A method for improving recovery of fractured bottom water gas reservoirs by horizontal well low part drainage

Abstract

The application discloses a method for improving the recovery ratio of a fractured bottom water gas reservoir by draining water in a low position of a horizontal well, and comprises the following steps: S1, dividing a bottom water breakthrough zone of a target fractured bottom water gas reservoir, and delimiting a development favorable zone of the target fractured bottom water gas reservoir in the bottom water breakthrough zone; S2, determining a high gas saturation horizon and a gas-water interface position of the target fractured bottom water gas reservoir; S3, obtaining actual production data of the target fractured bottom water gas reservoir, and determining a production straight well of the target fractured bottom water gas reservoir which has completely watered out and stopped production according to the actual production data; and S4, drilling a horizontal well by using a well shaft of the production straight well according to the development favorable zone, the high gas saturation horizon and the gas-water interface position, draining water in the horizontal well and improving the recovery ratio. The application can improve the recovery ratio of a carbonate rock fractured bottom water gas reservoir in a middle and late development stage.

Description

Technical Field

[0001] This invention relates to the field of carbonate rock fractured bottom water gas reservoir development technology, and in particular to a method for improving the recovery rate of fractured bottom water gas reservoirs by draining the lower part of a horizontal well. Background Technology

[0002] With the advent of the concepts of carbon peaking and carbon neutrality, global demand for clean energy is constantly increasing, and natural gas, as a clean energy source, has received considerable attention. Statistics show that carbonate oil and gas resources account for approximately 70% of global oil and gas resources, of which proven recoverable reserves account for about 50%, indicating enormous future development potential. China's carbonate gas reservoirs are mainly distributed in the Sichuan Basin, Ordos Basin, and Tarim Basin. In the middle and late stages of development, in fractured bottom-water carbonate gas reservoirs, as the formation pressure decreases after natural gas production, bottom water invades production wells along fracture channels, forming a two-phase flow of gas and water. This increases the resistance to natural gas flow, leading to reduced well production and increased reservoir abandonment pressure. Furthermore, after water intrusion, most of the natural gas is sealed off, forming multiple "dead gas zones" that cannot be extracted, significantly reducing the overall reservoir recovery rate.

[0003] Currently, the main methods for improving the recovery rate of fractured bottom-water gas reservoirs in carbonate rocks through water control include drainage gas production technology and profile control and water shut-off technology. Drainage gas production technology is often used for combined drainage of multiple well groups, showing significant initial results. However, due to the complexity of the reservoir water intrusion mechanism and constraints from technical and economic conditions, it is difficult to determine the optimal timing and measures for water control. Furthermore, this technology only targets drainage of single wells, and its effectiveness in optimizing the gas-water space is limited after the gas-water relationship deteriorates in the middle and late stages of reservoir development. Profile control and water shut-off technology has high implementation costs and a long implementation cycle, requiring a period of injection and adjustment to achieve the desired effect, resulting in poor practical application results. Summary of the Invention

[0004] To address the aforementioned problems, this invention aims to provide a method for improving the recovery rate of fractured bottom water gas reservoirs by draining water from the lower part of a horizontal well.

[0005] The technical solution of the present invention is as follows:

[0006] A method for improving the recovery rate of fractured bottom water gas reservoirs by draining the lower part of a horizontal well includes the following steps:

[0007] S1: Delineate the bottom water breakthrough zone of the target fractured bottom water gas reservoir, and delineate the favorable development area of ​​the target fractured bottom water gas reservoir within the bottom water breakthrough zone;

[0008] S2: Determine the high gas saturation strata and gas-water interface location of the target fractured bottom water gas reservoir;

[0009] S3: Obtain the actual production data of the target fractured bottom water gas reservoir, and determine the production wells of the target fractured bottom water gas reservoir that have been completely flooded and shut down based on the actual production data;

[0010] S4: Based on the favorable development area, the high gas saturation layer, and the gas-water interface location, a horizontal well is drilled using the wellbore of the production vertical well to drain water and improve the recovery rate.

