Horizontal well long-section multi-cluster staged fracturing parameter optimization and implementation method

Abstract

The invention discloses a horizontal well long-section multi-cluster staged fracturing parameter optimization and implementation method, which belongs to the technical field of unconventional oil and gas reservoir hydraulic fracturing and comprises the following steps: step 1, designing staged fracturing stages and temporary plugging times in a section on the basis of a stress interference action principle between balance fractures; 2, based on the principle of step-by-step opening of multi-stage fracturing cracks and multi-cluster crack balanced expansion in the process of each stage of fracturing, perforation parameters of each stage of fracturing are designed; 3, based on the principle that the liquid inlet amount of each cluster of cracks is the same, the graded temporary plugging time and the temporary plugging agent dosage are determined; and 4, carrying out site construction according to the optimized construction parameters. According to the method, synchronous opening and balanced expansion of multiple clusters of hydraulic fractures in the long fracturing section of the horizontal well can be achieved, the defect that in the prior art, due to the fact that the number of perforation clusters in the fracturing section is too large, application is difficult is overcome, the fracturing operation cost is reduced, and the oil and gas well yield is effectively improved.

Description

Technical Field

[0001] The invention belongs to the technical field of hydraulic fracturing of unconventional oil and gas reservoirs, and in particular relates to a method for optimizing and implementing parameters of long-section multi-cluster graded fracturing of horizontal wells. Background Art

[0002] Horizontal well multi-cluster fracturing technology is the main means of shale oil and gas resource development and is widely used in shale oil and gas reservoir transformation. Due to the influence of factors such as inter-fracture stress interference and reservoir heterogeneity, it is difficult for multiple clusters of hydraulic fractures in the same fracturing section to start and expand synchronously during the horizontal well multi-cluster fracturing process, resulting in poor fracturing transformation effects, thus limiting the efficient improvement of oil and gas well production capacity.

[0003] In the horizontal well fracturing design, the number of fracturing stages and the number of perforation clusters are key design parameters, which directly affect the fracturing transformation effect and cost investment. A reasonable segment cluster design scheme is conducive to fully utilizing the reservoir production potential, reducing the input-output ratio, and obtaining better economic benefits. The horizontal well long-segment multi-cluster fracturing technology reduces the construction cost by increasing the fracturing segment length and reducing the number of fracturing segments. However, the increase in the number of perforation clusters in the fracturing segment makes the problem of non-balanced development of multi-cluster fractures more significant.

[0004] At present, the methods to promote the balanced development of multi-cluster fractures mainly include: perforation flow limiting method and temporary plugging and diversion method. For conventional horizontal well segmented multi-cluster fracturing, the number of perforation clusters in the same fracturing section is small (less than 10 clusters), and both methods can achieve certain results. However, in the long-segment multi-cluster fracturing mode, the number of perforation clusters in a single section is too large (greater than 10 clusters), and the difficulty of synchronous opening and balanced expansion of multi-cluster hydraulic fractures is further increased, resulting in the above two methods no longer being applicable. It is urgent to establish an effective optimization design method. Summary of the invention

[0005] The purpose of the present invention is to provide a method for optimizing and implementing parameters of multi-cluster staged fracturing in a long section of a horizontal well, so as to achieve synchronous opening and balanced expansion of multi-cluster hydraulic fractures in a long fracturing section, and provide guidance for multi-cluster fracturing construction in a long section of a horizontal well.

[0006] To achieve the above object, the present invention provides a method for optimizing and implementing parameters of multi-cluster staged fracturing in a long section of a horizontal well, comprising the following steps:

[0007] Step 1: Based on the principle of balanced inter-fracture stress interference, design the number of staged fracturing and temporary plugging times within the section;

[0008] Step 2: Based on the principle of opening multi-stage fracturing cracks step by step and balanced expansion of multiple clusters of fractures during each stage of fracturing, the perforation parameters of each stage of fracturing are designed;

[0009] Step 3: Based on the principle that the amount of fluid inflow into each cluster of fractures is the same and each level of fracturing and perforation clusters are opened in sequence, the graded temporary plugging time and the amount of temporary plugging agent are determined;

[0010] Step 4: Carry out on-site construction according to the optimal construction parameters.

