Compact sandstone natural fracture shaft continuation zoning and zoning productivity evaluation method

Abstract

The invention provides a tight sandstone natural fracture shaft continuation zoning and zoning productivity evaluation method. The method comprises the steps that fracture distribution data are imported; then the single-well shaft is taken as the center, the single-well shaft is cut and zoned at the same distance from near to far, and the distance is determined according to the analysis target and the analysis accuracy; performing correlation analysis on the development density data of each zone crack and the open flow capacity, determining a single well production response range, and dividing into n zones according to the single well production response range; within the single-well production response range, a single-well shaft serves as the center, and the shaft is averagely divided into blocks according to the orientation; establishing a wellbore continuation dominant fracture evaluation model, carrying out correlation analysis on the open flow capacity of all single well fracturing sections in the research area and the wellbore continuation dominant fracture density to form a single well productivity prediction chart of the research area, and carrying out single well productivity prediction and evaluation based on the chart; through the method, the unnecessary exploitation cost is reduced, and the oil and gas development efficiency and the resource utilization rate are improved.

Description

Technical Field

[0001] The present invention belongs to the technical field of logging, and particularly relates to a method for evaluating the productivity of wellbore extension zoning and banding in natural fractures of tight sandstone. Background Technique

[0002] As one of the important types of unconventional natural gas, tight sandstone is widely distributed in major oil and gas basins around the world. Tight sandstone has low porosity and low permeability, and natural fractures are the main factors for oil and gas drainage, 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 key role in the productivity of the single well. The production influence range of a single well in a tight sandstone reservoir can be gradually divided into three main wellbore extension parts, namely the wellbore, near-wellbore zone, and far-wellbore zone, from near to far, from inside to outside, and from point to surface. The degree of development of natural fractures in different ranges and directions contributes differently to the productivity of a single well. Therefore, there is an urgent need for a method for evaluating the zoning and banding of single-well wellbore extension based on the degree of development of natural fractures to achieve accurate evaluation and prediction of single-well productivity, provide important references and guidance for productivity evaluation, and engineering exploration and development.

[0003] Currently, existing achievements mainly focus on the research of the influence of physical properties (such as length, angle, etc.) and development density of natural fractures on single-well productivity, and there is little in-depth analysis of the response characteristics of natural fractures around the wellbore and their actual influence on single-well productivity. Some predecessors believe that the conductivity and length of natural fractures are the key factors affecting the productivity of tight sandstone single wells, but these studies mostly stay at the quantitative description of fracture physical property parameters, lacking the evaluation of the spatial characteristics of fracture distribution and their influence on different regions around the wellbore. In addition, the existing technology differentiates fractures based on fracture permeability, failing to consider the overall action range of fractures between the wellbore and the far-wellbore zone and the comprehensive influence of different regions on single-well productivity. Such a research method cannot accurately identify the key fractures that truly affect single-well productivity, easily leading to limitations in fracture evaluation and application. In summary, there are still significant deficiencies in the existing technology in improving the accuracy of single-well productivity prediction and achieving refined control. Summary of the Invention

[0004] The purpose of the present invention is to solve the deficiencies of the existing technology in the accuracy of single-well productivity prediction and achieving refined control.

[0005] To achieve the above purpose, the present invention provides a method for evaluating the productivity of wellbore extension zoning and banding in natural fractures of tight sandstone, including: S1. Import fracture distribution data, import the predicted 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 wellbore; S2. Perform zonal treatment for a single wellbore. Centering on the single wellbore, cut and zone at the same distance from the single wellbore from near to far. The spacing is determined according to the analysis target and analysis accuracy. Conduct a correlation analysis between the fracture development density data of each zone and the open flow potential to clarify the single well production response range, and divide it into n zones according to the response range. S3. Perform block treatment for a single wellbore. Within the single well production response range, centering on the single wellbore, evenly divide the wellbore into blocks according to the azimuth. S4. Establish an evaluation model for the dominant fractures extending from the wellbore. Extract the fracture development density in zones with different distances and different directions respectively, and analyze the proportion within the well control range according to the volume weight, and calculate the dominant fracture density extending from the wellbore by weighted calculation. S5. Draw a prediction chart for the single well productivity in the study area. Conduct a correlation analysis between the open flow potential of all single well fracturing sections in the study area and the dominant fracture density extending from the wellbore to form a prediction chart for the single well productivity in the study area, and conduct single well productivity prediction and evaluation based on the chart.

