Drilling fluid pollution zone depth determination method
By establishing the relationship between the seepage volume and pore volume of drilling fluid intrusion into the formation, and combining it with the contamination conversion factor, the problems of difficult data acquisition and insufficient accuracy in the calculation of drilling fluid contamination zone depth are solved, realizing rapid and accurate calculation of contamination zone depth, which is suitable for field application of drilling fluid contamination zone depth.
Patent Information
- Application Number
- CN202410646091.X
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- Filing Date
- 2024-05-23
- Publication Date
- 2025-11-25
AI Technical Summary
Existing technologies for determining the depth of drilling fluid contamination zones suffer from challenges such as difficulty in obtaining basic data, lack of well logging interpretation data, and insufficient accuracy of calculation results. In particular, well logging interpretation data is difficult to obtain in some oilfields, resulting in insufficient applicability and accuracy of the evaluation methods.
By establishing the relationship between the seepage volume and pore volume of drilling fluid invading the formation, and combining it with the contamination conversion factor, the depth of the drilling fluid contamination zone is calculated using semi-empirical formulas based on relevant parameters of the reservoir, wellbore, and drilling fluid. This includes methods for determining the seepage volume, invasion radius, and contamination zone depth.
A simple and reliable method is provided to quickly and accurately calculate the depth of the drilling fluid contamination zone. It has strong applicability, and the calculation results are close to the actual situation, meeting the needs of field applications with an error of less than 5%.
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Figure CN121006944A_ABST
Abstract
Description
Technical Field
[0001] This disclosure relates to the field of calculating the contamination depth of drilling fluid in vertical wells of sandstone reservoirs. Background Technology
[0002] The depth of the drilling fluid contamination zone refers to the radial depth of the contamination zone formed after the reservoir is contaminated by drilling fluid during the drilling process. It is an important parameter for evaluating the contamination status of the reservoir and an important basis for determining the perforation penetration depth in the optimization design of perforation technology.
[0003] Currently, there are three main methods for obtaining the depth of the contaminated zone: First, drilling contamination tests are conducted using core samples. This method has high accuracy, but in most cases, core samples cannot be provided on-site for laboratory testing. Second, well logging interpretation data is analyzed and calculated. Well logging results such as spontaneous potential and sonic transit time are used to observe the pattern of drilling fluid invasion, and deep and shallow dual-lateral logging methods are used to quantitatively describe the depth of contaminated zone invasion. This method is currently widely used, but for some oilfields, the testing workload is small, and well logging interpretation data is difficult to obtain. Third, perforation optimization software is used for calculation. This method is simple to operate, but currently commonly used domestic and foreign perforation optimization software has certain limitations in practical applications, requiring many parameters, and the accuracy of the calculation results needs to be improved. Summary of the Invention
[0004] In view of this, this disclosure provides a method for determining the depth of drilling fluid contamination zones, which solves the problems of difficulty in obtaining basic data for target oilfields, lack of laboratory test data and well logging interpretation data, and the need to improve the applicability and accuracy of drilling fluid contamination zone evaluation methods.
[0005] To achieve the above-mentioned objective, the method for determining the depth of the drilling fluid contamination zone includes:
[0006] Determine the seepage volume of drilling fluid entering the formation;
[0007] Establish the relationship between the pore volume through which drilling fluid flows into the formation and the radius of drilling fluid intrusion;
[0008] The drilling fluid invasion radius is determined based on the fact that the seepage volume is equal to the pore volume through which the drilling fluid flows during the process of drilling fluid invading the formation.
[0009] The depth of the drilling fluid contamination zone is determined using the contamination conversion factor and the drilling fluid invasion radius.
[0010] In this disclosure and possible embodiments, the method for calculating the pollution conversion factor includes:
[0011] By using data on mud invasion depth and equivalent contamination depth under different pressure differentials and core physical parameters, the relationship between drilling fluid invasion depth and equivalent contamination depth can be obtained.
[0012] The pollution reduction factor is determined using the aforementioned relationship.
[0013] In this disclosure and possible embodiments, the method for determining the depth of the drilling fluid contamination zone using a contamination conversion factor and the drilling fluid invasion radius includes:
[0014] Obtain the wellbore radius;
[0015] The depth of the drilling fluid contamination zone is obtained by multiplying the difference between the drilling fluid intrusion radius and the wellbore radius by the contamination conversion factor.
