An optimization method for temporary plugging knots and temporary plugging balls in multi-cluster diversion fracturing of horizontal wells

Abstract

The present invention discloses an optimization method for temporary plugging knots and temporary plugging balls in multi-cluster diversion fracturing of horizontal wells, comprising the steps of: conducting a stepped discharge reduction test on the fractured interval, obtaining the stable pressures at different discharge rates, and getting the discharge reduction test data; importing the discharge reduction test data into a dedicated numerical simulation software to calculate the optimal dosages of the temporary plugging knots and the temporary plugging balls; conducting a stepped discharge reduction test again at the end of the displacement stage of the first-stage fracturing, obtaining the stable pressures at different discharge rates, and importing them into the dedicated numerical simulation software to calculate the number of effectively opened liquid inlet holes after sand addition; based on the change in the number of effectively opened liquid inlet holes after sand addition, combining physical simulation experiments and high-definition visual imaging analysis data to deduce the change in the perforation hole diameter, and combining the proportion of each diameter to select the optimal particle sizes of the temporary plugging knots and the temporary plugging balls. The present invention improves the success rate of temporary plugging diversion fracturing by optimizing the dosages and particle sizes of the temporary plugging knots and the temporary plugging balls.

Description

Technical Field

[0001] The present invention relates to the technical field of unconventional oil and gas production enhancement, and particularly to an optimization method for temporary plugging knots and temporary plugging balls in multi-cluster diversion fracturing of horizontal wells. Background Technique

[0002] In recent years, with the exploitation of unconventional oil and gas, the fracturing technology has shifted from conventional sand fracturing to large-scale high-volume fracturing, and then to closely spaced temporary plugging diversion fracturing. The fracturing technology has been gradually improved and upgraded, making it more in line with the requirements of unconventional oil and gas reservoir production enhancement. Among them, the closely spaced multi-cluster diversion fracturing technology is widely used in the development of shale and tight oil and gas. This is mainly because the reservoir has a relatively high starting pressure gradient. If the fracture spacing is too large, there will be unmodified areas in the horizontal section, which is not conducive to production enhancement. The closely spaced multi-cluster modification method can maximize the reservoir modification. In terms of the construction method, there are certain blind spots in the closely spaced multi-cluster construction mode. Due to the heterogeneity between each perforation cluster and at the perforation positions, the modification uniformity between each perforation cluster in the section or between each perforation hole in the cluster is different. There may even be unmodified clusters or incomplete overall modification in all directions within the cluster. To improve the reservoir modification uniformity, the method of injecting temporary plugging materials can be used to block the already fractured perforation holes during the fracturing process, prompting the fluid to divert to the unfractured perforation clusters or holes, thereby achieving uniform modification of multiple clusters within the section. From the perspective of the temporary plugging process, the plugging effect of the already fractured perforation clusters or holes within the section is closely related to the overall swept volume and fracturing modification effect of the fracturing.

[0003] With the development of the temporary plugging diversion technology, the existing temporary plugging materials are mainly divided into two types: temporary plugging knots and temporary plugging balls, and temporary plugging agents. Among them, the temporary plugging knots and temporary plugging balls have large particle sizes, usually 5 - 30 mm. Their main function is to block the already fractured perforation holes, thereby increasing the net pressure in the wellbore, causing the formation of the unfired perforation clusters to fracture, realizing fluid diversion, and ultimately increasing the effective modified volume. The dosage and particle size selection of the temporary plugging knots and temporary plugging balls are closely related to the success of the temporary plugging diversion. However, there is currently no algorithm with strong well-matching to obtain the optimal solution for the use of the temporary plugging knots and temporary plugging balls. The core problem is the optimization of the quantity and particle size of the temporary plugging knots and temporary plugging balls. Therefore, there is an urgent need for a method to calculate and optimize the dosage and particle size of the temporary plugging knots and temporary plugging balls. Summary of the Invention

[0004] The purpose of the present invention is to provide an optimization method for temporary plugging knots and temporary plugging balls in multi-cluster diversion fracturing of horizontal wells, which can improve the success rate of temporary plugging diversion fracturing by optimizing the dosage and particle size of the temporary plugging knots and temporary plugging balls.