[0011] Preferably, in step 1, it is ensured that the perforation clusters of each level of fracturing are arranged in a staggered manner during staged fracturing of the target fracturing section, and the distance between adjacent perforation clusters in each level is not less than 10m but not more than 20m. The calculation formula for the staged fracturing number and the temporary plugging number in the section is as follows:

[0012]

[0013] Where: N j is the number of staged fracturing stages in the target fracturing section (rounded up), dimensionless; N is the number of perforation clusters per stage, it is recommended that no more than 4 clusters, dimensionless; N T is the total number of perforation clusters in the fracturing stage, dimensionless; N d is the number of temporary plugging times, dimensionless; L is the length of the fracturing section, m; d is the perforation cluster spacing of each level of fracturing (10≤d≤20), m.

[0014] Preferably, the calculation process of the perforation parameters at each level in step 2 is as follows:

[0015] S21. Considering the interference effect of induced stress between fractures, the perforation parameters of each perforation cluster of the first-stage fracturing are calculated. The specific process is as follows:

[0016] First, the net pressure in a single hydraulic fracture is solved based on the analytical solution of the PKN hydraulic fracture model:

[0017]

[0018] Secondly, calculate the interference intensity value of the induced stress between fractures when multiple clusters of fractures expand synchronously during the first stage of fracturing:

[0019]

[0020] Where: p is the net pressure in a single hydraulic fracture, MPa; Δp s is the interference strength value of the induced stress between fractures, MPa; E is the static Young's modulus, MPa; μ is the viscosity, mPa·s; Q is the injection displacement, m3 / min; N is the number of perforation clusters corresponding to the first-stage fracturing, dimensionless; υ is the Poisson's ratio, dimensionless; h r is the height of hydraulic fracture, m;

[0021] Finally, considering the interference effect of induced stress between perforations by balancing the friction resistance of perforations, the number of perforations for balanced development of multiple clusters of fractures in the first stage of fracturing is calculated:

[0022]

[0023] Where: n p1 is the number of perforations in each perforation cluster of the first-stage fracturing, dimensionless; ρ s is the density of fracturing fluid, kg / m 3 ;d p is the perforation hole diameter, m; K d is the hole flow coefficient, which reflects the influence of the shape of the perforation hole entrance on the flow of fracturing fluid and hole friction, with a value range of 0.5 to 0.95 and dimensionless; i is the i-th fracturing stage, dimensionless;

[0024] S22. Considering the superposition of the induced stress between the first two hydraulic fractures and the constraint that the second-stage hydraulic fracture perforation cluster is not opened when the first-stage hydraulic fracture perforation cluster is fractured and expanded (the friction resistance pressure drop of the second-stage hydraulic fracture perforation should be higher than that of the first-stage hydraulic fracture perforation), the number of perforations for the second-stage hydraulic fracture is calculated:

[0025]

[0026] Where: n p2 is the number of perforations in each perforation cluster of the second-stage fracturing, dimensionless; α is the difference between the frictional pressure drop of the second-stage perforation holes and the frictional pressure drop of the first-stage holes, which is determined based on the experience of the target work area and is usually 5, MPa;

[0027] S23, and so on to calculate the perforation parameters of the third and subsequent fracturing stages:

[0028]

[0029] Where: n pi is the number of perforations in each perforation cluster of the i-th stage fracturing, dimensionless;

[0030] S24, requiring the number of perforations in the last level of perforation cluster to be no less than 2, otherwise returning to step 1 to reduce the number of levels and recalculate.

