional water drive to hot water drive of offshore heavy oil has a fuzzy viscosity limit, and brings inconvenience to screening of a hot water drive target block.

Regarding the determination of the viscosity limit of the crude oil for the hot water injection flooding, the current research mainly focuses on the development indexes of numerical simulation research on different schemes, or experimental research is adopted to compare the oil displacement efficiency under different viscosities, but the temperature resistance limit of the conventional water flooding of a target block in different water-containing stages without changing a pipe column and tools and the like are not considered, so that the research on determining the viscosity limit of the crude oil for the hot water injection flooding under the conditions of different water-containing stages of the conventional water flooding of the offshore heavy oil is not available at present.

Disclosure of Invention

The invention aims to overcome the defects in the prior art and provides a method for determining the viscosity limit of the hot water injection flooding crude oil at different water-containing stages of offshore heavy oil. The patent achievement provides basis for screening of the offshore heavy oil water drive-to-hot water drive target block and design of geological oil reservoir schemes. The achievement of the patent is applied to a plurality of thick oil fields in the Bohai sea, and guidance and reference can be provided for hot water injection scheme design of the Bohai sea thick oil field. The invention has innovativeness.

The purpose of the invention is realized by the following technical scheme:

the method for determining the viscosity limit of the water injection flooding crude oil at different water-containing stages of the offshore heavy oil comprises the following steps:

s101, determining the maximum temperature value T of the downhole hot water injection and drive of the target area according to the temperature resistance limits of the well completion pipe column and the tool_max；

S102, determining the viscosity mu of the degassed crude oil in the target area_odA relation with temperature T; testing the viscosity values of the degassed crude oil under different temperature conditions by collecting crude oil samples of the target block; drawing a scatter diagram in a rectangular coordinate system, and obtaining the viscosity mu of the thick oil degassing crude oil through fitting_odAnd temperature T.

LgLgμ_od＝A-BT (A-1)

In the formula: mu.s_odViscosity, mPa · s, for the degassed crude oil; t is temperature, DEG C; a is a constant needing regression, B is a slope to be regressed;

s103, determining the viscosity mu of the crude oil under the stratum condition of the target area_oA relation with temperature T; the viscosity of the water phase is not changed greatly, and the value is 1mPa & s under different temperature conditions; determining the crude oil viscosity under the stratum condition through the viscosity of the degassed crude oil at the oil layer temperature, and calculating to obtain the crude oil viscosity mu under the stratum condition of the target block_oAnd temperature T;

E＝4.4044(ρ_oR_s+17.7935)^-0.515 (A-4)

F＝3.0352(ρ_oR_s+26.6904)^-0.338 (A-5)

in the formula: mu.s_oIs the viscosity of the crude oil under formation conditions, mPa · s; rho_oDensity of crude oil degassed for surface, g/m³；R_sM is the dissolved gas-oil ratio³T; e and F are coefficients to be calculated;

obtaining the crude oil viscosity mu under the stratum condition of the target block by fitting_oAnd temperature T is:

LgLgμ_o＝A₁-B₁T (A-6)；

in the formula: a. the₁Constants for which regression is required, B₁Is the slope to be regressed;

s104, determining the relative permeability ratio K of the oil phase and the water phase_ro/K_rwCalculating the water content of different water saturation degrees according to a relational expression of the water saturation degrees; selecting a rock core and an oil sample of a target block, and testing the relative permeability K of oil and water phases with different water saturations under different temperature conditions_roAnd K_rw；

S105, calculating a mobility ratio M value of the stratum under different temperature conditions;

s106, calculating the quasi-fluidity value ratio M and the area sweep coefficient E at different temperatures_VAnd determining the sweep coefficient E_VInflection point value E of_{V inflection point}；

S107, according to the obtained sweep coefficient inflection point value E_{V inflection point}Selecting a calculation formula corresponding to the well pattern form according to the well pattern form of water injection, and back-calculating the corresponding pseudo-mobility ratio M_{Inflection point}；

S108, calculating to M according to the water content and the maximum heat injection temperature_{Inflection point}Hot water flooding viscosity inflection point mu_{o inflection point}And will mu_{o inflection point}The crude oil viscosity limit value mu is obtained by reverse calculation under the condition of oil reservoir temperature_omax。

Further, in step S101, a maximum temperature limit value that the string and the tool can withstand is used as a condition, so as to determine a maximum temperature value of the downhole water injection pump in the target zone.

