阅读说明：本技术 一种储层优势通道物性参数计算方法 (Reservoir dominant channel physical property parameter calculation method ) 是由 冯国庆 何玉俊 唐凡 薛芳芳 于 2019-11-18 设计创作，主要内容包括：本发明公开了一种储层优势通道物性参数计算方法,包括：步骤1,大孔道位置分布的确定；步骤2,孔径分布的计算；步骤3,流水区域横向非均质性的计算；步骤4,各级孔道体积的计算；步骤5,裂缝性储层的模拟计算。本发明的优点是：准确计算出水驱区域内各级孔道的大小和体积,以往的技术仅限于识别出井间存在的优势通道,并没有涉及到各级通道体积的计算。(The invention discloses a method for calculating physical property parameters of a reservoir dominant channel, which comprises the following steps: step 1, determining the distribution of large pore channel positions; step 2, calculating the pore size distribution; step 3, calculating the transverse heterogeneity of the flowing water area; step 4, calculating the volume of each level of pore channel; and 5, simulating and calculating the fractured reservoir. The invention has the advantages that: the size and the volume of each level of pore canal in the water drive area are accurately calculated, the prior art is only limited to identifying the dominant channel existing between wells, and the calculation of the volume of each level of channel is not involved.)

1. A reservoir dominant channel physical property parameter calculation method is characterized by comprising the following steps:

step 1, determining the distribution of large pore channel positions;

in a pair of injection and production well control areas of a homogeneous, equal-thickness and single-production layer, the crude oil industrial recovery rate reaches B% and the water content of a production well reaches A% after the time t from production; recording a water injection well point O, a production well as a point W, the pressure gradient near a line segment OW is maximum, and taking OE and OF as length units, the method comprises

Determination of the parameter α, Curve

y＝x^α(x∈[0,1])

The lower boundary of the high permeability zone, the upper boundary and the lower boundary being symmetric about the diagonal OW; thus, the distribution position of the large pore channel is calculated and simulated, for the heterogeneous stratum, the distribution area of the large pore channel is determined by using the oil deposit description result, the water absorption profile and other data, the area of the large pore channel is equal to B percent and is reflected in the injection and production well control area, the crude oil in the area of B percent is produced, the area contains a dominant seepage channel, the crude oil is basically displaced, the seepage fluid in the pore channel is water, and the crude oil in the area of (1-B percent) is not produced;

different α values correspond to different lower boundary curves, that is, different distribution regions of hypertonic strips, and for a non-five-point well pattern, the control region is determined by the midpoint of the connecting line of the left and right adjacent wells, and the area is marked as S₁The production level therein is still marked as B%, α corresponding to the lower boundary curve₁Satisfies the equation:

step 2, calculating the pore size distribution;

setting the reservoir to be n layers according to longitudinal heterogeneous, setting a certain time in the later stage of water injection exploitation, and determining the actual recovery ratio B of each layer by splitting according to the water absorption profile, the water absorption index and the liquid extraction index_i％，i＝1,2,…,n；

If the horizontal direction is not homogeneous, the flow water area roughly drawn on the ith layer is still marked as B_iSo that it contains sites of high permeability, the volume of which is equal to B of the total volume of the layer_iPercent; if there is no transverse heterogeneity, draw B_iB having an area equal to the total area of the layer_i% water-to-oil flow ratio of i-th layer

A_iIs the water content of the i-th layer of produced liquid, and

here K_io、μ_o、μ_w、B_i% is known, and the water phase permeability of the i-th layer at that time can be determined

Average radius of flooded pores of the layer

Wherein phi_iwPorosity of the injected water wave area; if K is Darcy, r is in centimeters, there is an approximation

The average pore diameter of the rest un-watered parts is

Note the book

I.e. lambda_iTable i ratio of pore radius at the water flowing area and the oil flowing area of the layer i, the pore radius obeys the log normal distribution and the approximate normal distribution

Wherein the standard deviation sigma io of the radius of the pore throat of the ith undisturbed stratum is calculated by the formula (11);

the radius of the channels can be divided into several stages as required,

the pore passage grading and the division standard thereof are determined according to the geological condition and the engineering requirement;

when no special consideration is given, the principle of aperture classification is that the probability that the apertures calculated by a majority of one-injection one-sampling control areas belong to each level is proper, and the situation that the probability of one or two levels is particularly high or particularly low is avoided;

subdividing a well group control area by using a three-dimensional grid and falling on a well group control area B_iPoint in (3) corresponds to pore throat radius

