Flow distribution simulation method for phase-change self-supporting chemical fracturing fluid system

Abstract

The invention discloses a phase change self-supporting chemical fracturing fluid system flow distribution simulation method, and belongs to the field of petroleum and natural gas exploration. Comprising the following steps: selecting an injection displacement and a total injection amount in a chemical fracturing construction scheme to carry out a physical simulation experiment, and observing the flow distribution condition of the phase-change self-supporting chemical fracturing system; calculating the geometric dimension of an artificial fracture formed by phase change self-supporting chemical fracturing; calculating the flow distribution condition of the phase-change self-supporting chemical fracturing system under the conditions of the selected injection displacement and the selected total injection amount according to the geometric dimension of the fracture; comparing a physical simulation experiment result with a calculation result, and adjusting values of parameters adopted when the flow distribution condition of the phase change self-supporting chemical fracturing system is calculated according to the difference of the results; and calculating the flow distribution condition of the phase-change self-supporting chemical fracturing system under the conditions of other injection displacement and total injection amount by utilizing the obtained adjusted parameter values. According to the method, the workload is reduced, the experiment input cost is reduced, and time and labor are saved.

Description

Technical Field

[0001] The invention relates to the technical field of oil and gas exploration and development, and more specifically to a flow distribution simulation method for a phase-change self-supporting chemical fracturing fluid system. Background Art

[0002] After decades of development, hydraulic fracturing technology has become the most important means of increasing production and transformation of oil and gas reservoirs, especially low-permeability and ultra-low-permeability oil and gas reservoirs. Conventional hydraulic fracturing technology has promoted the efficient development of oil and gas reservoirs, but there are still unavoidable problems such as high friction resistance, high pump pressure, complex sand fracturing construction, high requirements for construction equipment, sand plugging, difficulty in flowback, and residue damage.

[0003] A new hydraulic fracturing technology, phase-change self-supporting chemical fracturing technology, is currently under development. This technology injects a phase-change self-supporting chemical fracturing fluid system composed of phase-change fracturing fluid and non-phase-change fracturing fluid into the formation. Under formation temperature conditions, the phase-change fracturing fluid undergoes a phase change, changing from liquid to solid chemical proppant particles, replacing conventional proppants such as ceramsite and quartz sand to support hydraulic fractures, which serve as high-speed flow channels for underground oil and gas. When carrying out the phase-change self-supporting chemical fracturing technology construction, the key to achieving a higher conductivity and forming effective support is to form a good distribution morphology of phase-change fracturing fluid. The distribution of phase-change fracturing fluid determines the distribution of chemical proppant particles formed by phase change. The flow distribution of the phase-change self-supporting chemical fracturing fluid system belongs to the field of liquid-liquid two-phase flow interface tracking research.

[0004] Invention patent CN110939423A discloses an experimental device for pressure-resistant visual simulation of the flow law of self-supporting fracturing fluid. The experimental device includes the following components: four bolt fixing frames, four long fixing bolts, two upper and lower plexiglass, an injection end, an outflow end, and short sealing bolts. The above components are combined together to form a continuous internal flow channel with a liquid pressure resistance of 5MPa. According to different experimental parameters, this device can intuitively and visually observe the distribution of self-supporting fracturing fluid in simulated formation cracks. However, this tracking simulation method is carried out through physical experiments, which has problems such as large workload, high experimental investment cost, and time-consuming and labor-intensive.

[0005] Therefore, how to achieve comprehensive simulation of the liquid-liquid two-phase flow interface tracking involved in the flow distribution of phase-change self-supporting chemical fracturing fluid system with less experimental amount has become the goal of this field. Summary of the invention

[0006] The object of the present invention is to provide a method for simulating flow distribution of a phase-change self-supporting chemical fracturing fluid system.

