A method for evaluating low-abundance shale gas horizontal well sweet spots

Abstract

The present application relates to a kind of low-abundance shale gas horizontal well dessert evaluation method, belong to oil and gas field development geology technical field in petroleum industry.The natural gamma and gas logging total hydrocarbon value of the horizontal well to be evaluated in target area are standardized processing;Sensitivity rock mechanics parameters of coring well of target shale gas layer are obtained, and the obtained natural gamma is standardized processing, and according to sensitivity rock mechanics parameters and standardized natural gamma, buildability while drilling interpretation model is established, and the buildability index of the horizontal well to be evaluated is obtained using the model, the gas logging total hydrocarbon value of the horizontal well to be evaluated after standardization is processed by drilling time average, and drilling fluid density linear normalization processing obtains the gas logging gas content index of the horizontal well to be evaluated, using the gas logging gas content index and the gas logging buildability index to obtain the gas logging dessert comprehensive index of the horizontal well to be evaluated.The method can be aimed at low-abundance shale gas horizontal well, provide an effective and fast dessert evaluation method.

Description

TECHNICAL FIELD

[0001] The present application relates to a low-abundance shale gas horizontal well dessert evaluation method, and belongs to the technical field of oil and gas field development in the petroleum industry. BACKGROUND

[0002] In recent years, shale oil and gas resource exploration and development has made breakthroughs, which to some extent has delayed the contradiction between supply and demand of oil and gas in China, but due to the restriction of geological conditions, process technology, topography and other factors, how to reduce cost and increase benefit while the shale oil and gas reserves are rising rapidly has become a difficult problem that must be solved by geologists. At present, whether it is marine shale or terrestrial shale, the horizontal well group + well factory mode is adopted for benefit 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, technology and data suitable for marine shale gas development are applied to low-abundance shale gas reservoirs, a strong mismatch phenomenon will occur. At the same time, the low-abundance characteristics also force the reduction of various cost links in the development process of this type of shale oil and gas reservoirs, so the horizontal section logging data collection work of each horizontal well of the shale gas well group is often very cautious. In the case of low-abundance shale gas horizontal wells as the research object, how to complete the dessert evaluation and grading of the horizontal section of the horizontal well faster, better and more economically is the key to the benefit development of low-abundance shale gas reservoirs.

[0004] The current dessert grading evaluation is generally based on the development of pilot wells, and various 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 sensitive to a variety of test data. However, for low-abundance shale gas reservoirs, especially terrestrial shale gas reservoirs, high TOC shale layers are usually low-compressibility formations, which leads to the inadaptability of the marine shale gas dessert evaluation method. In addition, for low-abundance shale gas horizontal wells, it is more difficult to carry out evaluation due to the lack of systematic horizontal well logging data. Therefore, it is urgent to establish a low-abundance shale gas horizontal well dessert evaluation method to lay a solid foundation for the development of terrestrial shale oil and gas and even the benefit development of low-abundance marine shale gas. SUMMARY

[0005] The purpose of the present application is to provide a low-abundance shale gas horizontal well dessert evaluation method to solve the problem that the existing dessert evaluation method cannot accurately realize the dessert evaluation of low-abundance shale horizontal wells.

[0006] To achieve the above-mentioned purpose, the scheme of the present application includes:

[0007] The low-abundance shale gas horizontal well dessert evaluation method of the present application comprises the following steps:

[0008] 1) Obtain the natural gamma, gas logging total hydrocarbon value and drilling time data of the horizontal well to be evaluated in the drilling process of the drilling well 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 a target shale gas layer, extract a lithology sample of the coring well, obtain the compressive strength, Poisson's ratio, Young's modulus and stress difference of the lithology sample, obtain the average value of the natural gamma in the coring well and standardize the average value, select one parameter from the compressive strength, Poisson's ratio, Young's modulus and stress difference to be fitted with the standardized average value of the natural gamma in the coring well, establish a drillability-while-drilling interpretation model according to the fitting result, input the standardized natural gamma of the horizontal well to be evaluated into the drillability-while-drilling interpretation model, and obtain a logging drillability index of the horizontal well to be evaluated;

