Low-abundance shale gas horizontal well dessert evaluation method

Abstract

The invention relates to a low-abundance shale gas horizontal well dessert evaluation method, and belongs to the technical field of oil and gas field development geology in the petroleum industry. Performing standardization processing on natural gamma and gas logging total hydrocarbon values of the horizontal well to be evaluated in the target area; the method comprises the following steps: acquiring sensitive rock mechanical parameters of a cored well of a target shale gas layer, standardizing the acquired natural gamma, establishing a compressibility while-drilling interpretation model according to the sensitive rock mechanical parameters and the standardized natural gamma, and obtaining a compressibility index of a to-be-evaluated horizontal well by using the model. And performing drilling time equalization processing and drilling fluid density linear normalization processing on the standardized gas logging total hydrocarbon value of the horizontal well to be evaluated to obtain a logging gas-bearing index of the horizontal well to be evaluated, and obtaining a sweet spot comprehensive index of logging of the horizontal well to be evaluated by using the logging gas-bearing index and the logging compressibility index. According to the method, the effective and rapid dessert evaluation method can be provided for the low-abundance shale gas horizontal well.

Description

Technical Field

[0001] The invention relates to a method for evaluating sweet spots in low-abundance shale gas horizontal wells, and belongs to the technical field of oil and gas field development geology in the petroleum industry. Background Art

[0002] In recent years, the exploration and development of shale oil and gas resources have made continuous breakthroughs, which has to some extent alleviated the contradiction between oil and gas supply and demand in my country. However, due to the constraints of geological conditions, process technology, topography and other factors, how to reduce costs and increase efficiency while shale oil and gas reserves are rising rapidly has become a difficult problem that geologists must solve. At present, whether it is marine shale or continental shale in my country, the horizontal well group + well factory model is adopted for efficient development.

[0003] With the development of terrestrial shale oil and gas, it is found that the resource abundance is much lower than that of marine shale, and the resource quality is also different from that of marine shale gas. If the means, technologies and data suitable for the development of marine shale gas are applied to low-abundance shale gas reservoirs, there will be a strong mismatch phenomenon. At the same time, the low abundance characteristics also force all kinds of cost links to be reduced as much as possible in the development process of such shale oil and gas reservoirs. Therefore, the horizontal logging data collection work for each horizontal well in the shale gas well group is often very cautious. When the research object is a low-abundance shale gas horizontal well, how to complete the sweet spot evaluation and grading of the horizontal section of the horizontal well faster, better and more economically is the key to the efficient development of low-abundance shale gas reservoirs.

[0004] The current sweet spot classification evaluation is generally based on pilot wells, and a variety of materials are used. For high-abundance marine shale gas reservoirs, high U (uranium content), high TOC (carbon content), high POR (porosity), high gas content and high compressibility are all positively correlated, and various parameters are highly sensitive to various test data. However, for low-abundance shale gas reservoirs, especially continental shale gas reservoirs, high TOC shale layers are usually low-compressibility formations, which leads to the inadaptability of the marine shale gas sweet spot evaluation idea. In addition, for low-abundance shale gas horizontal wells, the lack of systematic horizontal well logging data makes it even more difficult to carry out evaluation. Therefore, it is urgent to establish a low-abundance shale gas horizontal well sweet spot evaluation method to lay a solid foundation for the development of continental shale oil and gas and even the efficient development of low-abundance marine shale gas. Summary of the invention

[0005] The purpose of the present invention is to provide a method for evaluating the sweet spot of a low-abundance shale gas horizontal well, so as to solve the problem that the existing sweet spot evaluation method cannot accurately realize the sweet spot evaluation of a low-abundance shale horizontal well.

[0006] To achieve the above object, the solution of the present invention includes:

[0007] A method for evaluating sweet spots in low-abundance shale gas horizontal wells of the present invention comprises the following steps:

[0008] 1) Obtain the natural gamma, logging gas logging total hydrocarbon value and drilling time data of the horizontal well to be evaluated during the drilling process in the target area, and standardize the natural gamma and gas logging total hydrocarbon value of the horizontal well to be evaluated in the target area;

[0009] 2) Select a coring well of the target shale gas layer, extract lithology samples from the coring well, and obtain the compressive strength, Poisson's ratio, Young's modulus and stress difference of the lithology samples; obtain the mean value of natural gamma in the coring well and perform standardization processing, select one parameter among the compressive strength, Poisson's ratio, Young's modulus and stress difference and fit it with the standardized mean value of natural gamma in the coring well, establish a compressibility while drilling interpretation model according to the fitting result, input the standardized natural gamma of the horizontal well to be evaluated into the compressibility while drilling interpretation model, and obtain the logging compressibility index of the horizontal well to be evaluated;