[0011] Preferably, in step S1, when the water intrusion volume of a single grid in the three-dimensional numerical model of the target fractured bottom water gas reservoir is greater than the water intrusion threshold, the corresponding grid region is the bottom water breakthrough zone.

[0012] Preferably, in step S1, when delineating the favorable development area, the delineation principle adopted is as follows:

[0013] (1) The abundance of reserves is greater than the abundance threshold;

[0014] (2) The formation pressure is greater than the formation pressure threshold;

[0015] (3) The reservoir permeability is greater than the reservoir permeability threshold.

[0016] Preferably, in step S2, the high gas saturation layer refers to a layer with a gas saturation greater than 0.5; when the water saturation is equal to 1, the location is below the gas-water interface; when the water saturation is equal to the water saturation of the target fractured bottom water gas reservoir geological model, the location is above the gas-water interface.

[0017] Preferably, in step S4, when drilling a horizontal well, the horizontal section of the horizontal well is located in the bottom water breakthrough zone on the plane, and the horizontal section of the horizontal well is located 50m away from the pure gas reservoir in the gas-water transition zone above the gas-water interface.

[0018] Preferably, the following steps are also included:

[0019] S5: Obtain the basic parameters of the target fractured bottom water gas reservoir, and establish a three-dimensional numerical model of the target fractured bottom water gas reservoir based on the basic parameters;

[0020] S6: Based on the three-dimensional numerical model, and using the existing development strategy for the target fractured bottom water gas reservoir for many years, calculate the cumulative gas production of the existing development strategy for many years, and calculate the recovery rate of the existing development strategy based on the cumulative gas production.

[0021] S7: Based on the three-dimensional numerical model, develop the target fractured bottom water gas reservoir by drilling horizontal wells for the same number of years as the existing development strategy, calculate the cumulative gas production of the horizontal well drilling method II, and calculate the recovery rate II of the horizontal well drilling method based on the cumulative gas production II.

[0022] S8: Calculate the recovery rate increase of the horizontal well drilling method based on the recovery rate one and the recovery rate two.

[0023] Preferably, in step S5, the basic parameters include formation porosity, permeability, gas saturation, water saturation, relative permeability curve of the gas phase, relative permeability curve of the water phase, capillary pressure curve, reservoir burial depth, gas-water interface depth, effective reservoir thickness, degree of reservoir heterogeneity, formation temperature, formation pressure, well location coordinates of a single well, wellbore data of a single well, perforation data of a single well, and fracturing data of a single well.

[0024] Preferably, in step S5, after establishing the three-dimensional numerical model of the target fractured bottom water gas reservoir based on the basic parameters, the following steps are also included:

[0025] Historical production dynamic data of the target fractured bottom water gas reservoir are obtained, and the three-dimensional numerical model is historically fitted based on the historical production dynamic data; the three-dimensional numerical model is updated based on the historical fitting results.

[0026] Preferably, the historical production dynamic data includes daily gas production, daily water production, bottom hole flowing pressure, wellhead pressure, production time, and water cut of a single well.

[0027] Preferably, historical data fitting includes block historical data fitting and single-well historical data fitting; the block historical data fitting includes reserve fitting; the single-well historical data fitting includes single-well daily gas production fitting, single-well daily water production fitting, single-well wellhead pressure fitting, and single-well cumulative gas production fitting.

[0028] The beneficial effects of this invention are:

[0029] This invention utilizes horizontal wells drilled within vertical wellbores. Leveraging the large water control area and strong drainage capacity of horizontal wells, it significantly extracts bottom water that has invaded early gas reservoirs, causing the gas-water interface to lower. Simultaneously, horizontal wells prevent bottom water from rising upwards, improving the seepage conditions of natural gas within the reservoir. This allows adjacent production vertical wells, previously shut down due to flooding, to resume production, transforming intermittent production wells into continuous production wells, thereby enhancing the recovery rate of carbonate fractured bottom water gas reservoirs. The invention has demonstrated significant effectiveness in field applications and has broad application value in enhancing the recovery rate of mid-to-late stages of carbonate fractured bottom water gas reservoir development. Attached Figure Description