[0010] 3) According to the drilling fluid density and drilling time data obtained in the drilling process, the gas logging total hydrocarbon value of the horizontal well to be evaluated is processed by drilling time averaging and drilling fluid density linear normalization, and a logging gas-bearing property index of the horizontal well to be evaluated is obtained;

[0011] 4) Obtain a sweet spot comprehensive index of the logging of the horizontal well to be evaluated according to the logging drillability index and the logging gas-bearing property index of the horizontal well to be evaluated, and complete the sweet spot evaluation of the horizontal well to be evaluated according to the sweet spot comprehensive index.

[0012] Beneficial effects: the low-abundance shale gas horizontal well dessert evaluation method of the application, for low-abundance shale gas horizontal well, by using the while drilling natural gamma, logging total hydrocarbon data and drilling time data, a fast, economical and reliable method is provided for horizontal well logging dessert. The dessert comprehensive index is obtained by the logging gas content index and the logging compressibility index of the horizontal well, 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 drilling time mean value and the drilling fluid density linear normalization processing are carried out on the standardized gas logging total hydrocarbon value to be evaluated. The drilling time mean value reduces the influence of the non-homogeneity of the drilling process flow, the target shale gas layer rock drillability and the fracture development degree on the gas logging total hydrocarbon value. The drilling fluid density linear normalization reduces the influence of the drilling fluid density caused by various reasons (such as well control safety, overflow, leakage prevention and the like) on the gas logging total hydrocarbon value. The gas logging total hydrocarbon data in the process of drilling the target shale gas layer is the first-hand data reflecting the degree of oil and gas enrichment, and the natural gamma and logging gas logging total hydrocarbon can quickly realize the real-time evaluation of the compressibility on site. The method can not only realize the real-time evaluation of the horizontal well dessert in the drilling process, but also lay a foundation for the benefit development of the development well group.

[0013] Further, the logging gas content index and the logging compressibility index of the horizontal well logging dessert to be evaluated are the standardized logging gas content index and the standardized logging compressibility index, and the dessert comprehensive index formula is:

[0014]

[0015] In the formula, Sweets is the horizontal well logging dessert comprehensive index of the horizontal well to be evaluated, GI is the logging gas content index of each measuring point, GI and GI are the maximum and minimum values of the logging gas content index of the horizontal well to be evaluated, CMI is the logging compressibility index of each measuring point, CMI and CMI are the maximum and minimum values of the logging compressibility index of the horizontal well to be evaluated. 录井 Max Min Max Min

[0016] Further, one of 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 standardized natural gamma mean value in the coring well.

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

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

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

[0020] Further, the horizontal well logging gas-bearing index is:

[0021]

[0022] wherein GI 水平段 is the horizontal well logging gas-bearing index to be evaluated, Gas dhw is the normalized gas logging total hydrocarbon value of the horizontal well to be evaluated, Z is the drilling time data, DEN is the real-time drilling fluid density during drilling, DEN min and DEN max are the minimum and maximum drilling fluid densities used during drilling, respectively.

[0023] Further, the normalization process of the GR is:

[0024]

[0025] wherein GR dhw is the normalized GR value, is the average GR value of the stable shale section of the selected standard well, is the average GR value of the target shale gas layer, N is the number of standard wells uniformly distributed in the target area, N≥1, and GR is the GR value of the horizontal well to be standardized; the standard well is a well that does not take core, does not overflow, and does not drill through a fault in the target shale gas layer.

[0026] Further, the normalization process of the gas logging total hydrocarbon value is:

[0027]

[0028] wherein GAS dhw is the normalized gas logging total hydrocarbon value of the horizontal well to be evaluated, is the gas logging total hydrocarbon value of the stable shale section of the selected standard well, is the gas logging total hydrocarbon value of the target shale gas layer, GAS 随钻 is the measured gas logging total hydrocarbon value of the horizontal well to be evaluated, DEPTH1-DEPTH N are the burial depths of the target shale gas layer of the standard well in the target area, and DEPTH 水平井中深The horizontal section of the horizontal well to be evaluated is buried in the middle and deep.

