A multi-stage ball-throwing optimization method and device

Abstract

This invention provides a multi-stage ball-drop optimization method and apparatus, belonging to the field of oil and gas reservoir fracturing. The method first obtains perforation diameter variation curves and perforation friction variation curves experimentally. Then, it uses these curves to determine the optimized number of ball-drop stages, the number of balls dropped, and the diameter of the temporary plugging ball. This invention effectively solves the problem of insufficient optimization methods for the number of plugging stages, the number of balls dropped, and the diameter of the temporary plugging ball in ball-drop temporary plugging fracturing, thus helping to improve the effectiveness of ball-drop temporary plugging fracturing.

Description

Technical Field

[0001] This invention belongs to the field of oil and gas reservoir fracturing and stimulation, specifically relating to a multi-stage ball-drop optimization method and apparatus. Background Technology

[0002] In shale gas horizontal well fracturing, ball-dropping is a common method to plug the perforation hole to promote balanced stimulation and increase the stimulation volume. Currently, the optimization of the number of ball-dropping stages and the diameter of the temporary plugging ball relies mainly on experience, lacking corresponding optimization methods.

[0003] Chinese patent publication CN202010498554.4 discloses an optimization method for ball-dropped temporary plugging and diversion fracturing in shale gas horizontal wells, belonging to the field of oil and gas field hydraulic fracturing technology. It includes the following steps: (1) analyzing the forces acting on the temporary plugging ball during its movement in the wellbore; (2) establishing a formula for the movement speed of the temporary plugging ball in the wellbore based on the principle of mechanical equilibrium; (3) defining the temporary plugging ball setting factor as the ratio of drag force to inertial force; (4) calculating the temporary plugging ball setting factor based on field construction data and studying the feasibility of ball-dropped temporary plugging and diversion construction under field conditions. When the temporary plugging ball setting factor calculated in step (4) is much greater than 1, step (5) is also included: (5) calculating the number of temporary plugging balls: optimizing the construction parameters of the temporary plugging balls based on the calculated number of temporary plugging balls. This invention can be used to optimize the design of construction parameters for ball-dropped temporary plugging and diversion fracturing in shale gas horizontal wells, study the factors affecting the sealing effect of the temporary plugging balls, calculate the number of temporary plugging balls used under different construction conditions, and provide theoretical guidance for field construction decisions. However, the patent publication does not consider the change in perforation diameter during fracturing; it only optimizes the number of plugging balls without addressing a method for optimizing the plugging ball diameter. Furthermore, it does not propose an optimization method for the number of ball drops during fracturing.

[0004] In the publicly available Chinese literature "Numerical Simulation Study and Pilot Experiment of Multi-Cluster Fracturing and Temporary Plugging Technology in Horizontal Shale Gas Wells" (Natural Gas Industry, March 2021), in order to provide technical support for optimizing the fracturing process parameters of horizontal shale gas wells, the relevant parameters of the "single-section 5-cluster perforation + ball-dropping temporary plugging and diversion" process were optimized based on numerical simulation. A pilot test of "multi-cluster fracturing + temporary plugging and diversion within a section" was carried out in the YS112HX-1 horizontal well in the Zhaotong National Shale Gas Demonstration Zone. Finally, a comprehensive post-fracturing evaluation was conducted by combining microseismic monitoring, micro-deformation monitoring, and pressure recovery well test analysis. The research results show that: ① The timing for ball deployment is when the injection volume of fracturing fluid is 900 m3, the number of balls deployed is 1.0 to 1.2 times the number of required plugging holes, and the diameter of the temporary plugging balls is not less than 13.5 mm; ② The results of microseismic, inclinometer, and well test results are consistent. Single-section 5-cluster perforation + ball deployment and temporary plugging diversion fracturing has better fracture complexity than conventional 3-cluster perforation fracturing. Although the permeability of the matrix zone of well HX-1 is low, the permeability of the high-permeability zone is higher, resulting in better stimulation effect; ③ Well test interpretation shows that the fracture half-length of well HX-1 does not exceed 100 m, which has a certain error with the fracture half-length in numerical simulation. The well test results can be used to optimize the numerical simulation parameters; ④ Well HX-1, which adopts the "multi-cluster within a section + temporary plugging diversion" technology, has the characteristics of early gas breakthrough, high wellhead pressure, and high daily gas production. The conclusion is that the research and experimental results have guiding significance for the optimization of fracturing process parameters of shale gas horizontal wells.

