Array lateral logging resistivity anisotropy correction method

Abstract

The invention relates to the technical field of exploration data processing, in particular to an array lateral logging resistivity anisotropy correction method. The method comprises the following steps: 1) establishing an anisotropic reservoir array lateral logging three-dimensional finite element model based on array lateral logging instrument parameters and anisotropic formation parameters, and forward simulating the influence of anisotropy on array lateral logging in different hole drift angle stratums; and 2) making an anisotropy correction plate according with four detection modes of array lateral logging by using data obtained by forward modeling. And 3) correcting the three-layer stratum model data by using the anisotropy correction plate. And verifying the validity of the plate. And a new method for correcting the anisotropic formation array lateral logging response of the highly-deviated well by using the plate is constructed. The resistivity corrected by the method has good consistency with the stratum horizontal resistivity set by the model, and the effectiveness of the corrected chart is verified.

Description

Technical Field

[0001] The invention relates to the technical field of exploration data processing, and in particular to an array laterolog resistivity anisotropy correction method. Background Art

[0002] With the continuous advancement of oil and gas exploration technology, logging evaluation work has become increasingly complex, and traditional lateral logging equipment can no longer meet the current interpretation needs. When the current emitted by the lateral logging equipment penetrates the formation, the surrounding rock on the formation and the low-resistivity area within the layer will cause the current to be diverted, resulting in a significant deviation between the current and the true resistivity of the formation. In actual logging, due to the anisotropy of the formation, the apparent resistivity measured by lateral logging in the inclined well is not only affected by the horizontal resistivity of the formation, but also by the vertical resistivity, which further increases the measurement error and makes it difficult to accurately evaluate the oil content of the formation.

[0003] As one of the key technologies for reservoir oil content evaluation, array lateral logging technology has the core principle of using shielding electrodes and main electrodes to release currents of the same polarity to achieve current focusing, thereby driving the main current to penetrate the formation perpendicular to the wellbore direction. This technology is an innovative improvement based on the traditional dual lateral logging technology. Compared with traditional methods, array logging technology can capture formation information more comprehensively by increasing the detection path. Under the condition of vertical wells, the current direction emitted by the main electrode in array lateral logging technology is parallel to the bedding plane of the formation, and its measurement results are mainly affected by the horizontal resistivity of the formation. However, under the condition of inclined wells, especially when the formation exhibits significant anisotropy, the angle difference between the current direction emitted by the main electrode and the formation causes the measured apparent resistivity to become the result of the combined effect of horizontal resistivity and vertical resistivity. Under such conditions, directly applying apparent resistivity to evaluate reservoir oil content will lead to significant errors. Therefore, for formations with anisotropic characteristics in highly deviated wells, anisotropy correction must be performed on the measured apparent resistivity to ensure the scientificity and accuracy of reservoir oil-bearing evaluation.

[0004] At present, the interpretation technology of lateral logging is becoming more and more mature, and there are in-depth studies on the anisotropy of logging under various well conditions at home and abroad. However, the electrical anisotropy correction method of array lateral logging in deviated wells is still an under-researched field. This study is committed to developing an electrical anisotropy correction method for array lateral logging in anisotropic formations in highly deviated wells, and through this correction process, a set of effective correction methods are summarized, in order to provide new perspectives and solutions for research in this field. Summary of the invention

[0005] In view of the shortcomings of the prior art, the present invention provides a method for correcting the anisotropy of array lateral logging resistivity. Based on the correction chart, the present invention corrects the apparent resistivity measured by the instrument under the anisotropic formation conditions of different well inclination angles. The resistivity corrected by the present invention has good consistency with the horizontal resistivity of the formation set by the model, which verifies the effectiveness of the correction chart.

[0006] The technical solution of the present invention is: a method for correcting anisotropy of array lateral logging resistivity, characterized in that it comprises the following steps:

[0007] Step 1) based on array lateral logging instrument parameters and anisotropic formation parameters, forward modeling the influence of anisotropy on array lateral logging in formations with different well inclination angles;

[0008] The conductivity perpendicular to the bedding direction of the formation is the vertical conductivity of the formation σ v , the conductivity parallel to the bedding direction is the horizontal conductivity σ h ; λ represents the formation anisotropy coefficient, and the conductivity is used to represent the formation anisotropy. The formula is:

[0009]

[0010] θ represents the angle between the well axis and the formation normal, and the expression of the formation conductivity in a highly deviated well is:

[0011]

[0012] For array laterolog logging, the apparent resistivity formula is:

[0013]

[0014] In formula (3), K i is the electrode coefficient of the ith detection mode, U Mi is the potential at the monitoring electrode M1 in the i-th detection mode; where K i and T 0 is a certain constant