[0029] Beneficial effects: the burial depth parameter is considered in the gas logging total hydrocarbon value standardization processing of the present application, and the influence of the change of shale oil and gas reservoir enrichment degree with burial depth on gas logging total hydrocarbon is reduced.

[0030] Further, when the drilling time 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 time data.

[0031] Further, the method further comprises the process of using the sweet spot comprehensive index to standardize and grade the sweet spot: when there is a test well in the target area, the sweet spot comprehensive index of the test well is used to make a cross plot with the daily gas production per hundred meters, the sweet spot of the whole horizontal section is graded by using the cross plot to obtain a sweet spot grading standard; when there is no test well in the target area, a box plot is made according to the sweet spot comprehensive index, and the sweet spot of the whole horizontal section is graded by using the box plot and the gas content threshold to obtain a sweet spot grading standard.

[0032] Beneficial effects: through the coupling of geology-engineering quality (sweet spot comprehensive index and daily gas production per hundred meters) and through the box plot obtained by the sweet spot comprehensive index and scientific processing, the individual sweet spot grading scheme for a single well is effectively improved, and strong support is provided for the individual fracturing scheme design of a single well. BRIEF DESCRIPTION OF DRAWINGS

[0033] Figure 1 is the process block diagram of the shale gas development horizontal well logging sweet spot rapid evaluation method based on the while-drilling gamma in the embodiments of the present application;

[0034] Figure 2 is the correlation diagram of the GR of the coring well and the four rock mechanics parameters in the example target area in the embodiments of the present application;

[0035] Figure 3 is the logging rapid sweet spot grading evaluation diagram of the example well PLY1HF in the embodiments of the present application;

[0036] Fig. 4(a) is the correlation diagram of the logging sweet spot index and the daily gas production per hundred meters equivalent of the example well PLY1HF in the embodiments of the present application when the cementing quality is qualified;

[0037] Fig. 4(b) is the correlation diagram of the logging sweet spot index and the daily gas production per hundred meters equivalent of the example well PLY1HF in the embodiments of the present application when the cementing quality is unqualified;

[0038] Figure 5 is the logging rapid sweet spot grading evaluation diagram of the example well PLY1-1H in the embodiments of the present application. DETAILED DESCRIPTION

[0039] The present invention will now be described in further detail with reference to the accompanying drawings.

[0040] Example of a method for evaluating sweet spots in low-abundance shale gas horizontal wells:

[0041] like Figure 1 This paper presents a method for evaluating sweet spots in low-abundance shale gas horizontal wells. Using natural gamma ray during drilling, cuttings logging data, total hydrocarbon logging data, and drilling time data, the method obtains the horizontal well logging gas content index and logging compressibility index. A comprehensive sweet spot index is then derived using these indices, along with standardized versions of both indices. Based on this comprehensive index, the sweet spot in the horizontal well is segmented in real-time during drilling. The specific implementation method is as follows:

[0042] In the Puguang area of ​​the Sichuan Basin, the No. 3 sub-layer of the Qianfoya Formation (Member 1) contains a typical semi-deep lacustrine dark-colored high-clay shale. Two sets of dark black shale, approximately 10m and 6m thick respectively, develop from top to bottom. In 2020, the Puluye-1 well, deployed in this area, achieved a high-yield gas flow of 104,000 cubic meters per day. This breakthrough in exploration has propelled the development of shale gas in the region. This paper further explains the sweet spot evaluation method for low-abundance shale gas horizontal wells in this embodiment, based on the shale formations of the Puguang gas field.

