Dsc modified hydrate inhibitor loss prediction method for multiphase flow systems

Abstract

The present application relates to natural gas hydrate technical field, especially relates to a kind of hydrate inhibitor loss prediction method of multiphase flow system based on DSC correction, first by two kinds of DSC test obtains the water activity and vaporization enthalpy of sample under target salinity and proportion, and accordingly regression thermodynamic model obtains liquid phase activity coefficient;Again, the saturated vapor pressure of inhibitor is calculated with DSC inversion vaporization enthalpy and anchor point method, combined with Poynting pressure correction and gas fugacity coefficient obtains component distribution coefficient, solves Rachford-Rice flash equation and obtains equilibrium phase and composition;Subsequently, the first-order overall mass transfer model is introduced to correct actual vaporization loss, and the total loss of inhibitor flow under multiphase flow system is obtained by superimposing droplet entrainment correlation.The present application can accurately calculate the total flow loss of hydrate inhibitor under high pressure, low temperature and salt-containing multiphase flow conditions, thereby providing theoretical support for real-time adjustment of inhibitor injection strategy.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of natural gas hydrate, and particularly relates to a hydrate inhibitor loss prediction method based on DSC correction for a multiphase flow system. BACKGROUND

[0002] During deepwater oil and gas drilling and long-distance submarine transportation, the low-temperature and high-pressure environment near the submarine mud line meets the thermodynamic conditions for the formation of natural gas hydrate. The gas produced from the formation and water can easily form natural gas hydrate in this environment, which is deposited and attached to the pipe wall, causing the effective flow passage to decrease. If not properly handled, the pipe string can be easily blocked, causing great economic losses. The current natural gas hydrate prevention and control method commonly used in the field is to add hydrate inhibitors such as methanol (MeOH) and ethylene glycol (MEG) to the pipe string. After the inhibitors are dissolved in the water phase, they will be vaporized and lost to different degrees under the gas carrying of the multiphase flow system, causing the effective inhibitor concentration in the actual liquid phase to gradually decrease, and the situation of "excess upstream and insufficient downstream" occurs, which still increases the risk of natural gas hydrate formation. In order to ensure safety, the engineering must adopt the "excess injection" strategy to completely eliminate the formation of natural gas hydrate, which leads to a substantial increase in operating costs. According to statistics, 15-40% of the hydrate prevention and control costs of deepwater oil and gas fields are related to the excess injection and loss of inhibitors.

[0003] The loss mechanisms of the two commonly used hydrate inhibitors in the multiphase flow system are different. Methanol has strong volatility, and the vaporization loss is significant. The pipeline example of JMCampbell shows that the sum of methanol loss (gas + liquid hydrocarbon) can reach twice the required injection amount. The loss of ethylene glycol is mainly caused by the entrainment of the gas phase. The GoM practice of JPT points out that there is still considerable loss of ethylene glycol under the recovery system and the entrainment conditions of the circular flow. The existing research on fluid loss is mainly based on the measurement of the distribution ratio of alcohols in the gas / water / hydrocarbon phase under static conditions through multiphase flash experiments, and a flash calculation model is established which depends on the general property library and empirical coefficients, ignoring the influence of the activity coefficient of the liquid phase components on the inhibitor in water and the physical property parameters in the real production conditions, as well as the mass transfer limitation between the inhibitor and the gas phase and the entrainment effect of the gas phase under the multiphase flow conditions. This leads to the difficulty in real-time prediction of the flow loss of the hydrate inhibitor in the long-distance multiphase flow system, and the injection strategy of the inhibitor cannot be adjusted in real time according to the effective concentration of the inhibitor in the pipeline. SUMMARY

[0004] The present application aims at the above-mentioned defects existing in the prior art, and provides a hydrate inhibitor loss prediction method based on DSC correction, which is realized by integrating differential scanning calorimeter (DSC) experiment and multiphase flash-mass transfer-entrainment coupling model calculation, so as to accurately calculate the total flow loss of the hydrate inhibitor under the conditions of high pressure, low temperature and salt-containing multiphase flow, thereby providing theoretical support for real-time adjustment of the injection strategy of the hydrate inhibitor.

[0005] The hydrate inhibitor loss prediction method based on DSC correction provided by the present application has the technical scheme that the method comprises the following steps:

[0006] I. A sample for DSC test is prepared according to the components of formation produced fluid, and the heat flow curve of the sample is measured by using DSC to obtain the water activity and vaporization enthalpy of the sample;

[0007] II. The water activity of the sample is processed by using a liquid phase model eNRTL to calculate the inhibitor activity coefficient under the target formula;

[0008] III. The sample vaporization enthalpy is processed by using a Clausius-Clapeyron straight line formula to obtain the inhibitor saturated vapor pressure under the target formula;

[0009] IV. The Poynting correction index and the fugacity coefficient of each component are calculated;

[0010] V. The gas / water distribution coefficient is solved based on the parameters obtained in steps II, III and IV by using multiphase flash calculation, and the molar fraction of each component in the liquid phase and the gas phase after flash equilibrium is obtained;

[0011] VI. The upper limit of vaporization loss in step V is corrected by considering the mass transfer limitation in the gas-liquid mass transfer process, and the real vaporization loss of the inhibitor is obtained;

[0012] VII. The loss rate of the inhibitor caused by the gas entrainment is calculated by considering the influence of high-speed gas entrainment on the loss of the inhibitor;

[0013] VIII. The inhibitor loss of the multiphase flow system is obtained by adding the two processes in steps VI and VII, and the inhibitor loss rate of the whole pipe section is solved by iteration along the pipe length.

[0014] Preferably, the sample preparation for DSC test in step I and the two types of DSC test processes are as follows:

[0015] S1.1. According to the components of formation produced fluid and the inhibitor concentration after injection and sufficient mixing, a sample for DSC test is prepared, and the liquid phase mass fraction is converted into the molar fraction in the liquid phase and the gas phase x i 、 y i , which is used for balance equation calculation;

[0016] S1.2 Temperature scanning of the DSC test sample at the target temperature using DSC to obtain the ice melting onset temperature T f , and the water activity of the sample is converted using formula (1) α w ;

[0017] (1),

[0018] In the formula, , R = 8.314 J / (mol·K); T f is the ice melting onset temperature, K; α w is the water activity, dimensionless;

[0019] S1.3 Isothermal vaporization energy test of the sample is carried out using open DSC, and the heat flow curve is recorded, and the vaporization heat is obtained by integrating the baseline after deduction Q ; the mass loss before and after the DSC experiment is recorded by weighing and converted into the number of moles Δ n , and the vaporization enthalpy Δ H vap, in is obtained using formula (2)

[0020] (2),

[0021] In the formula, Δ H vap, in is the vaporization enthalpy, J / mol; Q is the evaporation heat of the inhibitor, J; Δ n and Δ m are the number of moles and mass lost before and after evaporation, mol, g; M in is the molar mass of the inhibitor, g / mol; q corr is the heat flow, W; t is time, s.

[0022] Preferably, the detailed process of step two is as follows:

[0023] The water activity α w is converted using formula (3) T , temperature, salinity) and the molar fraction of the sample formula x w to obtain the activity coefficient of water gamma w The binary interaction parameters are obtained by regression using the liquid phase model eNRTL (formula (4)-(6)) at the target salinity tau 12 with tau21 ; and then the inhibitor activity coefficient of the target formula is calculated by formula (7) gamma in ;

[0024] (3),

[0025] (4),

[0026] (5),

[0027] (6),

[0028] (7),

[0029] wherein, x w is the mole fraction of water in the liquid phase, %; x in is the mole fraction of inhibitor in the liquid phase, %; gamma w DSC is the activity coefficient of water obtained according to the DSC experiment, dimensionless; gamma w model is the activity coefficient of water obtained according to the liquid phase model eNRTL, dimensionless; G 12 and G 21 is a calculated intermediate parameter, dimensionless; k is the number of formulas; S is the objective function, dimensionless; gamma in is the inhibitor activity coefficient of the target formula, dimensionless;

[0030] wherein, the non-random parameter ω is generally taken as 0.3, tau 12 the initial value is taken as 0.5, tau 21 the initial value is taken as 0.1, and is substituted into formula (5) for calculation gamma w model the multiple of the actual DSC measurement in S1.2 α w ,temperature, salinity) are taken as the fitting target and an objective function is established, as shown in formula (6); iterative calculation is performed until the calculated T w model matches the actual DSC measurement value; the inhibitor activity coefficient gamma in is obtained by formula (7). gamma vap, in

[0031] Preferably, the detailed procedure of step three is as follows:

[0032] The Δ H vap, in is given by DSC P sat ( T ) using Clausius-Clapeyron linear or piecewise integral form P sat,in ( T ) ; where the Clausius-Clapeyron differential form is equation (8), if Δ H vap ( T ) is approximated as a constant Δ H vap , the integral gives the linear equation (9), substitute the selected anchor point T , P sat ) to calculate the intercept of the linear equation C , then substitute the target temperature T j and Δ H vap, in into equation (9) to get the saturated vapor pressure of the inhibitor P sat,in ( T j ) ;

[0033] (8),

[0034] (9),

[0035] where, P sat ( T ) is the anchor point saturated vapor pressure, Pa; C is the linear intercept, determined by single point anchoring; T is the temperature, K; P sat,in ( T ) is the saturated vapor pressure of the inhibitor, Pa.

[0036] Preferably, the detailed procedure of step four is as follows:

[0037] Use equation (10) to calculate the Poynting correction index, which represents the integral correction of the liquid phase reference state from the saturated pressure P sat,in to the target P j pressure;

[0038] (10),

[0039] where П is Poynting correction index, dimensionless; rho in is the inhibitor density, kg / m 3 ; P j is the pressure in the calculation section, Pa;

[0040] The fugacity coefficients of each component are calculated by using Peng-Robinson EOS equation, inputting the critical constants, eccentric factors and gas phase composition of each component phi i .

[0041] The detailed process of step five is as follows:

[0042] Gas / water partition coefficient calculation: gas / water partition coefficient K i Component i The ratio of the mole fraction in the gas phase to that in the water phase at equilibrium, for volatile components i , the partition coefficient of component i in the gas-liquid two-phase is solved by using equation (11) K i ;

[0043] (11);

[0044] where K i is the partition coefficient in the gas-liquid two-phase, dimensionless; gamma i is the activity coefficient of different components, dimensionless; phi i is the fugacity coefficient of component, dimensionless; P sat,i is the saturated vapor pressure of different components, Pa;

[0045] Rachford-Rice two-phase flash calculation:

[0046] Given the mole fraction of feed z i , the mole fraction of gas phase is solved by using dichotomy to solve equation (12) β ; and then the mole fraction of each component in the liquid phase and gas phase after flash equilibrium is calculated by using equation (13) x i 、 y i ;

[0047] (12),

[0048] (13)

[0049] In the formula, β The mole fraction of the gas phase. z i The mole fraction of different components in the total feed stream. x i Components after flash evaporation equilibrium i Mole fraction in the liquid phase y i Components after flash evaporation equilibrium i Mole fraction in the gas phase.

[0050] Preferably, the detailed process of step six is ​​as follows:

[0051] The upper limit of the thermodynamic loss of the inhibitor after the gas-liquid equilibrium is fully reached in the calculation segment (mass transfer is not limited) is calculated using Equation (14). However, the interfacial mass transfer is affected by the gas-liquid contact area, flow pattern and turbulence degree, and can only reach a part of the upper limit of loss in reality. Therefore, a first-order global mass transfer model (Equation 15) is needed to calculate the actual vaporization loss of the inhibitor.

[0052] (14)

[0053] (15)

[0054] In the formula, xi eq and xi vap The maximum vaporization loss and the actual vaporization loss rate are dimensionless. k L The mass transfer coefficient in the liquid phase is commonly calculated using empirical correlation formulas. a Specific surface area, determined by the flow pattern in the wellbore, is dimensionless; tau Residence time, in seconds, can be calculated as liquid volume / liquid volumetric flow rate.

[0055] Preferably, the detailed process of step seven is as follows:

[0056] High-speed gas phase can entrain droplets and carry inhibitors to the gas phase. The entrainment rate of droplets varies with the flow pattern, Reynolds number, and Weber number. First, the droplet entrainment rate is calculated using equation (16). E Then, the loss rate of the inhibitor lost through gas entrainment is calculated using equation (17);

[0057] (16)

[0058] (17)

[0059] In the formula,E for droplet entrainment rate, dimensionless; We, Fr, Re are gas phase Weber number, Froude number and Reynolds number, respectively, dimensionless; rho L and rho G are gas and liquid phase density, respectively, kg / m 3 ; mu L and mu G are gas and liquid phase viscosity, respectively, Pa-s; xi aero is the inhibitor loss rate due to entrainment, dimensionless; m in,aero is the mass of MeOH lost due to entrainment, g / s; n F is the total moles of feed, mol / s; m g is the gas phase flow rate, g / s; M g is the gas phase molar mass, g / mol; w in is the inhibitor mass fraction, %.

[0060] Preferably, the detailed procedure of step eight is as follows:

[0061] Calculation segment j The total loss rate of inhibitor due to evaporation loss and entrainment loss during flow can be calculated by equation (18); cut the pipeline into N segments, in order j =1→ N accumulate, set R in 1 =1, the fraction of inhibitor that has not been lost at the pipeline inlet, then the calculation segment j contributes to the total inlet loss is calculated by equation (19); update the inhibitor fraction for the next calculation segment, see equation (20), accumulate to obtain the inhibitor loss rate in the entire pipeline segment, see equation (21);

[0062] (18),

[0063] (19),

[0064] (20),

[0065] (21),

[0066] wherein, xi totalLoss_of_Total is the total loss rate of inhibitor, and is calculated by the section j Contribution of the inner to the total inlet loss, dimensionless R in With R out Loss_of_Total is the total loss rate of inhibitor, and is calculated by the section j Inhibitor fraction at the inlet and outlet, and is the loss rate of inhibitor in the whole pipe section.

[0067] Compared with the prior art, the present application has the following beneficial effects:

[0068] Firstly, the present application is closer to the field conditions:

[0069] The water activity and vaporization enthalpy of the real sample solution are directly measured by a differential scanning calorimeter (DSC) experiment to obtain the empirical parameters required by the multiphase flash calculation model, avoiding the deviation caused by relying on a general database, so that the accurate calculation of the vaporization loss of the hydrate inhibitor can be realized under the conditions of high pressure, salt content and non-ideal liquid; at the same time, the method introduces the distribution of multiphase flow in the real pipeline into the calculation, which can consider the additional loss caused by droplet entrainment, and is more in line with the actual operation characteristics of the deepwater oil and gas pipeline.

[0070] Secondly, the present application has wide applicability:

[0071] The present application is not only suitable for loss evaluation of different types of inhibitors such as methanol and ethylene glycol, but also can cover various complex scenes such as subsea wellheads, long-distance subsea pipelines and ground separators; no matter in the undulating pipeline, variable-diameter pipeline or separation equipment, the present application can accurately calculate according to different working conditions and inhibitor characteristics, so as to provide a unified loss evaluation tool for the whole process of deepwater oil and gas development.

[0072] Thirdly, the present application can realize the calculation of the spatial and temporal distribution of the hydrate inhibitor concentration:

[0073] Under field conditions, the inhibitor is usually injected into the wellhead or pipeline through a single-point injection method, but since the flow path length can reach thousands of meters, the concentration distribution of the inhibitor along the way is often unknown, and targeted hydrate risk management cannot be realized; the present method can calculate the loss amount of the inhibitor under different positions and time conditions of the pipeline in real time by establishing a multiphase flash-mass transfer-entrainment coupling model, so as to obtain the real-time concentration distribution of the inhibitor, and provide a scientific basis for the injection strategy, optimization control and risk prevention and control of the inhibitor. BRIEF DESCRIPTION OF DRAWINGS

[0074] Figure 1 The present application is based on the multiphase flow system hydrate inhibitor flow loss prediction flowchart modified by DSC;

[0075] Figure 2The heat flow curve measured by DSC in the process of water activity measurement by ice melting method;

[0076] Figure 3 The heat flow curve measured by DSC in the process of measuring evaporation intensity. DETAILED DESCRIPTION

[0077] The preferred embodiments of the present application are described below in conjunction with the accompanying drawings, and it should be understood that the preferred embodiments described herein are only used to illustrate and explain the present application, and are not used to limit the present application.

[0078] Embodiment 1, a hydrate inhibitor loss prediction method based on DSC correction for a multiphase flow system mentioned in the present application, comprising the following steps:

[0079] First, the water activity and vaporization enthalpy of the sample at the target salinity and ratio are obtained by two types of DSC tests, and the liquid phase activity coefficient is obtained by regressing the thermodynamic model according to the water activity and vaporization enthalpy; then the saturated vapor pressure of the inhibitor is calculated by DSC inversion and anchor point method, and the component distribution coefficient is obtained by combining Poynting pressure correction and gas phase fugacity coefficient; the equilibrium phase and composition are obtained by solving the Rachford-Rice flashing equation; then a first-order overall mass transfer model is introduced to correct the actual vaporization loss, and the total loss of the inhibitor under the multiphase flow system is obtained by superimposing the droplet entrainment correlation.

[0080] To achieve the above object, the specific technical scheme adopted by the present application is as follows:

[0081] S1 sample preparation and two types of DSC test

[0082] S1.1 According to the components of the formation produced fluid and the inhibitor concentration after injection and sufficient mixing, the sample for DSC test is prepared, and the liquid phase mass fraction is converted into the molar fraction in the liquid phase and the gas phase x i , y i (for equilibrium equation calculation).

[0083] S1.2 The DSC is used to perform temperature scanning on the DSC test sample at the target temperature to obtain the ice melting starting temperature T f , and the water activity of the sample is converted by formula (1) α w .

[0084] (1),

[0085] In the formula, , R=8.314 J / (mol·K); T f is the ice melting starting temperature, K; αw Aw, dimensionless;

[0086] Note: The prepared sample needs to cover the inhibitor and salt concentration series of the field interval, and the water activity at different temperatures / formulas is measured by ice melting method using a sealed DSC α w T , temperature, salinity) to completely freeze the sample; then, the temperature is scanned back to +25°C at a slow speed of 0.1-0.5 K / min. Record the ice melting peak and extract the starting temperature T f

[0087] S1.3 Perform isothermal vaporization energy test on the sample using open DSC and record the heat flow curve, and integrate the vaporization heat after baseline subtraction Q ; record the mass loss before and after the DSC experiment by weighing and convert it to moles Δ n , and obtain the vaporization enthalpy Δ H vap, in

[0088] (2),

[0089] In the formula, Δ H vap, in is the vaporization enthalpy, J / mol; Q is the evaporation heat absorption of the inhibitor, J; Δ n and Δ m are the moles and mass lost before and after evaporation, mol and g; M in is the molar mass of the inhibitor, g / mol; q corr is the heat flow, W; t is the time, s.

[0090] Note: During the experiment, the sample is slowly heated from 20°C to 80°C (1-2°C / min), and the latent heat needs to be absorbed during the evaporation of the inhibitor from the liquid state to the gas state to ensure clear evaporation peak resolution. The heat flow after baseline subtraction in the evaporation interval q corr is integrated to obtain the evaporation heat Q

[0091] S2 Activity coefficient regression (γ)

[0092] Use formula (3) to obtain the water activity α w T , temperature, salinity) and the molar fraction of the sample formula x w to obtain the activity coefficient of water​​​​​gamma w Binary interaction parameters are regressed from liquid phase model eNRTL (equations (4)-(6)) at target salinity tau 12 with tau 21 And inhibitor activity coefficient of target formulation is calculated by equation (7) gamma in .

[0093] (3),

[0094] (4),

[0095] (5),

[0096] (6),

[0097] (7),

[0098] Wherein, x w is the mole fraction of water in liquid phase, %; x in is the mole fraction of inhibitor in liquid phase, %; gamma w DSC is the activity coefficient of water obtained from DSC experiment, dimensionless; gamma w model is the activity coefficient of water obtained from liquid phase model eNRTL, dimensionless; G 12 and G 21 are intermediate parameters calculated, dimensionless; k is the number of formulations; S is the objective function, dimensionless; gamma in is the inhibitor activity coefficient of target formulation, dimensionless.

[0099] Note: Only one α w cannot be directly obtained gamma in , binary interaction parameters tau 12 and tau 21 are calculated by means of liquid phase model. Non-random parameter ω is generally taken as 0.3, tau 12 The initial value is suggested to be taken as 0.5, tau 21 The initial value is suggested to be taken as 0.1, and is calculated in equation (5)gamma w model The actual measured values of DSC in S1.2 are multiple α w ( T , temperature, salinity) as the fitting target and establish the objective function (equation 6), iterative calculation until the model calculated gamma w model The measured values of DSC match. Using equation (7) can get the activity coefficient of inhibitor gamma in .

[0100] S3 DSC anchoring of the saturated vapor pressure P sat (T) of the inhibitor

[0101] Using DSC to give Δ H vap, in With the anchor point pressure P sat ( T ) (a reliable reference point can be taken, such as the vapor pressure of water at 298.15 K P sat or self-measured), using Clausius-Clapeyron linear equation or piecewise integral equation to get P sat,in ( T ). Where Clausius-Clapeyron differential equation is equation (8), if Δ H vap ( T ) is approximately constant Δ H vap , the integral gets the linear equation (9), substituting the selected anchor point T , P sat ) can calculate the intercept of the linear equation C , then the target temperature T j Substitute Δ H vap, in into equation (9) can get the saturated vapor pressure of the inhibitor P sat,in ( T j ).

[0102] (8),

[0103] (9),

[0104] In the equation, P sat (T ) is the anchor point saturation vapor pressure, Pa; C is the linear intercept, determined by single point anchoring; T is the temperature, K; P sat,in ( T ) is the inhibitor saturation vapor pressure, Pa.

[0105] S4 Poynting correction index calculation

[0106] The Poynting correction index is calculated using equation (10), which represents the integral correction of the liquid phase reference state from the saturation pressure P sat,in to the target P j pressure.

[0107] (10),

[0108] where П is the Poynting correction index, dimensionless; rho in is the inhibitor density, kg / m 3 ; P j is the pressure in the calculation section, Pa.

[0109] S5 Gas phase fugacity coefficient φ (Equation of State EOS calculation)

[0110] Using the Peng-Robinson EOS equation, input the critical constants, eccentric factors, and gas phase composition of each component to obtain the fugacity coefficient of each component phi i .

[0111] S6 Gas / water partition coefficient calculation

[0112] The gas / water partition coefficient K i component i is the ratio of the mole fraction in the gas phase to that in the water phase at equilibrium, and for volatile components i , the partition coefficient of component i in the gas-liquid two-phase is solved using equation (11) K i .

[0113] (11),

[0114] where, K i is the partition coefficient in the gas-liquid two-phase, dimensionless; gamma i is the activity coefficient of different components, dimensionless;phi i dimensionless; P sat,i saturated vapor pressure of different components, Pa.

[0115] S7 Rachford-Rice two-phase flash solution

[0116] Given feed mole fraction z i , the gas phase mole fraction is solved by using dichotomy to solve equation (12) β ; and the mole fraction of each component in the liquid phase and the gas phase after flash equilibrium is calculated by using formula (13) x i , y i .

[0117] (12),

[0118] (13),

[0119] In the formula, β is the gas phase mole fraction, z i is the mole fraction of different components in the total feed stream, x i is the mole fraction of component i in the liquid phase after flash equilibrium, y i is the mole fraction of component i in the gas phase after flash equilibrium.

[0120] S8 Actual vaporization loss (mass transfer discount)

[0121] The upper limit of the thermodynamic loss of the inhibitor after the gas-liquid equilibrium in the calculation section is calculated by using formula (14) (mass transfer is not limited), but the interface mass transfer is affected by the gas-liquid contact area, flow pattern and turbulence degree, so only a part of the upper limit can be actually achieved, therefore, a first-order overall mass transfer model (formula 15) is needed to convert the actual inhibitor vaporization loss.

[0122] (14),

[0123] (15),

[0124] In the formula, xi eq and xi vap are the maximum vaporization loss and the actual vaporization loss rate, dimensionless; k LKLa is liquid phase mass transfer coefficient, which is calculated by empirical correlation; a S is specific surface area, dimensionless, which is determined by wellbore flow pattern; tau t is residence time, s, which is calculated by liquid phase volume / liquid phase flow rate.

[0125] S9 Entrainment loss calculation xi aero (entrained droplet carries away inhibitor)

[0126] High-speed gas phase will entrain liquid droplets and take the inhibitor to the gas phase, the entrainment rate of liquid droplets changes with flow pattern, Reynolds number and Weber number, first use formula (16) to calculate the entrainment rate of liquid droplets E , then use formula (17) to calculate the loss rate of inhibitor lost by gas entrainment.

[0127] (16),

[0128] (17),

[0129] In the formula, E is the entrainment rate of liquid droplets, dimensionless; We, Fr and Re are gas phase Weber number, Froude number and Reynolds number, respectively, dimensionless; rho L and rho G are the densities of gas phase and liquid phase, respectively, kg / m 3 ; mu L and mu G are the viscosities of gas phase and liquid phase, respectively, Pa·s; xi aero is the loss rate of inhibitor caused by entrainment, dimensionless; m in,aero is the mass of MeOH lost by entrainment, g / s; n F is the total number of moles of feed, mol / s; m g is the gas phase flow rate, g / s; M g is the molar mass of gas phase, g / mol; w in is the mass fraction of inhibitor, %.

[0130] S10 Total loss of inhibitor

[0131] Calculation section j The total loss rate of inhibitor in the flow process due to evaporation loss and entrainment loss can be calculated by formula (18). The pipeline is cut into N sections, in order j= 1 → N Cumulative, set R in 1 = 1 (the fraction of inhibitor that has not been lost at the inlet of the pipe), then the calculation section j The loss contribution to the total inlet is calculated using equation (19). The fraction of inhibitor for the next calculation section is updated, see equation (20), and the cumulative solution gives the loss rate of inhibitor in the entire pipe section, see equation (21).

[0132] (18),

[0133] (19),

[0134] (20),

[0135] (21),

[0136] where, xi total Loss of Total is the total loss rate of inhibitor, %; Loss of Inlet is the loss contribution to the total inlet, dimensionless; j R in and R out Loss of Outlet is the fraction of inhibitor at the outlet of the calculation section, %; Ξ is the loss rate of inhibitor in the entire pipe section, %. j

[0137] Example 2, a DSC correction-based hydrate inhibitor loss prediction method for a multiphase flow system, specifically includes the following:

[0138] The test temperature of this example is 10°C, the pressure is 30 MPa, the pipe size is 0.1524 m, the flow rate is 5 m / s, the gas component is pure methane, the liquid phase contains NaCl, and the thermodynamic inhibitor is methanol MeOH, wherein the mass fraction of NaCl is 3wt%, and the mass fraction of methanol MeOH is 50wt%. In the total fluid component, the mole fraction of methane z CH4 = 0.9 (gas-dominated, natural gas production environment), and the mole fraction of the liquid phase is 0.1. Under this condition, the gas density rho G = 228.967 kg / m 3 , the viscosity mu G = 3 × 10 -5 , the liquid phase density rho L = 1013.542 kg / m 3 , the viscosity​​mu L =0.00128, the flow loss of methanol MeOH under this condition is calculated.

[0139] S1 Sample preparation and two types of DSC tests

[0140] S1.1 Conversion of liquid phase mass fraction to liquid phase mole fraction x i Take 100 g of liquid phase as a reference for easy calculation:

[0141] The mass of methanol MeOH is 50 g, and the molar mass is 32.04 g / mol, so the number of moles is 1.5599 mol; similarly, the number of moles of NaCl is 0.05133 mol, and the number of moles of water is 2.609 mol. Therefore, the mole fraction of each component in the liquid phase is: x MeOH =0.3695, x w =0.6183, x NaCl =0.0122. Since the total liquid phase is 0.1, the mole fraction of each component in the total feed is: z MeOH =0.03695, z w =0.06183, z NaCl =0.00122.

[0142] Prepare samples for DSC testing according to the components of the formation produced fluid. The samples need to cover the inhibitor and salt concentration series of the field interval, and the sample components prepared in this example are shown in Table 1.

[0143] Table 1

[0144]

[0145] S1.2 Measure the ice melting onset temperature of the prepared samples with different components using DSC by ice melting method T f : First, put 10-20 mg of sample into a sealed crucible, and reduce the sample from 25℃ to -40℃ at a rate of 5 K / min, so that the sample can freeze completely; then slowly scan at a rate of 0.1-0.5 K / min, and raise the sample temperature to 25℃, to obtain the heat flow curve shown in FIG. 1; Figure 2 Figure 2 The baseline in FIG. 1 is obtained by using an empty crucible with the same temperature scanning program. The point where the heat flow curve deviates from the baseline is the Onset point, and the corresponding temperature T f is the temperature at which the sample begins to melt. Substituting it into equation (1) gives the water activity under this component​α w ( T (Temperature, salinity), listed in Table 2.

[0146] Table 2

[0147]

[0148] S1.3 Take 5-15 mg of sample into an open crucible and weigh it. m sample,0 The sample was slowly heated from 20℃ to 40℃ (1-2 K / min) to evaporate it from a liquid to a gaseous state. The heat flow curve was recorded and the DSC baseline was subtracted (using the same temperature scanning program for an empty crucible) to obtain the desired result. Figure 3 The heat flow curve is shown. After evaporation, immediately cool to room temperature and weigh. m sample, end The mass loss Δ can be obtained. m The heat of vaporization is obtained by integrating the heat flow curve. Q Substituting into equation (2), we can obtain the vaporization enthalpy Δ. H vap, in In this embodiment, combined with Figure 3 The total heat of vaporization within the insulation zone is 5.4261 J, and the mass loss due to evaporation is 4.967 mg. Therefore, the enthalpy of vaporization Δ H vap, in =35 kJ / mol.

[0149] S2 activity coefficient regression (γ)

[0150] The components at each experimental point in Table 1 are converted into the mole fractions of water and MeOH in the liquid phase and listed in Table 3. The activity coefficient of water measured by DSC at different experimental points can be obtained using equation (3). gamma w DSC In the bivariate formula for the liquid phase model eNRTL, the non-random parameter ω is taken as 0.3, and the bivariate interaction parameter... tau 12 The initial value is 0.5. tau 21 The initial value is taken as 0.1, and it is substituted into equations (4) and (5) for calculation. gamma w model The experimental measurements were compared with those calculated using the liquid phase model. gamma w Substituting into the objective function (6) yields the model calculation error. If the model calculation value does not match the DSC measured value, the binary interaction parameters are corrected and recalculated. This is achieved by using the experimentally obtained components... gamma w DSCThe binary interaction parameters were corrected until the model calculated gamma w model The binary interaction parameters were corrected until the model calculated tau 12 The DSC experimental values were matched, and the binary interaction parameters tau 21 were determined. Substituting the determined values into equation (7) gave the activity coefficient of MeOH gamma in . The relevant parameters calculated in this example are listed in Table 3.

[0151] Table 3

[0152]

[0153] S3 Saturation vapor pressure P sat DSC anchoring of (T)

[0154] The saturation vapor pressure of MeOH at 298.15 K was 16900 Pa, and this point was used as the anchor point to substitute into equation (9) to calculate the intercept of the straight line equation C . Then the target temperature T j and Δ H vap, in were substituted into equation (9) to obtain the saturation vapor pressure of the inhibitor P sat,in . T In this example, the intercept C = 23.886, and substituting T j = 283.15 K, Δ H vap, in = 35 kJ / mol gave P sat, in = 8250 Pa.

[0155] S4 Poynting correction index calculation

[0156] Substituting M in = 32.04 g / mol, rho in = 0.79 g / cm 3 , P j = 30 MPa, T j = 283.15 K, P sat, in=8250 Pa into equation (10) to obtain Poynting correction index П=1.6859. This value represents that the Poynting factor of MeOH at 30 MPa, 283.15 K increases the gas / water partition coefficient by 68.59%. Similarly, the Poynting correction index of water is П=1.2573.

[0157] S5 Gas fugacity coefficient φ (calculated by equation of state EOS)

[0158] The Peng-Robinson EOS equation was used to input the critical temperature, critical pressure, eccentric factor, target temperature, target pressure, and gas phase mole fraction of each component, as shown in Table 4, to obtain the fugacity coefficient of each component phi i Since the model for this part of the calculation is mature, the detailed calculation process is not described, and the calculation results of this case are also listed in Table 4.

[0159] Table 4

[0160]

[0161] S6 Gas / water partition coefficient calculation

[0162] The parameters obtained from the above experiments and model calculations are substituted into equation (11) to calculate the gas / water partition coefficient. NaCl does not have volatility and does not enter the gas phase, so it is assumed that K NaCl =0. For CH4, a light gas, the solubility in water at 10°C and 30 MPa is very low, as long as K CH4 is much greater than 1, the result of S7 flash calculation will not be sensitive, and K CH4 =100 is commonly used in engineering as an approximation to save calculation. The parameters used to calculate MeOH are: gamma in =1.44, P sat, in =8250, П=1.6859, phi in =0.023, P j =3×10 7 , resulting in K in =0.029; The parameters used to calculate H2O are: gamma w =1.1395, P sat, in =4240 (obtained from steam table), П=1.2573, phi w= 0.044, P j = 3 x 10 7 , we get K w = 0.0046.

[0163] S7 Rachford-Rice two-phase flash solution

[0164] The molar fraction of CH4, MeOH, H2O in the total feed z CH4 = 0.9, z in = 0.03695, z w = 0.06183 into equation (12), we can get β = 0.916, into equation (13), we can get the molar fraction of each component in the liquid phase after flash equilibrium x CH4 = 0.00986, x MeOH = 0.32156, x w = 0.66739, the molar fraction of each component in the gas phase y CH4 = 0.98637, y MeOH = 0.00933, y w = 0.00307.

[0165] S8 Actual vaporization loss (mass transfer discount)

[0166] The upper limit of the thermodynamic loss of the inhibitor in the calculation section is 0.2303 calculated by equation (14), which represents that if "mass transfer is infinitely fast / contact is long enough", the section will lose up to 23.03% of MeOH vaporization into the gas phase. The liquid phase mass transfer coefficient k L Take 10 -4 , the specific surface area is 3 x 10 3 , the residence time is 3 s, and the above values are substituted into the first-order overall mass transfer model (equation 15) to convert the actual inhibitor vaporization loss rate to 13.67%.

[0167] S9 entrainment loss calculation xi aero

[0168] The flow rate is 5 m / s, the pipe size is 0.1524 m, rho G = 228.967 kg / m 3 ,mu G =3×10 -5 , mu L =1013.542kg / m 3 , ​ L Substituting 0.00128 into equation (16), we can obtain the entrainment rate of the droplet as 4.4938%, and further substituting it into equation (17), we can obtain the MeOH loss rate caused by the entrainment of the droplet as 2.47%.

[0169] Total loss of S10 inhibitor

[0170] Calculate the calculation segment using equation (18). j The total loss rate of the internal inhibitor during flow, due to evaporation and entrainment losses, is 16.14%. The pipeline is cut into... N Sections, in order j =1→ N Cumulative, set R in 1 =1 (the inhibitor fraction not yet lost at the pipe inlet), then this calculation segment j The contribution of the total inlet loss is calculated using equation (19). The inhibitor fraction of the next calculation segment is updated as shown in equation (20), and the cumulative solution yields the inhibitor loss rate within the entire pipe segment as shown in equation (21).

[0171] The above description is merely a partial preferred embodiment of the present invention. Any person skilled in the art can modify the above-described technical solutions or modify them into equivalent technical solutions. Therefore, any simple modifications or equivalent transformations made based on the technical solutions of the present invention fall within the scope of protection claimed by the present invention.

Claims

1. A method for predicting hydrate inhibitor loss in multiphase flow systems based on DSC correction, characterized by: Includes the following steps: I. Prepare DSC test samples based on the composition of the formation fluids, and use DSC to measure the heat flow curve of the samples to obtain the water activity and vaporization enthalpy of the samples; The sample preparation and two types of DSC testing procedures in step one are as follows: S1.1 Based on the composition of the formation produced fluids and the concentration of the inhibitor after injection and thorough mixing, samples for DSC testing were prepared, and the liquid phase mass fraction was converted into the mole fraction in the liquid and gas phases. x i , y i , used for equilibrium equation calculations; S1.2 Use DSC to perform a temperature scan on the DSC test sample at the target temperature to obtain the ice melting initiation temperature. T f The water activity of the sample is converted using equation (1). α w ; （1）， In the formula, R = 8.314 J / (mol·K); T f The melting point of the ice is the initial temperature, in K; α w Water activity is a dimensionless quantity. S1.3 An isothermal vaporization energy test was conducted on the sample using an open-type DSC, and the heat flow curve was recorded. The heat of vaporization was obtained by integrating after baseline subtraction. Q The mass loss before and after the DSC experiment was recorded by weighing and converted into mole count Δ. n The vaporization enthalpy Δ is obtained using equation (2). H vap, in ; （2）， In the formula, Δ H vap, in Here, enthalpy of vaporization is expressed in J / mol. Q The heat absorbed by the evaporation of the inhibitor is J; Δ n With Δ m The moles and mass lost before and after evaporation, in mol and g; M in The molar mass of the inhibitor is in g / mol. q corr Heat flux is W; time is s. II. Calculate the inhibitor activity coefficient under the target formulation by processing the water activity of the sample using the eNRTL liquid phase model; III. The saturated vapor pressure of the inhibitor under the target formulation was obtained by linearly processing the vaporization enthalpy of the sample using the Clausius–Clapeyron method. IV. Calculate the Poynting correction index and the fugacity coefficient of each component; V. Using multiphase flash evaporation calculations, the gas / water partition coefficient is solved based on the parameters obtained in steps II, III, and IV, and the mole fractions of each component in the liquid and gas phases after flash evaporation equilibrium are obtained. VI. Considering the mass transfer limitations in the gas-liquid mass transfer process, the upper limit of vaporization loss in step 5 is corrected to obtain the true vaporization loss of the inhibitor. The detailed process of step six is ​​as follows: The upper limit of the thermodynamic loss of the inhibitor after the gas-liquid equilibrium is fully reached within the calculation segment is calculated using Equation (14). However, the interfacial mass transfer is affected by the gas-liquid contact area, flow pattern and turbulence degree, and can only reach a part of the upper limit of loss in reality. Therefore, a first-order global mass transfer model is needed to calculate the actual vaporization loss of the inhibitor, as shown in Equation (15). （14）， （15）， In the formula, ξ eq and ξ vap The maximum vaporization loss and the actual vaporization loss rate are dimensionless. k L The mass transfer coefficient in the liquid phase is commonly calculated using empirical correlation formulas. a Specific surface area, determined by the flow pattern in the wellbore, is dimensionless; τ Residence time, in seconds, can be calculated as liquid volume / liquid volumetric flow rate; 7. Considering the impact of high-speed gas entrainment on inhibitor loss, calculate the inhibitor loss rate caused by gas entrainment. The detailed process of step seven is as follows: High-speed gas phase can entrain droplets and carry inhibitors to the gas phase. The entrainment rate of droplets varies with the flow pattern, Reynolds number, and Weber number. First, the droplet entrainment rate is calculated using equation (16). E Then, the loss rate of the inhibitor lost through gas entrainment is calculated using equation (17); （16）， （17）， In the formula, E The droplet entrainment rate is dimensionless; We, Fr, and Re are the gas phase Weber number, Froude number, and Reynolds number, respectively, and are dimensionless. ρ L and ρ G Densities of the gas phase and liquid phase, respectively, in kg / m³ 3 ; μ L and μ G The viscosity of the gas phase and liquid phase are respectively, in Pa·s; ξ aero The percentage of inhibitor loss due to entrainment is dimensionless. m in,aero The mass of MeOH lost due to entrainment, in g / s; n F The total number of moles of feed, in mol / s; m g Gas phase flow rate, g / s; M g The molar mass in the gas phase is g / mol. w in The inhibitor mass fraction is %; 8. The inhibitor loss in the multiphase flow system comes from the sum of the two processes in step six and step seven. The total inhibitor loss rate of the entire pipe section can be obtained by iteratively accumulating the solution along the pipe length.

