Oil pipe assembly for gas well and gas well hydrate control method

Abstract

The oil pipe assembly comprises a lifting mechanism, a heat preservation oil pipe and a probing oil pipe, the lifting mechanism is connected with a fixed oil pipe, the fixed oil pipe is vertically arranged, the lifting mechanism can enable the fixed oil pipe to ascend and descend in the axial direction, and the fixed oil pipe is provided with a safety valve; the heat preservation oil pipe and the fixed oil pipe are coaxially and detachably connected, and the heat preservation oil pipe is wrapped with a heat preservation sleeve. The probing oil pipe is coaxially and detachably connected with the end, away from the fixed oil pipe, of the heat-preservation oil pipe. Two measures of water jacket furnace ground heating and hydrate inhibitor adding can be replaced, and various problems generated by water jacket furnace ground heating and hydrate inhibitor adding are solved on the premise that it is guaranteed that no hydrate is generated after throttling. A gas well hydrate control method can solve the problem that hydrate is generated after ground throttling.

Description

Technical Field

[0001] The invention relates to the technical field of oil and gas production engineering in the petroleum industry, and in particular to an oil pipe assembly for a gas well and a method for preventing and controlling hydrates in the gas well. Background Art

[0002] During the production process of natural gas wells, due to the high wellhead pressure, throttling is required to reduce the pressure to the external transmission pressure. Throttling will produce a sharp pressure drop, causing the natural gas temperature to drop suddenly. If the temperature after throttling is lower than the hydrate formation temperature corresponding to the pressure after throttling, hydrates will be generated, blocking the wellbore and ground gas production pipeline, affecting the normal production of the gas well.

[0003] The production site usually adopts water jacket furnace ground heating, injection of hydrate inhibitors or downhole throttling and pressure reduction to prevent hydrate formation. The essence of water jacket furnace ground heating is to raise the air flow temperature to above the temperature of hydrate formation. It is an indirect heating with water and steam as heat transfer medium. This process heating method requires supporting ground heating process, equipment and corresponding management personnel. The process is complicated and the construction cycle is long. At the same time, it also consumes a lot of electricity or natural gas, and there are high one-time investment and later operation and maintenance costs; injection of hydrate inhibitors is to reduce the dew point of natural gas so that the air flow does not form hydrates at a lower temperature. There are many types of antifreeze, including methanol, ethylene glycol, diethylene glycol, calcium chloride aqueous solution, etc. Ethylene glycol is commonly used in gas production. It effectively inhibits the large-scale formation and aggregation of hydrates at low dosages, but there are problems such as complex alcohol-containing wastewater treatment process, high cost, and environmental protection. The downhole throttling process uses rope operations to place a downhole throttle at an appropriate position in the wellbore, and throttles and reduces the pressure of the fluid downhole through the throttling nozzle, thereby reducing the wellhead pressure. The fluid after throttling absorbs formation heat, making the fluid temperature after throttling higher than the hydrate formation temperature, preventing hydrate formation. This method requires the insertion of downhole tools, which affects the dynamic monitoring and analysis of gas wells during test production. In addition, wells with sand and a lot of impurities and dirt will affect the fixing of the throttle, causing the throttle to be blocked or difficult to salvage. Summary of the invention

[0004] The first purpose of the present invention is to provide an oil pipe assembly for a gas well, which can replace the two measures of ground heating of water jacket furnace and adding hydrate inhibitors, and solve the various problems caused by ground heating of water jacket furnace and adding hydrate inhibitors while ensuring that hydrates are not generated after throttling.

[0005] The second object of the present invention is to provide a method for preventing and controlling gas well hydrates, which can solve the problem of hydrate generation after surface throttling.

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

[0007] A tubing assembly for a gas well comprises: a lifting mechanism, the lifting mechanism being connected to a fixed tubing, the fixed tubing being vertically arranged, the lifting mechanism being capable of lifting and lowering the fixed tubing axially, the fixed tubing being provided with a safety valve; an insulating tubing, the insulating tubing being coaxially and detachably connected to the fixed tubing, the insulating tubing being covered with an insulating sleeve; and an exploratory tubing, the exploratory tubing being coaxially and detachably connected to an end of the insulating tubing away from the fixed tubing.

