Method for predicting construction pressure of pumping bridge plug and perforating joint operation and corresponding construction method

Abstract

The present invention discloses a method for predicting the construction pressure of pumping bridge plug and perforation and a corresponding construction method, and belongs to the technical field of hydraulic fracturing in oil and gas fields. The basic law of pumping friction resistance is studied by gap flow and Bernoulli equation, a mathematical model of wellhead pressure considering pumping friction resistance is established, and an automatic fitting method for pumping bridge plug and perforation construction is established by genetic algorithm and least square method, the perforation hole parameters and crack mouth pressure are determined, and then the construction pressure of pumping bridge plug and perforation is predicted, providing more accurate pressure prediction for construction, adjusting construction process parameters according to pressure prediction results, avoiding the reopening of cracks, and reducing construction risks.

Description

Technical Field

[0001] The invention belongs to the technical field of hydraulic fracturing in oil and gas fields, and relates to a method for predicting the construction pressure of pumping bridge plug and perforation joint operation and a corresponding construction method. Background Art

[0002] Pumping bridge plug and perforation joint construction is an important part of shale gas completion engineering. This technology uses cable transmission to freely lower the perforating gun string and bridge plug in the vertical well section, and relies on hydraulic pumping to the target well depth in the horizontal section. A multi-stage ignition controller is used to detonate the bridge plug setting tool to achieve multi-stage segmentation of the horizontal wellbore, and then the perforating gun is detonated to achieve multi-cluster perforation in the segment. At present, shale gas hydraulic fracturing segmentation tools mostly use soluble bridge plugs, which can dissolve quickly in high-mineralization formation water. The construction requires the use of clean water pumping, and the fracturing construction must be completed within 4 hours after the bridge plug is pumped into place to avoid the failure of the bridge plug to dissolve and seal the transformed well section. Therefore, the Fuling work area carried out pumping bridge plug and perforation joint construction in the early morning. The interval between the previous fracturing construction was long, and the pressure diffusion in the well caused the closure of the fracturing fracture. The pressure increase process during the pumping bridge plug and perforation joint construction was accompanied by the reopening of the closed fracture. This causes a sudden drop in pumping pressure, and the force generated will bring the risk of pumping out the perforating tool string. After the tool string falls into the well, it needs to be salvaged using continuous tubing, which seriously affects the progress of fracturing and gas test completion, and thus affects the construction efficiency and safety.

[0003] At present, the research on pumping bridge plug and perforation technology by domestic and foreign scholars mainly focuses on the migration law and stress of tool string in horizontal wellbore, as well as the utilization of construction pressure of pumping bridge plug and perforation, such as diagnosing hydraulic fracture characteristics, understanding fracture closure pressure, fracture opening pressure, formation filtration coefficient and fracturing fluid efficiency. However, there is still a lack of relevant research on the calculation of construction pressure of pumping bridge plug and perforation. Unlike the mature calculation of net pressure of hydraulic fracturing, the construction pressure of pumping bridge plug and perforation is not only related to formation pressure, friction resistance along the wellbore, friction resistance of perforation hole, but also to pumping friction resistance. Pumping friction resistance is the fluid energy loss caused by the movement of tool string during the construction of pumping bridge plug and perforation, but domestic and foreign scholars have neglected the research on pumping friction resistance, resulting in inaccurate calculation of pumping perforation construction pressure. Summary of the invention

[0004] In view of the above problems, the present invention studies the basic law of pumping friction resistance through gap flow and Bernoulli equation, establishes a mathematical model of wellhead pressure considering pumping friction resistance, and uses genetic algorithm and least square method to establish an automatic fitting method for pumping bridge plug perforation joint construction, determines the perforation hole parameters and crack mouth pressure, and then predicts the construction pressure of pumping bridge plug perforation joint construction, provides more accurate pressure prediction for construction, adjusts construction process parameters according to pressure prediction results, avoids reopening of cracks, and reduces construction risks. The specific technical scheme of the present invention is as follows.

[0005] The present invention provides a method for predicting the construction pressure of pumping bridge plug and perforating, comprising the following steps:

[0006] (1) Calculation of fracturing fluid friction △ p fp During the shale gas pumping perforation construction, clean water is used for pumping to prevent the soluble bridge plug from dissolving and failing in the high-mineralization fracturing fluid. Therefore, the present invention uses the friction resistance of clean water along the way to calculate the friction resistance of the fracturing fluid. The specific formula is as follows:

[0007]

[0008] Where: p fp is the fracturing fluid friction, in Pa; D is the casing diameter, in m; q is the displacement of fracturing fluid, in m 3 / min; L is the wellbore length in meters.

