Shale core homing method

Abstract

The invention relates to the technical field of core homing research, and particularly discloses a shale core homing method. The method comprises the following steps: accurately analyzing an Al element in a rock core sample through an energy dispersion X-ray fluorescence spectrophotometer, combining the Al element and a natural gamma logging curve by utilizing the obvious positive correlation between the Al element and the natural gamma logging curve, and gradually adjusting the marking depth of the rock core to obtain the target value of the rock core. The homing result is optimized by utilizing the correlation between the Al element content change and the natural gamma logging curve, the influence of human subjective factors is reduced in the process, the homing accuracy and consistency are ensured, the operation process is simplified, the homing process cost is reduced, the defects in the prior art are effectively overcome through the technical scheme, and the homing efficiency is improved. And a more reliable technical support is provided for accurate exploration of shale resources.

Description

Technical Field

[0001] The invention relates to the technical field of core retrieval research, and in particular discloses a shale core retrieval method. Background Art

[0002] As global energy demand continues to grow, shale oil, as an important component of unconventional oil and gas resources, has received widespread attention. The Ordos Basin, Sichuan Basin, and Bohai Bay Basin in China have made significant progress in shale oil exploration, and large-scale exploration and development have been launched in many regions. Shale oil is usually distributed in mudstone in semi-deep lake to deep lake environments. Due to the complex sedimentary environment, this type of rock shows significant lithological changes and heterogeneity, which brings great challenges to the identification and development of resources.

[0003] In the exploration of shale oil, cores are the most direct and reliable data for obtaining underground geological characteristics. Through core analysis, formation comparison can be carried out, and important characteristics such as lithology, electrical properties and physical properties of the formation can be studied. However, due to the difference between the drill pipe tension during the coring process and the cable tension in the logging system, the core drilling depth is inconsistent with the logging depth. Therefore, before conducting a detailed analysis, the core needs to be accurately positioned. The accuracy of core positioning directly affects the subsequent logging data analysis and reservoir evaluation, and is a crucial step in the entire exploration process.

[0004] Existing core retrieval methods usually rely on manual operation, by visually observing typical lithology sections or lithology combination sections, and performing segmentation control based on marker layers. This method is relatively effective in sandstone and mudstone combination profiles, but in mudstone, due to the complex lithology and difficult identification of marker layers, the retrieval process is not only difficult, but also easily affected by the operator's subjective judgment. In recent years, the accuracy of retrieval has been improved by introducing advanced technologies such as high-resolution nuclear magnetic resonance logging and helium injection porosity analysis, but its high cost and complex operation limit its application in large-scale exploration.

[0005] Therefore, the main challenges facing core retrieval in mud shale include: large retrieval errors due to complex lithology, strong human subjectivity, and poor consistency of results; the existing technology is costly and complex to operate. In order to solve these problems, it is urgent to develop a more accurate, simple and suitable core retrieval method for mud shale to reduce the influence of subjective factors, adapt to the complex lithological characteristics of mud shale, and thus support the efficient exploration and development of unconventional oil and gas resources. Summary of the invention

[0006] The purpose of the present invention is to solve the deficiencies in the prior art and provide a shale core retrieval method based on natural gamma ray logging response and Al element analysis to improve the accuracy of core retrieval in shale formations, reduce exploration risks, and increase the exploration success rate of high-yield well locations.

[0007] The specific technical steps of the present invention are as follows: S1. Core sample preparation and data collection For key continuous coring wells, all core samples are cut, polished and scanned by general light to obtain high-resolution core scanning images and perform centimeter-level detailed descriptions. After processing, the core's general light scanning images, detailed description data, natural gamma ray GR logging curve data and other related analysis data are imported into Resform geological software to prepare for subsequent core retrieval analysis.

[0008] S2, Al element content data collection The portable energy dispersive X-ray fluorescence spectrometer pXRF is used to accurately analyze the Al element in the core samples. As an indicator of mud composition, the Al element has a significant positive correlation with the natural gamma logging curve. By collecting Al element content data at fixed intervals, reliable basic data is provided for subsequent core retrieval.

[0009] S3. Construction of core homing dataset Based on the collected Al element data and GR logging curve data, the core homing data set is sorted and constructed. The specific operations include: taking the marked depth of each Al element sampling point as the benchmark, collecting and sorting the GR logging curve data of the corresponding depth. Considering that shale is more continuous and dense than conventional sandstone, and the conventional core homing depth is limited, additional GR logging curve data exceeding the upper and lower limits of this coring (4m, which can also be adjusted according to actual conditions) is collected and sorted to ensure the integrity and accuracy of the data set.

[0010] S4. Core return adjustment and optimization During the homing process, the marked depth of the core is gradually adjusted, and the homing result is optimized by analyzing the correlation between the Al element content and the GR logging curve. The specific operation includes gradually adjusting the marked depth within a certain depth range, performing multiple correlation calculations and comparisons, and saving the correlation coefficient R after each adjustment. 2 The value is calculated and the adjusted depth corresponding to the maximum correlation coefficient is finally selected as the final homing depth of the core section.