[0005] The publicly available Chinese literature, "Study on the Sealing Effect of Temporary Plugging Balls in Shale Gas Horizontal Well Fracturing" (Drilling and Production Technology, November 2020), established a motion equation for temporary plugging balls by studying the stress conditions of the balls near the wellbore and perforation holes, as well as the pressure changes before and after plugging. Three indicators for evaluating the setting effect of the temporary plugging balls were proposed. Based on field fracturing data, a model feasibility study was conducted, and the sealing effect of temporary plugging balls in the fracturing of a shale gas horizontal well was analyzed. The study found that this model can be used to evaluate the sealing effect of temporary plugging balls. In the fracturing of the Fuling shale gas horizontal well, the effective utilization rate of temporary plugging balls exceeded 50% in 72.73% of the sections, and the setting efficiency of the temporary plugging balls was between 0.25 and 0.59, effectively sealing the fluid ingress perforation and achieving the purpose of diversion fracturing. The effective utilization rate of a single ball deployment in secondary fracturing was high, while the effective utilization rate of two ball deployments in tertiary fracturing was low. Therefore, the single ball deployment method in secondary fracturing is recommended for fracturing operations.

[0006] In the publicly available Chinese literature "Simulation of fracture propagation and optimization of ball-dropping temporary plugging under the influence of non-uniform stress field" (Natural Gas Industry, March 2020), a fully coupled model of horizontal well "wellbore-hole-fracture propagation" was established based on the boundary element method. A calculation method for the distribution of temporary plugging balls was proposed, and then the number of balls dropped, the timing of ball dropping, the number of ball droppings, and their influence on the propagation of multiple clusters of fractures were simulated when the section was temporarily plugged and turned under the initial non-uniform stress field conditions. The research results show that: ① During fracturing, the flow-limiting effect of perforation friction balances the difference in fluid inflow caused by induced stress interference, thus reducing the resistance difference in fluid flow among different fracture clusters; ② After considering the influence of the non-uniform distribution of the initial stress field, the fluid inflow of each fracture cluster changes significantly, and even ineffective perforation clusters without fluid inflow appear in high-stress areas. After ball-dropping, these ineffective perforation clusters will generate new fractures; ③ When the initial minimum horizontal principal stress difference (Δσh) exceeds 3MPa, appropriately increasing the number of balls dropped in the middle stage of construction (greater than half of the total number of perforations in a single section), or temporarily plugging the perforations with balls in the early and middle stages (including dropping balls in batches in the early and middle stages), is beneficial to reducing the degree of non-uniform propagation of fracture clusters; ④ When the initial Δσh is less than 2MPa, the number of balls dropped should be reduced or balls should be dropped in the middle and later stages of construction, otherwise the non-uniform propagation of fracture clusters will be aggravated.

[0007] The Chinese publicly available literature, "Horizontal Well Ball-Drop Fracturing Technology and Field Application" (Petroleum Drilling and Production Technology, December 2009), proposes a horizontal well ball-drop fracturing technology for horizontal wells that have already undergone extensive perforation and cannot be equipped with downhole tools. Employing a systematic optimization design method, this technology, based on fracture type prediction, fine reservoir geology segmentation, fracture parameter optimization, fracturing material selection, ball-drop batch and quantity optimization, and construction pressure prediction, forms an integrated ball-drop fracturing technology that does not require special downhole tools.

[0008] The four published documents mentioned above mainly studied the timing of ball deployment, the diameter of temporary plugging balls, the distribution method of temporary plugging balls, and the evaluation method of the plugging effect of temporary plugging balls. However, they did not achieve the optimization of the number of ball deployment levels, the number of temporary plugging balls, and the diameter of temporary plugging balls in fracturing operations. Summary of the Invention

[0009] The purpose of this invention is to solve the problems existing in the prior art and provide a multi-stage ball-drop optimization method and device to optimize the multi-stage ball-drop method during horizontal well fracturing, and to solve the problem of lack of optimization methods for the number of ball-drop stages and the diameter of the temporary plugging balls during ball-drop temporary plugging fracturing.