[0006] Furthermore, the fracture development density data in step S1 includes: Obtain the fracture density curve of each single wellbore and multiple seismic attribute curves corresponding to multiple seismic attributes from imaging logging data and seismic data. Based on the relationship between seismic attributes and the effective fracture development density within the single wellbore, calculate the effective fracture development density around the single well.

[0007] Furthermore, the specific method of step S4 is as follows: Let the dominant fracture density extending from the wellbore be Y, and the average fracture density of each range be to ; Centering on the single wellbore, starting from the due north direction clockwise, evenly divide the wellbore extension block into azimuth blocks at intervals of °. Each azimuth is represented by . If is a valid azimuth, then , otherwise it is 0; is the azimuth, and M is the number of valid blocks; The specific formula is: The distance division of the zone and the azimuth division are adjusted according to the fracture development degree.

[0008] Beneficial effects: The present invention provides a more accurate single - well productivity prediction and evaluation technology through the well -bore extension zoning and sub - zoning method, fully considering the extensibility of natural fractures outside the well -bore. This technology is based on the single - well well -bore fracture response characteristics of tight sandstone reservoirs. It gradually divides the production zones from the well -bore to the near - wellbore and then to the far - wellbore, and combines the fracture development distribution density data to extract the correlation between the fracture development density and the open - flow potential in different zones, and clarifies the zones that contribute to the single - well productivity. Finally, an evaluation model of the dominant fracture density of well -bore extension is constructed by weighted volume ratio. This method helps to scientifically evaluate the development potential of oil and gas reservoirs, reduce unnecessary production costs, improve the efficiency of oil and gas development, and ultimately increase the utilization rate and production benefits of resources. BRIEF DESCRIPTION OF THE DRAWINGS

[0009] Figure 1 is a flowchart of the productivity evaluation method for natural fracture well -bore extension zoning and sub - zoning provided by the present invention; Figure 2 is a schematic diagram of the zone division within the control range of a single - well production well provided by the present invention; Figure 3 is a relationship diagram between the open - flow potential and the effective fracture density at different distances in the far - wellbore provided by the present invention; Figure 4 is a schematic diagram of the zone division in the superposition direction of a single - well provided by the present invention; Figure 5 is a relationship diagram between the open - flow potential and the effective fracture density in different azimuths in the far - wellbore (within 300m) provided by the present invention; Figure 6 is a relationship diagram between the open - flow potential and the dominant fracture density of well -bore extension in the Z - well area provided by the present invention. DETAILED DESCRIPTION OF THE EMBODIMENTS

[0010] In order to make the objectives, technical solutions and advantages of the present invention more clear and understandable, the present invention will be further described in detail below in conjunction with embodiments. It should be understood that the specific embodiments described herein are only used to explain the present invention and are not used to limit the present invention.

[0011] The application principle of the present invention will be further described below in conjunction with the drawings and specific embodiments.

[0012] Embodiment 1: As Figure 1 shown, the present invention takes a single - well in a tight sandstone reservoir as the research object and conducts a productivity evaluation method for natural fracture well -bore extension zoning and sub - zoning.

