Fractured reservoir SDVA self-diverting acid two-phase acidification numerical simulation method

Abstract

The invention discloses a fractured reservoir SDVA self-diverting acid two-phase acidification numerical simulation method. The method comprises the following steps: S1, constructing a fractured reservoir SDVA self-diverting acid two-phase acidification numerical simulation physical model; s2, performing matrix grid and fracture grid division on the physical model, and endowing the model with physical parameters; s3, constructing a fractured reservoir SDVA self-diverting acid two-phase acidification numerical simulation model based on the embedded discrete fracture model; s4, the fractured reservoir SDVA self-diverting acid two-phase acidification numerical simulation model of the current time step is solved through coupling iteration, and physical property parameters are updated; s5, judging whether the wormhole of the current time step breaks through or not: if not, continuing numerical simulation of the next time step, updating the model parameters, and repeating the steps S4-S5; and if so, obtaining a fractured reservoir SDVA self-diverting acid two-phase acidification numerical simulation result. According to the method, the two-phase acidification process of the SDVA self-diverting acid of the fractured reservoir can be accurately simulated, and the method has important theoretical and practical significance on acidification development of the fractured reservoir.

Description

Technical Field

[0001] The invention relates to the technical field of acidizing, and in particular to a numerical simulation method for SDVA self-diverting acid two-phase acidizing of a fractured reservoir. Background Art

[0002] In fractured reservoirs, acidizing is often used to increase or restore productivity. However, in reservoirs with large differences in pore structure or permeability characteristics, the acid often enters the highest permeability area first, while the low permeability area that needs improvement the most receives little acid, resulting in increasing changes in permeability characteristics within and between layers. Therefore, for such reservoirs, whether the acid can smoothly enter the area that needs improvement is the key to acidizing.

[0003] Self-diverting acid is a liquid used for acidizing fractured reservoirs. It uses specific surfactants (such as viscoelastic surfactants) to achieve self-guiding and distribution of acid in the reservoir. By changing the viscosity and rheological properties of the acid, the acid is guided to the low permeability area for acidizing, thereby improving the production efficiency of the oil well. However, the rheological behavior and diversion mechanism of self-diverting acid are relatively complex, and there is currently a lack of self-diverting acid two-phase acidizing models for multiphase flow and complex multi-physics coupling. In addition, oil-water two-phase flow acidizing is a complex multi-physics field coupling problem: the reaction between the self-diverting acid and the rock will generate heat; the temperature of the self-diverting acid-rock contact surface will affect the acid etching efficiency; there is convective heat transfer between the self-diverting acid and the rock; there is heat exchange between the self-diverting acid and the oil phase; there is heat exchange between the matrix and the fracture, and the above physical fields also exist in the fracture at the same time. Summary of the invention

[0004] In view of the above problems, the present invention aims to provide a numerical simulation method for SDVA self-diverting acid two-phase acidizing of fractured reservoirs.

[0005] The technical solution of the present invention is as follows:

[0006] A numerical simulation method for SDVA self-diverting acid two-phase acidizing of fractured reservoirs comprises the following steps:

[0007] S1: Construct a physical model for numerical simulation of SDVA self-diverting acid two-phase acidizing in fractured reservoirs;

[0008] S2: Divide the physical model into matrix grid and fracture grid, and assign physical parameters to the model;

[0009] S3: constructing a numerical simulation model of SDVA self-diverting acid two-phase acidizing of fractured reservoirs based on an embedded discrete fracture model, wherein the numerical simulation model of SDVA self-diverting acid two-phase acidizing of fractured reservoirs includes a matrix and fracture self-diverting acid two-phase seepage model, a matrix and fracture chemical transport model, and a matrix and fracture heat transfer model;

[0010] S4: solving the SDVA self-diverting acid two-phase acidizing numerical simulation model of the fractured reservoir at the current time step by coupling iteration, and updating the physical property parameters;

[0011] S5: Determine whether the wormhole in the current time step has been broken through:

[0012] If there is no breakthrough, continue the numerical simulation of the next time step, update the model parameters, and repeat steps S4-S5;

[0013] If a breakthrough is achieved, the numerical simulation results of SDVA self-diverting acid two-phase acidizing in fractured reservoirs are obtained.