[0011] S5. Relocation processing of the entire well section The core homing process of the entire well section is carried out in the same way, section by section, and finally the core homing process of the entire well section is completed.

[0012] Beneficial effects of the present invention: (1) The present invention makes full use of the Al element analysis data and natural gamma logging curves of shale core samples, and significantly improves the accuracy of shale core homing through a systematic homing adjustment method. By using the positive correlation between the Al element and the mud component and combining the natural gamma logging data, the depth calibration of the core is more accurate, while reducing the influence of human subjective factors and ensuring the consistency of the homing results.

[0013] (2) The portable energy dispersive X-ray fluorescence spectrometer (pXRF) is used for elemental analysis. It is easy to operate, low cost, suitable for large-scale application, and has good economic benefits.

[0014] (3) The present invention effectively overcomes the shortcomings of the prior art, has strong operability, and produces accurate results. It can be widely used in the exploration and development of shale and other fine-grained sedimentary rocks, has good prospects for promotion and application, and provides more reliable technical support for the precise exploration of shale resources. BRIEF DESCRIPTION OF THE DRAWINGS

[0015] The present invention will be further described below in conjunction with the accompanying drawings.

[0016] Figure 1 It is a flow chart of an embodiment of a method for shale core homing according to the present invention; Figure 2 It is a graph showing the trend of correlation coefficient changes during core depth adjustment in a specific embodiment; Figure 3 It is a comparison diagram of the matching effect of Al element curve and natural gamma (GR) logging curve at different depths before and after the core is returned to the specific embodiment; Figure 4 It is a cross-comparison diagram of the Al element and the GR logging value before and after the core return of the specific embodiment. DETAILED DESCRIPTION

[0017] In order to make the technical solution of the present invention clearer and easier to understand, the shale core homing method of the present invention is described in detail below using the core of the upper 4th section of the Shahejie well NY1 in the Dongying Sag as a specific embodiment. The described embodiment is a part of the embodiment of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0018] Figure 1 As shown, the lacustrine shale sequence stratigraphic division method based on principal component analysis of the present invention has the following specific implementation steps: S1. Core sample preparation and data collection The processing of core samples is particularly important. First, continuous coring is required for the selected well section, and each section of the core is cut and polished to obtain a clear core surface to ensure that the details of the core surface can be fully captured. Subsequently, a high-resolution scanning device is used to perform a general optical scan of the processed core samples, and a detailed geological description is completed to record every subtle feature of the core. These images and descriptions will be input into the Resform geological analysis software together with the natural gamma logging curve data to provide data support for homing.

[0019] S2, Al element content data collection In the relocation adjustment, the Al element concentration is a key reference indicator. A portable X-ray fluorescence spectrometer (pXRF) is used to perform high-precision element analysis on the processed core samples. The Al element concentration is collected at intervals of 0.125m, and the measurement results show that its changes are highly correlated with the GR logging curve. These measurements will serve as an important data basis for subsequent core depth relocation adjustments, providing more accurate support for relocation adjustments.

[0020] S3. Construction of core homing dataset When constructing the homing data set, the marked depth of each Al element collection point is used as the benchmark to sort out the GR logging curve values ​​at the corresponding depth. In order to ensure the accuracy of shale homing, in addition to sorting out the GR logging curve of the coring section, it is also necessary to collect additional GR logging data within the range of 2 meters above the upper and lower limits of the coring. This extended data processing helps to reduce the errors that may occur during the homing process and improve the accuracy of the final results. Taking the mth coring of the upper subsection of Sha 4 in Niuye 1 well as an example, this coring was sampled at a sampling interval of 0.125 meters and a total of 140 sample points were collected. The Al element concentration data of each sample point and the corresponding GR logging response value are summarized in the data set. The Al element concentration reflects the changes in the mud composition, while the GR logging curve provides physical property information of the formation. The correlation between the two is the key basis for core homing. For example, data from some sample points show that at depths of 3359.72 meters, 3362.72 meters, and 3365.72 meters, the Al concentrations were 5178ppm, 4954ppm, and 3462ppm, respectively, and the GR logging response values ​​were 67.963, 83.015, and 69.196, respectively, clearly showing a positive correlation between the two, and the fluctuation of the Al concentration was accompanied by a corresponding change in the GR logging response value. Through these detailed data collation, a complete homing data set was formed, which provided a solid foundation for the subsequent core depth homing adjustment and ensured that the accuracy of the core homing was improved.

[0021] Table 1 is a comparison table of Al element concentration and natural gamma ray (GR) logging response values ​​collected from some sample points of the mth coring in the upper subsection of Sha 4 in Well Niuye 1, showing the changes in Al elements and GR logging values ​​at different depths, providing a reliable data basis for relocation adjustment.

[0022]

[0023] S4. Core return adjustment and optimization During the repositioning adjustment process, the adjustment interval is set to -2m to +2m with a step length of 0.1m. The marked depth of the core section is gradually adjusted within this interval, and multiple adjustment operations are performed. Specifically, during each adjustment, the concentration of the Al element is compared with the GR logging curve value corresponding to the newly marked core depth, and the correlation coefficient R is calculated. 2 Each adjusted R 2 The values ​​will be saved, and the adjustment depth corresponding to the maximum correlation coefficient will be finally selected as the final homing adjustment depth of the coring section.