Wherein: sigma_iw＝λ_iσ_io(13)

Calculating r_iwThe probabilities belonging to the above classes are given by probability values of [0, 1%]The interval is divided into k subintervals, and the length corresponds to a probability value;

generating random numbers X uniformly distributed in the [0,1] interval, and if X falls in the kth subinterval, the pore throat radius at the point is the kth level, and the point is marked with a kth mark;

step 3, calculating the transverse heterogeneity of the flowing water area;

one injection and one extraction unit interval [0, R_e]Dividing into 100 equal parts;

each part area is regarded as the one-way flow of the incompressible fluid, and macroscopically, the flow of each part is different, and 100 parts of the incompressible fluid and the flow of each part macroscopically form the flow between one injection well and one production well; the flow formula of the jth part according to Darcy's law is

In the formula A_jThe J-th water cross-sectional area, m²；

K_j-permeability, md;

ΔP_j-the pressure difference, MPa, across the jth portion;

Q_jflow of the jth portion, m³/d；

L-length per fraction, well spacing R_e/100，m；

μ -viscosity, mPas;

a-unit correction factor, a-0.3858;

from this, the permeability at the j-th part can be obtained

Formula (15) shows that the permeability can be obtained for the known pressure difference, the known seepage cross-sectional area and the known flow rate, and the calculation method of the pressure difference, the known seepage cross-sectional area and the known flow rate is described below to obtain the permeability at each position;

1. calculation of flow

By monthly water uptake of injection well at layer j₁Monthly liquid production quantity Q of corresponding layer of production well₂The linear combination of (2) can determine the flow rate Q of the liquid in the i-th portion_i

2. Calculation of pressure at various locations

Injecting water into the well A, producing liquid from the well B, and determining the pressure of any point M of the stratum as

Wherein

Wherein r is₁-distance of point M to water injection well a;

r₂-distance of point M to production well B;

r_e-a feed radius;

r_w-a wellbore radius;

r is well spacing;

p_WA、p_WBinjecting water into the well A, producing liquid from the well B and the bottom pressure of the two wells;

3. method for determining cross-sectional area A

Let the circle with radius r and curve y be x^αIntersect at point (x, y) and solve the system of equations

The intersection coordinates (x, y) can be obtained, and β ═ tan can be obtained^-1(y/x) such that θ ═ pi/2-2 β, assuming reservoir thickness h, the cross-sectional area at radius r is

The cross-sectional areas A, Δ p and the flow rate Q_iSubstituting the equivalent value into a formula (15) to obtain the permeability K of the section with the radius r, and calculating the probability that the radius of the pore throat at the section belongs to each level by using the method in the previous section;

step 4, calculating the volume of each level of pore channel;

after the position and the size distribution of the large pore passage are quantitatively analyzed, the volume of each level of pore passage is calculated, and the calculation process of each level of pore passage is as follows: r_eIndicating the distance between the water injection well O and the oil production well W,

To obtain (x)_r,y_r)，tgβ＝(x_r/a)^α-1，β＝tan^-1((x_r/a)^α-1)，θ＝π/2－2 β area of sector AOB S_AOB＝πθr²A 2, a straight line y xtg β and a curve y a^1-αx^αArea of enclosed pattern

The area of the large pore channel distribution area in a circle with the radius of r is

Let the distribution probability of the ultra-large pore channel, the middle pore channel and the small pore channel at the radius r be p respectively₁(r)，p₂(r)，p₃(r)，p₄(R) the interval [0, R ]_e]100 equal parts, with an interval R_eN, obtaining the volume of the grade i pore canal of the r part

Wherein the content of the first and second substances,

x_rby solving a system of equations

step 5, simulation calculation of fractured reservoir

Calculating the permeability K and the porosity phi of each of 100 parts in the flowing water area, and then calculating the permeability K and the porosity phi according to a formula

Wherein b is_i-width of crack, mm;

calculating the crack width b of the i-th part_iWherein the crack permeability of the ith part

while

Firstly, fitting the porosity and permeability of three well groups according to the following formula;

φ＝αlnK+β

that is to say

K＝Ae^Bφ(28)