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

[0044] First, the natural gamma ray and total hydrocarbons from stable mudstone sections of standard wells evenly distributed within the target area were selected as standard values. These standard wells were those drilled without coring, overflow, or encountering faults in the target shale gas layer. The natural gamma ray and total hydrocarbons from the horizontal wells to be evaluated within the target area were standardized by arithmetic averaging the values ​​of the standard wells at the medium burial depth of the shale gas layer. The standardization process for natural gamma ray was as follows:

[0045]

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

[0047] The standardization process for the total hydrocarbon values ​​of gas logging in horizontal wells to be evaluated is as follows:

[0048]

[0049] GAS dhw is a normalized gas logging total hydrocarbon value of the standard well, is a gas logging total hydrocarbon value of a stable mudstone section of the selected standard well, is a gas logging total hydrocarbon value of the target shale gas layer, GAS 随钻 is a measured gas logging total hydrocarbon value of the horizontal well to be evaluated, DEPTH1-DEPTH N are respectively burial depths of the target shale gas layer of the standard well in the target area, unit: m, DEPTH 水平井中深 is a burial depth of the horizontal section of the horizontal well to be evaluated, unit: m.

[0050] 2) Select a coring well of the target shale gas layer, extract lithology samples of the coring well, 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 of the compressive strength, Poisson's ratio, Young's modulus and stress difference to perform fitting with the normalized natural gamma average value in the coring well, and establish a compactibility while drilling interpretation model according to the fitting result, input the normalized natural gamma of the horizontal well to be evaluated into the compactibility while drilling interpretation model, and obtain the logging compactibility index of the horizontal well to be evaluated.

[0051] Specifically, the coring well of the target shale gas layer (3 small layers, the lithology is mainly mudstone, shale, argillaceous siltstone and fine sandstone) is selected in combination with the geological characteristics of the target shale gas layer in the target area, lithology samples of the coring well are extracted, four 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 shale) of the coring well are obtained according to the coring well, the normalized natural gamma average value GR sample of the lithology samples in the corresponding coring well is obtained by using the standardization formula (such as formula (1)) of the natural gamma value, and linear regression fitting is performed between the normalized natural gamma average value GR sample of the coring well and one parameter of the four rock mechanics test results, as shown in formula (2). Figure 2 In the formula, the selected one parameter of the compressive strength, Poisson's ratio, Young's modulus and stress difference in the embodiment is the parameter with the highest correlation with the fitting result of the normalized natural gamma average value of the coring well. The rock mechanics parameter with the highest correlation coefficient is selected and fitted with the natural gamma average value GR sampleLinear regression is used as the compressibility-while-drilling interpretation model. The standardized natural gamma value of the horizontal well to be evaluated is input into the model to obtain the logging compressibility index of the horizontal well to be evaluated. In this embodiment, univariate linear regression or multivariate linear regression can be used, depending on the actual project and the need for correlation. The univariate linear regression formula is:

[0052] CMI 水平段 =a×GR sample (3)

[0053] The formula for the binary linear regression model is:

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

[0055] In equations (3) and (4), CMI 水平段 GR is the compressibility index for coring well logging. sample The mean natural gamma ray in the core well (i.e., the normalized mean natural gamma ray of the mudstone / sandstone samples used for rock compressibility testing) is expressed in API (relative density). a, b, and c are dimensionless coefficients of the compressibility interpretation model during drilling.

[0056] Among them, such as Figure 2 As shown, this embodiment uses a binary linear regression model with generally good correlation.

[0057] 3) Based on 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 during 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 the horizontal well logging is:

[0059]

[0060] In equation (5), GI 水平段 The gas content index of the horizontal section to be evaluated is expressed in units of (%·m / min) and Gas. dhw Z represents the standardized total hydrocarbon value measured in gas at each measuring point to be evaluated, Z represents the drilling time data in min / m, and DEN represents the real-time drilling fluid density during drilling. min and DEN max These are the minimum and maximum drilling fluid densities used during the drilling process, respectively.