2. The method for predicting hydrate inhibitor loss in multiphase flow systems based on DSC correction according to claim 1, characterized in that: The detailed process of step two is as follows: Using equation (3) to measure water activity α w mole fraction of the sample formulation x w The activity coefficient of water can be obtained by solving the simultaneous equations. γ w The binary interaction parameters were obtained by regression analysis using the liquid phase model eNRTL at the target salinity. τ 12 With τ 21 Then, the inhibitor activity coefficient of the target formulation is calculated using equation (7). γ in ; （3）， （4）， （5）， （6）， （7）， In the formula, x w The mole fraction of water in the liquid phase, % x in The value represents the molar fraction of the inhibitor in the liquid phase, %; γ w DSC The activity coefficient of water obtained from the DSC experiment is dimensionless. γ w model G represents the activity coefficient of water obtained from the eNRTL liquid phase model; it is dimensionless. 12 With G 21 These are intermediate parameters for calculation and are dimensionless. k For the quantity of the formula; S The objective function is dimensionless. γ in The inhibitor activity coefficient of the target formulation is dimensionless. Wherein, the non-random parameter ω is taken as 0.

3. τ 12 The initial value is 0.

5. τ 21 The initial value is taken as 0.1, and it is substituted into equation (5) for calculation. γ w model The multiple measurements obtained from the actual DSC measurements in S1.2 α w As the fitting target, an objective function is established, as shown in equation (6); iterative calculations are performed until the model is calculated. γ w model The inhibitor activity coefficient can be obtained by matching the DSC measured value with equation (7). γ in .

3. The method for predicting hydrate inhibitor loss in multiphase flow systems based on DSC correction according to claim 1, characterized in that: The detailed process of step three is as follows: Using the Δ given by DSC H vap, in With anchor pressure P sat ( T The Clausius–Clapeyron linear or piecewise integral formula is used to obtain the results. P sat,in ( T ); where the Clausius–Clapeyron differential is equation (8), if Δ is used in a small temperature region H vap ( T ) is approximately a constant Δ H vap Integrating, we obtain the equation of the straight line (9), and substituting it into the selected anchor point ( T , P sat Calculate the intercept of the equation of the line. C Then target temperature T j With Δ H vap, in Substituting into equation (9) yields the saturated vapor pressure of the inhibitor. P sat,in ( T j ); （8）， （9）， In the formula, P sat ( T () represents the saturated vapor pressure at the anchor point, in Pa; C The linear intercept is determined by single-point anchoring. T Temperature, K; P sat,in ( T () represents the saturated vapor pressure of the inhibitor, in Pa.

4. The method for predicting hydrate inhibitor loss in multiphase flow systems based on DSC correction according to claim 1, characterized in that: The detailed process of step four is as follows: The Poynting correction index is calculated using equation (10), which represents the change in the liquid phase reference state from saturation pressure. P sat,in Reach the target P j Pressure integral correction; （10）， In the formula, П is the Poynting correction exponent, which is dimensionless; ρ in Inhibitor density, kg / m³ 3 ; P j To calculate the pressure within the section, in Pa; The Peng–Robinson EOS equation is used to calculate the fugacity coefficients of each component by inputting the critical constants, eccentricity factors, and gas phase composition. φ i .

5. The method for predicting hydrate inhibitor loss in multiphase flow systems based on DSC correction according to claim 1, characterized in that: The detailed process of step five is as follows: Calculation of gas / water partition coefficient: Gas / water partition coefficient K i Components i The ratio of the mole fractions in the gas phase to the aqueous phase at equilibrium is important for the volatile components. i Solve for the components using equation (11) i Distribution coefficient in gas-liquid two-phase system K i ; （11）； In the formula, K i is the partition coefficient in the gas-liquid two-phase system, which is dimensionless; γ i These are the activity coefficients of different components, dimensionless; φ i The component fugacity coefficient is dimensionless. P sat,i The saturated vapor pressures (Pa) of the different components are given. Rachford–Rice two-phase flash solution: Given feed mole fraction z i The gas phase mole fraction was obtained by solving equation (12) using the bisection method. β Then, use equation (13) to calculate the mole fraction of each component in the liquid and gas phases after flash evaporation equilibrium. x i , y i ; （12）， （13）， In the formula, β The mole fraction of the gas phase. z i The mole fraction of different components in the total feed stream. x i Components after flash evaporation equilibrium i Mole fraction in the liquid phase y i Components after flash evaporation equilibrium i Mole fraction in the gas phase.

6. The method for predicting hydrate inhibitor loss in multiphase flow systems based on DSC correction according to claim 1, characterized in that: The detailed process of step eight is as follows: Calculation segment j The total loss rate of the internal inhibitor during flow due to evaporation loss and entrainment loss can be calculated using equation (18); the pipeline is cut into N Sections, in order j =1→ N Cumulative, set R in 1 =1, the inhibitor fraction that has not yet been lost at the pipe inlet, then this calculation segment j The contribution of the total inlet to the loss is calculated using equation (19); the inhibitor fraction of the next calculation segment is updated as shown in equation (20), and the total inhibitor loss rate in the entire pipe segment can be obtained by cumulative solution as shown in equation (21). （18）， （19）， （20）， （21）， In the formula, ξ total The total loss rate of the inhibitor is %; Loss_of_Total is the calculation segment. j The internal contribution to the total entrance loss is dimensionless. R in and R out For calculation segment j Inhibitor fractions at the inlet and outlet, %; Ξ represents the inhibitor loss rate throughout the entire pipe segment, %.

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