Calculation model and method for phase equilibrium temperature of ice crystal drilling fluid

Abstract

The invention relates to the technical field of petroleum drilling, in particular to an ice crystal drilling fluid phase equilibrium temperature calculation model and method comprehensively considering a water phase, an oil phase, a soil phase and salt, and aims to improve the accuracy and applicability of phase equilibrium temperature prediction and prevent faults caused by the influence of underground high temperature on downhole tools and measuring instruments. Therefore, safe and smooth drilling operation is guaranteed. According to the model, components are analyzed through a system, the effective water mole fraction is calculated, and a comprehensive formula is obtained based on chemical potential balance derivation. According to the method, the influence rule of each factor on the equilibrium temperature can be determined, accurate prediction and regulation are realized, the method is effectively adapted to the temperature environments of different deep well stratums, and key technical support is provided for optimizing the cooling performance of the ice crystal drilling fluid and solving the problem of high-temperature heat damage of the deep well.

Description

TECHNICAL FIELD

[0001] The present application relates to the field of oil drilling technology, and particularly relates to a calculation model and method of phase equilibrium temperature of ice crystal drilling fluid considering water phase, oil phase, soil phase and salt-containing ice crystal comprehensively, which is used for regulating and controlling wellbore temperature through ice crystal effect in the process of drilling deep well and ultra-deep well, and ensuring stable operation of drilling fluid, downhole tools and measuring instruments. BACKGROUND

[0002] In the process of drilling deep well and ultra-deep well, the bottom of the well often faces high temperature and high pressure environment. The ice crystal drilling fluid has important application value in these complex working conditions due to its unique low temperature fluidity and inhibition. Accurate prediction of its phase equilibrium temperature is the key to ensuring the safety of drilling and the normal operation of downhole tools and measuring instruments at high temperature.

[0003] Traditional models mostly only consider a single salt component or ignore the influence of oil phase and soil phase, and cannot accurately reflect the multi-phase and multi-component characteristics of actual drilling fluid. For high salt concentration or complex salt mixture system, the prediction error of existing models (such as models based on the assumption of ideal solution) is large. Most models are only for specific temperature and pressure range or specific drilling fluid formula, and are difficult to adapt to the diversified needs of different well conditions. Some high-precision models rely on complex iterative algorithms, and the calculation time is long, which is not conducive to real-time application on site. Moreover, in terms of temperature reduction, the ground and downhole equipment temperature control technology is now mostly used, and the high-temperature drilling fluid returning in the drilling process not only affects the safety of equipment and personnel, but also causes problems such as high temperature at the inlet of drilling fluid and high temperature of downhole drilling fluid circulation, resulting in unstable temperature reduction effect and difficulty in meeting the needs of actual engineering. SUMMARY

[0004] The purpose of the present application is to provide a calculation model and method of phase equilibrium temperature of ice crystal drilling fluid, so as to improve the accuracy and applicability of phase equilibrium temperature prediction, prevent downhole tools and measuring instruments from being affected by high temperature underground and malfunctioning, and thus ensure the safety and smooth progress of drilling operation.

[0005] To achieve the above-mentioned purpose, the present application provides the following technical solutions: In a first aspect, the present application provides a calculation model of phase equilibrium temperature of ice crystal drilling fluid, which is characterized in that: Through the modified Clapeyron equation, the ice crystal curvature radius (Gibbs-Thomson effect) is introduced, and an ice crystal phase transition critical temperature model is established: , : actual melting point of ice crystal (K), : freezing point of pure water (273.15 K), : ice-water interface energy, : ice density (kg / m3), : latent heat of phase transition (J / kg), : ice crystal radius (m), : pressure correction coefficient (0.074 K / MPa), : pressure (MPa), : freezing point depression fitting number, is the mass molar concentration of salt in the drilling fluid, is the dilution coefficient of the inert dispersed phase. In a second aspect, the present application provides a method for calculating the phase equilibrium temperature of ice crystal drilling fluid, which is characterized in that it comprises the following steps:

[0006] calculating the mass and amount of substance of each component of the water phase, oil phase, soil phase and salt-containing phase in the drilling fluid system; determining the effective water molar fraction in the system based on the amount of substance of each phase component ; calculating the chemical potential of the effective water phase based on the effective water molar fraction according to the dilute solution theory ; establishing the phase equilibrium condition between the ice crystal phase and the effective water phase, and solving the phase equilibrium temperature of the ice crystal drilling fluid by combining the chemical potential of ice, the chemical potential of the effective water phase, the pressure correction term and the ice crystal size correction term , the effective water molar fraction is calculated by the following formula: .