[0010] This invention is achieved through the following technical solution:

[0011] In a first aspect, the present invention provides a multi-stage ball-throwing optimization method, wherein the method first obtains a perforation orifice diameter variation curve and a perforation orifice friction variation curve through experiments, and then uses the perforation orifice diameter variation curve and the perforation orifice friction variation curve to obtain the optimized ball-throwing stage, the number of balls thrown, and the diameter of the temporarily blocked ball.

[0012] A further improvement of the present invention is that the method includes:

[0013] (1) Conduct perforation erosion experiments under different sand ratios, discharge rates and proppant particle sizes to obtain perforation diameter variation curves.

[0014] (2) Conduct hole friction test experiments under different hole numbers, hole diameters and discharge rates, and obtain the hole friction variation curves of the perforation holes.

[0015] (3) Determine the pitching level and the number of pitches;

[0016] (4) Determine the diameter of the temporary plugging ball.

[0017] The operation of step (1) includes:

[0018] Erosion experiments were conducted on perforation holes under different sand ratios, discharge rates, and proppant particle sizes to obtain discrete data points.

[0019] Draw a graph with time on the horizontal axis and the diameter of the perforation hole on the vertical axis;

[0020] By fitting discrete data points, multiple curves are obtained showing the change of perforation orifice diameter over time under different sand ratios, discharge rates, and proppant particle sizes, thus obtaining a perforation orifice diameter variation curve chart.

[0021] A further improvement of the present invention is that the operation of step (2) includes:

[0022] Experiments were conducted to test the friction of the orifice under different numbers of orifices, orifice diameters and discharge rates, and discrete data points were obtained.

[0023] The graph is drawn with the number of holes as the horizontal axis and the hole friction as the vertical axis.

[0024] By fitting discrete data points, multiple curves are obtained that show the variation of perforation friction with the number of holes under different discharge rates and orifice diameters, thus obtaining the perforation orifice friction variation curve chart.

[0025] A further improvement of the present invention is that the operation of step (3) includes:

[0026] (31) The pitching level N is calculated using the following formula:

[0027] N=(P max -Pmin ) / p i (1)

[0028] Among them, P max P min It refers to the maximum and minimum values ​​in the predicted or actual construction pressure data, p i This refers to the increase in pressure during each construction phase;

[0029] (32) Obtain the increase p of the perforation eye friction from the perforation eye friction change curve. i The number of holes that need to be blocked is used to determine the number of balls thrown.

[0030] A further improvement of the present invention is that the operation of step (32) includes:

[0031] Determine the construction discharge rate, borehole diameter, and number of boreholes n2;

[0032] Find the curve corresponding to the construction flow rate and hole diameter in the perforation hole friction variation curve chart, and use the number of holes n2 to find the hole friction p2 under the flow rate, hole diameter and number of holes on the curve.

[0033] Then find the orifice friction as p2+p on the curve. i The corresponding number of holes is n1;

[0034] The number of holes n that need to be plugged can be calculated using the following formula:

[0035] n = n2 - n1

[0036] The number of pitches is

[0037] A further improvement of the present invention is that the operation of step (4) includes:

[0038] (41) Divide the designed pumping scheme into N stages;

[0039] (42) Determine the discharge rate, sand ratio, and proppant particle size for each stage according to the pumping scheme;

[0040] (43) Obtain the orifice diameter φ at the end of each stage based on the orifice diameter variation curve chart. i This diameter is the diameter of the temporary plugging ball.

[0041] A further improvement of the present invention is that the operation of step (43) includes:

[0042] Calculate the average sand ratio, average discharge rate, average proppant particle size, and duration of each stage at the end of each stage.

[0043] Find the corresponding curve on the perforation orifice diameter variation curve chart based on the average sand ratio, average discharge rate, and average proppant particle size values.

[0044] Find the corresponding orifice diameter on the curve based on the duration; this orifice diameter is the temporary plugging ball diameter.

[0045] A second aspect of the present invention provides a perforation hole erosion experimental apparatus for performing the perforation hole erosion experiment in the above-mentioned multi-stage ball-throwing optimization method. The perforation hole erosion experimental apparatus includes: an erosion pumping assembly, a safety shield, and an experimental tubing column disposed within the inner cavity of the safety shield.

[0046] The safety shield is a cylindrical structure with a liquid discharge channel at its lower end.