[0007] In order to achieve the above technical objectives, the technical solution adopted by the present invention is as follows:

[0008] According to one aspect of the present invention, a method for simulating flow distribution of a phase-changing self-supporting chemical fracturing fluid system is provided, comprising the following steps:

[0009] Step S1: selecting an injection displacement and a total injection amount in the phase change self-supporting chemical fracturing construction scheme to conduct a physical simulation experiment, and observing the flow distribution of the phase change self-supporting chemical fracturing system under the selected injection displacement and total injection amount conditions;

[0010] Step S2: Calculating the geometric dimensions of the artificial fractures formed by phase change self-supporting chemical fracturing according to the geological and engineering parameters of the target oil and gas well;

[0011] Step S3: Calculate the flow distribution of the phase change self-supporting chemical fracturing system under the injection displacement and total injection volume conditions selected in step S1 according to the fracture geometry calculated in step S2;

[0012] Step S4: Compare the physical simulation experiment results in step S1 with the calculation results in step S3, adjust the values ​​of the parameters used in calculating the flow distribution of the phase change self-supporting chemical fracturing system in step S3 according to the difference in the results, and calculate the flow distribution of the phase change self-supporting chemical fracturing system again until the difference between the physical simulation experiment results in step S1 and the calculation results in step S3 is within a set range;

[0013] Step S5: using the adjusted parameter values ​​obtained in step S4, calculate the flow distribution of the phase change self-supporting chemical fracturing system under other injection displacement and total injection conditions given in the phase change self-supporting chemical fracturing construction plan.

[0014] According to one embodiment of the present invention, the physical simulation experiment is used to simulate liquid-liquid two-phase flow interface tracking.

[0015] According to one embodiment of the present invention, the flow distribution of the phase-change self-supporting chemical fracturing system in step S1 is represented by the volume fraction of phase-change phase droplets in the image obtained in the physical simulation experiment.

[0016] According to an embodiment of the present invention, the flow distribution of the phase-change self-supporting chemical fracturing system in step S3 is represented by the volume fraction of the phase-change phase droplets in the image obtained by numerical calculation.

[0017] According to one embodiment of the present invention, in step S2, the continuity equation and the fluid loss v are used according to the geological and engineering parameters of the target oil and gas well. l The geometric dimensions of the artificial fractures formed by phase change self-supporting chemical fracturing are calculated using the calculation equation, fluid pressure drop equation, fracture width equation and fracture height equation.

[0018] According to one embodiment of the present invention, the continuity equation is as follows:

[0019]

[0020] Among them, x is the position in the direction of the seam length, in m; t is the construction time, in s; q(x, t) is the flow rate at point x in the seam at time t, in m 3 / s;v l (x, t) is the fluid loss at point x in the joint at time t, in m 2 / s; A(x, t) is the cross-sectional area of ​​the crack at time t, in m 2 .

[0021] According to one embodiment of the present invention, the fluid loss v l The calculation equation is as follows:

[0022]

[0023] Among them, x is the position in the direction of the seam length, in meters; t is the construction time, in seconds; v l is the fluid loss, in m 2 / s;h p is the fracture height, in m; C(x, t) is the fluid loss coefficient at point x in the fracture at time t, in m / s 0.5 ; τ is the time it takes for the fluid to reach the fracture x, in seconds.

[0024] According to one embodiment of the present invention, the fluid pressure drop equation is as follows:

[0025]

[0026] Among them, x is the position in the direction of the seam length, in m; t is the construction time, in s;

[0027] p(x, 0, t) is the pressure at point x in the crack at time t, in MPa; μ f is the viscosity of the fracturing fluid, in mPa·s; q(x, t) is the flow rate at point x in the fracture at time t, in m 3 / s; h(x, t) is the seam height at point x in the seam at time t, in m; w f (x, 0, t) is the half crack width at point x in the crack at time t, in m.

[0028] According to one embodiment of the present invention, the crack width equation is as follows:

[0029]

[0030]

[0031] Among them, x is the position in the direction of seam length, in meters; t is the construction time, in seconds; z is the position in the direction of seam height, in meters; w f (x, z, t) is the crack width at the crack length x at the crack height z at time t, in m; ν is the Poisson's ratio, dimensionless; E is the elastic modulus, in MPa; p(z) is the net pressure at the crack height position z, in MPa; h(x, t) is the crack height at the crack at time t, in m; τ is the time it takes for the fluid to reach the crack x, in s.

[0032] According to one embodiment of the present invention, the crack height equation is as follows:

[0033]

[0034] Where x is the position in the fracture length direction, in m; p is the pressure in the fracture, in MPa; H is the half-height of the fracture, in m; Δs is the stress difference, in MPa; f is the ratio of the oil layer thickness to the fracture height, dimensionless; K c is the stress intensity factor, in MPa·m 0.5 .