[0010] 3) According to the drilling fluid density and drilling time data obtained during the drilling process, the normalized gas logging total hydrocarbon value of the horizontal well to be evaluated is processed by drilling time averaging and the drilling fluid density is linearly normalized to obtain the logging gas content index of the horizontal well to be evaluated;

[0011] 4) Obtaining a comprehensive index of the sweet spot of the horizontal well to be evaluated based on the logging gas content index and the logging compressibility index of the horizontal well to be evaluated, and completing the sweet spot evaluation of the horizontal well to be evaluated based on the comprehensive index of the sweet spot.

[0012] Beneficial effects: The method for evaluating sweet spots in low-abundance shale gas horizontal wells of the present invention provides a fast, economical and reliable method for horizontal well logging sweet spots by utilizing natural gamma, logging total hydrocarbon data and drilling time data while drilling for low-abundance shale gas horizontal wells. The comprehensive index of sweet spots is obtained by the horizontal well logging gas content index and the logging compressibility index, and the logging gas content index is obtained by the drilling fluid density, drilling time data and the gas logging total hydrocarbon value of the horizontal well to be evaluated, and the logging compressibility index is obtained by the compressibility while drilling interpretation model. In the process of calculating the logging gas content index, the present invention performs drilling time averaging and drilling fluid density linear normalization on the standardized gas logging total hydrocarbon value to be evaluated. Drilling time averaging is to reduce the drilling process and target due to on-site torque, friction, complex working conditions, short start-up and other drilling process and target. The influence of the heterogeneity of the rock drillability of the shale gas layer and the heterogeneity of the degree of fracture development on the gas logging total hydrocarbon value, the linear normalization of the drilling fluid density reduces the influence of the increase / decrease of the drilling fluid density ratio on the gas logging total hydrocarbon value due to various reasons (such as well control safety, overflow, leak prevention, etc.) during the drilling process, and the gas logging total hydrocarbon data of the horizontal well in the target shale gas layer is the first-hand data on the field reflecting the degree of oil and gas enrichment. Through natural gamma and logging gas logging total hydrocarbon, the instant evaluation of field compressibility can be quickly realized. This method can not only realize the instant evaluation of the sweet spot of the horizontal well during the drilling process, but also lay the foundation for the efficient development of the development well group.

[0013] Furthermore, the logging gas content index and the logging compressibility index used in the sweet spot comprehensive index of the horizontal well logging to be evaluated are the standardized logging gas content index and the standardized logging compressibility index, respectively. The formula of the sweet spot comprehensive index is:

[0014]

[0015] In the formula, Sweets 录井 is the comprehensive index of the horizontal well logging sweet spot to be evaluated, GI is the gas content index of the horizontal well logging at each measuring point, and GI Max and GI Min is the maximum and minimum value of the gas content index of the horizontal well to be evaluated, CMI is the compressibility index of the horizontal well logging at each measuring point; CMI Max and CMI Min It is the maximum and minimum value of the compressibility index of the horizontal well to be evaluated.

[0016] Furthermore, one of the selected parameters among the compressive strength, Poisson's ratio, Young's modulus and stress difference is the parameter with the highest correlation with the fitting result of the normalized natural gamma mean in the coring well.

[0017] Furthermore, the compressibility while drilling interpretation model is:

[0018] CMI 水平段=a×GR sample 2 +b×GR sample +c

[0019] Where, CMI 水平段 is the compressibility index of horizontal logging, GR sample is the normalized natural gamma value in the horizontal well, and a, b, and c are dimensionless coefficients of the compressibility while drilling interpretation model.

[0020] Furthermore, the gas content index of horizontal well logging is:

[0021]

[0022] In the formula, GI 水平段 Gas is the gas content index of the horizontal well to be evaluated. dhw is the standardized total hydrocarbon value of the horizontal well to be evaluated, Z is the drilling time data, DEN is the instantaneous drilling fluid density during the drilling process, and DEN min and DEN max They are the minimum and maximum drilling fluid density used during the drilling process.

[0023] Furthermore, the standardization process of natural gamma is:

[0024]

[0025] In the formula, GR dhw is the normalized natural gamma value, is the natural gamma mean value of the stable mudstone section of the selected standard well, is the mean natural gamma value of the target shale gas layer, N is the number of standard wells evenly distributed in the target area, N≥1, GR is the natural gamma value of the horizontal well to be standardized; the standard well is a well drilled in the target shale gas layer without coring, overflow and fault.