[0047] One end of the experimental tubular column is open, and the other end is closed;

[0048] The erosion pumping assembly is connected to the open end of the experimental tubing via a pipeline.

[0049] A further improvement of the present invention is that the erosion pumping assembly includes a small plunger pump, a proppant fracturing fluid mixer, a proppant delivery device, and a proppant storage tank connected in sequence.

[0050] The outlet of the small plunger pump is connected to the open end of the experimental column via a pipeline.

[0051] The erosion pumping assembly further includes a fracturing fluid injection pump and a fracturing fluid storage tank connected in sequence, and the outlet of the fracturing fluid injection pump is connected to the proppant fracturing fluid mixer.

[0052] The proppant delivery device, proppant fracturing fluid mixer, mini plunger pump, and fracturing fluid injection pump are also connected to the control and data recording terminal.

[0053] A third aspect of the present invention provides a perforation friction test apparatus for performing the perforation friction test experiment in the above-described method. The perforation friction test apparatus includes: a fracturing fluid pumping assembly, a safety shield, and an experimental tubing column disposed within the inner cavity of the safety shield.

[0054] The safety shield is a cylindrical structure with a liquid discharge channel at its lower end.

[0055] One end of the experimental tubular column is open, and the other end is closed;

[0056] The fracturing fluid pumping assembly is connected to the open end of the experimental tubing via a pipeline.

[0057] A further improvement of the present invention is that the fracturing fluid injection assembly includes a small plunger pump, a fracturing fluid injection pump, and a fracturing fluid storage tank connected in sequence.

[0058] The outlet of the small plunger pump is connected to the open end of the experimental column via a pipeline.

[0059] The small piston pump is also connected to a control and data logging terminal;

[0060] The control and data recording terminal measures the pressure in the experimental tubing using a pressure gauge.

[0061] Compared with the prior art, the beneficial effects of the present invention are: the present invention can effectively solve the problem of the lack of optimization methods for the number of temporary plugging stages, the number of plugging balls, and the diameter of the temporary plugging balls in ball-throwing temporary plugging fracturing, and helps to improve the effect of ball-throwing temporary plugging fracturing. Attached Figure Description

[0062] Figure 1 A flowchart illustrating the steps of the method of this invention;

[0063] Figure 2 A schematic diagram of the perforation hole erosion experimental device in this embodiment of the invention;

[0064] Figure 3 A graph showing the variation curve of the perforation aperture diameter in an embodiment of the present invention;

[0065] Figure 4 A schematic diagram of the hole friction testing experimental device in an embodiment of the present invention;

[0066] Figure 5 A graph showing the variation curve of the perforation hole friction in an embodiment of the present invention; Detailed Implementation

[0067] The present invention will now be described in further detail with reference to the accompanying drawings:

[0068] like Figure 1 As shown, the method of the present invention includes:

[0069] 1) Conduct perforation erosion experiments under different sand ratios, discharge rates, and proppant particle sizes to obtain perforation diameter variation curves:

[0070] Erosion experiments were conducted on perforation holes under different sand ratios, discharge rates, and proppant particle sizes to obtain curves showing the change of perforation hole diameter with sand ratio, discharge rate, particle size, and time. Specifically, discrete data points were obtained through the perforation hole erosion experiments, and then a graph was plotted with time as the abscissa and perforation hole diameter as the ordinate. The discrete data points were fitted to obtain multiple curves showing the change of perforation hole diameter with time under different sand ratios, discharge rates, and proppant particle sizes. Each curve corresponds to a combination of sand ratio, discharge rate, and proppant particle size.