[0031] Preferably, the process of calculating the graded temporary plugging time and the amount of temporary plugging agent in step 3 is as follows:

[0032] S31. Based on the principle that the amount of liquid inflow into each cluster of fractures is the same, calculate the temporary plugging time at each level:

[0033]

[0034] In the formula, t j is the construction time of the jth level temporary blockage, min; T is the total construction time, min; N j is the number of perforation clusters corresponding to the j-th level of fracturing, dimensionless;

[0035] S32. Based on the principle of opening the perforation clusters of each level of fracturing in sequence, that is, after temporary plugging, it is ensured that all the cracks opened by the previous level of fracturing are blocked, and the perforation clusters of each level of the next level of fracturing can be effectively opened, the calculation formula for the amount of temporary plugging agent is as follows:

[0036]

[0037] The calculation formula of the seam width is as follows:

[0038]

[0039] Where m is the dosage of temporary plugging agent, kg; λ is the temporary plugging agent concentration per unit joint height section, which can be measured by indoor experiments, kg / m 2 ; w is the width of the crack in the temporary plugging section, m; is the concentration retention rate, based on engineering experience, the value range is 70%-90%, dimensionless; n is the number of fracture clusters that need to be temporarily plugged, dimensionless; C L is the filtration coefficient, m / min 0.5 .

[0040] Preferably, in step 4, on-site construction is carried out according to the optimal construction parameters.

[0041] Compared with the prior art, the beneficial effects of the present invention are:

[0042] The present invention promotes the gradual fracturing of the perforation clusters in the long fracturing section by differentially setting the perforation parameters of each cluster and injecting temporary plugging agents multiple times. For the perforation clusters opened at the same level, the perforation parameters are further optimized to ensure the balanced expansion of multiple clusters of hydraulic fractures in the level. Finally, the synchronous opening and balanced expansion of multiple clusters of hydraulic fractures in the long fracturing section of the horizontal well are achieved, overcoming the defect that the existing technology is difficult to apply due to too many perforation clusters in the fracturing section, reducing the cost of fracturing operations and effectively improving the fracturing transformation effect. BRIEF DESCRIPTION OF THE DRAWINGS

[0043] Figure 1 It is an overall flow chart of a method for optimizing and implementing parameters of long-section multi-cluster staged fracturing of horizontal wells according to the present invention. DETAILED DESCRIPTION

[0044] The following detailed description of the embodiments of the present invention provided in the accompanying drawings is not intended to limit the scope of the invention claimed for protection, but merely represents selected embodiments of the present invention. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0045] like Figure 1As shown, in step 1, it is ensured that the perforation clusters of each level of fracturing are staggered during staged fracturing of the target fracturing section, and the distance between adjacent perforation clusters in each level is not less than 10m but not more than 20m. The calculation formula for the staged fracturing number and temporary plugging times in the section is as follows:

[0046]

[0047] Where: N j is the number of staged fracturing stages in the target fracturing section (rounded up), dimensionless; N is the number of perforation clusters per stage, it is recommended that no more than 4 clusters, dimensionless; N T is the total number of perforation clusters in the fracturing stage, dimensionless; N d is the number of temporary plugging times, dimensionless; L is the length of the fracturing section, m; d is the perforation cluster spacing of each level of fracturing (10≤d≤20), m.

[0048] The calculation process of perforation parameters at each level in step 2 is as follows:

[0049] S21. Considering the interference effect of induced stress between fractures, the perforation parameters of each perforation cluster of the first-stage fracturing are calculated. The specific process is as follows:

[0050] First, the net pressure in a single hydraulic fracture is solved based on the analytical solution of the PKN hydraulic fracture model:

[0051]

[0052] Secondly, calculate the interference intensity value of the induced stress between fractures when multiple clusters of fractures expand synchronously during the first stage of fracturing:

[0053]

[0054] Where: p is the net pressure in a single hydraulic fracture, MPa; Δp s is the interference strength value of the induced stress between fractures, MPa; E is the static Young's modulus, MPa; μ is the viscosity, mPa·s; Q is the injection displacement, m3 / min; N is the number of perforation clusters corresponding to the first-stage fracturing, dimensionless; υ is the Poisson's ratio, dimensionless; h r is the height of hydraulic fracture, m;

[0055] Finally, considering the interference effect of induced stress between perforations by balancing the friction resistance of perforations, the number of perforations for balanced development of multiple clusters of fractures in the first stage of fracturing is calculated:

[0056]

[0057] Where: n p1 is the number of perforations in each perforation cluster of the first-stage fracturing, dimensionless; ρ s is the density of fracturing fluid, kg / m 3 ;d p is the perforation hole diameter, m; Kd is the hole flow coefficient, which reflects the influence of the shape of the perforation hole entrance on the flow of fracturing fluid and hole friction, with a value range of 0.5 to 0.95 and dimensionless; i is the i-th fracturing stage, dimensionless;

