Stratum true resistivity solving method and system, electronic equipment and storage medium

Abstract

The invention relates to the technical field of geophysical logging, and particularly discloses a stratum true resistivity solving method and system, electronic equipment and a storage medium, and the method comprises the steps: calculating a pressure value of a target stratum through a stratum fluid mass continuity equation, and obtaining the three-phase saturation of the target stratum according to the pressure value; the three-phase saturation is substituted into an expression representing the incidence relation between saturation and resistivity for calculation, and first stratum resistivity of the target stratum is obtained; and the target stratum conductivity of the target stratum is obtained, and the stratum true resistivity of the target stratum is determined based on the first stratum resistivity and the target stratum conductivity. According to the method, the calculation error of the formation resistivity can be reduced, so that the real formation resistivity can be obtained, and the method plays an extremely important role in accurately evaluating the oil-gas possibility of the formation.

Description

Technical Field

[0001] This invention relates to the field of geophysical logging technology, and in particular to a method, system, electronic device, and storage medium for determining the true resistivity of a formation. Background Technology

[0002] During oil drilling, due to special circumstances, logging cannot be completed on time after drilling, and the drilling fluid pressure exceeds the formation pressure, causing drilling mud to invade the formation. The longer the drilling mud soaks in the wellbore, the deeper it penetrates into the formation, resulting in a larger volume of drilling mud intrusion, greater changes in formation fluid properties, and a greater change in formation resistivity. Even if timely logging is completed after drilling, drilling mud will still invade the formation, altering its properties. If the drilling mud salinity is greater than that of formation water, the mud invasion is considered drag-reducing invasion; conversely, if the drilling mud salinity is less than that of formation water, it is considered drag-increasing invasion. Regardless of whether it is drag-reducing or drag-increasing invasion, the oil, gas, and water in the formation pores will be completely or partially replaced by the mud filtrate, leading to changes in formation resistivity. This makes it difficult to measure the true resistivity of the formation, resulting in significant errors in evaluating the formation's oil and gas content. Timely logging after drilling can significantly reduce the impact of mud invasion on formation true resistivity measurements. In this case, the radii of the flushed zone and the invasion zone will be relatively small, as will the invasion depth. Depending on the formation characteristics, the radii of the flushed zone, the invasion zone, and the invasion depth will vary. Modern drilling operations have much stricter requirements for drilling safety than before, especially with more comprehensive preventative measures against extreme safety events such as blowouts. The focus has shifted from timeliness and formation protection to well control safety. The density of drilling fluids and mud used is increasing, and the drilling fluid pressure exceeds the formation pressure, leading to greater damage to the original formation. Increased drilling mud density, coupled with the unique characteristics of the formation, and sometimes delays in logging due to unforeseen circumstances, can lead to over-balanced drilling penetration, invasion of high-salinity salt mud, prolonged soaking of the target formation mud, and loss of the target formation mud. These situations further disrupt the original formation, resulting in significant discrepancies between the formation resistivity measured by electrical and induction logging and the true formation resistivity. This can lead to erroneous conclusions in assessing the formation's hydrocarbon potential. When the original formation is disrupted by drilling mud penetration, accurately calculating the invasion profile and true formation resistivity, especially determining the radius of the flushed zone and the invasion zone, and subsequently the true resistivity of the flushed zone and the invasion zone, is crucial for accurately evaluating the formation's hydrocarbon potential.

[0003] In actual production, the intrusion of drilling mud into the formation damages the reservoir, especially in reservoirs that have been soaked in drilling mud for extended periods. This results in unclear oil-water reservoir characteristics on array induction logging curves, making it impossible for interpreters to effectively identify the reservoir using the array induction logging response. To eliminate the impact of drilling mud intrusion, field personnel typically use methods such as calibration charts and resistivity inversion to correct the apparent resistivity of the array induction logging. Drilling mud intrusion is a dynamic seepage process that varies over time. Due to the complexity of underground reservoirs, the impact of drilling mud intrusion on the wellbore medium is highly complex, making drilling mud intrusion calibration charts quite limited.

[0004] After the advent of array induction logging, in order to accurately determine the true resistivity of the formation after mud invasion, the logging community, driven by Schlumberger, conducted extensive and in-depth research on mud invasion:

[0005] 1) In "Numerical Simulation and Microscopic Mechanism of Mud Intrusion Based on Digital Core", Cui Likai used the digital core model obtained by core CT scanning as a basis, and used the lattice Boltzmann method to simulate the mud intrusion process. He combined the finite element method to calculate the changes in the electrical properties of the core during the mud intrusion process, and combined the core pore structure parameters to understand the mud intrusion process at the microscale. Thus, he systematically analyzed the microscopic mechanism of mud intrusion and found that among the pore microstructure parameters, permeability, pore connectivity and pore throat radius have a significant impact on mud intrusion and resistivity.

[0006] 2) In his paper "Research on Forward Modeling Response of Array Lateral Logging Based on Dynamic Mud Invasion," Feng Jiaming constructed a forward model of dynamic mud invasion formation using the two-phase flow-convection-diffusion theory. Combining this with the actual formation porosity and permeability characteristics of the research block, he categorized reservoir properties into three types and studied the distribution characteristics of the wellbore resistivity under different invasion times, differences in mud filtrate and formation water salinity, wellbore-formation pressure differences, mud cake permeability, reservoir porosity and permeability characteristics, and original formation water saturation conditions. He established an array lateral logging forward model of formation using the finite element method and investigated the effects of well inclination angle, wellbore size, mud resistivity, surrounding rock resistivity, target layer thickness, invasion radius, and invasion zone resistivity on the array lateral logging response. He also created array lateral logging wellbore environment correction charts, layer thickness / surrounding rock correction charts, and static mud invasion correction charts. A forward model for lateral logging of dynamic mud invasion array was constructed using the finite element method, realizing the three-field coupling of two-phase seepage, convection diffusion, and electric field.