[0071] Example 1

[0072] This invention can employ, for example Figure 2 The perforation erosion test apparatus shown is used to conduct perforation erosion experiments. The apparatus includes an erosion pumping assembly, a safety shield 1, and an experimental string 2 housed within the safety shield 1. The safety shield 1 is a cylindrical structure with a liquid discharge channel 3 at its lower end. One end of the experimental string 2 is open, and the other end is closed. The erosion pumping assembly is connected to the open end of the experimental string 2 via a pipeline. Specifically, the erosion pumping assembly includes a small plunger pump 4, a proppant fracturing fluid mixer 5, a proppant delivery device 6, and a proppant storage tank 7 connected in sequence. The outlet of the small plunger pump 4 is connected to the open end of the experimental string 2 via a pipeline. The erosion pumping assembly further includes a fracturing fluid injection pump 10 and a fracturing fluid storage tank 9 connected in sequence. The outlet of the fracturing fluid injection pump 10 is connected to the proppant fracturing fluid mixer 5. Meanwhile, the proppant delivery device 6, the proppant fracturing fluid mixer 5, the mini plunger pump 4, and the fracturing fluid injection pump 10 are also connected to the control and data recording terminal 8. The control and data recording terminal 8 controls them and records experimental data. The control and data recording terminal 8 can be any existing terminal such as a computer. The proppant delivery device 6, the proppant fracturing fluid mixer 5, the mini plunger pump 4, the fracturing fluid injection pump 10, the fracturing fluid storage tank 9, and the proppant storage tank 7 are all existing products and will not be described in detail here.

[0073] The specific experimental procedure is as follows:

[0074] 1. Use dimensional analysis to perform similarity analysis and calculate the experimental parameters corresponding to the fracturing operation parameters, including the size of the experimental tubing, the size of the perforation holes, the flow rate, the sand concentration, and the viscosity of the experimental liquid.

[0075] 2. Based on the optimized tubing dimensions and perforation hole dimensions, fabricate experimental tubing using materials consistent with those used in production casing and perforate it.

[0076] 3. Prepare proppant and fracturing fluid according to the experimental design, store the proppant in the proppant storage tank, and store the fracturing fluid in the fracturing fluid storage tank;

[0077] 4. Set the proppant delivery rate, liquid discharge rate, and plunger pump injection rate on the control and data recording terminal according to the experimental design, and then conduct the experiment. During the experiment, the proppant is delivered from the proppant storage tank to the proppant fracturing fluid mixer using the proppant delivery device. At the same time, the fracturing fluid is delivered from the fracturing fluid storage tank to the proppant fracturing fluid mixer using the fracturing fluid pump. After the proppant and fracturing fluid are mixed in the proppant fracturing fluid mixer, they are pumped into the inner cavity of the experimental tubing through a small plunger pump, and then ejected through the perforations on the experimental tubing. The ejected liquid is finally discharged through the liquid discharge channel at the bottom of the safety shield.

[0078] 5. Pause the experiment at set intervals (e.g., 2 minutes), open the safety shield, measure and record the diameter of all holes, and repeat this process until the experiment ends.

[0079] 6. Repeat steps 1-5 to obtain curves showing the change in perforation orifice diameter over time under different sand ratios, discharge rates, and proppant particle sizes. This will yield a graph showing the change in perforation orifice diameter. Figure 3 As shown.

[0080] 2) Conduct orifice friction tests with different numbers of holes, orifice diameters, and discharge rates to obtain orifice friction variation curves:

[0081] Experiments were conducted to test the orifice friction resistance under different orifice numbers, orifice diameters, and displacements, and to obtain curves showing the variation of orifice friction resistance with displacement, orifice diameter, and orifice number. Specifically, discrete data points were obtained through orifice friction resistance testing, and then a graph was plotted with orifice number as the x-axis and orifice friction resistance as the y-axis. The discrete data points were fitted to obtain multiple curves showing the variation of orifice friction resistance with orifice number under different displacements and orifice diameters.

[0082]

Example 2

[0083] This invention can be employed as follows: Figure 4The aperture friction test apparatus shown is used for aperture friction testing. The apparatus includes a fracturing fluid pump assembly, a safety shield 1, and an experimental string 2 housed within the safety shield 1. The safety shield 1 is a cylindrical structure with a liquid discharge channel 3 at its lower end. One end of the experimental string 2 is open, and the other end is closed. The fracturing fluid pump assembly is connected to the open end of the experimental string via a pipeline. Specifically, the fracturing fluid pump assembly includes a small plunger pump 4, a fracturing fluid injection pump 10, and a fracturing fluid storage tank 9 connected in sequence. The outlet of the small plunger pump 4 is connected to the open end of the experimental string 2 via a pipeline. The small plunger pump 4 is also connected to a control and data recording terminal 8, which controls the small plunger pump 4 and records experimental data. The control and data recording terminal 8 can be any existing terminal, such as a computer. Furthermore, the control and data recording terminal 8 measures the pressure in the experimental string 2 using a pressure gauge 11. The small plunger pump 4, fracturing fluid injection pump 10, fracturing fluid storage tank 9, and pressure gauge 11 are all existing products and will not be described in detail here.