Wherein the content of the first and second substances,k (mD), phi is the value of percent removal;

the relationship between fracture permeability and porosity can be represented by the following formula

K_f＝8.33×10⁶φ_fw²(29)

Wherein, w is the width of the crack, mm;

K_f-fracture permeability, D;

let aK equal to K_f(a is determined by the water cut, where a is taken to be approximately 0.5),then, by equations (28) and (29) and noting the dimensional change, it can be obtained

aAe^Bφ＝8.33×10⁵φ_fw²(30)

Note the book

The calculation formula of the known seam width w and the hole radius r is as follows

K in the formula (32) is crack permeability, and K in the formula (33) is high permeability strip permeability needing plugging regulation calculated according to a gap medium; because now

Porosity of fracture medium

micro-cracking: w is less than or equal to 3.6;

middle crack: w is more than or equal to 3.6 and less than or equal to 6.1;

wide crack: w is more than or equal to 6.1 and less than or equal to 9.7;

extra wide crack: w is more than or equal to 9.7;

according to the division standard, the calculation is carried out by using the method, and the volume and the percentage of each stage of fracture are listed in detail in a calculation result data table.

Technical Field

The invention relates to the technical field of oil and gas field development, in particular to a method for calculating physical property parameters of a reservoir dominant channel.

Background

In the process of long-term water injection development of an oil field, as a reservoir is soaked and washed by water injected by a person for a long time, the properties, the dynamic characteristics and the physical properties of the reservoir are obviously changed, so that a superior seepage channel exists between oil and water wells, the water injection ineffective circulation is caused, and the oil field recovery ratio is influenced. At present, the research on the dominant channel is mainly based on qualitative identification of the dominant channel, such as a mine field data direct method, a production dynamic data identification method, a tracer monitoring method and the lack of an effective method for calculating the volume and physical property parameters of the dominant channel. The invention provides a method for calculating the physical property parameters of an advantageous channel by depending on-site conventional dynamic and static data on the basis of the seepage mechanics theory of an oil-gas layer, and provides a theoretical basis for deep profile control or well pattern adjustment measures in the middle and later stages of oil field development.

Disclosure of Invention

Aiming at the defects of the prior art, the invention provides a method for calculating the physical property parameters of the dominant channel of the reservoir, which can effectively solve the problems in the prior art.

In order to realize the purpose, the technical scheme adopted by the invention is as follows:

a reservoir dominant channel physical property parameter calculation method comprises the following steps:

step 1, determining the distribution of large pore channel positions;

in a pair of injection and production well control areas of a homogeneous, equal-thickness and single-production layer, the industrial recovery rate of crude oil reaches B% and the water content of a production well reaches A% after the time t from production. Recording a water injection well point O, a production well as a point W, the pressure gradient near a line segment OW is maximum, and taking OE and OF as length units, the method comprises

Determination of the parameter α, Curve

y＝x^α(x∈[0,1])

It is the lower boundary of the high permeability zone, which is symmetric about the diagonal OW. Thus, the distribution position of the large pore channel is calculated and simulated, for the heterogeneous stratum, the distribution area of the large pore channel is determined by using the oil deposit description result, the water absorption profile and other data, the area of the large pore channel is equal to B percent and is reflected in the injection and production well control area, the crude oil in the area of B percent is produced, the area contains a dominant seepage channel, the crude oil is basically displaced, the seepage fluid in the pore channel is water, and the crude oil in the area of (1-B percent) is not produced.

Different α values correspond to different lower boundary curves, and thus to different valuesThe distribution area of the high permeability zone is determined by the midpoint of the connecting line of the left and right adjacent wells for a non-five-point well pattern, and the area is recorded as S₁The production level therein is still marked as B%, α corresponding to the lower boundary curve₁Satisfies the equation:

step 2, calculating the pore size distribution;

setting the reservoir to be n layers according to longitudinal heterogeneous, setting a certain time in the later stage of water injection exploitation, and determining the actual recovery ratio B of each layer by splitting according to the water absorption profile, the water absorption index and the liquid extraction index_i％，i＝1,2,…,n。

If the horizontal direction is not homogeneous, the flow water area roughly drawn on the ith layer is still marked as B_iSo that it contains sites of high permeability, the volume of which is equal to B of the total volume of the layer_iPercent; if there is no transverse heterogeneity, draw B_iB having an area equal to the total area of the layer_i% water-to-oil flow ratio of i-th layer