Further, step S104 specifically includes: in rectangular coordinate system, in K_ro/K_rwAs ordinate, water saturation S_wFor the abscissa, a scatter plot is drawn, fitting K_ro/K_rwAnd S_wThe relational expression of (1); calculating the water content of different water saturation; fitting K_ro/K_rwAnd S_wThe relation of (1):

Ln(K_ro/K_rw)＝C-DS_w (A-8)

in the formula: k_roRelative permeability of the oil phase; k_rwRelative permeability of water phase; s_wThe water saturation; c is a constant requiring regressionD is the slope to be regressed;

the water content calculation formula is:

in the formula: f. of_wThe water content was determined.

Further, in step S105, a pseudo-fluidity ratio M value is calculated using the formula (a-13):

in the formula: mu.s_oIs the viscosity of the crude oil under formation conditions, mPa · s; mu.s_wIs the viscosity of the aqueous phase at formation conditions, mPa · s; k is a radical of_ro(S_wc) Relative permeability of the oil phase at irreducible water saturation; k is a radical of_ro(S_w) Is the relative permeability of the oil phase at the average saturation of displacement front water; k is a radical of_rw(S_w) Is the relative permeability of the water phase at the average saturation of the displacement front water; s_wcIrreducible water saturation; s_wTo displace the average saturation of the water at the leading edge.

Further, in step S106, for water injection systems with different well patterns, the area sweep coefficients during water breakthrough are different, and a calculation formula corresponding to the well pattern form needs to be selected;

for a linear water injection system, the area sweep coefficient calculation formula during water breakthrough is as follows:

in the formula: a is the distance between wells on the well row, m; d is the distance between well rows, m; m is a pseudo-fluidity ratio;

for a five-point area water injection system, the area sweep coefficient calculation formula during water breakthrough is as follows:

for a reverse nine-point area water injection system, the area sweep coefficient calculation formula during water breakthrough is as follows:

for the reverse seven-point area water injection system, the area sweep coefficient calculation formula during water breakthrough is as follows:

further, in step S108,

to obtain

Then, by modifying (A-6), the viscosity limit calculation formula can be obtained:

in the formula: mu.s_omaxThe viscosity limit value of crude oil injected with hot water flooding under stratum conditions, mPa & s; mu.s_{o inflection point}To approximate a flow ratio M_{Inflection point}The viscosity inflection point value of the crude oil under the corresponding stratum condition, mPa & s; b is₁Is the slope of regression, with no dimension; t is_maxThe maximum heat injection temperature at the bottom of the well is DEG C; t is_{Oil reservoir}The original temperature of the oil reservoir is DEG C.

Compared with the prior art, the technical scheme of the invention has the following beneficial effects:

1. the method for determining the viscosity limit of the hot water injection flooding crude oil at different water content stages of the conventional water flooding of the offshore heavy oil is provided by considering the temperature resistance limit of the conventional cold production well completion string and tools, the influence of different rock cores and fluid properties on permeability and other factors.

2. The method provided by the invention considers the factors of the oil-water phase seepage changing along with the temperature in different water-containing stages, the considered factors are more comprehensive, the whole development stage of cold recovery heavy oil reservoir development is covered, the method is more accurate, and the applicability is stronger.

3. The conventional water flooding of the heavy oil reservoir has the problems of large oil-water fluidity ratio, easiness in sudden entry of injected water and the like, and further improvement of the recovery ratio after the conventional water flooding is the focus of current attention. The technology for improving the recovery ratio by converting conventional water flooding into hot water flooding of thickened oil is a new technology which is currently researched and tested, has a fuzzy viscosity limit and brings inconvenience to screening of a hot water flooding target block. The method provided by the invention provides a basis for screening the target block of the offshore heavy oil water drive-to-hot water drive and designing the geological oil reservoir scheme.