[0084] The specific experimental procedure is as follows:

[0085] 1. Use dimensional analysis to perform similarity analysis and calculate the experimental parameters corresponding to the fracturing operation parameters, including the size of the experimental tubing, the size and number of perforations, the flow rate, and the viscosity of the experimental liquid.

[0086] 2. Based on the optimized tubing dimensions, perforation hole dimensions, and number of holes, fabricate experimental tubing using materials consistent with those used in production casing and perforate it.

[0087] 3. Prepare fracturing fluid according to the experimental design and store the fracturing fluid in the fracturing fluid storage tank;

[0088] 4. Set the liquid discharge rate and plunger pump injection rate on the control and data recording terminal according to the experimental design, and then conduct the experiment. During the experiment, fracturing fluid is pumped from the fracturing fluid storage tank into the small plunger pump using the fracturing fluid pump. The small plunger pump then pumps the fracturing fluid into the inner cavity of the experimental tubing, and then sprays it out through the various perforations on the experimental tubing. The sprayed liquid is finally discharged through the liquid discharge channel at the bottom of the safety shield.

[0089] 5. Record the pressure data after the pressure gauge reading stabilizes.

[0090] 6. Repeat steps 1-5 to obtain the curves showing the variation of orifice friction with the number of orifices under different displacements and orifice diameters, thus obtaining the orifice friction variation curve chart, as shown below. Figure 5 As shown.

[0091] 3) Optimize pitching levels and number of pitches, and determine pitching levels and number of pitches:

[0092] Determine the maximum value P of the predicted or actual construction pressure data based on the fracturing design scheme. max and minimum value P min (Both the design plan and the construction pressure data contain maximum and minimum values), according to the predetermined pressure increase p for each construction period. i (A pressure value set by the user) is used to calculate the pitching level N:

[0093] N=(P max -P min ) / p i (1)

[0094] That is, the pressure starts from the minimum value and goes through N p times. i Then it increases to the maximum value.

[0095] The increase in perforation friction p was obtained from the curve of perforation eye friction variation. i The number of holes n that need to be sealed is as follows:

[0096]

Example 3

[0097] First, determine the construction flow rate, borehole diameter (which can be obtained from the perforation borehole diameter variation curve and specific construction data), and number of boreholes (n2). Figure 5 Find the corresponding curve (e.g., the curve for displacement 3 and orifice diameter 3), then determine the orifice friction p2 for that displacement, orifice diameter, and number of orifices. Then find the orifice friction p2+p on the curve for displacement 3 and orifice diameter 3. i If the number of holes corresponding to P1 is n1, then the number of holes n = n2 - n1. Therefore, the number of balls thrown is... That is, find 1.1 times n and round up.

[0098] 4) Determine the diameter of the temporary plugging ball.

[0099] The designed pumping scheme is divided into N stages based on the number of throwing stages N. The displacement, sand ratio, and proppant particle size for each stage are determined (this is based on the pumping scheme, which includes pumping stages (e.g., 1-40 stages, each with data on displacement, sand ratio, and proppant size (particle size). For example, if every 8 pumping stages constitute one (throwing) stage, then N equals 5. Therefore, the displacement, sand ratio, and proppant particle size for each stage of the throwing stage are known). Then, the orifice diameter φ at the end of each stage is obtained from the perforation orifice diameter variation curve. i This diameter is the diameter of the temporary plugging ball.

[0100]

Example 4

[0101] Calculate the average sand ratio, average discharge rate, average proppant particle size, and duration of each stage at the end of each stage: The construction record sheet contains the sand ratio, discharge rate, and proppant particle size at each moment, as well as the corresponding duration of the stage. Sum the sand ratio, discharge rate, and proppant particle size values ​​separately, and then divide by the duration of the stage to obtain the average sand ratio, discharge rate, and proppant particle size of that stage.