[0035] According to an embodiment of the present invention, the geological and engineering parameters of the target oil and gas well are taken from reservoir geological data, indoor experimental test data, or selected based on experience.

[0036] According to one embodiment of the present invention, step S3 of calculating the flow distribution of the phase change self-supporting chemical fracturing system includes solving the flow volume fraction model of the phase change self-supporting chemical fracturing system according to the mass conservation equation, the momentum equation and the phase change fracturing liquid volume fraction calculation equation.

[0037] According to one embodiment of the present invention, the mass conservation equation is as follows:

[0038]

[0039] Among them, x is the position in the direction of the seam length, the unit is m; u is the speed in the x direction, the unit is m / s; v is the speed in the y direction, the unit is m / s; y is the position in the direction of the seam width, the unit is m.

[0040] According to one embodiment of the present invention, the momentum equation is as follows:

[0041]

[0042]

[0043]

[0044]

[0045] Among them, x is the position in the fracture length direction, in m; y is the position in the fracture height direction, in m; p is the pressure inside the artificial fracture, in Pa; α is the interfacial tension, in N / m; g is the gravitational acceleration, in m / s 2 ; ρ is the equivalent density; u is the velocity in the x direction, in m / s; v is the velocity in the y direction, in m / s.

[0046] According to one embodiment of the present invention, the phase change fracturing fluid volume fraction calculation equation is as follows:

[0047]

[0048] Among them, β is the volume rate of phase change fracturing fluid in each calculation unit, dimensionless; t is the construction time, unit is s; u is the speed in the x direction, unit is m / s; v is the speed in the y direction, unit is m / s.

[0049] According to an embodiment of the present invention, the setting range is 5%.

[0050] Due to the adoption of the above technical scheme, the phase-change self-supporting chemical fracturing fluid system flow distribution simulation method provided by the present invention is significantly more advanced than the prior art. The method simulates the liquid-liquid two-phase flow interface tracking involved in the flow distribution of the phase-change self-supporting chemical fracturing fluid system by means of numerical simulation, thereby reducing the workload, reducing the experimental investment cost, and saving time and effort. BRIEF DESCRIPTION OF THE DRAWINGS

[0051] The accompanying drawings are used to provide a further understanding of the present invention and constitute a part of the specification. Together with the following specific embodiments, they are used to explain the present invention but do not constitute a limitation of the present invention. In the accompanying drawings:

[0052] Figure 1 is an exemplary flow chart of a method for simulating flow distribution of a phase-changing self-supporting chemical fracturing fluid system according to an embodiment of the present invention;

[0053] Figure 2 It is a schematic diagram of the physical simulation experiment results of Example 1;

[0054] Figure 3 This is a schematic diagram of the first numerical calculation simulation result of Example 1;

[0055] Figure 4 This is a schematic diagram of the second numerical calculation simulation results of Example 1;

[0056] Figure 5 This is a schematic diagram of the physical simulation experiment results of Example 2;

[0057] Figure 6 This is a schematic diagram of the first numerical calculation simulation result of Example 2;

[0058] Figure 7 This is a schematic diagram of the second numerical calculation simulation results of Example 2;

[0059] Figure 8 This is a schematic diagram of the third numerical calculation simulation results of Example 2. DETAILED DESCRIPTION

[0060] The specific implementation of the present disclosure is described in detail below in conjunction with the accompanying drawings. It should be understood that the specific implementation described herein is only used to illustrate and explain the present disclosure, and is not used to limit the present disclosure.

[0061] In addition, reference to "embodiments" herein means that a particular feature, structure, or characteristic described in conjunction with the embodiments may be included in at least one embodiment of the present invention. The appearance of the phrase in various places in the specification does not necessarily refer to the same embodiment, nor is it an independent or alternative embodiment that is mutually exclusive with other embodiments. It is explicitly and implicitly understood by those skilled in the art that the embodiments described herein may be combined with other embodiments.

[0062] It will be understood by those skilled in the art that, unless otherwise defined, all terms (including technical terms and scientific terms) used herein have the same meaning as the general understanding of those skilled in the art to which this application belongs. It should also be understood that terms such as those defined in general dictionaries should be understood to have the same meaning as in the context of the prior art, and will not be interpreted with an idealized or overly formal meaning unless specifically defined as in the embodiments of this application.

