A method for selecting shale gas horizontal well segmentation scheme based on difference analysis

Abstract

The present invention belongs to the field of oil and gas field exploration and development technology, and specifically relates to a method for selecting a shale gas horizontal well segmentation scheme based on difference analysis. First, the horizontal well is divided into several lithofacies segments based on the drilled layer and the well logging curve; the lithofacies segment division results are incorporated into all segmentation schemes that meet the engineering applicability. In each segmentation scheme, the difference coefficient within each single fracturing segment is calculated based on the proportion of the lithofacies segment division results within each fracturing segment, and the full-well segment difference coefficient of the corresponding segmentation scheme is calculated based on the difference coefficient within the single fracturing segment. The segmentation scheme with the smallest full-well difference coefficient is selected. This technical scheme, by proposing the concept of full-well segment difference coefficient, establishes a reasonable evaluation standard for fracturing segmentation, realizes the quantification, standardization and proceduralization of segmentation scheme screening work, reduces the complexity of the splitting scheme screening process, and improves the efficiency of shale gas well segmentation.

Description

Technical Field

[0001] The present invention belongs to the field of oil and gas field exploration and development, and in particular relates to a method for selecting a shale gas horizontal well segmentation scheme based on difference analysis. Background Art

[0002] Shale gas extraction has become a hotspot in domestic oil and gas resource development due to factors such as the decline in conventional oil and gas resources and the increasing difficulty of development, the intensification of the imbalance between domestic oil and gas supply and demand, and the challenges facing national oil and gas security. However, shale gas reservoirs are characterized by low porosity and low permeability, necessitating maximum fracture network complexity and conductivity during extraction. This necessitates that staged fracturing in shale gas horizontal wells is one of the primary technical approaches for achieving high-yield shale gas wells. However, there is currently no quantitative and standardized method for fracturing staged wells in shale gas horizontal wells. The staged design process for shale gas horizontal wells relies heavily on the subjective judgment of the planner, lacking quantitative parameters to constrain it. This leads to a certain degree of arbitrariness, resulting in significant variability in staged design between different designers and low staged design efficiency. Consequently, there is currently no quantitative, standardized, or procedural staged design method or shale gas staged design method. Summary of the Invention

[0003] In response to the current development needs in the field of oil and gas field exploration and development, the present invention provides a method for selecting shale gas horizontal well segmentation schemes based on difference analysis. This method evaluates the overall difference of horizontal well segmentation schemes through difference coefficients, and quantitatively compares and selects shale gas horizontal well segmentation schemes with the smallest overall difference and the highest segmentation uniformity, thereby improving the efficiency and standardization of shale gas well segmentation.

[0004] This is achieved specifically through the following technical solutions:

[0005] A method for selecting a shale gas horizontal well segmentation scheme based on difference analysis is characterized by comprising the following steps:

[0006] Step S1: For several different segmentation schemes, evaluate whether any of them exceed the project applicability. If any exceed the project applicability, the segmentation scheme is deemed to fail the project applicability test. If no exceed the project applicability test, the segmentation scheme is deemed to meet the project applicability test. Meeting the project applicability test is a fundamental requirement for project implementation, and any segmentation scheme that does not meet the project applicability test is eliminated.

[0007] Step S2: First, the actual field horizontal well is preliminarily segmented based on the drilled layer, and the actual field horizontal well is divided into several layers. Then, based on the preliminary segmentation results, it is further divided according to the logging curve, and each layer is divided into several lithofacies segments according to the lithology reflected in the logging curve.

[0008] Step S3: The results of the lithofacies segment division are incorporated into all segmentation schemes that meet the engineering applicability. In each segmentation scheme, the difference coefficient within each single fracturing segment is calculated based on the proportion of the lithofacies segment division results within each fracturing segment, and the full-well segment difference coefficient of the corresponding segmentation scheme is obtained based on the difference coefficient within the single fracturing segment.

[0009] Step S4: Compare the full-well section difference coefficients of all segmentation schemes, and select the segmentation scheme with the smallest full-well difference coefficient.