Drawings

FIG. 1 is a schematic flow diagram of the process of the present invention.

FIG. 2 is a plot of the viscosity versus temperature of the test data points of the test in a logarithmic coordinate system for the ground degassed crude oil at the target zone.

FIG. 3 is a fitting relation of the crude oil viscosity and temperature data of the original layer condition of the target block in a logarithmic coordinate system.

FIG. 4 is a graph showing the relative permeability ratio K of oil and water in a target block_ro/K_rwFitting relation with water saturation.

FIG. 5 shows the pseudo-fluidity ratio M and the area sweep efficiency E of the target block_VAnd fitting the relation in stages.

Detailed Description

The invention is described in further detail below with reference to the figures and specific examples. It should be understood that the specific embodiments described herein are merely illustrative of the invention and are not intended to limit the invention.

In order to make the purpose, technical scheme and advantages of the invention clearer, the invention is further explained in detail by taking the Bohai sea LD5-2 heavy oil reservoir as an example. As shown in fig. 1 to 5, the method for determining the viscosity limit of the water injection flooding crude oil at different water-containing stages of the offshore heavy oil comprises the following steps:

s101, determining the maximum temperature value T of the downhole hot water injection and drive of the target area according to the temperature resistance limits of the well completion pipe column and the tool_max. In order to improve the economy of a hot water flooding project, the offshore hot water flooding scheme is designed on the basis that the offshore platform ground facility is minimum in modification amount, a water injection well is not overhauled and a downhole separator is not replaced, and the maximum temperature limit value which can be borne by a pipe column and a tool is taken as a condition, so that the maximum temperature value of the downhole hot water flooding in a target area is determined.

According to multi-professional verification, the temperature resistance limit value of the downhole tool of the Luda 5-2 heavy oil reservoir is 120 ℃, the heat injection temperature of a wellhead is determined to be 120 ℃, the heat loss of a shaft is considered, and the corresponding bottom hole maximum temperature value Tmax is 108 ℃.

S102, determining the viscosity mu of the degassed crude oil in the target area_odWith temperature T. Collecting crude oil samples of the target block, and testing the viscosity values of the degassed crude oil under different temperature conditions; drawing a scatter diagram in a rectangular coordinate system, and obtaining the viscosity mu of the thick oil degassing crude oil through fitting_odAnd temperature T.

LgLgμ_od＝A-BT (A-1)

In the formula: mu.s_odViscosity, mPa · s, for the degassed crude oil; t is temperature, DEG C; a is the constant for which regression is desired and B is the slope to be regressed.

As shown in FIG. 2, the viscosity μ of the thickened oil was fitted based on the viscosity values of the degassed crude oil measured_odAnd temperature T, yielding coefficients a and B of 0.7059 and 0.0035, respectively (fig. 2).

LgLgμ_od＝0.7059-0.0035T(R²＝0.9937) (A-2)。

S103, determining the viscosity mu of the crude oil under the stratum condition of the target area_oWith temperature T. The viscosity of the water phase is not changed greatly, and the value can be 1mPa & s under different temperature conditions; crude oil viscosity μ under formation conditions_oThe calculation formula can adopt a Beggs calculation formula, the viscosity of crude oil under the stratum condition is determined through the viscosity of degassed crude oil under the oil layer temperature, and the stratum of the target block is obtained through calculationCrude oil viscosity μ under conditions_oAnd temperature T.

E＝4.4044(ρ_oR_s+17.7935)^-0.515 (A-4)

F＝3.0352(ρ_oR_s+26.6904)^-0.338 (A-5)

In the formula: mu.s_oIs the viscosity of the crude oil under formation conditions, mPa · s; rho_oDensity of crude oil degassed for surface, g/m³；R_sM is the dissolved gas-oil ratio³T; e and F are coefficients that need to be calculated.

Obtaining the crude oil viscosity mu under the stratum condition of the target block by fitting_oAnd temperature T is:

LgLgμ_o＝A₁-B₁T (A-6)

in the formula: a. the₁Constants for which regression is required, B₁Is the slope to be regressed.