[0063] The present invention provides a method for simulating flow distribution of a phase-changing self-supporting chemical fracturing fluid system, which generally comprises the following steps:

[0064] Step S1: selecting an injection displacement and a total injection amount in the phase change self-supporting chemical fracturing construction scheme to conduct a physical simulation experiment, and observing the flow distribution of the phase change self-supporting chemical fracturing system under the selected injection displacement and total injection amount conditions;

[0065] Step S2: Calculating the geometric dimensions of the artificial fractures formed by phase change self-supporting chemical fracturing according to the geological and engineering parameters of the target oil and gas well;

[0066] Step S3: Calculate the flow distribution of the phase change self-supporting chemical fracturing system under the injection displacement and total injection volume conditions selected in step S1 according to the fracture geometry calculated in step S2;

[0067] Step S4: Compare the physical simulation experiment results in step S1 with the calculation results in step S3, adjust the values ​​of the parameters used in calculating the flow distribution of the phase change self-supporting chemical fracturing system in step S3 according to the difference in the results, and calculate the flow distribution of the phase change self-supporting chemical fracturing system again until the difference between the physical simulation experiment results in step S1 and the calculation results in step S3 is within a set range;

[0068] Step S5: using the adjusted parameter values ​​obtained in step S4, calculate the flow distribution of the phase change self-supporting chemical fracturing system under other injection displacement and total injection conditions given in the phase change self-supporting chemical fracturing construction plan.

[0069] The following is combined with Figure 1 The flowchart shown is described in detail by way of example.

[0070] First, an injection displacement and a total injection amount in the phase-change self-supporting chemical fracturing construction scheme are selected for physical simulation experiments to observe the flow distribution of the phase-change self-supporting chemical fracturing system under the selected injection displacement and total injection amount conditions. Specifically, in the phase-change self-supporting chemical fracturing construction scheme, multiple injection displacements and total injection amounts of the phase-change self-supporting chemical fracturing system are generally provided. When conducting the physical simulation experiment, one of the injection displacements and total injection amount is selected for simulation.

[0071] The physical simulation experiment used is used to simulate the tracking of the liquid-liquid two-phase flow interface. For example, a device such as that disclosed in patent document CN110805437A is used, and an image acquisition device is used in the device to capture the dynamic flow, static distribution, etc. of the self-supporting fracturing fluid system in the main frame below the tempered glass. The physical simulation results are used as a reference object to compare the subsequent numerical simulation results so as to adjust the parameters of the numerical simulation model. The flow distribution of the phase-change self-supporting chemical fracturing system can be represented by the volume fraction of the phase-change phase droplets in the obtained image (the proportion of the sum of the areas of all droplets to the total spread area). For example, the image captured by the image acquisition device can be processed to calculate the volume fraction of the phase-change phase droplets therein.

[0072] When determining the flow model of the phase-change self-supporting chemical fracturing system, it is necessary to first calculate some parameters to be used in the model. Here, the geometric dimensions of the artificial fractures formed by the phase-change self-supporting chemical fracturing are calculated based on the geological and engineering parameters of the target oil and gas wells.

[0073] The three-dimensional fracture extension mathematical model consists of four fracture-related equations: continuity equation, fluid loss v l Calculation equation, fluid pressure drop equation, fracture width equation and fracture height equation.

[0074] The continuity equation is a mathematical equation that expresses the conservation of fluid matter in hydraulic fractures. If the fluid in the fracture is assumed to be incompressible, its expression is as follows:

[0075]

[0076] Among them, x is the position in the direction of the seam length, in m; t is the construction time, in s; q(x, t) is the flow rate at point x in the seam at time t, in m 3 / s;v l (x, t) is the fluid loss at point x in the joint at time t, in m 2 / s; A(x, t) is the cross-sectional area of ​​the crack at time t, in m 2 .

[0077] Assuming that fluid loss only occurs inside the reservoir, the fluid loss v l The expression is as follows:

[0078]

[0079] Among them, x is the position in the direction of the seam length, in meters; t is the construction time, in seconds; v l is the fluid loss, in m 2 / s;h p is the fracture height, in m; C(x, t) is the fluid loss coefficient at point x in the fracture at time t, in m / s 0.5 ; τ is the time it takes for the fluid to reach the fracture x, in seconds.