[0009] (2) Calculation of perforation hole friction △ p perf . Perforation hole friction (pressure drop near the hole) △ p perf It is closely related to the number of holes, and the specific calculation formula is as follows:

[0010]

[0011] Where: p perf is the friction resistance of the perforating blasthole, in Pa; ρ l is the density of fracturing fluid, in kg / m 3 ; d perf is the blasthole diameter, in m; C D is the flow coefficient, dimensionless; n perf is the number of effective liquid inlet holes, dimensionless.

[0012] (3) Calculation of pumping perforation friction p pd When pumping perforating, part of the fracturing fluid pressure is used to push the tool string to the bottom of the well, causing a certain amount of hydraulic energy to be converted into kinetic energy of the tool string. According to the Bernoulli equation, the driving force of the pumping perforating tool string consists of two parts: one is the static pressure on both sides of the tool string. p 1 , p 2The force generated by the pumping perforation friction is the dynamic pressure caused by the different speeds of the fracturing fluid and the tool string. p pd It is composed of net pressure friction and dynamic pressure friction. The specific calculation formula is as follows:

[0013]

[0014] In the formula, p pd is the pumping perforation friction, unit is Pa; p n is the net pressure friction, in Pa; p d is the dynamic pressure friction, the unit is Pa.

[0015] The calculation formula of dynamic pressure friction is:

[0016]

[0017] In the formula, v f , v p are the fracturing fluid flow rate and tool string movement speed, both in m / min; C is the surface morphology coefficient of the tool string, dimensionless.

[0018] The net pressure friction calculation formula is:

[0019]

[0020] In the formula, p 1 , p 2 are the static pressures on both sides of the tool string, both in Pa; η is the fracturing fluid viscosity, in Pa•s; l is the length of the tool string, in m; d is the diameter of the tool string, in m; h is the gap between the tool string and the casing, in m; ε It is the eccentricity, dimensionless, and ranges from 0 to 1. The larger the eccentricity, the greater the friction resistance of the tool string.

[0021] (4) Calculation of net water column pressure of fracturing fluid p h :

[0022]

[0023] In the formula, p h is the net water column pressure of the fracturing fluid, in Pa; gis the acceleration due to gravity, in m / s 2 ; H is the vertical depth of the horizontal well, in m.

[0024] (5) Fitting fracture pressure p w :

[0025] Fitting fracture pressure based on historical data of pumping perforation construction p w , unit is Pa.

[0026] The historical fitting method is a calculation method that uses selected construction parameters to invert formation parameters. Automatic historical fitting of pumping perforation construction can more accurately determine wellbore parameters and formation parameters based on ground monitoring parameters, providing guidance for pumping perforation construction technology. There are two main historical fitting methods: empirical fitting and artificial intelligence fitting. Recently, researchers at home and abroad have mostly used artificial intelligence fitting to screen the optimal solution to reduce the time consumption of historical fitting and improve fitting accuracy.

[0027] (6) Predicting the construction pressure of pumping bridge plug and perforating p s The construction pressure of pumping bridge plug and perforation is related to the fracture pressure, fracturing fluid friction, perforation hole friction, fracturing fluid hydrostatic column pressure, and pumping perforation friction. The specific calculation formula is:

[0028]

[0029] In the formula, p s It is the construction pressure of pumping bridge plug and perforating joint operation, the unit is Pa.

[0030] Furthermore, the present invention adopts a genetic algorithm (GA) to fit the fracture pressure p w . Genetic algorithm (GA) was proposed by Professor Holland of the University of Michigan in 1995. It is an algorithm for searching for optimal solutions by drawing on the genetic mechanism of nature and biological evolution. Genetic algorithm has good global search capability, and the search process is neither constrained by the continuity of the optimization function nor requires the optimization function to be differentiable. The basic idea of ​​the algorithm is simple, and it has the advantages of global parallel search, simplicity, generality, and strong robustness. The present invention applies genetic algorithm to the process of pressure prediction in the joint construction of pumping bridge plug perforation as follows:

[0031] ①Gene coding and generation of initial population

[0032] The gene encoding is determined by the internal program of Matlab; the tool string parameters and water performance parameters are known parameters in the pumping perforation construction process, some wellbore parameters are known, but the formation pressure and borehole friction are unknown. Therefore, the formation pressure, the number of effective liquid-inlet holes and the flow coefficient are used as variables for automatic history matching research, and the dimension of the problem is 3. The number of selected populations is N s , the specific format of the initial group is as follows:

[0033]

[0034] ②Fitness

[0035] The least square method is a mathematical optimization technique that finds the best function match for data by minimizing the sum of squares of errors. The present invention selects the shale gas horizontal well pumping perforation construction pressure as the sample for history matching, and selects the residual sum of squares of the least square method as the fitness function.

[0036]

[0037] In the formula, F t is the residual sum of squares; p s ( i ) is the i The pumping perforation mathematical model calculates the pressure value at each point, in Pa; p a ( i ) is the i The actual pumping perforating construction pressure value of each point is in Pa; num is the number of actual pumping perforating construction pressures monitored on the ground, which is dimensionless.

[0038] ③Judgment criteria

[0039] Given a maximum number of iterations (for example, 150), when the number of iterations exceeds the maximum number of iterations, the iteration is stopped and the optimal result X( p w , C D , n perf ), otherwise a selection operation is performed.

[0040] ④Select

[0041] According to the size of individual fitness, roulette selection operation is performed.

[0042] ⑤Cross

[0043] The crossover probability is calculated according to the size of individual fitness, and the crossover operation is performed.

[0044] ⑥Variation

[0045] The mutation probability is calculated according to the size of individual fitness, and the mutation operation is performed.

[0046] The present invention also provides a pumping bridge plug and perforating joint construction method. According to the above method, the construction pressure of the pumping bridge plug and perforating joint construction is predicted, and then the construction process parameters are adjusted according to the prediction results to avoid reopening of cracks and reduce the risk of pumping out of the perforating gun string.

[0047] Furthermore, the construction process parameter is pumping displacement.

[0048] The present invention can be used to predict the pressure of pumping perforation construction, provide more accurate pressure prediction for pumping construction, avoid reopening of cracks, and reduce the risk of pumping out of the perforating gun string. BRIEF DESCRIPTION OF THE DRAWINGS

[0049] Figure 1 It is a schematic diagram of tool string movement.

[0050] Figure 2 It is the pressure fitting curve of pumping bridge plug and perforating joint construction.

[0051] Figure 3 It is the pressure prediction curve for the construction of pumping bridge plug and perforating. DETAILED DESCRIPTION

[0052] The technical solution of the present invention is described clearly and completely below in conjunction with the accompanying drawings of the specification. Obviously, the described implementation is only a part of the implementation of the present invention, not all of the implementations. Based on the implementation of the present invention, all other implementations obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0053] Figure 1 It is a schematic diagram of tool string movement. The basic law of pumping friction is obtained through gap flow and Bernoulli equation. The fracturing fluid friction, perforating hole friction, pumping perforating friction and hydrostatic column pressure of fracturing fluid are calculated according to the method provided in the invention content.

[0054] During the construction of pumping-bridge-plug-perforating joint operation, parameters such as cable tension, tool string lowering speed, pumping displacement, liquid volume and pump pressure can be obtained in real time, and a section of the pumping-bridge-plug-perforating joint operation curve of a well can be selected for automatic historical fitting.

[0055] The basic parameters of the pumping bridge plug and perforation joint construction are shown in Table 1.

[0056] Table 1: Basic parameters of pumping bridge plug and perforating joint operation

[0057]

[0058] The construction data of pumping perforation in the first section are summarized in Table 2.

[0059] Table 2: Construction data of pump perforation in the first stage

[0060]

[0061] According to the method provided in the Summary of the Invention, the construction pressure of the first stage of pumping bridge plug and perforation is fitted, and the results are as follows: Figure 2 As shown. Figure 2 It can be seen that the pumping perforation construction pressure theoretical model has a good fitting effect with the actual data, indicating that the pumping perforation construction pressure model is accurate and reliable and can be used for pumping perforation pressure prediction. Through fitting, it was found that during the early morning fracturing construction, the number of blastholes opened was 3, the flow coefficient was about 0.6, and the seam pressure was about 40MPa.