The basic parameters of the 5-2 heavy oil reservoir, such as the density of the ground degassed crude oil is 0.976g/m³(ii) a The dissolved gas-oil ratio is 25m³The viscosity mu of the degassed crude oil in the target zone at different temperatures measured in the second step can be determined by substituting/t into the formulae (A-3), (A-4), (A-5)_odConversion to crude oil viscosity μ under formation conditions_o. FIG. 3 shows that the viscosity mu of crude oil under the condition of stratum of a certain block of Bohai sea is obtained by fitting_oAnd temperature T is:

LgLgμ_o＝0.6218-0.0042T(R²＝0.9984) (A-7)。

s104, determining the relative permeability ratio K of the oil phase and the water phase_ro/K_rwAnd calculating the water content of different water saturation degrees according to the relation of the water saturation degrees. Selecting a rock core and an oil sample of a target block, and testing the relative permeability K of oil and water phases with different water saturations under different temperature conditions_roAnd K_rw. In rectangular coordinate system, in K_ro/K_rwIs a vertical coordinate of the main body of the device,water saturation degree S_wFor the abscissa, a scatter plot is drawn, fitting K_ro/K_rwAnd S_wThe relational expression (c) of (c). And calculating the water content of different water saturation.

Fitting K_ro/K_rwAnd S_wThe relation of (1):

Ln(K_ro/K_rw)＝C-DS_w (A-8)

in the formula: k_roRelative permeability of the oil phase, decimal; k_rwRelative permeability of water phase, decimal; s_wWater saturation, decimal; c is a constant to be regressed and D is the slope to be regressed.

The water content calculation formula is:

in the formula: f. of_wThe water content is decimal fraction.

TABLE 1 Bohai sea oil and water relative permeability curve (temperature 100 deg.C) of a typical heavy oil reservoir

As shown in table 1, the relative oil-water permeability of the rock core and the sample of the sojourn 5-2 reservoir at 100 ℃ is shown in the 1 st, 2 nd and 3 rd columns of table 1; the water content is shown in Table 1, column 6. As shown in FIG. 4, K can be fit according to the data at 100 deg.C, 150 deg.C, and 200 deg.C_ro/K_rwAnd S_wThe coefficients C at 100 ℃, 150 ℃ and 200 ℃ were 12.4286, 11.8827 and 11.4044, respectively, and D were 20.3642, 18.4626 and 17.1997, respectively.

Data points for the 100 ℃ experimental test:

Ln(K_ro/K_rw)＝12.4286-20.3642S_w(R²＝0.9960) (A-10)

data points for the 150 ℃ experimental test:

Ln(K_ro/K_rw)＝11.8827-18.4626S_w(R²＝0.9980) (A-11)

data points for the 200 ℃ experimental test:

Ln(K_ro/K_rw)＝11.4044-17.1997S_w(R²＝0.9974) (A-12)

s105, calculating a pseudo-mobility ratio M value of the stratum under different temperature conditions. The pseudo-mobility ratio M of water and oil is an important parameter for judging the plunging capacity of injected water, and the larger the value is, the easier the plunging is performed, and the lower the area sweep coefficient is. Calculating a pseudo-fluidity ratio M value by using the formula (A-13):

in the formula: mu.s_oIs the viscosity of the crude oil under formation conditions, mPa · s; mu.s_wIs the viscosity of the aqueous phase at formation conditions, mPa · s; k is a radical of_ro(S_wc) Relative permeability of the oil phase at irreducible water saturation, decimal; k is a radical of_ro(S_w) The relative permeability of the oil phase at the average saturation of the displacement front water, decimal; k is a radical of_rw(S_w) The relative permeability of the water phase under the average saturation of the displacement front water is decimal; s_wcIrreducible water saturation, decimal; s_wTo displace the average saturation of the water at the leading edge.

Wherein, K_ro(S_wc) And K_ro(S_w)+K_rw(S_w) Values can be obtained from the data measured in the fourth step, see columns 4, 5 of Table 1. Mu.s_wThe viscosity of the water phase under the stratum condition is smaller, so that the influence of temperature change on the viscosity of the water phase can be ignored, and the viscosity of the water phase under different temperatures is 1mPa & s. Mu.s_oFor the viscosity of the crude oil under the formation condition, the viscosity value of the crude oil under the formation condition corresponding to the phase permeation curve needs to be considered, for example, the bottom heat injection temperature of the 5-2 oil reservoir at sojourn is 108 ℃, and referring to fig. 3, the viscosity of the crude oil under the formation condition corresponding to the temperature is 26mPa · s.