[0080] The mathematical model of three-dimensional hydraulic fracture extension assumes that the fluid flows in one dimension and expands in the length, width and height directions, but the fracture width is much smaller than the fracture length and height, and the fracture cross section is approximately elliptical, but it can be approximately treated as a flat plate fracture. When the fracture vertical cross section is elliptical and the fluid in the fracture is a Newtonian fluid, the fluid pressure drop equation is as follows:

[0081]

[0082] Among them, x is the position in the direction of the seam length, in m; t is the construction time, in s;

[0083] p(x, 0, t) is the pressure at point x in the crack at time t, in MPa; μ f is the viscosity of the fracturing fluid, in mPa·s; q(x, t) is the flow rate at point x in the fracture at time t, in m 3 / s; h(x, t) is the seam height at point x in the seam at time t, in m; w f (x, 0, t) is the half crack width at point x in the crack at time t, in m.

[0084] When the stress value of the crack wall is distributed in the form of an even function P(z), the crack width of any coordinate (x, z) of a two-dimensional narrow crack in a linear elastic medium is:

[0085]

[0086] Among them, x is the position in the direction of seam length, in meters; t is the construction time, in seconds; z is the position in the direction of seam height, in meters; w f (x, z, t) is the crack width at the crack length x at the crack height z at time t, in m; ν is the Poisson's ratio, dimensionless; E is the elastic modulus, in MPa; p(z) is the net pressure at the crack height position z, in MPa; h(x, t) is the crack height at the crack at time t, in m; τ is the time it takes for the fluid to reach the crack x, in s.

[0087] The crack height equation is as follows:

[0088]

[0089] Where x is the position in the fracture length direction, in m; p is the pressure in the fracture, in MPa; H is the half-height of the fracture, in m; Δs is the stress difference, in MPa; f is the ratio of the oil layer thickness to the fracture height, dimensionless; K c is the stress intensity factor, in MPa·m 0.5 .

[0090] The parameters required in the above formulas (a)-(e) are taken from reservoir geological data, indoor experimental test data, or selected based on experience, and the solution method is differential iterative solution.

[0091] Next, based on the calculated fracture geometry, the flow distribution of the phase-change self-supporting chemical fracturing system under the selected injection displacement and total injection volume conditions is calculated. The calculation of the flow distribution of the phase-change self-supporting chemical fracturing system includes solving the numerical model of the flow distribution of the phase-change self-supporting chemical fracturing system based on the mass conservation equation, momentum equation and phase-change fracturing liquid volume fraction calculation equation. The relevant mathematical models of fluid flow are all based on conservation: the transport of material mass satisfies the law of conservation of mass, the transport of momentum satisfies Newton's second law, and the transport of energy satisfies the law of conservation of energy. A finite closed region with a fixed space and no change with time is taken as the control body of the fluid. By applying the conservation law to each control body, the control equation of the corresponding physical quantity can be derived. When the fracturing fluid system flows in the fracture, it satisfies the following mass conservation equation:

[0092]

[0093] Among them, x is the position in the direction of the seam length, the unit is m; u is the speed in the x direction, the unit is m / s; v is the speed in the y direction, the unit is m / s; y is the position in the direction of the seam width, the unit is m.

[0094] The momentum equation is shown below:

[0095]

[0096]

[0097]

[0098]

[0099] Among them, x is the position in the fracture length direction, in m; y is the position in the fracture height direction, in m; p is the pressure inside the artificial fracture, in Pa; α is the interfacial tension, in N / m; g is the gravitational acceleration, in m / s 2 ; ρ is the equivalent density; u is the velocity in the x direction, in m / s; v is the velocity in the y direction, in m / s.

[0100] The volume fraction β is used to represent the volume rate of the phase-change fracturing fluid in each calculation unit, and the volume rate of the non-phase-change fracturing fluid is 1-β. The equivalent density ρ and equivalent viscosity μ of the fluid in each calculation unit are expressed as:

[0101]

[0102] Where: ρ0 is the density of phase change fracturing fluid, ρ1 is the density of non-phase change fracturing fluid, μ0 is the viscosity of phase change fracturing fluid, and μ1 is the viscosity of non-phase change fracturing fluid.