[0061] In the embodiment, the drilling time average and the linear normalization of the drilling fluid density are used to process the normalized gas logging total hydrocarbon value of the evaluation object, specifically, the drilling time average is used to reduce the influence of the torque, friction, complex working conditions, short tripping, and the heterogeneity of the rock drillability and the fracture development degree of the target shale gas layer on the gas logging total hydrocarbon value, and the linear normalization of the drilling fluid density is used to reduce the influence of the increase / decrease of the drilling fluid density on the gas logging total hydrocarbon value.

[0062] In the formula (5), Gas is the normalized gas logging total hydrocarbon value of each measurement point of the evaluation object. dhw The interval depth of the measurement point is used to calculate the drilling fluid density non-dimensional coefficient at the corresponding interval depth.

[0063] If the drilling time data Z and the normalized gas logging total hydrocarbon value (the gas logging total hydrocarbon value on site) of each measurement point of the evaluation object are inconsistent (for example, Z is 1 m / 1 data point, and Gas is 2 m / 1 data point), the normalized gas logging total hydrocarbon value of each measurement point is encrypted by the interpolation method. dhw dhw If the drilling time data Z and the normalized gas logging total hydrocarbon value (the gas logging total hydrocarbon value on site) of each measurement point of the evaluation object are inconsistent (for example, Z is 1 m / 1 data point, and Gas is 2 m / 1 data point), the normalized gas logging total hydrocarbon value of each measurement point is encrypted by the interpolation method. dhw The data body is integrated with Z as a matching data. dhw The data body is integrated with Z as a matching data.

[0064] 4) The sweet spot comprehensive index of the evaluation object is obtained according to the evaluation object horizontal well logging gas content index and the evaluation object horizontal well logging compressibility index, and the sweet spot evaluation of the evaluation object horizontal well is completed according to the sweet spot comprehensive index.

[0065] Specifically, the horizontal well logging gas content index and the horizontal well logging compressibility index are the normalized horizontal well logging gas content index and the normalized horizontal well logging compressibility index.

[0066] Specifically, the formula (4) is applied to the horizontal section of the evaluation object, and the logging gas content index GI is interpolated according to the drilling time natural gamma data interval (for example, 0.125 m / 1 data point). 水平段 After the interpolation, the horizontal well logging gas content index GI is multiplied by the horizontal well logging compressibility index CMI. 水平段 After the interpolation, the horizontal well logging gas content index GI is multiplied by the horizontal well logging compressibility index CMI. 水平段 After the standard deviation normalization, the two types of data bodies are multiplied to obtain the continental shale horizontal well logging sweet spot comprehensive index, specifically, the sweet spot comprehensive index of the evaluation object horizontal well logging is:

[0067]

[0068] In the formula (6), Sweets is the sweet spot comprehensive index of the evaluation object horizontal well logging. 录井 ​GI represents the comprehensive sweet spot index of the horizontal well logging data to be evaluated, and GI is the gas content index of the horizontal well logging data at each logging point. Max and GI Min The maximum and minimum values ​​of the gas-bearing index in the logging of the horizontal well to be evaluated are given; CMI is the compressibility index of the horizontal well logging at each logging point; GMI is the gas-bearing index in the horizontal well to be evaluated. Max and CMI Min These represent the maximum and minimum values ​​of the logging compressibility index for the horizontal well to be evaluated.

[0069] The method also includes a process of standardizing and classifying sweet spots using a sweet spot composite index: when there are test wells in the target area, a cross-plot is made using the sweet spot composite index of the test wells and the daily gas production per 100 meters, and the sweet spots in the entire horizontal well section are classified using the cross-plot to obtain the sweet spot classification standard; when there are no test wells in the target area, a box-and-whisker diagram is made based on the sweet spot composite index, and the sweet spots in the entire horizontal well section are classified using the box-and-whisker diagram and the gas content threshold to obtain the sweet spot classification standard.

