CN117973243A - Core-well scale reservoir damage degree evaluation method - Google Patents
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Abstract
The invention provides a core-well scale reservoir damage degree evaluation method, which comprises the steps of selecting a representative Roodhart model to simulate dynamic fluid loss, and clearly dividing the fluid loss process into three stages: a transient fluid loss stage, a mud cake forming stage and a constant fluid loss stage; the laboratory obtains the data required in the model through dynamic filtration test; then converting the permeability recovery value into a well site scale, and calculating the permeability recovery value; and establishing a relation model between the permeability recovery value and the epidermis coefficient. According to the invention, the permeability recovery value data is linked with the surface coefficient of the well, the factors such as the fluid loss rate, the drilling rate and the like are considered, the invasion depth of the drilling fluid along the horizontal section is not linearly distributed, and the surface coefficient is gradually reduced. Laboratory data are converted into well site dimensions, and the damage degree of the drilling fluid to the reservoir core is described by replacing the previous single permeability recovery value with double parameters, so that a basis is provided for the selection of the drilling fluid.
Description
Technical Field
The invention belongs to the technical field of oil and gas exploitation, relates to establishment of a reservoir damage evaluation method, and particularly relates to a core-well scale reservoir damage degree evaluation method.
Background
Preferably, the drilling fluid to open the reservoir is beneficial to reduce reservoir damage and increase the production or injection capacity of the well. Often, drilling fluids are screened through indoor permeability recovery experiments based on preliminary selection of several drilling fluids. However, the fluid loss and permeability recovery values are different for different drilling fluids, and selecting a drilling fluid by the permeability recovery value or the fluid loss often lacks scientific basis. The existing reservoir damage research is mainly judged according to a single permeability recovery value measured by a laboratory experiment, and the influences of time, core permeability and overbalance differential pressure are generally considered. In fact, during drilling, the duration of invasion of drilling fluid into reservoirs of different depths and different properties is also different, so that a single experimental condition in a laboratory cannot represent the actual damage condition of different positions in a well, and the damage of the reservoir in the well site scale is mainly described by the skin coefficient, which is more complicated.
Disclosure of Invention
In order to solve the defects in the prior art, the invention provides a core-well scale reservoir damage degree evaluation method, which is used for establishing a relation between permeability recovery value data and well skin coefficients, using double parameters to replace the previous single permeability recovery value to describe the damage degree of drilling fluid to a reservoir core, and providing a basis for the selection of the drilling fluid.
The invention adopts the technical proposal for solving the technical problems that:
A method for evaluating the damage degree of a rock core-well scale reservoir, comprising the following steps:
S1: establishing a model to simulate the dynamic filtration of drilling fluid, and dividing the filtration process of the drilling fluid into stages;
S2: the laboratory obtains the data required in the model through dynamic filtration test;
S3: converting the experimental data to well site dimensions;
S4: calculating a permeability recovery value;
S5: calculating the surface coefficient of the well site;
S6: and obtaining the relation between the permeability recovery value and the surface coefficient of the well site.
Further, the step S1 specifically includes: the Roodhart model was selected to simulate the dynamic loss, and the Roodhart dynamic loss model was represented by the following formula:
Wherein: v and v s are total and instantaneous fluid loss, respectively; t eq is the transition time from the non-steady state to the steady state; t is the time of filtration; c s is the fluid loss coefficient during the transition time; c d is the dynamic loss coefficient;
The Roodhart dynamic filtration model divides the fluid filtration process into three phases, namely a transient filtration phase, a mud cake formation phase and a constant filtration phase.