[0010] Specifically, in step S1, situations exceeding engineering applicability include the following: the distance between the bridge plug setting position and the casing coupling is greater than 0.5 m, the distance between the perforation position and the casing coupling is greater than 0.5 m, and the perforation position is at a location with a dogleg angle of less than or equal to 5°.

[0011] Preferably, the logging curves include natural gamma ray curves, resistivity curves and mineral composition curves.

[0012] Preferably, during the subdivision process of step S2, the natural gamma curve, resistivity curve and mineral composition curve of the horizontal well are compared, and the curve that best reflects the lithologic differences is used as the basis for subdivision.

[0013] Preferably, the step S2 further includes searching for a corresponding logging curve interval according to each lithofacies segment, and for each single lithofacies segment, setting the minimum value of the corresponding curve interval to be , the maximum value is The average value is , then the logging curve change rate of this curve interval is ,and

[0014] .

[0015] Preferably, the step S2 also includes the retention and re-division of the lithofacies segment, that is, when the logging curve change rate of the curve interval segment When the original lithofacies segment division result is retained, the logging curve change rate of the curve interval segment is When the lithofacies segment is re-divided, the lithofacies segment after re-division must meet the logging curve change rate of its curve interval segment. .

[0016] Preferably, in step S3, the number of lithofacies segments in a single fracturing segment is ,and The lithofacies section with the highest drilling rate is , which is equal to the longest lithofacies segment length among all lithofacies segments of the fracturing segment; let the intra-segment difference coefficient of the fracturing segment be ,when hour, ;when hour, ,in, is the lithofacies section number in the split section, and its value range is , is the length of the corresponding lithofacies section.

[0017] Preferably, in step S3, the number of fracturing segments is ,and ; The difference coefficient of the whole well section is ,and ,in, is the fracturing segment number, is the intra-segment difference coefficient of the corresponding fracturing segment.

[0018] Beneficial effects brought by this technical solution:

[0019] 1) By proposing the concept of full-well section difference coefficient, a reasonable evaluation standard for fracturing segments was established, achieving quantification, standardization, and proceduralization of segmentation scheme screening, reducing the complexity of the splitting scheme screening process, and achieving rapid and accurate determination of the final scheme. The final result is reasonable and reliable, ensuring the rationality of splitting scheme screening. In addition, this technical solution is easy and quick to implement, facilitating the screening of splitting schemes and improving the efficiency of shale gas well segmentation.

[0020] 2) This technical solution adopts three logging curves, including natural gamma ray curve, resistivity curve and mineral composition curve, as the basis for determining lithology, which facilitates the re-division work and ensures the reliability and rationality of the division results;

[0021] 3) This technical solution proposes a division standard for lithofacies segments by limiting the logging curve change rate V of the curve interval segment corresponding to a single lithofacies segment. This standard can ensure the calculation accuracy of the difference coefficient within the fracturing segment and further ensure the calculation accuracy of the difference coefficient of the panoramic segment, making the comparison result of the difference coefficient of the entire well section in step 4 more reliable. BRIEF DESCRIPTION OF THE DRAWINGS

[0022] The foregoing and following detailed description of the present invention will become more apparent when read in conjunction with the following drawings, in which:

[0023] Figure 1 Schematic diagram of the process of this technical solution;

[0024] Figure 2 This is the first segmentation plan for a shale gas horizontal well in Weiyuan area;

[0025] Figure 3 Scheme 2 for the segmentation of a shale gas horizontal well in Weiyuan area;

[0026] Figure 4 Comparison statistics of the difference coefficients within each section and the whole well section for a shale gas horizontal well plan in Weiyuan area;

[0027] Figure 5 The calculation formula for the rate of change of the logging curve in the curve interval segment;

[0028] Figure 6 is the intra-segment variation coefficient of the fracturing segment;

[0029] Figure 7 is the calculation formula for the difference coefficient of the entire well section. DETAILED DESCRIPTION

[0030] The following is a further explanation of the technical solutions for achieving the purpose of the present invention through several specific embodiments. It should be noted that the technical solutions claimed to be protected by the present invention include but are not limited to the following embodiments.