[0103] The volume fraction β calculation equation is:

[0104] Among them, β is the volume rate of phase change fracturing fluid in each calculation unit, dimensionless; t is the construction time, unit is s; u is the speed in the x direction, unit is m / s; v is the speed in the y direction, unit is m / s.

[0105] The parameters required for calculation in the above formulas (f)-(l) include the geometric size of artificial fractures, the injection displacement of the phase-change self-supporting chemical fracturing system, the density of the phase-change fracturing fluid, the density of the non-phase-change fracturing fluid, the viscosity of the phase-change fracturing fluid, the viscosity of the non-phase-change fracturing fluid, and the interfacial tension between the phase-change fracturing fluid and the non-phase-change fracturing fluid. The parameters used are taken from the calculation results of the previous step, the phase-change self-supporting chemical fracturing construction plan, the indoor experimental test data, or selected based on experience, and the solution method is finite element discrete solution. After obtaining the numerical model of the flow distribution of the phase-change self-supporting chemical fracturing system, the flow distribution of the phase-change self-supporting chemical fracturing system under the selected injection displacement and total injection amount is calculated. The flow distribution can be represented by the volume fraction of the phase-change phase droplets in the obtained image (the proportion of the sum of the areas of all droplets to the total spread area). For example, the obtained image can be processed to calculate the volume fraction of the phase-change phase droplets therein.

[0106] Then compare the results of the physical simulation experiment with the results of the numerical simulation calculation (i.e., the volume fraction of the phase change phase droplets obtained from the physical simulation experiment and the volume fraction of the phase change phase droplets obtained from the numerical simulation calculation), adjust the values ​​of the parameters used in the numerical simulation calculation of the flow distribution of the phase change self-supporting chemical fracturing system according to the difference in the results, and calculate the flow distribution of the phase change self-supporting chemical fracturing system again until the difference between the physical simulation experiment results and the calculation results is within the set range. Specifically, the volume ratio of the phase change phase droplets in the phase change fracturing fluid in the two simulation results can be compared. If the calculated volume ratio of the phase change phase droplets of the phase change fracturing fluid is significantly larger than the droplet volume ratio in the physical simulation experiment, then the interfacial tension is lowered and recalculated, otherwise the interfacial tension is increased and recalculated, until the difference between the calculated volume ratio of the phase change fracturing fluid droplets and the droplet volume ratio in the physical simulation experiment is within an acceptable range (e.g., no more than 5%), then the parameters of the numerical simulation calculation are fixed.

[0107] After obtaining the numerical simulation results of the flow distribution of the phase change self-supporting chemical fracturing system that are relatively close to the physical simulation, the final interfacial tension parameters obtained in the numerical simulation are used to calculate the flow distribution of the phase change self-supporting chemical fracturing system under other injection displacement and total injection conditions given in the phase change self-supporting chemical fracturing construction plan.

[0108] In order to make the technical means, creative features, objectives and effects of the present invention easy to understand, the present invention is further explained below in conjunction with specific implementation methods.

[0109] Embodiment 1:

[0110] (1) Select the injection displacement as 5m 3 / min, the total injection volume is 200m 3 The parameters of the physical simulation experiment are shown in Figure 2 .

[0111] (2) Calculate the geometric dimensions of the artificial fracture formed by phase change self-supporting chemical fracturing. The calculated artificial fracture is 100m long and 40m high.

[0112] (3) Based on the fracture geometry calculated in step (2), the injection rate is calculated to be 5m 3 / min, the total injection volume is 200m 3 The flow distribution of the phase change self-supporting chemical fracturing system under the conditions of Figure 3 .

[0113] (4) Figure 2 and Figure 3 The images were processed separately, and the proportion of the phase change phase droplets in the entire shooting area was calculated and compared. It was found that the calculated droplet volume ratio was larger than the droplet volume ratio in the physical simulation experiment. Therefore, the interfacial tension needs to be reduced from 0.00024N / m to 0.0002N / m, and then calculated again. The calculation results are as follows: Figure 4 As shown, it can be found that the calculated results are not much different from the physical simulation experimental results, that is, the final interfacial tension is selected as 0.0002N / m.

[0114] (5) The interfacial tension is selected as 0.0002 N / m, and the flow distribution of the phase change self-supporting chemical fracturing system under other injection displacement and total injection conditions given in the phase change self-supporting chemical fracturing construction plan is calculated again.