Further, the step S3 specifically includes: the unit area loss parameters are used for conversion, the effective permeability of crude oil is used as the permeability parameter, and the following assumption is made:
(1) The time required for the mud cake in the laboratory and the on-site shaft to reach the equilibrium state is the same;
(2) Piston displacement is considered when calculating the intrusion volume;
(3) The over-balance pressure difference is kept unchanged in the drilling process;
The instantaneous fluid loss at the wellsite scale is:
Wherein: subscripts 1 and 2 represent laboratory and wellsite conditions, respectively, μ is filtrate viscosity, Δp is overbalanced differential pressure, r w is wellbore radius, r e is supply radius of the reservoir perpendicular to wellbore direction, L is total wellbore length in the reservoir, K is permeability;
The total fluid loss at any location in the well is:
the total drilling time is:
Wherein L is the total length of the well bore in the reservoir, R is the drilling rate, and 4 units are hours;
The intrusion radius is:
Wherein, Is the displaceable effective porosity, and as derived from equations (3) - (5), r d is not linear with L, i.e., the invasion depth of the drilling fluid is not a linear function.
Further, the step S4 specifically includes: the final permeability recovery profile for the linear core lesion is expressed as:
RPx＝1-ae-bx (6)
wherein x is the dimensionless invasion depth, RP x is the final permeability recovery value at the position x, a reflects the damage condition at the invasion end face, and b reflects the distribution condition of the damage of the invasion zone;
substituting formula (6) into a radial damage formula to obtain a permeability recovery value of an invaded end face:
The average permeability recovery value in the invaded zone from the dimensionless invaded depth x 1 to the dimensionless invaded depth x 2 is:
further, the calculation steps of the values of a and b are as follows:
And calculating the permeability recovery value of the whole rock core:
wherein L d is the invasion depth, L is the total length of the wellbore in the reservoir;
the values of a and b are calculated by an iterative method using the formulas (7) and (8).
Further, step S5 includes:
S5.1: calculating the filtration loss and the invasion depth;
S5.2: calculating the permeability recovery value of the invaded zone;
s5.3: calculating local skin coefficients along the wellbore;
s5.4: the total equivalent skin coefficient is calculated.
Further, step S5.1 specifically includes:
Assume that:
uHuV＝u2 (11)
Wherein u is the fluid loss rate of mud cakes on a well wall, u H and u V are the fluid loss rates in the vertical and horizontal directions respectively, I ani is an anisotropy index, and K H and K V are the permeabilities in the vertical and horizontal directions respectively;
the filtration loss per unit area is:
vH＝Ianiv (12)
v H and v V are the unit area of the fluid loss in the vertical and horizontal directions, respectively, and v is the total fluid loss;
The invasion depth in the horizontal direction was calculated using the formulas (5) and (21).
Further, the invaded zone permeability recovery value in step S5.2 is calculated by the following formula:
Wherein: r d is the invasion radius, r w is the wellbore radius, r i is the radius of the ith reservoir; r i-1 is the radius of the i-1 th segment reservoir; k i is the permeability recovery value corresponding to the ith section of reservoir.
Further, the local skin coefficient in step S5.3 is calculated by the following formula:
wherein: k is permeability, K dx is permeability of the invaded zone; i ani is the anisotropy index, r dxH is the invaded zone radius; r w is the wellbore radius.
Further, the total equivalent skin factor in step S5.4 is calculated by the following formula:
Wherein: l is the total length of the wellbore in the reservoir; i ani is an anisotropy index; x is the dimensionless penetration depth; h is the reservoir thickness; r w is the wellbore radius, S x is the skin factor at a dimensionless invasion depth x; Δx is the dimensionless penetration depth segmentation interval length; s xi is the epidermis coefficient corresponding to the i-th section dimensionless invasion depth segment.
The beneficial effects of the invention include: the model of the invention clearly expresses the relationship between the permeability recovery value and the well site skin coefficient. It is pointed out that under the action of factors such as fluid loss speed and drilling speed, the leakage of drilling fluid is not linearly distributed along the horizontal section, and the skin coefficient is gradually reduced. The model is utilized to convert the filter loss of laboratory scale to single well scale, and the influence of various parameters is utilized to describe the damage degree of the rock core, so that the previous result of singly utilizing the permeability recovery value parameter is replaced. In summary, the model establishes a relationship between permeability recovery data and well skin coefficients to more accurately describe the damage of drilling fluid to the reservoir.