[0013] Taking the single - well drilling position as the center point, zoning is carried out at the same interval distance from the wellbore to the near - wellbore and then to the far - wellbore. Based on the fracture development distribution density data predicted from seismic data, the average fracture development density in different ranges is calculated. A correlation analysis is carried out between the open - flow capacity of the single - well fracturing section and the average effective fracture development density of each zone in the fracturing section to clarify the single - well production - control response range of tight sandstone reservoirs; within the determined production - control response range, with the single - well wellbore as the center, a target interval is set is used to evenly divide the wellbore into 360 / blocks. Using the fracture development distribution density data predicted from seismic data, the average fracture development density of each block is calculated. A correlation analysis is carried out between the open - flow capacity of the single - well fracturing section and the average fracture development density of each block to clarify the single - well production - control response azimuth of tight sandstone reservoirs. Finally, within the single - well production - control response zone, the wellbore - extended dominant fracture density is constructed by volume weighting, and a correlation analysis is carried out between the open - flow capacity of all single - well fracturing sections in the study area and the wellbore - extended dominant fracture density to form a single - well production prediction chart for the study area, and single - well production prediction and evaluation are carried out based on this chart. The specific steps are as follows:

[0014] S1. Import of fracture distribution data: Import the fracture development density data around the single well predicted from seismic data.

[0015] Taking the Tarim study area as an example, collect the seismic data, core data, logging data and fracture development density data around all single wells in the study area.

[0016] From the imaging logging data and seismic data, the fracture density curve of each single - well wellbore and multiple seismic attribute curves corresponding to multiple seismic attributes are obtained. Based on the relationship between seismic attributes and the effective fracture development density in the single - well wellbore, the effective fracture development density of each zone in the far - wellbore of the single well is calculated. The specific calculation method can refer to Patent CN116359980A.

[0017] S2. Zoning treatment of the single - well wellbore: Taking the single - well wellbore as the center, cutting and zoning are carried out at the same distance from the near - wellbore to the far - wellbore. The spacing is determined according to the analysis target and analysis accuracy.

[0018] Taking the single - well wellbore as the center, cutting and zoning are carried out at a distance of 50 meters from the near - wellbore to the far - wellbore, and it is divided into: 0 - 50 meters, 50 meters - 100 meters, 100 meters - 150 meters, 150 meters - 200 meters, 200 meters - 250 meters, 250 meters - 300 meters, 300 meters - 350 meters, 350 - 400 meters, as Figure 2 shown.

[0019] The effective fracture density calculated for each point based on seismic attribute data (each point is related to the resolution of the seismic data) is averaged for all points within each divided zone to obtain the average fracture development density of each zone.

[0020] This application selects the open-flow potential when both the oil casing and the tubing are fully open for analysis. The open-flow potential, also known as the flowing potential, refers to the gas well production when the casing is closed and the tubing outlet is fully open, that is, the tubing absolute pressure is 0.1 MPa. If the tubing is closed and the casing outlet is fully open, and the casing absolute pressure is 0.1 MPa, the production is called the casing open-flow potential. Simply put, when both the oil casing and the tubing are fully open without setting wellhead production restrictions, it is called the open and unobstructed flow potential, which is the most accurate indicator of the formation production capacity. This open-flow potential is measured on-site using a flow tester, which is a measured indicator and a commonly used indicator.

[0021] Perform a correlation analysis on the effective fracture development density data of each zone in the fracturing section and the open-flow potential of the fracturing section to clarify the single-well production response range. The single-well production response range can be divided into n zones; among them, the correlation analysis uses a scatter plot to represent the fracture development density and the open-flow potential, visually showing the relationship between the two. The single-well production response range is generally between several hundred meters and 1 - 2 kilometers. The extension range of the single-well wellbore is divided into n zones at a certain interval r. The value of the interval r can be further subdivided according to the actual on-site production requirements, such as 25 m or 10 m, to be used to determine the production response range. The example division interval is 50 m, which can meet the well control range evaluation requirements of this study area. Perform a correlation analysis on the average effective fracture development density of each zone and the open-flow potential. The results are as Figure 3 shown. R represents the correlation coefficient, and its magnitude determines the quality of the linear trend. Generally, when R > 0.6, the linear trend is good; the correlation coefficient within the range of 0 - 50 meters from the single well is 0.7549, the correlation coefficient within the range of 50 - 100 meters from the single well is 0.6946, the correlation coefficient within the range of 100 - 150 meters from the single well is 0.6831, the correlation coefficient within the range of 150 - 200 meters from the single well is 0.6506, the correlation coefficient within the range of 200 - 250 meters from the single well is 0.7685, the correlation coefficient within the range of 250 - 300 meters from the single well is 0.7477, the correlation coefficient within the range of 300 - 350 meters from the single well is 0.5151, and the correlation coefficient within the range of 350 - 400 meters from the single well is 0.4832; based on the above analysis, it is obtained that the single-well open-flow potential has a good positive correlation with the zoned fracture density (within 300 m) of the fracturing section, and the correlation decreases in the range greater than 300 m.

