Method for establishing capacitance resistance-tracer model of carbonate fractured-vuggy reservoir

Abstract

The invention relates to the technical field of geological exploration, in particular to a method for establishing a capacitance resistance-tracer model of a carbonate fractured-vuggy reservoir, which comprises the following steps of: respectively establishing a capacitance resistance model and a tracer seepage model; the tracer seepage model comprises a tracer seepage model in a crack channel, a tracer seepage model in a karst cave channel and a tracer seepage model in a crack-karst cave channel; respectively coupling the capacitance resistance model with a tracer seepage model in a crack channel and a tracer seepage model in a crack-karst cave channel, determining a time constant # imgabs0 # of the capacitance resistance-tracer model, then introducing a Peclet number and a connectivity coefficient f, and establishing a capacitance resistance-tracer model; and finally, constructing an objective function, and carrying out inversion solving on parameters in the capacitance resistance model and the capacitance resistance-tracer model. According to the method for establishing the capacitance resistance-tracer model, the flowing and flowback rules of the tracer in different fracture-cavity structure reservoirs are determined.

Description

Technical Field

[0001] The invention relates to the technical field of geological exploration, in particular to a method for establishing a capacitance resistance-tracer model of a carbonate rock fracture-cavity reservoir. Background Art

[0002] Carbonate oil and gas reservoirs have well-developed fractures and caves, diverse reservoir types, and strong heterogeneity. Tracer technology has the advantages of small dosage, low cost, and no need to put in monitoring tools. It has broad application prospects in the dynamic monitoring of deep carbonate gas reservoirs.

[0003] In the prior art, a Chinese invention patent document with a publication number of CN107989597A and a publication date of May 4, 2018 is proposed. The technical solution disclosed in the patent document is as follows: a fracture data screening method, device and storage medium, comprising: calculating the amount of simulated produced tracer according to a sub-fracture data set in the fracture data set between target well groups and well field tracer experimental data; wherein the fracture data is used to represent the orientation and attributes of the fractures between the target well groups; generating a target function according to the amount of real produced tracer and the amount of simulated produced tracer; wherein the target function is used to represent the ratio of the area enclosed by the change curve of the real produced tracer amount and the change curve of the simulated produced tracer amount within a certain time range to the area enclosed by the change curve of the real produced tracer amount in the coordinate system; changing the sub-fracture data set to obtain the minimum value of the target function; wherein the sub-fracture data set corresponding to the minimum value is used as the fracture screening result.

[0004] The above technical solution may encounter the following problems during actual use: the technical solution designs the fracture structure through numerical simulation method, does not consider the influence of cave channels and fracture-cave channels on tracer seepage, and fails to characterize the flow law of tracers in carbonate reservoirs. Summary of the invention

[0005] In order to solve the above technical problems, the present invention proposes a method for establishing a capacitance resistance-tracer model for carbonate fracture-cavity reservoirs, which clarifies the flow and backflow laws of tracers in reservoirs with different fracture-cavity structures, and can provide experimental support for clarifying the seepage mechanism and flow laws of tracers in porous media, thereby laying a foundation for quantitatively characterizing fracture-cavity characteristic parameters.

[0006] The present invention is achieved by adopting the following technical solutions:

[0007] The method for establishing a capacitance resistance-tracer model for carbonate fracture-cavity reservoirs comprises the following steps:

[0008] Step S 1. Establishing a capacitance-resistance model and a tracer seepage model respectively, wherein the tracer seepage model includes a tracer seepage model in a fracture channel and a tracer seepage model in a cave channel; and considering the fracture-cavity reservoir as a form of fractures and caves in series, establishing a tracer seepage model in a fracture-cavity channel;

[0009] Step S 2 . The capacitance-resistance model is coupled with the tracer seepage model in the fracture channel and the tracer seepage model in the fracture-cavern channel, respectively, the time constant τ of the capacitance-resistance-tracer model is clarified, and then the Peclet number and the connectivity coefficient f are introduced to establish the capacitance-resistance-tracer model, wherein the capacitance-resistance-tracer model includes the capacitance-resistance-tracer model in the fracture channel and the capacitance-resistance-tracer model in the fracture-cavern channel;

[0010] Step S 3 .Construct the objective function and inversely solve the parameters in the capacitor-resistance model and the capacitor-resistance-tracer model.

[0011] The time constant τ of the CR-tracer model is:

[0012]

[0013] In the formula, C t is the comprehensive compression coefficient of the formation, V p is the controlled pore volume of a single well, and J is the fluid production index.

[0014] The connectivity coefficient f is:

[0015] f=q(t) / i(t)

[0016]

[0017] Where q(t) is the flowback volume corresponding to time t, i(t) is the injection volume of the injection well corresponding to time t, and q(t 0 ) is the initial time t 0 The corresponding return flow volume, τ is the time constant of the capacitor resistor-tracer model, t 0 is the initial time of tracer migration, t is the tracer migration time, J is the liquid production index, p wf (t 0 ) is the initial time t 0 The corresponding bottom hole pressure, p wf (t) is the bottom hole flowing pressure corresponding to time t.

[0018] The capacitance resistance-tracer model in the crack channel is:

[0019]

[0020]

[0021]

[0022] Where C is the tracer flowback concentration, C 0 is the initial tracer concentration at the inlet, R is the tracer particle adsorption factor, t D is the dimensionless time, η is the dimensionless quantity related to the Peclet number, k dep is the sedimentation coefficient of the tracer particles, L is the migration distance, D is the diffusion coefficient of the tracer, v is the flow rate of the tracer, t is the migration time of the tracer, i(t) is the injection volume of the injection well corresponding to time t, V p is the controlled pore volume of a single well, N pe is the Peclet number, C t is the comprehensive compression coefficient of the formation, τ is the time constant of the capacitance resistance-tracer model, and J is the liquid production index.