[0008] Optionally, the fixed oil pipe, the insulating oil pipe and the probe oil pipe are coaxially and detachably connected via threads.

[0009] Optionally, the thermal insulation sleeve comprises a first half hoop, a second half hoop and a plurality of fixing parts, the first half hoop and the second half hoop can be embraced to form the thermal insulation sleeve, and the fixing parts can maintain the embraced state of the first half hoop and the second half hoop.

[0010] Optionally, the fixing piece is in the shape of a circular ring, and is sleeved outside the first half hoop and the second half hoop that are embraced.

[0011] Optionally, the insulation cover includes a pair of fixing parts; the outer diameters of the two ends of the first clamp and the second clamp in the length direction are smaller than the outer diameter of the middle part, so as to form support edges at both ends respectively; the inner diameter of the fixing part matches and is fitted with the outer diameters of the two ends of the first clamp and the second clamp in the length direction, and the fixing part is in contact with the support edge.

[0012] Optionally, the outer walls of both ends of the first clamp and the second clamp in the length direction are provided with external threads, the corresponding ends of the fixed oil pipe and the exploration oil pipe are provided with internal threads, and the fixing piece is clamped between the supporting edge and the corresponding ends of the fixed oil pipe or the exploration oil pipe.

[0013] Optionally, an insulation layer is sandwiched between the insulation sleeve and the insulation oil pipe, and the insulation layer is evenly applied on the outer wall of the insulation oil pipe and compacted by the insulation sleeve; the material of the insulation layer includes: any one or more combinations of aerogel felt, microporous calcium silicate, titanium ceramic insulation board, aluminum silicate fiber blanket, plate-like aerogel and aerogel coating.

[0014] A method for preventing and controlling hydrate in a gas well comprises the following steps:

[0015] Obtain the preset length of the insulation oil pipe;

[0016] After any one of the above-mentioned insulated oil pipes of the oil pipe assembly for a gas well is lowered into the well to the preset length, surface throttling is implemented.

[0017] Optionally, obtaining a preset length of the insulating oil pipe comprises the following steps:

[0018] Establish a wellbore temperature-pressure coupling model;

[0019] According to the wellbore temperature-pressure coupling model, the hydrate formation temperature after surface throttling and the wellhead temperature without hydrate formation are obtained;

[0020] Fitting any of the above parameters of the tubing assembly for the gas well with the wellbore temperature-pressure coupling model to obtain a thermal insulation tubing running length-wellhead temperature model;

[0021] The wellhead temperature at which hydrate is not generated is brought into the insulated oil pipe running length-wellhead temperature model to obtain the preset length.

[0022] Optionally, the establishing of the wellbore temperature-pressure coupling model comprises the following steps:

[0023] The calculation formula of the total heat transfer coefficient of the wellbore is established:

[0024]

[0025] Among them: U is the total heat transfer coefficient of the wellbore; R1 is the convection heat transfer thermal resistance between the production fluid and the inner wall of the oil pipe, the unit is (m2·℃) / W; R2 is the thermal conductivity thermal resistance of the oil pipe, the unit is (m2·℃) / W; R3 is the thermal conductivity thermal resistance of the insulation layer, the unit is (m2·℃) / W; R4 is the radiation heat transfer thermal resistance of the annulus medium, the unit is (m2·℃) / W; R5 is the convection heat transfer thermal resistance of the annulus medium, the unit is (m2·℃) / W; R6 is the thermal conductivity thermal resistance of the casing, the unit is (m2·℃) / W; R7 is the thermal conductivity thermal resistance of the cement layer, the unit is (m2·℃) / W;

[0026] According to the calculation formula of the total heat transfer coefficient of the wellbore, the spatial distribution of the formation thermal physical properties is introduced to establish the wellbore temperature-pressure coupling model, which satisfies the following calculation formula:

[0027]