Drawings
Fig. 1 is a graph of permeability recovery values versus dimensionless penetration depth (a=0.8, a=0.2);
fig. 2 is a graph of permeability recovery values versus dimensionless penetration depth (b=3, b=10);
FIG. 3 is a graph of permeability recovery versus dimensionless penetration depth under different conditions;
FIG. 4 is a graph of the effect of a value on the surface coefficient;
FIG. 5 is a graph of the effect of b-value on the surface coefficient;
FIG. 6 is a graph of the distribution of skin factor over the length of a horizontal segment;
FIG. 7 is the effect of rate of penetration on skin coefficient;
FIG. 8 is a graph comparing K/K d with S eq (I ani＝1);K/Kd for permeability recovery; S eq for total equivalent skin factor;
FIG. 9 is a graph comparing K/K d with S eq (I ani＝3);K/Kd represents permeability recovery value; S eq represents total equivalent skin factor;
fig. 10 is a graph of intrusion depth over horizontal segment length.
Detailed Description
The following description of the embodiments of the present invention will be made apparent and fully in view of the accompanying drawings, in which some, but not all embodiments of the invention are shown. All other embodiments, which can be made by those skilled in the art based on the embodiments of the invention without making any inventive effort, are intended to be within the scope of the invention.
In addition, the technical features of the different embodiments of the present invention described below may be combined with each other as long as they do not collide with each other.
The invention provides a core-well scale reservoir damage degree evaluation method, which aims to establish a relation between permeability recovery value data and well skin coefficients, and considers factors such as fluid loss rate, drilling rate and the like, wherein drilling fluid is not distributed linearly along the invasion depth of a horizontal section, and the skin coefficients are gradually reduced. Laboratory data are converted into well site dimensions, and the damage degree of the drilling fluid to the reservoir core is described by replacing the previous single permeability recovery value with double parameters, so that a basis is provided for the selection of the drilling fluid.
The technical scheme of the invention is as follows: a representative Roodhart model is selected to simulate the dynamic loss, and the fluid loss process is clearly divided into three stages: a transient fluid loss stage, a mud cake forming stage and a constant fluid loss stage; the laboratory obtains the data required in the model through dynamic filtration test; then converting the permeability recovery value into a well site scale, and calculating the permeability recovery value; and establishing a relation model between the permeability recovery value and the epidermis coefficient.
Example 1
1. Modeling
And a Roodhart model is selected to simulate the dynamic loss, and the model is simple, clear in description and easy to obtain related parameters. Roodhart dynamic fluid loss model is represented by formula (1):
Wherein v and v s are total and instantaneous fluid loss, respectively; t eq is the transition time from the non-steady state to the steady state; t is the time of filtration; c s is the fluid loss coefficient during the transition time; c d is the dynamic loss coefficient.
When t is less than or equal to t eq,
When t is greater than t eq, the method comprises,
Equation (1) divides the fluid loss process into three phases, a transient fluid loss phase, a mud cake formation phase and a constant fluid loss phase. The first two reveal early fluid loss characteristics of the drilling fluid.
2. Laboratory test acquisition data
The laboratory can obtain the data required in the model through a dynamic loss experiment. Drawing total filtration v per unit areaWherein the intercept on the v-axis is instantaneous fluid loss and C s is the slope. C d is the slope of the straight line segment of the curve, and the time at the beginning of the straight line segment is the transition time t eq.