A_iIs the water content of the i-th layer of produced liquid, and

here K_io、μ_o、μ_w、B_i% is known, and the water phase permeability of the i-th layer at that time can be determined

Average radius of flooded pores of the layer

Wherein phi_iwIs the porosity of the region swept by the injected water. If K is Darcy, r is in centimeters, there is an approximation

The average pore diameter of the rest un-watered parts is

Note the book

I.e. lambda_iTable i ratio of pore radius at the water flowing area and the oil flowing area of the layer i, the pore radius obeys the log normal distribution and the approximate normal distribution

Namely, it is

Wherein the standard deviation σ io of the ith undisturbed formation pore throat radius is calculated by equation (11).

The radius of the channels can be divided into several stages as required,

and (4) determining the pore passage grading and the division standard thereof according to the geological condition and the engineering requirement.

When no special consideration is given, the principle of aperture classification is that the probability that the apertures calculated for most of the control areas with one injection and one extraction belong to each level is proper, and the situation that the probability of one or two levels is particularly high or low does not occur.

Subdividing a well group control area by using a three-dimensional grid and falling on a well group control area B_iPoint in (3) corresponds to pore throat radius

Wherein: sigma_iw＝λ_iσ_io(13)

Calculating r_iwThe probabilities belonging to the above classes are given by probability values of [0, 1%]The interval is divided into k sub-intervals, and the length corresponds to the probability value.

And generating random numbers X uniformly distributed in the [0,1] interval, and if X falls in the kth subinterval, the pore throat radius at the point is of the kth level, and the point is marked with the kth mark.

Step 3, calculating the transverse heterogeneity of the flowing water area;

one injection and one extraction unit interval [0, R_e]Dividing into 100 equal parts;

each region is regarded as a unidirectional flow of incompressible fluid, and macroscopically each flow is different, and the 100 parts together constitute a flow between injection and production wells. The flow formula of the jth part according to Darcy's law is

In the formula A_jThe J-th water cross-sectional area, m²；

K_j-permeability, md;

ΔP_j-the pressure difference across the jth aliquot, mPa;

Q_jflow of the jth portion, m³A month;

l-length per fraction, well spacing R_e/100，m；

μ -viscosity, mPas;

a is a unit correction coefficient, and a is 0.3858.

From this, the permeability at the j-th part can be obtained

Equation (15) shows that the permeability can be obtained for the known pressure difference, cross-sectional area of seepage and flow rate, and the calculation method of the pressure difference, cross-sectional area of seepage and flow rate at each position is described below to obtain the permeability at each position.

1. Calculation of flow

By monthly water uptake of injection well at layer j₁Monthly liquid production quantity Q of corresponding layer of production well₂The linear combination of (2) can determine the flow rate Q of the liquid in the i-th portion_i

2. Calculation of pressure at various locations

Injecting water into the well A, producing liquid from the well B, and determining the pressure of any point M of the stratum as

Wherein

Wherein r is₁-distance of point M to water injection well a;

r₂-distance of point M to production well B;

r_e-a feed radius;

r_w-a wellbore radius;

r is well spacing.

p_WA、p_WBInjecting water into the well A, producing liquid from the well B and obtaining the bottom pressure of the two wells.

3. Method for determining cross-sectional area A

Let the circle with radius r and curve y be x^αIntersect at point (x, y) and solve the system of equations

The intersection coordinates (x, y) can be obtained, and β ═ tan can be obtained^-1(y/x) such that θ ═ pi/2-2 β, assuming reservoir thickness h, the cross-sectional area at radius r is

The cross-sectional areas A, Δ p and the flow rate Q_iSubstituting the equivalent value into the formula (15) to obtain the permeability K of the section with the radius r, and calculating the probability that the pore throat radius at the section belongs to each order by using the method described in the previous section.