[0023] The tracer seepage model in the cave channel is:

[0024]

[0025] in,

[0026]

[0027]

[0028]

[0029]

[0030] P=-(Δr) 2

[0031] In the formula, is the tracer concentration in the i-1th grid, is the tracer concentration in the ith grid, is the tracer concentration in the i+1th grid, is the tracer concentration of the ith grid in the previous time step, D is the tracer diffusion coefficient, R is the tracer particle adsorption factor, Δt is the time step, Δr is the radius step, and r i is the radial radius in the i-th grid, Q is the flow rate per unit thickness, φ is the porosity, k dep is the sedimentation coefficient of the tracer particles.

[0032] The capacitance resistance-tracer model in the crack-cavern channel is:

[0033]

[0034]

[0035]

[0036] Where, CF 1 is the first crack on the channel, C 0 is the initial tracer concentration at the inlet, R is the tracer particle adsorption factor, t D is the dimensionless time, η is the dimensionless quantity related to the Peclet number, k dep is the sedimentation coefficient of the tracer particles, L is the migration distance, D is the diffusion coefficient of the tracer, CF j is the jth crack on the channel, CV j is the j-th cave on the channel, N is the total time step, k is the k-th time step in the total time step N, Δt is the time step, Δr is the radius step, is the tracer concentration in the i-1th grid, Q is the flow rate per unit thickness, φ is the porosity, r i is the radial radius in the i-th grid, is the tracer concentration in the ith grid, is the tracer concentration in the i+1th grid, The tracer concentration of the i-th grid in the previous time step; v is the tracer flow rate, t is the tracer migration time, i(t) is the injection volume of the injection well corresponding to time t, V p is the controlled pore volume of a single well, N pe is the Peclet number, τ is the time constant of the capacitor-resistor-tracer model, C t is the comprehensive compression coefficient of the formation, and J is the liquid production index.

[0037] The tracer seepage model in the fracture channel is:

[0038]

[0039] Where C is the tracer flowback concentration, C 0 is the initial concentration of the tracer at the inlet, D is the tracer diffusion coefficient, R is the tracer particle adsorption factor, t is the tracer migration time, L is the migration distance, k dep is the sedimentation coefficient of the tracer particles, and v is the flow rate of the tracer.

[0040] The tracer seepage model in the fracture-cavern channel is:

[0041]

[0042] Where, CF 1 is the first crack on the channel, L1 is the migration distance of the tracer when it passes through the first fracture; N is the total time step, k is the kth time step in the total time step N, Δt is the time step, Δr is the radius step, C 0 is the initial tracer concentration at the inlet, D is the tracer diffusion coefficient, R is the tracer particle adsorption factor, k dep is the sedimentation coefficient of the tracer particles, v is the average seepage velocity, Q is the flow rate per unit thickness, φ is the porosity, CF j is the jth crack on the channel, L j is the displacement distance of the tracer when it passes through the jth crack, CV j is the jth cave on the channel, is the tracer concentration in the i-1th grid, r i is the radial radius in the i-th grid, is the tracer concentration in the ith grid, is the tracer concentration in the i+1th grid, Tracer concentration at the ith grid cell in the previous time step.

[0043] The step S 3 The objective function in is:

[0044]

[0045] In the formula, q jcal (t) is the calculated liquid production of production well j at time t, q jobs (t) is the measured liquid production of production well j at time t, C ijcal (t) is the tracer concentration value calculated at time t for production well j, C ijobs (t) is the tracer concentration value measured at production well j at time t, t n is the total number of time steps.

[0046] It also includes the use of particle swarm algorithm to solve the objective function.

[0047] It also includes the use of indoor flow physics simulation experiments to verify the accuracy of the capacitance resistance-tracer model.

[0048] The indoor flow physics simulation experiment includes:

[0049] Numerical characterization of typical fracture-cavity structures and preparation of visualization models, wherein the visualization models include fracture models, cave models and fracture-cavity models;

[0050] The tracer flow simulation experiment was completed in a visual model using a tracer flow simulation experimental device.

[0051] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0052] 1. The present invention proposes a method for establishing a capacitance resistance-tracer model for carbonate fracture-cavity reservoirs. The capacitance resistance model is coupled with the tracer seepage model in the fracture channel and the tracer seepage model in the cave channel, respectively, and the model characterizing the tracer injection and extraction process is compared with the voltage relationship in the circuit. The time constant τ of the capacitance resistance-tracer model is calculated, and then the Peclet number and the connectivity coefficient f are introduced to establish the capacitance resistance-tracer model. The capacitance resistance-tracer model established by this method can accurately evaluate the connectivity relationship of carbonate fracture-cavity reservoirs, quantify the fracture-cavity structure of the connected channel, and improve the reliability of the judgment of the connectivity relationship of the reservoir. Finally, the flow and backflow laws of the tracer in reservoirs with different fracture-cavity structures can be clarified, and experimental support can be provided for clarifying the seepage mechanism and flow law of the tracer in porous media, thereby laying the foundation for quantitatively characterizing the fracture-cavity characteristic parameters.

[0053] 2. When establishing the tracer seepage model, the present invention introduces the tracer particle sedimentation coefficient k dep As well as the tracer particle adsorption factor R, it can more accurately characterize the flow law of the tracer.

[0054] 3. In the present invention, the fracture-cavity reservoir is regarded as a form of fractures and caves connected in series, which is convenient for simplifying the model.