[0058] S22. Considering the superposition of the induced stress between the first two hydraulic fractures and the constraint that the second-stage hydraulic fracture perforation cluster is not opened when the first-stage hydraulic fracture perforation cluster is fractured and expanded (the friction resistance pressure drop of the second-stage hydraulic fracture perforation should be higher than that of the first-stage hydraulic fracture perforation), the number of perforations for the second-stage hydraulic fracture is calculated:

[0059]

[0060] Where: n p2 is the number of perforations in each perforation cluster of the second-stage fracturing, dimensionless; α is the difference between the frictional pressure drop of the second-stage perforation holes and the frictional pressure drop of the first-stage holes, which is determined based on the experience of the target work area and is usually 5, MPa;

[0061] S23, and so on to calculate the perforation parameters of the third and subsequent fracturing stages:

[0062]

[0063] Where: n pi is the number of perforations in each perforation cluster of the i-th stage fracturing, dimensionless;

[0064] S24, requiring the number of perforations in the last level of perforation cluster to be no less than 2, otherwise returning to step 1 to reduce the number of levels and recalculate.

[0065] The process of calculating the graded temporary plugging time and the amount of temporary plugging agent in step 3 is as follows:

[0066] S31. Based on the principle that the amount of liquid inflow into each cluster of fractures is the same, calculate the temporary plugging time at each level:

[0067]

[0068] In the formula, t j is the construction time of the jth level temporary blockage, min; T is the total construction time, min; N j is the number of perforation clusters corresponding to the j-th level of fracturing, dimensionless;

[0069] S32. Based on the principle of opening the perforation clusters of each level of fracturing in sequence, that is, after temporary plugging, it is ensured that all the cracks opened by the previous level of fracturing are blocked, and the perforation clusters of each level of the next level of fracturing can be effectively opened, the calculation formula for the amount of temporary plugging agent is as follows:

[0070]

[0071] The calculation formula of the seam width is as follows:

[0072]

[0073] Where m is the dosage of temporary plugging agent, kg; λ is the temporary plugging agent concentration per unit joint height section, which can be measured by indoor experiments, kg / m 2 ; w is the width of the crack in the temporary plugging section, m; is the concentration retention rate, based on engineering experience, the value range is 70%-90%, dimensionless; n is the number of fracture clusters that need to be temporarily plugged, dimensionless; C L is the filtration coefficient, m / min 0.5 .

[0074] In step 4, on-site construction is carried out according to the optimal construction parameters.

[0075] Taking the horizontal well section of shale oil in a certain area as an example, the construction parameters of this section are shown in Table 1 below:

[0076] Table 1 Construction parameters

[0077] Parameter Type Value Parameter Type Value <![CDATA[Construction displacement (m 3 / min)]]> 16 Hydraulic fracture height (m) 30 Fracturing fluid viscosity (mPa·s) 5 <![CDATA[Fracturing fluid density (kg / m 3 )]]> 1050 Young's modulus (MPa) 30000 Hole flow coefficient 0.95 Total construction time (min) 120 Poisson's ratio (dimensionless) 0.2 Initial perforation diameter (m) 0.01 Fracturing section length (m) 60 Number of perforation clusters within the segment 12 <![CDATA[Temporary plugging agent plugging concentration (kg·m -2 )]]> 200 Crack height (m) 30 Temporary plugging agent concentration retention rate 85％ <![CDATA[Filtration loss coefficient (m / min 0.5 )]]> <![CDATA[1×10 -4 ]]>

[0078] The specific process is as follows:

[0079] Step 1: According to the on-site construction data of the target well section, the number of staged fracturing and the number of temporary plugging in the target fracturing section are calculated, and the designed fracturing mode is implemented. According to formula (1), the number of staged fracturing and the number of temporary plugging in the section are calculated to be 3 and 2 respectively.