[0007] 3) In his paper "Research on the Response Characteristics of Array Induction Logging Based on Dynamic Mud Invasion," Liu Yufeng established a dynamic mud invasion model based on the mechanism of mud invasion using the two-phase flow equation and the convection-diffusion equation. Combining Archie's formula and the finite element numerical simulation method, he simulated the response characteristics of the wellbore resistivity during dynamic mud invasion. He analyzed the response characteristics of the wellbore resistivity under different invasion times, mud cake permeability, salinity differences, wellbore pressure differences, and formation water saturation conditions when freshwater and saline mud filtrate invaded three types of reservoirs (A, B, and C). By replacing the Gaussian function with a target function, he derived the geometric factor solution for the apparent resistivity of the array induction logging. He calculated and analyzed the array induction logging response characteristics under different conditions of dynamic mud invasion, and fitted the reservoir invasion depth formula and the calibration chart for dynamic mud filtrate invasion.

[0008] Due to the complexity of mud invasion control and influencing factors, the application value of experimental results is limited. Numerical simulation of the dynamic process of mud invasion is extremely difficult, leading to coarse, unreliable, and even erroneous results when directly using commercial reservoir simulation software for dynamic simulations of mud-invaded formations. Furthermore, current resistivity inversion correction programs are mostly based on forward simulations of static step models, which cannot reflect the response characteristics of the wellbore resistivity during dynamic mud invasion, resulting in inaccurate resistivity inversion results. The contradiction between ultra-deep mud invasion and the limited detection depth of array induction logging reduces the ability of array induction logging to describe the formation invasion profile, resulting in significant errors in the calculation of true formation resistivity, invasion zone resistivity, and invasion depth using currently available domestic and international technologies.

[0009] To obtain the true formation resistivity, it is necessary to conduct in-depth research on the mud invasion response and the response characteristics of dynamic mud invasion to array induction logging, and to obtain a solution model for the true formation resistivity under deep formation invasion conditions, so as to solve the above-mentioned technical problems. Summary of the Invention

[0010] To address the aforementioned technical problems, this invention provides a method, system, electronic device, and storage medium for determining the true resistivity of a formation.

[0011] Firstly, the present invention provides a method for determining the true resistivity of a formation, the technical solution of which is as follows:

[0012] The pressure value of the target formation is calculated using the formation fluid mass continuity equation, and the three-phase saturation of the target formation is obtained based on the pressure value.

[0013] The three-phase saturation is substituted into the expression characterizing the relationship between saturation and resistivity to calculate the first formation resistivity of the target formation.

[0014] Obtain the target formation conductivity of the target formation, and determine the true resistivity of the target formation based on the first formation resistivity and the target formation conductivity.

[0015] The beneficial effects of the method for determining the true resistivity of a formation according to the present invention are as follows:

[0016] The method of this invention can reduce the error in obtaining formation resistivity, thereby obtaining the true formation resistivity, which plays an extremely important role in accurately evaluating the oil and gas content of formations.

[0017] Based on the above scheme, the method for determining the true resistivity of a formation according to the present invention can be further improved as follows.

[0018] In one alternative approach, a formation volume model of the wellbore and formation radial direction is constructed in a one-dimensional cylindrical coordinate system;

[0019] The formation fluid mass continuity equation is constructed by using Darcy's law and the seepage equation based on mass continuity, combined with the formation volume model.

[0020] In one alternative approach, the step of calculating the pressure value of the target formation using the formation fluid mass continuity equation includes:

[0021] The pressure value of the target formation is calculated using the catch-up method and in conjunction with the formation fluid mass continuity equation.

[0022] In one alternative approach, the step of determining the true resistivity of the target formation based on the first formation resistivity and the target formation conductivity includes:

[0023] Obtain the resistivity profile information of the first formation and the differential geometric factor of the target formation, and calculate the conductivity of the first formation based on the resistivity profile information and the differential geometric factor;

[0024] When the difference between the first formation conductivity and the target formation conductivity is less than a threshold, the reciprocal of the first formation conductivity is determined as the true resistivity of the formation; otherwise, the value of the first formation resistivity is adjusted within a preset range, and the process returns to the step of obtaining the resistivity profile information of the first formation resistivity until the true resistivity of the formation is determined.

[0025] Secondly, this invention provides a system for determining the true resistivity of a formation, the technical solution of which is as follows:

[0026] It includes: a first operating module, a second operating module, and a third operating module;

[0027] The first operating module is used to: calculate the pressure value of the target formation using the formation fluid mass continuity equation, and obtain the three-phase saturation of the target formation based on the pressure value;

[0028] The second operating module is used to: substitute the three-phase saturation into the expression characterizing the relationship between saturation and resistivity to calculate the first formation resistivity of the target formation;

[0029] The third operating module is used to: obtain the target formation conductivity of the target formation, and determine the true resistivity of the target formation based on the first formation resistivity and the target formation conductivity.

[0030] The beneficial effects of the formation true resistivity determination system of the present invention are as follows:

[0031] The system of this invention can reduce the error in obtaining formation resistivity, thereby obtaining the true formation resistivity, which plays an extremely important role in accurately evaluating the oil and gas content of formations.

[0032] Based on the above scheme, the formation true resistivity determination system of the present invention can be further improved as follows.

