Method for calibrating resistivity in horizontal well shale reservoir

Abstract

This invention discloses a method for correcting the logging resistivity of shale reservoirs in horizontal wells. The method involves acquiring logging data of the shale reservoir to be corrected, including the apparent resistivity Ra and the logging inclination angle IP at the corresponding depth point. A correction coefficient K is calculated based on the acquired logging inclination angle IP. Finally, the corrected logging resistivity Rt at that depth point is calculated based on the apparent resistivity Ra and the calculated correction coefficient K. This invention solves the problem of logging resistivity correction required for rapid on-site evaluation of shale reservoirs in horizontal wells. The method is simple, easy to implement, widely applicable, and low-cost, providing a new technology for shale oil and gas exploration and development.

Description

Technical Field

[0001] This invention belongs to the field of shale oil and gas exploration and development technology, specifically relating to a method for correcting the logging resistivity of horizontal well shale reservoirs. Background Technology

[0002] Shale oil and gas is a crucial component of unconventional oil and gas, and the precise evaluation of shale reservoirs is a recognized global challenge. China possesses abundant shale oil and gas resources, but the formation mechanisms and reservoir geological characteristics differ significantly from those of the United States. Limited technologies can be directly applied, necessitating continuous technological innovation based on practical experience to develop exploration and development engineering technologies adapted to the geological characteristics of shale oil and gas formation and accumulation in China, thereby achieving large-scale, commercial, and efficient development. In the precise interpretation and evaluation of shale reservoirs (commonly referred to as shale layers or shale), shale reservoir resistivity logging is a vital parameter for evaluating the primary quality of shale, determining reservoir oil and gas saturation, and monitoring development dynamics. It plays a key role in assessing the physical properties, oil and gas content, and production capacity of shale reservoirs.

[0003] Through searching relevant literature and patents, it was learned that, based on the quantitative relationship between the logging resistivity of shale reservoirs in straight-line wells and horizontal wells in the same stratigraphic group, the logging resistivity of shale reservoirs in horizontal wells can be corrected to that of shale reservoirs in vertical wells for basic lateral comparison. However, research on methods for this purpose is currently lacking, and there is an urgent need for a fast, simple, easy-to-implement, and relatively accurate and reliable method to provide logging resistivity data of shale reservoirs for rapid on-site evaluation.

[0004] CN117031563A discloses a method for resistivity correction in wells with high deviation and horizontal wells in layered formations. The method involves selecting several discrete well deviation data points and corresponding resistivity logging responses from the same set of layered formation data, well deviation data, and resistivity logging data. The selected dataset is then fitted to a given correction model to determine the correction coefficients, thereby achieving resistivity correction in layered wells with high deviation and horizontal wells. This invention achieves resistivity logging correction in wells with high deviation and horizontal wells, eliminating reliance on rock physics experiments. However, from the perspective of the correction mathematical model, the determined correction coefficients only consider the influence of the horizontal component, which limits the calculation results.

[0005] Chinese invention patent CN112115592A discloses a resistivity correction method for highly deviated / horizontal wells based on rock physics experiments. The core of this method is to conduct rock physics experiments using downhole cored samples to determine key parameters in the correction model and construct a resistivity anisotropy inversion model. The drawbacks of this method are that it requires costly coring, the surface experimental environment differs significantly from downhole logging conditions, its application scope is limited, and it is costly. Summary of the Invention

[0006] The purpose of this invention is to solve the above-mentioned technical problems and provide a simple, easy-to-implement, widely applicable, low-cost method for quickly determining the logging resistivity of shale reservoirs on-site.

[0007] To achieve the above objectives, this invention provides a method for correcting the logging resistivity of horizontal well shale reservoirs, the specific steps of which are as follows:

[0008] 1) Obtain logging data of the shale reservoir in the horizontal well to be corrected

[0009] Well logging data includes the apparent resistivity Ra and the well inclination angle IP at the depth point corresponding to the apparent resistivity Ra;

[0010] The unit of measurement for apparent resistivity Ra in well logging is Ω·m, and the unit of measurement for well inclination angle IP in well logging is °.