[0026] Furthermore, the standardization process of the total hydrocarbon value of gas measurement is as follows:

[0027]

[0028] Where, GAS dhw is the standardized total hydrocarbon value of the horizontal well to be evaluated. is the total hydrocarbon value of the gas logging of the stable mudstone section of the selected standard well, GAS is the total hydrocarbon value of the target shale gas layer. 随钻 is the total hydrocarbon value of the measured gas test of the horizontal well to be evaluated, DEPTH1-DEPTH N They are the medium burial depth of the target shale gas layer of the standard well in the target area, DEPTH 水平井中深The horizontal section of the horizontal well to be evaluated is buried at a medium depth.

[0029] Beneficial effect: The standardization process of the total hydrocarbon value of gas logging of the present invention takes into account the parameters of medium-depth burial, thereby reducing the influence of the characteristic that the enrichment degree of shale oil and gas reservoirs changes with burial depth on the total hydrocarbon value of gas logging.

[0030] Furthermore, when the data interval of the drilling data is inconsistent with the standardized total hydrocarbon value of the horizontal well to be evaluated, the standardized total hydrocarbon value of the horizontal well to be evaluated is interpolated and encrypted to make it consistent with the data interval of the drilling data.

[0031] Furthermore, the method also includes a process of using the sweet spot comprehensive index to perform standardized sweet spot classification: when there is a test well in the target area, an intersection diagram is made using the sweet spot comprehensive index of the test well and the daily gas production per 100 meters, and the intersection diagram is used to classify the sweet spots in the entire horizontal well section to obtain a sweet spot classification standard; when there is no test well in the target area, a box-and-whisker diagram is made based on the sweet spot comprehensive index, and the box-and-whisker diagram and the gas content threshold are used to classify the sweet spots in the entire horizontal well section to obtain a sweet spot classification standard.

[0032] Beneficial effects: Through the coupling of geological and engineering quality (sweet spot comprehensive index and daily gas production per 100 meters) and the box-whisker plot obtained through the sweet spot comprehensive index, and scientific processing, the personalized sweet spot classification scheme for single wells is effectively improved, providing strong support for the design of personalized fracturing schemes for single wells. BRIEF DESCRIPTION OF THE DRAWINGS

[0033] Figure 1 It is a flowchart of a method for rapid evaluation of sweet spots in horizontal well logging for shale gas development based on gamma while drilling in an embodiment of the present invention;

[0034] Figure 2 is a correlation diagram between the core well GR of the target area and four rock mechanics parameters in the embodiment of the present invention;

[0035] Figure 3 It is a quick sweet spot classification evaluation diagram of the example well PLY1HF in the embodiment of the present invention;

[0036] FIG. 4( a ) is a correlation diagram of the logging sweet spot index and the daily gas production equivalent per 100 meters when the cementing quality of the example well PLY1HF well is qualified in an embodiment of the present invention;

[0037] FIG4( b ) is a correlation diagram of the logging sweet spot index and the daily gas production equivalent per 100 m when the cementing quality of the example well PLY1HF in the embodiment of the present invention is unqualified;

[0038] Figure 5 It is a quick sweet spot classification evaluation diagram of the example well PLY1-1H in the embodiment of the present invention. DETAILED DESCRIPTION

[0039] The present invention will be further described in detail below in conjunction with the accompanying drawings.

[0040] Example of sweet spot evaluation method for low-abundance shale gas horizontal wells:

[0041] like Figure 1 A method for evaluating sweet spots of low-abundance shale gas horizontal wells is shown. The gas content index and the compressibility index of the horizontal well logging are obtained by using natural gamma while drilling, logging cuttings data, logging total hydrocarbon data and drilling time data. The sweet spot comprehensive index is obtained by using the horizontal well logging gas content index and the compressibility index of the horizontal well logging, as well as the horizontal well logging gas content index and the horizontal well logging compressibility index after standardized processing. The sweet spot of the horizontal well is segmented in real time during the drilling process according to the sweet spot comprehensive index. The specific implementation method is as follows:

[0042] A typical semi-deep lake-facies dark high-clay shale is developed in the No. 3 sublayer of the first section of the Qianfoya Formation in the Puguang area of ​​the Sichuan Basin. Two sets of dark black shales are developed from top to bottom, with thicknesses of about 10m and 6m respectively. In 2020, the Puluye 1 well deployed in the area obtained a high-yield gas flow of 104,000 cubic meters per day. The breakthrough in exploration has also promoted the development of shale gas in the area. The sweet spot evaluation method of low-abundance shale gas horizontal wells in this embodiment is further explained in combination with the shale formation of the Puguang gas field.