[0015] U is the potential in the domain, and its extreme value of the functional solution is

[0016]

[0017] U A is the surface potential of the constant current electrode I A The current provided by the constant current electrode A, x, y, z represent the direction of the measuring point;

[0018] By changing the vertical resistivity R v The size of is used to realize the change of formation anisotropy, and the formula is as follows:

[0019]

[0020] Among them, R h1 To set the horizontal resistivity of the formation for the formation model;

[0021] Step 2) using the data obtained from the forward modeling to produce anisotropic correction plates that conform to the four detection modes of array lateral logging;

[0022] Step 3) Use the anisotropic correction plate to correct the three-layer formation model data. The specific process is as follows: After the correction plate is produced, the forward simulation data of the three-layer formation model is corrected, and the apparent resistivity obtained by each detection mode is recorded as R RLa , the first detection mode to the fourth detection mode are R RL1 ~R RL4 After obtaining the anisotropy coefficient and the well inclination of the target layer, the correction plate is interpolated and fitted. The correction coefficient is obtained by interpolating the anisotropy coefficient and the well inclination of the target layer. The corrected horizontal resistivity of the formation is calculated by the correction coefficient and the measured apparent resistivity.

[0023] According to the array laterolog resistivity anisotropy correction method as described above, it is characterized in that: in step 2), the true horizontal resistivity R of the formation is calculated. h The calculation formula is:

[0024]

[0025] R a It is the apparent resistivity measured in the inclined well formation.

[0026] According to the array laterolog resistivity anisotropy correction method as described above, it is characterized in that: in step 3), the well inclination angle and the anisotropy coefficient are used to obtain the corresponding correction coefficient Y in the correction plate.

[0027] According to the array laterolog resistivity anisotropy correction method as described above, it is characterized in that: in step 3), the true formation horizontal resistivity R of each point after interpolation is h The calculation formula is:

[0028]

[0029] Where R RLa is the apparent resistivity measured in each detection mode, and Y is the correction coefficient. BRIEF DESCRIPTION OF THE DRAWINGS

[0030] Figure 1 Schematic diagram of anisotropic formation array lateral logging in highly deviated wells.

[0031] Figure 2 Array Laterolog Mode One Calibration Chart.

[0032] Figure 3 Array laterolog mode 2 calibration chart.

[0033] Figure 4 Array Laterolog Mode Three Correction Chart.

[0034] Figure 5 Array Laterolog Mode Four Correction Chart.

[0035] Figure 6 Anisotropic formation model.

[0036] Figure 7 Response curve of numerical simulation of anisotropic formation array laterolog.

[0037] Figure 8 Anisotropic formation array laterolog calibration curve.

[0038] Fig. 9 Anisotropic formation model.

[0039] Fig.10 Response curve of numerical simulation of anisotropic formation array laterolog.

[0040] Fig.11 Anisotropic formation array laterolog calibration curve. DETAILED DESCRIPTION

[0041] The technical solution of the present invention is further described below in conjunction with the accompanying drawings.

[0042] The present invention provides a method for correcting the apparent resistivity measured by array lateral logging in anisotropic formations in highly deviated wells, and the specific implementation scheme is as follows:

[0043] Step 1) Based on the array lateral logging instrument parameters and anisotropic formation parameters, a three-dimensional finite element model of anisotropic reservoir array lateral logging is established, and the influence of anisotropy on array lateral logging in formations with different well inclination angles is simulated forward.

[0044] Step 2) Use the data obtained from the forward modeling to produce anisotropic correction plates that conform to the four detection modes of array lateral logging.

[0045] Step 3) Correct the three-layer formation model data using the anisotropic correction chart. Verify the validity of the chart. Construct a new method for correcting the anisotropic formation array lateral logging response of highly deviated wells using the chart.

[0046] Further, in step 1), for anisotropic formations, the conductivity is usually expressed by electrical conductivity, where the conductivity perpendicular to the bedding direction of the formation is the vertical conductivity σ v , the conductivity parallel to the bedding direction is the horizontal conductivity σ h Usually λ represents the formation anisotropy coefficient, and the formation anisotropy can be expressed by conductivity, the formula is:

[0047]

[0048] When the well inclination angle is not 0, the apparent resistivity measured by array lateral logging is affected by the anisotropy of the formation, and its measurement size is also affected by the formation σ v and σ h We let θ represent the angle between the well axis and the formation normal. If the horizontal conductivity of the formation σ h Without changing due to azimuth, the expression of formation conductivity in a highly deviated well is:

[0049]

[0050] For array laterolog logging, the apparent resistivity formula is:

[0051]

[0052] In formula (3), K i is the electrode coefficient of the ith detection mode, U Mi is the potential at the monitoring electrode M1 in the i-th detection mode. K i and T 0 is a definite constant.