[0011] 2) Calculate the correction coefficient K for the depth point corresponding to the well inclination angle IP collected in step 1);

[0012] 3) Calculate the corrected logging resistivity Rt at the depth point based on the apparent resistivity Ra from step 1) and the calculated correction coefficient K for the corresponding depth point.

[0013] Furthermore, in step 1), the apparent resistivity Ra of the well logging is sampled at sampling points according to the actual well logging data, with sampling points ranging from 0.1 to 1.0 m.

[0014] Furthermore, in step 1), the depth correspondence error between the logging inclination angle IP and the logging resistivity Ra does not exceed 0.5m.

[0015] Furthermore, in step 2), the calculation process of the correction coefficient K is as follows:

[0016] Based on the well inclination angle IP collected in step 1), the exponential model K = A·e is used. B·IP Calculate the correction coefficient K for the depth point corresponding to the well inclination angle IP in the well logging, where A and B are regression coefficients.

[0017] Furthermore, in step 3), the calculation process for the corrected logging resistivity Rt is as follows:

[0018] Based on the apparent resistivity Ra collected in step 1) and the calculated correction coefficient K for the corresponding depth point, the corrected logging resistivity Rt at that depth point is calculated using the formula Rt = K·Ra.

[0019] Furthermore, the calculation process for the regression coefficients A and B is as follows:

[0020] 21) Obtain the logging resistivity Rav of the shale reservoir in the standard straight-through well and the logging resistivity Rah of the shale reservoir in the same side-drilled horizontal well corresponding to the standard straight-through well, as well as the logging inclination angle IP corresponding to all depth points of the logging resistivity Rah of the shale reservoir in the horizontal well.

[0021] 22) Based on the standard straight-hole well shale reservoir logging resistivity Rav and the corresponding side-drilled horizontal well shale reservoir logging resistivity Raah in step 21), the standard correction coefficient K0 for multiple depth points is calculated using the formula K0 = Rav / Rah.

[0022] 23) Substitute the standard correction coefficient K0 for multiple depth points and the logging inclination angle IP corresponding to the depth points into the exponential model K0 = A·e B·IP Calculate the regression coefficients A and B.

[0023] Furthermore, in step 21), the depth error between the logging inclination angle IP and the logging resistivity Rah of the shale reservoir in the horizontal well does not exceed 0.5m.

[0024] Further, in step 22), data samples are obtained according to the principle that the relative error of the natural gamma values ​​of corresponding depth points in the same layer and the same layer group is less than 20%, and the standard correction coefficient K0 of multiple depth points is calculated according to the formula K0 = Rav / Rah based on the data samples.

[0025] Compared with the prior art, the beneficial effects of the present invention are as follows: The present invention solves the problem of logging resistivity correction required for rapid on-site determination of shale reservoirs in horizontal wells. The method is simple, easy to implement, widely applicable, and low in cost, providing a new technology for shale oil and gas exploration and development. Attached Figure Description

[0026] Figure 1 This is a schematic diagram of the process for correcting the resistivity of horizontal well shale reservoir logging according to the present invention.

[0027] Figure 2 Linear regression analysis diagram for obtaining the logging resistivity correction coefficient of the Wufeng-Longmaxi Formation shale reservoir in Block S of Fuling Shale Gas Field;

[0028] Figure 3 Exponential regression analysis diagram obtained for the logging resistivity correction coefficient of the Wufeng-Longmaxi Formation shale reservoir in Block S of Fuling Shale Gas Field;

[0029] Figure 4 Logarithmic regression analysis diagram obtained for the correction coefficient of logging resistivity of the Wufeng-Longmaxi Formation shale reservoir in Block S of Fuling Shale Gas Field;

[0030] Figure 5The binomial regression analysis diagram is obtained by taking the reciprocal of the logging resistivity correction coefficient of the Wufeng-Longmaxi Formation shale reservoir in Block S of the Fuling shale gas field.