[0102] Then, find the corresponding orifice diameter on the perforation orifice diameter variation curve chart. This diameter is the temporary plugging ball diameter. Specifically, first find the corresponding curve based on the average sand ratio, average discharge rate, and average proppant particle size values, and then find the corresponding orifice diameter on that curve based on the time duration T. For example... Figure 3 As shown, for example, the average sand ratio, discharge rate, and proppant particle size of this stage are calculated. Figure 3 Given the displacement 2, sand ratio 2, and proppant 2, the orifice diameter is found on the curve corresponding to displacement 2, sand ratio 2, and proppant 2 based on the elapsed time T. This diameter is the temporary plugging ball diameter.

[0103] The following are examples of applications of the present invention:

[0104] Example 5

[0105] This invention was applied in a shale gas well in the periphery of the Sichuan Basin. Based on the well fracturing design scheme, the predicted maximum and minimum construction pressure data were determined to be 85 MPa and 65 MPa, respectively. Assuming a predetermined pressure increase of 10 MPa per construction operation, the number of ball-dropping stages was calculated to be 2 ((85-65) / 10). According to the perforation friction variation curve, the number of balls required for the first 10 MPa increase in perforation friction was 33, with a temporary plugging ball diameter of 16 mm. The number of balls required for the second 10 MPa increase in perforation friction was 15, with a temporary plugging ball diameter of 18 mm. After applying this technology, the volume of fracturing fluid used in a single section of this well was the same as that of a single section of fracturing fluid used in an adjacent well (the two wells had the same process parameters except for the difference in the ball-dropping process optimization method). That is, the amount of fluid used was reduced by 200 cubic meters, but the volume of fracturing fluid remained unchanged. This is because the conventional method increases the volume of fracturing fluid by increasing the amount of fluid used. Therefore, the use of this invention has played a role in improving the fracturing effect.

[0106] This invention analyzes the problems existing in the optimization of the number of ball-dropping stages and the diameter of the temporary plugging balls in the current horizontal well ball-dropping fracturing technology, and proposes a multi-stage ball-dropping optimization technology. This technology achieves the optimization of the number of ball-dropping stages, the number of balls, and the diameter of the temporary plugging balls by obtaining the perforation diameter variation curve, the perforation friction variation curve, the optimization method of the number of ball-dropping stages and the number of balls, and the determination method of the diameter of the temporary plugging balls.

[0107] In the description of this invention, it should be noted that, unless otherwise explicitly specified and limited, the terms "connected" and "linked" should be interpreted broadly. For example, they can refer to a fixed connection, a detachable connection, or an integral connection; they can refer to a mechanical connection or an electrical connection; they can refer to a direct connection or an indirect connection through an intermediate medium. Those skilled in the art can understand the specific meaning of the above terms in this invention according to the specific circumstances.

[0108] In the description of this invention, unless otherwise stated, the terms "upper," "lower," "left," "right," "inner," "outer," etc., indicate the orientation or positional relationship based on the orientation or positional relationship shown in the accompanying drawings. They are used only for the convenience of describing this invention and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation. Therefore, they should not be construed as limitations on this invention.

[0109] Finally, it should be noted that the above technical solution is only one embodiment of the present invention. For those skilled in the art, based on the application methods and principles disclosed in the present invention, it is easy to make various types of improvements or modifications, and not limited to the methods described in the above specific embodiments of the present invention. Therefore, the methods described above are only preferred and have no limiting significance.