[0053] The core of the numerical simulation of array lateral logging response is to obtain the potential U in the solution domain. According to the Laplace equation satisfied by U in the solution domain, the boundary conditions are substituted, and then according to the finite element variational principle, the problem that needs to be solved finally becomes the problem of solving the extreme value of the functional:

[0054]

[0055] U A is the surface potential of the constant current electrode I A The current provided by the constant current electrode A, x, y, z represent the direction of the measuring point;

[0056] Set the horizontal resistivity R of the formation model h1 is 100Ω.m, by changing the vertical resistivity R v The size of is used to realize the change of formation anisotropy, and the formula is as follows:

[0057]

[0058] In order to obtain the anisotropic correction plate, the formation model did not consider the influence of formation factors such as wellbore, surrounding rock, and intrusion zone, and forward calculations were performed at 6 different λ and 10 different θ.

[0059] The present invention uses formula (2), the horizontal resistivity is fixed, and the vertical resistivity is changed to achieve the change of the anisotropy coefficient. The angle θ can be measured at intervals of 10°, and a smooth curve is used for processing when drawing.

[0060] Further, in step 2), in the traditional anisotropy correction experiment, an empirical formula is used to describe the resistivity R measured by the instrument. a , well inclination angle θ and formation horizontal resistivity R h Relationship:

[0061]

[0062] The above formula (6) can be used to calculate the electrical anisotropy correction chart of array lateral logging. In actual logging, the apparent resistivity obtained by the formation measurement in the inclined well can be used as R a After obtaining the formation anisotropy coefficient λ and the well inclination angle θ, the corrected true formation horizontal resistivity R can be calculated. h , here we get R h It is the horizontal resistivity of the formation after calculation and correction, which is different from the horizontal resistivity set by the model in step 1. Through this formula, the true horizontal resistivity R of the formation can be calculated. h This formula is widely used in anisotropy correction. However, due to the influence of anisotropy and the differences in various detection modes, there is a certain error between the apparent resistivity of the instrument and the actual instrument response. Therefore, a formation model in step (1) is established and forward calculation is performed. Based on the data obtained from the forward simulation, an electrical anisotropy correction chart that conforms to each detection mode of array lateral logging is produced.

[0063] Further, in step 3), after the correction chart is produced, the forward simulation data of the three-layer formation model (surrounding rock-target layer-surrounding rock) is corrected, and the apparent resistivity obtained by each detection mode is recorded as R RLa , the first detection mode to the fourth detection mode are R RL1 ~R RL4 After obtaining the anisotropy coefficient and well inclination of the target layer, the correction chart can be interpolated and fitted. Matlab is used for interpolation. By inputting the values ​​of the anisotropy coefficient λ and the well inclination θ, the anisotropy coefficient corresponding to the interpolation can be obtained. A set of corresponding well inclination angles, anisotropy coefficients and correction coefficients is obtained. The correction coefficient is the ordinate in the correction chart:

[0064]

[0065] Where R RLa is the apparent resistivity measured in each detection mode, R Rla With R a Both represent the measured apparent resistivity. Since array lateral logging has many detection modes, R RLa It is more reasonable to express it as . Y is the correction coefficient. Using the well inclination angle and anisotropy coefficient, the corresponding correction coefficient Y is obtained in the correction chart. Substituting into formula (7) can obtain the true horizontal resistivity R of each point after interpolation: h The corrected resistivity is in good agreement with the horizontal resistivity of the formation set by the model, which verifies the validity of the correction chart.

[0066] Application effect analysis:

[0067] In order to better explain the present invention, the main contents of the present invention are further explained below in conjunction with specific embodiments, but the contents of the present invention are not limited to the following embodiments.

[0068] The formation model of this experiment is a three-layer formation model (surrounding rock-target layer-surrounding rock). The working schematic diagram of the anisotropic formation measurement in a highly deviated well is as follows: Figure 1 shown.

[0069] In order to simulate the change of formation anisotropy, the horizontal resistivity of the model was set to 100Ω.m. The change of formation anisotropy was achieved by changing the value of vertical resistivity. The forward simulation of the array lateral logging response under the conditions of anisotropy coefficient λ of 1, 2, 4, 6, 8, 10 and well inclination θ of 0°, 10°, 20°, 30°, 40°, 50°, 60°, 70°, 80°, 90° was carried out. The data obtained by forward simulation can be plotted as follows Figures 2 to 5 Anisotropy correction plates for the four modes shown.