[0014] Preferably, in step S3, the matrix and fracture self-diverting acid two-phase seepage model includes a pressure equation and a saturation equation;

[0015] The pressure equation is:

[0016]

[0017] μ t =μ o S o +μ w S w (5)

[0019]

[0020] Where: and They are the divergence operators in the overall three-dimensional rectangular coordinate system of the fractured medium and the local two-dimensional rectangular coordinate system of the fracture surface respectively; and are the gradient operators in the overall three-dimensional rectangular coordinate system of the fractured medium and the local two-dimensional rectangular coordinate system of the fracture respectively; K m , K f are matrix permeability scalar and fracture permeability scalar, respectively, m 2 ;μ t , μ o , μ w are total viscosity, water phase viscosity and oil phase viscosity, Pa·s; P m , P f are respectively the pressure of the matrix and the pressure of the crack, Pa; Pc m (S m，o ), Pc f (S f，o ) are the matrix capillary pressure at matrix oil phase saturation and the fracture capillary pressure at fracture oil phase saturation, Pa, respectively; are the cross-flow rates between matrix and cracks, and between cracks, respectively, m3 / s;Q m , Q f are the source phase of the matrix and the source phase of the fracture, respectively, m 3 / s;v m , ν f are the flow velocity in the matrix and the flow velocity in the fracture, m / s; S o , S w are the oil phase saturation and water phase saturation, respectively, dimensionless; v, v w 、v o are the total seepage velocity, water phase seepage velocity and oil phase seepage velocity in the matrix or fracture, m / s;

[0021] The saturation equation is:

[0022]

[0023] Where: φ m ,φ f are the porosity of the matrix and the porosity of the fracture medium, dimensionless; S m，o , S m，w are the saturation of oil phase and water phase in the matrix, dimensionless; S f，o , S f，w are the saturation of oil phase and water phase in the fracture, dimensionless; t is time, s; f o 、f w are the coefficients of oil phase and water phase seepage velocity, dimensionless; λ o , w are the fluidities of the oil phase and the water phase, 1 / (Pa·s); Pc m 、Pc f are the matrix capillary pressure and fracture capillary pressure, Pa; Q m，o , Q m，w The source phases of oil phase and water phase in the matrix, m 3 / s;Q f，o , Q f，w are the source phases of oil phase and water phase in the fracture, respectively, 3 / s.

[0024] Preferably, the crosstalk between the matrix and the cracks, and between the cracks is calculated by the following formulas:

[0025]

[0026] Where: ε is the cross-flow coefficient between matrix and fracture, dimensionless; K is the permeability, m 2 ; μ is viscosity, Pa·s; Tf i，j is the overall crossflow coefficient between fracture unit i and fracture unit j, dimensionless; P i , Pj are the pressure of fracture unit i and the pressure of fracture unit j, Pa, respectively.

[0027] Preferably, each crossflow coefficient is calculated by the following formula:

[0028]

[0029] Where: L i，k is the length of crack unit k within matrix unit i, m; <d> i，k is the average distance between matrix unit i and crack unit k, m; α i , α j are the crossflow coefficients of fracture unit i and fracture unit j, dimensionless; FA i is the aperture of fracture unit i, m; λ t，i is the total fluidity of fracture unit i, dimensionless; dx f is the spacing of crack unit i, m.

[0030] Preferably, in step S3, the chemical transport model between the matrix and the fracture includes H + Transport equation, Ca 2+ transport equation, SDVA transport equation and SDVA residual acid variable viscosity equation;

[0031] The H + The transport equation is:

[0032]

[0033] Where: S m，w , S f，w are the saturation of water phase in the matrix and fracture, dimensionless; C f，m , C f，f are the hydrogen ion concentrations in the matrix and cracks, kmol / m 3 ;v m，w , ν f，w are the water phase seepage velocities in the matrix and fractures, m / s; is the cross-flow rate between the fracture and the matrix, m 3 / s; Both Function, kmol / m 3 ; are the effective diffusion coefficients of hydrogen ions in the matrix and cracks, m / s; R(C s，m )、R(C s，f ) are the acid consumption rates in the matrix and fracture, kmol / (s·m 2 );a v，m 、a v，f are the specific pore surface areas of matrix and fractures, m 2 / m 3 ;

[0034] The Ca 2+ The transport equation is:

[0035]

[0036] Where: φ is the porosity, dimensionless; C Ca，m , C Ca，f are the calcium ion concentrations in the matrix and cracks, kmol / m 3 ; C Ca，m up , C Ca，f up Both Function, kmol / m 3 ; are the effective diffusion coefficients of calcium ions in the matrix and cracks, respectively, m / s;

[0037] The SDVA transport equation is:

[0038]