[0033] In an alternative embodiment, it further includes: a building module; the building module is used for:

[0034] Construct a formation volume model of the wellbore and formation radial direction in a one-dimensional cylindrical coordinate system;

[0035] The formation fluid mass continuity equation is constructed by using Darcy's law and the seepage equation based on mass continuity, combined with the formation volume model.

[0036] In one alternative approach, the step of calculating the pressure value of the target formation using the formation fluid mass continuity equation in the first operating module includes:

[0037] The pressure value of the target formation is calculated using the catch-up method and in conjunction with the formation fluid mass continuity equation.

[0038] In one alternative approach, the step of determining the true resistivity of the target formation based on the first formation resistivity and the target formation conductivity in the third operating module includes:

[0039] Obtain the resistivity profile information of the first formation and the differential geometric factor of the target formation, and calculate the conductivity of the first formation based on the resistivity profile information and the differential geometric factor;

[0040] When the difference between the first formation conductivity and the target formation conductivity is less than a threshold, the reciprocal of the first formation conductivity is determined as the true resistivity of the formation; otherwise, the value of the first formation resistivity is adjusted within a preset range, and the process returns to the step of obtaining the resistivity profile information of the first formation resistivity until the true resistivity of the formation is determined.

[0041] Thirdly, the technical solution of an electronic device according to the present invention is as follows:

[0042] It includes a memory, a processor, and a program stored in the memory and running on the processor, wherein the processor executes the program to implement the steps of the formation true resistivity determination method of the present invention.

[0043] Fourthly, the technical solution of a computer-readable storage medium provided by the present invention is as follows:

[0044] The computer-readable storage medium stores instructions that, when read, cause the computer-readable storage medium to perform the steps of the formation true resistivity determination method of the present invention.

[0045] The above description is merely an overview of the technical solution of the present invention. In order to better understand the technical means of the present invention and to implement it in accordance with the contents of the specification, and in order to make the above and other objects, features and advantages of the present invention more apparent and understandable, specific embodiments of the present invention are described below. Attached Figure Description

[0046] The accompanying drawings are for illustrative purposes only and are not intended to limit the invention. Furthermore, the same reference numerals denote the same parts throughout the drawings. In the drawings:

[0047] Figure 1 This is a schematic flowchart of an embodiment of the method for determining the true resistivity of a formation according to the present invention.

[0048] Figure 2 This is one of the schematic diagrams of a stratigraphic model in cylindrical coordinates.

[0049] Figure 3 This is the second schematic diagram of a stratigraphic model in cylindrical coordinates.

[0050] Figure 4 One of the schematic diagrams of the radial differential geometric factor after focusing;

[0051] Figure 5 The second schematic diagram of the radial differential geometric factor after focusing;

[0052] Figure 6 Logic diagram of the program for iterative calculation of formation true resistivity;

[0053] Figure 7 This is one of the simulation results of the three-phase saturation varying with formation depth;

[0054] Figure 8 The second figure shows the simulation results of the three-phase saturation varying with formation depth.

[0055] Figure 9 This is a graph showing the variation of true resistivity of a sandstone reservoir section in a well that has been soaked in mud for a long time in an oilfield, as a function of formation depth.

[0056] Figure 10 The diagram shows the calculated true resistivity and intrusion zone radius of the formation in the 7370-7400 meter section of well K after prolonged soaking with drilling mud.

[0057] Figure 11 This is a detailed flowchart of this embodiment;

[0058] Figure 12 This is a schematic diagram of an embodiment of the system for determining the true resistivity of a formation according to the present invention.

[0059] Figure 13 This is a schematic diagram of an embodiment of an electronic device according to the present invention. Detailed Implementation

[0060] Exemplary embodiments of the invention will now be described in more detail with reference to the accompanying drawings. While exemplary embodiments of the invention are shown in the drawings, it should be understood that the invention can be implemented in various forms and should not be limited to the embodiments set forth herein.

[0061] Figure 1 This diagram illustrates a flowchart of an embodiment of a method for determining the true resistivity of a formation provided by the present invention. This method can be executed by an electronic device such as a terminal device or a server. The terminal device can be any fixed or mobile terminal, such as user equipment (UE), mobile device, user terminal, terminal, cellular phone, cordless phone, personal digital assistant (PDA), handheld device, computing device, vehicle-mounted device, or wearable device. The server can be a single server or a server cluster consisting of multiple servers. Any electronic device can implement the method for determining the true resistivity of a formation by having its processor call computer-readable instructions stored in its memory. Figure 1 As shown, it includes the following steps:

[0062] S1. Calculate the pressure value of the target formation using the formation fluid mass continuity equation, and obtain the three-phase saturation of the target formation based on the pressure value.

[0063] The target formation is the formation for which true resistivity needs to be determined in this embodiment. Three-phase saturation includes: water saturation, oil saturation, and mud filtrate saturation.

[0064] S2. Substitute the three-phase saturation into the expression characterizing the relationship between saturation and resistivity to calculate the first formation resistivity of the target formation.

[0065] Specifically, based on Archie's formula, an expression characterizing the relationship between saturation and resistivity is constructed. The first formation resistivity is the formation resistivity obtained through the steps (forward simulation) in S1-S2 above, and is not the final true resistivity.

[0066] S3. Obtain the target formation conductivity of the target formation, and determine the true resistivity of the target formation based on the first formation resistivity and the target formation conductivity.

[0067] The target formation conductivity is the formation conductivity of the target formation as measured by an array induction instrument.