[0028] Where: θ is the angle between the wellbore and the horizontal plane; dz is the microelement cut along the wellbore; cp is the specific heat capacity at constant pressure, in J / (kg·℃); α v is the volume expansion coefficient, unit is K -1 ; r ins is the outer diameter of the insulation layer, in m; G is the mass flow rate of the produced liquid, in kg / s; Te is the original formation temperature, in °C; Ke is the formation thermal conductivity at the location of the microelement segment, in W / (m·°C); f(t D) is the dimensionless temperature; Tm is the temperature of the produced liquid in the tubing, in °C; Ti is the inner diameter of the tubing, in m; Km is the thermal conductivity of the produced liquid in the tubing, in W / (m·°C); νm is the average flow rate of the produced fluid in the tubing, in m / s; λ is the Darcy friction coefficient; ρm is the average density of the produced fluid, in kg / m 3 .

[0029] Compared with the prior art, the present invention has the following advantages and beneficial effects:

[0030] The present invention provides a tubing assembly for a gas well. The tubing is provided with an insulation sleeve to significantly reduce its thermal conductivity, thereby reducing the heat loss of the wellbore, so as to increase the wellhead temperature to make it higher than the hydrate formation temperature, thereby preventing the problem of hydrate formation after throttling and cooling on the surface of the gas well; on this basis, a fixed tubing is provided to be detachably connected with the insulation tubing, providing a connection basis for the insulation tubing, and further connected with the fixed tubing by providing a lifting mechanism, and the insulation tubing can be indirectly driven to extend along the well by using the lifting mechanism to adjust the extension length of the insulation tubing, thereby adjusting the wellhead temperature; on this basis, a probe tubing is provided to compensate for the length of the insulation tubing, so that the entire tubing assembly can penetrate deep into the gas well to collect natural gas. Through the mutual cooperation of the above-mentioned components, the tubing assembly for the gas well can solve the problem of hydrate formation after throttling, so as to replace the two measures of ground heating of the water jacket furnace and adding hydrate inhibitors, thereby directly avoiding the various problems of the two measures. BRIEF DESCRIPTION OF THE DRAWINGS

[0031] The drawings described herein are used to provide a further understanding of the embodiments of the present invention, constitute a part of this application, and do not constitute a limitation of the embodiments of the present invention. In the drawings:

[0032] Figure 1 A schematic diagram of an oil pipe assembly for a gas well provided by an embodiment of the present invention;

[0033] Figure 2 A side cross-sectional view of an oil pipe assembly for a gas well provided by an embodiment of the present invention;

[0034] Figure 3 A schematic diagram of an oil pipe assembly for a gas well provided by an embodiment of the present invention when in operation;

[0035] Figure 4 A flow chart of a gas well hydrate prevention and control method provided by an embodiment of the present invention;

[0036] Figure 5 A calculation flow chart of a numerical solution program for a pseudo-three-dimensional fracture propagation model of a gas well hydrate prevention and control method provided in an embodiment of the present invention;

[0037] Figure 6 A seepage model diagram of a fracture in a gas well hydrate prevention and control method provided by an embodiment of the present invention;

[0038] Figure 7 A diagram of a wellbore temperature-pressure coupling model of a gas well hydrate prevention and control method provided in an embodiment of the present invention;

[0039] Figure 8 A model diagram of the running length of the insulated oil pipe-wellhead temperature for the gas well hydrate prevention and control method provided in an embodiment of the present invention.

[0040] Marks and corresponding parts names in the attached drawings:

[0041] 10-fixed oil pipe; 11-safety valve; 20-insulated oil pipe; 21-insulation sleeve; 211-first half hoop; 212-second half hoop; 213-fixed part; 214-support edge; 22-insulation layer; 30-insulated oil pipe. DETAILED DESCRIPTION

[0042] In order to make the objectives, technical solutions and advantages of the present invention more clearly understood, the present invention is further described in detail below in conjunction with embodiments and drawings. The exemplary embodiments of the present invention and their description are only used to explain the present invention and are not intended to limit the present invention.