[0070] The anisotropy coefficient of the formation is generally small, generally between 1 and 2. Figures 6 to 8 , is a calibration experiment to simulate general formations. The anisotropy coefficient λ of the target layer is 2, and the well inclination angle is 30°. Figure 6 is the stratigraphic model of the stratum, Figure 7 To correct the curve before Figure 8 To correct the curve, observe the formation model and the curve before correction. We can clearly see that the horizontal resistivity and vertical resistivity in the formation are larger. Due to the influence of anisotropy, the apparent resistivity of the measured formation section will increase relatively. Among them, since the depth of measurement in one detection mode is the shallowest, the increase in the apparent resistivity measured by the instrument is the largest. The corrected curve is as follows Figure 8The apparent resistivity measured by the first detection mode after correction is in good agreement with the true horizontal resistivity of the formation, which verifies the effectiveness of the correction chart for the resistivity correction of general anisotropic formation array lateral logging.

[0071] However, for carbonate formations with high inclination, the anisotropy coefficient may sometimes be very large. Figures 9 to 11 , is a calibration experiment to simulate a formation with a large anisotropy coefficient. The anisotropy coefficient λ of the target layer is 4, and the well inclination angle is 30°. Fig. 9 is the stratigraphic model of the stratum, Fig.10 To correct the curve before Fig.11 To observe the corrected curve, the apparent resistivity measured by the first detection mode after correction is in good agreement with the true horizontal resistivity of the formation, which verifies the effectiveness of the correction chart for the array lateral logging resistivity correction of formations with large anisotropy coefficients.

[0072] The present invention proposes a method for correcting the electrical anisotropy of array lateral logging by using a correction chart, and verifies the effectiveness of the correction chart. The chart takes into account the detection characteristics of each detection mode of array lateral logging. Compared with the correction using traditional empirical formulas, the correction using this chart is more in line with the actual situation.

[0073] Although it is feasible to use the correction plate to perform anisotropy correction in the present invention, the detection depth increases with the change of the array lateral logging detection mode. For detection modes with greater detection depth, the influence of the surrounding rock is greater. Therefore, the present invention can only accurately correct the first detection mode, and the other three detection modes require subsequent surrounding rock correction.

Claims

1. A method for correcting anisotropy of array lateral logging resistivity, characterized in that: The following steps are involved: Step 1) based on array lateral logging instrument parameters and anisotropic formation parameters, forward modeling the influence of anisotropy on array lateral logging in formations with different well inclination angles; The conductivity perpendicular to the bedding direction of the formation is the vertical conductivity of the formation σ v , the conductivity parallel to the bedding direction is the horizontal conductivity σ h ; λ represents the formation anisotropy coefficient, and the conductivity is used to represent the formation anisotropy. The formula is: θ represents the angle between the well axis and the formation normal, and the expression of the formation conductivity in a highly deviated well is: For array laterolog logging, the apparent resistivity formula is: In formula (3), K i is the electrode coefficient of the ith detection mode, U Mi is the potential at the monitoring electrode M1 in the i-th detection mode; where K i and I0 are constants U is the potential in the domain, and its extreme value of the functional solution is U A is the surface potential of the constant current electrode I A The current provided by the constant current electrode A, x, y, z represent the direction of the measuring point; U A represents the average potential of the constant current electrode A, and X, Y, and Z represent the vector directions. By changing the vertical resistivity R v The size of is used to realize the change of formation anisotropy, and the formula is as follows: Among them, R h1 To set the horizontal resistivity of the formation for the formation model; Step 2) using the data obtained from the forward modeling to produce anisotropic correction plates that conform to the four detection modes of array lateral logging; Step 3) Use the anisotropic correction plate to correct the three-layer formation model data. The specific process is as follows: After the correction plate is produced, the forward simulation data of the three-layer formation model is corrected, and the apparent resistivity obtained by each detection mode is recorded as R RLa , the first detection mode to the fourth detection mode are R RL1 ~R RL4 After obtaining the anisotropy coefficient and the well inclination of the target layer, the correction plate is interpolated and fitted. The correction coefficient is obtained by interpolating the anisotropy coefficient and the well inclination of the target layer. The corrected horizontal resistivity of the formation is calculated by the correction coefficient and the measured apparent resistivity.

2. The array laterolog resistivity anisotropy correction method according to claim 1, characterized in that: Step 2) Calculate the true horizontal resistivity R of the formation h The calculation formula is: R a It is the apparent resistivity measured in the inclined well formation.

3. The array laterolog resistivity anisotropy correction method according to claim 1, characterized in that: In step 3), the well inclination angle and the anisotropy coefficient are used to obtain the corresponding correction coefficient Y in the correction chart.

4. The array laterolog resistivity anisotropy correction method according to claim 1, characterized in that: The actual horizontal resistivity R of each point after interpolation in step 3) h The calculation formula is: Where R RLa is the apparent resistivity measured in each detection mode, and Y is the correction coefficient.

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