Step 4, calculating the volume of each level of pore channel;

after the position and the size distribution of the large pore passage are quantitatively analyzed, the volume of each level of pore passage is calculated, and the calculation process of each level of pore passage is as follows: r_eIndicating the distance between the water injection well O and the oil production well W,let a be the radius r of a circle and curve y^1-αx^αIntersect (x, y), solve the system of equations

To obtain (x)_r,y_r)，tgβ＝(x_r/a)^α-1，β＝tan^-1((x_r/a)^α-1) θ is π/2-2 β, and sector AOB has area S_AOB＝πθr²A 2, a straight line y xtg β and a curve y a^1-αx^αArea of enclosed pattern

The area of the large pore channel distribution area in a circle with the radius of r is

Let the distribution probability of the ultra-large pore channel, the middle pore channel and the small pore channel at the radius r be p respectively₁(r)，p₂(r)，p₃(r)，p₄(R) the interval [0, R ]_e]100 equal parts, with an interval R_eN, obtaining the volume of the grade i pore canal of the r part

Wherein the content of the first and second substances,

x_rby solving a system of equations

Thus obtaining the product.

Step 5, simulation calculation of fractured reservoir

Calculating the permeability K and the porosity phi of each of 100 parts in the flowing water area, and then calculating the permeability K and the porosity phi according to a formula

Wherein b is_i-width of crack, mm;

-fracture permeability, D, of part i;

-fracture porosity of ith fraction.

Calculating the crack width b of the i-th part_iWherein the crack permeability of the ith part

Approximating K calculated by the original software_iInstead, this is because the fracture permeability is much greater than the matrix permeability, i.e., water is considered to have passed along the fracture;

whileIs measured data, and is determined by the following method in the case where there is no measured data

The porosity and permeability of the three well groups are first fitted as follows.

φ＝αlnK+β

That is to say

K＝Ae^Bφ(28)

Wherein the content of the first and second substances,

k (mD), phi is the value of% removal.

The relationship between fracture permeability and porosity can be represented by the following formula

K_f＝8.33×10⁶φ_fw²(29)

Wherein, w is the width of the crack and mm.

K_f-fracture permeability, D;

let aK equal to K_f(a is determined by the water cut, where a is taken to be approximately 0.5),then, by equations (28) and (29) and noting the dimensional change, it can be obtained

aAe^Bφ＝8.33×10⁵φ_fw²(30)

Note the book

Into formula (30)

The calculation formula of the known seam width w and the hole radius r is as follows

K in the formula (32) is the crack permeability, and K in the formula (33) is the permeability of the high permeability strip which needs to be adjusted and blocked and is calculated according to the void medium. Because now

The pore size distribution calculated for the pore medium can be used to calculate the gap width distribution of the crack medium, i.e. the percentage of the cracks with various gap widths.

Ratio of slot width to hole radius

Porosity of fracture medium

Is 1% of the comprehensive porosity phi of the seepage medium provided by geological data, and the average gap width is 1.21 times of the average pore radius. The aperture division is limited to 3, 5 and 8, and the slit width is limited to 3.6, 6.1 and 9.7, namely the slit width range corresponding to each stage of cracks is as follows (mum):

micro-cracking: w is less than or equal to 3.6;

middle crack: w is more than or equal to 3.6 and less than or equal to 6.1;

wide crack: w is more than or equal to 6.1 and less than or equal to 9.7;

extra wide crack: w is more than or equal to 9.7.

According to the division standard, the calculation is carried out by using the method, and the volume and the percentage of each stage of fracture are listed in detail in a calculation result data table.

Compared with the prior art, the invention has the advantages that: the size and the volume of each level of pore canal in the water drive area can be accurately calculated, the prior art is only limited to identifying the dominant channel existing between wells, and the calculation of the volume of each level of channel is not involved.

Drawings

FIG. 1 is a schematic diagram of a distribution area of a high permeability strip of a five-point well network in accordance with an embodiment of the present invention;

FIG. 2 is a schematic diagram of a distribution area of a non-five point well pattern high permeability strip in accordance with an embodiment of the present invention;

FIG. 3 is a graph of a normal density function according to an embodiment of the present invention;

FIG. 4 is a schematic diagram of an aliquot of a first injection and sampling unit according to an embodiment of the present invention;

FIG. 5 is a graph of pressure distribution during a first injection and a first extraction according to an embodiment of the present invention;

FIG. 6 is a schematic cross-sectional area A of an embodiment of the present invention;

FIG. 7 is a diagram of an embodiment of the present invention dividing a [0,1] interval into 4 sub-intervals according to 4 probability values.

Detailed Description

In order to make the objects, technical solutions and advantages of the present invention more apparent, the present invention will be described in further detail by referring to the following examples.