3. Converting laboratory data
The same model was applied to calculate well site dimensions and fluid loss of laboratory drilling fluid. Fluid loss only has an effect on the formation of early mudcake, after which the flow resistance of the drilling fluid comes mainly from the mudcake, which is much smaller in thickness than the wellbore. Therefore, calculating the fluid loss through the mud cake, typically using a linear flow model; the depth of penetration of the filtrate was calculated using a radial flow model. To simplify the calculation, the unit area fluid loss parameters are used for conversion, the effective permeability of crude oil is used as the permeability parameter, and the following assumption is made:
(1) The time required for the mud cake in the laboratory and the on-site shaft to reach the equilibrium state is the same;
(2) Piston displacement is considered when calculating the intrusion volume;
(3) The overbalanced differential pressure remains unchanged during the drilling process.
The instantaneous fluid loss at the wellsite scale is:
Subscripts 1 and 2 represent laboratory and wellsite conditions, r w is wellbore radius, r e is supply radius of the reservoir perpendicular to the wellbore direction, μ is filtrate viscosity, and K is permeability. Equation (4) assumes that instantaneous fluid loss is a function of pressure gradient, permeability, and viscosity. The differential overbalance ΔP 2 is a dynamic differential overbalance under cycling conditions and is related to factors such as cycling speed, wellbore diameter, well depth, drilling fluid performance, etc. Well at the center of rectangular horizontal reservoir:
y b is half the radius of the reservoir supply perpendicular to the wellbore direction and h is the reservoir thickness. For anisotropic reservoirs:
K H and K V are the permeability in the horizontal and vertical directions, respectively. The fluid loss coefficient of the transition zone is calculated as follows:
m is the mud cake compression coefficient determined by different differential pressure filtration experiments, and the range of the coefficient is 0.5-1. The dynamic loss coefficient is calculated as follows:
thus, the total fluid loss at any location in the well is:
Although there is a long-time static filtration process in the drilling process, the filtration stall rate in the static filtration process is obviously reduced and can be ignored compared with dynamic filtration. For the convenience of calculation, the length of the well bore and the drilling rate are used for representing the soaking time of the drilling fluid, and the additional 4 hours are added as the time for cleaning the mud cake, so the total drilling time is as follows:
L is the total length of the wellbore in the reservoir, and R is the rate of penetration. If the fluid loss volume per unit area is v, then the intrusion radius is:
Is the effective porosity of the displaceable, equal to the porosity multiplied by the saturation of the displaceable phase. As can be seen from equations (9) - (11), r d is not linearly related to L, i.e., the depth of invasion of drilling fluid is not a linear function.
4. Conversion of permeability recovery values
The final permeability recovery profile of the linear core lesion is represented by formula (12):
RPx＝1-ae-bx (12)
Where x is the dimensionless invasion depth, RP x is the final permeability recovery value at position x, and as seen from equation (12), reservoir damage is an exponential function of the decreasing dimensionless invasion depth. Substituting the permeability recovery value distribution function into a radial damage formula to obtain the following formula:
the average permeability recovery values from x 1 to x 2 in the invaded zone are:
where x 1、x2 is the dimensionless invasion depth, the average permeability calculated from the core end face to x 2 when x 1 = 0, if it is considered as dynamically damaging the two pressure tap locations on the core holder. As seen from equation (13), the average permeability recovery value of the invaded zone is constant. In practice, the damage to the invasive leading edge is the weakest, and as the invasive depth increases, the damage becomes more severe, thus compensating each other.
In reservoir damage indoor experiments, it is difficult to determine the duration of the drilling fluid invasion phase, and the termination of this phase cannot be determined with only a specific time or a specific filtrate volume.
In the formula (12), a reflects the damage condition at the invaded end face, and b reflects the distribution condition of the damage in the invaded zone. When x=0, rp=1-a is the permeability recovery value of the end face, and a higher value of a indicates that the damage to the invaded end face is more serious and the permeability recovery value is lower. When x=1, rp=1-ae -b is the permeability recovery value of the leading edge of the invaded zone. If the value of b is large, the RP value approaches 1, and no damage exists in the depth of the invaded zone. However, if the b value is relatively small, the leading edge of the invaded zone is also severely damaged. If b is zero, this means that the lesions are evenly distributed in the invaded zone. Sometimes for fitting data, the value a may be greater than 1, in which case the permeability recovery value of the invaded face is negative, obviously unreasonable. The value of a should be set to a value slightly less than 1 at this time.