[0005] To achieve the above purpose, the present invention provides the following solution:

[0006] An optimization method for temporary plugging knots and temporary plugging balls in multi-cluster diversion fracturing of horizontal wells, comprising the following steps:

[0007] Step 1) Optimization of the amount of temporary plugging knots and temporary plugging balls:

[0008] Step 1.1) During or before the fracturing process, a step-by-step flow reduction test is performed on the fractured layer to obtain stable pressures at different flow rates and obtain flow reduction test data;

[0009] Step 1.2) Import the discharge reduction test data into the dedicated digital simulation software to calculate the optimal amount of temporary plugging knots and temporary plugging balls;

[0010] Step 2) Optimization of temporary plugging knot and temporary plugging ball particle size:

[0011] Step 2.1) Perform a step-down displacement test again at the end of the first stage of fracturing displacement to obtain the stable pressure under different displacements, and import it into a dedicated numerical simulation software to calculate the number of effective liquid inlet holes after sand addition;

[0012] Step 2.2) The difference between the number of effectively opened liquid inlet holes after sand addition and the actual number of liquid inlet holes is used to characterize the degree of abrasion of the perforation holes. The change in the diameter of the perforation holes is calculated based on the results of the previous physical model experiment in the laboratory and the high-definition visual imaging analysis data of the on-site blastholes. The optimal particle size of the temporary plugging knot and the temporary plugging ball is selected based on the proportion of each diameter.

[0013] Optionally, the step-reduction test in step 1.1) is specifically designed to conduct 3-5 step-reduction tests with different displacements before stopping the pump at the end of the small-scale fracturing test. The different displacements must last for at least 15 seconds to obtain stable pressures at different displacements.

[0014] Optionally, in step 1.2), the discharge reduction test data is imported into a dedicated digital modeling software to calculate the amount of temporary plugging knots and temporary plugging balls, specifically including:

[0015] Step 1.2.1) Calculate the hole friction ΔP perf and near wellbore friction ΔP near-wellbore , the formula is:

[0016] ΔP perf =K perf Q 2

[0017] ΔP near-wellbore =K near-wellbore Q β

[0018] Where: K near-wellbore is the friction coefficient near the wellbore, K perf is the friction coefficient of the hole, Q is the pumping displacement, and β is the friction index near the wellbore, which is taken as 0.5;

[0019] Step 1.2.2) Calculate the number of effectively opened liquid inlet holes N effective , the formula is:

[0020] N effective =(N shot 2 / P erf C oefficient M ultiplier ) 0.5

[0021] Wherein: N shot is the number of perforation holes fired by the perforating gun, and P erf C oefficient M ultiplier is the ratio of the actual hole friction to the theoretically calculated hole friction ΔP perf ;

[0022] Step 1.2.3) Calculate the effective rate e of the perforation holes, and the formula is:

[0023] e = N effective / N shot

[0024] Step 1.2.4) Based on the homogeneity assumption, calculate the number m of effectively opened liquid inlet holes for any section of the horizontal well, and the formula is:

[0025] m = e × total number of perforations in a single section

[0026] Step 1.2.5) Calculate the optimal dosage Z of the temporary plugging knot and the temporary plugging ball 用量 , the formula is:

[0027] Z 用量 = m × k

[0028] Wherein: k is a guarantee coefficient, and its value ranges from 1.2 to 1.8.

[0029] Optionally, the laboratory pre - physical model experiment described in Step 2.2) specifically includes:

[0030] Step 2.2.1) For perforation holes with different apertures, select critical temporary plugging knots and temporary plugging ball particle sizes that meet the pressure - resistance requirements;

[0031] Step 2.2.2) Characterize and represent the erosion degree of the perforation holes.

[0032] According to the specific embodiments provided by the present invention, the following technical effects are disclosed: The optimization method of the temporary plugging knot and the temporary plugging ball in the multi - cluster diversion fracturing of horizontal wells provided by the present invention improves the success rate of temporary plugging diversion fracturing by optimizing the dosage and particle size of the temporary plugging knot and the temporary plugging ball, and obtaining the optimal solution for the use of the temporary plugging knot and the temporary plugging ball. Description of the Drawings

[0033] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the following will briefly introduce the accompanying drawings required for use in the embodiments. Obviously, the accompanying drawings in the following description are only some embodiments of the present invention. For those of ordinary skill in the art, without creative efforts, other accompanying drawings can be obtained based on these drawings.

[0034] Figure 1a It is the simulated plugging efficiency diagram of the temporary plugging knot by the digital simulation software in the embodiment of the present invention;

[0035] Figure 1b It is the simulated plugging efficiency diagram of the temporary plugging ball by the digital simulation software in the embodiment of the present invention;

[0036] Figure 2 It is the stepwise decreasing displacement test curve of the digital simulation software in the embodiment of the present invention;

[0037] Figure 3 It is the temporary plugging fracturing construction curve in the embodiment of the present invention. Detailed implementation manners

[0038] The following will clearly and completely describe the technical solutions in the embodiments of the present invention in conjunction with the accompanying drawings in the embodiments of the present invention. Obviously, the described embodiments are only some embodiments of the present invention, rather than all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative efforts belong to the scope of protection of the present invention.