[0055] 4. Since the objective function needs to be solved by programming to obtain the various unknown parameters in the two-part model, including both the reservoir connectivity evaluation parameters obtained by the capacitance and resistance model part and the fracture-cavity structure parameters obtained by the capacitance and resistance-tracer model part inversion, the programming calculation amount is large and the data is complicated. The present invention adopts the particle swarm algorithm as the solution method of the objective function, which can solve the above problems to a certain extent.

[0056] 5. The present invention also verifies the accuracy of the capacitor-resistance-tracer model by conducting indoor flow physics simulation experiments, and can further explore the applicability of the capacitor-resistance-tracer model. BRIEF DESCRIPTION OF THE DRAWINGS

[0057] The present invention will be further described in detail below with reference to the accompanying drawings and specific embodiments, wherein:

[0058] Figure 1 This is a comparison diagram for the fracture structure fitting verification in the present invention;

[0059] Figure 2 This is a comparison diagram for the fracture-cavern structure fitting verification in the present invention;

[0060] Figure 3 This is a comparison diagram of the fitting verification of the multi-crack structure in the present invention;

[0061] Figure 4 is a schematic diagram of a crack model in the present invention;

[0062] Figure 5 It is a schematic diagram of the cave model in the present invention;

[0063] Figure 6 Schematic diagram of the crack hole model in the present invention;

[0064] Figure 7 It is a structural schematic diagram of the tracer flow simulation experimental device in the present invention;

[0065] Markings in the figure:

[0066] 1. Tracer storage container, 2. Water storage container, 3. Control switch valve, 4. Peristaltic pump, 5. Visualization model, 6. Sampling bottle. DETAILED DESCRIPTION

[0067] Example 1

[0068] This embodiment includes a method for establishing a capacitance resistance-tracer model for a carbonate fracture-vuggy reservoir, comprising the following steps:

[0069] Step S 1 .Establish a capacitance-resistance model and a tracer seepage model respectively, wherein the tracer seepage model includes a tracer seepage model in a fracture channel and a tracer seepage model in a cave channel. Then, the fracture-cavity reservoir is regarded as a fracture and a cave in series, and a tracer seepage model in a fracture-cavity channel is established.

[0070] Step S 2 .The capacitance-resistance model is coupled with the tracer seepage model in the fracture channel and the tracer seepage model in the fracture-cavern channel respectively, the time constant τ of the capacitance-resistance-tracer model is clarified, and then the Peclet number and the connectivity coefficient f are introduced to establish the capacitance-resistance-tracer model. The capacitance-resistance-tracer model includes the capacitance-resistance-tracer model in the fracture channel and the capacitance-resistance-tracer model in the fracture-cavern channel.

[0071] Step S 3 .Construct the objective function and inversely solve the parameters in the capacitor-resistance model and the capacitor-resistance-tracer model.

[0072] Example 2

[0073] This embodiment includes a method for establishing a capacitance resistance-tracer model for a carbonate fracture-vuggy reservoir, comprising the following steps:

[0074] Step S 1.Establish a capacitance-resistance model and a tracer seepage model respectively, wherein the tracer seepage model includes a tracer seepage model in a fracture channel and a tracer seepage model in a cave channel; then, the fracture-cavity reservoir is regarded as a form of fractures and caves in series, and a tracer seepage model in a fracture-cavity channel is established.

[0075] Step S 2 The capacitance-resistance model is coupled with the tracer seepage model in the fracture channel and the tracer seepage model in the fracture-cavern channel, respectively, to clarify the time constant τ of the capacitance-resistance-tracer model:

[0076]

[0077] In the formula, C t is the comprehensive compression coefficient of the formation, V p is the controlled pore volume of a single well, and J is the fluid production index.

[0078] Then, the Peclet number and the connectivity coefficient f are introduced to establish a capacitance-resistance-tracer model, which includes a capacitance-resistance-tracer model in a fracture channel and a capacitance-resistance-tracer model in a fracture-cavern channel.

[0079] Wherein, the connectivity coefficient f is:

[0080] f=q(t) / i(t)

[0081]

[0082] Where q(t) is the flowback volume corresponding to time t, i(t) is the injection volume of the injection well corresponding to time t, and q(t 0 ) is the initial time t 0 The corresponding return flow volume, τ is the time constant of the capacitor resistor-tracer model, t 0 is the initial time of tracer migration, t is the tracer migration time, J is the liquid production index, p wf (t 0 ) is the initial time t 0 The corresponding bottom hole pressure, p wf (t) is the bottom hole flowing pressure corresponding to time t.

[0083] The capacitance resistance-tracer model in the crack channel is:

[0084]

[0085] The capacitance resistance-tracer model in the crack-cavern channel is:

[0086]

[0087] in,

[0088]

[0089]

[0090] In the above formula, C is the tracer flowback concentration, C 0 is the initial tracer concentration at the inlet, R is the tracer particle adsorption factor, t D is the dimensionless time, η is the dimensionless quantity related to the Peclet number, k dep is the sedimentation coefficient of the tracer particles, L is the migration distance, D is the diffusion coefficient of the tracer, v is the flow rate of the tracer, t is the migration time of the tracer, i(t) is the injection volume of the injection well corresponding to time t, V p is the controlled pore volume of a single well, N pe is the Peclet number, C t is the comprehensive compression coefficient of the formation, τ is the time constant of the capacitance resistance-tracer model, J is the liquid production index, CF 1 is the first crack on the channel, CF j is the jth crack on the channel, CV j is the j-th cave on the channel, N is the total time step, k is the k-th time step in the total time step N, Δt is the time step, Δr is the radius step, is the tracer concentration in the i-1th grid, Q is the flow rate per unit thickness, φ is the porosity, r i is the radial radius in the i-th grid, is the tracer concentration in the ith grid, is the tracer concentration in the i+1th grid, Tracer concentration at the ith grid cell in the previous time step.