[0080] Step 2: According to formula (2) and formula (3), the data in the construction parameter table are substituted to calculate the net pressure of the first-stage fracturing crack as 1.35 MPa, and the difference in induced stress between the first-stage multi-cluster cracks is 0.44 MPa; according to formula (4)-(6), the first-stage multi-cluster cracks are taken as the reference cluster, and the initial perforation number of the reference cluster is set to 12. The perforation numbers for the second-stage and third-stage multi-cluster cracks to initiate step-by-step fractures and ensure balanced development of the cracks are 8 and 6, respectively.

[0081] Step 3: According to formula (7), the temporary plugging time for the first and second stages in the section is calculated to be 40 minutes and 80 minutes respectively; the concentration retention rate of the temporary plugging agent in the target section after being put into the wellhead and transported through the wellbore to the fracture is 85%, the fracture width is calculated to be 5.3 mm according to formula (9), and the dosage of temporary plugging agent at each level is calculated to be 233 kg according to formula (8).

[0082] Step 4: According to the recommended fracturing scheme, the target well section is subjected to graded temporary plugging and fracturing transformation. The first temporary plugging operation is performed when the construction time is 40 minutes, and the temporary plugging agent dosage is 233 kg, and then the second-level cracks are fracturing; the second temporary plugging operation is performed when the construction time is 80 minutes, and the temporary plugging agent dosage is 233 kg, and then the third-level cracks are fracturing.

[0083] Microseismic monitoring results show that after fracturing, the balanced opening and expansion of multiple clusters of hydraulic fractures in the example well are better than those of neighboring wells fracturing by conventional methods. The production after fracturing can be increased to 1.6 times that of neighboring wells, which verifies the beneficial effects and engineering application value of the method of the present invention.

[0084] Therefore, the present invention adopts the above-mentioned horizontal well long section multi-cluster staged fracturing parameter optimization and implementation method. Compared with the traditional perforating technology, the core advantage lies in its comprehensive use of perforating flow limiting and temporary plugging diversion technology, considering factors such as stress interference between fractures within the section and friction resistance pressure drop of the hole, and performing perforating parameter design and temporary plugging parameter design to achieve fine optimization of the fracturing scheme, so that the long section multi-cluster fracturing fractures can be opened step by step and the fracture expansion balance can be improved. At the same time, it can reduce cost investment and maximize benefits.

[0085] The above is only an embodiment of the present invention, and the common knowledge such as the known specific structure and / or characteristics in the scheme is not described in detail here. It should be pointed out that for those skilled in the art, several deformations and improvements can be made without departing from the structure of the present invention, which should also be regarded as the protection scope of the present invention, and these will not affect the effect of the implementation of the present invention and the practicality of the patent. The scope of protection required by this application shall be based on the content of its claims, and the specific implementation methods and other records in the specification can be used to interpret the content of the claims.

Claims

1. A method for optimizing and implementing parameters of long-section multi-cluster staged fracturing in horizontal wells, characterized in that: The following steps are involved: Step 1: Based on the principle of balanced inter-fracture stress interference, design the number of staged fracturing and temporary plugging times within the section; Step 2: Based on the principle of opening multi-stage fracturing cracks step by step and balanced expansion of multiple clusters of fractures during each stage of fracturing, the perforation parameters of each stage of fracturing are designed; Step 3: Based on the principle that the amount of liquid inflow into each cluster of fractures is the same, determine the graded temporary plugging time and the amount of temporary plugging agent; Step 4: Carry out on-site construction according to the optimal construction parameters.

2. A method for optimizing and implementing parameters of long-section multi-cluster staged fracturing in horizontal wells according to claim 1, characterized in that: In step 1, it is ensured that the perforation clusters of each level of fracturing are staggered during staged fracturing of the target fracturing section, and the distance between adjacent perforation clusters in each level is not less than 10m but not more than 20m. The calculation formula for the staged fracturing number and temporary plugging times in the section is as follows: Where: N j is the number of staged fracturing stages in the target fracturing section (rounded up), dimensionless; N is the number of perforation clusters per stage, it is recommended that no more than 4 clusters, dimensionless; N T is the total number of perforation clusters in the fracturing stage, dimensionless; N d is the number of temporary plugging times, dimensionless; L is the length of the fracturing section, m; d is the perforation cluster spacing of each level of fracturing (10≤d≤20), m.