A reservoir dominant channel physical property parameter calculation method comprises the following steps:

step 1, determining the distribution of large pore channel positions;

in a pair of injection and production well control areas of a homogeneous, equal-thickness and single-production layer, the production degree of crude oil is B% and the water content of a production well reaches A% after the time t from production. Referring to FIG. 1, the water injection well point O is marked, the production well is marked as the point W, the pressure gradient near the line segment OW is the maximum, and OE and OF are taken as length units

Determination of the parameter α, Curve

y＝x^α(x∈[0,1])

It is the lower boundary of the high permeability zone, which is symmetric about the diagonal OW. Thus, the distribution position (equivalent area) of the large pore channel is calculated and simulated, and is shown in the shaded part of fig. 1. For the heterogeneous stratum, the distribution area of the large pore canal is determined by using the oil reservoir description result, water absorption profile and other data, the area (volume is the product of thickness) of the distribution area is equal to B%, the distribution area is reflected in the injection and production well control area, crude oil in the area of B% is produced, the area contains a dominant seepage channel, the crude oil is basically displaced, the seepage fluid in the pore canal is water, and crude oil in the area of (1-B%) is not produced.

Different α values correspond to different lower boundary curves, i.e. to different distribution regions of hypertonic strips, and for non-five-point well patterns, the midpoint of the connecting line of the left and right adjacent wells is used to determine the control region (fig. 2), the area is marked as S₁The production level therein is still marked as B%, α corresponding to the lower boundary curve₁Satisfies the equation:

step 2, calculating the pore size distribution;

assuming that the reservoir is longitudinally inhomogeneously divided into n layers, such as an upper layer, a middle layer and a lower layer, n is 3. Setting a certain moment in the later stage of water injection exploitation, and according to the water absorption profile, water absorption index and liquid extraction index, the actual recovery ratio B of each layer can be determined by splitting_i％，i＝1,2,…,n。

If the horizontal direction is not homogeneous, the flow water area roughly drawn on the ith layer is still marked as B_iSo that it contains sites of high permeability, the volume of which is equal to B of the total volume of the layer_iPercent; if there is no transverse unevennessWhen nature is too high, B is drawn as shown in FIG. 1_iB having an area equal to the total area of the layer_i% water-to-oil flow ratio of i-th layer

A_iIs the water content of the i-th layer of produced liquid, and

here K_io、μ_o、μ_w、B_i% is known, and the water phase permeability of the i-th layer at that time can be determined

Average radius of flooded pores of the layer

Wherein phi_iwIs the porosity of the flowing water portion. If K is Darcy, r is in centimeters, there is an approximation

The average pore diameter of the rest un-watered parts is

Note the book

I.e. lambda_iIn the table, the ratio of the pore radius of the i-th laminar flow water to the pore radius of the flow oil is shown in the textbook of reservoir physics, and the pore radius is subject to the pairNumber normal distribution, approximately following normal distribution

Namely, it is

The standard deviation sigma io of the radius of the pore throat of the ith undisturbed formation is measured by a mercury intrusion experiment, can also be obtained by measurement statistics of core slices, or is estimated by using a permeability coefficient of variation, and can also be calculated by using a formula (11).

The radius of the channels can be divided into several stages as required, e.g.

Ultra-large pore path: rw is more than or equal to 8 mu m;

large pore path: rw belongs to [5 μm,8 μm ];

a mesopore: rw belongs to [3 μm,5 μm ];

small pore canal: rw is less than or equal to 3 mu m.

The pore canal classification and the classification standard thereof are generally determined appropriately according to geological conditions (such as whether sand is produced) and engineering requirements (such as consideration of the particle size of the plugging agent). For example, the production well does not see sand, the pore structure of the formation is basically judged to have no large change, the structure of the slug is not complicated, the slug can be only divided into a large pore passage, a middle pore passage and a small pore passage, and the value range of each pore diameter is properly estimated according to the porosity and the permeability of the undisturbed formation by referring to the table 1.

When no special consideration is given (for example, a specified range needs to be customized to one level), the principle of aperture classification is that the probability that the apertures calculated for most of the one-injection-one-sampling control areas belong to each level is proper, and the situation that the probability of one level or two levels is extremely high or extremely low does not occur. Referring to fig. 3, assuming classification points of 5, 10, 15, the majority of wells will exhibit no large channels and no extra-large channels; similarly, if the classification points are 1, 2, and 3, the channels will be substantially all large and extra-large, which does not achieve the purpose of classification into 4 classes.