[0039] The purpose of the present invention is to provide an optimization method for temporary plugging knots and temporary plugging balls in multi-cluster diversion fracturing of horizontal wells. By optimizing the dosage and particle size of temporary plugging knots and temporary plugging balls, the success rate of temporary plugging diversion fracturing is improved.

[0040] To make the above objects, features, and advantages of the present invention more obvious and understandable, the present invention will be further described in detail below in conjunction with the accompanying drawings and specific implementation manners.

[0041] The optimization method for temporary plugging knots and temporary plugging balls in multi-cluster diversion fracturing of horizontal wells provided by the embodiments of the present invention includes the following steps:

[0042] Step 1) Optimization of the dosage of temporary plugging knots and temporary plugging balls:

[0043] Step 1.1) Conduct a stepwise decreasing displacement test on the fractured intervals during or at the end of the fracturing process, obtain the stable pressures at different displacements, and obtain the displacement reduction test data;

[0044] Step 1.2) Import the displacement reduction test data into a dedicated digital simulation software to calculate the optimal dosage of temporary plugging knots and temporary plugging balls;

[0045] Step 2) Optimization of temporary plugging knot and temporary plugging ball particle size:

[0046] Step 2.1) Perform a step-down displacement test again at the end of the first stage of fracturing displacement to obtain the stable pressure under different displacements, and import it into a dedicated numerical simulation software to calculate the number of effective liquid inlet holes after sand addition;

[0047] Step 2.2) The difference between the number of effectively opened liquid inlet holes after sand addition and the actual number of liquid inlet holes is used to characterize the degree of abrasion of the perforation holes. The change in the diameter of the perforation holes (expansion rate) is calculated based on the results of the previous physical model experiment in the laboratory and the high-definition visual imaging analysis data of the on-site blastholes. The optimal particle size of the temporary plugging knot and temporary plugging ball is selected based on the proportion of each diameter.

[0048] In step 1.1), firstly, a small-scale fracturing test of the first stage of shale oil and gas horizontal well fracturing is used to calculate the liquid efficiency, permeability, closure pressure, closure time and other parameters of the formation. The calculation of these parameters requires the pressure drop data after the pump is stopped in the small-scale fracturing test; to provide a basis for the subsequent optimization of the dosage of temporary plugging knots and temporary plugging balls, the step-down displacement test is designed, specifically: 3-5 step-down displacement tests with different displacements are designed before the pump is stopped at the end of the small-scale fracturing test, and different displacements must last for at least 15s to obtain stable pressures under different displacements.

[0049] In step 1.2), the test data of the reduction rate is imported into the special numerical simulation software, and the friction resistance near the wellbore and the friction resistance of the hole can be calculated. At the same time, the number of effective opening holes for liquid inlet can be obtained according to the friction resistance of the hole, and finally the dosage of the temporary plugging knot and the temporary plugging ball can be obtained. It should be noted here that in the process of horizontal well fracturing, conventionally only the first section adopts the method of small-scale fracturing test to obtain the formation parameters, so it is assumed that the overall horizontal section is homogeneous, that is, the calculated perforation hole efficiency is applicable to any section of the well fracturing. The specific process includes:

[0050] Step 1.2.1) Calculate the hole friction ΔP perf and near wellbore friction ΔP near-wellbore , the formula is:

[0051] ΔP perf =K perf Q 2

[0052] ΔP near-wellbore =K near-wellbore Q β

[0053] Where: K near-wellbore is the friction coefficient near the wellbore, K perf is the friction coefficient of the hole, Q is the pumping displacement, and β is the friction index near the wellbore, which is taken as 0.5;

[0054] Step 1.2.2) Calculate the number of effectively opened liquid inlet holes N effective (The number of holes with effective liquid inlet during the fracturing process of the perforated interval), and the formula is:

[0055] N effective＝ (N shot 2 / P erf C oefficient M ultiplier ) 0.5

[0056] Where: N shot is the number of perforation holes fired by the perforating gun, and P erf C oefficient M ultiplier is the ratio of the actual hole friction to the theoretically calculated hole friction ΔP perf ;

[0057] Step 1.2.3) Calculate the effective rate e of the perforation holes, and the formula is:

[0058] e = N effective / N shot

[0059] Step 1.2.4) Based on the homogeneity assumption, calculate the number of effectively opened liquid inlet holes m for any section of the horizontal well, and the formula is:

[0060] m = e × total number of perforations in a single section

[0061] Under the condition of allowing, multiple stepwise reduced displacement tests can be carried out according to the distribution of specific construction sub-layers, which can make the effective rate e of the perforation holes more accurate and targeted;

[0062] As Figure 1a and Figure 1b shown, in Step 1.2.5), through the effective rate of the perforation holes obtained by numerical simulation, the number of effective holes in the section, that is, the number of holes to be plugged, can be further obtained. To ensure the temporary plugging effect, according to the numerical simulation results and on-site construction experience values, a guarantee coefficient is added to calculate the optimal dosage Z 用量 of the temporary plugging knot and the temporary plugging ball, and the formula is:

[0063] Z 用量 = m × k

[0064] Where: k is the guarantee coefficient, and generally takes a value of 1.2 - 1.8.

[0065] In Step 2.1), the orifice erosion caused by sand addition will increase the orifice diameter. On the premise of the same displacement and the same number of effectively opened liquid inlet orifices, the orifice friction will decrease. Importing the test data of the stepped reduction of displacement at the end of displacement replacement into the numerical simulation software can obtain the number of effectively opened liquid inlet orifices after sand addition. It should be noted that the number of effectively opened liquid inlet orifices at this time is not the actual number of orifices, but the calculation result becomes larger due to the reduction of orifice friction. The difference in the number of effectively opened liquid inlet orifices between Step 2.1) and Step 2.2) can characterize the erosion degree of the perforation orifices.

[0066] Based on the previous physical simulation experiments in the indoor laboratory and the analysis data of the high-definition imaging of the wellbore in the field, the erosion of the perforation wellbore is characterized and described, and the temporary plugging knot and the particle size of the temporary plugging ball are optimized. The previous physical simulation experiments in the laboratory described in Step 2.2) specifically include:

[0067] Step 2.2.1) For wellbores with different apertures, select the critical temporary plugging knot and the particle size of the temporary plugging ball that meet the pressure resistance requirements.

[0068] Step 2.2.2) Characterize and describe the erosion degree of the wellbore.

[0069] Through a large number of physical simulation experiments and the analysis data of the high-definition imaging of the wellbore in the field, the erosion regularity of the wellbore is analyzed as a whole to obtain the erosion degree distribution in a general sense. Based on the difference in the number of effectively opened liquid inlet orifices and the results of the physical simulation experiments, the erosion degree distribution and the proportion of the size are analyzed, and then the combination ratio of the temporary plugging knot and the particle size of the temporary plugging ball can be optimized and determined.

[0070] The following uses an example to further illustrate the method of the present invention:

[0071] The construction well is a horizontal well in the shale reservoir of an oilfield, with a total of 24 sections. Among them, in the 16th section, there are 3 clusters of perforations with a total length of 6 m, the number of perforations is 96, and the perforation aperture is 12.2 mm. To achieve a better stimulation effect, multi-cluster diversion fracturing is designed.

[0072] As Figure 2 shown, a small-scale fracturing test was carried out on this section before construction. Based on the stepped reduction of displacement test data, numerical simulation calculations were carried out, and the results were obtained as follows: the number of effectively opened liquid inlet orifices is 36.92, and the perforation efficiency is 38%, that is, the effective liquid inlet channels during construction are 37 holes. The goal of the multi-cluster diversion fracturing temporary plugging is to temporarily plug these 37 holes after the first-stage sand fracturing, forcing the liquid to turn and fracture the un-stimulated perforation clusters to achieve uniform stimulation between clusters within the section. According to the formula Z 用量 = m×k, select k = 1.8, and the designed dosage of the temporary plugging knot and the temporary plugging ball for this section is 37×1.8 = 66.6, that is, the number of balls to be dropped is optimized to 67.

[0073] At the end of the first-stage fracturing displacement stage, the step-down displacement test was carried out again, and digital simulation calculation was introduced. The number of effectively opened liquid inlet holes after the first-stage fracturing was 46.73, and the difference in the number of effectively opened liquid inlet holes reached 10. That is, the first-stage fracturing had a greater degree of hole erosion. When optimizing the particle size, the high degree of erosion of some holes and the increase in the aperture due to erosion should be considered.