[0070] Specifically, through the logging dessert comprehensive index Sweets 录井 A rapid analysis of the logging sweet spot is performed on the horizontal well to obtain the sweet spot index data volume for the entire horizontal section. If a test well and its production profile data exist in the target area, the process of calculating the comprehensive sweet spot index is applied to the test well to obtain the comprehensive sweet spot index of the test well, such as... Figure 3 As shown, a cross-plot is plotted between the logging sweet spot index of the test well and the daily gas production equivalent per 100 meters. Considering the cementing quality and fracturing effect, the daily gas production per 100 meters is set as the dividing line for Class I, Class II, Class III, and Class IV shale gas layers, respectively, based on 8,000 cubic meters, 6,000 cubic meters, and 4,000 cubic meters. This quickly identifies the "brittle and rich" shale gas sections. Furthermore, this sweet spot classification boundary is applied to the shale gas wells to be evaluated to predict the daily gas production of the shale gas wells to be evaluated. If there are no test wells in the target area, a box plot (also known as a box graph) is created using the logging sweet spot index of the entire horizontal section as a database. Following the principle of grouping relatively homogeneous shale into the same category, this method utilizes chart drawing techniques and thresholds (median, upper quartile, and lower quartile) to classify all horizontal well sections into Class I, II, III, and IV shale gas reservoirs. After trial production of the horizontal well to be evaluated, the logging sweet spot index grading standard for the four levels of shale gas reservoirs was further verified based on the production profile results. Ultimately, the goal of rapid logging sweet spot evaluation for the horizontal wells to be evaluated was achieved.

[0071] The following uses the PLY1-1H well in the Puguang Gas Field of the Sichuan Basin as a specific example to explain in detail the sweet spot evaluation method of this embodiment.

[0072] Step one, select Pugu 106-2H, Pugu 4, Pugu 12, Pugu 107-1H as the standard well of the target area, and select the regional stable mudstone section and the target shale gas layer. The stable mudstone section of Pugu 12 well is 3219.77m-3254.37m, the average gamma is 172.67 API, and the average gas logging is 0.0012%; the target shale gas layer is 3408.09m-3433.55m, the average gamma is 180.01 API, and the average gas logging is 0.0384%. The medium depth of the shale gas layer is 3420.82m. The corresponding depth sections of Pugu 4 well are 3074.28-3100.96m and 3206.80-3231.88m, the average natural gamma is 107.71 API and 105.27 API, the average gas logging is 0.262 and 1.279%, and the medium depth is 3219.34m. The corresponding depth sections of Pugu 107-1H well are 3195.24-3230.20m and 3396.80-3428.24, the average natural GR is 88.37 API and 88.25 API, the average gas logging is 0.005 and 0.322%, and the medium depth is 3412.52m. The corresponding depth sections of Pugu 106-2H well are 3039.50-3059.85m and 3217.92-3244.56, the average natural GR is 74.61 API and 68.50 API, the average gas logging is 0.001 and 0.0026%, and the medium depth is 3231.24m. The natural gamma of the real drilled well in the target area is standardized to the unified natural gamma interval and the unified gas logging interval by using formula (1) and formula (2).

[0073] Step two, extract the main lithology and its four rock mechanics test results of rock compressibility, and use formula (1) to calculate the corresponding GR sta-sample of the test sample; simultaneously analyze the correlation between GR and the four rock mechanics parameters, such as Figure 2 and 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 Core rock mechanics parameters and standardized natural gamma statistics of Pulu page 1 well 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 of the while-drilling natural gamma is the compressive strength, and the corresponding while-drilling compressibility interpretation model is established, as shown in formula (7).

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

[0078] Step 3: After processing the gas logging total hydrocarbon value according to formula (2), the drilling time average and drilling fluid density linear normalization are performed to obtain the gas content logging index of the horizontal well, as shown in formula (8):

[0079]

[0080] Meanwhile, the total hydrocarbon value (Gas) measured during drilling and in-situ well logging were compared. dhw The data intervals are consistent, therefore no further encryption of GI using interpolation is required. 水平段 Data body.