[0039] Where: C SDVA,m , C SDVA，f are the SDVA concentrations in the matrix and fractures, kmol / m 3 ; C SDVA，m up , C SDVA，f up Both Function, kmol / m 3 ; are the effective diffusion coefficients of the self-diverting acid in the matrix and fractures, respectively, m / s;

[0040] The SDVA residual acid variable viscosity equation is:

[0041]

[0042] pH = -1g (C f ) (29)

[0044] Where: μ eff , μ0, μ max are the apparent viscosity of the self-diverting acid, the initial viscosity of the self-diverting acid and the maximum viscosity of the acid solution, Pa / s; n is the power index; K is the permeability, m 2 ; C SDVA , C Ca , C f are the concentrations of SDVA, calcium ions, and hydrogen ions, kmol / m 3 ; C SDVA,max , C Ca，max are SDVA, maximum concentration of calcium ions, kmol / m 3 ; W1, W2, W3, b, c are all empirical coefficients; PH is the pH value of the system at this moment.

[0045] Preferably, in step S3, the heat transfer model of the matrix and the fracture includes a fluid heat conduction equation and a rock heat conduction equation;

[0046] The fluid heat conduction equation is:

[0047]

[0048] Where: subscript i = w, o represents water phase or oil phase; S m，i , S f，i are the saturation of phase i in the matrix and fractures, dimensionless; ρ i is the density of phase i, kg / m 3 ; C p，i is the specific heat capacity of phase i, J / (Kg·K); T m，l , T f，l , T m，r are the temperature of the fluid in the matrix, the temperature of the rock in the matrix and the temperature of the fluid in the fracture, K; v m，i , ν f，i are the seepage velocity of phase i in the matrix and the seepage velocity of phase i in the fracture, m / s; Both function, K; k i is the thermal conductivity of phase i, W / (m·K); H m is the convection heat transfer coefficient between fluid and rock, W / (m 2 K);

[0049] The rock heat conduction equation is:

[0050]

[0051] Where: r is the density of rock, kg / m 3 ; C p，r is the specific heat capacity of rock, J / (Kg·K); T f，r is the temperature of the rock in the crack, K; k r is the thermal conductivity of rock, W / (m·K); ΔH r (T m，r ), ΔH r (T f，r ) are the exothermic enthalpies of the acid-rock reaction in the matrix and fractures, J / mol, respectively.

[0052] Preferably, the exothermic enthalpy of the acid-rock reaction in the matrix and the fracture is calculated by the following formula:

[0053]

[0054] Where: T r is the temperature of the rock, K.

[0055] The beneficial effects of the present invention are:

[0056] The present invention proposes a numerical simulation model for SDVA self-diverting acid two-phase acidizing of fractured reservoirs constructed based on an embedded discrete fracture model, takes into account the effects of self-diverting acid two-phase seepage, chemical transport and heat transfer on self-diverting acid SDVA acidizing, and accurately simulates the SDVA self-diverting acid two-phase acidizing process of fractured reservoirs. A numerical simulation method for SDVA self-diverting acid two-phase acidizing of fractured reservoirs is provided, which has important theoretical and practical significance for the acidizing development of fractured reservoirs. BRIEF DESCRIPTION OF THE DRAWINGS

[0057] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings required for use in the embodiments or the description of the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying creative labor.

[0058] Figure 1 It is a schematic flow chart of the numerical simulation method of SDVA self-diverting acid two-phase acidizing of fractured reservoirs of the present invention;

[0059] Figure 2 A schematic diagram of a physical model used in calculations of a specific embodiment of the present invention;

[0060] Figure 3 A cloud diagram of the morphology of wormholes in conventional acid two-phase acidification according to a specific embodiment of the present invention;

[0061] Figure 4 This is a cloud diagram of the morphology of wormholes in a specific embodiment of the present invention in a SDVA self-diverting acid single-phase acidification process; wherein W represents the water phase, FA: 3.46e -6 The representative crack aperture is 3.46×10 -6 m;

[0062] Figure 5 A cloud diagram of the morphology of wormholes in SDVA self-diverting acid two-phase acidification according to a specific embodiment of the present invention; DETAILED DESCRIPTION

[0063] The present invention is further described below in conjunction with the accompanying drawings and embodiments. It should be noted that, in the absence of conflict, the embodiments in this application and the technical features in the embodiments can be combined with each other. It should be noted that, unless otherwise specified, all technical and scientific terms used in this application have the same meanings as those generally understood by those of ordinary skill in the art to which this application belongs. The words "including" or "comprising" and the like used in the disclosure of the present invention mean that the elements or objects appearing before the word cover the elements or objects listed after the word and their equivalents, without excluding other elements or objects.