[0031] Example 1

[0032] This embodiment discloses a method for selecting a shale gas horizontal well segmentation scheme based on difference analysis, which, as a preferred embodiment of the present invention, includes the following steps:

[0033] Step S1: For several different segmentation schemes, evaluate whether any of them exceed the project applicability. If any exceed the project applicability, the segmentation scheme is deemed to fail the project applicability test. If no exceed the project applicability test, the segmentation scheme is deemed to meet the project applicability test. Meeting the project applicability test is a fundamental requirement for project implementation, and any segmentation scheme that does not meet the project applicability test is eliminated.

[0034] Step S2: First, the actual field horizontal well is preliminarily segmented based on the drilled layer, and the actual field horizontal well is divided into several layers. Then, based on the preliminary segmentation results, it is further divided according to the logging curve, and each layer is divided into several lithofacies segments according to the lithology reflected in the logging curve.

[0035] Step S3: Incorporating the lithofacies segment division results into all segmentation schemes that meet engineering applicability, in each segmentation scheme, calculating the difference coefficient within each single fracturing segment based on the proportion of lithofacies segment division results within each fracturing segment, and then calculating the difference coefficient of the entire well section of the corresponding segmentation scheme based on the difference coefficient within the single fracturing segment;

[0036] Step S4: Compare the full-well section difference coefficients of all segmentation schemes, and select the segmentation scheme with the smallest full-well difference coefficient.

[0037] In this technical solution, by proposing the concept of full-well section difference coefficient, a reasonable evaluation standard for fracturing segments is established, and the quantification, standardization and proceduralization of segmentation scheme screening are realized, thereby reducing the complexity of the splitting scheme screening process, achieving rapid and accurate determination of the final scheme, and the final result is reasonable and reliable, which can ensure the rationality of splitting scheme screening; in addition, this technical solution is easy and quick to implement, which provides convenience for the screening of splitting schemes.

[0038] Example 2

[0039] This embodiment discloses a method for selecting a shale gas horizontal well segmentation scheme based on difference analysis, which, as a preferred embodiment of the present invention, includes the following steps:

[0040] Step S1: For several different segmentation schemes, evaluate whether any of them exceed engineering applicability. If so, the segmentation scheme is deemed to fail engineering applicability. If not, the segmentation scheme is deemed to meet engineering applicability. Meeting engineering applicability is a fundamental requirement for project implementation; any segmentation scheme that fails to meet engineering applicability is eliminated. Specifically, scenarios exceeding engineering applicability include the distance between the bridge plug setting position and the casing collar being greater than 0.5m, the distance between the perforation position and the casing collar being greater than 0.5m, and the perforation position being located at a dogleg angle of 5° or less.

[0041] Step S2: Initially, the actual horizontal well is segmented based on the drilled horizons, dividing it into several intervals. Based on this initial segmentation, the well is further segmented based on well logging curves, with each interval divided into several lithofacies segments based on the lithology revealed by the well logging curves. Specifically, well logging curves include natural gamma ray (Gamma Ray) curves, resistivity curves, and mineral composition curves. The Gamma Ray, resistivity, and mineral composition curves of the horizontal well are compared, and the curve that best reflects the lithologic differences is used as the basis for further segmentation.

[0042] Step S3: Incorporating the lithofacies segment division results into all segmentation schemes that meet engineering applicability, in each segmentation scheme, calculating the difference coefficient within each single fracturing segment based on the proportion of lithofacies segment division results within each fracturing segment, and then calculating the difference coefficient of the entire well section of the corresponding segmentation scheme based on the difference coefficient within the single fracturing segment;

[0043] Step S4: Compare the full-well section difference coefficients of all segmentation schemes, and select the segmentation scheme with the smallest full-well difference coefficient.

[0044] In actual situations, the more obvious the lithologic differences are, the faster the re-division can be achieved, and the reliability and rationality of the division results can be ensured. Therefore, this technical solution adopts three logging curves including natural gamma curve, resistivity curve and mineral composition curve as the basis for judging lithology, which facilitates the re-division work and ensures the reliability and rationality of the division results.