[0062] Next, the pressure prediction of the second stage of pumping bridge plug perforation joint operation is carried out. The opening pressure of the second stage of construction is 14.44MPa. According to the number of blastholes opened (3), flow coefficient (0.6) and seam pressure (40MPa) obtained by fitting in the first stage, the prediction is as follows: Figure 3 The analysis shows that the predicted results are basically consistent with the actual pumping curve change trend, the pressure change range is also basically consistent, and the model is accurate and reliable.

[0063] In the subsequent pumping bridge plug and perforating joint construction, the pumping displacement is adjusted according to the prediction results to avoid the reopening of the cracks and reduce the risk of pumping out of the perforating gun string.

[0064] Although the embodiments of the present invention have been shown and described above, it is understood that the above embodiments are exemplary and cannot be understood as limiting the present invention. A person skilled in the art may change, modify, replace and modify the above embodiments within the scope of the present invention without departing from the principles and purpose of the present invention. The protection scope of the present invention is defined by the claims and their equivalent technical solutions.

Claims

1. A method for predicting the construction pressure of pumped bridge plug and perforation, characterized in that: The following steps are involved: (1) Calculation of fracturing fluid friction △ p fp : Where: p fp is the fracturing fluid friction, in Pa; D is the casing diameter, in m; q is the displacement of fracturing fluid, in m 3 / min; L is the wellbore length, in m; (2) Calculation of perforation hole friction △ p perf : Where: p perf is the friction resistance of the perforating blasthole, in Pa; ρ l is the density of fracturing fluid, in kg / m 3 ; d perf is the blasthole diameter, in m; C D is the flow coefficient, dimensionless; n perf is the number of effective liquid inlet holes, dimensionless; (3) Calculation of pumping perforation friction p pd : In the formula, p pd is the pumping perforation friction, unit is Pa; p n is the net pressure friction, in Pa; p d is the dynamic pressure friction, in Pa; The calculation formula of dynamic pressure friction is: In the formula, v f , v p are the fracturing fluid flow rate and tool string movement speed, both in m / min; C is the surface topography coefficient of the tool string, dimensionless; The net pressure friction is calculated as: In the formula, p 1. p 2 are the static pressures on both sides of the tool string, both in Pa; η is the fracturing fluid viscosity, in Pa•s; l is the length of the tool string, in m; d is the diameter of the tool string, in m; h is the gap between the tool string and the casing, in m; ε is the eccentricity, dimensionless; (4) Calculation of net water column pressure of fracturing fluid p h : In the formula, p h is the net water column pressure of the fracturing fluid, in Pa; g is the acceleration due to gravity, in m / s 2 ; H is the vertical depth of the horizontal well, in m; (5) Fitting fracture pressure p w : Fitting fracture pressure based on historical data of pumping perforation construction p w , unit is Pa; (6) Prediction of construction pressure of pumping bridge plug and perforating p s : In the formula, p s It is the construction pressure of pumping bridge plug and perforating joint operation, the unit is Pa.

2. The method according to claim 1, characterized in that Fitting fracture pressure using genetic algorithm p w , the specific process is as follows: ①Gene coding and generation of initial population The gene code is determined by the internal program of Matlab; the selected population size is N s , the specific format of the initial group is as follows: ②Fitness Select the residual sum of squares of the least squares method as the fitness function: In the formula, F t is the residual sum of squares; p s ( i ) is the i The pumping perforation mathematical model calculates the pressure value at each point, in Pa; p a ( i ) is the i The actual pumping perforation construction pressure value of each point, in Pa; num is the number of actual pumping perforation construction pressures monitored on the ground, dimensionless; ③Judgment criteria Given a maximum number of iterations, when the number of iterations exceeds the maximum number of iterations, the iteration is stopped and the optimal result X( p w , C D , n perf ), otherwise, select operation; ④Select According to the size of individual fitness, roulette selection operation is performed; ⑤Cross Calculate the crossover probability according to the size of individual fitness and perform crossover operation; ⑥Variation The mutation probability is calculated according to the size of individual fitness, and the mutation operation is performed.

3. The pumping bridge plug and perforation joint construction method is characterized by: The method according to claim 1 or 2 predicts the construction pressure of the pumping bridge plug and perforating combination, and then adjusts the construction process parameters according to the prediction results to avoid the reopening of the cracks and reduce the risk of the perforating gun string pumping out.

4. The pumping bridge plug and perforation joint construction method according to claim 3 is characterized in that: The construction process parameter is the pumping displacement.

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