A method for evaluating the productivity of a compacted sandstone natural fracture wellbore extension partition and zone

Abstract

The application provides a compacted sandstone natural fracture wellbore extension zoning and zoned productivity evaluation method, which comprises the following steps: fracture distribution data import; then cutting and zoning at the same distance of single wellbore from near to far, the interval is determined according to the analysis target and analysis accuracy; correlation analysis is carried out on the fracture development density data and the open flow capacity of each zone, and the single well production response range is determined; the single well production response range is divided into n zones; in the single well production response range, the wellbore is evenly divided into blocks according to the direction with the single wellbore as the center; an evaluation model of wellbore extension dominant fracture is established, correlation analysis is carried out on the open flow capacity of all single well fracturing sections and the wellbore extension dominant fracture density in the research area, a single well productivity prediction chart is formed in the research area, and single well productivity prediction and evaluation are carried out based on the chart; through the method, unnecessary exploitation cost is reduced, oil and gas development efficiency and resource utilization rate are improved.

Description

Technical Field

[0001] This invention belongs to the field of well logging technology, and in particular relates to a method for evaluating the productivity of wellbore extension, zoning, and zoning in tight sandstone with natural fractures. Background Technology

[0002] Tight sandstone, as an important type of unconventional natural gas, is widely distributed in major oil and gas basins worldwide. Tight sandstone is characterized by low porosity and low permeability, and natural fractures are the main factors influencing oil and gas conduction, enrichment, and permeability improvement. Therefore, the degree of development of natural fractures within the production influence range of a single well in a tight sandstone reservoir plays a crucial role in its productivity. The production influence range of a single well in a tight sandstone reservoir can be gradually divided into three main wellbore extension sections: the wellbore itself, the near-wellbore periphery, and the far-wellbore periphery, from near to far, from inside to outside, and from point to area. The contribution of the degree of development of natural fractures in different ranges and orientations to the productivity of a single well varies. Therefore, there is an urgent need for a method for evaluating the wellbore extension zoning and zonation based on the degree of natural fracture development, providing important reference and guidance for accurate evaluation and prediction of single-well productivity, productivity assessment, and engineering exploration and development.

[0003] Currently, existing research mainly focuses on the impact of the physical properties (such as length and angle) and development density of natural fractures on single-well productivity, with little in-depth analysis of the response characteristics of natural fractures around the wellbore and their actual impact on single-well productivity. Some previous studies have identified the conductivity and length of natural fractures as key factors influencing single-well productivity in tight sandstone, but these studies largely remain at the level of quantitative description of fracture physical parameters, lacking an assessment of the spatial characteristics of fracture distribution and its impact on different areas around the wellbore. Furthermore, existing technologies differentiate fractures based on permeability, failing to consider the overall range of fracture action from the wellbore to the far periphery and the comprehensive impact of different areas on single-well productivity. Such research methods cannot accurately identify the key fractures that truly affect single-well productivity, easily leading to limitations in fracture assessment and application. In summary, existing technologies still have significant shortcomings in improving the accuracy of single-well productivity prediction and achieving refined control. Summary of the Invention

[0004] The purpose of this invention is to address the shortcomings of existing technologies in terms of accuracy in single-well productivity prediction and the achievement of refined control.

[0005] To achieve the above objectives, the present invention provides a method for evaluating the productivity of wellbore extension, zoning, and segmentation in tight sandstone natural fractures, comprising:

[0006] S1. Import fracture distribution data: Import fracture development density data around a single well based on seismic data and imaging logging data, and calculate the effective fracture development density of the single well shaft.

[0007] S2. Single-wellbore zoning: Taking the single wellbore as the center, the wellbore is divided into zones at equal intervals from near to far. The spacing is determined based on the analysis objectives and accuracy. Correlation analysis is performed between the fracture development density data of each zone and the unobstructed flow rate to clarify the production response range of the single well. Based on the response range, the wellbore is divided into n zones.

[0008] S3. Single well shaft zoning: Within the production response range of a single well, the well shaft is divided into blocks based on its orientation, with the single well shaft as the center.

[0009] S4. Establish a wellbore extension dominant fracture evaluation model, extract fracture development density in zones with different distances and directions, analyze the proportion within the well control range according to volume weight, and calculate the wellbore extension dominant fracture density by weighting.

[0010] S5. Draw a single-well productivity prediction chart for the study area, conduct correlation analysis between the unobstructed flow rate of the fracturing section of all single wells in the study area and the density of dominant fractures in the wellbore extension, form a single-well productivity prediction chart for the study area, and carry out single-well productivity prediction and evaluation based on the chart.