[0024] Figure 2 The trend chart of the correlation coefficient change during the core depth adjustment process shows the change in the correlation coefficient between the Al element concentration and the natural gamma GR logging curve value corresponding to each adjusted depth when the core depth is gradually adjusted in steps of 0.1m in the coring section depth interval of 3359.72m-3377.33m. In this example, by gradually adjusting the core depth in the coring section depth interval of 3359.72m-3377.33m, it is found that when the depth is adjusted by 1.2m, the correlation coefficient reaches a maximum value of 0.6190, which is 0.3805 higher than 0.2385 before adjustment. Figure 4 As shown, the effectiveness and accuracy of the homing method of the present invention are significantly verified.

[0025] Figure 3 This is a comparison chart of the matching effect of the Al element curve and the natural gamma (GR) logging curve at different depths before and after the core is returned. After the core marking depth is lowered by 1.2m, the change trend of the Al element curve and the natural gamma GR logging curve is most consistent.

[0026] S5. Relocation processing of the entire well section After adjusting a single coring section and obtaining the optimal homing result, the same technical steps are used to perform homing processing on the cores of the entire well section section by section. Each coring section will be adjusted and optimized for the marked depth to ensure that each core section can achieve the best homing accuracy. By sequentially processing and accurately adjusting the coring samples of the entire well section, the core homing results of the entire well section are ensured to be consistent and accurate. Finally, the core homing work of the entire coring well is completed, providing a comprehensive and reliable data basis for subsequent geological analysis.

[0027] Through the above specific implementation scheme, the present invention realizes the accurate homing of shale cores, reduces the influence of human subjective factors, and significantly improves the accuracy and consistency of homing. The method has an optimized operation process and low cost, is particularly suitable for the exploration and development of shale resources, and has a good prospect for promotion and application.

[0028] In the description of this specification, the description with reference to the terms "one embodiment", "example", "specific example", etc. means that the specific features, structures, materials or characteristics described in conjunction with the embodiment or example are included in at least one embodiment or example of the present invention. In this specification, the schematic representation of the above terms does not necessarily refer to the same embodiment or example. Moreover, the specific features, structures, materials or characteristics described can be combined in any one or more embodiments or examples in a suitable manner.

[0029] The above contents are merely examples and explanations of the present invention. Those skilled in the art may make various modifications or additions to the specific embodiments described or replace them in a similar manner. As long as they do not deviate from the invention or exceed the scope defined by the claims, they shall all fall within the protection scope of the present invention.

Claims

1. A shale core homing method, characterized in that: The method comprises the following steps: S1. Core sample preparation and data collection For key continuous coring wells, all core samples are cut, polished and scanned by general light to obtain high-resolution core scanning images and make centimeter-level detailed descriptions. After processing, the general light scanning images, detailed description data, natural gamma logging curve data and other relevant analysis data of the core are imported into the geological analysis software to prepare for the subsequent core retrieval analysis; S2, Al element content data collection The portable energy dispersive X-ray fluorescence spectrometer is used to accurately analyze the Al element in the core samples. Based on the fact that Al is an indicator of mud composition and has a significant positive correlation with the natural gamma logging curve, the Al element content data is collected at fixed intervals to provide reliable basic data for subsequent core retrieval. S3. Construction of core homing dataset Based on the collected Al element data and GR logging curve data, the core homing data set was sorted and constructed; S4. Core return adjustment and optimization During the homing process, the annotated depth of the core was gradually adjusted, and the homing results were optimized by analyzing the correlation between the Al element content and the GR logging curve; S5. Relocation processing of the entire well section The core retrieval of the entire well section is processed section by section, and finally the core retrieval work of the entire well section is completed.

2. A shale core homing method according to claim 1, characterized in that: The fixed interval in step S2 is 0.125 m.

3. A shale core homing method according to claim 1, characterized in that: The specific method of step S3 is to collect and organize the GR logging curve data of the corresponding depth based on the marked depth of each Al element sampling point. Considering that mudstone is more continuous and dense than conventional sandstone and the conventional core retrieval depth is limited, additional GR logging curve data exceeding the upper and lower limits of 4m of coring are collected and organized to ensure the integrity and accuracy of the data set.

4. A shale core homing method according to claim 1, characterized in that: The specific method of step S4 is to gradually adjust the annotation depth, perform multiple correlation calculations and comparisons, and save the correlation coefficient R after each adjustment. 2 The value is calculated and the adjusted depth corresponding to the maximum correlation coefficient is finally selected as the final homing depth of the core section.

5. The shale core homing method according to claim 1, characterized in that: The specific method of step S5 is to adjust and optimize the marked depth of each coring section to ensure that each core section can achieve the best homing accuracy, and to ensure that the core homing results of the entire well section are consistent and accurate by sequentially processing and accurately adjusting the coring samples of the entire well section.

Images