[0068] In one alternative approach, it also includes:

[0069] Construct a formation volume model of the wellbore and formation radial direction in a one-dimensional cylindrical coordinate system.

[0070] The formation fluid mass continuity equation is constructed by using Darcy's law and the seepage equation based on mass continuity, combined with the formation volume model.

[0071] In this process, a formation model is constructed in a one-dimensional cylindrical coordinate system for the wellbore and formation radial direction. The formation model is then meshed to obtain a formation volume model.

[0072] In one alternative approach, the step of calculating the pressure value of the target formation using the formation fluid mass continuity equation includes:

[0073] The pressure value of the target formation is calculated using the catch-up method and in conjunction with the formation fluid mass continuity equation.

[0074] In one alternative approach, the step of determining the true resistivity of the target formation based on the first formation resistivity and the target formation conductivity includes:

[0075] Obtain the resistivity profile information of the first formation and the differential geometric factor of the target formation, and calculate the conductivity of the first formation based on the resistivity profile information and the differential geometric factor.

[0076] When the difference between the first formation conductivity and the target formation conductivity is less than a threshold, the reciprocal of the first formation conductivity is determined as the true resistivity of the formation; otherwise, the value of the first formation resistivity is adjusted within a preset range, and the process returns to the step of obtaining the resistivity profile information of the first formation resistivity until the true resistivity of the formation is determined.

[0077] The following embodiments illustrate this solution:

[0078] S10. Construct a formation model of the wellbore and formation radial direction in a one-dimensional cylindrical coordinate system, and mesh the formation model to obtain a formation volume model.

[0079] Among them, the stratigraphic model is as follows Figure 2 As shown, Figure 2 The stratigraphic model is meshed to obtain the stratigraphic volume model.

[0080] S20. Using Darcy's law and the seepage equation based on mass continuity, and combined with the formation volume model, a formation fluid mass continuity equation is constructed.

[0081] The study specifies limitations on the fluid medium and its properties within the formation, assuming that the seepage of mud filtrate, water, and oil conforms to Darcy's law. These assumptions include: ① The reservoir contains only three phases of seepage: mud filtrate, water, and oil. These three phases are immiscible and each conforms to Darcy's law. ② The effect of capillary forces is ignored. ③ Gravity is ignored.

[0082] Specifically, by combining the formation volume model, a three-phase mass continuity equation for the oil phase, water phase, and mud filtrate phase is established based on the seepage equation for mass continuity.

[0083] ① Equation of continuity of water phase mass (differential equation of water phase seepage):

[0084]

[0085] ② Oil phase mass continuity equation (water phase seepage differential equation):

[0086]

[0087] ③ Equation for continuity of mud filtrate phase mass (differential equation for mud filtrate phase seepage):

[0088]

[0089] ④ Saturation reduced to 1:

[0090] S w +S o +S m =1 (4)

[0091] ⑤ Ignoring the effect of capillary force, there are:

[0092] P w =P o =P m =P (5)

[0093] Where, q w q represents the mass of water injected per unit time. o q represents the mass of oil injected per unit time. m This represents the mass of mud filtrate injected per unit time.

[0094] Adding equations (1), (2), and (3), we get:

[0095]

[0096] It should be noted that equation (6) is the formation fluid mass continuity equation in this embodiment.

[0097] S30. Calculate the pressure value of the target formation using the formation fluid mass continuity equation.

[0098] For equation (6), discretization along the radial radius r forms a sequence {r0 = r0, r1, ..., r...}. j-1 r j r j+1 , ..., r N-1 r N After performing the transformation x = ln(r) - ln(r0), we obtain an equally spaced monotonically increasing sequence {x0 = 0, x1, ..., x2} on the variable x. j-1 x j x j+1 , ..., x N-1 x N Let h be the spacing on variable x. The unknowns to be solved are:

[0099] ① Pressure:

[0100]

[0101] ② Water saturation:

[0102] When n = 0,

[0103] ③ Oil saturation:

[0104]

[0105] When n = 0,

[0106] ④ Saturation of mud filtrate:

[0107]

[0108] The expression of the mud filtrate intrusion term in the discrete equations. The radius of the flow per unit time is r0 = r w Quality of the well wall arc surface:

[0109]

[0110] Among them, because So Q w0 =0; because So Q o0 =0. Q m0 This refers to the mass of mud filtrate that intrudes per unit time.

[0111] Numbering rules are as follows for stratigraphic models in cylindrical coordinate systems. Figure 3 As shown, for cell j ([r j-1 r j ]), j=2,…,n, the general formula is:

[0112]

[0113] Equation (7) is the formula for calculating the mass increment of each flow phase in the units other than Unit 1.

[0114] Since there is no injection term, equation (6) becomes:

[0115]

[0116] The right side of equation (6A):

[0117]

[0118] The results obtained by combining and rearranging are as follows:

[0119]

[0120] According to equation (6C), the pressure value P is solved using the chasing method.

[0121] It should be noted that, Porosity, S w S represents water saturation. o S represents oil saturation. m K represents the saturation of the mud filtrate, and K represents the permeability. rw K represents the relative permeability of water. ro K represents the relative permeability of oil. rm ρ represents the relative permeability of the mud filtrate. w ρ is the density of water. o Let ρ be the density of the oil.m Let G represent the density of the mud filtrate, G represent the inflow / outflow mass, and Q represent the volume. Element j is the cylinder from surface j-1 to surface j; the volume of element j is: Volume of water flowing out through cylinder j: Volume of water flowing into cylinder j-1: Water volume increment in unit j:

[0122] S40. Based on the pressure value, obtain the three-phase saturation of the target formation.