[0115] Embodiment 2:

[0116] (1) Select the injection displacement as 3m 3 / min, the total injection volume is 100m 3 Physical simulation experiments were carried out and the results are shown in Figure 5 .

[0117] (2) Calculation shows that the artificial crack is 50 m long and 20 m high.

[0118] (3) Based on the fracture geometry calculated in step (2), the injection rate is calculated to be 3m 3 / min, the total injection volume is 100m 3 The flow distribution of the phase change self-supporting chemical fracturing system is shown in Figure 6 .

[0119] (4) Figure 5 and Figure 6The images were processed separately, and the proportion of phase change phase droplets in the entire shooting area was calculated and compared. It was found that the calculated droplet volume ratio was smaller than the droplet volume ratio in the physical simulation experiment. Therefore, the interfacial tension needs to be increased from 0.0002N / m to 0.00024N / m, and the calculation is repeated. The calculation results are as follows: Figure 7 As shown in Figure 2, it can be found that the calculated droplet volume ratio of the phase change fracturing fluid is significantly larger than the droplet volume ratio in the physical simulation experiment. Therefore, the interfacial tension needs to be further reduced from 0.00024N / m to 0.00022N / m. The calculated results are shown in Figure 2. Figure 8 As shown, it can be found that the calculated results are not much different from the physical simulation experimental results, that is, the final interfacial tension is selected as 0.00022N / m.

[0120] (5) The interfacial tension is selected as 0.00022 N / m, and the flow distribution of the phase change self-supporting chemical fracturing system under other injection displacement and total injection conditions given in the phase change self-supporting chemical fracturing construction plan is calculated again.

[0121] The phase-change self-supporting chemical fracturing fluid system flow distribution simulation method of the present invention simulates the liquid-liquid two-phase flow interface tracking involved in the flow distribution of the phase-change self-supporting chemical fracturing fluid system by means of numerical simulation, thereby reducing the workload, reducing the experimental investment cost, and saving time and effort.

[0122] The preferred embodiments of the present invention are described in detail above. However, the present invention is not limited to the specific details in the above embodiments. Within the technical concept of the present invention, a variety of simple modifications can be made to the technical solution of the present invention, and these simple modifications all belong to the protection scope of the present invention.

[0123] It should also be noted that the various specific technical features described in the above specific embodiments can be combined in any suitable manner without contradiction. In order to avoid unnecessary repetition, the present invention will not further describe various possible combinations.

[0124] In addition, various embodiments of the present invention may be arbitrarily combined, and as long as they do not violate the concept of the present invention, they should also be regarded as the contents disclosed by the present invention.

Claims

1. A method for simulating flow distribution of a phase-changing self-supporting chemical fracturing fluid system, characterized in that: The following steps are involved: Step S1: selecting an injection displacement and a total injection amount in the phase change self-supporting chemical fracturing construction scheme to conduct a physical simulation experiment, and observing the flow distribution of the phase change self-supporting chemical fracturing system under the selected injection displacement and total injection amount conditions; Step S2: Calculating the geometric dimensions of the artificial fractures formed by phase change self-supporting chemical fracturing according to the geological and engineering parameters of the target oil and gas well; Step S3: Calculate the flow distribution of the phase change self-supporting chemical fracturing system under the injection displacement and total injection volume conditions selected in step S1 according to the fracture geometry calculated in step S2; Step S4: Compare the physical simulation experiment results in step S1 with the calculation results in step S3, adjust the values ​​of the parameters used in calculating the flow distribution of the phase change self-supporting chemical fracturing system in step S3 according to the difference in the results, and calculate the flow distribution of the phase change self-supporting chemical fracturing system again until the difference between the physical simulation experiment results in step S1 and the calculation results in step S3 is within a set range; Step S5: using the adjusted parameter values ​​obtained in step S4, calculate the flow distribution of the phase change self-supporting chemical fracturing system under other injection displacement and total injection conditions given in the phase change self-supporting chemical fracturing construction plan.

2. The method according to claim 1, characterized in that: The physical simulation experiment is used to simulate liquid-liquid two-phase flow interface tracking.

3. The method according to claim 2, characterized in that The flow distribution of the phase-change self-supporting chemical fracturing system in step S1 is represented by the volume fraction of phase-change phase droplets in the image obtained in the physical simulation experiment.