[0043] 1) Obtain the natural gamma, logging gas logging total hydrocarbon value and drilling time data of the horizontal well to be evaluated during the drilling process in the target area, and standardize the natural gamma and gas logging total hydrocarbon value of the horizontal well to be evaluated in the target area.

[0044] First, the natural gamma and total hydrocarbon values ​​of the stable mudstone section of the standard wells evenly distributed in the target area are selected as standard values, where the standard wells are drilled in the target shale gas layer without coring, overflow, and faults. The natural gamma and total hydrocarbon values ​​of the horizontal wells to be evaluated in the target area are standardized based on the shale gas layer burial depth and total hydrocarbon values ​​of the standard wells under the arithmetic average. The standardization process of natural gamma is:

[0045]

[0046] In formula (1), GR dhw is the normalized natural gamma value, is the natural gamma mean value of the stable mudstone section of the selected standard well, is the mean natural gamma value of the target shale gas layer, N is the number of standard wells evenly distributed in the target area, N ≥ 1, and GR is the natural gamma value of the horizontal well to be standardized.

[0047] The standardized processing process of the total hydrocarbon value of the gas logging of the horizontal well to be evaluated is as follows:

[0048]

[0049] In formula (2), GAS dhw is the standardized total hydrocarbon value of the horizontal well to be evaluated. is the total hydrocarbon value of the gas logging of the stable mudstone section of the selected standard well, GAS is the total hydrocarbon value of the target shale gas layer. 随钻 is the total hydrocarbon value of the measured gas test of the horizontal well to be evaluated, DEPTH1-DEPTH N are the burial depth of the target shale gas layer of the standard well in the target area, in m, DEPTH 水平井中深 It is the medium burial depth of the horizontal section of the horizontal well to be evaluated, in meters.

[0050] 2) Select a coring well of the target shale gas layer, extract lithological samples from the coring well, and obtain the compressive strength, Poisson's ratio, Young's modulus and stress difference of the lithological samples; obtain the natural gamma value in the coring well and perform standardization processing, select a parameter of the compressive strength, Poisson's ratio, Young's modulus and stress difference and fit it with the standardized natural gamma mean value in the coring well, establish a compressibility while drilling interpretation model based on the fitting results, input the standardized natural gamma of the horizontal well to be evaluated into the compressibility while drilling interpretation model, and obtain the logging compressibility index of the horizontal well to be evaluated.

[0051] Specifically, based on the geological characteristics of the target shale gas layer in the target area, the core wells of the target shale gas layer (3 small layers, the lithology is mainly mudstone, shale, mud siltstone and fine sandstone) are selected, and the lithology samples of the core wells are extracted. According to the rock mechanics test results (i.e., compressive strength, Poisson's ratio, Young's modulus and stress difference) of the main lithology (such as mudstone and sandstone) extracted from the core wells, the standardized natural gamma mean GR of the lithology samples in the corresponding core wells is obtained using the standardized formula of the natural gamma value (as shown in formula (1)): sample , and the natural gamma mean GR after normalization of the core well is used sample A linear regression fit is performed with one parameter of the four rock mechanics test results, such as Figure 2 As shown in FIG. 1 , one of the parameters selected in this embodiment, namely, compressive strength, Poisson's ratio, Young's modulus and stress difference, is the parameter with the highest correlation with the fitting result of the normalized natural gamma mean in the coring well. The rock mechanics parameter with the highest correlation coefficient is selected to be fitted with the natural gamma mean GR sampleThe linear regression is used as the compressibility while drilling interpretation model, and the normalized natural gamma value of the horizontal well to be evaluated is input into the compressibility while drilling interpretation model to obtain the logging compressibility index of the horizontal well to be evaluated. The linear regression in this embodiment can select a univariate linear regression or a multivariate linear regression, which can be selected according to the actual project and the demand for correlation. The univariate linear regression formula is:

[0052] CMI 水平段 =a×GR sample (3)

[0053] The binary linear regression model formula is:

[0054] CMI 水平段 =a×GR sample 2 +b×GR sample +c (4)

[0055] In formula (3) and formula (4), CMI 水平段 is the core well logging compressibility index, GR sample is the mean natural gamma in the core well (i.e., the standardized natural gamma mean of the shale / sandstone samples for rock compressibility experiment), the unit is API (relative density), a, b, c are the dimensionless coefficients of the compressibility while drilling interpretation model.

[0056] Among them Figure 2 As shown, in this embodiment, a binary linear regression model with generally good correlation is adopted.