[0123] The water saturation S is obtained by substituting the pressure value P into equation (7A) and solving iteratively. w Substituting the pressure value P into equation (7B) and iteratively solving, the oil saturation S is obtained. o Substituting the pressure value P into equation (7C) and iteratively solving, the mud filtrate saturation S is obtained. m .

[0124]

[0125] S50. Substitute the three-phase saturation into the expression characterizing the relationship between saturation and resistivity to calculate the first formation resistivity of the target formation.

[0126] The expression characterizing the relationship between saturation and resistivity is as follows:

[0127]

[0128] σ mixw0 This indicates the electrical conductivity of the mixture, which is a mixture of water, oil, and mud filtrate; S mixw0 =S m +S w S mixw0 R represents the saturation of the mixture. t0 Let be the resistivity of the first formation, and a, b, m, and n are all coefficients.

[0129] S60. Obtain the target formation conductivity, the resistivity profile information of the first formation resistivity, and the differential geometric factor of the target formation.

[0130] The target formation conductivity is measured by an array inductive instrument. Resistivity profile information of the first formation is obtained using intrusion simulation based on seepage theory. The differential geometric factor of the target formation is the focused radial differential geometric factor. Multiplying the first formation resistivity by the focused radial differential geometric factor yields the conductivity of seven curves, as shown in the differential geometric factor graph. Figure 4 and Figure 5 As shown.

[0131] S70. Calculate the first formation conductivity based on the resistivity profile information and the differential geometric factor. When the difference between the first formation conductivity and the target formation conductivity is less than a threshold, determine the reciprocal of the first formation conductivity as the true formation resistivity; otherwise, adjust the value of the first formation resistivity within a preset range and return to the step of obtaining the resistivity profile information of the first formation resistivity in S60 until the true formation resistivity is determined.

[0132] The preset range is determined based on actual conditions and is not limited here. The process of determining the true resistivity of the formation is automated through a program. The program's algorithm calculation logic is as follows: Figure 6 As shown. Through continuous iterative calculations by the program algorithm, the formation resistivity R obtained from the inversion calculation is... t Initially, resistivity profile information is obtained using intrusion simulation based on seepage theory. From the resistivity profile, the inner diameter, outer diameter, and radius of the intrusion zone are derived. Then, using the formation resistivity profile and differential geometric factors, the first formation conductivity is calculated by the program. When the first formation conductivity infinitely approaches the target formation conductivity measured by the array induction instrument, the reciprocal of this first formation conductivity is determined to be the true formation resistivity. Otherwise, the value of the first formation resistivity is adjusted, and the process returns to the step of obtaining the resistivity profile information for the first formation resistivity until the true formation resistivity is determined.

[0133] It should be noted that two coefficient library files are designed during the program calculation process, including: ①HDILRGF.DAT -- geometric factor parameter library; ②IMI_HDIL_v2.dll -- deep penetration dynamic library. The coefficient library files are read in by the function SEC_appbegin(path,lnpath), where path is the folder path where the coefficient library files are located.

[0134] This embodiment provides a method for determining the true resistivity of a formation based on intrusion simulation. A formation model in a radial one-dimensional cylindrical coordinate system is established for both the wellbore and the formation. The one-dimensional formation is meshed, and a three-phase mass continuity equation for the oil, water, and mud filtrate phases is established using Darcy's law and a seepage equation based on mass continuity. By adding the three-phase mass continuity equations, the formation fluid mass continuity equation is obtained. Using formation porosity, three-phase fluid saturation, three-phase fluid permeability, and three-phase fluid density, combined with formation volume elements in the cylindrical coordinate system, the fluid volume passing through the cylindrical surface is calculated. Finally, the pressure value is solved using the chasing method, and the three saturations of the three phases—water saturation, oil saturation, and mud filtrate saturation—are obtained. The relationship between saturation and resistivity was established using Archie's formula, and the intrusion profile of the strata was calculated. From the intrusion profile, the inner diameter, outer diameter, and radius of the intrusion zone were obtained. Finally, through continuous iterative calculations using the obtained conductivity and geometric factors, the true resistivity of the strata was obtained.

[0135] During the simulation, the water saturation S on the first day obtained using the technical solution of this embodiment was... w Oil saturation S o and mud filtrate saturation S m The simulation results of the variation with formation depth are as follows: Figure 7 As shown, the water saturation S on the fifth day w Oil saturation S o and mud filtrate saturation S m The simulation results of the variation with formation depth are as follows: Figure 8 As shown in the figure. Using the technical solution of this embodiment, the true resistivity of a sandstone reservoir section with high porosity in a well in a domestic oilfield that has been soaked in mud for a long time was obtained. After drilling, the well was not logged in time and was soaked in mud for more than 20 days, during which the mud had deeply penetrated the formation. The changes in formation resistivity with formation depth after 1 day, 10 days, 50 days, 100 days and 200 days of mud soaking are as follows. Figure 9 As shown.

[0136] Using the technical solution of this embodiment, the radius of the formation invasion zone, the radius of the transition zone, and the true resistivity of the formation at a certain depth in a well that has been soaked in mud for a long time in an oil field are calculated. The calculation results are shown in the figure below. Figure 10 As shown, Figure 10 The calculation results of the formation invasion transition zone radius and formation true resistivity show that the formation mud invasion in the 7370-7400 meter section of this well is very deep, with an invasion depth of about 3 meters. The formation true resistivity calculated in this embodiment is reasonable. Therefore, the technical solution of this embodiment has obvious effect and can be applied to formation mud invasion correction, calculation of formation invasion zone radius, transition zone radius, invasion depth and formation true resistivity.