[0031] Figure 6 Linear regression analysis diagram for obtaining the logging resistivity correction coefficient of the Wujiaping Formation shale reservoir in the H well area of ​​Hongxing District;

[0032] Figure 7 An exponential regression analysis diagram for calculating the logging resistivity correction coefficient of the Wujiaping Formation shale reservoir in the H well area of ​​the Hongxing region. Detailed Implementation

[0033] The present invention will be further described below with reference to the accompanying drawings and specific embodiments.

[0034] like Figure 1 The method for correcting the logging resistivity of the horizontal well shale reservoir shown is as follows:

[0035] 1) Obtain logging data of the shale reservoir in the horizontal well to be corrected

[0036] Well logging data includes the apparent resistivity Ra and the well inclination angle IP at the depth point corresponding to the apparent resistivity Ra;

[0037] The above-mentioned well logging apparent resistivity Ra is sampled at actual well logging points, with sampling points ranging from 0.1 to 1.0 m, preferably 0.5 m;

[0038] The depth correspondence error between the logging inclination angle IP and the logging resistivity Ra does not exceed 0.5m;

[0039] The unit of measurement for apparent resistivity Ra in well logging is Ω·m, and the unit of measurement for well inclination angle IP in well logging is °.

[0040] The resistivity obtained by depth-of-sight lateral logging, shallow-of-sight lateral logging, induction logging (the reciprocal of induction logging resistivity), and other logging methods are collectively referred to as logging apparent resistivity.

[0041] The well inclination angle measured by the visual inclination logging tool, the formation dip logging tool, and the micro-resistivity scanning imaging logging tool are collectively referred to as the well inclination angle IP.

[0042] 2) Calculate the correction coefficient K for the depth point corresponding to the well inclination angle IP collected in step 1);

[0043] The calculation process for the correction coefficient K is as follows:

[0044] Based on the well inclination angle IP collected in step 1), the exponential model K = A·e is used. B·IP Calculate the correction coefficient K for the depth point corresponding to the well inclination angle IP in well logging, where A and B are regression coefficients;

[0045] 3) Calculate the corrected logging resistivity Rt at the depth point based on the apparent resistivity Ra from step 1) and the calculated correction coefficient K for the corresponding depth point;

[0046] The calculation process for the corrected logging resistivity Rt is as follows:

[0047] Based on the apparent resistivity Ra collected in step 1) and the calculated correction coefficient K for the corresponding depth point, the corrected logging resistivity Rt at that depth point is calculated using the formula Rt = K·Ra.

[0048] The calculation process of regression coefficients A and B in step 2) of this invention is as follows:

[0049] 21) Obtain the logging resistivity Rav of the shale reservoir in the standard straight-hole well and the logging resistivity Rah of the shale reservoir in the horizontal well side-drilled in the same well as the logging resistivity Rah of the shale reservoir in the horizontal well at all depth points;

[0050] The depth error between the logging inclination angle IP and the logging resistivity Rah of shale reservoirs in horizontal wells does not exceed 0.5m;

[0051] Prioritize detecting the resistivity of deep lateral logging at greater depths;

[0052] 22) Based on the standard straight-hole well shale reservoir logging resistivity Rav and the shale reservoir logging resistivity Rah of the same horizontal well sidetracked in the same well as the standard straight-hole well, data samples are obtained according to the principle that the relative error of the natural gamma values ​​of the corresponding depth points is less than 20% and the corresponding layer group is corresponding. Based on the data samples, the standard correction coefficient K0 of multiple depth points is calculated using the formula K0 = Rav / Rah.

[0053] 23) Substitute the standard correction coefficient K0 for multiple depth points and the logging inclination angle IP corresponding to the depth points into the exponential model K0 = A·e B·IP Calculate the regression coefficients A and B.

[0054] Based on the quantitative correlation between logging resistivity and well inclination correction of shale in vertical and horizontal wells, this invention establishes a method for correcting the logging resistivity of shale reservoirs in horizontal wells to that of shale reservoirs in vertical wells. Through field logging applications, the corrected logging resistivity can be used to determine the hydrocarbon saturation of shale reservoirs and to compare resistivity across multiple wells, thus expanding the application scope of logging resistivity in horizontal wells.