[0016] In this disclosure and possible embodiments, the method for determining the seepage volume of drilling fluid intruding into the formation includes:
[0017] Establish the relationship between the seepage volume V of the drilling fluid entering the formation and the drilling fluid flow rate Q per unit time, the influence coefficient C of the equivalent seepage resistance of the drilling fluid entering the formation (mud cake), and the drilling fluid soaking time t. The relationship is as follows:
[0018] V = CQt.
[0019] In this disclosure and possible embodiments, the method for determining the influence coefficient C of the equivalent seepage resistance of the mud cake includes:
[0020] The influence coefficient of the equivalent seepage resistance of the drilling fluid intrusion into the formation is determined by using drilling fluid soaking time, formation permeability, and the relationship between the three is as follows:
[0021] C = α + e -βkt ;
[0022] Where C is the influence coefficient of the mud cake equivalent seepage resistance of drilling fluid intrusion into the formation, which varies with time and formation permeability and is inversely proportional to the mud cake seepage resistance; t is the drilling fluid soaking time, day; k is the formation permeability; α and β are regression coefficients.
[0023] In this disclosure and possible embodiments, the method for determining the regression coefficients includes:
[0024] Drilling fluid loss experiments were conducted on different core samples to determine the relationship between unobstructed loss and the actual loss measured in the experiment. The values of coefficients α and β were obtained through regression.
[0025] In this disclosure and possible embodiments, the method for determining the drilling fluid flow rate Q per unit time of drilling fluid intrusion into the formation includes:
[0026] The drilling fluid flow rate Q per unit time invading the formation is determined by the drilling fluid invasion pressure difference ΔP.
[0027] In this disclosure and possible embodiments, when drilling fluid column depth data is available, the drilling fluid invasion pressure differential ΔP is calculated using the fluid column depth; the calculation formula is:
[0028]
[0029] Where ρ is the density of the drilling fluid, in g / cm³. 3 g is the acceleration due to gravity, in m / s². 2 h l is the depth of the drilling fluid column, in meters; P is the formation pressure, in MPa.
[0030] When drilling fluid column depth data is unavailable, the drilling fluid intrusion pressure difference ΔP is calculated using the positive pressure balance coefficient α. The calculation formula is as follows:
[0031]
[0032] Where H represents the medium depth of the reservoir, in meters (m);
[0033] Using a drilling mud level monitoring system, the positive pressure balance coefficient 'a' is determined by analyzing actual drilling fluid density data from multiple single wells at different depths and formation pressures, as well as drilling fluid level depth data under medium-deep reservoir and formation pressure conditions; and / or,
[0034] The formula for calculating the drilling fluid flow rate Q per unit time when the drilling fluid penetrates the formation is:
[0035]
[0036] Where k is the formation permeability, in μm 2 μ is the drilling fluid viscosity, mPa·s; r e Let r be the oil drain radius, in meters (m); w Let be the radius of the wellbore, in meters (m).
[0037] In this disclosure and possible embodiments, the relationship between the pore volume through which the drilling fluid flows into the formation and the drilling fluid invasion radius is:
[0038] V φ =V l φ=π(r0 2 -r w 2 )Hφ;
[0039] in, V1 represents the pore volume through which the drilling fluid flows into the formation; V2 represents the formation volume through which the drilling fluid enters. r is porosity; r0 is the drilling fluid intrusion radius, in meters.
[0040] In this disclosure and possible embodiments, the formula for calculating the drilling fluid invasion radius is:
[0041]
[0042] This disclosure has the following beneficial effects:
[0043] The method for determining the depth of drilling fluid contamination zone disclosed herein establishes a semi-empirical formula based on the correlation between the depth of drilling fluid contamination zone and relevant parameters of the reservoir, wellbore, and drilling fluid in the study area. The required basic reservoir fluid parameters, wellbore parameters, and drilling fluid property parameters are readily available in the oilfield. This semi-empirical formula can then be used to quickly and directly calculate the depth of drilling fluid contamination zone in the target well within the study area. Furthermore, this method modifies and improves existing calculation methods through sensitivity analysis of relevant parameters, and the data source is stable and reliable, so the calculation results are closer to the actual situation. In summary, this method is simple, reliable, and highly applicable, meeting the requirements of practical field applications and providing strong technical support for the calculation of drilling fluid contamination zone depth. Attached Figure Description
[0044] The above and other objects, features, and advantages of this disclosure will become clearer from the following description of embodiments with reference to the accompanying drawings, in which:
[0045] Figure 1 This is a flowchart of the method for determining the depth of the drilling fluid contamination zone disclosed herein. Detailed Implementation
[0046] The present disclosure is described below based on embodiments; however, it is worth noting that the present disclosure is not limited to these embodiments. In the detailed description of the present disclosure below, certain specific details are described in detail. However, those skilled in the art will fully understand the present disclosure for the parts not described in detail.