[0030] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0031] Figure 1 This is a schematic diagram illustrating the technical principle of the present invention for improving the recovery rate;

[0032] Figure 2 The production curve of a gas well that transforms from a flooded gas well to a gas-producing gas well after horizontal well drainage is implemented in a specific embodiment;

[0033] Figure 3 This is a production curve of a gas well that transitioned from intermittent to continuous production after horizontal well drainage was implemented in a specific embodiment.

[0034] Figure 4 This is a schematic diagram of the water saturation distribution of a gas reservoir before horizontal well drainage is implemented in a specific embodiment.

[0035] Figure 5 This is a schematic diagram of the water saturation distribution of a gas reservoir after horizontal well drainage in a specific embodiment. Detailed Implementation

[0036] The present invention will be further described below with reference to the accompanying drawings and embodiments. It should be noted that, unless otherwise specified, the embodiments and technical features described in this application can be combined with each other. It should also be pointed out that, unless otherwise indicated, all technical and scientific terms used in this application have the same meaning as commonly understood by one of ordinary skill in the art to which this application pertains. The terms "comprising" or "including" and similar words used in this invention refer to elements or objects preceding the word that encompass the elements or objects listed following the word and their equivalents, without excluding other elements or objects.

[0037] like Figure 1 As shown, the present invention provides a method for improving the recovery rate of fractured bottom water gas reservoirs by draining water from the lower part of a horizontal well, comprising the following steps:

[0038] S1: Delineate the bottom water breakthrough zone of the target fractured bottom water gas reservoir, and delineate the favorable development area of ​​the target fractured bottom water gas reservoir within the bottom water breakthrough zone.

[0039] In one specific embodiment, when the water intrusion volume of a single grid in the three-dimensional numerical model of the target fractured bottom-water gas reservoir exceeds the water intrusion threshold, the corresponding grid region is designated as the bottom-water breakthrough zone. Optionally, the area of ​​a single grid is 100 × 100 m, and the water intrusion threshold is 0.1 m.3 / d.

[0040] In one specific embodiment, the delineation principle used when defining the favorable development area is as follows:

[0041] (1) The abundance of reserves is greater than the abundance threshold;

[0042] (2) The formation pressure is greater than the formation pressure threshold;

[0043] (3) The reservoir permeability is greater than the reservoir permeability threshold.

[0044] In the above embodiments, the favorable development zone is delineated within the bottom water breakthrough zone because water intrusion provides a pressurized supply and fractures have good permeability; delineating areas with a reserve abundance greater than the reserve abundance threshold (i.e., large remaining reserves) as favorable development zones ensures the material basis for potential tapping; delineating areas with formation pressure greater than the formation pressure threshold (i.e., high formation pressure) as favorable development zones helps gas wells carry fluid and provide long-term energy supply; delineating areas with reservoir permeability greater than the reservoir permeability threshold (i.e., high reservoir permeability) as favorable development zones helps natural gas seepage; all of these factors enable subsequent horizontal wells to better improve recovery rates.

[0045] In one specific embodiment, the abundance threshold is 1.0 × 10⁻⁶. 8 m 3 / km 2 The formation pressure threshold is 19 MPa, and the reservoir permeability threshold is 0.045 mD.

[0046] S2: Determine the high gas saturation layer and gas-water interface location of the target fractured bottom water gas reservoir.

[0047] In one specific embodiment, the high gas saturation layer refers to a layer with a gas saturation greater than 0.5; when the water saturation is equal to 1, the location is below the gas-water interface; when the water saturation is equal to the water saturation of the target fractured bottom water gas reservoir geological model, the location is above the gas-water interface.