[0045] Example 3

[0046] This embodiment discloses a method for selecting a shale gas horizontal well segmentation scheme based on difference analysis, which, as a preferred embodiment of the present invention, includes the following steps:

[0047] Step S1: For several different segmentation schemes, evaluate whether any of them exceed the project applicability. If any exceed the project applicability, the segmentation scheme is deemed to fail the project applicability test. If no exceed the project applicability test, the segmentation scheme is deemed to meet the project applicability test. Meeting the project applicability test is a fundamental requirement for project implementation, and any segmentation scheme that does not meet the project applicability test is eliminated.

[0048] Step S2: First, perform a preliminary segmentation of the actual field horizontal well based on the drilled layer, and divide the actual field horizontal well into several layers; then, based on the preliminary segmentation results, perform a further segmentation based on the logging curve, and divide each layer into several lithofacies segments according to the lithology reflected by the logging curve. Specifically, the logging curve includes a natural gamma curve, a resistivity curve, and a mineral composition curve. Among them, since different lithologies may have similar natural gamma curves, resistivity curves, or mineral composition curves, if the layers are to be subdivided according to the lithology, preferably, the natural gamma curves, resistivity curves, and mineral composition curves of the horizontal well are compared, and the curve that best reflects the lithology difference is used as the basis for the subdivision. Furthermore, according to each lithofacies segment, find the corresponding logging curve interval segment, and for each single lithofacies segment, let the minimum value on the corresponding curve interval segment be , the maximum value is The average value is , then the logging curve change rate of this curve interval is ,and

[0049] ; In the actual well logging curve, the curve is connected based on several logging values. Therefore, each curve interval is formed based on a limited number of logging values. Therefore, when calculating the average value, all the logging values ​​in the corresponding curve interval are added up and then divided by the number of logging values. Furthermore, based on the logging curve change rate V of the curve interval, the division result can be evaluated to make a decision on whether to retain or re-divide the lithofacies division. Specifically, when the logging curve change rate V of the curve interval is When the original lithofacies segment division result is retained, the logging curve change rate of the curve interval segment is When the lithofacies segment is re-divided, the lithofacies segment after re-division must meet the logging curve change rate of its curve interval segment. .

[0050] Step S3: The results of the lithofacies segment division are incorporated into all segmentation schemes that meet the engineering applicability. In each segmentation scheme, the difference coefficient within each single fracturing segment is calculated based on the proportion of the lithofacies segment division results within each fracturing segment, and the full-well segment difference coefficient of the corresponding segmentation scheme is obtained based on the difference coefficient within the single fracturing segment.

[0051] Step S4: Compare the full-well section difference coefficients of all segmentation schemes, and select the segmentation scheme with the smallest full-well difference coefficient.

[0052] This technical solution limits the logging curve change rate of the curve interval corresponding to a single lithofacies segment. , a division standard is proposed for the division of lithofacies sections, which can ensure the calculation accuracy of the difference coefficient within the fracturing section and further ensure the calculation accuracy of the difference coefficient of the panoramic section, making the comparison result of the difference coefficient of the whole well section in step 4 more reliable.

[0053] Example 4

[0054] This embodiment discloses a method for selecting a shale gas horizontal well segmentation scheme based on difference analysis. As a preferred embodiment of the present invention, in Example 1, in step S3, the results of the division of the lithofacies segment are included in all segmentation schemes that meet the engineering applicability. In each segmentation scheme, the difference coefficient within each single fracturing segment is calculated based on the proportion of the lithofacies segment division results within each fracturing segment, and the full-well segment difference coefficient of the corresponding segmentation scheme is obtained based on the difference coefficient within the single fracturing segment. Specifically, let the number of lithofacies segments in a single fracturing segment be ,and The lithofacies section with the highest drilling rate is , which is equal to the longest lithofacies segment length among all lithofacies segments of the fracturing segment; let the intra-segment difference coefficient of the fracturing segment be ,when hour, ;when hour, ,in, is the lithofacies section number in the split section, and its value range is , is the length of the corresponding lithofacies section; further, let the number of fracturing segments be ,and ; The difference coefficient of the whole well section is ,and ,in, is the fracturing segment number, is the intra-segment difference coefficient of the corresponding fracturing segment.