[0047] Furthermore, unless the context explicitly requires it, the words "comprising," "including," and similar terms throughout the specification and claims should be interpreted as including rather than exclusive or exhaustive; that is, meaning "including but not limited to."
[0048] Figure 1 This is a flowchart of the method for determining the depth of the drilling fluid contamination zone disclosed herein; by Figure 1 As shown, the method for determining the depth of the drilling fluid contamination zone includes the following steps:
[0049] Step 1: Obtain basic data related to the reservoir, wellbore, and drilling fluid: formation permeability (k), porosity. Formation pressure P, reservoir depth H, wellbore radius r w Oil drain radius r eDrilling fluid density ρ, drilling fluid viscosity μ, and drilling fluid soaking time t.
[0050] Step 2: Calculate the drilling fluid intrusion pressure differential ΔP:
[0051] The drilling fluid invasion pressure differential is one of the important factors affecting the degree of drilling fluid invasion. The greater the invasion pressure differential, the more fluid the drilling mud filtrate displaces in the formation pores; conversely, the less fluid is displaced. In actual field conditions, the drilling fluid column depth should be used for calculation. However, some oilfields cannot provide the drilling fluid column depth, therefore, calculations are performed in two cases:
[0052] (1) If the drilling fluid column depth h1 can be provided, the drilling fluid intrusion pressure difference ΔP is calculated as follows:
[0053]
[0054] Where ρ is the density of the drilling fluid, in g / cm³. 3 g is the acceleration due to gravity, in m / s². 2 h1 is the depth of the drilling fluid column, in meters; P is the formation pressure, in MPa.
[0055] (2) If drilling fluid column depth data is unavailable, an empirical algorithm is used in conjunction with field data. Introducing a positive pressure balance coefficient a, the drilling fluid intrusion pressure difference ΔP is calculated as follows:
[0056]
[0057] Where a is the positive pressure balance coefficient, which is related to the degree of fluctuation of the drilling fluid level and height; H is the depth of the reservoir, in meters.
[0058] The calculation method for the positive pressure balance coefficient 'a' is as follows: using a drilling mud level monitoring system, by statistically analyzing the actual drilling fluid density of multiple single wells at different depths and formation pressures, and the drilling fluid level depth under medium-deep reservoir and formation pressure conditions, the average value of the positive pressure balance coefficient 'a' is calculated to be 0.6657, as shown in Table 1. The applicant further verified the result using data from other oilfields, proving that the error is small. Therefore, in the absence of drilling fluid column depth data, the positive pressure balance coefficient of 0.6657 can be directly taken.
[0059] Table 1 Calculation table of positive pressure balance coefficient a
[0060]
[0061] Step 3: Establish a planar radial seepage model of drilling fluid intrusion into the formation to obtain the relationship between the flow rate Q per unit time and the drilling fluid intrusion pressure difference ΔP:
[0062]
[0063] Where k is the formation permeability, in μm 2 μ is the drilling fluid viscosity, mPa·s; r e Let r be the oil drain radius, in meters (m); w Let be the radius of the wellbore, in meters (m).
[0064] Step 4: Establish the relationship between the mud cake equivalent seepage resistance influence coefficient C of drilling fluid intrusion into the formation and the drilling fluid soaking time t and formation permeability k:
[0065] C = α + e -βkt ;
[0066] Where C is the influence coefficient of the mud cake equivalent seepage resistance of drilling fluid intrusion into the formation, which varies with time and formation permeability and is inversely proportional to the mud cake seepage resistance; t is the drilling fluid soaking time, day; α and β are regression coefficients.
[0067] The shorter the soaking time of the drilling fluid or the lower the formation permeability, the less likely the solid particles of the drilling fluid are to migrate in the pores, resulting in a smaller equivalent mud cake seepage resistance and a greater impact on the penetration depth of the drilling fluid outside the mud cake; the longer the soaking time or the higher the formation permeability, the smaller the impact on the penetration depth.