TABLE 1 table of the relationship between porosity, permeability and pore size

Subdividing a well group control area by using a three-dimensional grid and falling on a well group control area B_iPoint in (3) corresponds to pore throat radius

Wherein: sigma_iw＝λ_iσ_io(13)

Calculating r_iwThe probabilities belonging to the above 4 classes are divided into [0,1] by 4 probability values]The interval is divided into 4 sub-intervals, and the length corresponds to 4 probability values, as shown in fig. 7.

Generating random number X with evenly distributed [0,1] interval, if X falls in kth subinterval, the pore throat radius at this point is kth grade, and for the sake of intuition, this point is marked with kth mark, such as color. The communication condition of the large pore channel is calculated, analyzed and observed.

Step 3, calculating the transverse heterogeneity of the flowing water area;

when water injection is carried out for exploitation, the pressure gradients of all parts in the reservoir are different, for example, the pressure gradient at the position close to a well is large, the scouring capability of water on the stratum is also large, the formation of a large pore channel is more easily caused, and the further analysis and calculation are as follows.

One injection and one extraction unit interval [0, R_e]100 equal parts, i.e. the interval [ O, W ] in scheme 4]100 equal parts, with an interval R_e/100。

Each region is regarded as a unidirectional flow of incompressible fluid, and macroscopically each flow is different, and the 100 parts together constitute a flow between injection and production wells. The flow formula of the jth part according to Darcy's law is

In the formula A_jThe J-th water cross-sectional area, m²；

K_j-permeability, md;

ΔP_j-the pressure difference across the jth aliquot, mPa;

Q_jflow of the jth portion, m³A month;

l-length per fraction, well spacing R_e/100，m；

μ -viscosity, mPas;

a is a unit correction coefficient, and a is 0.3858.

From this, the permeability at the j-th part can be obtained

Equation (15) shows that the permeability can be obtained for the known pressure difference, cross-sectional area of seepage and flow rate, and the calculation method of the pressure difference, cross-sectional area of seepage and flow rate at each position is described below to obtain the permeability at each position.

1. Calculation of flow

By monthly water uptake of injection well at layer j₁Monthly liquid production quantity Q of corresponding layer of production well₂The linear combination of (2) can determine the flow rate Q of the liquid in the i-th portion_i

2. Calculation of pressure at various locations

As shown in FIG. 5, if well A is injected with water and well B is producing fluid, the pressure at any point M in the formation can be determined by derivation

Wherein

Wherein r is₁-distance of point M to water injection well a;

r₂-distance of point M to production well B;

r_e-a feed radius;

r_w-a wellbore radius;

r is well spacing.

p_WA、p_WBInjecting water into the well A, producing liquid from the well B and obtaining the bottom pressure of the two wells.

3. Method for determining cross-sectional area A

As shown in fig. 6, let x be the radius r of a circle and the curve y^αIntersect at point (x, y) and solve the system of equations

The intersection coordinates (x, y) can be obtained, and β ═ tan can be obtained^-1(y/x) such that θ ═ pi/2-2 β, assuming reservoir thickness h, the cross-sectional area at radius r is

The cross-sectional areas A, Δ p and the flow rate Q_iSubstituting the equivalent value into the formula (15) to obtain the permeability K of the section with the radius r, and calculating the probability that the pore throat radius at the section belongs to each order by using the method described in the previous section.

Step 4, calculating the volume of each level of pore channel;

after the quantitative analysis of the large pore channel position and size distribution, the method also needs to be usedAnd calculating the volume of each stage of pore passage, wherein the volume calculation process of each stage of pore passage is as follows: as shown in FIG. 6, R_eIndicating the distance between the water injection well O and the oil production well W,let a be the radius r of a circle and curve y^1-αx^αIntersect (x, y), solve the system of equations

To obtain (x)_r,y_r)，tgβ＝(x_r/a)^α-1，β＝tan^-1((x_r/a)^α-1) θ is π/2-2 β, and sector AOB has area S_AOB＝πθr²A 2, a straight line y xtg β and a curve y a^1-αx^αArea of enclosed pattern

The area of the large pore channel distribution area in a circle with the radius of r is

Let the distribution probability of the ultra-large pore channel, the middle pore channel and the small pore channel at the radius r be p respectively₁(r)，p₂(r)，p₃(r)，p₄(R) the interval [0, R ]_e]100 equal parts, with an interval R_eN, obtaining the volume of the grade i pore canal of the r part

Wherein the content of the first and second substances,

x_rby solving a system of equationsThus obtaining the product.