[0091] Step S 3 .Construct the objective function and inversely solve the parameters in the capacitor-resistance model and the capacitor-resistance-tracer model.

[0092] Example 3

[0093] This embodiment includes a method for establishing a capacitance resistance-tracer model for a carbonate fracture-vuggy reservoir, comprising the following steps:

[0094] Step S 1 .Establish a capacitance-resistance model and a tracer seepage model respectively, wherein the tracer seepage model includes a tracer seepage model in a fracture channel and a tracer seepage model in a cave channel; then, the fracture-cavity reservoir is regarded as a form of fractures and caves in series, and a tracer seepage model in a fracture-cavity channel is established.

[0095] Step S 2.The capacitance-resistance model is coupled with the tracer seepage model in the fracture channel and the tracer seepage model in the fracture-cavern channel respectively, the time constant τ of the capacitance-resistance-tracer model is clarified, and then the Peclet number and the connectivity coefficient f are introduced to establish the capacitance-resistance-tracer model. The capacitance-resistance-tracer model includes the capacitance-resistance-tracer model in the fracture channel and the capacitance-resistance-tracer model in the fracture-cavern channel.

[0096] Step S 3 .Construct the objective function and inversely solve the parameters in the capacitor-resistance model and the capacitor-resistance-tracer model.

[0097] Wherein, the step S 3 The objective function in is:

[0098]

[0099] In the formula, q jcal (t) is the calculated liquid production of production well j at time t, q jobs (t) is the measured liquid production of production well j at time t, C ijcal (t) is the tracer concentration value calculated at time t for production well j, C ijobs (t) is the tracer concentration value measured at production well j at time t, t n is the total number of time steps.

[0100] Example 4

[0101] This embodiment includes a method for establishing a capacitance resistance-tracer model for a carbonate fracture-vuggy reservoir, comprising the following steps:

[0102] Step S 1 .Establish a capacitance-resistance model and a tracer seepage model respectively, wherein the tracer seepage model includes a tracer seepage model in a fracture channel and a tracer seepage model in a cave channel; then, the fracture-cavity reservoir is regarded as a form of fractures and caves in series, and a tracer seepage model in a fracture-cavity channel is established.

[0103] Specifically, the tracer injection process, the production process and the reservoir connection channel after injection are regarded as a whole system. The tracer injection process is the excitation part of the system, which is equivalent to the power supply excitation part in the circuit; and the tracer production process is the response part of the system, which is equivalent to the voltage across the capacitor C'. The seepage resistance encountered by the fluid in the formation during propagation and production is equivalent to the resistance in the circuit, and the storage capacity of the reservoir is equivalent to the role played by the capacitor in the circuit.

[0104] When the capacitor in a first-order capacitor-resistor series circuit is charged, the voltage in the circuit satisfies:

[0105] U S (t) = U C' (t)+U R' (t) (1)

[0106] In the above formula, U S (t) is the power supply excitation voltage, V; U C' (t) is the voltage across the capacitor, V; U R' (t) is the resistance divided voltage in the circuit, V; t is the time, s.

[0107] According to the relationship between charge, voltage and current in the circuit, we have:

[0108] ΔQ'=C'×ΔU (2)

[0109] ΔQ'=I C ×Δt (3)

[0110] In the above formula, C' is the capacitance; ΔQ' is the amount of charge that changes within Δt; ΔU is the voltage that changes within Δt, that is, the charging voltage; I C is the current corresponding to the capacitance in the circuit, and is also the current in the circuit.

[0111] According to the series circuit current relationship:

[0112]

[0113] The resistor voltage division with a resistance value of R' can be obtained:

[0114]

[0115] Substituting the resistor voltage divider formula into formula (4-1), we can get the voltage relationship in the circuit:

[0116]

[0117] Solve the first-order nonhomogeneous linear differential equation, the general solution formula is:

[0118]

[0119] y=Ce -∫P(x)dx +e -∫P(x)dx ∫Q(x)e ∫P(x)dx dx (8)

[0120] Let τ'=R'C', and we can get the relationship between the voltage across the capacitor and time during the circuit charging process:

[0121]

[0122] The τ' in the formula is defined as the time constant of the capacitor-resistance model, which causes a certain delay in the process of the voltage across the capacitor reaching the power supply excitation voltage during the charging process, and changes with time. The time constant is a key physical quantity that can measure the charging efficiency of the capacitor and reflect the hysteresis and attenuation of the charging process.

[0123] Further analogizing the charging process in the circuit to the oil and gas reservoir, the injection and return of the tracer into the reservoir has a certain delay and attenuation. The tracer injection process and the capacitor charging process in the circuit have certain similarities, as shown in Table 1 below. The capacitor resistance model applied to the reservoir can be derived by analogy with the circuit capacitor model, and there is also a corresponding relationship between the various physical quantities.

[0124] Table 1 Comparative analysis of tracer injection, flowback and circuit charging process

[0125]

[0126] The tracer seepage model in the fracture channel, that is, the analytical formula of the output concentration when the tracer is injected into the fracture, is:

[0127]

[0128] Where C is the tracer flowback concentration, C 0 is the initial concentration of the tracer at the inlet, D is the tracer diffusion coefficient, R is the tracer particle adsorption factor, t is the tracer migration time, L is the migration distance, k dep is the sedimentation coefficient of the tracer particles, and v is the flow rate of the tracer.