[0057] 3) According to the drilling fluid density and drilling time data obtained during the drilling process, the standardized gas logging total hydrocarbon value of the horizontal well to be evaluated is averaged by drilling time and linearly normalized by drilling fluid density to obtain the logging gas content index of the horizontal well to be evaluated.

[0058] Specifically, the gas content index of horizontal well logging is:

[0059]

[0060] In formula (5), GI 水平段 Gas index of the horizontal section to be evaluated, unit (%·m / min), Gas dhw is the standardized total hydrocarbon value of each measuring point to be evaluated, Z is the drilling time data, the unit is min / m, DEN is the instantaneous drilling fluid density during the drilling process, DEN min and DEN max They are the minimum and maximum drilling fluid density used during the drilling process.

[0061] Among them, in the present embodiment, in the process of calculating the gas content index of the horizontal section to be evaluated, the standardized gas logging total hydrocarbon value to be evaluated is subjected to drilling time averaging and drilling fluid density linear normalization processing. Specifically, drilling time averaging is to reduce the influence of drilling process such as on-site torque, friction, complex working conditions, short tripping, etc., the heterogeneity of the drillability of the target shale gas layer rock and the heterogeneity of the degree of fracture development on the gas logging total hydrocarbon value. The drilling fluid density linear normalization is to reduce the influence of increasing / decreasing the density ratio of the drilling fluid due to various reasons (such as for well control safety, overflow, leakage prevention, etc.) during the drilling process, thereby increasing / decreasing the influence of the gas logging total hydrocarbon value.

[0062] Wherein, formula (5) is based on the standardized gas total hydrocarbon value Gas of each measuring point to be evaluated. dhw The interval depth of the measuring point is used to calculate the dimensionless coefficient of the drilling fluid density at the corresponding interval depth.

[0063] If the drilling data Z and the standardized gas logging total hydrocarbon value of each measuring point to be evaluated (field logging gas logging total hydrocarbon value) Gas dhw Inconsistent data intervals (e.g. Z is 1m / 1 data point, Gas dhw 2m / 1 data point), and the standardized gas total hydrocarbon value Gas of each measuring point is encrypted by interpolation method dhw Data body, Gas dhw Integrate with Z as supporting data.

[0064] 4) Obtaining a comprehensive index of the sweet spot of the horizontal well to be evaluated based on the logging gas content index and the logging compressibility index of the horizontal well to be evaluated, and completing the sweet spot evaluation of the horizontal well to be evaluated based on the comprehensive index of the sweet spot.

[0065] Specifically, the horizontal well logging gas content index and the logging compressibility index adopt the horizontal well logging gas content index and the horizontal well logging compressibility index after standardized processing.

[0066] Specifically, formula (4) is applied to the horizontal section of the horizontal well to be evaluated, and the logging gas content index GI is calculated according to the natural gamma data interval (such as 0.125 m / 1 data point) during drilling. 水平段 After interpolation, the horizontal well logging gas content index GI 水平段 Compressibility Index (CMI) of horizontal well logging 水平段 The two types of data bodies are respectively normalized by standard deviation and then multiplied to obtain the comprehensive index of the sweet spot for logging of continental shale horizontal wells. Specifically, the comprehensive index of the sweet spot for logging of the horizontal well to be evaluated is:

[0067]

[0068] In formula (6), Sweets 录井is the comprehensive index of the horizontal well logging sweet spot to be evaluated, GI is the gas content index of the horizontal well logging at each measuring point, and GI Max and GI Min is the maximum and minimum value of the gas content index of the horizontal well to be evaluated, CMI is the compressibility index of the horizontal well logging at each measuring point; GMI Max and CMI Min It is the maximum and minimum value of the compressibility index of the horizontal well to be evaluated.

[0069] The method also includes a process of using the sweet spot comprehensive index to perform standardized sweet spot classification: when there is a test well in the target area, an intersection diagram is made using the sweet spot comprehensive index of the test well and the daily gas production per 100 meters, and the intersection diagram is used to classify the sweet spots in the entire horizontal well section to obtain a sweet spot classification standard; when there is no test well in the target area, a box-and-whisker diagram is made according to the sweet spot comprehensive index, and the box-and-whisker diagram and the gas content threshold are used to classify the sweet spots in the entire horizontal well section to obtain a sweet spot classification standard.