[0064] like Figure 1 As shown, the present invention provides a numerical simulation method for SDVA self-diverting acid two-phase acidizing of a fractured reservoir, comprising the following steps:

[0065] S1: Construct a physical model for numerical simulation of SDVA self-diverting acid two-phase acidizing in fractured reservoirs.

[0066] S2: Divide the physical model into matrix grid and fracture grid, and assign physical parameters to the model.

[0067] In a specific embodiment, the physical parameters include reservoir matrix porosity, fracture porosity, fracture permeability, and acid solubility.

[0068] S3: A numerical simulation model of SDVA self-diverting acid two-phase acidizing of fractured reservoirs is constructed based on an embedded discrete fracture model. The numerical simulation model of SDVA self-diverting acid two-phase acidizing of fractured reservoirs includes a matrix and fracture self-diverting acid two-phase seepage model, a matrix and fracture chemical transport model, and a matrix and fracture heat transfer model.

[0069] In a specific embodiment, the matrix and fracture self-diverting acid two-phase seepage model includes a pressure equation and a saturation equation;

[0070] The pressure equation is:

[0071]

[0072] μ t =μ o S o +μ w S w (5)

[0074]

[0075] Where: and They are the divergence operators in the overall three-dimensional rectangular coordinate system of the fractured medium and the local two-dimensional rectangular coordinate system of the fracture surface respectively; and are the gradient operators in the overall three-dimensional rectangular coordinate system of the fractured medium and the local two-dimensional rectangular coordinate system of the fracture respectively; K m , K f are matrix permeability scalar and fracture permeability scalar, respectively, m 2 ;μ t , μ o , μ w are total viscosity, water phase viscosity and oil phase viscosity, Pa·s; P m , P f are respectively the pressure of the matrix and the pressure of the crack, Pa; Pc m (S m,o ), Pc f (S f,o ) are the matrix capillary pressure at matrix oil phase saturation and the fracture capillary pressure at fracture oil phase saturation, Pa, respectively; are the cross-flow rates between matrix and cracks, and between cracks, respectively, m 3 / S;Q m , Q f are the source phase of the matrix and the source phase of the fracture, respectively, m 3 / s;v m , ν f are the flow velocity in the matrix and the flow velocity in the fracture, m / s; S o , S w are the oil phase saturation and water phase saturation, respectively, dimensionless; v, v w 、v o are the total seepage velocity, water phase seepage velocity and oil phase seepage velocity in the matrix or fracture, m / s;

[0076] The saturation equation is:

[0077]

[0078] Where: φ m ,φ f are the porosity of the matrix and the porosity of the fracture medium, dimensionless; S m，o , S m，w are the saturation of oil phase and water phase in the matrix, dimensionless; S f，o , S f，w are the saturation of oil phase and water phase in the fracture, dimensionless; t is time, s; f o 、f w are the coefficients of oil phase and water phase seepage velocity, dimensionless; λ o , w are the fluidities of the oil phase and the water phase, 1 / (Pa·s); Pc m 、Pc f are the matrix capillary pressure and fracture capillary pressure, Pa; Q m，o , Q m，w The source phases of oil phase and water phase in the matrix, m 3 / s;Q f，o , Q f，w are the source phases of oil phase and water phase in the fracture, respectively, 3 / s.

[0079] In a specific embodiment, the crosstalk between the matrix and the crack, and between the cracks are calculated by the following formulas:

[0080]

[0081] Where: ε is the cross-flow coefficient between matrix and fracture, dimensionless; K is the permeability, m 2 ; μ is viscosity, Pa·s; Tf i，j is the overall crossflow coefficient between fracture unit i and fracture unit j, dimensionless; P i , P j are the pressure of fracture unit i and the pressure of fracture unit j, Pa, respectively.

[0082] In a specific embodiment, each crossflow coefficient is calculated by the following formula:

[0083]

[0084] Where: L i，k is the length of crack unit k within matrix unit i, m; <d> i，k is the average distance between matrix unit i and crack unit k, m; α i , α j are the crossflow coefficients of fracture unit i and fracture unit j, dimensionless; FA i is the aperture of fracture unit i, m; λ t，i is the total fluidity of fracture unit i, dimensionless; dx f is the spacing of crack unit i, m.