[0011] Furthermore, the crack development density data in step S1 includes:

[0012] Fracture density curves and multiple seismic attribute curves corresponding to various seismic attributes are obtained for each single wellbore from imaging logging data and seismic data;

[0013] Based on the relationship between seismic properties and the effective fracture development density within a single wellbore, the effective fracture development density around the wellbore is calculated.

[0014] Furthermore, the specific method for step S4 is as follows:

[0015] Let Y be the dominant fracture density in the wellbore extension, and let the average fracture density in each range be respectively... arrive Centered on a single well shaft, starting from due north and proceeding clockwise at intervals... ° The wellbore extension blocks were divided equally. Each direction is a block, with each direction defined by... It means that if For a valid orientation, then Otherwise, it is 0; Where M is the location and M is the number of valid blocks; the specific formula is:

[0016]

[0017]

[0018]

[0019] The division of zones by distance and orientation is adjusted according to the degree of crack development.

[0020] Beneficial effects:

[0021] This invention provides a more accurate single-well productivity prediction and evaluation technology by employing a wellbore extension zoning and partitioning method, fully considering the extension of natural fractures outside the wellbore. Based on the fracture response characteristics of single wells in tight sandstone reservoirs, this technology progressively divides production zones from the wellbore to the near-wellbore and then to the far-wellbore. Combining fracture development and distribution density data, it extracts the correlation between fracture development density and unobstructed flow rate in different zones for correlation analysis, identifying zones that contribute to single-well productivity. Finally, a wellbore extension dominant fracture density evaluation model is constructed using volume weighting. This method helps to scientifically assess the development potential of oil and gas reservoirs, reduce unnecessary extraction costs, improve oil and gas development efficiency, and ultimately enhance resource utilization and extraction benefits. Attached Figure Description

[0022] Figure 1 This is a flowchart of the method for evaluating the productivity of natural fracture wellbore extension, zoning, and segmentation provided by the present invention;

[0023] Figure 2 This is a schematic diagram of the zone division within the production well control area of ​​a single well provided by the present invention;

[0024] Figure 3 This invention provides a graph showing the relationship between unobstructed flow rate and effective fracture density at different distances from the wellbore.

[0025] Figure 4 This is a schematic diagram of the directional zoning of a single well provided by the present invention;

[0026] Figure 5 This invention provides a graph showing the relationship between unobstructed flow rate and effective fracture density at different azimuths around the well (within 300m).

[0027] Figure 6 This is a graph showing the relationship between the unobstructed flow rate in the Z-well zone and the density of dominant fractures in the wellbore, provided by this invention. Detailed Implementation

[0028] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to embodiments. It should be understood that the specific embodiments described herein are merely illustrative and not intended to limit the invention.

[0029] The application principle of the present invention will be further described below with reference to the accompanying drawings and specific embodiments.

[0030] Example 1:

[0031] like Figure 1 As shown, this invention takes a single well in a tight sandstone reservoir as the research object and carries out a method for evaluating the productivity of wellbore extension zones and bands based on natural fractures.

[0032] Centered on the drilling location of a single well, zones were created at equal intervals from the wellbore to the near-wellbore and then to the far-wellbore. Based on fracture development distribution density data predicted from seismic data, the average fracture development density of different zones was calculated. Correlation analysis was conducted between the unobstructed flow rate of the fracturing section of the single well and the effective average fracture development density of each zone within the fracturing section to clarify the production control response range of a single well in tight sandstone reservoirs. Within the determined production control response range, target intervals were set centered on the wellbore. The wellbore is divided into 360 sections. In each block, the average fracture density was calculated using fracture development distribution density data predicted from seismic data. Correlation analysis was conducted between the unobstructed flow rate of the fracturing section in each well and the average fracture density of each block to clarify the orientation of the production-controlling response of single wells in tight sandstone reservoirs. Finally, within the production-controlling response zone of each well, a volume-weighted wellbore extension dominant fracture density was constructed. Correlation analysis was then conducted between the unobstructed flow rate of the fracturing section in all single wells in the study area and the wellbore extension dominant fracture density to form a single-well production capacity prediction map for the study area. Based on this map, single-well production capacity prediction and evaluation were carried out. The specific steps are as follows:

[0033] S1. Import fracture distribution data: Import fracture development density data around a single well based on seismic data prediction.

[0034] Taking the Tarim study area as an example, we collected seismic data, core data, well logging data, and fracture development density data around all single wells in the study area.

[0035] Fracture density curves and multiple seismic attribute curves corresponding to various seismic attributes are obtained from imaging logging data and seismic data for each single well. Based on the relationship between seismic attributes and the effective fracture development density within the single well, the effective fracture development density of each zone around the far well perimeter of the single well is calculated. The specific calculation method can be found in patent CN116359980A.