[0068] The method for determining the regression coefficients α and β can be as shown in Table 2. Drilling fluid filtration loss experiments were conducted using core samples from three different regions. The relationship between the unobstructed filtration loss and the actual filtration loss measured in the experiment was analyzed. The values of coefficients α and β were obtained through regression, and their values were 9.457 and 0.013, respectively.
[0069] Table 2 Results of Drilling Fluid Filtration Test
[0070]
[0071] Step 5: Establish the relationship between the seepage volume V of drilling fluid entering the formation and the flow rate Q, the influence coefficient of equivalent seepage resistance C, and the drilling fluid soaking time t:
[0072] V = CQt.
[0073] Step 6: Establish the pore volume through which the drilling fluid penetrates the formation. The relationship between the drilling fluid invasion radius r0 and the drilling fluid invasion radius is as follows:
[0074] V φ =V l φ=π(r0 2 -r w 2 )Hφ;
[0075] in, r is porosity, a decimal; r0 is the drilling fluid intrusion radius, in meters.
[0076] Step 7: Establish the seepage volume V of drilling fluid entering the formation and the pore volume it flows through. The relationship between the seepage volume V through the formation and the pore volume through which the drilling fluid flows during the drilling fluid intrusion into the formation is expressed as follows: Similarly, substituting the values, we obtain the relationship between the drilling fluid invasion radius r0 and the following:
[0077] V = V φ ;
[0078]
[0079]
[0080] Step 8: Establish the relationship between the depth Δr of the drilling fluid contamination zone and the drilling fluid invasion radius r0:
[0081] △r=b·(r0-r w );
[0082] Where b is the contamination reduction factor. Not all formation pores invaded by drilling fluid will be contaminated. Therefore, the contamination reduction factor is introduced to characterize the relationship between the depth of the drilling fluid contamination zone and the invasion radius.
[0083] The method for determining the pollution conversion factor b can be as follows: the mud penetration depth refers to the radial depth of the formation reached by the mud filtrate, and the pollution depth refers to the equivalent radial depth at which the formation porosity is damaged. As shown in Table 3, by combining experimental data of core mud penetration and pollution under multiple sets of different pressure differentials and physical property parameters, the relationship between drilling fluid penetration depth and equivalent pollution depth is obtained, and the average value is further calculated as the pollution conversion factor b, which is taken as 0.8488.
[0084] Table 3. Calculation of Pollution Conversion Factors
[0085]
[0086]
[0087] Furthermore, the formula for calculating the depth Δr of the drilling fluid contamination zone is:
[0088]
[0089] Example 1
[0090] Taking well X1 in block T as an example, block T is an overseas sandstone reservoir, and well X1 is a vertical well undergoing well testing. Given the known drilling fluid column depth parameters, the process for determining the drilling fluid contamination zone depth according to the method of this invention is as follows:
[0091] Step 1: Obtain basic reservoir data: Formation permeability 0.156 μm 2 Porosity 0.235, formation pressure 19.1 MPa, reservoir depth 2000 m, drilling fluid column depth 1845 m, wellbore radius 0.113 m, drainage radius 200 m, drilling fluid density 1.43 g / cm³ 3 The drilling fluid viscosity was 70 mPa·s, and the drilling fluid soaking time was 7 days.
[0092] Step 2: Calculate the drilling fluid invasion pressure differential ΔP in near-equilibrium drilling:
[0093]
[0094] Step 3: Calculate the flow rate Q of drilling fluid entering the formation per unit time:
[0095]
[0096] Step 4: Introduce regression coefficients α and β (α and β have values of 9.457 and 0.013, respectively), and calculate the equivalent seepage resistance influence coefficient C of drilling fluid intrusion into the formation:
[0097] C = α + e -βkt =10.442.
[0098] Step 5: Calculate the seepage volume V of drilling fluid entering the formation during the drilling fluid soaking time:
[0099] V = CQt = 1765.2m 3 .
[0100] Step 6: Establish the pore volume through which the drilling fluid penetrates the formation. The relationship between the drilling fluid invasion radius r0 and the pore volume is used to calculate the pore volume.