[0022] S3. Processing of the single-well wellbore partition Within the single-well production response range, with the single-well borehole as the center, the borehole is evenly divided into eight blocks according to the azimuth at 45°. In the determined single-well production response range (within 300m), zoning is carried out every 45° according to the azimuth, divided into 0-45°, 45-90°, 90-135°, 135-180°, 180-225°, 225-270°, 270-315°, 315-360°; as Figure 4 shown. The azimuth within the single-well production response range is a total of 360°, which is divided according to the angular interval θ. The number of angular intervals θ can be further subdivided according to the actual on-site production requirements, such as 30° or 10°, to be used to determine the production response azimuth. Here, the example division interval is 45°, which can meet the well control range evaluation requirements of this research area.

[0023] According to the previous data analysis results, clarify the range that has a high contribution to the single-well productivity. By plotting a scatter plot of the effective fracture development density in each area of the fracturing section and the open flow rate of the fracturing section, observe the existing linear trend. R represents the correlation coefficient, and its size determines the quality of the linear trend. Generally, when R>0.6, the linear trend is good; the results are as Figure 5 shown. The correlation coefficient within the range of 0-45° is 0.7068, the correlation coefficient within the range of 45-90° is 0.6833, the correlation coefficient within the range of 90-135° is 0.6473, the correlation coefficient within the range of 135-180° is 0.6656, the correlation coefficient within the range of 180-225° is 0.6034, the correlation coefficient within the range of 225-270° is 0.6568, the correlation coefficient within the range of 270-315° is 0.7348, and the correlation coefficient within the range of 315-360° is 0.7901; based on the above analysis, within the range of 300m from the far wellbore, there is a good relationship between the open flow rate of the single well and the effective fracture density in each azimuth (analyzing 8 directions separately), indicating that the development of effective fractures around the wellbore has a good contribution to the productivity.

[0024] S4. Establish the dominant fracture density for wellbore extension: The fracture development density in different distance and different direction zones can be extracted respectively, and the proportion in the well control range can be analyzed according to the volume weight. The dominant fracture density for wellbore extension is calculated by weighted calculation. The volume weight proportion is actually the coefficient in front of each zone range obtained by (zone volume / wellbore volume). For the zones separated by the same distance interval in the wellbore here, their coefficients are regular. According to mathematical induction, their rule is an arithmetic sequence with a common difference of 2. Let the dominant fracture density for wellbore extension be Y, and the average fracture density of each range is respectively to ; with the single-well borehole as the center, starting from the due north direction clockwise, the wellbore extension blocks are evenly divided every °. a number of azimuth blocks, each azimuth is represented by If is a valid azimuth, then , otherwise it is 0; M is the number of valid blocks; the formula is organized as:

[0025] Note: The distance division and azimuth division of the zone can be adjusted according to the fracture development degree.