[0137] Figure 11 This is a schematic diagram of the specific process of this embodiment, divided into eight parts: determining the running time, calculating the relative permeability, solving for pressure by constructing a matrix, calculating the pressure gradient, calculating the mass increment of the fluid phase in each unit, calculating the saturation of each unit, calculating the minimum time required for the step size, and finally calculating the radius of the intrusion zone, the radius of the transition zone, the intrusion depth, and the true resistivity of the formation. Specifically:

[0138] 1) Determine the running time. During calculation, continuously check whether the current cumulative calculation time tsum is less than the given maximum time Tmax. If the condition is met, continue according to... Figure 11 The calculation process shown calculates the saturation of each unit. If the saturation is not satisfied, the calculation is terminated, and the final radius of the intrusion zone, the radius of the transition zone, and the true resistivity of the formation are given.

[0139] 2) Calculate the relative permeability. Using the three-phase relative permeability calculation model proposed in this embodiment, calculate the relative permeability of the aqueous phase, the relative permeability of the oil phase, and the relative permeability of the mud filtrate phase.

[0140] 3) Solve for the pressure using a matrix, and use the chasing method to solve the system of equations to calculate the pressure P.

[0141] 4) Use the pressure P calculated in step 3 to calculate the pressure gradient of pressure P as time t changes.

[0142] 5) Calculate the mass increment of the unit flow phase. In the cylindrical coordinate system model of the wellbore and formation, use this embodiment to calculate the volume of cylindrical unit j, then calculate the volume of water flowing out through cylindrical unit j, calculate the volume of water flowing in through cylindrical unit j-1, and calculate the water volume and mass increment of unit j. Similarly, calculate the volume and mass increase or decrease of oil and mud filtrate.

[0143] 6) Calculate the saturation of each unit. For a certain unit cylinder j, substitute the pressure P calculated in step 4 into equations (7A), (7B), and (7C) of this embodiment to iteratively solve the oil phase saturation, water phase saturation, and mud filtrate phase saturation of unit cylinder j. Iteratively solve the oil phase saturation, water phase saturation, and mud filtrate phase saturation of all unit cylinders in the wellbore and formation model under the cylindrical coordinate system to obtain the distribution of oil phase saturation, water phase saturation, and mud filtrate phase saturation in the formation.

[0144] 7) Calculate the minimum time required for the step size. Using the adaptive time calculation algorithm of this embodiment, calculate the saturation of each unit cylinder at a certain intrusion time. The adaptive time calculation formula is as follows:

[0145]

[0146]

[0147] The cumulative time tsum is obtained by accumulating Δt in the above adaptive time calculation formula.

[0148] 8) Calculate the radius of the intrusion zone, the radius of the transition zone, and the true resistivity of the formation. If the cumulative time tsum calculated in step 7 is greater than or equal to the given maximum time Tmax, then terminate the calculation of the relative permeability and saturation of the three phases after intrusion. Iteratively judge the changes of oil phase, water phase, and mud filtrate phase in the cylindrical units of the wellbore and formation model in the cylindrical coordinate system. When the oil phase or water phase is completely replaced by the mud filtrate phase, it is judged as the formation flushing zone. When the oil phase or water phase and the mud filtrate phase coexist, it is judged as the formation mud intrusion zone. After obtaining the change of the three-phase saturation with radius, the relationship between resistivity and saturation with radius is found by back-applying Archie's formula. That is, the relationship between conductivity and saturation with radius is obtained by forward modeling. Finally, the radius of the intrusion zone, the radius of the transition zone, the intrusion depth, and the true resistivity of the formation are calculated.

[0149] This embodiment takes Well K in the X oilfield in China as an example to calculate the true resistivity of the formation in the 7370-7400 meter well section, and simultaneously calculates the radius of the invasion zone and the radius of the transition zone. According to the theoretical numerical model of this embodiment, two coefficient library files are obtained. These are the model library files used to calculate the true resistivity, flushed zone radius, and invasion zone radius from the seven 2-foot resolution VRM curves induced by the array in this well: ①HDILRGF.DAT -- Geometric factor parameter library; ②IMI_HDIL_v2.dll -- Deep invasion dynamic library. The coefficient library files are read by the program function SEC_appbegin(path,lnpath), where path is the folder containing the coefficient library files, ending with a backslash "\", and lnpath is the path length of path (including the trailing backslash "\"). The seven 2-foot resolution VRM curves induced by the array in this well are used as input curves, as shown in Table 1 below.

[0150] Table 1:

[0151]

[0152] Using two coefficient library files from the invasion simulation, and given 25 control parameters including formation porosity, absolute permeability, wellbore radius, model outer radius, wellbore pressure, saturation of each phase, permeability of each phase, and conductivity of each phase, the radius of the invasion zone, the radius of the transition zone, the invasion depth, and the true resistivity of the formation were calculated from seven 2-foot resolution VRM curves in the 7370-7400 meter interval of this well. The physical meaning and numerical values ​​of each control parameter are shown in Table 2 below.

[0153] Table 2:

[0154]

[0155] Using the aforementioned seven 2-foot resolution VRM curves and 25 control parameters of the model, six output curves were calculated, including the inner diameter of the intrusion zone, the outer diameter of the intrusion zone, the intrusion radius, the resistivity of the flushed zone, the resistivity of the undisturbed formation, and the error. The inner diameter of the intrusion zone is the outer diameter of the flushed zone, the outer diameter of the intrusion zone is the radius of the transition zone, and the intrusion radius is the intrusion depth. The true resistivity of the formation, the true resistivity of the flushed zone, and the inner and outer diameters of the intrusion transition zone calculated for well K are shown below. Figure 10 As shown.