[0048] In the above embodiments, the location of the gas-water interface is specifically determined based on the actual logging and well test results of the target fractured bottom-water gas reservoir. In this invention, determining the location of the gas-water interface is to ensure that the horizontal well is vertically positioned above the gas-water interface, providing a fundamental theoretical basis for the design depth of the subsequent horizontal section of the horizontal well and improving the drainage effect of the horizontal well.

[0049] S3: Obtain the actual production data of the target fractured bottom water gas reservoir, and determine the production wells of the target fractured bottom water gas reservoir that have been completely flooded and shut down based on the actual production data.

[0050] S4: Based on the favorable development area, the high gas saturation layer, and the gas-water interface location, a horizontal well is drilled using the wellbore of the production vertical well to drain water and improve the recovery rate.

[0051] In one specific embodiment, when drilling a horizontal well, the horizontal section of the horizontal well is located in the bottom water breakthrough zone on the plane, and the horizontal section of the horizontal well is located 50m above the gas-water interface in the gas-water transition zone from the pure gas reservoir.

[0052] This invention utilizes newly drilled horizontal wells to drain bottom water that has intruded into gas reservoirs through fractures, thereby reducing the water saturation at the bottom of adjacent vertical wells, improving seepage conditions at the bottom of vertical wells, and ultimately increasing the recovery rate of fractured carbonate bottom-water gas reservoirs. Specifically, leveraging the advantages of the newly drilled horizontal well's large water control area and strong drainage capacity, a large amount of bottom water that has intruded into the gas reservoir in the early stages is extracted, causing the gas-water interface to drop. Simultaneously, the horizontal well can prevent bottom water from rising upwards, improving the seepage conditions of natural gas within the reservoir. This allows production vertical wells adjacent to the newly drilled horizontal well, which had been shut down due to flooding, to resume production, transforming previously intermittent production vertical wells into continuous production wells, thus achieving the goal of increasing the recovery rate of fractured carbonate bottom-water gas reservoirs.

[0053] In one specific embodiment, the method for improving the recovery rate of fractured bottom water gas reservoirs by draining the lower part of a horizontal well according to the present invention further includes the following steps:

[0054] S5: Obtain the basic parameters of the target fractured bottom water gas reservoir, and establish a three-dimensional numerical model of the target fractured bottom water gas reservoir based on the basic parameters.

[0055] In a specific embodiment, the basic parameters include formation porosity, permeability, gas saturation, water saturation, relative permeability curves of the gas phase and water phase, capillary pressure curves, reservoir burial depth, gas-water interface depth, effective reservoir thickness, degree of reservoir heterogeneity, formation temperature, formation pressure, well location coordinates of a single well, wellbore data of a single well, perforation data of a single well, and fracturing data of a single well. When establishing the three-dimensional numerical model, the three-dimensional numerical model includes a pressure system, a capillary pressure system, a porosity model, a permeability model, a fluid saturation model, a rock physics model, and a wellbore flow model, etc.

[0056] In a specific embodiment, after establishing a three-dimensional numerical model of the target fractured bottom water gas reservoir based on the basic parameters, the method further includes the following steps: obtaining historical production dynamic data of the target fractured bottom water gas reservoir, and performing historical fitting on the three-dimensional numerical model based on the historical production dynamic data; updating the three-dimensional numerical model based on the historical fitting results.

[0057] In the above embodiments, historical fitting of the three-dimensional numerical model can improve the accuracy of the three-dimensional numerical model and provide technical support for subsequent calculation of the accurate recovery rate improvement.

[0058] In one specific embodiment, the historical production dynamic data includes daily gas production, daily water production, bottom hole flowing pressure, wellhead pressure, production time, and water cut of a single well; when performing historical fitting, it includes block historical fitting and single well historical fitting; the block historical fitting includes reserve fitting; the single well historical fitting includes single well daily gas production fitting, single well daily water production fitting, single well wellhead pressure fitting, and single well cumulative gas production fitting.

[0059] S6: Based on the three-dimensional numerical model, and considering the existing development strategy for the target fractured bottom water gas reservoir over many years, calculate the cumulative gas production of the existing development strategy over many years, and calculate the recovery rate of the existing development strategy based on the cumulative gas production.