[0070] Sweets 录井 Perform a quick analysis of the logging sweet spots in the horizontal well to be evaluated, and obtain the logging sweet spot index data of the entire horizontal section. If there are test wells and their production profile data in the target area, apply the process of calculating the sweet spot comprehensive index to the test well to obtain the sweet spot comprehensive index of the test well, such as Figure 3 As shown in the figure, the logging sweet spot index of the test well and the daily gas production equivalent per 100 meters are used as an intersection diagram. Considering the cementing quality and fracturing effect, the daily gas production of 8000 cubic meters, 6000 cubic meters and 4000 cubic meters per 100 meters are used as the division boundaries of Class I shale gas layer, Class II shale gas layer, Class III shale gas layer and Class IV shale gas layer, so as to quickly identify the "brittle and rich" shale gas section. Furthermore, the sweet spot classification boundary is applied to the shale gas well to be evaluated to predict the daily gas production of the shale gas well to be evaluated. If there is no test well in the target area, the logging sweet spot index of the entire horizontal section is used as a database to make a box-and-whisker diagram (also known as a box diagram). According to the principle of classifying relatively homogeneous shales into the same category, the entire horizontal well section is also divided into Class I, Class II, Class III and Class IV shale gas layers through the drawing skills and thresholds (median, upper quartile and lower quartile) of this type of map, and the four levels of shale gas layer logging sweet spot index classification standards are further verified based on the production profile results after the trial production of the horizontal well to be evaluated. Finally, the purpose of rapid evaluation of the logging sweet spot of the horizontal well to be evaluated is achieved.

[0071] The sweet spot evaluation method of this embodiment is described in detail below by taking the PLY1-1H well in the Puguang gas field in the Sichuan Basin as a specific example.

[0072] Step 1: Puguang 106-2H, Puguang 4, Puguang 12, and Puguang 107-1H in the target area are selected as standard wells in the target area, and the regional stable mudstone section and the target shale gas layer section are selected. The stable mudstone section of Puguang 12 well 3219.77m-3254.37m is a stable mudstone formation in the region, with a gamma average of 172.67API and a gas logging average of 0.0012%; the target shale gas layer is 3408.09m-3433.55m, with a gamma average of 180.01API and a gas logging average of 0.0384%. The medium depth of the shale gas layer is 3420.82m. The corresponding depth sections of Puguang 4 well are 3074.28-3100.96m and 3206.80-3231.88m, the average natural gamma values ​​are 107.71API and 105.27API, the average gas logging total hydrocarbon values ​​are 0.262 and 1.279%, and the medium depth is 3219.34m. The corresponding depth sections of Puguang 107-1H well are 3195.24-3230.20m and 3396.80-3428.24, the average natural GR values ​​are 88.37API and 88.25API, the average gas logging total hydrocarbon values ​​are 0.005 and 0.322%, and the medium depth is 3412.52m. The corresponding depth sections of Puguang 106-2H well are 3039.50-3059.85m and 3217.92-3244.56 respectively, the natural GR averages are 74.61API and 68.50API respectively, the gas logging total hydrocarbon averages are 0.001 and 0.0026% respectively, and the medium depth is 3231.24m. The actual drilling natural gamma in the target area is standardized into a unified natural gamma interval and a unified gas logging total hydrocarbon average interval using formula (1) and formula (2).

[0073] Step 2: Extract the rock mechanics test results of the main lithology and its four items representing rock compressibility, and use formula (1) to calculate the corresponding GR of the test sample: sta-sample ; Simultaneously analyze the correlation between GR and four rock mechanical parameters, such as Figure 2 As shown in Table 1, the correlation between GR and compressive strength under the binary polynomial equation in this embodiment is the best.

[0074] Table 1 Statistics of rock mechanical parameters and normalized natural gamma of cores from Well Puluye 1 in the target area

[0075] Logging depth Lithology GR / API Compressive strength / Mpa Elastic modulus / Gpa Poisson's ratio Stress difference / Mpa 3346.91 Fine sandstone 71.9 244.89 40.5 0.234 8.46 3372.43 shale 122.01 113.98 28.4 0.225 8.5 3374.54 Mudstone 122.61 150.36 35.3 0.223 8.51 3397.81 Argillaceous siltstone 95.67 78.5 26.9 0.226 8.57 3402.39 shale 126.25 92.8 27.5 0.222 8.53 3415.99 shale 131.67 116.2 32 0.237 8.56 3445.41 Mudstone 116.94 91.3 29.5 0.229 11.16 3452.58 Mudstone 126.58 107.3 31 0.227 8.58

[0076] Therefore, based on the binary fitting method, the compressibility index with the highest sensitivity to the natural gamma while drilling is selected as compressive strength, and the corresponding compressibility while drilling interpretation model is established, as shown in formula (7).