[0055] In actual work, assuming that the number of lithofacies segments in a single fracturing segment is 5, the corresponding lithofacies segment numbers are 1, 2, 3, 4, and 5, and the corresponding segment lengths are 、 、 、 、 , ;when When , it means that there is no difference within the segment; when the number of lithofacies encountered is greater and the segment lengths are closer, The larger the value, the greater the intra-segment difference, and the more likely it is to cause engineering complexity. Further, assuming that the number of fracturing segments in the segmentation scheme is 5, then the intra-segment difference coefficients of the corresponding fracturing segments 1, 2, 3, 4, and 5 are 、 、 、 、 ,in, The larger the value, the greater the panorama difference, and the more likely it is to cause engineering complexity. Therefore, the solution with a small difference coefficient for the entire well section is selected.

Claims

1. A method for selecting a shale gas horizontal well segmentation scheme based on difference analysis, characterized in that: The following steps are involved: Step S1: For several different segmentation schemes, evaluate whether there are any issues exceeding the project applicability in the segmentation schemes; if there are any issues exceeding the project applicability, then the segmentation scheme is determined to not meet the project applicability; if there are no issues exceeding the project applicability, then the segmentation scheme is determined to meet the project applicability; Step S2: First, the actual field horizontal well is preliminarily segmented based on the drilled layer, and the actual field horizontal well is divided into several layers; then, based on the preliminary segmentation results, it is further divided according to the logging curve, and each layer is divided into several lithofacies segments according to the lithology reflected by the logging curve; the corresponding logging curve interval segment is found according to each lithofacies segment, and for each single lithofacies segment, the minimum value of the corresponding curve interval segment is set to , the maximum value is The average value is , then the logging curve change rate of this curve interval is ,and ； Step S3: The results of the lithofacies segment division are incorporated into all the segmentation schemes that meet the engineering applicability. In each segmentation scheme, the difference coefficient within each single fracturing segment is calculated based on the proportion of the lithofacies segment division results within each fracturing segment, and the difference coefficient of the entire well section of the corresponding segmentation scheme is calculated based on the difference coefficient within the single fracturing segment; wherein, the number of lithofacies segments in a single fracturing segment is ,and , and the lithofacies section with the highest drilling rate is , which is equal to the longest lithofacies segment length among all lithofacies segments of the fracturing segment; let the intra-segment difference coefficient of the fracturing segment be ,when hour, ;when hour, ,in, is the lithofacies section number in the fracturing segment, and its value range is , is the length of the corresponding lithofacies section; Step S4: Compare the full-well section difference coefficients of all segmentation schemes, and select the segmentation scheme with the smallest full-well difference coefficient.

2. The method for selecting a shale gas horizontal well segmentation scheme based on difference analysis according to claim 1, characterized in that: In step S1, situations exceeding engineering applicability include the distance between the bridge plug setting position and the casing collar being greater than 0.5 m, the distance between the perforation position and the casing collar being greater than 0.5 m, and the perforation position being at a location with a dogleg angle of less than or equal to 5°.

3. The method for selecting a shale gas horizontal well segmentation scheme based on difference analysis according to claim 1, characterized in that: The logging curves include natural gamma curves, resistivity curves and mineral composition curves.

4. The method for selecting a shale gas horizontal well segmentation scheme based on difference analysis according to claim 3, characterized in that: During the subdivision process in step S2, the natural gamma curve, resistivity curve and mineral composition curve of the horizontal well are compared, and the curve that best reflects the lithologic differences is used as the basis for subdivision.

5. The method for selecting a shale gas horizontal well segmentation scheme based on difference analysis according to claim 1, characterized in that: The step S2 also includes the retention and re-division of the lithofacies segment, that is, when the logging curve change rate of the curve interval segment When the original lithofacies segment division result is retained, the logging curve change rate of the curve interval segment is When the lithofacies segment is re-divided, the lithofacies segment after re-division must meet the logging curve change rate of its curve interval segment. .

6. A method for selecting a shale gas horizontal well segmentation scheme based on difference analysis according to claim 1, characterized in that In step S3, the number of fracturing segments is ,and ; The difference coefficient of the whole well section is ,and ,in, is the fracturing segment number, is the intra-segment difference coefficient of the corresponding fracturing segment.

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