[0060] S7: Based on the three-dimensional numerical model, calculate the cumulative gas production of the horizontal well drilling method for the same number of years as the existing development strategy, using the same method of developing the target fractured bottom water gas reservoir with horizontal wells, and calculate the recovery rate of the horizontal well drilling method based on the cumulative gas production of the horizontal well drilling method.

[0061] S8: Calculate the recovery rate increase of the horizontal well drilling method based on the recovery rate one and the recovery rate two.

[0062] In one specific embodiment, both steps S6 and S7 involve a development period of 20 years. It should be noted that the development period is a manually set value and can be set according to actual needs.

[0063] In one specific embodiment, the increase in recovery rate is calculated by subtracting the first recovery rate from the second recovery rate.

[0064] In a specific embodiment, taking a fractured bottom-water gas reservoir in the Sichuan Basin as an example, the method of improving the recovery rate of fractured bottom-water gas reservoirs by draining water from the lower part of a horizontal well as described in this invention is used to improve its recovery rate. Specifically, the following steps are included:

[0065] (1) A three-dimensional numerical model of the target gas reservoir was established. The horizontal grid size of the established three-dimensional numerical model is 100×100m, and the vertical grid size is 1m per grid, with a total of 280×187×414=21,677,040 grids. The model matrix porosity is between 0 and 0.1, and the fracture porosity is generally less than 0.01; the average permeability of the model matrix is ​​0.13mD, and the average porosity of the fractures is 1.87mD; the average water saturation of the model matrix is ​​0.66, and the reservoir abundance is between 1 and 9×10⁻⁶. 8 m / km2 The model matrix gas-water interface is at -2489m, and the fracture gas-water interface is at -2434m. The original formation pressure is 29.53MPa, the formation temperature is 118℃, the relative density of the gas phase is 0.64, and the density of the formation water is 1.055g / cm³. 3 The formation water viscosity is 0.27 cp, the gas reservoir volume factor is 0.00445, and the rock compressibility factor is 1.133 × 10⁻⁶. -5 MPa -1 The standard temperature is 16.15℃ and the standard pressure is 0.098MPa.

[0066] (2) Historical data fitting was performed on the 82 production wells of the aforementioned three-dimensional numerical model. The fitting process included fitting the overall gas production of the block, fitting the water production, and fitting the water production and wellhead pressure of individual wells. The fitting of individual wells mainly employed the approach of trial calculations, coarse adjustment by dividing the area into zones, and fine adjustment of individual well attributes. This was achieved by adjusting parameters such as fracture permeability, breakpoint water saturation, water body size, and water permeability. The fitting results show that the overall historical fitting accuracy of the three-dimensional numerical model exceeds 85%, indicating strong model reliability, and it can be used for subsequent production prediction.

[0067] (3) Delineate the bottom water breakthrough zone of the target gas reservoir, and delineate the favorable development zone of the target gas reservoir within the bottom water breakthrough zone. Based on the principle of favorable development zone delineation, four favorable development zones are delineated, with the first favorable zone having a reserve abundance of 1.2 × 10⁻⁶. 8 m 3 / km 2 The formation pressure is 20.2 MPa, and the average permeability is greater than 0.045 mD; the reserve abundance in favorable area 2 is 1.1 × 10⁻⁶ m³ / s. 8 m 3 / km 2 The formation pressure is 22.3 MPa, and the average permeability is greater than 0.05 mD; the reserve abundance in favorable area 3 is 1.3 × 10⁻⁶. 8 m 3 / km 2 The formation pressure is 19.5 MPa, and the average permeability is greater than 0.045 mD; the reserve abundance in favorable area four is 0.9 × 10⁻⁶ mD. 8 m 3 / km 2 The formation pressure is 20.5 MPa, and the average permeability is greater than 0.1 mD.

[0068] (4) Based on the actual logging and well test results of the gas reservoir, determine the gas-water interface location of the target gas reservoir.