[0101]
[0102] Step 7: Establish the pore volume through which the drilling fluid penetrates the formation. The relationship between the drilling fluid and the seepage volume V is used to calculate the drilling fluid invasion radius r0:
[0103] V = V φ ;
[0104]
[0105] Step 8: Introduce the pollution reduction factor b (value is 0.8488) to calculate the final pollution zone depth Δr:
[0106]
[0107] The well test interpretation showed that the drilling fluid contamination depth was 0.862 meters. The error between the drilling fluid contamination depth calculated by the semi-empirical formula and the actual measured drilling fluid contamination depth was 0.0271 meters, which is less than 5%, and fully meets the requirements of field application.
[0108] Example 2
[0109] Taking well X2 in block M as an example, block M is an overseas low-permeability sandstone reservoir. This well is a vertical well undergoing well testing, and the drilling fluid column depth parameters are unknown. The process of determining the drilling fluid contamination zone depth according to the method of this invention is as follows:
[0110] Step 1: Obtain basic reservoir data: Formation permeability 0.00513 μm 2 Porosity 0.152, formation pressure 25.2 MPa, reservoir depth 2500 m, wellbore radius 0.084 m, drainage radius 150 m, drilling fluid density 1.22 g / cm³ 3 The drilling fluid viscosity was 45 mPa·s, and the drilling fluid soaking time was 4 days.
[0111] Step 2: Calculate the drilling fluid invasion pressure differential ΔP in near-equilibrium drilling:
[0112]
[0113] Step 3: Calculate the flow rate Q of drilling fluid entering the formation per unit time:
[0114]
[0115] Step 4: Introduce regression coefficients α and β (α and β have values of 9.457 and 0.013, respectively) to calculate the influence coefficient of equivalent seepage resistance of drilling fluid intrusion into the formation:
[0116] C = α + e -βkt =10.457.
[0117] Step 5: Calculate the seepage volume V of drilling fluid entering the formation during the drilling fluid soaking time:
[0118] V = CQt = 31.2m 3 .
[0119] Step 6: Establish the pore volume through which the drilling fluid penetrates the formation. The relationship between the drilling fluid invasion radius r0 and the pore volume is used to calculate the pore volume.
[0120] V φ =V l φ=π(r0 2 -r w2 Hφ=1193.2(r0) 2 -0.007).
[0121] Step 7: Establish the pore volume through which the drilling fluid penetrates the formation. The relationship between the drilling fluid and the seepage volume V is used to calculate the drilling fluid invasion radius r0:
[0122] V = V φ ;
[0123]
[0124] Step 8: Introduce the pollution reduction factor b (value is 0.8488) to calculate the final pollution zone depth Δr:
[0125]
[0126] The well test interpretation showed that the drilling fluid contamination depth was 0.0868 meters. The error between the drilling fluid contamination depth calculated by the semi-empirical formula and the actual measured drilling fluid contamination depth was 0.0038 meters, which is less than 5%, and fully meets the requirements of field application.
[0127] As can be seen from the above embodiments, the method of the present invention utilizes semi-empirical formulas and basic parameters related to the properties of reservoir fluids, wellbore, and drilling fluid. According to the method of the present invention, the depth of the contaminated zone in sandstone reservoirs can be calculated. The required parameters are easy to obtain and are stable and reliable, with high accuracy. The calculated depth of the contaminated zone has a small error compared with the measured data, which can fully meet the requirements of actual field applications.
[0128] In addition, the method of the present invention does not require the use of well test, well logging and other related data, which can better solve the problems of incomplete basic data and small testing workload in some oil fields. The method is simple, reliable and has strong applicability.
[0129] The embodiments described above are merely illustrative of implementation methods of this disclosure, and while the descriptions are specific and detailed, they should not be construed as limiting the scope of this patent disclosure. It should be noted that those skilled in the art can make various modifications, equivalent substitutions, and improvements without departing from the concept of this disclosure, and these all fall within the protection scope of this disclosure. Therefore, the protection scope of this patent disclosure should be determined by the appended claims.
Claims
1. A method for determining the depth of drilling fluid contamination zone, characterized in that, include: Determine the seepage volume of drilling fluid entering the formation; Establish the relationship between the pore volume through which drilling fluid flows into the formation and the radius of drilling fluid intrusion; The drilling fluid invasion radius is determined based on the fact that the seepage volume is equal to the pore volume through which the drilling fluid flows during the process of drilling fluid invading the formation. The depth of the drilling fluid contamination zone is determined using the contamination conversion factor and the drilling fluid invasion radius.