[0007] Preferably, the freezing point depression constant is defined by the following formula: , wherein, R R is the gas constant, T 0 is the freezing point of pure water, 273.15 K, L and latent heat of phase transition (J / kg).

[0008] Preferably, the effective water molar fraction is specifically:

[0009] wherein, ,​ , , are the mass of water, salt, oil, and clay, respectively.

[0010] Preferably, in the ice-crystal drilling fluid engineering application, the effective water mole fraction is calculated as follows: , Substitute the mass expressions of each substance and eliminate m total : , wherein, S is the mass fraction of salt, ω oil is the mass fraction of oil, ω ben is the mass fraction of clay, M oil , M ben are the molar masses of oil and clay, respectively.

[0011] Preferably, the chemical potential of the effective water phase μ water_effective is calculated as follows: , Let water,effective ≈1 Δ, Δ is a small quantity, and by using mathematical approximation, we have: , wherein: ， m : the mass molar concentration of salt (mol / kg), α: the dilution coefficient of the inert dispersed phase.

[0012] In a third aspect, the present application further provides an ice-crystal drilling fluid temperature prediction system, which is characterized in that it comprises: a data input module, configured to receive the salt mass fraction S , the oil mass fraction ω oil , the clay mass fraction ω ben , the system pressure P , and the ice-crystal radius r ; a data processing module, configured to execute the ice-crystal drilling fluid phase equilibrium temperature calculation method as described above, and calculate the phase equilibrium temperature T melt ; The results display module is used to output the phase equilibrium temperature. T melt .

[0013] Fourthly, the present invention also proposes a computer-readable storage medium having a computer program stored thereon, characterized in that, when the program is executed by a processor, it implements the above-mentioned method for calculating the liquid phase equilibrium temperature in ice crystal drilling.

[0014] Fifthly, the present invention also proposes an electronic device, including a memory, a processor, and a computer program stored in the memory and executable on the processor, characterized in that, when the processor executes the program, it implements the above-mentioned method for calculating the liquid phase equilibrium temperature in ice crystal drilling.

[0015] The technical effects and advantages of this invention are as follows: 1. This invention provides a calculation model for the phase equilibrium temperature of ice crystal drilling fluid that comprehensively considers the water phase, oil phase, soil phase and salt-containing phase. It systematically integrates the common influence of all components such as water, salt, soil and oil on phase equilibrium, so that the model can accurately simulate the synergistic or antagonistic effects that may occur when multiple additives coexist with the soil phase. 2. The model proposed in this invention can provide a more realistic temperature-pressure "safety window", thereby effectively guiding operations. Based on the accurate prediction of this model, drilling fluid performance or circulation parameters can be actively adjusted to fundamentally prevent downhole high temperatures from affecting the operation of downhole tools and measuring instruments, ensuring the safety and efficiency of drilling projects. 3. The model proposed in this invention elevates drilling fluid design from relying on engineers' personal experience and conservative estimates to a scientific design stage based on accurate physicochemical models. Attached Figure Description

[0016] Figure 1 A graph showing the effect of different ice crystal sizes on the melting point; Figure 2 This is a graph showing the effect of different pressures on the melting point. Figure 3 This is a graph showing the effect of different salinities on the melting point. Figure 4 The graph shows the effect of different bentonite mass fractions on the melting point. Figure 5 This is a graph showing the effect of different oil mass fractions on the melting point. Detailed Implementation

[0017] Clearly, the described embodiments are only a part of the embodiments of the present application, rather than all the embodiments. Based on the embodiments in the present application, all other embodiments obtained by those of ordinary skill in the art without creative efforts fall within the protection scope of the present application.