[0074] Based on the differences in the test results of the front and back step-down displacements and considering the physical simulation results comprehensively, the particle size was optimized. The perforation aperture was 12.2 mm, and the designed particle sizes of the temporary plugging rope knots and temporary plugging balls were 13.5 mm + 15 mm + 20 mm, with 15 mm as the main particle size, and the quantities were 6, 50, and 11 respectively. As Figure 3 shown, after the temporary plugging was completed, from the fracturing construction curve, it was observed that under the same displacement conditions before and after the temporary plugging, the construction pressure increased by 4.5 MPa after the temporary plugging, achieving a good temporary plugging effect. The downhole high-definition imaging analysis system showed that the degree of uniform opening of the gun holes was high, the liquid intake was relatively uniform, and the area of the holes after grinding was 322.58 mm 2 . The hole diameter changed from 12.2 mm before grinding to 15 - 20 mm, indicating that the grinding effect was obvious after the gun holes were filled with sand and liquid, and the transformation effect was good.

[0075] The optimization method of the temporary plugging rope knots and temporary plugging balls in the multi-cluster steering fracturing of horizontal wells provided by the present invention obtains the optimal solution for the use of the temporary plugging rope knots and temporary plugging balls by optimizing the dosage and particle size of the temporary plugging rope knots and temporary plugging balls, and improves the success rate of the temporary plugging steering fracturing.

[0076] In this article, specific examples are used to elaborate on the principle and implementation mode of the present invention. The description of the above embodiments is only used to help understand the method and its core idea of the present invention; at the same time, for those of ordinary skill in the art, according to the idea of the present invention, there will be changes in the specific implementation mode and application scope. In summary, the content of this specification should not be construed as a limitation to the present invention.

Claims

1. An optimization method for temporary plugging knots and temporary plugging balls in multi-cluster diversion fracturing of horizontal wells, characterized in that, The following steps are involved: Step 1) Optimization of the amount of temporary plugging knots and temporary plugging balls: Step 1.1) During or before the fracturing process, a step-by-step flow reduction test is performed on the fractured layer to obtain stable pressures at different flow rates and obtain flow reduction test data; Step 1.2) Import the emission reduction test data into the dedicated digital simulation software to calculate the optimal amount of temporary plugging knots and temporary plugging balls; specifically including: Step 1.2.1) Calculate the hole friction ΔP perf and the near-wellbore friction ΔP near-wellbore , and the formula is: ΔP perf = K perf Q 2 ΔP near-wellbore = K near-wellbore Q β Where: K near-wellbore is the near-wellbore friction coefficient, K perf is the perforation friction coefficient, Q is the pumping displacement, β is the near-wellbore friction exponent, and its value is 0.5; Step 1.2.2) Calculate the number of effectively opened liquid inlet holes N effective , and the formula is: N effective = (N shot 2 / P erf C oefficient M ultiplier ) 0.5 Where: N shot is the number of perforation holes fired by the perforating gun, P erf C oefficient M ultiplier is the ratio of the actual hole friction to the theoretically calculated hole friction ΔP perf ; Step 1.2.3) Calculate the perforation efficiency e, the formula is: e = N effective / N shot Step 1.2.4) Based on the homogeneity assumption, calculate the number of effective open fluid inlets m in any section of the horizontal well. The formula is: m=e×total number of perforations in a single stage Step 1.2.5) Calculate the optimal dosage Z of temporary plugging knot and temporary plugging ball, the formula is: Z dosage = m × k Where: k is the guarantee coefficient, ranging from 1.2 to 1.8; Step 2) Optimization of temporary plugging knot and temporary plugging ball particle size: Step 2.1) Perform a step-down displacement test again at the end of the first stage of fracturing displacement to obtain the stable pressure under different displacements, and import it into a dedicated numerical simulation software to calculate the number of effective liquid inlet holes after sand addition; Step 2.2) The difference between the number of effectively opened liquid inlet holes after sand addition and the actual number of liquid inlet holes is used to characterize the degree of abrasion of the perforation holes. The change in the diameter of the perforation holes is calculated based on the results of the previous physical model experiment in the laboratory and the high-definition visual imaging analysis data of the on-site blastholes. The optimal particle size of the temporary plugging knot and the temporary plugging ball is selected based on the proportion of each diameter.

2. The optimization method of the temporary plugging knot and the temporary plugging ball in the horizontal well multi-cluster diversion fracturing according to claim 1, characterized in that, The step-down displacement test described in step 1.1) is specifically designed to conduct 3-5 step-down displacement tests with different displacements before stopping the pump at the end of the small-scale fracturing test. The different displacements must last for at least 15 seconds to obtain stable pressures at different displacements.

3. The optimization method of the temporary plugging knot and the temporary plugging ball in the multi-cluster steering fracturing of horizontal wells according to claim 1, wherein The preliminary laboratory model experiment described in step 2.2) specifically includes: Step 2.2.1) For blastholes with different apertures, select critical temporary plugging knots and temporary plugging ball sizes that meet the pressure resistance requirements; Step 2.2.2) Characterize and characterize the degree of blasthole erosion.

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