[0069] (5) Based on the actual production data of the gas reservoir, identify 5 production wells (vertical wells) that have been completely flooded and shut down. Use the wellbore of the 5 production wells (vertical wells) to drill horizontal wells. The horizontal section of the horizontal well is located in the bottom water breakthrough zone on the plane, and its horizontal section length is 500m. Vertically, it is located 50m away from the pure gas reservoir in the gas-water transition zone above the gas-water interface.

[0070] After implementing the above-mentioned enhanced oil recovery method on the target gas reservoir, one gas well in the target gas reservoir resumed production after being shut in by water flooding, and the production curve is as follows. Figure 2 As shown, the three gas wells transitioned from intermittent to continuous production, as indicated by the production curves. Figure 3 As shown.

[0071] The reservoir water saturation of the target gas reservoir before implementing the above method in the three-dimensional numerical model is as follows: Figure 4 As shown, the reservoir water saturation after implementing the above method is as follows: Figure 5 As shown, comparison Figure 4 and Figure 5 It can be observed that the reservoir water saturation is significantly reduced after implementing the horizontal well drainage method.

[0072] Using the aforementioned three-dimensional numerical model fitted with historical data, and employing the existing production strategy for the target gas reservoir over 20 years, the cumulative gas production over this 20-year development method is estimated to be 37.09 × 10⁻⁶. 8 m 3 The calculation showed that the final recovery rate of the gas reservoir produced by this method over 20 years was 43.98%.

[0073] Using the aforementioned three-dimensional numerical model fitted with historical data, and employing the horizontal well drainage method described above, the cumulative gas production over 20 years was 62.12 × 10⁻⁶. 8 m 3 The calculation showed that the final recovery rate of the gas reservoir produced by this method over 20 years was 49.79%.

[0074] Subtracting the recovery rate from the recovery rate developed using the horizontal well drainage method, the recovery rate of the gas reservoir improved by 5.81% is obtained by developing the horizontal well drainage method.

[0075] In summary, this invention addresses the challenges of developing fractured carbonate bottom-water gas reservoirs in the late stages, after the deterioration of the gas-water relationship. It leverages the advantages of horizontal wells—large water control area and strong drainage capacity—to significantly drain intrusive bottom water, causing the gas-water interface to lower. Simultaneously, horizontal wells prevent bottom water from rising upwards, improving the seepage conditions of natural gas within the reservoir. This allows production wells near newly drilled horizontal wells, which had been shut down due to water flooding, to resume production, transforming previously intermittent production wells into continuous production wells. Ultimately, this invention aims to improve the recovery rate of fractured carbonate bottom-water gas reservoirs. Compared to existing technologies, this invention represents a significant advancement.

[0076] The above description is merely a preferred embodiment of the present invention and is not intended to limit the present invention in any way. Although the present invention has been disclosed above with reference to preferred embodiments, it is not intended to limit the present invention. Any person skilled in the art can make some modifications or alterations to the above-disclosed technical content to create equivalent embodiments without departing from the scope of the present invention. Any simple modifications, equivalent changes, and alterations made to the above embodiments based on the technical essence of the present invention without departing from the scope of the present invention shall still fall within the scope of the present invention.

Claims

1. A method for improving the recovery rate of fractured bottom water gas reservoirs by draining water from the lower part of a horizontal well, characterized in that, Includes the following steps: S1: Delineate the bottom water breakthrough zone of the target fractured bottom water gas reservoir, and delineate the favorable development area of ​​the target fractured bottom water gas reservoir within the bottom water breakthrough zone; S2: Determine the high gas saturation strata and gas-water interface location of the target fractured bottom water gas reservoir; The high gas saturation layer refers to a layer with a gas saturation greater than 0.5; when the water saturation is equal to 1, the location is below the gas-water interface; when the water saturation is equal to the water saturation of the target fractured bottom water gas reservoir geological model, the location is above the gas-water interface. S3: Obtain the actual production data of the target fractured bottom water gas reservoir, and determine the production wells of the target fractured bottom water gas reservoir that have been completely flooded and shut down based on the actual production data; S4: Based on the favorable development area, the high gas saturation layer and the gas-water interface location, use the wellbore of the production vertical well to drill a horizontal well to drain water and improve the recovery rate. When drilling a horizontal well, the horizontal section of the horizontal well is located in the bottom water breakthrough zone on the plane, and the horizontal section of the horizontal well is located 50 m above the gas-water interface in the gas-water transition zone from the pure gas reservoir.