[0129] The tracer seepage model in the cave channel, that is, the output concentration model when the tracer is injected into the cave, is explained as follows:

[0130]

[0131]

[0132] It is difficult to solve equation (11) analytically, so a numerical solution method is needed to solve the model. Differentiating equation (11) yields:

[0133]

[0134] To simplify the calculation, let:

[0135]

[0136]

[0137]

[0138] P=-(Δr) 2 (17)

[0139] Substituting equations (13) to (15) into equation (12), we can write:

[0140]

[0141] In the formula, is the tracer concentration in the i-1th grid, is the tracer concentration in the ith grid, is the tracer concentration in the i+1th grid, is the tracer concentration of the ith grid in the previous time step, r i is the radial radius in the i-th grid, Q is the flow rate per unit thickness, and φ is the porosity. Δr and Δt are the radius step and time step, respectively, representing the radius and time that the injected tracer can just fill the formation.

[0142] Formula (18) can be written in matrix form and solved iteratively by programming:

[0143]

[0144] Considering the series connection of fractures and holes, when the tracer enters the first fracture, according to the tracer concentration output equation (10) obtained above, that is:

[0145]

[0146] Similarly, when the tracer passes through the first cave and enters the second fracture, due to the larger volume of the cave, the concentration at the entrance of the second fracture can be considered as the superposition of instantaneous point sources at each moment. The tracer is considered to be injected into the second fracture by continuous injection, so the concentration at any position in the j+1th fracture (j≥1) can be derived:

[0147]

[0148] Where: N is the total time step.

[0149] By combining the mathematical models of tracer seepage in fractures and caves, we can establish a mathematical model of tracer seepage in the case of multiple fractures and caves:

[0150]

[0151] Where CF 1 is the first crack on the channel, L 1 is the migration distance of the tracer when it passes through the first fracture; N is the total time step, k is the kth time step in the total time step N, Q is the flow rate per unit thickness, φ is the porosity, CFj is the jth crack on the channel, L j is the displacement distance of the tracer when it passes through the jth crack, CV j is the jth cave on the channel.

[0152] Step S 2 .The capacitance-resistance model is coupled with the tracer seepage model in the fracture channel and the tracer seepage model in the fracture-cavern channel respectively, the time constant τ of the capacitance-resistance-tracer model is clarified, and then the Peclet number and the connectivity coefficient f are introduced to establish the capacitance-resistance-tracer model. The capacitance-resistance-tracer model includes the capacitance-resistance-tracer model in the fracture channel and the capacitance-resistance-tracer model in the fracture-cavern channel.

[0153] Specifically, the tracer is injected into the reservoir along with the working fluid, and part of the working fluid will be retained in the formation. The connectivity coefficient f represents the ratio of the flowback fluid volume to the injected fluid volume.

[0154] The formula for calculating the return flow volume is: q(t) = J(p r -p wf ) (twenty three)

[0155] Where q(t) is the flowback volume corresponding to time t in the total flowback time when the tracer is injected, m 3 ; J is the liquid production index, m 3 / (d·MPa); p r is the formation pressure (the formation pressure tested when the well is shut in), MPa; p wf It is the bottom hole flowing pressure (read by the downhole permanent pressure gauge or converted by the wellhead oil pressure), MPa.

[0156] From the above formula, we can get:

[0157] Combined with the liquid production index and based on the material balance principle, the model that characterizes the tracer injection and production process is:

[0158]

[0159] Among them, C t is the comprehensive compression coefficient of the formation, MPa -1 ; V p is the controlled pore volume of a single well, m 3 ; i(t) is the injection volume of the injection well corresponding to time t, m 3 ; q(t) is the return flow volume corresponding to time t, m 3 ; t is the tracer migration time.

[0160] The voltage relationship in the analog circuit, equation (6), defines the time constant in the tracer model as:

[0161]

[0162] Among them, C t is the comprehensive compression coefficient of the formation, MPa -1 ; V p is the controlled pore volume of a single well, m 3 ; J is the liquid production index.

[0163] Substituting formula (26) into formula (25), we can obtain:

[0164]

[0165] Solving the first-order nonhomogeneous linear differential equation, the expression of the flowback volume during the tracer monitoring process is:

[0166]

[0167] Where q(t) represents the flowback volume at time t during the tracer monitoring process; q(t 0 ) represents the initial time t 0 The corresponding return fluid volume; τ is the time constant of the capacitance resistance-tracer model; t 0 represents the initial time of tracer migration; t is the tracer migration time.

[0168] A new parameter specially introduced to describe the law of solute migration is the Peclet number, which reflects the relationship between the longitudinal diffusion coefficient of the solute and the molecular diffusion coefficient during the seepage process. The larger the Peclet number, the greater the flow rate. Its mathematical expression is as follows:

[0169]

[0170] Where v is the average flow velocity (L / T); L is the characteristic length of the porous medium, which here refers to the migration distance (T); and D is the hydrodynamic dispersion coefficient (L2 / T).

[0171] The following dimensionless quantities are defined, and the connectivity factor f and the time constant τ of the capacitor-resistance-tracer model are introduced:

[0172]

[0173]

[0174]

[0175] According to the above formula, the capacitance resistance-tracer model in the crack channel can be obtained by non-dimensionalizing formula (10):

[0176]

[0177] The capacitance-resistance-tracer model in the fracture-cavity channel is:

[0178]

[0179] Where, CF j is the jth crack on the channel; CV j is the jth cave on the channel.