[0036] S2, Single-well shaft zoned treatment:

[0037] Centered on a single wellbore, the wellbore is divided into zones at equal intervals from near to far, with the spacing determined based on the analysis target and the required accuracy.

[0038] Centered on a single well shaft, the well is divided into zones at 50-meter intervals from near to far, resulting in the following zones: 0-50 meters, 50-100 meters, 100-150 meters, 150-200 meters, 200-250 meters, 250-300 meters, 300-350 meters, and 350-400 meters. Figure 2 As shown.

[0039] The effective fracture density is calculated for each point based on the seismic attribute data (each point is related to the resolution of the seismic data). The average fracture development density of each zone is obtained by averaging the fracture densities of all points within each zone.

[0040] This application uses the unobstructed flow rate when both the oil and casing are fully open for analysis. Unobstructed flow rate, also known as free-flow rate, refers to the gas well production when the casing is closed and the tubing is fully open, i.e., when the absolute pressure of the tubing is 0.1 MPa. If the tubing is closed and the casing is fully open, the production rate when the absolute pressure of the casing is 0.1 MPa is called the casing unobstructed flow rate. Simply put, when both the oil and casing are fully open simultaneously, without any wellhead production limits, it is called the free-flow rate, which is the most accurate indicator of formation productivity. This unobstructed flow rate was measured in the field using a flow meter; it is a measured indicator and a commonly used indicator.

[0041] Correlation analysis was performed between the effective fracture development density data of each zone in the fracturing section and the unobstructed flow rate of the fracturing section to clarify the production response range of a single well. The production response range of a single well can be divided into n zones. The correlation analysis was performed by representing the fracture development density and unobstructed flow rate using a scatter plot to visually illustrate the relationship between the two. The production response range of a single well is generally between several hundred meters and 1-2 kilometers. The wellbore extension range of a single well is divided into n zones at a certain interval r. The interval r can be further subdivided according to the actual field production needs, such as 25m or 10m, to determine the production response range. In the example, the interval is 50m, which can meet the well control range evaluation needs of this study area. The correlation analysis was performed between the average effective fracture development density and the unobstructed flow rate of each zone. The results are as follows: Figure 3As shown, R represents the correlation coefficient, the magnitude of which determines the strength of the linear trend. Generally, a linear trend is considered to be strong when R > 0.6. The correlation coefficients are as follows: 0.7549 for wells 0-50 meters away; 0.6946 for wells 50-100 meters away; 0.6831 for wells 100-150 meters away; 0.6506 for wells 150-200 meters away; 0.7685 for wells 200-250 meters away; 0.7477 for wells 250-300 meters away; 0.5151 for wells 300-350 meters away; and 0.4832 for wells 350-400 meters away. In summary, the analysis shows a strong positive correlation between the unobstructed flow rate of a single well and the fracture density within 300m of the fracturing section, with the correlation decreasing beyond 300m.

[0042] S3, Single-well shaft zoning treatment

[0043] Within the single-well production response range, the wellbore is divided into eight equal blocks at 45° intervals, centered on the wellbore. Within the defined single-well production response range (within 300m), the wellbore is further divided into zones at 45° intervals: 0-45°, 45-90°, 90-135°, 135-180°, 180-225°, 225-270°, 270-315°, and 315-360°. Figure 4 As shown, the azimuth within the production response range of a single well is 360°, divided according to angular intervals θ. The angular intervals θ can be further subdivided according to actual field production needs, such as 30° or 10°, to determine the production response azimuth. Here, the example division interval is 45°, which can meet the well control range evaluation requirements of this study area.

[0044] Based on the preceding data analysis, the range that contributes significantly to single-well productivity was identified. A scatter plot was then created comparing the effective fracture development density and the unobstructed flow rate of each zone in the fracturing section to observe the linear trend. R represents the correlation coefficient, and its magnitude determines the strength of the linear trend; generally, an R > 0.6 indicates a strong linear trend. The results are as follows: Figure 5As shown, the correlation coefficients are 0.7068 in the 0-45° range, 0.6833 in the 45-90° range, 0.6473 in the 90-135° range, 0.6656 in the 135-180° range, 0.6034 in the 180-225° range, 0.6568 in the 225-270° range, 0.7348 in the 270-315° range, and 0.7901 in the 315-360° range. The analysis shows that within a 300m distance from the wellbore perimeter, the unobstructed flow rate of a single well is well-related to the effective fracture density in each direction (distinguishing between 8 directions), indicating that the development of effective fractures around the well contributes significantly to production capacity.