[0043] Please refer to Figures 1 to 3 The present embodiment provides an oil pipe assembly for a gas well, comprising a lifting mechanism, wherein the lifting mechanism is connected to a fixed oil pipe 10, wherein the fixed oil pipe 10 is vertically arranged, and the lifting mechanism can lift and lower the fixed oil pipe 10 axially, and the fixed oil pipe 10 is provided with a safety valve 11; the second comprises an insulated oil pipe 20, wherein the insulated oil pipe 20 is coaxially detachably connected to the fixed oil pipe 10, and the insulated oil pipe 20 is covered with an insulation sleeve 21; the third comprises an exploratory oil pipe 30, wherein the exploratory oil pipe 30 is coaxially detachably connected to one end of the insulated oil pipe 20 away from the fixed oil pipe 10.

[0044] The oil pipe assembly for gas wells provided by the present invention is provided with an insulating oil pipe 20, which is provided with an insulating sleeve 21 to greatly reduce its thermal conductivity, thereby reducing the heat loss of the wellbore, so as to increase the wellhead temperature to make it higher than the hydrate formation temperature, thereby preventing the problem of hydrate formation after throttling and cooling on the ground of the gas well; on this basis, by providing a fixed oil pipe 10, it is detachably connected with the insulating oil pipe 20, providing a connection basis for the insulating oil pipe 20, and further by providing a lifting mechanism connected with the fixed oil pipe 10, the insulating oil pipe 20 can be indirectly driven to extend along the well by the lifting mechanism to adjust the extension length of the insulating oil pipe 20, thereby adjusting the wellhead temperature; on this basis, by providing a probe oil pipe 30, the length of the insulating oil pipe 20 is compensated, so that the entire oil pipe assembly can penetrate deep into the gas well to collect natural gas. Through the mutual cooperation of the above-mentioned components, the oil pipe assembly for gas wells can solve the problem of hydrate formation after throttling, so as to replace the two measures of ground heating of the water jacket furnace and adding hydrate inhibitors, thereby directly avoiding the various problems of the two measures.

[0045] It should be noted that the above-mentioned lifting mechanism can adopt any lifting mechanism for oil pipes in the prior art, and the connection method generally adopts an embedded type, which is convenient for putting on and taking off the oil pipe.

[0046] Preferably, in order to facilitate the making and breaking of the buckle, the fixed oil pipe 10, the thermal insulation oil pipe 20 and the exploration oil pipe 30 are coaxially detachably connected through threads.

[0047] In order to further explain the specific structure of the insulation sleeve 21, the insulation sleeve 21 includes a first half hoop 211, a second half hoop 212 and a plurality of fixing parts 213. The first half hoop 211 and the second half hoop 212 can be embraced to form the insulation sleeve 21, and the fixing parts 213 can maintain the embraced state of the first half hoop 211 and the second half hoop 212.

[0048] Through the above arrangement, the insulation sleeve 21 is assembled in an embracing manner, which will not affect the docking of the two ends of the insulation oil pipe 20 on the one hand, and is convenient for arranging other insulation materials between the outer wall of the insulation oil pipe 20 and the inner wall of the insulation sleeve 21 on the other hand.

[0049] In order to further explain the specific shape and fixing method of the fixing member 213, the fixing member 213 is in a circular ring shape, and the fixing member 213 is sleeved outside the first half hoop 211 and the second half hoop 212 that are embraced.

[0050] Through the above arrangement, the first half hoop 211 and the second half hoop are fixed in position by means of sleeve tightening, which is convenient for installation.

[0051] Preferably, in order to limit the installation position of the fixing part 213 and prevent it from unnecessary sliding along the axial direction of the insulated oil pipe 20, the insulation sleeve 21 includes a pair of the fixing parts 213; the outer diameters of the two ends of the length direction of the first clamp 211 and the second clamp 212 are smaller than the outer diameter of the middle part, so as to form support edges 214 at both ends respectively; the inner diameter of the fixing part 213 matches and is fitted with the outer diameters of the two ends of the length direction of the first clamp 211 and the second clamp 212, and the fixing part 213 is in contact with the support edge 214.