[0077] CMI 水平段 =0.1071×GR dhw ×GRdhw -23.489×GR dhw +1372.1 (7)

[0078] Step 3: The total hydrocarbon value of gas logging after processing by formula (2) is averaged by drilling time and linearly normalized by drilling fluid density, and the gas logging index of horizontal well is obtained, as shown in formula (8):

[0079]

[0080] At the same time, the well was drilled and the field logging gas logging total hydrocarbon value Gas dhw The data interval is consistent, so the GI is not further encrypted by interpolation. 水平段 Data body.

[0081] Step 4: Since the natural gamma measurement interval of this well is 0.125m / 1 data point, further convert the GI 水平段 After that, the horizontal well logging gas content index GI 水平段 Compressibility Index (CMI) of horizontal well logging 水平段 The two types of data bodies are standardized by standard deviation and then multiplied to obtain the sweet spot expression formula for continental shale horizontal well logging, as shown in formula (9):

[0082]

[0083] Step 5: Since there is a test well, Puluye 1HF, in the target area, formulas (7) to (9) are applied to Puluye 1HF to obtain the logging sweet spot index data body, as follows: Figure 3 As shown. Furthermore, the test production layer sections are divided into sections with qualified cementing quality and sections with unqualified cementing quality, and the Puluye 1HF logging sweet spot index data body is intersected with the gas production equivalent per 100 meters, as shown in Figure 4(a) and Figure 4(b). In this example, the unqualified cementing quality of the well section has a greater impact on the logging sweet spot index classification. Therefore, the shale gas layer sweet spot classification threshold is determined based on the well section data with qualified cementing quality. According to Figure 4(b), the logging sweet spot index thresholds between level I, level II, level III and level IV shale gas layers are determined to be 130.26, 268.06 and 565.86 at 4000 cubic meters, 6000 cubic meters and 8000 cubic meters per 100 meters. Furthermore, the logging sweet spot classification threshold is applied to the horizontal well PLY1-1 to be evaluated, and the sweet spot segmentation bar chart of the PLY1-1 well is obtained, as shown Figure 5 Further, according to the formula in Figure 4(a), the daily gas production of PLY1-1 well is calculated to be 45,900 cubic meters.

[0084] In summary, the method for rapid evaluation of horizontal well logging sweet spots, using natural gamma while drilling, logging cuttings data, logging total hydrocarbon data and drilling time data, provides a fast, economical and reliable method for horizontal well logging sweet spot segmentation. It can not only achieve instant segmentation of horizontal well sweet spots during drilling, but also lay the foundation for the efficient development of development well groups. Although shale gas sweet spots (i.e. shale gas layers with high oil and gas enrichment) are controlled by many factors such as lithofacies, organic matter abundance, porosity, pore structure, microfractures and structural position, the total hydrocarbon data of gas logging during the drilling of the target shale gas layer is the first-hand data on the field reflecting the degree of oil and gas enrichment; in addition, by selecting the compressibility index of the target area that is sensitive to natural gamma, the instant evaluation of the compressibility on the field can be quickly realized. Through the coupling of geological-engineering quality and the scientific processing of coupling parameters (box plot / box-whisker plot), the personalized sweet spot classification scheme for single wells is effectively improved, providing strong support for the design of personalized fracturing schemes for single wells.

Claims

1. A method for evaluating sweet spots in low-abundance shale gas horizontal wells, characterized in that: The following steps are involved: 1) Obtain the natural gamma, logging gas logging total hydrocarbon value and drilling time data of the horizontal well to be evaluated during the drilling process in the target area, and standardize the natural gamma and gas logging total hydrocarbon value of the horizontal well to be evaluated in the target area; 2) Select a coring well of the target shale gas layer, extract lithology samples from the coring well, and obtain the compressive strength, Poisson's ratio, Young's modulus and stress difference of the lithology samples; obtain the natural gamma value in the coring well and perform standardization processing, select one parameter among the compressive strength, Poisson's ratio, Young's modulus and stress difference and fit it with the standardized natural gamma mean value in the coring well, establish a compressibility while drilling interpretation model according to the fitting result, input the standardized natural gamma of the horizontal well to be evaluated into the compressibility while drilling interpretation model, and obtain the logging compressibility index of the horizontal well to be evaluated; 3) According to the drilling fluid density and drilling time data obtained during the drilling process, the normalized gas logging total hydrocarbon value of the horizontal well to be evaluated is processed by drilling time averaging and the drilling fluid density is linearly normalized to obtain the logging gas content index of the horizontal well to be evaluated; 4) Obtaining a comprehensive index of the sweet spot of the horizontal well to be evaluated based on the logging gas content index and the logging compressibility index of the horizontal well to be evaluated, and completing the sweet spot evaluation of the horizontal well to be evaluated based on the comprehensive index of the sweet spot.