[0180] Step S 3 In order to accurately evaluate the connectivity of carbonate fracture-vuggy reservoirs and quantify the fracture-vuggy structure of the connected channels, and improve the reliability of reservoir connectivity judgment, it is necessary to couple the capacitance-resistance model with the tracer seepage model to form a capacitance-resistance-tracer model, construct the objective function, and invert and solve the parameters in the capacitance-resistance model and the capacitance-resistance-tracer model. The objective function is as follows:

[0181]

[0182] In the formula, q jcal (t) is the calculated liquid production of production well j at time t, q jobs (t) is the measured liquid production of production well j at time t, C ijcal (t) is the tracer concentration value calculated at time t for production well j, C ijobs (t) is the tracer concentration value measured at production well j at time t, t n is the total number of time steps.

[0183] Since the objective function needs to be solved by programming to obtain the unknown parameters in the two-part model, including both the reservoir connectivity evaluation parameters obtained by the capacitance and resistance model part and the fracture-cavity structure parameters obtained by the capacitance and resistance-tracer model part, the programming calculation is large and the data is complicated, so the particle swarm algorithm is selected as the solution method for the objective function.

[0184] Assuming that the dimension of the search space is D, the position and velocity of the i-th particle in the particle swarm at the t-th iteration can be expressed as and The historical optimal position (individual optimal value) of each particle in the iteration process is recorded as The historical optimal position of the entire particle swarm is recorded as So the velocity and position of the particle in the t+1th iteration are updated as:

[0185]

[0186]

[0187] In the formula, c1 、c 2 is the learning factor, which is generally set to 2; r 1 、r 2 is a random number between (0, 1); ω is the inertia weight.

[0188] The inertia weight ω is a parameter introduced to balance the local search and global search capabilities. The larger the ω, the stronger the global search capability and the weaker the local search capability. The commonly used inertia weight reduction strategy is to set the initial value of ω to a larger value, and then gradually reduce it so that the particle swarm switches from global search to local search, and then the global optimal solution is more accurate. The expression of ω is:

[0189]

[0190] In the formula, ω max is the maximum value of inertia weight; ω min is the minimum inertia weight; t is the current iteration number; t max is the maximum number of iterations.

[0191] The main calculation steps of the particle swarm optimization algorithm are:

[0192] (1) Initialization: Set the particle swarm size, maximum number of iterations, initial position, and initial velocity.

[0193] (2) Calculate the initial fitness value of each particle and set it to p i . Select the optimal fitness value of the group and set it to p g .

[0194] (3) Update the speed and position of each particle.

[0195] (4) Calculate the current fitness value of each particle after the update and compare it with p i Compare, if the current fitness value is better, replace p i and save it.

[0196] (5) Compare the optimal fitness value of each particle with p g In comparison, if the current fitness value of a particle is better, then replace p g and save it.

[0197] (6) If the search result meets the stopping condition (reaching the maximum number of iterations or meeting the accuracy requirement), the search is terminated and the optimal value is output; otherwise, return to step (3) to continue searching.

[0198] Example 5

[0199] This embodiment is a further detailed supplement and elaboration of the technical solution of the present invention on the basis of any one of the above embodiments 1 to 4.

[0200] In order to explore the applicability of the capacitor-resistance-tracer model, this embodiment also includes using an indoor flow physics simulation experiment to verify the accuracy of the capacitor-resistance-tracer model. The capacitor-resistance-tracer model includes a capacitor-resistance-tracer model in a fracture channel and a capacitor-resistance-tracer model in a fracture-cavern channel.

[0201] Specifically, the indoor flow physics simulation experiment includes:

[0202] Typical fracture-cavity structure numerical characterization and visualization model preparation. Specifically, it includes the following steps:

[0203] 1) Based on the thin sections of real rock samples, core experiments such as CT scanning are used to analyze the rock skeleton and pore channels, and the corresponding pore network model is extracted and established through relevant software;

[0204] 2) Through laser etching technology, a typical fracture-cavity structure visualization model is prepared, including a fracture model, a cave model, and a fracture-cavity model. The visualization model is as shown in the attached manual. Figures 4 to 6 shown.

[0205] The tracer flow simulation experiment device was used to complete the tracer flow simulation experiment in the fracture model, cave model and fracture-cavity model.

[0206] Among them, refer to the instructions attached Figure 7 The tracer flow simulation experimental device includes a tracer storage 1, a water storage 2, a peristaltic pump 4, a control switch valve 3, a visualization model 5, a sampling bottle 6 and corresponding connecting pipes. The tracer storage 1 is used to store tracer solution, and the water storage 2 is used to store water.

[0207] The experiment was carried out at room temperature and pressure (20°C, 0.1 MPa), and the simulated water was pure water (ρ = 1 g / cm 3 ); the tracer is water-soluble granular fluorescent powder. Other experimental equipment include: beaker, glass rod, electronic scale, measuring cylinder, stopwatch, hose, hose connector, plug, etc.

[0208] The tracer flow simulation experiment was carried out according to the following steps:

[0209] 1) Prepare a tracer solution with a concentration of 1.33 mg / mL;

[0210] 2) Connect the tracer flow simulation experimental device;

[0211] 3) Use the constant flow peristaltic pump 4 to inject water into the visualization model 5 until the space of the visualization model 5 is full;

[0212] 4) Obtain a tracer-free sample of the blank control group at the outlet;

[0213] 5) injecting a tracer solution from the injection well position on the visualization model 5;

[0214] 6) injecting water into the visualization model 5 at a constant speed, and taking samples at intervals at the corresponding outlet ends, and the amount of liquid taken by each sampling bottle 6 is controlled to be about 2 mL;

[0215] 7) Use a spectrophotometer to test the absorbance change of each sample solution, calculate the tracer concentration in each sample, and draw a curve of the tracer output concentration change over time.