3. A method for optimizing and implementing parameters of long-segment multi-cluster staged fracturing in horizontal wells according to claim 1, characterized in that: The calculation process of perforation parameters at each level in step 2 is as follows: S21. Considering the interference effect of induced stress between fractures, the perforation parameters of each perforation cluster of the first-stage fracturing are calculated. The specific process is as follows: First, the net pressure in a single hydraulic fracture is solved based on the analytical solution of the PKN hydraulic fracture model: Secondly, calculate the interference intensity value of the induced stress between fractures when multiple clusters of fractures expand synchronously during the first stage of fracturing: Where: p is the net pressure in a single hydraulic fracture, MPa; Δp s is the interference strength value of the induced stress between fractures, MPa; E is the static Young's modulus, MPa; μ is the viscosity, mPa·s; Q is the injection displacement, m3 / min; N is the number of perforation clusters corresponding to the first-stage fracturing, dimensionless; υ is the Poisson's ratio, dimensionless; h r is the height of hydraulic fracture, m; Finally, considering the interference effect of induced stress between perforations by balancing the friction resistance of perforations, the number of perforations for balanced development of multiple clusters of fractures in the first stage of fracturing is calculated: Where: n p1 is the number of perforations in each perforation cluster of the first-stage fracturing, dimensionless; ρ s is the density of fracturing fluid, kg / m 3 ;d p is the perforation hole diameter, m; K d is the hole flow coefficient, which reflects the influence of the shape of the perforation hole entrance on the flow of fracturing fluid and hole friction, with a value range of 0.5 to 0.95 and dimensionless; i is the i-th fracturing stage, dimensionless; S22. Considering the superposition of the induced stress between the first two hydraulic fractures and the constraint that the second-stage hydraulic fracture perforation cluster is not opened when the first-stage hydraulic fracture perforation cluster is fractured and expanded (the friction resistance pressure drop of the second-stage hydraulic fracture perforation should be higher than that of the first-stage hydraulic fracture perforation), the number of perforations for the second-stage hydraulic fracture is calculated: Where: n p2 is the number of perforations in each perforation cluster of the second-stage fracturing, dimensionless; α is the difference between the frictional pressure drop of the second-stage perforation holes and the frictional pressure drop of the first-stage holes, which is determined based on the experience of the target work area and is usually 5, MPa; S23, and so on to calculate the perforation parameters of the third and subsequent fracturing stages: Where: n pi is the number of perforations in each perforation cluster of the i-th stage fracturing, dimensionless; S24, requiring the number of perforations in the last level of perforation cluster to be no less than 2, otherwise returning to step 1 to reduce the number of levels and recalculate.

4. A method for optimizing and implementing parameters of long-section multi-cluster staged fracturing in horizontal wells according to claim 1, characterized in that: The process of calculating the graded temporary plugging time and the amount of temporary plugging agent in step 3 is as follows: S31. Based on the principle that the amount of liquid inflow into each cluster of fractures is the same, calculate the temporary plugging time at each level: Where, t j is the construction time of the jth level temporary blockage, min; T is the total construction time, min; N j is the number of perforation clusters corresponding to the j-th level of fracturing, dimensionless; S32. Based on the principle of opening the perforation clusters of each level of fracturing in sequence, that is, after temporary plugging, it is ensured that all the cracks opened by the previous level of fracturing are blocked, and the perforation clusters of each level of the next level of fracturing can be effectively opened, the calculation formula for the amount of temporary plugging agent is as follows: The calculation formula of the seam width is as follows: Where m is the dosage of temporary plugging agent, kg; λ is the temporary plugging agent concentration per unit joint height section, which can be measured by indoor experiments, kg / m 2 ; w is the width of the crack in the temporary plugging section, m; is the concentration retention rate, based on engineering experience, the value range is 70%-90%, dimensionless; n is the number of fracture clusters that need to be temporarily plugged, dimensionless; C L is the filtration coefficient, m / min 0.5 .

5. The method for optimizing and implementing parameters of long-section multi-cluster staged fracturing in horizontal wells according to claim 1, characterized in that: In step 4, on-site construction is carried out according to the optimal construction parameters.

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