[0081] Step four: Since the interval between natural gamma measurement points during drilling in this well is 0.125m / 1 data point, the GI will be further... 水平段 Encrypted interpolation processing. Subsequently, the gas content index (GI) of the horizontal well logging is... 水平段 Compressibility Index (CMI) of Horizontal Well Logging 水平段 After standardizing the two types of data volumes according to their standard deviations, they are then multiplied to obtain the expression formula for the logging sweet spot of continental shale horizontal wells, as shown in formula (9):

[0082]

[0083] Step 5: Since the test well Puluye 1HF exists in the target area, formulas (7) to (9) are applied to the Puluye 1HF well to obtain the logging sweet spot index data, such as... Figure 3 As shown in Figure 4(a) and Figure 4(b), the sweet spot index data of the PLY1-HF shale gas layer was plotted against the gas production equivalent per 100 meters for sections with qualified and unqualified cementing quality. In this example, the unqualified cementing quality of the well section has a significant impact on the sweet spot index classification. Therefore, the sweet spot classification threshold of the shale gas layer was determined based on the data of the well section with qualified cementing quality. According to Figure 4(b), the sweet spot index thresholds between Class I, Class II, Class III, and Class IV shale gas layers were determined to be 130.26, 268.06, and 565.86, respectively, based on 4000 cubic meters, 6000 cubic meters, and 8000 cubic meters per 100 meters. Furthermore, this sweet spot classification threshold was applied to the horizontal well PLY1-1 to be evaluated, and a sweet spot segment histogram of the PLY1-1 well was obtained, as shown in Figure 4(a) and Figure 4(b). Figure 5 As shown in Figure 4(a). Furthermore, 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] The sweet spot evaluation method for horizontal well logging provides a fast, economical and reliable method for horizontal well logging sweet spot segmentation by using the data of natural gamma ray, logging cuttings, logging total hydrocarbon and drilling time. It can not only realize the real-time segmentation of horizontal well sweet spot during drilling, but also lay the foundation for the benefit development of the well group. Although the shale gas sweet spot (i.e. the shale gas layer with high oil and gas enrichment) is controlled by many factors such as lithofacies, organic matter abundance, porosity, pore structure, microfracture and structural position, etc., the gas logging total hydrocarbon data during drilling in the target shale gas layer is the first-hand data reflecting the degree of oil and gas enrichment. In addition, by selecting the compressibility index sensitive to natural gamma ray in the target area, the real-time evaluation of compressibility can be quickly realized. Through the coupling of geology-engineering quality and the scientific processing of coupling parameters (box plot / box whisker plot), the individual sweet spot classification scheme for single well is effectively improved, which provides strong support for the individual fracturing scheme design of single well.

Claims

1. A method for evaluating low abundance shale gas horizontal well sweet spots, characterized in that, The method comprises the following steps: 1) obtaining the natural gamma, gas logging total hydrocarbon value and drilling time data of the horizontal well to be evaluated in the drilling process of the well in the target area, and standardizing the natural gamma and gas logging total hydrocarbon value of the horizontal well to be evaluated in the target area; 2) selecting a coring well of a target shale gas layer, extracting a lithology sample of the coring well, obtaining the compressive strength, Poisson's ratio, Young's modulus and stress difference of the lithology sample, obtaining the natural gamma value in the coring well and standardizing the natural gamma value, selecting one parameter from the compressive strength, Poisson's ratio, Young's modulus and stress difference to be fitted with the standardized natural gamma average value in the coring well, and establishing a drillability-while-drilling interpretation model according to the fitting result, inputting the standardized natural gamma of the horizontal well to be evaluated into the drillability-while-drilling interpretation model to obtain a logging drillability index of the horizontal well to be evaluated; 3) performing drilling time averaging processing and drilling fluid density linear normalization processing on the standardized gas logging total hydrocarbon value of the horizontal well to be evaluated according to the drilling fluid density and drilling time data obtained in the drilling process to obtain a logging gas content index of the horizontal well to be evaluated; 4) obtaining a sweet spot comprehensive index of the logging of the horizontal well to be evaluated according to the logging gas content index of the horizontal well to be evaluated and the logging drillability index of the horizontal well to be evaluated, and completing sweet spot evaluation of the horizontal well to be evaluated according to the sweet spot comprehensive index; the formula used for the sweet spot comprehensive index is: In the formula, Sweets 录井 is the comprehensive index of the sweet spot of the logging in the horizontal well to be evaluated, GI is the gas-bearing index of the logging in the horizontal well to be evaluated, GI Max and GI Min are the maximum and minimum values of the gas-bearing index of the logging in the horizontal well to be evaluated, and CMI is the compressibility index of the logging in the horizontal well to be evaluated; CMI Max and CMI Min are the maximum and minimum values of the compressibility index of the logging in the horizontal well to be evaluated.