S106, calculating the ratio M of the quasi-fluidity values and the area sweep at different temperaturesCoefficient E_VAnd determining the sweep coefficient E_VInflection point value E of_{V-shaped crutch}. In the water injection systems with different well patterns, the area sweep coefficients during water breakthrough are different, and a calculation formula corresponding to the well pattern form needs to be selected.

For a linear water injection system, the area sweep coefficient calculation formula during water breakthrough is as follows:

in the formula: a is the distance between wells on the well row, m; d is the distance between well rows, m; m is the pseudo-fluidity ratio, decimal.

For a five-point area water injection system, the area sweep coefficient calculation formula during water breakthrough is as follows:

for a reverse nine-point area water injection system, the area sweep coefficient calculation formula during water breakthrough is as follows:

for the reverse seven-point area water injection system, the area sweep coefficient calculation formula during water breakthrough is as follows:

the target block of the 5-2 oil reservoir in the journey is a row-shaped water injection system, the distance between wells on a well row is 150m, and the distance between well rows is 200 m. Therefore, the formula (A-14) is selected to calculate the area sweep coefficient E_VDrawing to obtain a quasi-fluidity value ratio M and an area sweep coefficient E_VScatter diagram, fitting by stages to obtain a relation, a sweep coefficient E_VInflection point value E of_{V-shaped crutch}0.4924, as shown in FIG. 5.

S107, inverse calculation of the summation systemSeveral inflection points E_{V inflection point}Corresponding pseudo-flow ratio M_{Inflection point}. According to the sweep coefficient inflection point value obtained in the sixth step and according to the well pattern form of water injection, selecting the calculation formulas of the corresponding well pattern forms of (A-14), (A-15), (A-16) and (A-17), and inversely calculating the corresponding pseudo-mobility ratio value M_{Inflection point}。

The Luoda 5-2 oil reservoir is a drainage water injection system and is obtained according to the fifth step_{V-shaped crutch}To 0.4924, a reverse-calculated pseudo-fluidity ratio M was selected (A-14)_{Inflection point}Determining M_{Inflection point}Is 12. At M_{Inflection point}Here, the relationship between the sweep efficiency and the pseudo-streaming ratio can be clearly divided into two sections.

When M is less than or equal to 12:

E_A1＝0.6356-0.0643 ln M(R²＝0.9045) (A-18)

when M > 12:

E_A2＝0.4961-0.0043 ln M(R²＝0.8114) (A-19)

s108, calculating to M according to the water content and the maximum heat injection temperature_{Inflection point}Hot water flooding viscosity inflection point mu_{o inflection point}And will mu_{o inflection point}The crude oil viscosity limit value mu is obtained by reverse calculation under the condition of oil reservoir temperature_omax。

To obtain

Then, by modifying (A-6), the viscosity limit calculation formula can be obtained:

in the formula: mu.s_omaxThe viscosity limit value of crude oil injected with hot water flooding under stratum conditions, mPa & s; mu.s_{o inflection point}To approximate a flow ratio M_{Inflection point}The viscosity inflection point value of the crude oil under the corresponding stratum condition, mPa & s; b is₁Is the slope of regression, with no dimension;T_maxthe maximum heat injection temperature at the bottom of the well is DEG C; t is_{Oil reservoir}The original temperature of the oil reservoir is DEG C.