[0156] Figure 10 The first track (from left to right) is the depth track, the second track is the lithology track, the third track is the 2-foot resolution VRM curve of the array induction logging, the fourth track is the formation true resistivity curve and the flushed zone true resistivity curve calculated using the technical solution of this embodiment, and the fifth track is the formation invasion transition zone radius curve (including the inner radius curve and the outer radius curve of the invasion transition zone) calculated using the technical solution of this embodiment. Figure 10 The calculation results of the radius of the intrusion transition zone and the true resistivity of the formation show that the formation mud intrusion in the 7370-7400 meter section of this well is very deep, with an intrusion depth of about 3 meters. The true resistivity of the formation obtained by the technical solution in this embodiment is reasonable. The technical effect of this embodiment is obvious and can be applied to the correction of formation mud intrusion, calculating the inner diameter of the intrusion zone, the outer diameter of the intrusion zone, the intrusion radius, the resistivity of the flushed zone, the resistivity of the original formation, and the calculation error.

[0157] The technical solution of this embodiment can reduce the error in obtaining formation resistivity, thereby obtaining the true formation resistivity, which plays an extremely important role in accurately evaluating the oil and gas content of the formation.

[0158] Figure 12 A schematic diagram of an embodiment of a formation true resistivity determination system 200 provided by the present invention is shown. Figure 12 As shown, the system 200 includes: a first operating module 210, a second operating module 220, and a third operating module 230;

[0159] The first operating module 210 is used to: calculate the pressure value of the target formation using the formation fluid mass continuity equation, and obtain the three-phase saturation of the target formation based on the pressure value;

[0160] The second operating module 220 is used to: substitute the three-phase saturation into the expression characterizing the relationship between saturation and resistivity to calculate the first formation resistivity of the target formation;

[0161] The third operation module 230 is used to: obtain the target formation conductivity of the target formation, and determine the true resistivity of the target formation based on the first formation resistivity and the target formation conductivity.

[0162] In an alternative embodiment, it further includes: a building module; the building module is used for:

[0163] Construct a formation volume model of the wellbore and formation radial direction in a one-dimensional cylindrical coordinate system;

[0164] The formation fluid mass continuity equation is constructed by using Darcy's law and the seepage equation based on mass continuity, combined with the formation volume model.

[0165] In an alternative embodiment, the step of calculating the pressure value of the target formation using the formation fluid mass continuity equation in the first operating module 210 includes:

[0166] The pressure value of the target formation is calculated using the catch-up method and in conjunction with the formation fluid mass continuity equation.

[0167] In one alternative approach, the step of determining the true resistivity of the target formation based on the first formation resistivity and the target formation conductivity in the third operating module 230 includes:

[0168] Obtain the resistivity profile information of the first formation and the differential geometric factor of the target formation, and calculate the conductivity of the first formation based on the resistivity profile information and the differential geometric factor;

[0169] When the difference between the first formation conductivity and the target formation conductivity is less than a threshold, the reciprocal of the first formation conductivity is determined as the true resistivity of the formation; otherwise, the value of the first formation resistivity is adjusted within a preset range, and the process returns to the step of obtaining the resistivity profile information of the first formation resistivity until the true resistivity of the formation is determined.

[0170] The technical solution of this embodiment can reduce the error in obtaining formation resistivity, thereby obtaining the true formation resistivity, which plays an extremely important role in accurately evaluating the oil and gas content of the formation.

[0171] The parameters and steps for each module in the formation true resistivity determination system 200 described above to achieve their respective functions can be found in the parameters and steps in the above-described embodiment of the formation true resistivity determination method, and will not be repeated here.

[0172] like Figure 13As shown, an electronic device 300 according to an embodiment of the present invention includes a processor 320 coupled to a memory 310. The memory 310 stores at least one computer program 330, which is loaded and executed by the processor 320 to enable the electronic device 300 to implement any of the above-mentioned methods for determining the true resistivity of a formation. Specifically:

[0173] The electronic device 300 can vary considerably due to differences in configuration or performance. It may include one or more processors 320 (Central Processing Units, CPUs) and one or more memories 310. The one or more memories 310 store at least one computer program 330, which is loaded and executed by the one or more processors 320 to enable the electronic device 300 to implement any of the methods for determining the true resistivity of the formation provided in the above embodiments. Of course, the electronic device 300 may also have wired or wireless network interfaces, a keyboard, and input / output interfaces for input and output. The electronic device 300 may also include other components for implementing device functions, which will not be elaborated upon here.

[0174] An embodiment of the present invention provides a computer-readable storage medium storing at least one computer program, which is loaded and executed by a processor to enable a computer to implement any of the above-described methods for determining the true resistivity of a formation.

[0175] Alternatively, the computer-readable storage medium may be a read-only memory (ROM), a random access memory (RAM), a compact disc read-only memory (CD-ROM), magnetic tape, a floppy disk, and an optical data storage device, etc.

[0176] In an exemplary embodiment, a computer program product or computer program is also provided, which includes computer instructions stored in a computer-readable storage medium. A processor of an electronic device reads the computer instructions from the computer-readable storage medium and executes the computer instructions, causing the electronic device to perform any of the above-described methods for determining the true resistivity of a formation.

[0177] It should be noted that the terms "first," "second," etc., used in the specification and claims of this application are used to distinguish similar objects and represent a limitation on a specific order or sequence. Where appropriate, the order of use for similar objects can be interchanged so that the embodiments of this application described herein can be implemented in an order other than that shown or described.