[0085] In a specific embodiment, the matrix-fracture chemical transport model includes H + Transport equation, Ca 2+ transport equation, SDVA transport equation and SDVA residual acid variable viscosity equation;

[0086] The H + The transport equation is:

[0087]

[0088] Where: S m，w , S f，w are the saturation of water phase in the matrix and fracture, dimensionless; C f，m , C f，f are the hydrogen ion concentrations in the matrix and cracks, kmol / m 3 ;v m，w 、v f，w are the water phase seepage velocities in the matrix and fractures, m / s; is the cross-flow rate between the fracture and the matrix, m 3 / s; Both Function, kmol / m 3 ; are the effective diffusion coefficients of hydrogen ions in the matrix and cracks, m / s; R(C s，m )、R(C s，f ) are the acid consumption rates in the matrix and fracture, kmol / (s·m 2 );a v，m 、a v，f are the specific pore surface areas of matrix and fractures, m 2 / m 3 ;

[0089] The Ca 2+ The transport equation is:

[0090]

[0091] Where: φ is the porosity, dimensionless; C Ca，m , C Ca，f are the calcium ion concentrations in the matrix and cracks, kmol / m 3 ; C Ca，m up , C Ca，f up Both Function, kmol / m 3 ; are the effective diffusion coefficients of calcium ions in the matrix and cracks, respectively, m / s;

[0092] The SDVA transport equation is:

[0093]

[0094] Where: C SDVA,m , C SDVA，f are the SDVA concentrations in the matrix and fractures, kmol / m 3 ; C SDVA，m up , C SDVA，f up Both Function, kmol / m 3 ; are the effective diffusion coefficients of the self-diverting acid in the matrix and fractures, respectively, m / s;

[0095] The SDVA residual acid variable viscosity equation is:

[0096]

[0097] pH = -1g (C f ) (29)

[0099] Where: μ eff , μ0, μ max are the apparent viscosity of the self-diverting acid, the initial viscosity of the self-diverting acid and the maximum viscosity of the acid solution, Pa / s; n is the power index; K is the permeability, m 2 ; C SDVA , C Ca , C f are the concentrations of SDVA, calcium ions, and hydrogen ions, kmol / m 3 ; C SDVA,max , C Ca，max are SDVA, maximum concentration of calcium ions, kmol / m 3 ; W1, W2, W3, b, c are all empirical coefficients; PH is the pH value of the system at this moment.

[0100] In a specific embodiment, the heat transfer model of the matrix and the fracture includes a fluid heat conduction equation and a rock heat conduction equation;

[0101] The fluid heat conduction equation is:

[0102]

[0103] Where: subscript i = w, o represents water phase or oil phase; S m，i , S f，i are the saturation of phase i in the matrix and fractures, dimensionless; ρ i is the density of phase i, kg / m 3 ; C p，i is the specific heat capacity of phase i, J / (Kg·K); T m，l , T f，l , T m，r are the temperature of the fluid in the matrix, the temperature of the rock in the matrix and the temperature of the fluid in the fracture, K; v m，i , ν f，i are the seepage velocity of phase i in the matrix and the seepage velocity of phase i in the fracture, m / s; Both function, K; k i is the thermal conductivity of phase i, W / (m·K); H m is the convection heat transfer coefficient between fluid and rock, W / (m 2 K);

[0104] The rock heat conduction equation is:

[0105]

[0106] Where: r is the density of rock, kg / m 3 ; C p,r is the specific heat capacity of rock, J / (Kg·K); T f,r is the temperature of the rock in the crack, K; k r is the thermal conductivity of rock, W / (m·K); ΔH r (T m,r ), ΔH r (T f,r ) are the exothermic enthalpies of the acid-rock reaction in the matrix and fractures, J / mol, respectively.

[0107] In a specific embodiment, the exothermic enthalpy of the acid-rock reaction in the matrix and the fracture is calculated by the following formula:

[0108]

[0109] Where: T r is the temperature of the rock, K.

[0110] It should be noted that the reaction exothermic enthalpy calculation method of the above embodiment is only a preferred parameter calculation method of the present invention, and other methods capable of obtaining the parameter in the prior art may also be applicable to the present invention.

[0111] S4: Coupled iteratively solve the SDVA self-diverting acid two-phase acidizing numerical simulation model of the fractured reservoir at the current time step, and update the physical property parameters.

[0112] In a specific embodiment, the physical property parameters include porosity and permeability.

[0113] S5: Determine whether the wormhole in the current time step has been broken through:

[0114] If there is no breakthrough, continue the numerical simulation of the next time step, update the model parameters, and repeat steps S4-S5;

[0115] If a breakthrough is achieved, the numerical simulation results of SDVA self-diverting acid two-phase acidizing in fractured reservoirs are obtained.