2. The method for evaluating sweet spots in low-abundance shale gas horizontal wells according to claim 1, characterized in that: The sweet spot comprehensive index of the horizontal well logging to be evaluated adopts the logging gas content index and the logging compressibility index, which are the standardized logging gas content index and the standardized logging compressibility index, respectively. The formula of the sweet spot comprehensive index is: In the formula, Sweets 录井 is the comprehensive index of the horizontal well logging sweet spot to be evaluated, GI is the gas content index of the horizontal well logging at each measuring point, and GI Max and GI Min is the maximum and minimum value of the gas content index of the horizontal well to be evaluated, CMI is the compressibility index of the horizontal well logging at each measuring point; CMI Max and CMI Min It is the maximum and minimum value of the compressibility index of the horizontal well to be evaluated.

3. The method for evaluating sweet spots in low-abundance shale gas horizontal wells according to claim 1, characterized in that: The selected parameter among compressive strength, Poisson's ratio, Young's modulus and stress difference is the parameter with the highest correlation with the fitting result of the normalized natural gamma mean in the cored well.

4. The method for evaluating sweet spots in low-abundance shale gas horizontal wells according to claim 1, characterized in that: The compressibility while drilling interpretation model is: CMI 水平段 =a×GR sample 2 +b×GR sample +c Where, CMI 水平段 is the compressibility index of horizontal logging, GR sample is the normalized natural gamma value in the horizontal well, and a, b, and c are dimensionless coefficients of the compressibility while drilling interpretation model.

5. The method for evaluating sweet spots in low-abundance shale gas horizontal wells according to claim 2, characterized in that: The gas content index of horizontal well logging is: In the formula, GI 水平段 Gas is the gas content index of the horizontal well to be evaluated. dhw is the standardized total hydrocarbon value of the horizontal well to be evaluated, Z is the drilling time data, DEN is the instantaneous drilling fluid density during the drilling process, and DEN min and DEN max They are the minimum and maximum drilling fluid density used during the drilling process.

6. The method for evaluating sweet spots in low-abundance shale gas horizontal wells according to claim 1, characterized in that: The standardization process of natural gamma is: In the formula, GR dhw is the normalized natural gamma value, is the natural gamma mean value of the stable mudstone section of the selected standard well, is the mean natural gamma value of the target shale gas layer, N is the number of standard wells evenly distributed in the target area, N≥1, GR is the natural gamma value of the horizontal well to be standardized; the standard well is a well drilled in the target shale gas layer without coring, overflow and fault.

7. The method for evaluating sweet spots in low-abundance shale gas horizontal wells according to claim 5, characterized in that: The standardized processing process of gas testing total hydrocarbon value is: In the formula, GAS dhw is the standardized total hydrocarbon value of the horizontal well to be evaluated. is the total hydrocarbon value of the gas logging of the stable mudstone section of the selected standard well, GAS is the total hydrocarbon value of the target shale gas layer. 随钻 is the total hydrocarbon value of the measured gas test of the horizontal well to be evaluated, DEPTH1-DEPTH N They are the medium burial depth of the target shale gas layer of the standard well in the target area, DEPTH 水平井中深 The horizontal section of the horizontal well to be evaluated is buried at a medium depth.

8. The method for evaluating sweet spots in low-abundance shale gas horizontal wells according to claim 5, characterized in that: When the drilling data and the data interval of the standardized gas logging total hydrocarbon value of the horizontal well to be evaluated are inconsistent, the standardized gas logging total hydrocarbon value of the horizontal well to be evaluated is interpolated and encrypted to make it consistent with the data interval of the drilling data.

9. The method for evaluating sweet spots in low-abundance shale gas horizontal wells according to claim 1, characterized in that: The method also includes a process of using the sweet spot comprehensive index to perform standardized sweet spot classification: when there is a test well in the target area, an intersection diagram is made using the sweet spot comprehensive index of the test well and the daily gas production per 100 meters, and the intersection diagram is used to classify the sweet spots in the entire horizontal well section to obtain a sweet spot classification standard; when there is no test well in the target area, a box-and-whisker diagram is made according to the sweet spot comprehensive index, and the box-and-whisker diagram and the gas content threshold are used to classify the sweet spots in the entire horizontal well section to obtain a sweet spot classification standard.

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