To calculate the values of a and b, at least permeability recovery value data of two different sections of the same core are obtained. I.e. on the basis of conventional impairment experiments, at least one set of differential pressure measurement data is added. Thus, a dynamic lesion instrument with multiple pressure taps may be used for the measurement. And calculating the permeability recovery value of each section of the core, obtaining the invasion depth from the section permeability recovery value, and obtaining the values a and b through regression analysis, so that a calculation result can be accurately obtained.
The steps of calculating the values of a, b are as follows, first calculating the dimensionless invasion volume of the two pressure points based on the total invasion volume and the core parameters, and calculating the average permeability recovery value of the first segment and to the invasion front or to the core outlet end. According to equation (15), the average permeability of the intrusion front is calculated:
Where L d is the invasion depth, RP avg is the average permeability recovery value of the invasion zone, and RP d is the permeability recovery value of the whole core. Finally, the values of a and b are calculated by an iterative method by using the formulas (13) and (14). This example investigated the relationship between penetration depth and permeability recovery values for different values of a, b, as shown in figures 1-3.
5. Calculating the skin coefficient of well site
The permeability recovery distribution under radial conditions is assumed to be the same as in the linear core. In the core, the extent of damage at a point is related to the volume of filtrate flowing through that point. Thus, under radial conditions, the dimensionless depth of invasion is replaced by a dimensionless volume. For linear cores, the cross-sectional area of the core is the same, and the application invasion depth or invasion volume calculation results are the same.
(1) Fluid loss and depth of invasion were calculated. The reservoir has anisotropy and should take into account the transitions in both the horizontal and vertical directions. When there is anisotropy in permeability, the liquid flows in a high-permeability direction more easily, and the amount of flow in each direction is controlled by the difference in permeability, assuming that:
uHuV＝u2 (17)
Wherein u is the fluid loss rate of mud cake passing through the well wall, u H and u V are the fluid loss rates in the vertical and horizontal directions respectively, I ani is the anisotropy index, and K H and K V are the permeabilities in the vertical and horizontal directions respectively. Using formula (16) and formula (17), it is possible to obtain:
uH＝Ianiu (18)
The filtration loss per unit area is
vH＝Ianiv (20)
V H and v V are the unit area of the fluid loss in the vertical and horizontal directions, respectively, and v is the total fluid loss;
based on the converted fluid loss coefficients and the drilling rates, the invasion times and invasion volumes of different sections are calculated first, and the invasion depths in the horizontal direction are calculated by using the formulas (11) and (21).
(2) And calculating the permeability recovery value of the invaded zone. The permeability recovery profile represented by equation (12) is used to convert the permeability of the invaded zone. Radial flow at well site conditions is considered by assuming permeability recovery values as a function of invasion volume. In the calculation process, it is assumed that the flow resistance generated by mud cakes on the walls of each section of the reservoir does not change with time, and fluid loss does not generate fluid channeling among each section.
To simplify the calculation, the permeability recovery values for the center points of the segments are calculated first, and then the average permeability recovery values for the different segments are calculated using equation (22).
Wherein: r d is the invasion radius, r w is the wellbore radius, r i is the radius of the ith reservoir; r i-1 is the radius of the i-1 th segment reservoir; k i is the permeability recovery value corresponding to the ith section of reservoir.
(3) Local skin coefficients along the wellbore are calculated. The intrusion zone is considered to be oval frustum-shaped. Using the depth of invasion in the horizontal direction, the local skin coefficient is calculated by equation (23):
wherein: k is permeability, K dx is permeability of the invaded zone; i ani is the anisotropy index, r dxH is the invaded zone radius; r w is the wellbore radius.