[0216] The relationship between the absorbance A of a substance to monochromatic light and the solution concentration C" of the absorbing substance and the thickness of the liquid layer l can be described by the Lambert-Beer law: when a beam of parallel monochromatic light passes through a dilute solution containing an absorbing substance, the absorbance of the solution is proportional to the product of the concentration of the absorbing substance and the thickness of the liquid layer, that is:

[0217] A=kC”l (1)

[0218] In the above formula, k is a proportional constant, which is related to factors such as the light-absorbing substance and the intensity of the incident light:

[0219] k=2.303φI 0 εb (2)

[0220] Where φ is the quantum efficiency of fluorescence, a dimensionless quantity; I 0 is the incident light intensity; ε is the absorption coefficient, L / (mg·cm); b is the liquid layer thickness, cm.

[0221] The specific concentration of tracer solution prepared by the fluorescent tracer used in this experiment is measured, and its absorbance is measured to draw a standard curve. The tracer concentration of the sample can be inversely calculated using this linear equation and the absorbance of the solution obtained by the test.

[0222] A tracer flow experiment under different fracture-cavity structures was designed and carried out. The tracer production curve characteristics under different types of fracture-cavity structure combinations were close to the model prediction results, which can verify the accuracy of the model.

[0223] Example 6

[0224] Typical experiments of single fracture structure, fracture-cavern structure and multi-fracture-cavern structure (fracture-cavern-fracture-cavern structure) were selected to verify the applicability of the capacitance-resistance-tracer model. The capacitance-resistance-tracer model was used to perform synchronous inversion and solution for the tracer output concentration obtained in each experimental group. The time constant results obtained by partial fitting of the capacitance-resistance model (hereinafter referred to as CRM) are shown in Table 2 below, and the summary table of partial fitting parameters of the capacitance-resistance-tracer model is shown in Table 3 below. The model curve fitting determination coefficient is shown in Table 4, and the comparison chart of the tracer concentration curve of each experimental group is shown in the attached manual. Figures 1 to 3 shown.

[0225] Table 2. CRM time constant fitting results of the capacitance resistance-tracer model

[0226]

[0227] Table 3 Capacitance resistance-tracer model tracer concentration fitting parameters

[0228] Fitting parameters Single crack Fissure-Cave Multi-crack structure (average) Crack channel length cm 14.1 13.7 14.5 Crack diffusion coefficient 1.602 1.196 0.875 Crack adsorption factor 1.598 0.154 0.707 Crack settlement coefficient 0.277 0.287 0.236 Peclet number 98 10.1 10.3 Cave diameter cm / 18 6 Cave diffusion coefficient / 1.975 1.571 Cave sedimentation coefficient / 1.262 1.765 Cave adsorption factor / 0.521 2.028

[0229] Table 4 Comparison of determination coefficients of tracer concentration curve fitting in each experimental group

[0230]

[0231] The determination coefficient of the capacitance resistance-tracer model is generally higher than that of the tracer seepage model, and the fitting effect is better. The fracture length and cave size obtained by fitting in the tracer concentration fitting parameter table (Table 2) are compared with the actual size of the structure in the physical model. As shown in Table 5 below, the error rate of the capacitance resistance-tracer model fitting parameter results is lower than that of the tracer seepage model, which is more in line with reality.

[0232] Table 5 Comparison of determination coefficients of tracer concentration curve fitting in each experimental group

[0233]

[0234] In summary, the capacitance-resistance-tracer model can provide an accurate and quantitative explanation of the fracture-hole structure within the model.

[0235] In summary, after reading the present invention document, ordinary technicians in this field can make various other corresponding transformation schemes based on the technical scheme and technical concept of the present invention without creative mental labor, which all fall within the scope of protection of the present invention.

Claims

1. The establishment method of capacitance resistance-tracer model for carbonate fracture-cavity reservoirs, Features: The following steps are involved: Step S 1 . Establishing a capacitance-resistance model and a tracer seepage model respectively, wherein the tracer seepage model includes a tracer seepage model in a fracture channel and a tracer seepage model in a cave channel; and considering the fracture-cavity reservoir as a form of fractures and caves in series, establishing a tracer seepage model in a fracture-cavity channel; Step S 2 . The capacitance-resistance model is coupled with the tracer seepage model in the fracture channel and the tracer seepage model in the fracture-cavern channel, respectively, the time constant τ of the capacitance-resistance-tracer model is clarified, and then the Peclet number and the connectivity coefficient f are introduced to establish the capacitance-resistance-tracer model, wherein the capacitance-resistance-tracer model includes the capacitance-resistance-tracer model in the fracture channel and the capacitance-resistance-tracer model in the fracture-cavern channel; Step S 3 .Construct the objective function and inversely solve the parameters in the capacitor-resistance model and the capacitor-resistance-tracer model.

2. The method for establishing a capacitance resistance-tracer model for a carbonate fracture-cavity reservoir according to claim 1, Features: The time constant τ of the CR-tracer model is: In the formula, C t is the comprehensive compression coefficient of the formation, V p is the controlled pore volume of a single well, and J is the fluid production index.

3. The method for establishing a capacitance resistance-tracer model for a carbonate fracture-cavity reservoir according to claim 2, Features: The connectivity coefficient f is: f=q(t) / i(t) Where q(t) is the flowback volume corresponding to time t, i(t) is the injection volume of the injection well corresponding to time t, and q(t 0 ) is the initial time t 0 The corresponding return flow volume, τ is the time constant of the capacitor resistor-tracer model, t 0 is the initial time of tracer migration, t is the tracer migration time, J is the liquid production index, pwf(t 0 ) is the initial time t 0 The corresponding bottom hole pressure, p wf (t) is the bottom hole flowing pressure corresponding to time t.