[0116] It should be noted that the method for determining whether a wormhole has been breached is a prior art, and the specific determination method will not be described in detail here.

[0117] It should be noted that, in addition to being applicable to SDVA self-steering acid, other self-steering acids in the prior art that have a similar mechanism to SDVA self-steering acid may also be applicable to the present invention.

[0118] In a specific embodiment, taking a fractured reservoir as an example, the SDVA self-diverting acid two-phase acidizing numerical simulation method for fractured reservoirs of the present invention is used to perform SDVA self-diverting acid two-phase acidizing numerical simulation on the fractured reservoir, which specifically includes the following steps:

[0119] (1) Construct a physical model for numerical simulation of SDVA self-diverting acid two-phase acidizing in fractured reservoirs.

[0120] In this embodiment, the physical model used is as follows: Figure 2 As shown in the figure, the core scale with a size of 0.3m×0.1m (length×height), the rock contains natural fractures and is saturated with liquid (water (acid) or oil). The self-redirecting acid is injected from the left side of the rock, dissolving the rock and producing Ca 2+ Mixed with the waste acid, it forms a high viscosity area, forcing the acid to change its flow direction and achieve uniform acidification.

[0121] (2) Divide the physical model into matrix grid and fracture grid, and assign physical parameters to the model.

[0122] In this embodiment, a structured uniform grid is used to mesh the matrix region of the physical model in step (1). Complex cracks are randomly generated, and a structured uniform grid is used to mesh the cracks generated in the physical model ( Figure 2 The figure is a schematic diagram, in which the number of grids is not the number of grids actually divided in this embodiment). The natural fractures are located inside the matrix. The physical property values ​​include the reservoir matrix porosity of 0.02, the fracture porosity of 0.99, and the fracture permeability of 1e -10 m 2 and acid solubility of 50 kg / kmol.

[0123] (3) Based on the embedded discrete fracture model, the two-phase seepage model shown in equations (1)-(13), the chemical transport model shown in equations (19)-(29), and the heat transfer model shown in equations (30)-(34) are constructed respectively.

[0124] In this embodiment, the empirical coefficients W1, W2, W3, b, and c in the SDVA residual acid variable viscosity equation are 0.0173, 1.1, 2, 1, and 1, respectively.

[0125] (4) coupling the model established in step (3) and solving the coupled model, and updating the physical property parameters of the physical model of the numerical simulation of SDVA self-diverting acid two-phase acidizing of the fractured reservoir according to the solution results.

[0126] (5) Determine whether the wormhole at the current time step has been broken through: If not, repeat steps (4)-(5) to determine whether the wormhole at the next time step has been broken through; if so, obtain the numerical simulation results of SDVA self-diverting acid two-phase acidizing in fractured reservoirs.

[0127] In this embodiment, the breakthrough condition for determining whether the wormhole is broken through is defined as the acid injection pressure being reduced to 2% of the initial acid injection pressure.

[0128] In this embodiment, the conventional acid two-phase acidizing wormhole morphology cloud diagram, the SDVA self-diverting acid single-phase acidizing wormhole morphology cloud diagram and the SDVA self-diverting acid two-phase acidizing wormhole morphology cloud diagram are as follows: Figure 3-5 As shown. Figure 3 and Figure 5 It can be seen that the extension direction of the wormholes in conventional acid two-phase acidizing is the direction of the main natural fractures, and the acid fluid is diverted, with weak steering ability. However, the extension of the wormholes in SDVA self-steering acid two-phase acidizing has obvious branches, strong steering ability, and obvious deflection of the wormhole extension direction.

[0129] In order to highlight the difference between SDVA self-diverting acid two-phase acidification and SDVA self-diverting acid single-phase acidification, the Figure 4 and Figure 5 It can be seen that the two-phase acidification presents a wormhole morphology with one main trunk and multiple branches. The development state of the branch wormholes on the main trunk is better than that in the single-phase acidification, forming a longer and more complex branch structure, and the turning ability is stronger than that of the single-phase acidification.

[0130] In summary, the present invention can accurately simulate the SDVA self-diverting acid two-phase acidizing process of fractured reservoirs. Compared with the prior art, the present invention has significant progress.