(4) The total equivalent skin coefficient is calculated. The total flow is obtained by calculating the flow to each section along the horizontal well bore, and the total skin factor is calculated. In this section, the effect of the horizontal section pressure drop is not important for selecting a drilling fluid system based on the damage evaluation results, and therefore, the effect of the horizontal section pressure drop is not considered. For a homogeneous anisotropic reservoir, ignoring pressure drop in the wellbore, the total skin factor is available from equation (24):
L is the total length of the wellbore in the reservoir; i ani is an anisotropy index; x is the dimensionless penetration depth; h is the reservoir thickness; r w is the wellbore radius, S x is the skin factor at a dimensionless invasion depth x; Δx is the dimensionless penetration depth segmentation interval length; s xi is the epidermis coefficient corresponding to the i-th section dimensionless invasion depth segment.
6. Simulation results
Substituting reservoir basic parameters and experimental parameters of drilling fluid into the model to obtain simulation results of the model, as shown in fig. 4-10. The simulation result shows that under the condition of different values of a and b, the influence on the surface skin coefficient is larger; the skin coefficient gradually decreases along the horizontal segment and is obviously affected by the drilling speed. By comparing different models, the model considers the influence of factors such as the fluid loss rate, the drilling speed and the like, so that drilling fluid is distributed in a nonlinear manner along the invasion depth of the horizontal section, and the simulation result is more accurate.
In summary, the method for converting the permeability recovery value into a single well scale is established in the embodiment, and the method is connected with the surface coefficient of the well site, so that the method for evaluating the damage degree of the drilling fluid to the reservoir core by using the single permeability recovery value is replaced. Finally, a method for converting the laboratory core scale damage data into single well scale damage degree is obtained. By using the method, the influence of a plurality of drilling parameters on reservoir damage can be analyzed, and a reference is provided for the selection of drilling fluid.
It is apparent that the above examples are given by way of illustration only and are not limiting of the embodiments. Other variations or modifications of the above teachings will be apparent to those of ordinary skill in the art. It is not necessary here nor is it exhaustive of all embodiments. While still being apparent from variations or modifications that may be made by those skilled in the art are within the scope of the invention.
Claims (10)
1. A method for evaluating the damage degree of a rock core-well scale reservoir, which is characterized by comprising the following steps:
S1: establishing a model to simulate the dynamic filtration of drilling fluid, and dividing the filtration process of the drilling fluid into stages;
S2: the laboratory obtains the data required in the model through dynamic filtration test;
S3: converting the experimental data to well site dimensions;
S4: calculating a permeability recovery value;
S5: calculating the surface coefficient of the well site;
S6: and obtaining the relation between the permeability recovery value and the surface coefficient of the well site.
2. The method for evaluating the damage degree of a core-well scale reservoir according to claim 1, wherein the step S1 specifically comprises: the Roodhart model was selected to simulate the dynamic loss, and the Roodhart dynamic loss model was represented by the following formula:
Wherein: v and v s are total and instantaneous fluid loss, respectively; t eq is the transition time from the non-steady state to the steady state; t is the time of filtration; c s is the fluid loss coefficient during the transition time; c d is the dynamic loss coefficient;
The Roodhart dynamic filtration model divides the fluid filtration process into three phases, namely a transient filtration phase, a mud cake formation phase and a constant filtration phase.