[0052] Through the above-mentioned arrangement, the installation position of the fixing piece 213 is limited to the two axial ends of the insulation sleeve 21, and the first clamp 211 and the second clamp 212 are tightened from both ends to facilitate installation, and the insertion depth of the fixing piece 213 is limited by the support along 214 to prevent it from sliding along the axial direction of the insulation oil pipe 20 to the middle of the insulation oil pipe 20.

[0053] In order to further improve the thermal insulation performance of the insulated oil pipe 20 and the thermal insulation sleeve 21, and to further limit the fixing part 213, the outer walls of the first clamp 211 and the second clamp 212 at both ends in the length direction are provided with external threads, and the corresponding ends of the fixed oil pipe 10 and the exploratory oil pipe 30 are provided with internal threads, and the fixing part 213 is clamped between the support edge 214 and the corresponding ends of the fixed oil pipe 10 or the exploratory oil pipe 30.

[0054] Through the above-mentioned arrangement, when the insulated oil pipe 20 is connected to the fixed oil pipe 10 and the probe oil pipe 30, the two ends of the insulation sleeve 21 in the length direction are screwed into the fixed oil pipe 10 and the probe oil pipe 30 to increase the contact area of ​​the sealing surface of the connecting end, further improving the insulation performance of the insulated oil pipe 20, and the end surfaces of the fixed oil pipe 10 and the probe oil pipe 30 can press the fixing part 213, completely limit the fixing part 213, and make the structure more stable.

[0055] Preferably, in order to further improve the thermal insulation performance, an insulation layer 22 is sandwiched between the insulation sleeve 21 and the insulation oil pipe 20, and the insulation layer 22 is evenly laid on the outer wall of the insulation oil pipe 20 and compacted by the insulation sleeve 21; the material of the insulation layer 22 includes: any one or more combinations of aerogel felt, microporous calcium silicate, titanium ceramic insulation board, aluminum silicate fiber blanket, plate-like aerogel and aerogel coating.

[0056] Please Figures 1 to 3 Based on the reference Figure 4 This embodiment also provides a method for preventing and controlling hydrates in a gas well, comprising the following steps:

[0057] S0, gas well productivity prediction;

[0058] S1, obtaining the preset length of the insulation oil pipe;

[0059] S2. After any one of the above-mentioned insulated oil pipes 20 used in the oil pipe assembly for a gas well is lowered into the well to the preset length, surface throttling is performed.

[0060] Specifically, step S0 includes the following specific steps:

[0061] S01. Establish a pseudo three-dimensional acid-etching crack extension model;

[0062] Specifically, gas well reservoir transformation is an effective means to increase gas well production. Currently, reservoir transformation is carried out before gas wells are put into production. The production capacity of the gas well after transformation is an important parameter that affects the depth of the insulating oil pipe, affecting the insulation effect and economy. Based on the existing two-dimensional acid fracturing model, it usually only considers the flow of fluid in the fracture along the length of the fracture and the diffusion and mass transfer along the fracture wall, ignoring the flow of acid in the fracture height direction and the change of acid concentration over time. When the longitudinal heterogeneity of the reservoir is obvious, the simulation results are often inaccurate. In order to solve the problem of the time-varying degree of acid-etched fractures, the principle of Newton iteration method is used to establish a pseudo-three-dimensional acid fracturing fracture extension model considering acid etching-acid loss, which improves the prediction accuracy of acid-etched fracture morphology;

[0063] The four basic equations constituting the pseudo-three-dimensional crack extension model are obtained, which are:

[0064] (1) Continuity equation:

[0065]

[0066] (2) Fluid pressure drop equation:

[0067]

[0068] (3) Crack width equation:

[0069] w(x,t)=f2(p(x,t),H(x,t))

[0070] (4) Crack height control equation:

[0071]

[0072] The above four equations constitute a nonlinear equation system about q(x, t), p(x, t), w(x, t), and H(x, t). In order to accurately solve them, the corresponding initial conditions and boundary conditions need to be supplemented:

[0073]