The original reservoir temperature of the Luda 5-2 heavy oil reservoir is 50 ℃, and if the conventional water-flooding water content is 10%, the maximum heat injection temperature is 108 ℃. To obtain the viscosity limit of the rotary water flooding, μ_wTaking the value of 1 mPas according to the seventh step M_{Inflection point}Determining a value 12, looking up a table 1, and obtaining the following corresponding rows with the water content of about 0.1: k is a radical of_ro(S_wc) The value is 0.81 (see column 4 of Table 1), k_ro(S_w)+k_rw(S_w) Taking the value of 0.643 (see column 5 in Table 1), and calculating to obtain mu by adopting (A-20)_{o inflection point}15.1 mPas. Slope B determined from the third step₁，B₁Taking the value of 0.0042, and calculating by adopting (A-21) to obtain the maximum viscosity limit mu applicable to hot water flooding under the original oil reservoir temperature condition_omaxWas 116 mPas.

If the water content is 50%, look up table 1 for the row with water content of about 0.5, obtain: k is a radical of_ro(S_wc) The value is 0.81 (see column 4 of Table 1), k_ro(S_w)+k_rw(S_w) Taking the value of 0.373 (see column 5 in Table 1), and calculating by using (A-20) to obtain mu_{o inflection point}26.06 mPas. Slope B determined from the third step₁，B₁Taking the value of 0.0042, and calculating by adopting (A-21) to obtain the maximum viscosity limit mu applicable to hot water flooding under the original oil reservoir temperature condition_omax303 mPas.

The invention only takes the viscosity limit of the crude oil of the conventional water drive of the offshore heavy oil at different water content stages as a main description, and other deformation modes (such as hot water + nitrogen compound drive, hot water + foam compound drive, hot water + surfactant + oil displacement agent and the like) mainly based on the hot water drive are still within the protection scope of the invention.

The present invention is not limited to the above-described embodiments. The foregoing description of the specific embodiments is intended to describe and illustrate the technical solutions of the present invention, and the above specific embodiments are merely illustrative and not restrictive. Those skilled in the art can make many changes and modifications to the invention without departing from the spirit and scope of the invention as defined in the appended claims.

Claims (6)

1. The method for determining the viscosity limit of the water injection flooding crude oil at different water-containing stages of the offshore heavy oil is characterized by comprising the following steps of:

s101, determining the maximum temperature value T of the downhole hot water injection and drive of the target area according to the temperature resistance limits of the well completion pipe column and the tool_max；

S102, determining the viscosity mu of the degassed crude oil in the target area_odA relation with temperature T; testing the viscosity values of the degassed crude oil under different temperature conditions by collecting crude oil samples of the target block; drawing a scatter diagram in a rectangular coordinate system, and obtaining the viscosity mu of the thick oil degassing crude oil through fitting_odAnd temperature T.

LgLgμ_od＝A-BT (A-1)

In the formula: mu.s_odViscosity, mPa · s, for the degassed crude oil; t is temperature, DEG C; a is a constant needing regression, B is a slope to be regressed;

s103, determining the viscosity mu of the crude oil under the stratum condition of the target area_oA relation with temperature T; the viscosity of the water phase is not changed greatly, and the value is 1mPa & s under different temperature conditions; determining the crude oil viscosity under the stratum condition through the viscosity of the degassed crude oil at the oil layer temperature, and calculating to obtain the crude oil viscosity mu under the stratum condition of the target block_oAnd temperature T;

E＝4.4044(ρ_oR_s+17.7935)^-0.515 (A-4)

F＝3.0352(ρ_oR_s+26.6904)^-0.338 (A-5)

in the formula: mu.s_oIs the viscosity of the crude oil under formation conditions, mPa · s; rho_oDensity of crude oil degassed for surface, g/m³；R_sTo dissolveGas-oil ratio, m³T; e and F are coefficients to be calculated;

obtaining the crude oil viscosity mu under the stratum condition of the target block by fitting_oAnd temperature T is:

LgLgμ_o＝A₁-B₁T (A-6)；

in the formula: a. the₁Constants for which regression is required, B₁Is the slope to be regressed;

s104, determining the relative permeability ratio K of the oil phase and the water phase_ro/K_rwCalculating the water content of different water saturation degrees according to a relational expression of the water saturation degrees; selecting a rock core and an oil sample of a target block, and testing the relative permeability K of oil and water phases with different water saturations under different temperature conditions_roAnd K_rw；

S105, calculating a mobility ratio M value of the stratum under different temperature conditions;

s106, calculating the quasi-fluidity value ratio M and the area sweep coefficient E at different temperatures_VAnd determining the sweep coefficient E_VInflection point value E of_{V inflection point}；