3. The method for evaluating the damage degree of a core-well scale reservoir according to claim 2, wherein the step S3 specifically comprises: the unit area loss parameters are used for conversion, the effective permeability of crude oil is used as the permeability parameter, and the following assumption is made:
(1) The time required for the mud cake in the laboratory and the on-site shaft to reach the equilibrium state is the same;
(2) Piston displacement is considered when calculating the intrusion volume;
(3) The over-balance pressure difference is kept unchanged in the drilling process;
The instantaneous fluid loss at the wellsite scale is:
Wherein: subscripts 1 and 2 represent laboratory and wellsite conditions, respectively, μ is filtrate viscosity, Δp is overbalanced differential pressure, r w is wellbore radius, r e is supply radius of the reservoir perpendicular to wellbore direction, L is total wellbore length in the reservoir, K is permeability;
The total fluid loss at any location in the well is:
the total drilling time is:
Wherein L is the total length of the well bore in the reservoir, R is the drilling rate, and 4 units are hours;
The intrusion radius is:
Wherein, Is the displaceable effective porosity, and as derived from equations (3) - (5), r d is not linear with L, i.e., the invasion depth of the drilling fluid is not a linear function.
4. The method for evaluating the damage degree of a core-well scale reservoir according to claim 3, wherein the step S4 specifically comprises: the final permeability recovery profile for the linear core lesion is expressed as:
RPx＝1-ae-bx (6)
wherein x is the dimensionless invasion depth, RP x is the final permeability recovery value at the position x, a reflects the damage condition at the invasion end face, and b reflects the distribution condition of the damage of the invasion zone;
substituting formula (6) into a radial damage formula to obtain a permeability recovery value of an invaded end face:
The average permeability recovery value in the invaded zone from the dimensionless invaded depth x 1 to the dimensionless invaded depth x 2 is:
5. The method for evaluating the damage degree of a core-well scale reservoir according to claim 4, wherein the calculating steps of the values a and b are as follows:
And calculating the permeability recovery value of the whole rock core:
wherein L d is the invasion depth, L is the total length of the wellbore in the reservoir;
the values of a and b are calculated by an iterative method using the formulas (7) and (8).
6. The method for evaluating the damage degree of a core-well scale reservoir according to claim 4, wherein the step S5 comprises:
S5.1: calculating the filtration loss and the invasion depth;
S5.2: calculating the permeability recovery value of the invaded zone;
s5.3: calculating local skin coefficients along the wellbore;
s5.4: the total equivalent skin coefficient is calculated.
7. The method for evaluating the damage degree of a core-well scale reservoir according to claim 6, wherein the step S5.1 specifically comprises:
Assume that:
uHuV＝u2 (11)
Wherein u is the fluid loss rate of mud cakes on a well wall, u H and u V are the fluid loss rates in the vertical and horizontal directions respectively, I ani is an anisotropy index, and K H and K V are the permeabilities in the vertical and horizontal directions respectively;
the filtration loss per unit area is:
vH＝Ianiv (12)
v H and v V are the unit area of the fluid loss in the vertical and horizontal directions, respectively, and v is the total fluid loss;
The invasion depth in the horizontal direction was calculated using the formulas (5) and (21).
8. The method of evaluating the damage degree of a core-well scale reservoir according to claim 6, wherein the invaded zone permeability recovery value in step S5.2 is calculated by the following formula:
Wherein: r d is the invasion radius, r w is the wellbore radius, r i is the radius of the ith reservoir; r i-1 is the radius of the i-1 th segment reservoir; k i is the permeability recovery value corresponding to the ith section of reservoir.
9. The method for evaluating the damage degree of a core-well scale reservoir according to claim 6, wherein the local skin coefficient in step S5.3 is calculated by the following formula:
wherein: k is permeability, K dx is permeability of the invaded zone; i ani is the anisotropy index, r dxH is the invaded zone radius; r w is the wellbore radius.
10. The method for evaluating the damage degree of a core-well scale reservoir according to claim 6, wherein the total equivalent skin coefficient in step S5.4 is calculated by the following formula:
Wherein: l is the total length of the wellbore in the reservoir; i ani is an anisotropy index; x is the dimensionless penetration depth; h is the reservoir thickness; r w is the wellbore radius, S x is the skin factor at a dimensionless invasion depth x; Δx is the dimensionless penetration depth segmentation interval length; s xi is the epidermis coefficient corresponding to the i-th section dimensionless invasion depth segment.
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