2. The method for improving the recovery rate of fractured bottom water gas reservoirs by draining the lower part of a horizontal well according to claim 1, characterized in that, In step S1, when the water intrusion volume of a single grid in the three-dimensional numerical model of the target fractured bottom water gas reservoir is greater than the water intrusion threshold, the corresponding grid region is the bottom water breakthrough zone.

3. The method for improving the recovery rate of fractured bottom water gas reservoirs by draining the lower part of a horizontal well according to claim 1, characterized in that, In step S1, the delineation principle used when defining the favorable development area is as follows: (1) The abundance of reserves is greater than the abundance threshold; (2) The formation pressure is greater than the formation pressure threshold; (3) The reservoir permeability is greater than the reservoir permeability threshold.

4. The method for improving the recovery rate of fractured bottom water gas reservoirs by draining the lower part of a horizontal well according to any one of claims 1-3, characterized in that, It also includes the following steps: S5: Obtain the basic parameters of the target fractured bottom water gas reservoir, and establish a three-dimensional numerical model of the target fractured bottom water gas reservoir based on the basic parameters; S6: Based on the three-dimensional numerical model, and using the existing development strategy for the target fractured bottom water gas reservoir for many years, calculate the cumulative gas production of the existing development strategy for many years, and calculate the recovery rate of the existing development strategy based on the cumulative gas production. S7: Based on the three-dimensional numerical model, calculate the cumulative gas production of the horizontal well drilling method for the same number of years as the existing development strategy, using the same method to develop the target fractured bottom water gas reservoir. Calculate the recovery rate of the horizontal well drilling method based on the cumulative gas production of the horizontal well drilling method. S8: Calculate the recovery rate increase of the horizontal well drilling method based on the recovery rate one and the recovery rate two.

5. The method for improving the recovery rate of fractured bottom water gas reservoirs by draining the lower part of a horizontal well according to claim 4, characterized in that, In step S5, the basic parameters include formation porosity, permeability, gas saturation, water saturation, relative permeability curve of the gas phase, relative permeability curve of the water phase, capillary pressure curve, reservoir burial depth, gas-water interface depth, effective reservoir thickness, degree of reservoir heterogeneity, formation temperature, formation pressure, well location coordinates of a single well, wellbore data of a single well, perforation data of a single well, and fracturing data of a single well.

6. The method for improving the recovery rate of fractured bottom water gas reservoirs by draining the lower part of a horizontal well according to claim 4, characterized in that, In step S5, after establishing the three-dimensional numerical model of the target fractured bottom water gas reservoir based on the basic parameters, the following steps are also included: Historical production dynamic data of the target fractured bottom water gas reservoir are obtained, and the three-dimensional numerical model is historically fitted based on the historical production dynamic data; the three-dimensional numerical model is updated based on the historical fitting results.

7. The method for improving the recovery rate of fractured bottom water gas reservoirs by draining the lower part of a horizontal well according to claim 6, characterized in that, The historical production dynamic data includes daily gas production, daily water production, bottom hole flowing pressure, wellhead pressure, production time, and water cut of a single well.

8. The method for improving the recovery rate of fractured bottom water gas reservoirs by draining the lower part of a horizontal well according to claim 7, characterized in that, Historical data fitting includes block historical data fitting and single-well historical data fitting; the block historical data fitting includes reserve fitting; the single-well historical data fitting includes single-well daily gas production fitting, single-well daily water production fitting, single-well wellhead pressure fitting, and single-well cumulative gas production fitting.

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