[0074] First, assume that the injection time is t and the crack length is L f, divide the crack into several units along the crack length direction, use the standard fourth-order Runge-Kutta method to solve the crack height control equation, combine the initial conditions and boundary conditions to solve the height h(x, t) and displacement q(x, t) of each unit section, and then calculate the crack net pressure p(x, t) and crack width w(x, t). Use the flow calculated to the crack mouth as the judgment condition for the next iteration, and finally calculate L by volume conservation. f (t). The crack length L will be assumed f And calculate L f (t) until the given accuracy requirement is met. Calculations show that this method has good convergence and high computational efficiency. The calculation flow chart is shown in Figure 5 As shown;

[0075] According to the above derivation, the numerical solution program of the pseudo-three-dimensional crack extension model was compiled using Matlab software, and the stress symmetry between the bottom layer and the cap layer of the crack was calculated;

[0076] S02. Establish a gas reservoir productivity prediction model based on fracture morphology prediction;

[0077] Specifically, based on the trilinear principle, a low-permeability gas reservoir productivity prediction model was established that takes into account the effects of fracture morphology, stress sensitivity, slippage effect, and high-speed non-Darcy flow in fractures. The seepage of gas from the reservoir to the fracture mouth is divided into two parts: one is the radial flow part in the gas reservoir matrix, including the radial flow with the fracture end point as the center and the linear flow on both sides of the fracture; the other is the seepage part from the fracture end to the bottom of the well. The fracture seepage model is shown in the figure Figure 6 As shown;

[0078] The flow equations between the fracture grid and the matrix and fracture grid are:

[0079]

[0080] The model is solved by iterative method from the end of the fracture to the fracture mouth. The outflow Q1 of the fracture mouth grid block is the fracture production, that is, the production after fracturing stimulation.

[0081] Further optionally, obtaining the preset length of the insulating oil pipe comprises the following steps:

[0082] S11, establishing a wellbore temperature-pressure coupling model;

[0083] S12, according to the wellbore temperature-pressure coupling model, obtaining the hydrate formation temperature after surface throttling and the wellhead temperature where hydrate is not formed;

[0084] S13, fitting any of the above parameters of the oil pipe assembly for the gas well with the wellbore temperature-pressure coupling model to obtain a thermal insulation oil pipe running length-wellhead temperature model;

[0085] S14, bringing the wellhead temperature at which hydrate is not generated into the insulated oil pipe running length-wellhead temperature model to obtain the preset length.

[0086] Further optionally, the establishing of the wellbore temperature-pressure coupling model comprises the following steps:

[0087] S111. The total heat transfer coefficient is used to describe the overall heat transfer performance of the wellbore. Each link in the fluid lifting process is quantified and integrated to establish a calculation formula for the total heat transfer coefficient of the wellbore based on the outer diameter of the insulation layer:

[0088]

[0089] Among them: U is the total heat transfer coefficient of the wellbore; R1 is the convection heat transfer thermal resistance between the production fluid and the inner wall of the oil pipe, the unit is (m2·℃) / W; R2 is the thermal conductivity thermal resistance of the oil pipe, the unit is (m2·℃) / W; R3 is the thermal conductivity thermal resistance of the insulation layer, the unit is (m2·℃) / W; R4 is the radiation heat transfer thermal resistance of the annulus medium, the unit is (m2·℃) / W; R5 is the convection heat transfer thermal resistance of the annulus medium, the unit is (m2·℃) / W; R6 is the thermal conductivity thermal resistance of the casing, the unit is (m2·℃) / W; R7 is the thermal conductivity thermal resistance of the cement layer, the unit is (m2·℃) / W;

[0090] S112, according to the calculation formula of the total heat transfer coefficient of the wellbore, the spatial distribution of the thermal physical properties of the formation is introduced to establish the wellbore temperature-pressure coupling model, and the wellbore temperature-pressure coupling model satisfies the following calculation formula:

[0091]

[0092] Where: θ is the angle between the wellbore and the horizontal plane; dz is the microelement cut along the wellbore; cp is the specific heat capacity at constant pressure, in J / (kg·℃); α v is the volume expansion coefficient, unit is K -1 ; r ins is the outer diameter of the insulation layer, in m; G is the mass flow rate of the produced liquid, in kg / s; Te is the original formation temperature, in °C; Ke is the formation thermal conductivity at the location of the microelement segment, in W / (m·°C); f(t D) is the dimensionless temperature; Tm is the temperature of the produced liquid in the tubing, in °C; Ti is the inner diameter of the tubing, in m; Km is the thermal conductivity of the produced liquid in the tubing, in W / (m·°C); ν m is the average flow rate of the produced fluid in the tubing, in m / s; λ is the Darcy friction coefficient; ρm is the average density of the produced fluid, in kg / m 3 .