[0055] This invention is simple and easy to implement, applicable to deviated wells with an inclination angle of 30° or greater, highly deviated wells with an inclination angle between 60° and 85°, and horizontal wells with an inclination angle greater than 85°. It is assumed that deviated wells with an inclination angle less than 30° do not require logging resistivity correction. This invention is also applicable to shale formations without oil and gas storage capacity. This invention has been applied to over 120 oil and gas wells in the Fuling shale gas field and Hongxing area, meeting the needs of rapid on-site evaluation of shale reservoirs and providing important reference for shale oil and gas exploration site selection and refined reservoir evaluation.

[0056] Example 1

[0057] Using 81 samples from Block S of the Fuling Shale Gas Field, the data came from the shale reservoir resistivity Rav of the Wufeng-Longmaxi Formation straight-through wells and the shale reservoir resistivity Raah of the same side-drilled horizontal wells. Typical data samples were obtained according to the principle that the relative error of the natural gamma values ​​of the corresponding depth points in the same layer and the same layer group should be less than 20%. Based on the data samples, the standard correction coefficient K0 of multiple depth points was calculated using the formula K0 = Rav / Rah.

[0058] The standard correction factor K0 for logging resistivity of horizontal shale reservoirs was linearly compared with the logging inclination angle IP of straight-hole sidetracked horizontal wells. Figure 2 ),index( Figure 3 ), logarithm ( Figure 4 ), polynomial ( Figure 5 Regression analysis, correlation strength R 2 All are greater than 0.5, specifically 0.85, 0.87, 0.83, and 0.85.

[0059] In the S block of the Fuling shale gas field, after the well inclination angle exceeds 70°, the linear increase of the standard correction coefficient K0 with the increase of the well inclination angle slows down, which is consistent with the exponential change law. The R of the exponential model... 2 Therefore, the exponential model is selected for calculating the logging resistivity correction coefficient K0 of horizontal well shale reservoirs, as it is the largest. Figure 4 ): K0 = A·e B·IP That is, K0 = -2.094e -0.024IP Correlation strength R 2 =0.87, A=2.094, B=-0.024.

[0060] The specific steps for correcting the logging resistivity of horizontal well shale reservoirs are as follows:

[0061] 1) Obtain logging data of the shale reservoir in the horizontal well to be tested.

[0062] Well logging data includes the apparent resistivity Ra and the well inclination angle IP at the depth point corresponding to the apparent resistivity Ra;

[0063] 2) Based on the well logging inclination angle IP collected in step 1), the exponential model K = A·e is used. B·IP Calculate the correction coefficient K for the depth point corresponding to the well inclination angle IP in well logging;

[0064] 3) Based on the apparent resistivity Ra of the well logging in step 1) and the calculated correction coefficient K for the corresponding depth point, the corrected well logging resistivity Rt at that depth point is calculated using the formula Rt=K·Ra.

[0065] In the above, when there is a lack of data samples for determining the logging resistivity correction coefficient K of shale reservoirs, and the well inclination angle is between 85° and 90°, K = 0.2 can be taken as the default value. The logging resistivity Rt of the shale reservoir in the horizontal well in the work area can be calculated using the model Rt = K·Ra.

[0066] Example 2

[0067] Thirty-four samples from well H in the Hongxing area were used. Data were obtained from the logging resistivity Rav of shale reservoirs in straight-hole wells of the Wujiaping Formation and the logging resistivity Rah of shale reservoirs in horizontally drilled wells of the same formation. Typical data samples were obtained according to the principle that the relative error of the natural gamma values ​​at corresponding depths within the same stratigraphic unit should be less than 20%. The standard correction coefficient K0 for logging resistivity was calculated point by point. Linearity was then performed using the standard correction coefficient K0 for shale reservoir logging in horizontal wells and the logging inclination angle IP of the straight-hole horizontal wells. Figure 6 ),index( Figure 7 ); After the well inclination angle is greater than 70°, the increase of the standard correction coefficient K0 with the increase of the well inclination angle slows down, which is consistent with the exponential change law. It is recommended to use the exponential model to calculate the logging resistivity correction coefficient K0 of horizontal well shale reservoirs. Figure 7 ): K0 = A·e B·IP That is, K0 = 1.112e -0.02IP Correlation strength R 2 =0.97, A=1.112, B=-0.02.