[0131] The above description is only a preferred embodiment of the present invention and does not limit the present invention in any form. Although the present invention has been disclosed as a preferred embodiment as above, it is not used to limit the present invention. Any technician familiar with this profession can make some changes or modify the technical contents disclosed above into equivalent embodiments without departing from the scope of the technical solution of the present invention. However, any simple modification, equivalent change and modification made to the above embodiments according to the technical essence of the present invention without departing from the content of the technical solution of the present invention still fall within the scope of the technical solution of the present invention.< / d> < / d>

Claims

1. A numerical simulation method for SDVA self-diverting acid two-phase acidizing of fractured reservoirs, characterized in that: The following steps are involved: S1: Construct a physical model for numerical simulation of SDVA self-diverting acid two-phase acidizing in fractured reservoirs; S2: Divide the physical model into matrix grid and fracture grid, and assign physical parameters to the model; S3: constructing a numerical simulation model of SDVA self-diverting acid two-phase acidizing of fractured reservoirs based on an embedded discrete fracture model, wherein the numerical simulation model of SDVA self-diverting acid two-phase acidizing of fractured reservoirs includes a matrix and fracture self-diverting acid two-phase seepage model, a matrix and fracture chemical transport model, and a matrix and fracture heat transfer model; S4: solving the SDVA self-diverting acid two-phase acidizing numerical simulation model of the fractured reservoir at the current time step by coupling iteration, and updating the physical property parameters; S5: Determine whether the wormhole in the current time step has been broken through: If there is no breakthrough, continue the numerical simulation of the next time step, update the model parameters, and repeat steps S4-S5; If a breakthrough is achieved, the numerical simulation results of SDVA self-diverting acid two-phase acidizing in fractured reservoirs are obtained.

2. The numerical simulation method for SDVA self-diverting acid two-phase acidification of fractured reservoirs according to claim 1 is characterized in that: In step S3, the matrix and fracture self-diverting acid two-phase seepage model includes a pressure equation and a saturation equation; The pressure equation is: m t =μ o S o +m w S w (5) Where: and They are the divergence operators in the overall three-dimensional rectangular coordinate system of the fractured medium and the local two-dimensional rectangular coordinate system of the fracture surface respectively; and are the gradient operators in the overall three-dimensional rectangular coordinate system of the fractured medium and the local two-dimensional rectangular coordinate system of the fracture respectively; K m , K f are matrix permeability scalar and fracture permeability scalar, respectively, m 2 ;μ t , μ o , μ w are total viscosity, water phase viscosity and oil phase viscosity, Pa·s; P m , P f are respectively the pressure of the matrix and the pressure of the crack, Pa; Pc m (S m,o ), Pc f (S f,o ) are the matrix capillary pressure at matrix oil phase saturation and the fracture capillary pressure at fracture oil phase saturation, Pa, respectively; are the cross-flow rates between matrix and cracks, and between cracks, respectively, m 3 / s;Q m , Q f are the source phase of the matrix and the source phase of the fracture, respectively, m 3 / s;v m 、v f are the flow velocity in the matrix and the flow velocity in the fracture, m / s; S o , S w are the oil phase saturation and water phase saturation, respectively, dimensionless; v, v w 、v o are the total seepage velocity, water phase seepage velocity and oil phase seepage velocity in the matrix or fracture, m / s; The saturation equation is: Where: φ m ,φ f are the porosity of the matrix and the porosity of the fracture medium, dimensionless; S m,o , S m,w are the saturation of oil phase and water phase in the matrix, dimensionless; S f,o , S f,w are the saturation of oil phase and water phase in the fracture, dimensionless; t is time, s; f o 、f w are the coefficients of oil phase and water phase seepage velocity, dimensionless; λ o , w are the fluidities of the oil phase and the water phase, 1 / (Pa·s); Pc m 、Pc f are the matrix capillary pressure and fracture capillary pressure, Pa; Q m,o , Q m,w The source phases of oil phase and water phase in the matrix, m 3 / s;Q f,o , Q f,w are the source phases of oil phase and water phase in the fracture, respectively, 3 / s.

3. The numerical simulation method for SDVA self-diverting acid two-phase acidification of fractured reservoirs according to claim 2, characterized in that: The crosstalk between the matrix and the cracks, and between the cracks is calculated by the following formulas: Where: ε is the cross-flow coefficient between matrix and fracture, dimensionless; K is the permeability, m 2 ; μ is viscosity, Pa·s; Tf i,j is the overall crossflow coefficient between fracture unit i and fracture unit j, dimensionless; P i , P j are the pressure of fracture unit i and the pressure of fracture unit j, Pa, respectively.