[0093] It should be noted that step S13 specifically includes the following steps:

[0094] S131. Given different production rates, the wellbore temperature-pressure coupling model is used to predict the wellhead temperature and pressure. The wellbore and surface processes are regarded as a unified production system. Based on the predicted wellhead temperature and pressure, combined with the transmission pressure, the graphical method or empirical formula method is used to predict the wellhead temperature of hydrate formation after surface throttling and the wellhead temperature of hydrate-free wells. Specifically, Figure 7 As shown;

[0095] It should be noted that step S14 specifically includes the following steps:

[0096] S141. Set different lengths of insulated tubing and ordinary tubing combinations, give production parameters, and use the wellbore temperature-pressure coupling model to calculate the wellhead temperature. When the wellhead temperature is higher than the temperature at which hydrates are not generated, it satisfies the requirement that hydrates are not generated on the ground, that is, the minimum length of the insulated tubing is determined, as shown in the following table:

[0097] Hydrate formation temperature corresponding to different wellhead pressures

[0098]

[0099] It should be noted that the insulation tubing running length-wellhead temperature model is as follows Figure 8 shown.

[0100] The specific implementation methods described above further illustrate the objectives, technical solutions and beneficial effects of the present invention in detail. It should be understood that the above description is only a specific implementation method of the present invention and is not intended to limit the scope of protection of the present invention. Any modifications, equivalent substitutions, improvements, etc. made within the spirit and principles of the present invention should be included in the scope of protection of the present invention.

Claims

1. A tubing assembly for a gas well, characterized in that: include: A lifting mechanism, wherein the lifting mechanism is connected to a fixed oil pipe (10), the fixed oil pipe (10) is arranged vertically, the lifting mechanism can make the fixed oil pipe (10) rise and fall in the axial direction, and the fixed oil pipe (10) is provided with a safety valve (11); A heat-insulating oil pipe (20), the heat-insulating oil pipe (20) being coaxially detachably connected to the fixed oil pipe (10), and the heat-insulating oil pipe (20) being covered with a heat-insulating sleeve (21); The oil probe pipe (30) is coaxially and detachably connected to an end of the heat-insulating oil pipe (20) away from the fixed oil pipe (10).

2. The oil pipe assembly for a gas well according to claim 1, characterized in that: The fixed oil pipe (10), the heat-insulating oil pipe (20) and the probe oil pipe (30) are coaxially detachably connected via threads.

3. The oil pipe assembly for a gas well according to claim 1, characterized in that: The thermal insulation sleeve (21) comprises a first half hoop (211), a second half hoop (212) and a plurality of fixing parts (213); the first half hoop (211) and the second half hoop (212) can be engaged to form the thermal insulation sleeve (21); and the fixing parts (213) can maintain the engaged state of the first half hoop (211) and the second half hoop (212).

4. The oil pipe assembly for a gas well according to claim 3, characterized in that: The fixing member (213) is in the shape of a circular ring and is sleeved outside the first half hoop (211) and the second half hoop (212) that are embraced.

5. The oil pipe assembly for a gas well according to claim 4, characterized in that: The thermal insulation sleeve (21) comprises a pair of fixing members (213); The outer diameters of the two ends of the first hoop (211) and the second hoop (212) in the length direction are smaller than the outer diameter of the middle part, so as to form support edges (214) at the two ends respectively; The inner diameter of the fixing member (213) matches and fits with the outer diameters of both ends of the first clamp (211) and the second clamp (212) in the length direction, and the fixing member (213) fits with the supporting edge (214).