[0018] The ice crystal drilling fluid phase equilibrium temperature calculation method provided by the present application specifically comprises the following steps: 1) Calculate the system component analysis and effective water molar fraction: Let the total mass of the system be m total , and the mass distribution of each component is as follows: The mass of the salt: m salt =S m total (S is the mass fraction of the salt), The amount of substance of the salt: , The mass of water: (Where ω oil is the mass fraction of the oil, and ω ben is the mass fraction of the bentonite), The amount of substance of water: ( The molar mass of water is M water ), The mass of the oil: , The amount of substance of the oil: , The mass of the bentonite: , The amount of substance of the bentonite: , The total amount of substance of the system is: , Define the effective water molar fraction x 水 , 有效 as the molar fraction of water in the total substance:

[0019] Step 2) Simplification of the dilute solution and expression of the chemical potential: In the engineering application of the ice crystal drilling fluid, the following simplification can be made:

[0020] Substitute the amount of substance expression of each substance and eliminate m total :

[0021] According to the dilute solution theory, the chemical potential of "effective water" in the system is lower than the standard chemical potential of pure water. The relationship is as follows:

[0022] make water,effective ≈1 Let Δ be a small quantity. Using mathematical approximation, we can obtain:

[0023] in:

[0024] m : Molar concentration of salt (mol / kg) α: Dilution factor of inert dispersed phase Therefore, the final approximate expression for the effective hydrochemical potential is:

[0025] Step 3) Derivation of phase equilibrium conditions and freezing point depression formula: When the ice crystals and drilling fluid system reach phase equilibrium, the following conditions are met:

[0026] (1) Expressing the chemical potentials of both sides in equilibrium: The chemical potential of ice unfolds near T0: , Because the salts in drilling fluid (mainly NaCl) are strong electrolytes, they completely dissociate into ions in water. According to the colligative property theory of electrolyte solutions, their effective particle concentration is a fraction of their molality. i (Van der Hoff factor), for NaCl, i ~ 2 The effective chemical potential of water is... T Expand around 0 and substitute into the expression: , (2) Substitute into the equilibrium condition

[0027] (3) Using the initial equilibrium condition at point T0, the above equation simplifies to: , (4) Simplify the equations , Substitute into the melting entropy relationship , , The freezing point depression value ΔT = T0 T melt , then T melt T0= ΔT. Substituting into the above equation: , Using linear approximation T melt ≈ T0: , Step 4) Introduce freezing point depression constant K f and adjust the final form: The freezing point depression constant is defined as

[0028] , Step 5) Add "pressure effect" - corrected by Clapeyron equation: Pressure will change the melting point of ice (such as when you step on snow, the pressure makes the snow temporarily melt), so the increase in pressure will lower the melting point of ice crystals, according to the Clapeyron equation (describing the effect of pressure on phase transition temperature), after integration to get the correction term of pressure on melting point:

[0029] β = -0.074 K / MPa (pressure correction coefficient, negative sign means "the greater the pressure, the lower the melting point"), P is the actual pressure (MPa). The increase in pressure is equivalent to "squeezing" the ice, making it easier for water molecules to become water, so the melting point decreases.

[0030] Step 6) Add "ice crystal size effect" - Gibbs-Thomson effect: When ice exists in the form of small particles (radius r), surface tension (γ) will significantly affect its chemical potential. The chemical potential equilibrium condition of ice and water is:

[0031] where is the specific volume of ice (volume per unit mass).

[0032] Near the reference temperature T0 (melting point when the interface is flat), the chemical potential difference can be linearly approximated as:

[0033] Substituting into the equilibrium condition gives:

[0034] Solving the curvature caused by the melting point temperature correction:

[0035] Step 7) Summary formula: All the formulas are superimposed on the freezing point T0, and finally we get: .

[0036] Example 1: Effect of different ice crystal sizes on melting point This example verifies the effect of ice crystal size on the melting point, and the flow chart is shown in Figure 1 .

[0037] Specifically includes the following steps: constructing a model of the relationship between ice crystal size and melting point in ice crystal drilling fluid, including the assumption conditions of the physical model and the establishment of the mathematical model, the physical model assumes that the drilling fluid system is a homogeneous mixed system, and the settling effect of solid particles (such as bentonite, cuttings, etc.) is ignored; The system pressure is constant at 5 MPa to exclude the interference of pressure on the melting point; fixed salinity (NaCl mass fraction is 3%), bentonite mass fraction is 2%, oil mass fraction is 0% (water-based drilling fluid system), only change the ice crystal size; Ice crystals are spherical particles with uniform size distribution and no agglomeration.

[0038] The mathematical model uses a modified ice phase equilibrium temperature model (combined with Gibbs-Thomson effect and Clapeyron equation), and the core formula is: , Where (the freezing point of pure water); (pressure correction coefficient); (constant pressure); (ice-water interface energy); (ice density); (ice phase change latent heat); r is the ice crystal radius (variable, unit ); (constant of freezing point reduction of water); (mass molar concentration of 3% NaCl solution).

[0039] An iterative solution method is used to solve the model, and the initial assumption of the melting point under different ice crystal radii , the theoretical melting point is calculated by substituting the above formula; compare the deviation of the calculated value and the assumed value, if the deviation , correct the assumed value and recalculate; repeat the iteration until the deviation , the final melting point data is output; in the model verification test, the system pressure is set to 5 MPa, the mass fraction of salt (NaCl) is 3%, the mass fraction of bentonite is 2%, the mass fraction of oil is 0%, the ice crystal radius is 1 μm, 20 μm, 40 μm, 60 μm, 80 μm and 100 μm respectively, and the environmental temperature is 275 K; under the above conditions, the melting point of the ice crystal drilling fluid at different ice crystal radii is simulated, the melting point corresponding to different ice crystal radii is calculated by the iterative solution method, each radius parameter is calculated repeatedly for 3 times, and the average value is taken as the final result, and the result is shown in Figure 1 .

[0040] Example Two: Influence of Different Pressures on Melting Point The flow chart is shown in Figure 2 .

[0041] Specifically, the following steps are included: a model of the relationship between the melting point of the ice crystal drilling fluid and the pressure is constructed. The physical model assumes that the ice crystal radius is fixed at 30 μm (to avoid size interference), the system is a water-based drilling fluid (with an oil mass fraction of 0%), the salinity (NaCl) mass fraction is 3%, the bentonite mass fraction is 2%, and the thermophysical parameters are constant; the small influence of pressure on the ice-water interface energy and the phase change latent heat is ignored, and only the Clapeyron equation correction term is considered.

[0042] The mathematical model follows the phase equilibrium model of Example One, and the core variable is the pressure P, that is: , In the formula , the other parameters are the same as in Example One.

[0043] The iterative solution method consistent with Example One is adopted, and the convergence criterion is the melting point calculation deviation ; in the model verification test, all parameters except the pressure are fixed, the basic data are set as the ice crystal radius , the salt (NaCl) mass fraction is 3%, the bentonite mass fraction is 2%, the oil mass fraction is 0%, the system pressure P is 0.1 MPa, 2 MPa, 4 MPa, 6 MPa, 8 MPa and 10 MPa, and the environmental temperature is 275 K; the melting point under each pressure is calculated by substituting the model, and the average value is taken for 3 times, and the result is shown in Figure 2 .

[0044] Example Three: Influence of Different Salinity on Melting Point This example verifies the influence of salinity on the melting point, and the flow chart is shown in Figure 3 .

[0045] Specifically, the steps include: constructing a model of the melting point relationship of ice crystal drilling fluid under different salinities, including the assumptions of the physical model and the establishment of the mathematical model. The physical model assumes that the ice crystal radius is fixed at 30 μm and the system pressure is constant at 5 MPa; the bentonite mass fraction is 2% and the oil mass fraction is 0%, eliminating the interference of inert components; the salinity is... NaCl Complete dissociation (van t Hoff factor) This conforms to the colligative property theory of dilute solutions.

[0046] The core variable in the mathematical model is the molality of the salt. m The model formula is the same as in Example 1, wherein... m Conversion from salt mass fraction: Salt mass fraction S and m Relationship: , The iterative solution method converges based on the melting point deviation. The focus is on correcting the salt concentration corresponding to item.

[0047] During model validation testing, the corresponding m for each salt mass fraction was calculated, and the basic data was set as the ice crystal radius. System pressure The bentonite content is 2% by mass, and the oil content is 0% by mass. NaCl With mass fractions S of 0%, 0.05%, 0.1%, 0.15%, 0.2%, 0.25%, and 0.3%, and an ambient temperature of 275 K, the melting point was calculated using the model. The calculation was repeated three times for each salinity point, and the average value was taken. The results are as follows: Figure 3 As shown.

[0048] Example 4: Effect of different bentonite mass fractions on melting point This embodiment verifies the effect of bentonite content on melting point, as shown in the flowchart below. Figure 4 As shown.

[0049] Specifically, the steps include: constructing a model of the melting point relationship of ice crystal drilling fluid under different bentonite mass fractions, including the assumptions of the physical model and the establishment of the mathematical model. The physical model assumes that the ice crystal radius is fixed at 30 μm, the system pressure is 5 MPa, and the salt content is... NaCl The mass fraction of bentonite is 3%; bentonite is an inert dispersed phase and does not participate in the phase change, but only dilutes the aqueous phase (reducing the effective water mole fraction); the mass fraction of oil is 0%, the system is a water-based drilling fluid, and the effect of bentonite adsorbed water on the phase change is ignored.

[0050] Mathematical model introduces bentonite mass fraction Corrected effective water mole fraction The model formula was adjusted to ,in , the molar mass of bentonite is calculated as 270 g / mol (estimated from the average molecular formula).

[0051] In iterative solution, the oil mass fraction is calculated first , and then the melting point is calculated by substituting the model, and the convergence deviation ; in model verification test, the corresponding of each oil mass fraction is calculated, the ice crystal radius , the system pressure , the NaCl mass fraction is 3%, the oil mass fraction is 0%, the bentonite mass fraction is 0%, 1%, 2%, 3%, 4%, 5%, the environmental temperature is 275K, the melting point is obtained by substituting the model, each parameter point is calculated 3 times to take the average value, and the results are shown in Figure 4 .

[0052] Example 5: Effect of different oil mass fraction on melting point This example verifies the effect of oil content on the melting point, and the flow chart is shown in Figure 5 .

[0053] Specifically includes the following steps: constructing the model of the relationship between the ice crystal drilling fluid melting point under different oil mass fraction, including the assumption conditions of the physical model and the establishment of the mathematical model, the physical model assumes that the ice crystal radius is fixed at 30μm, the system pressure is 5MPa, the salt NaCl mass fraction is 3%, the bentonite mass fraction is 2%; the oil is an inert component and does not participate in the ice-water phase change, only dilutes the water phase (reduces the effective water molar fraction); the influence of the oil-water interface effect on the phase change is ignored; the mathematical model introduces the oil mass fraction to correct the effective water molar fraction , the model formula is adjusted as , wherein , the molar mass of oil is calculated as 280 g / mol (estimated from the average hydrocarbon molecular formula); in iterative solution, the oil mass fraction is calculated first , and then the melting point is calculated by substituting the model, and the convergence deviation ; in model verification test, the corresponding of each oil mass fraction is calculated, the ice crystal radius , the system pressure , NaCl mass fraction is 3%, the bentonite mass fraction is 2%, the oil mass fraction is 0%, 5%, 10%, 15%, 20%, the environmental temperature is 275K, the melting point is obtained by substituting the model, each parameter point is calculated 3 times to take the average value, and the results are shown in Figure 5 .

[0054] Model verification and effect Comprehensive analysis of the simulation results of each of the above embodiments, the relative error of the predicted value of the model of the application and the experimental value / classical model value is only 1.3% on average, the accuracy is 98.7%, which meets the engineering precision requirement. The application can clearly show the influence of factors such as ice crystal size, salinity, pressure, and oil phase / soil phase ratio on the equilibrium temperature, realize accurate prediction and control of the ice crystal drilling fluid equilibrium temperature, effectively adapt to the temperature environment of different deep well formations, and provide key technical support for optimizing the cooling performance of ice crystal drilling fluid and solving the problem of deep well high temperature heat damage.

[0055] Based on the above method, the application further provides an ice crystal drilling fluid temperature prediction system, which comprises a data input module, a data processing module and a result display module. The data processing module is integrated with the algorithm of the above-mentioned calculation model. The system can be deployed on a computer, a server or a mobile terminal, and through the execution of the computer program in the storage medium, the rapid and accurate phase equilibrium temperature prediction is realized.

[0056] The above is only a specific embodiment of the application, but the protection scope of the application is not limited thereto. Any changes or replacements within the technical range disclosed by the application can be easily thought of by those skilled in the art, which should be covered within the protection scope of the application.

Claims

1. An ice-crystal drilling fluid phase equilibrium temperature calculation model, characterized in that, The model expression is: : Actual melting point of ice crystal (K), : Freezing point of pure water (273.15 K), : Ice-water interfacial energy, : Ice density (kg / m3), : Latent heat of phase change (J / kg), : Ice crystal radius (m), : Pressure correction coefficient, : Pressure (MPa), : Freezing point depression fitting number, is the mass molar concentration of salt in the drilling fluid, is the dilution coefficient of the inert dispersed phase.

2. A method for calculating the phase equilibrium temperature of ice crystal drilling fluid, characterized in that, The method comprises the following steps: The mass and the amount of substance of each component of the water phase, the oil phase, the soil phase and the salt-containing phase in the drilling fluid system are calculated; determining the effective water mole fraction in the system based on the amount of substance of the individual phase components ; According to the dilute solution theory, the chemical potential of the effective water phase is calculated based on the effective water molar fraction ; establishing phase equilibrium conditions between the ice crystal phase and the effective water phase, solving the ice crystal drilling fluid phase equilibrium temperature by combining the chemical potential of ice, the chemical potential of the effective water phase, the pressure correction term and the ice crystal size correction term , The calculated from the formula: 。 3. The ice crystal drilling fluid phase equilibrium temperature calculation method according to claim 2, characterized in that: The freezing point depression constant The defining equation is: ， wherein, R R is the gas constant, T 0 is the freezing point of pure water 273.15 K, L L is the latent heat of phase change (J / kg).

4. The ice crystal drilling fluid phase equilibrium temperature calculation method according to claim 3, characterized in that: The determining effective water molar fraction Specifically: wherein, , , , are the amounts of water, salt, oil, soil phase, respectively.

5. The method according to claim 4, characterized in that: In the engineering application of the ice crystal drilling fluid, the effective water mole fraction is calculated as follows: ， Substituting the amount expressions of each substance and canceling m total : ， wherein S mass fraction of salt, ω oil mass fraction of oil, ω ben mass fraction of soil phase, M oil , M ben molar mass of oil and soil phase, respectively.

6. The method according to claim 5, characterized in that: Chemical potential of the effective water phase μ water_effective The calculation expression is: Let water,effective ≈1 Δ, Δ is a small amount, using mathematical approximation, we can get: wherein: m : mass molarity of the salt (mol / kg), a: dilution factor of the inert dispersed phase.

7. An ice-crystal drilling fluid temperature prediction system characterized by, including: a data input module for receiving a salt mass fraction of the drilling fluid system S , an oil mass fraction ω oil , an earth phase mass fraction ω ben , a system pressure P and an ice crystal radius r ; The data processing module is configured to execute the ice crystal drilling fluid phase equilibrium temperature calculation method in any one of claims 2 to 6 to calculate the phase equilibrium temperature T melt ; a results display module for outputting the phase equilibrium temperature T melt .

8. A computer-readable storage medium having stored thereon a computer program, characterized in that, The program is executed by the processor to realize the ice crystal drilling fluid phase equilibrium temperature calculation method in any one of claims 2 to 6.

9. An electronic device comprising a memory, a processor, and a computer program stored on the memory and executable on the processor, characterized in that, The processor executes the program to realize the ice crystal drilling fluid phase equilibrium temperature calculation method in any one of claims 2 to 6.

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