[0068] The rest of the content is the same as in Example 1.

Claims

1. A method for correcting the logging resistivity of shale reservoirs in horizontal wells, characterized in that: The specific steps of the correction method are as follows: 1) Obtain logging data of the shale reservoir in the horizontal well to be corrected Well logging data includes the apparent resistivity Ra and the well inclination angle IP at the depth point corresponding to the apparent resistivity Ra; The unit of measurement for apparent resistivity Ra in well logging is Ω·m, and the unit of measurement for well inclination angle IP in well logging is °. 2) Calculate the correction coefficient K for the depth point corresponding to the well inclination angle IP collected in step 1); 3) Calculate the corrected logging resistivity Rt at the depth point based on the apparent resistivity Ra from step 1) and the calculated correction coefficient K for the corresponding depth point.

2. The method for correcting the logging resistivity of horizontal well shale reservoirs according to claim 1, characterized in that: In step 1), the apparent resistivity Ra of the well logging is sampled at points ranging from 0.1 to 1.0 m according to the actual well logging data.

3. The method for correcting the logging resistivity of horizontal well shale reservoirs according to claim 1, characterized in that: In step 1), the depth correspondence error between the logging inclination angle IP and the logging apparent resistivity Ra does not exceed 0.5m.

4. The method for correcting the logging resistivity of horizontal well shale reservoirs according to claim 1, characterized in that: In step 2), the calculation process of the correction coefficient K is as follows: According to the well inclination angle IP collected in step 1), the exponential model K=A·e B·IP The correction coefficient K of the well inclination angle IP corresponding to the depth point is calculated, and A and B are regression coefficients.

5. The method for correcting the logging resistivity of horizontal well shale reservoirs according to claim 1, characterized in that: In step 3), the calculation process for the corrected logging resistivity Rt is as follows: Based on the apparent resistivity Ra collected in step 1) and the calculated correction coefficient K for the corresponding depth point, the corrected logging resistivity Rt at that depth point is calculated using the formula Rt = K·Ra.

6. The method for correcting the logging resistivity of horizontal well shale reservoirs according to claim 4, characterized in that: The calculation process for the regression coefficients A and B is as follows: 21) Obtain the logging resistivity Rav of the shale reservoir in the standard straight-through well and the logging resistivity Rah of the shale reservoir in the same side-drilled horizontal well corresponding to the standard straight-through well, as well as the logging inclination angle IP corresponding to all depth points of the logging resistivity Rah of the shale reservoir in the horizontal well. 22) Based on the standard straight-hole well shale reservoir logging resistivity Rav and the corresponding side-drilled horizontal well shale reservoir logging resistivity Rah in step 21), the standard correction coefficient K0 for multiple depth points is calculated using the formula K0 = Rav / Rah. 23) According to the standard correction coefficient K0 of multiple depth points and the well inclination angle IP corresponding to the depth points, the exponential model K0=A·e B·IP The regression coefficients A and B are calculated in the middle.

7. The method for correcting the logging resistivity of horizontal well shale reservoirs according to claim 6, characterized in that: In step 21), the depth error between the logging inclination angle IP and the logging resistivity Rah of the shale reservoir in the horizontal well does not exceed 0.5m.

8. The method for correcting the logging resistivity of horizontal well shale reservoirs according to claim 6, characterized in that: In step 22), data samples are obtained according to the principle that the relative error of the natural gamma values ​​of corresponding depth points in the same layer and the same layer group is less than 20%. Based on the data samples, the standard correction coefficient K0 of multiple depth points is calculated using the formula K0 = Rav / Rah.

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