6. The oil pipe assembly for a gas well according to claim 5, characterized in that: The outer walls of both ends of the first clamp (211) and the second clamp (212) in the length direction are provided with external threads, the corresponding ends of the fixed oil pipe (10) and the probe oil pipe (30) are provided with internal threads, and the fixing member (213) is clamped between the supporting edge (214) and the corresponding ends of the fixed oil pipe (10) or the probe oil pipe (30).

7. The oil pipe assembly for a gas well according to any one of claims 1 to 6, characterized in that: A heat-insulating layer (22) is sandwiched between the heat-insulating sleeve (21) and the heat-insulating oil pipe (20); the heat-insulating layer (22) is evenly laid on the outer wall of the heat-insulating oil pipe (20) and compacted by the heat-insulating sleeve (21); The material of the thermal insulation layer (22) comprises: any one or more combinations of aerogel felt, microporous calcium silicate, titanium ceramic thermal insulation board, aluminum silicate fiber blanket, plate-shaped aerogel and aerogel coating.

8. A method for preventing and controlling hydrate in a gas well, characterized in that: The steps include: Obtain the preset length of the insulation oil pipe; After the insulated oil pipe (20) of the oil pipe assembly for a gas well according to any one of claims 1 to 7 is lowered into the well to the preset length, surface throttling is implemented.

9. The method for preventing and controlling hydrate in a gas well according to claim 8, characterized in that: The step of obtaining the preset length of the insulating oil pipe comprises the following steps: Establish a wellbore temperature-pressure coupling model; According to the wellbore temperature-pressure coupling model, the hydrate formation temperature after surface throttling and the wellhead temperature without hydrate formation are obtained; Fitting the parameters of the oil pipe assembly for a gas well as claimed in any one of claims 1 to 7 with a wellbore temperature-pressure coupling model to obtain a thermal insulation oil pipe running length-wellhead temperature model; The wellhead temperature at which hydrate is not generated is brought into the insulated oil pipe running length-wellhead temperature model to obtain the preset length.

10. The method for preventing and controlling gas well hydrates according to claim 9, characterized in that: The establishment of the wellbore temperature-pressure coupling model comprises the following steps: The calculation formula of the total heat transfer coefficient of the wellbore is established: in: U is the total heat transfer coefficient of the wellbore; R1 is the convection heat transfer resistance between the production fluid and the inner wall of the oil pipe, the unit is (m2·℃) / W; R2 is the thermal resistance of the oil pipe, in units of (m2·℃) / W; R3 is the thermal resistance of the insulation layer, in units of (m2·℃) / W; R4 is the thermal resistance of the annular medium for radiation heat transfer, in units of (m2·℃) / W; R5 is the thermal resistance of the annular medium for convection heat transfer, in units of (m2·℃) / W; R6 is the thermal resistance of the sleeve, in units of (m2·℃) / W; R7 is the thermal resistance of the cement layer, in units of (m2·℃) / W; According to the calculation formula of the total heat transfer coefficient of the wellbore, the spatial distribution of the formation thermal physical properties is introduced to establish the wellbore temperature-pressure coupling model, which satisfies the following calculation formula: in: θ is the angle between the wellbore and the horizontal plane; dz is the microelement of the length cut along the wellbore; cp is the specific heat at constant pressure, in J / (kg·℃); α v is the volume expansion coefficient, unit is K -1 ; r ins is the outer diameter of the insulation layer, in m; G is the mass flow rate of produced liquid, in kg / s; Te is the original formation temperature, in °C; Ke is the thermal conductivity of the formation at the location of the microelement segment, in W / (m·℃); f(t D) is the dimensionless temperature; Tm is the temperature of the produced fluid in the tubing, in °C; Ti is the inner diameter of the oil pipe, in m; Km is the thermal conductivity of the produced fluid in the tubing, in W / (m·℃); ν m is the average flow rate of produced fluid in the tubing, in m / s; λ is the Darcy friction coefficient; ρm is the average density of produced liquid, in kg / m 3 .

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