[0026] Specifically: According to the above analysis results, the zones effective for the single-well productivity are obtained (the effective range is within 300m, so 6 zones are divided, that is, n = 6; 0 - 360° are all valid azimuths and each azimuth interval is 45°, then the number of effective blocks is , that is , ). The average development density of effective fractures in zones with different distances and different directions are extracted respectively, and the proportion within the well control range is calculated according to the weight analysis, and the weighted calculation is used to obtain the density of dominant fractures for wellbore extension. The calculation formula is: Note: The results here are reserved to two decimal places; (0 - 50m) is the average density of dominant fractures within a 50m radius of the single well; (50 - 100m) is the average density of dominant fractures within the 50 - 100m annulus of the single well radius; (150 - 200m) is the average density of dominant fractures within the 150 - 200m annulus of the single well radius; (200 - 250m) is the average density of dominant fractures within the 200 - 250m annulus of the single well radius; (200 - 250m) is the average density of dominant fractures within the 200 - 250m annulus of the single well radius; (250 - 300m) is the average density of dominant fractures within the 250 - 300m annulus of the single well radius.

[0027] S5. Draw the prediction chart of single-well productivity in the study area In summary, the correlation analysis is carried out between the open flow potential of all single-well fracturing sections in the study area and the density of dominant fractures for wellbore extension, the prediction chart of single-well productivity in the study area is formed, and the single-well productivity prediction and evaluation are carried out based on this chart. As Figure 6 shown, it can be seen from the figure that the evaluation model of dominant fractures for wellbore extension provides guidance for the prediction and evaluation of single-well productivity in tight sandstone reservoirs.

[0028] The above are only the preferred embodiments of the present invention and are not intended to limit the present invention. Any modifications, equivalent replacements, improvements, etc. made within the spirit and principle of the present invention shall be included within the protection scope of the present invention.

Claims

1. A method for evaluating the productivity of natural fracture wellbore extension in tight sandstone by zoning and zone, characterized in that: include: S1. Import fracture distribution data: import fracture density data around a single well predicted based on seismic data and imaging logging data, and calculate fracture density in the wellbore of a single well; S2. Single well borehole zoning: With the single well borehole as the center, the single well borehole is cut and divided at the same distance from near to far. The spacing is determined according to the analysis target and analysis accuracy. According to the production response range of the single well, it is divided into n zones. The development density data of the fractures in each zone is correlated with the open flow rate to clarify the production response range of the single well. S3, single well borehole zoning processing; within the single well production response range, with the single well borehole as the center, set the target interval ,interval Divide the wellbore into 360 / For each block, the correlation analysis between the fracture density data and the open flow rate is carried out to identify the effective area within the single well generation response range; S4. Establish a wellbore extension dominant fracture evaluation model, extract the fracture development density in zones with different distances and directions, analyze the proportion within the well control range according to the volume weight, and calculate the wellbore extension dominant fracture density by weighted calculation; S5. Draw a single well capacity prediction chart for the study area; conduct a correlation analysis between the unimpeded 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 capacity prediction chart for the study area, and conduct single well capacity prediction and evaluation based on the chart.

2. The method for evaluating the productivity of natural fracture wellbore extension in tight sandstone by zoning and zone according to claim 1, characterized in that: The fracture density data in step S1 include: The fracture density curve of each single wellbore and multiple seismic attribute curves corresponding to multiple seismic attributes are obtained from imaging logging data and seismic data; Based on the relationship between seismic attributes and the effective fracture density in the wellbore of a single well, the fracture density around the wellbore is calculated.

3. The method for evaluating the productivity of natural fracture wellbore extension in tight sandstone by zoning and zones according to claim 1, characterized in that: The specific method of step S4 is: Assume that the density of the dominant fractures in the wellbore extension is Y, and the average density of fractures in each range is arrive ; Taking the single well as the center, start from the north direction and go clockwise at intervals of ° Divide the wellbore extension area equally Azimuth blocks, each with Indicates that if is a valid orientation, then , otherwise 0; is the direction, M is the number of valid blocks; the specific formula is: The distance and orientation divisions of the zones are adjusted according to the degree of fracture development.

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