S107, according to the obtained sweep coefficient inflection point value E_{V inflection point}Selecting a calculation formula corresponding to the well pattern form according to the well pattern form of water injection, and back-calculating the corresponding pseudo-mobility ratio M_{Inflection point}；

S108, calculating to M according to the water content and the maximum heat injection temperature_{Inflection point}Hot water flooding viscosity inflection point mu_{o inflection point}And will mu_{o inflection point}The crude oil viscosity limit value mu is obtained by reverse calculation under the condition of oil reservoir temperature_omax。

2. The method for determining the crude oil viscosity limit of the water injection water flooding at different water-containing stages of the offshore heavy oil according to claim 1, wherein the maximum temperature limit value which can be endured by the pipe column and the tool is taken as a condition in step S101, so as to determine the maximum temperature value of the water injection water flooding at the bottom of the well in the target area.

3. The method for determining viscosity limit of water injection flooding crude oil at different water-containing stages of offshore heavy oil according to claim 1The method of (1), wherein step S104 is specifically: in rectangular coordinate system, in K_ro/K_rwAs ordinate, water saturation S_wFor the abscissa, a scatter plot is drawn, fitting K_ro/K_rwAnd S_wThe relational expression of (1); calculating the water content of different water saturation; fitting K_ro/K_rwAnd S_wThe relation of (1):

Ln(K_ro/K_rw)＝C-DS_w (A-8)

in the formula: k_roRelative permeability of the oil phase; k_rwRelative permeability of water phase; s_wThe water saturation; c is a constant needing regression, and D is a slope to be regressed;

the water content calculation formula is:

in the formula: f. of_wThe water content was determined.

4. The method for determining the viscosity limit of the water flooding crude oil injected at different water-containing stages of the offshore heavy oil according to claim 1, wherein in step S105, the pseudo-mobility ratio M value is calculated by adopting the formula (A-13):

in the formula: mu.s_oIs the viscosity of the crude oil under formation conditions, mPa · s; mu.s_wIs the viscosity of the aqueous phase at formation conditions, mPa · s; k is a radical of_ro(S_wc) Relative permeability of the oil phase at irreducible water saturation; k is a radical of_ro(S_w) Is the relative permeability of the oil phase at the average saturation of displacement front water; k is a radical of_rw(S_w) Is the relative permeability of the water phase at the average saturation of the displacement front water; s_wcIrreducible water saturation; s_wTo displace the average saturation of the water at the leading edge.

5. The method for determining the viscosity limit of the water injection and water flooding crude oil at different water-containing stages of the offshore heavy oil according to claim 1, wherein in the step S106, the area sweep coefficients of the water injection systems of different well patterns during water breakthrough are different, and a calculation formula corresponding to the well pattern form needs to be selected;

for a linear water injection system, the area sweep coefficient calculation formula during water breakthrough is as follows:

in the formula: a is the distance between wells on the well row, m; d is the distance between well rows, m; m is a pseudo-fluidity ratio;

for a five-point area water injection system, the area sweep coefficient calculation formula during water breakthrough is as follows:

for a reverse nine-point area water injection system, the area sweep coefficient calculation formula during water breakthrough is as follows:

for the reverse seven-point area water injection system, the area sweep coefficient calculation formula during water breakthrough is as follows:

6. the method for determining the viscosity limit of the water injection flooding crude oil at different water-containing stages of the offshore heavy oil according to claim 1, wherein in step S108,

to obtain

Then, by modifying (A-6), the viscosity limit calculation formula can be obtained:

in the formula: mu.s_omaxThe viscosity limit value of crude oil injected with hot water flooding under stratum conditions, mPa & s; mu.s_{o inflection point}To approximate a flow ratio M_{Inflection point}The viscosity inflection point value of the crude oil under the corresponding stratum condition, mPa & s; b is₁Is the slope of regression, with no dimension; t is_maxThe maximum heat injection temperature at the bottom of the well is DEG C; t is_{Oil reservoir}The original temperature of the oil reservoir is DEG C.

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