2. The method for determining the depth of the drilling fluid contamination zone according to claim 1, characterized in that, The method for calculating the pollution conversion factor includes: By using data on mud invasion depth and equivalent contamination depth under different pressure differentials and core physical parameters, the relationship between drilling fluid invasion depth and equivalent contamination depth can be obtained. The pollution reduction factor is determined using the aforementioned relationship.
3. The method for determining the depth of the drilling fluid contamination zone according to claim 1 or 2, characterized in that, The method for determining the depth of the drilling fluid contamination zone using a contamination conversion factor and the drilling fluid invasion radius includes: Obtain the wellbore radius; The depth of the drilling fluid contamination zone is obtained by multiplying the difference between the drilling fluid intrusion radius and the wellbore radius by the contamination conversion factor.
4. The method for determining the depth of the drilling fluid contamination zone according to claim 3, characterized in that, The method for determining the seepage volume of drilling fluid entering the formation includes: Establish the relationship between the seepage volume V of the drilling fluid entering the formation and the drilling fluid flow rate Q per unit time, the influence coefficient C of the equivalent seepage resistance of the drilling fluid entering the formation (mud cake), and the drilling fluid soaking time t. The relationship is as follows: V = CQt.
5. The method for determining the depth of the drilling fluid contamination zone according to claim 4, characterized in that, The method for determining the influence coefficient C of the equivalent seepage resistance of the mud cake includes: The influence coefficient of the equivalent seepage resistance of the drilling fluid intrusion into the formation is determined by using drilling fluid soaking time, formation permeability, and the relationship between the three is as follows: C=α+e -βkt ; Where C is the influence coefficient of the mud cake equivalent seepage resistance of drilling fluid intrusion into the formation; t is the drilling fluid soaking time, day; k is the formation permeability; α and β are regression coefficients.
6. The method for determining the depth of the drilling fluid contamination zone according to claim 5, characterized in that, The method for determining the regression coefficients includes: Drilling fluid loss experiments were conducted on different core samples to determine the relationship between unobstructed loss and the actual loss measured in the experiment. The values of coefficients α and β were determined by regression.
7. The method for determining the depth of the drilling fluid contamination zone according to claim 4, characterized in that, The method for determining the drilling fluid flow rate Q per unit time of drilling fluid intrusion into the formation includes: The drilling fluid flow rate Q per unit time invading the formation is determined by the drilling fluid invasion pressure difference ΔP.
8. The method for determining the depth of the drilling fluid contamination zone according to claim 7, characterized in that: When drilling fluid column depth data is available, the drilling fluid invasion pressure differential ΔP is calculated using the fluid column depth; the calculation formula is: Where ρ is the density of the drilling fluid, in g / cm³. 3 g is the acceleration due to gravity, m / s² 2 h l is the depth of the drilling fluid column, in meters; P is the formation pressure, in MPa. When drilling fluid column depth data is unavailable, the drilling fluid intrusion pressure difference ΔP is calculated using the positive pressure balance coefficient α. The calculation formula is as follows: Where H represents the medium depth of the reservoir, in meters (m); Using a drilling mud level monitoring system, the positive pressure balance coefficient 'a' is determined by analyzing actual drilling fluid density data from multiple single wells at different depths and formation pressures, as well as drilling fluid level depth data under medium-deep reservoir and formation pressure conditions; and / or, The formula for calculating the drilling fluid flow rate Q per unit time when the drilling fluid penetrates the formation is: Where k is the formation permeability, in μm 2 μ is the drilling fluid viscosity, mPa·s; r e Let r be the oil drain radius, in meters (m); w Let be the radius of the wellbore, in meters (m).
9. The method for determining the depth of drilling fluid contamination zone according to any one of claims 1-8, characterized in that, The relationship between the pore volume through which the drilling fluid flows into the formation and the drilling fluid invasion radius is: V φ =V l φ=π(r0 2 -r w 2 )Hφ; in, V1 represents the pore volume through which the drilling fluid flows into the formation; V2 represents the formation volume through which the drilling fluid enters. r is porosity; r0 is the drilling fluid intrusion radius, in meters.
10. The method for determining the depth of the drilling fluid contamination zone according to claim 9, characterized in that, The formula for calculating the drilling fluid invasion radius is: