Phase-change microcapsule thermal insulation material for drilling fluid for offshore oil and gas drilling and preparation and application thereof

Abstract

The invention relates to the technical field of offshore oil and gas exploitation, and particularly discloses a phase change microcapsule thermal insulation material for offshore oil and gas drilling fluid as well as preparation and application of the phase change microcapsule thermal insulation material. N-dodecane and n-tetradecane are compounded to serve as a core material, acetaldehyde, urea and melamine react to generate a wall material, a phase change microcapsule is prepared through the technologies of emulsification, prepolymer synthesis and the like, and the phase change microcapsule thermal insulation material is prepared. By combining with a constructed efficient water-based drilling fluid system, the heat conductivity coefficient and the rheological property are optimized, and synergistic improvement of heat insulation and stability is realized. And based on a Hasan shaft energy equation, an unsteady-state shaft heat transfer analytical model is established by applying Laplace conversion, the microcapsule addition amount is dynamically calculated, and the shaft temperature field is precisely regulated and controlled. The problems that a traditional inorganic material is low in mechanical strength and an organic material is poor in thermal stability are solved, the composite material has the advantages of efficient heat insulation, low process cost and high adaptability, and technical support is provided for safe operation of deepwater drilling.

Description

Technical Field

[0001] This invention relates to a phase change microcapsule thermal insulation material for offshore oil and gas drilling fluid and a wellbore temperature control method, belonging to the field of offshore oil and gas extraction technology. Background Technology

[0002] The development of offshore oil and gas resources is gradually expanding into deep and ultra-deep water areas. The huge thermal gradient between the high-temperature and high-pressure environment downhole and the low-temperature seawater poses severe thermal management challenges to wellbore systems. As a key medium for heat conduction in the wellbore, the thermal insulation performance of drilling fluid directly affects the annular thermal convection efficiency, the distribution of thermal stress in the wellbore, and the degree of thermal damage to the reservoir. Traditional drilling fluid systems use inorganic thermal insulation materials such as ceramic microspheres and expanded perlite, which have inherent defects such as low mechanical strength, poor crush resistance, and high-temperature phase transformation instability. Under long-term dynamic cycling and complex geostress, these materials are prone to structural collapse, leading to a sharp increase in thermal conductivity.

[0003] Phase change microcapsules, as novel thermal insulation materials, have shown significant potential in the field of thermal management in recent years. Their core-shell structure physically encapsulates a phase change core material (such as paraffin or n-tetradecane), allowing it to absorb or release latent heat during the phase change process, thereby achieving dynamic thermal regulation and preventing core material leakage. However, traditional phase change materials are limited in their application under high temperature, high pressure, or complex conditions due to low thermal conductivity, poor thermal stability, and insufficient interfacial compatibility. For example, the thermal decomposition temperature of organic phase change materials is typically below 200℃, making them unsuitable for long-term high-temperature environments in deep strata or building envelopes. To address this, researchers have optimized microcapsule performance through material composite and structural modification strategies. On one hand, nanomaterials (such as graphene, titanium dioxide, and silicon dioxide) are introduced to enhance the thermal conductivity and mechanical strength of the shell. For example, graphene-modified microcapsules can increase thermal conductivity by more than 30% while maintaining latent heat stability during phase transition. On the other hand, functionalized shell designs (such as magnetic SiO2 / Fe3O4 composite shells and polydopamine photothermal coatings) endow microcapsules with multiple properties, such as photothermal conversion, magnetic response recovery, and selective ion adsorption capabilities, thereby expanding their applications in fields such as solar interfacial evaporation and precious metal extraction. Furthermore, by optimizing the microcapsule preparation process using response surface methodology (such as emulsifier type and core-shell ratio), the particle size distribution and thermal properties can be precisely controlled. For example, using high molecular weight styrene-maleic anhydride copolymer (SMAH) can produce microcapsules with smooth surfaces and a core material content of up to 71%, significantly improving the reflectivity and durability of thermal insulation coatings. However, the high cost and difficult synthesis of these microcapsules limit their application.

[0004] To address the aforementioned problems, this invention is proposed. Summary of the Invention

[0005] To address the shortcomings of existing technologies and solve the current technical challenges of deep-water drilling, this invention provides a phase change microcapsule insulation material for marine oil and gas drilling fluids and a wellbore temperature control method, specifically addressing the problems of high-temperature and high-pressure environments in deep-water drilling, such as increased temperature near the drill bit during drilling, leading to decreased drilling fluid performance and wellbore instability due to thermal decomposition of deep-water hydrate formations. The phase change microcapsules in this method continuously absorb heat at their phase change temperature, reducing the temperature of the drilling fluid in the wellbore annulus. It also constructs a highly efficient water-based drilling fluid system for marine applications and establishes a novel wellbore temperature field analytical model by creating a wellbore heat transfer equation during the drilling process. This allows for dynamic adjustment of the amount of phase change microcapsule insulation material added to the drilling fluid, achieving efficient and stable drilling in marine environments.

[0006] The technical solution of the present invention is as follows: Phase change microcapsule insulation materials for offshore oil and gas drilling fluids, including phase change microcapsule core materials and phase change microcapsule wall materials. The phase change microcapsule core material is obtained by compounding n-dodecane and n-tetradecane; the phase change microcapsule wall material is prepared by reacting acetaldehyde, urea and melamine.

[0007] Preferably, the particle size of the phase change microcapsule insulation material for offshore oil and gas drilling fluid is 0.7~10 μm. Through the absorption of latent heat via the phase change of the core material, the drilling fluid temperature is significantly reduced, and it possesses high enthalpy change value and wide temperature range characteristics.

[0008] The preparation method of the above-mentioned phase change microcapsule thermal insulation material for offshore oil and gas drilling fluid includes the following steps: (1) Preparation of phase change microcapsule core material emulsion An aqueous solution of n-dodecane and an aqueous solution of n-tetradecane were mixed, an emulsifier was added, and the mixture was preheated and then emulsified to obtain a premixed phase change microcapsule core material emulsion. (2) Preparation of phase change microcapsule wall material prepolymer A certain mass ratio of acetaldehyde, urea and melamine is poured into a three-necked flask containing deionized water, stirred, and then the pH is adjusted. After heating and stirring the reaction, a prepolymer solution is obtained. (3) Preparation of marine drilling fluid phase change microcapsules The premixed phase change microcapsule core material emulsion was added to a three-necked flask, and then the prepolymer solution was added dropwise at a certain rate with stirring. The pH of the mixture was then adjusted, and the reaction was allowed to stand. After centrifugation, washing, and drying of the reaction product, the final microcapsules were obtained.

[0009] According to a preferred embodiment of the present invention, in step (1), the concentration of the aqueous solution of n-dodecane is 0.25-0.3 g / mL.

[0010] According to a preferred embodiment of the present invention, in step (1), the concentration of the aqueous solution of n-tetradecane is 0.4-0.55 g / mL.

[0011] According to a preferred embodiment of the present invention, in step (1), the molar ratio of n-dodecane to n-tetradecane structural units is 0.45-0.75:1.

[0012] According to a preferred embodiment of the present invention, in step (1), the emulsifier is Tween 80, the stirring reaction temperature is 40 °C, and the emulsification conditions are shear emulsification at a speed of 2000 r / min for 10 min.

[0013] According to a preferred embodiment of the present invention, in step (2), the mass ratio of acetaldehyde, urea and melamine is 16:1:1.

[0014] According to a preferred embodiment of the present invention, in step (2), the stirring speed during the reaction is 100 r / min.

[0015] According to a preferred embodiment of the present invention, in step (2), the stirring reaction temperature is 70°C, the pH of the solution is adjusted to 8 with triethanolamine, and the stirring reaction time is 50 minutes.

[0016] According to a preferred embodiment of the present invention, in step (3), the stirring speed is 200 r / min and the dropping speed is 20 d / min when the prepolymer solution is added.

[0017] According to a preferred embodiment of the present invention, in step (3), during the reaction process, the pH is adjusted to 4 by titration with 10% hydrochloric acid solution, the reaction conditions are room temperature, and the reaction time is 4 hours.

[0018] According to a preferred embodiment of the present invention, in step (3), the centrifugation speed is 6000-10000 rpm and the centrifugation time is 5-10 minutes; the drying temperature is 70-90℃ and the drying time is 5-30 minutes; there are no special requirements for washing.

[0019] A method for wellbore temperature control using phase change microcapsule insulation materials in offshore oil and gas drilling fluids includes the following steps: Step S1: Design a high-efficiency marine water-based drilling fluid system. Add different amounts of phase change microcapsule heat insulation material to the drilling fluid to obtain multiple drilling fluids with different amounts of microcapsule heat insulation material. Use multiple drilling fluids to perform subsequent steps in sequence, analyze the heat transfer law between the fluid in the wellbore and the well wall and mud cake, and clarify the influence mechanism of drilling fluid heat insulation material on drilling fluid temperature.

[0020] Using the aforementioned marine drilling fluid phase change microcapsules as thermal insulation materials, a high-performance marine drilling fluid system with temperature regulation function was constructed by adding lubricants, inhibitors, viscosity-enhancing coating agents, viscosity modifiers, glass microspheres, filtration loss reducers, and reservoir bridging agents. The drilling fluid density, rheological parameters, and API filtration loss were measured, and the thermal conductivity of the drilling fluid system was also measured. The rheological parameters included apparent viscosity AV, plastic viscosity PV, and dynamic shear stress YP.

[0021] Thermal conductivity calculation: λ= (1) Thermal resistance calculation: R= (2) R: Thermal resistance, km 2 / w; TA: Hot surface temperature of the sample, K; TD: Cold surface temperature of the sample, K; A: Cross-sectional area of ​​the sample, m² 2 Q: Heat flow, w; L: Distance between heat source and cold source, m.

[0022] Step S2: Obtain the current drilling parameters (i.e., drilling fluid density, thermal conductivity, etc.) and reservoir physical property data, substitute them into the wellbore heat transfer equation of the drilling process established by the Hasan wellbore energy equation, and then apply the Laplace transform method to solve it. This avoids the steady-state assumption in the Hasan solution process and establishes a new analytical model of the wellbore temperature field that can simulate the fracturing process.

[0023] Preferably, the model is established as follows: Based on physical conditions, the following assumptions are made regarding the heat transfer process in the drilling wellbore: ① Each heat transfer medium is distributed symmetrically around the oil pipe as the center; ② The flow inside the wellbore is one-dimensional, and axial heat conduction is negligible; ③ The fluid properties are constants; ④ The drilling fluid injection rate at the wellhead is a constant value; ⑤ The rock's physical properties are homogeneous and isotropic; The wellbore heat transfer equation for the drilling process is calculated using the following formula: (3) Taking the limits of both sides of equation (3) with respect to time and space, we get: (4) In the formula, A is the cross-sectional area, m 2 ; rdenoted as: ρ = drilling fluid density; m = fluid mass per unit length (kg / m); m' = wellbore medium mass per unit length (kg / m); E = fluid internal energy per unit mass (J / kg); E' = wellbore medium internal energy per unit mass (J / kg); z = depth (m); t = time (s); H = enthalpy of a micro-element per unit mass (J / kg); v = flow velocity (m / s). w Mass flow rate, kg / s; Gravitational potential energy per unit mass is defined as follows: =- gzsinθ g is the acceleration due to gravity, m / s² 2 ; i The angle between the wellbore and the horizontal plane is denoted by ; Q is the heat flow rate per unit length of formation into the fluid, expressed in W / m.

[0024] The first term on the left-hand side of equation (4) represents the rate of change of internal energy per unit length of fluid; the second term on the left-hand side represents the rate of change of internal energy per unit length of wellbore medium (pipe wall, annulus, cement sheath); the change of internal energy of the wellbore medium can be expressed as a linear function of the change of internal energy of the fluid, i.e.: (5) Where C T This is the thermal storage coefficient, which needs to be taken as a different value under different conditions. It is taken as 3.0 when opening the well and 2.0 when shutting in the well. The first term on the right-hand side of equation (4) represents the energy flowing into and out of a unit cell. According to the standard equilibrium thermodynamic formula, dH = C Pf dT f -C Pf Jd p C Pf T is the molar isobaric heat capacity under constant pressure conditions. f The drilling fluid temperature is denoted as ; J is the coke-Thomson coefficient, °C / Pa; substituting these values ​​yields: (6) C p p represents the constant pressure heat capacity, where p is the pressure. The second term on the right side of equation (4) represents heat transfer from the formation to the fluid, which can be expressed as: Q= w C Pf (T surf +g G z sinth -T f L R (7) (8) (9) In the formula, T surf Surface temperature, °C; gG Geothermal gradient, °C / m; L R The relaxation distance is 1 / m; r to This represents the distance from the fluid center to the formation heat transfer point. l e The thermal conductivity of the formation is W / (m·°C); l o T represents the thermal conductivity of the drilling fluid, W / (m·°C); D It is a dimensionless time function; U to For the overall heat transfer coefficient, W / (m 2 ·°C); t D For dimensionless time, t D = l e t / (ρ e C pe ), ρ e C represents the formation fluid density. pe This represents the specific heat capacity of the formation fluid at that location.

[0025] Substituting equations (5), (6), and (7) into equation (4), we obtain the final form of the wellbore heat transfer equation during the drilling process: (10) in The lumped parameter is defined as: (11) The overall heat transfer coefficient in equation (8) U to The heat transfer characteristics from the drill pipe wall to the formation, neglecting the convective heat transfer resistance between the drilling fluid and the drill pipe, as well as thermal radiation, can be calculated using the following formula: (12) In the formula l h is the thermal conductivity of the mud cake, W / (m·°C); r e The mud cake thickness is measured in meters (m). h an The drilling fluid convective heat transfer coefficient is W / (m³). 2 (°C), using Dropkin and Sommerscales' formula for the equivalent heat transfer coefficient between flat plates, the following was applied: h an Approximation: (13) (14) (15) In the formula, Gr is the Grashoff number of the annular fluid; Pr an The Prandtl number for the annular fluid; r ci Let be the inner radius of the casing, in meters (m). r to The distance from the fluid center to the formation heat transfer point, in meters (m). r h Let be the outer radius of the drill pipe, in meters (m). l an is the thermal conductivity of the annular fluid, W / (m·°C); r an The density of the annular fluid is kg / m³. 3 μ an The viscosity of the annular fluid is Pa·s; C Pan The isobaric specific heat capacity of the annular fluid is J / (kg·°C); β an The coefficient of thermal expansion of the annulus fluid is 1 / °C. The solution obtained using the Laplace method is: (16) a、b、c It is a constant; In the formula For a step function, the following relationship exists: (17) The wellbore temperature calculated using a novel analytical model of the drilling wellbore temperature field is thus obtained. T f As a boundary condition for the formation temperature field, a semi-analytical model of the wellbore-formation temperature field is established, which can realize the calculation of the formation temperature field and construct a new analytical model of the wellbore temperature field (Formula 18).

[0026] Considering the formation is radially axisymmetric and making the following assumptions: ①The formation exhibits radial one-dimensional transient heat conduction; ② There is no fluid flow in the formation; ③The formation physical parameters are homogeneous and isotropic.

[0027] Based on the law of conservation of energy, the heat transfer equation and boundary conditions of the formation can be obtained as follows: (18) (19) In the formula T f The drilling fluid temperature after heat transfer is complete, in °C; T e Formation temperature, °C; T ei The initial temperature of the formation is °C.r Radial distance of the strata, in meters; r e The mud cake thickness is measured in meters (m). r h Let be the outer radius of the drill pipe, in meters (m). r=r h Boundary conditions T at point h It can be obtained using the following formula: (20) Among them, T f The drilling fluid temperature after heat transfer is complete, in °C; f (t) is T surf +g G z sinth -T f ; l e The thermal conductivity of the formation is W / (m·°C); T ei The initial temperature of the formation is °C. r to This represents the distance from the fluid center to the formation heat transfer point. U to For the overall heat transfer coefficient, W / (m 2 ·°C).

[0028] Step S3: After discretizing the wellbore heat transfer equation and the reservoir temperature field, the amount of insulation material added is calculated using a computer program; the amount of insulation material added changes the thermal conductivity of the annular fluid. l an The specific change pattern can be obtained through experimental methods. Since the change pattern of each batch of thermal insulation material may be different, this method first prepares the drilling fluid with different amounts of thermal insulation material, summarizes the change pattern of the amount of addition and the thermal conductivity of the drilling fluid, and then substitutes the thermal conductivity into the formula to calculate the wellbore heat transfer equation and the wellbore temperature analytical model. When adjusting, clearly define the target temperature T. f The model calculates the control at T f The required thermal conductivity of the drilling fluid is determined, and then the amount of thermal insulation material to be added is determined based on the previously prepared thermal insulation material and the relationship between its addition and thermal conductivity, so as to control the temperature.

[0029] A system for wellbore temperature control using phase change microcapsule insulation materials in offshore oil and gas drilling fluids includes a data acquisition module, a data analysis module, and a dynamic control module. The data acquisition module collects key performance parameters of the reservoir, drilling fluid, and wellbore mud cake. The data analysis module implements a synergistic control method of insulation materials and temperature field to establish a drilling temperature field model for offshore oil and gas fields. The dynamic control module achieves precise temperature control during drilling by adjusting the amount of insulation material added to the drilling fluid and the temperature and pressure parameters of the drilling fluid, providing theoretical support and technical assurance for ensuring the operational efficiency and dynamic control of drilling fluids during offshore oil and gas field drilling.

[0030] A computer-readable storage medium having a program stored thereon, which, when executed by a processor, implements the steps of the method for wellbore temperature control using phase change microcapsule insulation material in offshore oil and gas drilling fluids, as described above, for calculating the required amount of phase change microcapsule insulation material to be added.

[0031] An electronic device includes a memory, a processor, and a program stored in the memory and executable on the processor, wherein the processor executes the program to perform the steps of the method for wellbore temperature control using phase change microcapsule thermal insulation material in offshore oil and gas drilling fluids as described above.

[0032] This invention not only provides a phase change microcapsule thermal insulation material for offshore oil and gas drilling fluid and its preparation, but also establishes a wellbore heat transfer equation and a wellbore temperature field analytical model to determine the amount of thermal insulation material to be added and thus control the wellbore temperature.

[0033] The beneficial effects of this invention are as follows: 1. This invention provides a phase change microcapsule insulation material and a wellbore temperature control method for drilling in offshore oil and gas fields. Compared with conventional insulation materials, it can achieve a wider operating temperature range by adjusting the melting point of the core material inside the microcapsules. Simultaneously, under the same external temperature stimulus, it exhibits a higher enthalpy change during phase change, absorbing more heat and thus being more conducive to temperature control.

[0034] 2. The high-efficiency water-based drilling fluid system for marine applications provided by this invention possesses excellent low-temperature rheological properties, inhibition properties, coating properties, and thermal insulation properties. Compared with traditional marine drilling fluids, the high-efficiency water-based drilling fluid system of this invention has better temperature regulation capabilities, effectively absorbing the heat generated during drilling, thereby achieving the goal of safe and efficient drilling.

[0035] 3. The wellbore heat transfer equation and novel wellbore temperature field analytical model provided by this invention obtain the current drilling parameters and reservoir property data, input the wellbore heat transfer equation and novel wellbore temperature field analytical results, obtain the novel wellbore temperature field analytical model, and calculate the required amount of insulation material to be added according to the calculation scale storage medium provided by this invention, so as to achieve the purpose of regulating the wellbore temperature. Attached Figure Description

[0036] The accompanying drawings are provided to further illustrate the invention and form part of the specification. They are used in conjunction with the embodiments of the invention to explain the invention and do not constitute a limitation thereof. In the drawings:

[0037] Figure 1 The enthalpy change diagram of the phase change microcapsules prepared in Example 1 is obtained by DSC testing.

[0038] Figure 2 This is a schematic diagram of the physical model of the wellbore temperature field obtained in this invention.

[0039] Figure 3 The figure shows the thermal conductivity of the high-performance marine water-based drilling fluid system prepared in Example 1. Detailed Implementation

[0040] The present invention will be further described below with reference to the embodiments and accompanying drawings, but is not limited thereto.

[0041] Furthermore, unless otherwise specified, the experimental methods described in the following embodiments are all conventional methods; and unless otherwise specified, the reagents, materials and equipment are all commercially available.

[0042] Example 1 Taking a marine oil and gas field reservoir drilling well as an example, the phase change microcapsule heat insulation material used in marine oil and gas drilling fluid includes a phase change microcapsule core material and a phase change microcapsule wall material. The phase change microcapsule core material is obtained by compounding n-dodecane and n-tetradecane; the phase change microcapsule wall material is prepared by reacting acetaldehyde, urea, and melamine.

[0043] The preparation method of the above-mentioned phase change microcapsule thermal insulation material for offshore oil and gas drilling fluid includes the following steps: (1) Preparation of phase change microcapsule core material emulsion A 0.25 g / mL aqueous solution of n-dodecane and a 0.45 g / mL aqueous solution of n-tetradecane were mixed, and Tween 80 was added as an emulsifier. After preheating at 40 °C, the mixture was sheared and emulsified at 2000 r / min for 10 min to obtain a premixed marine drilling fluid phase change microcapsule core material emulsion.

[0044] (2) Preparation of phase change microcapsule wall material prepolymer Acetaldehyde, urea and melamine in a mass ratio of 16:1:1 were poured into a three-necked flask containing deionized water. The mixture was stirred at 100 r / min at 70°C. The pH was then adjusted to 8, and the reaction was continued with heating and stirring for 50 min to obtain a prepolymer solution. (3) Preparation of marine drilling fluid phase change microcapsules The premixed phase change microcapsule core material emulsion was added to a three-necked flask, and then the prepolymer solution was added dropwise at a rate of 20 d / min with stirring at 200 r / min. The pH of the mixture was then adjusted to 4 by titration with 10% hydrochloric acid solution, and the reaction was allowed to stand at room temperature for 4 h. The final microcapsules were obtained after centrifugation at 6000 rpm for 10 min, followed by routine washing and drying at 70℃ for 20 min.

[0045] The present invention relates to the preparation of marine drilling fluid phase change microcapsule thermal insulation material, and the enthalpy change value of the marine drilling fluid phase change microcapsule thermal insulation material during the phase change process is measured by differential scanning calorimetry (DSC).

[0046] The DSC experiment procedure is as follows: Sample preparation: Thoroughly dry the sample to be tested, and weigh a certain mass of the sample, generally 5-10 mg is appropriate. For hygroscopic samples such as polymer materials or pharmaceuticals, drying in a desiccator or operation under a dry nitrogen atmosphere is required.

[0047] Sample loading: Place the sample into the crucible of the DSC instrument, being careful not to let the sample touch the bottom and side walls of the crucible, so as not to affect the test results.

[0048] Parameter settings: Set the corresponding parameters according to the properties of the sample and the test requirements, such as temperature range, heating rate, atmosphere, etc.

[0049] Start the instrument: Turn on the power of the DSC instrument, wait for the instrument to stabilize, open the software, and enter the sample name, mass, and parameters.

[0050] Temperature rise test: Under the set parameters, the DSC instrument will automatically perform a temperature rise test according to the set temperature program. During the test, the instrument will record the heat change of the sample and generate the corresponding curve.

[0051] Data processing: After the test, the data is imported into computer software for processing and analysis. Depending on the needs, corresponding thermograms, heat flux curves, etc., can be generated.

[0052] Results analysis: Based on the processed data and curves, the thermal and chemical properties of the sample can be analyzed and evaluated.

[0053] The phase change microcapsule thermal insulation material for offshore oil and gas drilling fluids produced in the above steps, after DSC experimental testing, yielded the following results: Figure 1 As shown.

[0054] Example 2 A method for wellbore temperature control using the phase change microcapsule insulation material for marine oil and gas drilling fluid prepared in Example 1 includes the following steps: Step S1: Design a high-efficiency marine water-based drilling fluid system. Add different amounts of phase change microcapsule heat insulation material to the drilling fluid to obtain multiple drilling fluids with different amounts of microcapsule heat insulation material. Use multiple drilling fluids to perform subsequent steps in sequence, analyze the heat transfer law between the fluid in the wellbore and the well wall and mud cake, and clarify the influence mechanism of drilling fluid heat insulation material on drilling fluid temperature.

[0055] Using the aforementioned marine drilling fluid phase change microcapsules as thermal insulation materials, a high-performance marine drilling fluid system with temperature regulation function was constructed by adding lubricants, inhibitors, viscosity-enhancing coating agents, viscosity modifiers, glass microspheres, filtration loss reducers, and reservoir bridging agents. The drilling fluid density, rheological parameters, and API filtration loss were measured, and the thermal conductivity of the drilling fluid system was also measured. The rheological parameters included apparent viscosity AV, plastic viscosity PV, and dynamic shear stress YP.

[0056] The thermal conductivity of the drilling fluid system was determined using the DRPL-Ⅰ thermal conductivity tester. The operating procedure is as follows: 1. Turn on the instrument power switch (observe whether the display box under the heater temperature controller flashes "Stop"; otherwise, press the "▲" key to stop the heating program), turn on the computer, and start the DRPL thermal conductivity tester program.

[0057] 2. Enter the hot surface temperature value in the "Set Temperature" text box on the main program interface, and press the "Confirm Setting" key. At this time, the value in the upper display box and the "Stop" indicator will flash alternately in the lower display box of the heating temperature controller. Otherwise, please press the "Confirm Setting" key again. Then press the "Heating Start" key. At this time, the value in the upper display box will appear in the lower display box of the heating temperature controller and increase upwards. Otherwise, please press the "Heating Start" key again to turn on the instrument's "Heating Switch," and the instrument will enter the heating state. Then turn on the "Fan Switch."

[0058] 3. Sample loading: Apply a small amount of thermal grease to the hot and cold sides of the sample and place the sample in the center of the hot and cold sides. If the hot and cold sides are not a flat plane, use a mold to level it. Apply a small amount of thermal grease to both sides of the mold as well. Then, pull the temperature probe out of the measuring plate and insert it into the temperature measuring hole of the mold. Be sure to apply a small amount of thermal grease to it.

[0059] 4. After entering the sample thickness and cross-sectional area data, press the "Confirm" button.

[0060] 5. After entering the time interval and number of times for automatic data recording, press the "OK" button.

[0061] 6. Press the "Automatic Test" button. The instrument will enter automatic test mode. A report will be automatically generated upon completion. Please save it to the user-specified location and filename. Then close the Exec1 program. Experiment complete.

[0062] 7. Repeat steps 3, 4, 5, and 6 above to test other samples.

[0063] 8. Press the "Exit Program" button to exit the program, then turn off the heating and fan switches, and finally turn off the instrument's power switch.

[0064] Thermal conductivity calculation: λ= (1) Thermal resistance calculation: R= (2) R: Thermal resistance, km 2 / w; TA: Hot surface temperature of the sample, K; TD: Cold surface temperature of the sample, K; A: Cross-sectional area of ​​the sample, m² 2 Q: Heat flow, w; L: Distance between heat source and cold source, m.

[0065] Step S2: Obtain current drilling parameters (i.e., drilling fluid density, thermal conductivity, etc.) and reservoir property data. Substitute these into the wellbore heat transfer equation established through the Hasan wellbore energy equation, and apply the Laplace transform method to solve the problem. This avoids the steady-state assumptions in the Hasan solution process, establishing a novel analytical model of the wellbore temperature field capable of simulating the fracturing process. A schematic diagram of the analytical model's wellbore temperature field physical model is shown below. Figure 2 As shown.

[0066] The model is established as follows: Based on physical conditions, the following assumptions are made regarding the heat transfer process in the drilling wellbore: ① Each heat transfer medium is distributed symmetrically around the oil pipe as the center; ② The flow inside the wellbore is one-dimensional, and axial heat conduction is negligible; ③ The fluid properties are constants; ④ The drilling fluid injection rate at the wellhead is a constant value; ⑤ The rock's physical properties are homogeneous and isotropic.

[0067] (3) Taking the limits of both sides of equation (3) with respect to time and space, we get: (4) In the formula, A is the cross-sectional area, m 2 ; rdenoted as: ρ = drilling fluid density; m = fluid mass per unit length (kg / m); m' = wellbore medium mass per unit length (kg / m); E = fluid internal energy per unit mass (J / kg); E' = wellbore medium internal energy per unit mass (J / kg); z = depth (m); t = time (s); H = enthalpy of a micro-element per unit mass (J / kg); v = flow velocity (m / s). w Mass flow rate, kg / s; Gravitational potential energy per unit mass is defined as follows: =- gzsinθ g is the acceleration due to gravity, m / s² 2 ; i The angle between the wellbore and the horizontal plane is denoted by ; Q is the heat flow rate per unit length of formation into the fluid, expressed in W / m.

[0068] The first term on the left-hand side of equation (4) represents the rate of change of internal energy per unit length of fluid; the second term on the left-hand side represents the rate of change of internal energy per unit length of wellbore medium (pipe wall, annulus, cement sheath); the change of internal energy of the wellbore medium can be expressed as a linear function of the change of internal energy of the fluid, i.e.: (5) Where C T This is the thermal storage coefficient, which needs to be taken as a different value under different conditions. It is taken as 3.0 when opening the well and 2.0 when shutting in the well.

[0069] The first term on the right-hand side of equation (4) represents the energy flowing into and out of a unit cell. According to the standard equilibrium thermodynamic formula, dH = C Pf dT f -C Pf Jd p C Pf T is the molar isobaric heat capacity under constant pressure conditions. f The drilling fluid temperature is denoted as ; J is the coke-Thomson coefficient, °C / Pa; substituting these values ​​yields: (6) C p p represents the constant pressure heat capacity, where p is the pressure. The second term on the right side of equation (4) represents heat transfer from the formation to the fluid, which can be expressed as: Q= w C Pf (T surf +g G z sinth -T f L R (7) (8) (9) In the formula, T surfSurface temperature, °C; g G Geothermal gradient, °C / m; L R The relaxation distance is 1 / m; r to This represents the distance from the fluid center to the formation heat transfer point. l e The thermal conductivity of the formation is W / (m·°C); l o T represents the thermal conductivity of the drilling fluid, W / (m·°C); D It is a dimensionless time function; U to For the overall heat transfer coefficient, W / (m 2 ·°C); t D For dimensionless time, t D = l e t / (ρ e C pe ), ρ e C represents the formation fluid density. pe This represents the specific heat capacity of the formation fluid at that location.

[0070] Substituting equations (5), (6), and (7) into equation (4), we obtain the final form of the wellbore heat transfer equation during the drilling process: (10) in The lumped parameter is defined as: (11) The overall heat transfer coefficient in equation (8) U to The heat transfer characteristics from the drill pipe wall to the formation, neglecting the convective heat transfer resistance between the drilling fluid and the drill pipe, as well as thermal radiation, can be calculated using the following formula: (12) In the formula l h is the thermal conductivity of the mud cake, W / (m·°C); r e The mud cake thickness is measured in meters (m). h an The drilling fluid convective heat transfer coefficient is W / (m³). 2 (°C), using Dropkin and Sommerscales' formula for the equivalent heat transfer coefficient between flat plates, the following was applied: h an Approximation: (13) (14) (15) In the formula, Gr is the Grashoff number of the annular fluid; Pr an The Prandtl number for the annular fluid; r ci Let be the inner radius of the casing, in meters (m). r to The distance from the fluid center to the formation heat transfer point, in meters (m). r h Let be the outer radius of the drill pipe, in meters (m). l an is the thermal conductivity of the annular fluid, W / (m·°C); r an The density of the annular fluid is kg / m³. 3 μ an The viscosity of the annular fluid is Pa·s; C Pan The isobaric specific heat capacity of the annular fluid is J / (kg·°C); β an is the coefficient of thermal expansion of the annular fluid, 1 / °C.

[0071] The solution obtained using the Laplace method is: (16) a、b、c It is a constant; In the formula For a step function, the following relationship exists: (17) The wellbore temperature calculated using a novel analytical model of the drilling wellbore temperature field is thus obtained. T f As a boundary condition for the formation temperature field, a semi-analytical model of the wellbore-formation temperature field is established, which can realize the calculation of the formation temperature field and construct a new analytical model of the wellbore temperature field (Formula 18).

[0072] Considering the formation is radially axisymmetric and making the following assumptions: ①The formation exhibits radial one-dimensional transient heat conduction; ② There is no fluid flow in the formation; ③The formation physical parameters are homogeneous and isotropic.

[0073] Based on the law of conservation of energy, the heat transfer equation and boundary conditions of the formation can be obtained as follows: (18) (19) In the formula T f The drilling fluid temperature after heat transfer is complete, in °C; T e Formation temperature, °C;T ei The initial temperature of the formation is °C. r Radial distance of the strata, in meters; r e The mud cake thickness is measured in meters (m). r h Let be the outer radius of the drill pipe, in meters (m). r=r h Boundary conditions T at point h It can be obtained using the following formula: (20) Among them, T f The drilling fluid temperature after heat transfer is complete, in °C; f (t) is T surf +g G z sinth -T f ; l e The thermal conductivity of the formation is W / (m·°C); T ei The initial temperature of the formation is °C. r to This represents the distance from the fluid center to the formation heat transfer point. U to For the overall heat transfer coefficient, W / (m 2 ·°C).

[0074] Step S3: After discretizing the wellbore heat transfer equation and the reservoir temperature field, the amount of insulation material added is calculated using a computer program; the amount of insulation material added changes the thermal conductivity of the annular fluid. l an The specific change pattern can be obtained through experimental methods. Since the change pattern of each batch of thermal insulation material may be different, this method first prepares the drilling fluid with different amounts of thermal insulation material, summarizes the change pattern of the amount of addition and the thermal conductivity of the drilling fluid, and then substitutes the thermal conductivity into the formula to calculate the wellbore heat transfer equation and the wellbore temperature analytical model. When adjusting, clearly define the target temperature T. f The model calculates the control at T f The required thermal conductivity of the drilling fluid is determined, and then the amount of thermal insulation material to be added is determined based on the previously prepared thermal insulation material and the relationship between its addition and thermal conductivity, so as to control the temperature.

[0075] The system constructed in this embodiment is as follows: seawater + 0.1% NaOH + 7% NaCl + 3% CaCl2 + 3% BLWZ (glass microspheres) + 2% PF-FLOTROL (filtration loss reducer) + 0.1% PF-XC (xanthan gum) + 2% PF-EZCARB (reservoir bridging agent) + 1% phase change microcapsules + 0.1% PF-PLUS (viscosifying and coating agent) + 3% PF-UHIB (polyamine) + 2% PF-HLUB (mud removal lubricant) + 2% PF-LUBE (lubricant) + 1% PVP (hydrate formation inhibitor).

[0076] The thermal conductivity is calculated using a thermal conductivity meter, and the calculation formulas are as shown in formulas (1) and (2).

[0077] Table 1 Experimental Calculation Results

[0078] G` and G`` are two values ​​(initial shear value and final shear value) from the experiment of measuring the viscosity of drilling fluid. In summary, by fully considering the influence of reservoir and drilling fluid phase change microcapsule materials on drilling fluid temperature during the drilling process, the established wellbore heat transfer equation and reservoir temperature field are more realistic, thus completing the temperature control scheme for deepwater drilling and providing strong assistance for the flexible design of high-performance drilling fluid systems and performance parameters on site.

[0079] Example 3 A system for wellbore temperature control using phase change microcapsule insulation materials in offshore oil and gas drilling fluids includes a data acquisition module, a data analysis module, and a dynamic control module. The data acquisition module collects key performance parameters of the reservoir, drilling fluid, and wellbore mud cake. The data analysis module implements a synergistic control method of insulation materials and temperature field to establish a drilling temperature field model for offshore oil and gas fields. The dynamic control module adjusts the concentration of the drilling fluid insulation material and the temperature and pressure parameters of the drilling fluid to achieve precise temperature control during drilling, providing theoretical support and technical assurance for ensuring the operational efficiency and dynamic control of drilling fluids during offshore oil and gas field drilling.

[0080] Example 4 A computer-readable storage medium having a program stored thereon, which, when executed by a processor, implements the steps in the method for wellbore temperature control using phase change microcapsule thermal insulation material in offshore oil and gas drilling fluid as described in Example 2.

[0081] Example 5 An electronic device includes a memory, a processor, and a program stored in the memory and executable on the processor. When the processor executes the program, it implements the steps in the method for wellbore temperature control using phase change microcapsule thermal insulation material in offshore oil and gas drilling fluid as described in Example 2.

[0082] The above embodiments are merely illustrative of the principles and effects of the present invention and are not intended to limit the invention. Any person skilled in the art can modify or alter the above embodiments without departing from the spirit and scope of the present invention. Therefore, all equivalent modifications or alterations made by those skilled in the art without departing from the spirit and technical concept disclosed in the present invention should still be covered by the claims of the present invention.

Claims

1. A phase change microcapsule thermal insulation material for offshore oil and gas drilling fluids, characterized in that, Including phase change microcapsule core materials and phase change microcapsule wall materials, The phase change microcapsule core material is obtained by compounding n-dodecane and n-tetradecane; the phase change microcapsule wall material is prepared by reacting acetaldehyde, urea and melamine. The particle size of phase change microcapsule thermal insulation material used in offshore oil and gas drilling fluids is 0.7~10 μm.

2. A method for preparing the phase change microcapsule thermal insulation material for marine oil and gas drilling fluid as described in claim 1, characterized in that, The steps include the following: (1) Preparation of phase change microcapsule core material emulsion An aqueous solution of n-dodecane and an aqueous solution of n-tetradecane were mixed, an emulsifier was added, and the mixture was preheated and then emulsified to obtain a premixed phase change microcapsule core material emulsion. (2) Preparation of phase change microcapsule wall material prepolymer A certain mass ratio of acetaldehyde, urea and melamine is poured into a flask containing deionized water, stirred, and then the pH is adjusted. After heating and stirring the reaction, a prepolymer solution is obtained. (3) Preparation of marine drilling fluid phase change microcapsules The premixed phase change microcapsule core material emulsion was added to a flask, and then the prepolymer solution was added dropwise at a certain rate under stirring. The pH of the mixture was then adjusted, and the reaction was allowed to stand. After centrifugation, washing, and drying of the reaction product, the final microcapsules were obtained.

3. The preparation method of the phase change microcapsule thermal insulation material for offshore oil and gas drilling fluid according to claim 2, characterized in that, Step (1) includes selecting one or more of the following options: I. The concentration of the aqueous solution of n-dodecane is 0.25-0.3 g / mL; II. The concentration of the aqueous solution of n-tetradecane is 0.4-0.55 g / mL; III. The molar ratio of n-dodecane to n-tetradecane structural units is 0.45-0.75:1; IV. The stirring reaction temperature is 40 °C, and the emulsification conditions are shear emulsification at 2000 r / min for 10 min.

4. The method for preparing phase change microcapsule thermal insulation material for offshore oil and gas drilling fluid according to claim 2, characterized in that, Step (2) includes selecting one or more of the following options: I. The mass ratio of acetaldehyde, urea, and melamine is 16:1:1; II. The stirring speed during the reaction is 100 r / min; III. The stirring reaction temperature is 70℃, the pH of the solution is adjusted to 8 with triethanolamine, and the stirring reaction time is 50 minutes.

5. The method for preparing phase change microcapsule thermal insulation material for offshore oil and gas drilling fluid according to claim 2, characterized in that, Step (3) includes selecting one or more of the following options: Ⅰ. When adding the prepolymer solution, the stirring speed is 200 r / min and the dropping speed is 20 d / min; II. During the reaction, the pH was adjusted to 4 by titration with 10% hydrochloric acid solution. The reaction conditions were room temperature and the reaction time was 4 hours. III. The centrifugation speed is 6000-10000 rpm and the centrifugation time is 5-10 minutes; the drying temperature is 70-90℃ and the drying time is 5-30 minutes.

6. A method for wellbore temperature control using the phase change microcapsule insulation material for offshore oil and gas drilling fluid as described in claim 1, characterized in that, The steps include the following: Step S1: Design a high-efficiency marine water-based drilling fluid system, add different amounts of phase change microcapsule heat insulation material to the drilling fluid to obtain multiple drilling fluids with different amounts of capsule heat insulation material, and use multiple portions of drilling fluid to perform subsequent steps in sequence. Step S2: Obtain the current drilling parameters and reservoir properties data, input the wellbore heat transfer equation of the drilling process established by the Hasan wellbore energy equation, and then apply the Laplace transform method to solve it, and establish a new analytical model of the wellbore temperature field that can simulate the fracturing process. Step S3: After discretizing the wellbore heat transfer equation and the reservoir temperature field, the amount of insulation material to be added is calculated by computer program; based on the drilling fluid with multiple different amounts of insulation material, the variation law of the addition amount and the thermal conductivity of the drilling fluid is summarized, and then the thermal conductivity is substituted into the formula to calculate the wellbore heat transfer equation and the wellbore temperature analytical model. When adjusting, clearly define the target temperature T. f The model calculates the control at T f The required thermal conductivity of the drilling fluid is determined, and then the amount of thermal insulation material to be added is determined based on the previously prepared thermal insulation material and the relationship between its addition and thermal conductivity to control the temperature. A system for wellbore temperature control using phase change microcapsule insulation materials in offshore oil and gas drilling fluids includes a data acquisition module, a data analysis module, and a dynamic control module. The data acquisition module is used to collect performance parameters of the reservoir, drilling fluid, and wellbore mud cake. The data analysis module is used to implement a synergistic control method of insulation materials and temperature field to establish a drilling temperature field model for offshore oil and gas fields. The dynamic control module controls the temperature during drilling by adjusting the amount of insulation material added to the drilling fluid and the temperature and pressure parameters of the drilling fluid.

7. The method for wellbore temperature control using phase change microcapsule insulation material for offshore oil and gas drilling fluid according to claim 6, characterized in that, In step S1, phase change microcapsules are used as thermal insulation materials. By adding lubricants, inhibitors, thickening and coating agents, thickeners, glass microspheres, filtration loss reducers, and reservoir bridging agents, a marine drilling fluid system with temperature regulation function is constructed. The drilling fluid density, rheological parameters, and API filtration loss are measured, and the thermal conductivity of the drilling fluid system is measured. The rheological parameters include apparent viscosity AV, plastic viscosity PV, and dynamic shear force YP. Thermal conductivity calculation: λ= (1) Thermal resistance calculation: R= （2） R: Thermal resistance, km 2 / w; TA: Hot surface temperature of the sample, K; TD: Cold surface temperature of the sample, K; A: Cross-sectional area of ​​the sample, m² 2 Q: Heat flow, w; L: Distance between heat source and cold source, m.