4. The method for establishing a capacitance resistance-tracer model for a carbonate fracture-cavity reservoir according to claim 3, Features: The capacitance resistance-tracer model in the crack channel is: Where C is the tracer flowback concentration, C 0 is the initial tracer concentration at the inlet, R is the tracer particle adsorption factor, t D is the dimensionless time, η is the dimensionless quantity related to the Peclet number, k dep is the sedimentation coefficient of the tracer particles, L is the migration distance, D is the diffusion coefficient of the tracer, v is the flow rate of the tracer, t is the migration time of the tracer, i(t) is the injection volume of the injection well corresponding to time t, V p is the controlled pore volume of a single well, N pe is the Peclet number, C t is the comprehensive compression coefficient of the formation, τ is the time constant of the capacitance resistance-tracer model, and J is the liquid production index.

5. The method for establishing a capacitance resistance-tracer model for a carbonate fracture-cavity reservoir according to claim 3, Features: The tracer seepage model in the cave channel is: in, P=-(Δr) 2 In the formula, is the tracer concentration in the i-1th grid, is the tracer concentration in the ith grid, is the tracer concentration in the i+1th grid, is the tracer concentration of the ith grid in the previous time step, D is the tracer diffusion coefficient, R is the tracer particle adsorption factor, Δt is the time step, Δr is the radius step, and r i is the radial radius in the i-th grid, Q is the flow rate per unit thickness, φ is the porosity, k dep is the sedimentation coefficient of the tracer particles.

6. The method for establishing a capacitance resistance-tracer model for a carbonate fracture-cavity reservoir according to claim 3, Features: The capacitance resistance-tracer model in the crack-cavern channel is: Where CF 1 is the first crack on the channel, C 0 is the initial tracer concentration at the inlet, R is the tracer particle adsorption factor, t D is the dimensionless time, η is the dimensionless quantity related to the Peclet number, k dep is the sedimentation coefficient of the tracer particles, L is the migration distance, D is the diffusion coefficient of the tracer, CF j is the jth crack on the channel, CV j is the j-th cave on the channel, N is the total time step, k is the k-th time step in the total time step N, Δt is the time step, Δr is the radius step, is the tracer concentration in the i-1th grid, Q is the flow rate per unit thickness, φ is the porosity, r i is the radial radius in the i-th grid, is the tracer concentration in the ith grid, is the tracer concentration in the i+1th grid, The tracer concentration of the i-th grid in the previous time step; v is the tracer flow rate, t is the tracer migration time, i(t) is the injection volume of the injection well corresponding to time t, V p is the controlled pore volume of a single well, N pe is the Peclet number, τ is the time constant of the capacitor-resistor-tracer model, C t is the comprehensive compression coefficient of the formation, and J is the liquid production index.

7. The method for establishing a capacitance resistance-tracer model for a carbonate fracture-cavity reservoir according to claim 1, Features: The tracer seepage model in the fracture channel is: Where C is the tracer flowback concentration, C 0 is the initial concentration of the tracer at the inlet, D is the tracer diffusion coefficient, R is the tracer particle adsorption factor, t is the tracer migration time, L is the migration distance, k dep is the sedimentation coefficient of the tracer particles, and v is the flow rate of the tracer.

8. The method for establishing a capacitance resistance-tracer model for a carbonate fracture-cavity reservoir according to claim 1, Features: The tracer seepage model in the fracture-cavern channel is: Where CF 1 is the first crack on the channel, L 1 is the migration distance of the tracer when it passes through the first fracture; N is the total time step, k is the kth time step in the total time step N, Δt is the time step, Δr is the radius step, C 0 is the initial tracer concentration at the inlet, D is the tracer diffusion coefficient, R is the tracer particle adsorption factor, k dep is the sedimentation coefficient of the tracer particles, v is the average seepage velocity, Q is the flow rate per unit thickness, φ is the porosity, CF j is the jth crack on the channel, L j is the displacement distance of the tracer when it passes through the jth crack, CV j is the jth cave on the channel, is the tracer concentration in the i-1th grid, r i is the radial radius in the i-th grid, is the tracer concentration in the ith grid, is the tracer concentration in the i+1th grid, Tracer concentration at the ith grid cell in the previous time step.

9. The method for establishing a capacitance resistance-tracer model for a carbonate fracture-cavity reservoir according to claim 1, Features: The step S 3 The objective function in is: In the formula, q jcal (t) is the calculated liquid production of production well j at time t, q jobs (t) is the measured liquid production of production well j at time t, C ijcal (t) is the tracer concentration value calculated at time t for production well j, C ijobs (t) is the tracer concentration value measured at production well j at time t, t n is the total number of time steps.

10. The method for establishing a capacitance resistance-tracer model for a carbonate fracture-vuggy reservoir according to claim 9, Features: It also includes the use of particle swarm algorithm to solve the objective function.

11. The method for establishing a capacitance resistance-tracer model for a carbonate fracture-cavity reservoir according to claim 1, Features: This includes using indoor flow physics simulation experiments to verify the accuracy of the capacitance resistance-tracer model.

12. The method for establishing a capacitance resistance-tracer model for a carbonate fracture-vuggy reservoir according to claim 11, Features: The indoor flow physics simulation experiment includes: Numerical characterization of typical fracture-cavity structures and preparation of visualization models, wherein the visualization models include fracture models, cave models and fracture-cavity models; The tracer flow simulation experiment was completed in a visual model using a tracer flow simulation experimental device.

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