[0178] Those skilled in the art will recognize that this invention can be implemented as a system, method, or computer program product. Therefore, this disclosure can be specifically implemented in the following forms: it can be entirely hardware, entirely software (including firmware, resident software, microcode, etc.), or a combination of hardware and software, generally referred to herein as a "circuit," "module," or "system." Furthermore, in some embodiments, this invention can also be implemented as a computer program product in one or more computer-readable media containing computer-readable program code.

[0179] Any combination of one or more computer-readable media can be used. A computer-readable medium can be a computer-readable signal medium or a computer-readable storage medium. A computer-readable storage medium can be, for example, but not limited to, an electrical, magnetic, optical, electromagnetic, infrared, or semiconductor system, apparatus, or device, or any combination thereof. More specific examples (a non-exhaustive list) of computer-readable storage media include: an electrical connection having one or more wires, a portable computer disk, a hard disk, random access memory (RAM), read-only memory (ROM), erasable programmable read-only memory (EPROM or flash memory), optical fiber, portable compact disk read-only memory (CD-ROM), optical storage device, magnetic storage device, or any suitable combination thereof. In this application, a computer-readable storage medium can be any tangible medium containing or storing a program that can be used by or in conjunction with an instruction execution system, apparatus, or device.

[0180] Although embodiments of the present invention have been shown and described above, it is understood that the above embodiments are exemplary and should not be construed as limiting the present invention. Those skilled in the art can make changes, modifications, substitutions and variations to the above embodiments within the scope of the present invention.

Claims

1. A method for determining the true resistivity of a formation, characterized in that, include: The pressure value of the target formation is calculated using the formation fluid mass continuity equation, and the three-phase saturation of the target formation is obtained based on the pressure value. The three-phase saturation is substituted into the expression characterizing the relationship between saturation and resistivity to calculate the first formation resistivity of the target formation. Obtain the target formation conductivity of the target formation, and determine the true resistivity of the target formation based on the first formation resistivity and the target formation conductivity.

2. The method for determining the true resistivity of a formation according to claim 1, characterized in that, Also includes: Construct a formation volume model of the wellbore and formation radial direction in a one-dimensional cylindrical coordinate system; The formation fluid mass continuity equation is constructed by using Darcy's law and the seepage equation based on mass continuity, combined with the formation volume model.

3. The method for determining the true resistivity of a formation according to claim 1, characterized in that, The steps for calculating the pressure value of a target formation using the formation fluid mass continuity equation include: The pressure value of the target formation is calculated using the catch-up method and in conjunction with the formation fluid mass continuity equation.

4. The method for determining the true resistivity of a formation according to claim 1, characterized in that, The step of determining the true resistivity of the target formation based on the first formation resistivity and the target formation conductivity includes: Obtain the resistivity profile information of the first formation and the differential geometric factor of the target formation, and calculate the conductivity of the first formation based on the resistivity profile information and the differential geometric factor; When the difference between the first formation conductivity and the target formation conductivity is less than a threshold, the reciprocal of the first formation conductivity is determined as the true resistivity of the formation; otherwise, the value of the first formation resistivity is adjusted within a preset range, and the process returns to the step of obtaining the resistivity profile information of the first formation resistivity until the true resistivity of the formation is determined.

5. A system for determining the true resistivity of a formation, characterized in that, include: The first operating module, the second operating module, and the third operating module; The first operating module is used to: calculate the pressure value of the target formation using the formation fluid mass continuity equation, and obtain the three-phase saturation of the target formation based on the pressure value; The second operating module is used to: substitute the three-phase saturation into the expression characterizing the relationship between saturation and resistivity to calculate the first formation resistivity of the target formation; The third operating module is used to: obtain the target formation conductivity of the target formation, and determine the true resistivity of the target formation based on the first formation resistivity and the target formation conductivity.

6. The formation true resistivity determination system according to claim 5, characterized in that, Also includes: Build module; the build module is used for: Construct a formation volume model of the wellbore and formation radial direction in a one-dimensional cylindrical coordinate system; The formation fluid mass continuity equation is constructed by using Darcy's law and the seepage equation based on mass continuity, combined with the formation volume model.

7. The formation true resistivity determination system according to claim 5, characterized in that, The step in the first operating module to calculate the pressure value of the target formation using the formation fluid mass continuity equation includes: The pressure value of the target formation is calculated using the catch-up method and in conjunction with the formation fluid mass continuity equation.

8. The formation true resistivity determination system according to claim 5, characterized in that, The step in the third operating module to determine the true resistivity of the target formation based on the first formation resistivity and the target formation conductivity includes: Obtain the resistivity profile information of the first formation and the differential geometric factor of the target formation, and calculate the conductivity of the first formation based on the resistivity profile information and the differential geometric factor; When the difference between the first formation conductivity and the target formation conductivity is less than a threshold, the reciprocal of the first formation conductivity is determined as the true resistivity of the formation; otherwise, the value of the first formation resistivity is adjusted within a preset range, and the process returns to the step of obtaining the resistivity profile information of the first formation resistivity until the true resistivity of the formation is determined.

9. An electronic device, characterized in that, The electronic device includes a processor coupled to a memory storing at least one computer program, which is loaded and executed by the processor to enable the electronic device to implement the method for determining the true resistivity of a formation as described in any one of claims 1 to 4.

10. A computer-readable storage medium, characterized in that, The computer-readable storage medium stores at least one computer program, which is loaded and executed by a processor to enable the computer-readable storage medium to implement the method for determining the true resistivity of a formation as described in any one of claims 1 to 4.

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