Claims

1. A multi-level ball-throwing optimization method, characterized in that: The method first obtains the perforation orifice diameter variation curve and the perforation orifice friction variation curve through experiments, and then uses the perforation orifice diameter variation curve and the perforation orifice friction variation curve to obtain the optimized pitching level, number of pitches, and temporary block diameter. The method includes: (1) Conduct perforation erosion experiments under different sand ratios, discharge rates and proppant particle sizes to obtain perforation diameter variation curves. (2) Conduct hole friction test experiments under different hole numbers, hole diameters and discharge rates, and obtain the hole friction variation curves of the perforation holes. (3) Determine the pitching level and the number of pitches; (4) Determine the diameter of the temporary plugging ball; The operation of step (1) includes: Erosion experiments were conducted on perforation holes under different sand ratios, discharge rates, and proppant particle sizes to obtain discrete data points. Draw a graph with time on the horizontal axis and the diameter of the perforation hole on the vertical axis; By fitting discrete data points, multiple curves are obtained showing the change of perforation orifice diameter over time under different sand ratios, discharge rates, and proppant particle sizes, thus obtaining a perforation orifice diameter change curve chart. The operation of step (2) includes: Experiments were conducted to test the friction of the orifice under different numbers of orifices, orifice diameters and discharge rates, and discrete data points were obtained. The graph is drawn with the number of holes as the horizontal axis and the hole friction as the vertical axis. By fitting discrete data points, multiple curves are obtained showing the variation of orifice friction with the number of orifices under different discharge rates and orifice diameters, thus obtaining the orifice friction variation curve chart of the perforation. The operation of step (3) includes: (31) The pitching level N is calculated using the following formula: N=(P max -P min ) / p i (1) Among them, P max P min It refers to the maximum and minimum values ​​in the predicted or actual construction pressure data, p i This refers to the increase in pressure during each construction phase; (32) Obtain the increase p of the perforation friction from the perforation hole friction change curve. i The number of holes that need to be blocked, and the number of balls thrown is obtained by using the number of holes that need to be blocked; The operation of step (32) includes: Determine the construction discharge rate, borehole diameter, and number of boreholes n2; Find the curve corresponding to the construction flow rate and hole diameter in the perforation hole friction variation curve chart, and use the number of holes n2 to find the hole friction p2 under the flow rate, hole diameter and number of holes on the curve. Then find the orifice friction as p2+p on the curve. i The corresponding number of holes is n1; The number of holes n that need to be plugged can be calculated using the following formula: n = n2 - n1 The number of pitches is The operation of step (4) includes: (41) Divide the designed pumping scheme into N stages; (42) Determine the discharge rate, sand ratio, and proppant particle size for each stage according to the pumping scheme; (43) Obtain the orifice diameter φ at the end of each stage based on the orifice diameter variation curve chart. i This diameter is the diameter of the temporary plugging ball.

2. The multi-stage ball-throwing optimization method according to claim 1, characterized in that: The operation of step (43) includes: Calculate the average sand ratio, average discharge rate, average proppant particle size, and duration of each stage at the end of each stage. Find the corresponding curve on the perforation orifice diameter variation curve chart based on the average sand ratio, average discharge rate, and average proppant particle size values. Find the corresponding orifice diameter on the curve based on the duration; this orifice diameter is the temporary plugging ball diameter.

3. The multi-stage ball-throwing optimization method according to claim 1, characterized in that: The method employs a perforation hole erosion test apparatus to conduct a perforation hole erosion test. The perforation hole erosion test apparatus includes: an erosion pumping assembly, a safety shield, and an experimental tubing set inside the safety shield. The safety shield is a cylindrical structure with a liquid discharge channel at its lower end. One end of the experimental tubular column is open, and the other end is closed; The erosion pumping assembly is connected to the open end of the experimental tubing via a pipeline.

4. The multi-stage pitching optimization method according to claim 3, characterized in that: The erosion pumping assembly includes a small plunger pump, a proppant fracturing fluid mixer, a proppant delivery device, and a proppant storage tank connected in sequence. The outlet of the small plunger pump is connected to the open end of the experimental column via a pipeline. The erosion pumping assembly further includes a fracturing fluid injection pump and a fracturing fluid storage tank connected in sequence, and the outlet of the fracturing fluid injection pump is connected to the proppant fracturing fluid mixer. The proppant delivery device, proppant fracturing fluid mixer, mini plunger pump, and fracturing fluid injection pump are also connected to the control and data recording terminal.

5. The multi-stage pitching optimization method according to claim 1, characterized in that: The method employs a perforation friction test experimental device to conduct a perforation friction test experiment. The perforation friction test experimental device includes: a fracturing fluid pumping assembly, a safety guard, and an experimental tubing set in the inner cavity of the safety guard. The safety shield is a cylindrical structure with a liquid discharge channel at its lower end. The experimental tubular column has an open end at one end and a closed end at the other end; The fracturing fluid injection assembly is connected to the open end of the experimental tubing via a pipeline.

6. The multi-stage pitching optimization method according to claim 5, characterized in that: The fracturing fluid injection assembly includes a small plunger pump, a fracturing fluid injection pump, and a fracturing fluid storage tank connected in sequence. The outlet of the small plunger pump is connected to the open end of the experimental column via a pipeline. The small piston pump is also connected to a control and data logging terminal; The control and data recording terminal measures the pressure in the experimental tubing using a pressure gauge.

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