2. The sweet spot evaluation method for low abundance shale gas horizontal wells according to claim 1, characterized in that, The one parameter selected from 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 standardized natural gamma average value in the coring well.

3. The sweet spot evaluation method for low abundance shale gas horizontal wells according to claim 1, characterized in that, The drillability-while-drilling interpretation model is: CMI = a x GR sample 2 + b x GR sample + c In the formula, CMI is the level well logging compressibility index to be evaluated, 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.

4. The sweet spot evaluation method for low abundance shale gas horizontal wells of claim 1, wherein, The logging gas content index of the horizontal well to be evaluated is: wherein GI is the gas show index of the horizontal well to be evaluated, Gas dhw is the normalized gas logging total hydrocarbon value of the horizontal well to be evaluated, Z is the drilling time data, DEN is the real-time drilling fluid density during drilling, DEN min and DEN max are the minimum drilling fluid density and the maximum drilling fluid density used during drilling, respectively.

5. The sweet spot evaluation method for low abundance shale gas horizontal wells of claim 1, wherein, The standardization processing process of the natural gamma is: GR = GR0+ (GR1- GR0) * (D - D0) / (D1- D0) dhw GR = GR0+ (GR1- GR0) * (D - D0) / (D1- D0) GR = GR0+ (GR1- GR0) * (D - D0) / (D1- D0) GR = GR0+ (GR1- GR0) * (D - D0) / (D1- D0) GR = GR0+ (GR1- GR0) * (D - D0) / (D1- D0) 6. The sweet spot evaluation method for low abundance shale gas horizontal wells according to claim 4, characterized in that, The standardization processing process of the gas logging total hydrocarbon value is: wherein GAS dhw is the normalized gas test total hydrocarbon value of the target shale gas formation, is the gas test total hydrocarbon value of the stable shale section of the selected standard well, is the gas test total hydrocarbon value of the target shale gas formation, GAS 随钻 is the measured gas test total hydrocarbon value of the horizontal section of the target well, N is the burial depth of the target shale gas formation of the standard well in the target area, DEPTH 水平井中深 is the burial depth of the horizontal section of the target well.

7. The sweet spot evaluation method for low abundance shale gas horizontal wells according to claim 4, characterized in that, When the drilling time data and the standardized gas logging total hydrocarbon value of the horizontal well to be evaluated are inconsistent in data interval, the standardized gas logging total hydrocarbon value of the horizontal well to be evaluated is interpolated and encrypted to make the data interval consistent with the drilling time data.

8. The sweet spot evaluation method for low abundance shale gas horizontal wells of claim 1, wherein, The method further comprises a process of using the sweet spot comprehensive index to standardize and classify the sweet spot: when there is a production test well in the target area, a crossplot is made of the sweet spot comprehensive index and the daily gas production per hundred meters of the production test well, the sweet spot of the whole horizontal well section is classified by using the crossplot to obtain a sweet spot classification standard; when there is no production test well in the target area, a boxplot is made according to the sweet spot comprehensive index, and the sweet spot of the whole horizontal well section is classified by using the boxplot and a gas content threshold to obtain a sweet spot classification standard.

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