Step 5, simulation calculation of fractured reservoir

The original software can calculate the permeability K and the porosity phi of each part in 100 parts of the flowing water area, and on the basis, the permeability K and the porosity phi are calculated through a formula

Wherein b is_i-width of crack, mm;

-fracture permeability, D, of part i;

-fracture porosity of ith fraction.

Calculating the crack width b of the i-th part_iWherein the crack permeability of the ith part

Approximating K calculated by the original software_iInstead, this is because the fracture permeability is much greater than the matrix permeability, i.e., water is considered to have passed along the fracture; while

Is measured data, and is determined by the following method in the case where there is no measured data

The porosity and permeability of the three well groups are first fitted as follows.

φ＝αlnK+β

That is to say

K＝Ae^Bφ(28)

Wherein the content of the first and second substances,

k (mD), phi is the value of% removal.

The results of the fitting and calculation are shown in table 2.

TABLE 2 fitting parameters Table

According to reservoir physics, the relationship between fracture permeability and porosity can be represented by the following formula

K_f＝8.33×10⁶φ_fw²(29)

Wherein, w is the width of the crack and mm.

K_f-fracture permeability, D;

let aK equal to K_f(a is determined by the water content ratio, where a is approximately 0.5), then from equations (28) and (29), and noting dimensional changes, one can obtain

aAe^Bφ＝8.33×10⁵φ_fw²(30)

Note the book

Into formula (30)

Wherein the porosity of the three well groups was 17.8%. Since the fracture width typically varies from 2 μm to 10 μm, when w is taken to be 2 μm, the x values calculated for the three well groups F247, G198, J226 are equal to 0.2998, 0.3331, 0.0030, respectively; when w is 5 μm, three wells are obtained by calculationThe x values of the groups are equal to 0.04797, 0.05330, 0.00047, respectively; when taking w to 10 μm, the x values for the three well groups were calculated to be equal to 0.01199, 0.01332, 0.00012, respectively. Then the average of the three well groups x is 0.1199, 0.13324, 0.00359, respectively, and 0.01, which is closest to the empirical estimate, is taken as an approximation of x, i.e., #_f＝0.01φ。

The calculation formula of the known seam width w and the hole radius r is as follows

K in the formula (32) is the crack permeability, and K in the formula (33) is the permeability of the high permeability strip which needs to be adjusted and blocked and is calculated according to the void medium. Since now K_fi＝K_iAnd has a diameter of 0.01 phi_i＝φ_fiThe pore size distribution calculated for the pore medium can be used to calculate the gap width distribution of the crack medium, i.e. the percentage of the cracks with various gap widths. Ratio of slot width to hole radius

That is, the porosity of the fracture medium

The porosity is 1% of the comprehensive porosity phi of the seepage medium provided by geological data, and the average gap width is 1.21 times of the average pore radius, so that the description situation of the crack distribution can be conveniently converted on the basis of the simulation calculation of the pore medium hypertonic strip. The aperture division is limited to 3, 5 and 8, and the slit width is limited to 3.6, 6.1 and 9.7, namely the slit width range corresponding to each stage of cracks is as follows (mum):

micro-cracking: w is less than or equal to 3.6;

middle crack: w is more than or equal to 3.6 and less than or equal to 6.1;

wide crack: w is more than or equal to 6.1 and less than or equal to 9.7;

extra wide crack: w is more than or equal to 9.7.

According to the division standard, the calculation is carried out by using the method, and the volume and the percentage of each stage of fracture are listed in detail in a calculation result data table.

It will be appreciated by those of ordinary skill in the art that the examples described herein are intended to assist the reader in understanding the manner in which the invention is practiced, and it is to be understood that the scope of the invention is not limited to such specifically recited statements and examples. Those skilled in the art can make various other specific changes and combinations based on the teachings of the present invention without departing from the spirit of the invention, and these changes and combinations are within the scope of the invention.