4. The method according to claim 1, characterized in that: The flow distribution of the phase-change self-supporting chemical fracturing system in step S3 is represented by the volume fraction of the phase-change phase droplets in the numerically calculated image.

5. The method according to claim 1, characterized in that In step S2, according to the geological and engineering parameters of the target oil and gas well, the continuity equation, the fluid loss calculation equation, the fluid pressure drop equation, the fracture width equation and the fracture height equation are used to calculate the geometric dimensions of the artificial fractures formed by the phase change self-supporting chemical fracturing.

6. The method according to claim 5, characterized in that The continuity equation is as follows: Among them, x is the position in the direction of the seam length, in m; t is the construction time, in s; q(x, t) is the flow rate at point x in the seam at time t, in m 3 / s;v l (x, t) is the fluid loss at point x in the joint at time t, in m 2 / s; A(x, t) is the cross-sectional area of ​​the crack at time t, in m 2 .

7. The method according to claim 5, characterized in that The fluid loss calculation equation is as follows: Among them, x is the position in the direction of the seam length, in meters; t is the construction time, in seconds; v l is the fluid loss, in m 2 / s;h p is the fracture height, in m; C(x, t) is the fluid loss coefficient at point x in the fracture at time t, in m / s 0.5 ; τ is the time it takes for the fluid to reach the fracture x, in seconds.

8. The method according to claim 5, characterized in that The fluid pressure drop equation is as follows: Among them, x is the position in the direction of the seam length, in m; t is the construction time, in s; p(x, 0, t) is the pressure at point x in the crack at time t, in MPa; μ f is the viscosity of the fracturing fluid, in mPa·s; q(x, t) is the flow rate at point x in the fracture at time t, in m 3 / s; h(x, t) is the seam height at point x in the seam at time t, in m; w f (x, 0, t) is the half crack width at point x in the crack at time t, in m.

9. The method according to claim 5, characterized in that The crack width equation is as follows: Among them, x is the position in the direction of seam length, in meters; t is the construction time, in seconds; z is the position in the direction of seam height, in meters; w f (x, z, t) is the crack width at the crack length x at the crack height z at time t, in m; ν is the Poisson's ratio, dimensionless; E is the elastic modulus, in MPa; p(z) is the net pressure at the crack height position z, in MPa; h(x, t) is the crack height at the crack at time t, in m; τ is the time it takes for the fluid to reach the crack x, in s.

10. The method according to claim 5, characterized in that The crack height equation is as follows: Where x is the position in the fracture length direction, in m; p is the pressure in the fracture, in MPa; H is the half-height of the fracture, in m; Δs is the stress difference, in MPa; f is the ratio of the oil layer thickness to the fracture height, dimensionless; K c is the stress intensity factor, in MPa·m 0.5 .

11. The method according to claim 5, characterized in that The geological and engineering parameters of the target oil and gas well are taken from reservoir geological data, indoor experimental test data, or selected based on experience.

12. The method according to claim 5, characterized in that Step S3 of calculating the flow distribution of the phase-change self-supporting chemical fracturing system includes solving the flow volume fraction model of the phase-change self-supporting chemical fracturing system according to the mass conservation equation, the momentum equation and the phase-change fracturing liquid volume fraction calculation equation.

13. The method according to claim 12, characterized in that The mass conservation equation is as follows: Among them, x is the position in the direction of the seam length, the unit is m; u is the speed in the x direction, the unit is m / s; v is the speed in the y direction, the unit is m / s; y is the position in the direction of the seam width, the unit is m.

14. The method according to claim 12, characterized in that The momentum equation is as follows: Among them, x is the position in the fracture length direction, in m; y is the position in the fracture height direction, in m; p is the pressure inside the artificial fracture, in Pa; α is the interfacial tension, in N / m; g is the gravitational acceleration, in m / s 2 ; ρ is the equivalent density; u is the velocity in the x direction, in m / s; v is the velocity in the y direction, in m / s.

15. The method according to claim 12, characterized in that The phase change fracturing fluid volume fraction calculation equation is as follows: Among them, β is the volume rate of phase change fracturing fluid in each calculation unit, dimensionless; t is the construction time, unit is s; u is the speed in the x direction, unit is m / s; v is the speed in the y direction, unit is m / s.

16. The method according to claim 4, characterized in that The setting range is 5%.

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