8. The method for wellbore temperature control using phase change microcapsule insulation material for offshore oil and gas drilling fluid according to claim 6, characterized in that, In step S2, the model is established as follows: The following assumptions are made regarding the heat transfer process in the drilling wellbore: ① Each heat transfer medium is distributed symmetrically around the oil pipe as the center; ② The flow inside the wellbore is one-dimensional, and axial heat conduction is negligible; ③ The fluid properties are constants; ④ The drilling fluid injection rate at the wellhead is a constant value; ⑤ The rock's physical properties are homogeneous and isotropic; The wellbore heat transfer equation for the drilling process is calculated using the following formula: (3) Taking the limits of both sides of equation (3) with respect to time and space, we get: （4） In the formula, A is the cross-sectional area, m 2 ; ρ denoted as drilling fluid density; m is the fluid mass per unit length, kg / m; m' is the wellbore medium mass per unit length, kg / m; E is the fluid internal energy per unit mass, J / kg; E' is the wellbore medium internal energy per unit mass, J / kg; z is the depth, m; t is time, s; H is the enthalpy of a unit mass of infinitesimal element, J / kg; v is the flow rate, m / s; w Mass flow rate, kg / s; Gravitational potential energy per unit mass is defined as follows: =- gzsinθ g is the acceleration due to gravity, m / s² 2 ; θ The angle between the wellbore and the horizontal plane; Q is the heat flow rate per unit length of formation into the fluid, W / m; The first term on the left-hand side of equation (4) represents the rate of change of internal energy of the fluid per unit length; the second term on the left-hand side represents the rate of change of internal energy of the wellbore medium per unit length; the change of internal energy of the wellbore medium is expressed as a linear function of the change of internal energy of the fluid, that is: （5） Where C T This is the thermal storage coefficient, and different values ​​are required under different conditions. The first term on the right-hand side of equation (4) represents the energy flowing into and out of a unit cell. According to the standard equilibrium thermodynamic formula, dH = C Pf dT f -C Pf Jd p C Pf This represents the molar isobaric heat capacity under constant pressure conditions. T f The drilling fluid temperature is denoted as ; J is the coke-Thomson coefficient, °C / Pa; substituting these values, we get: （6） C p p represents the constant pressure heat capacity, where p is the pressure. The second term on the right side of equation (4) represents heat transfer from the formation to the fluid, expressed as: Q= w C Pf (T surf +g G z sinθ -T f ) L R (7) （8） （9） In the formula, T surf Surface temperature, °C; g G Geothermal gradient, °C / m; L R The relaxation distance is 1 / m; r to This represents the distance from the fluid center to the formation heat transfer point. λ e The thermal conductivity of the formation is W / (m·°C); λ o T represents the thermal conductivity of the drilling fluid, W / (m·°C); D It is a dimensionless time function; U to For the overall heat transfer coefficient, W / (m 2 ·°C); t D For dimensionless time, t D = λ e t / (ρ e C pe ), ρ e C represents the formation fluid density. pe This refers to the specific heat capacity of the formation fluid at that location. Substituting equations (5), (6), and (7) into equation (4), we obtain the final form of the wellbore heat transfer equation during the drilling process: （10） in The lumped parameter is defined as: （11） The overall heat transfer coefficient in equation (8) U to The heat transfer characteristics from the drill pipe wall to the formation are characterized by the following formula, neglecting the convective heat transfer resistance between the drilling fluid and the drill pipe, as well as thermal radiation: （12） In the formula λ h is the thermal conductivity of the mud cake, W / (m·°C); r e The mud cake thickness is measured in meters (m). h an The drilling fluid convective heat transfer coefficient is W / (m³). 2 (°C), using Dropkin and Sommerscales' formula for the equivalent heat transfer coefficient between flat plates, the following was applied: h an Approximation: （13） （14） （15） In the formula, Gr is the Grashoff number of the annular fluid; Pr an The Prandtl number for the annular fluid; r ci Let be the inner radius of the casing, in meters (m). r to The distance from the fluid center to the formation heat transfer point, in meters (m). r h Let be the outer radius of the drill pipe, in meters (m). λ an is the thermal conductivity of the annular fluid, W / (m·°C); ρ an The density of the annular fluid is kg / m³. 3 μ an The viscosity of the annular fluid is Pa·s; C Pan The isobaric specific heat capacity of the annular fluid is J / (kg·°C); β an The coefficient of thermal expansion of the annulus fluid is 1 / °C. The solution obtained using the Laplace method is: （16） a, b, c It is a constant; In the formula For a step function, the following relationship exists: （17） The wellbore temperature calculated using a novel analytical model of the drilling wellbore temperature field is thus obtained. T f As boundary conditions for the formation temperature field, a semi-analytical model of the wellbore-formation temperature field is established to realize the calculation of the formation temperature field and construct a new analytical model of the wellbore temperature field. Considering the formation is radially axisymmetric and making the following assumptions: ①The formation exhibits radial one-dimensional transient heat conduction; ② There is no fluid flow in the formation; ③The formation physical parameters are homogeneous and isotropic; Based on the law of conservation of energy, the heat transfer equation and boundary conditions of the formation are as follows: （18） （19） In the formula T f The drilling fluid temperature after heat transfer is complete, in °C; T e Formation temperature, °C; T ei The initial temperature of the formation is °C. r Radial distance of the strata, in meters; r e The mud cake thickness is measured in meters (m). r h Let be the outer radius of the drill pipe, in meters (m). r=r h Boundary conditions T at point h The following formula can be used to obtain: （20） Among them, T f The drilling fluid temperature after heat transfer is complete, in °C; f (t) is T surf +g G z sinθ -T f ; λ e The thermal conductivity of the formation is W / (m·°C); T ei The initial temperature of the formation is °C. r to This represents the distance from the fluid center to the formation heat transfer point. U to For the overall heat transfer coefficient, W / (m 2 ·°C).

9. A computer-readable storage medium having a program stored thereon, characterized in that, When executed by the processor, the program implements the steps in the method for wellbore temperature control using phase change microcapsule thermal insulation material in offshore oil and gas drilling fluid as described in claim 6, in order to calculate the required amount of phase change microcapsule thermal insulation material to be added.

10. An electronic device comprising a memory, a processor, and a program stored in the memory and executable on the processor, characterized in that, When the processor executes the program, it implements the steps in the method for wellbore temperature control using phase change microcapsule thermal insulation material in marine oil and gas drilling fluid as described in claim 6.

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