4. The numerical simulation method for SDVA self-diverting acid two-phase acidification of fractured reservoirs according to claim 3 is characterized in that: Each crossflow coefficient is calculated by the following formula: Where: L i,k is the length of crack unit k within matrix unit i, m; <d> i,k is the average distance between matrix unit i and crack unit k, m; α i , α j are the crossflow coefficients of fracture unit i and fracture unit j, dimensionless;< / d> FA i is the aperture of fracture unit i, m; λ t,i is the total fluidity of fracture unit i, dimensionless; dx f is the spacing of crack unit i, m.

5. The numerical simulation method for SDVA self-diverting acid two-phase acidification of fractured reservoirs according to claim 2, characterized in that: In step S3, the chemical transport model between the matrix and the crack includes H + Transport equation, Ca 2+ transport equation, SDVA transport equation and SDVA residual acid variable viscosity equation; The H + The transport equation is: Where: S m,w , S f,w are the saturation of water phase in the matrix and fracture, dimensionless; C f,m , C f,f are the hydrogen ion concentrations in the matrix and cracks, kmol / m 3 ;v m,w 、v f,w are the water phase seepage velocities in the matrix and fractures, m / s; is the cross-flow rate between the fracture and the matrix, m 3 / s; Both Function, kmol / m 3 ; are the effective diffusion coefficients of hydrogen ions in the matrix and cracks, m / s; R(C s,m )、R(C s,f ) are the acid consumption rates in the matrix and fracture, kmol / (s·m 2 );a v,m 、a v,f are the specific pore surface areas of the matrix and fractures, respectively, m 2 / m 3 ; The Ca 2+ The transport equation is: Where: φ is the porosity, dimensionless; C Ca,m , C Ca,f are the calcium ion concentrations in the matrix and cracks, kmol / m 3 ; C Ca,m up , C Ca,f up Both Function, kmol / m 3 ; are the effective diffusion coefficients of calcium ions in the matrix and cracks, respectively, m / s; The SDVA transport equation is: Where: C SDVA,m , C SDVA,f are the SDVA concentrations in the matrix and fractures, kmol / m 3 ; C SDVA,m up , C SDVA,f up Both Function, kmol / m 3 ; are the effective diffusion coefficients of the self-diverting acid in the matrix and fractures, respectively, m / s; The SDVA residual acid variable viscosity equation is: pH=-lg(C f ) (29) Where: μ eff , μ0, μ max are the apparent viscosity of the self-diverting acid, the initial viscosity of the self-diverting acid and the maximum viscosity of the acid solution, Pa / s; n is the power index; K is the permeability, m 2 ; C SDVA , C Ca , C f are the concentrations of SDVA, calcium ions, and hydrogen ions, kmol / m 3 ; C SDVA,max , C Ca,max are SDVA, the maximum concentration of calcium ions, kmol / m 3 ; W1, W2, W3, b, c are all empirical coefficients; PH is the pH value of the system at this moment.

6. The numerical simulation method for SDVA self-diverting acid two-phase acidification of fractured reservoirs according to claim 5, characterized in that: In step S3, the heat transfer model of the matrix and the fracture includes a fluid heat conduction equation and a rock heat conduction equation; The fluid heat conduction equation is: Where: subscript i = w, o represents water phase or oil phase; S m,i , S f,i are the saturation of phase i in the matrix and fractures, dimensionless; ρ i is the density of phase i, kg / m 3 ; C p,i is the specific heat capacity of phase i, J / (Kg·K); T m,l , T f,l , T m,r are the temperature of the fluid in the matrix, the temperature of the rock in the matrix and the temperature of the fluid in the fracture, K; v m,i 、v f,i are the seepage velocity of phase i in the matrix and the seepage velocity of phase i in the fracture, m / s; Both function, K; k i is the thermal conductivity of phase i, W / (m·K); H m is the convection heat transfer coefficient between fluid and rock, W / (m 2 K); The rock heat conduction equation is: Where: r is the density of rock, kg / m 3 ; C p,r is the specific heat capacity of rock, J / (Kg·K); T f,r is the temperature of the rock in the crack, K; k r is the thermal conductivity of rock, W / (m·K); ΔH r (T m,r ), ΔH r (T f,r ) are the exothermic enthalpies of the acid-rock reaction in the matrix and fractures, J / mol, respectively.

7. The numerical simulation method for SDVA self-diverting acid two-phase acidification of fractured reservoirs according to claim 6, characterized in that: The exothermic enthalpy of the acid-rock reaction in the matrix and the fractures is calculated by the following formula: Where: T r is the temperature of the rock, K.

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