[0045] S4. Establish the optimal fracture density in wellbore extension:

[0046] Fracture development density can be extracted from zones at different distances and in different directions. The proportion of these zones within the well control area is analyzed using volume weighting, and the weighted calculation yields the dominant fracture density extending into the wellbore. The volume weighting is essentially the coefficient preceding each zone range obtained by dividing the zone volume by the wellbore volume. In this case, zones spaced at equal distances within the wellbore exhibit a regular coefficient pattern, which, according to mathematical induction, forms an arithmetic sequence with an arithmetic progression of 2. Let the dominant fracture density extending into the wellbore be Y, and the average fracture density of each range be... arrive Centered on the single well shaft, starting from due north and proceeding clockwise at intervals... ° The wellbore extension blocks were divided equally. Each direction is a block, and each direction is defined by... It means that if For a valid orientation, then Otherwise, it is 0; M is the number of valid blocks; the formula is:

[0047]

[0048]

[0049]

[0050] Note: The distance and orientation of the zones can be adjusted according to the degree of crack development.

[0051] Specifically, based on the above analysis results, effective zones for single-well productivity were determined (the effective range is within 300m, thus dividing the area into 6 zones, i.e., n=6; 0-360° are all effective azimuths with each azimuth spaced 45° apart, therefore the number of effective blocks is...). ,Right now , The average development density of effective fractures in zones with different distances and directions was extracted, and the proportion of fractures within the well control area was analyzed according to weights. The weighted calculation of the dominant fracture density in the wellbore extension was then obtained, and the calculation formula is as follows:

[0052]

[0053]

[0054] Note: Results here are rounded to two decimal places; (0-50m) is the average dominant fracture density within a 50m radius of a single well; (50-100m) is the average dominant fracture density within a 50-100m radius ring of a single well; (150-200m) is the average dominant fracture density within a 150-200m radius ring of a single well; (200-250m) is the average dominant fracture density within a 200-250m radius ring of a single well; (250-300m) is the average dominant fracture density within a 250-300m radius ring of a single well.

[0055] S5. Draw a map showing the predicted single-well productivity of the study area.

[0056] In summary, a correlation analysis was conducted between the unobstructed flow rate of the fracturing section of all single wells in the study area and the density of dominant fractures in the wellbore extension, resulting in a single-well productivity prediction chart for the study area. Based on this chart, single-well productivity prediction and evaluation were carried out. Figure 6 As shown in the figure, the wellbore extension dominant fracture evaluation model provides guidance for the prediction and evaluation of single-well productivity in tight sandstone reservoirs.

[0057] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, and improvements made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A method for evaluating the productivity of wellbore extensions in tight sandstone with natural fractures, characterized in that, include: S1. Import fracture distribution data; import fracture development density data around a single well based on seismic data and imaging logging data, and calculate the fracture development density of the single well shaft. S2. Single wellbore zoning: Taking the single wellbore as the center, the wellbore is divided into zones at equal intervals from near to far. The spacing is determined according to the analysis target and the accuracy of the analysis. The single well is divided into n zones according to its production response range. The development density data of fractures in each zone is correlated with the unobstructed flow rate to clarify the production response range of the single well. S3. Single-well shaft zoning; Within the production response range of a single well, target intervals are set with the single well shaft as the center. ,interval The wellbore is divided into 360 / In each block, the development density data of fractures in each block are correlated with the unobstructed flow rate to identify the effective zone within the single well's generation response range; S4. Establish a wellbore extension dominant fracture evaluation model, extract fracture development density in zones with different distances and directions, analyze the proportion within the well control range according to volume weight, and calculate the wellbore extension dominant fracture density by weighting. S5. Draw a single-well productivity prediction map for the study area; conduct correlation analysis between the unobstructed flow rate of the fracturing section of all single wells in the study area and the density of dominant fractures in the wellbore extension to form a single-well productivity prediction map for the study area, and carry out single-well productivity prediction and evaluation based on the map.

2. The method for evaluating the productivity of wellbore extension zones and zonation in tight sandstone with natural fractures according to claim 1, characterized in that, The crack development density data in step S1 include: Fracture density curves and multiple seismic attribute curves corresponding to various seismic attributes are obtained for each single wellbore from imaging logging data and seismic data; Based on the relationship between seismic properties and the effective fracture development density within a single wellbore, the fracture development density around the wellbore is calculated.

3. The method for evaluating the productivity of wellbore extension zones and zonation in tight sandstone with natural fractures according to claim 1, characterized in that, The specific method for step S4 is as follows: Let Y be the dominant fracture density in the wellbore extension, and let the average fracture density in each range be respectively... arrive Centered on a single well shaft, starting from due north and proceeding clockwise at intervals... ° The wellbore extension blocks were divided equally. Each direction is a block, with each direction defined by... It means that if For a valid orientation, then Otherwise, it is 0; Where M is the location and M is the number of valid blocks; the specific formula is: The division of zones by distance and orientation is adjusted according to the degree of crack development.

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