Tubing assembly for gas wells and method for hydrate prevention in gas wells

Abstract

The application discloses a tubing assembly for a gas well, which comprises a lifting mechanism, a heat preservation tubing and a probe tubing, the lifting mechanism is connected with a fixed tubing, the fixed tubing is vertically arranged, the lifting mechanism can make the fixed tubing ascend and descend along the axial direction, and the fixed tubing is provided with a safety valve; the heat preservation tubing is coaxially and detachably connected with the fixed tubing, and the heat preservation tubing is covered with a heat preservation sleeve; and the probe tubing is coaxially and detachably connected with one end of the heat preservation tubing which is away from the fixed tubing. The tubing assembly can replace the two measures of water jacket furnace ground heating and hydrate inhibitor adding, and can solve various problems caused by the water jacket furnace ground heating and the hydrate inhibitor adding under the premise that hydrates are not generated after throttling. The hydrate prevention and treatment method for the gas well can solve the problem of hydrate generation after ground throttling.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of oil and gas production engineering in the petroleum industry, and particularly relates to a tubing assembly for a gas well and a hydrate prevention and treatment method for a gas well. BACKGROUND

[0002] During the production of a natural gas well, the wellhead pressure needs to be reduced to the external transmission pressure through throttling, and the throttling will cause a sharp pressure drop, which will suddenly reduce the temperature of the natural gas. If the temperature after throttling is lower than the hydrate formation temperature corresponding to the pressure after throttling, hydrates will be generated, which will block the wellbore and the surface gas production pipeline, and affect the normal production of the gas well.

[0003] The production site usually adopts a water jacket furnace ground heating, adds a hydrate inhibitor, or uses downhole throttling to prevent hydrate formation. The water jacket furnace ground heating essentially raises the temperature of the gas flow to above the hydrate formation temperature, and is an indirect heating method using water and steam as the heat transfer medium. This heating method needs to be matched with a ground heating process, equipment, and corresponding management personnel, and has a complex process, a long construction and production cycle, and needs to consume a large amount of electricity or natural gas, which has a high one-time investment and a high running and maintenance cost in the later period. The addition of a hydrate inhibitor is to lower the dew point of the natural gas, so that the gas flow does not generate hydrates at a lower temperature. There are many types of antifreeze agents, such as methanol, ethylene glycol, diethylene glycol, and calcium chloride aqueous solution. Ethylene glycol is commonly used in gas production, and can effectively inhibit the generation and aggregation of hydrates at a low dosage. However, there are problems such as a complex ethylene glycol-containing sewage treatment process, high cost, and environmental protection. The downhole throttling process uses a rope operation to set downhole throttlers at a proper position in the wellbore, and realizes the throttling and pressure reduction of the fluid in the wellbore through a throttle nozzle, so as to reduce the wellhead pressure. The fluid after throttling absorbs the heat of the formation, so that the temperature of the fluid after throttling is higher than the hydrate formation temperature, and the generation of hydrates is prevented. This method needs to lower downhole tools, which affects the dynamic monitoring and analysis of the gas well during the trial production, and affects the setting of the throttler in the well with a lot of sand and impurities, which causes the throttler to be blocked or difficult to fish. SUMMARY

[0004] The first object of the present application is to provide a tubing assembly for a gas well, which can replace the two measures of water jacket furnace ground heating and addition of a hydrate inhibitor, and solve the problems caused by the water jacket furnace ground heating and the addition of the hydrate inhibitor under the premise of ensuring that no hydrates are generated after throttling.

[0005] The second object of the present application is to provide a hydrate prevention and treatment method for a gas well, which can solve the problem of hydrate generation after ground throttling.

[0006] The present application is realized through the following technical scheme:

[0007] A tubing assembly for gas well, comprising: a lifting mechanism, a fixed tubing connected to the lifting mechanism, the fixed tubing being vertically arranged, the lifting mechanism being capable of lifting the fixed tubing along an axial direction, the fixed tubing being provided with a safety valve; a heat preservation tubing, the heat preservation tubing being coaxially and detachably connected to the fixed tubing, the heat preservation tubing being covered with a heat preservation sleeve; a probe tubing, the probe tubing being coaxially and detachably connected to an end of the heat preservation tubing away from the fixed tubing.

[0008] Optionally, the fixed tubing, the heat preservation tubing and the probe tubing are coaxially and detachably connected through threads.

[0009] Optionally, the heat preservation sleeve comprises a first half hoop, a second half hoop and a plurality of fixing members, the first half hoop and the second half hoop being capable of being embraced to form the heat preservation sleeve, the fixing members being capable of maintaining the embracing state of the first half hoop and the second half hoop.

[0010] Optionally, the fixing members are annular, and the fixing members are sleeved outside the embraced first half hoop and second half hoop.

[0011] Optionally, the heat preservation sleeve comprises a pair of fixing members; the outer diameter of the two ends of the first half hoop and the second half hoop in the length direction is smaller than the outer diameter of the middle part, so as to form a support ridge at each end; the inner diameter of the fixing members matches the outer diameter of the two ends of the first half hoop and the second half hoop in the length direction and is sleeved, and the fixing members are in contact with the support ridges.

[0012] Optionally, the outer wall of the two ends of the first half hoop and the second half hoop in the length direction is provided with external threads, the corresponding ends of the fixed tubing and the probe tubing are provided with internal threads, and the fixing members are clamped between the support ridges and the corresponding ends of the fixed tubing or the probe tubing.

[0013] Optionally, a heat preservation layer is clamped between the heat preservation sleeve and the heat preservation tubing, the heat preservation layer is uniformly applied to the outer wall of the heat preservation tubing and is compacted by the heat preservation sleeve; the material of the heat preservation layer comprises any one or a combination of more than one of aerogel felt, microporous calcium silicate, titanium ceramic heat preservation plate, aluminum silicate fiber blanket, plate-shaped aerogel and aerogel coating.

[0014] A gas well hydrate prevention and treatment method, comprising the following steps:

[0015] A predetermined length of the heat preservation tubing is lowered into the well;

[0016] After the heat preservation tubing of any one of the tubing assemblies for gas well is lowered into the well by the predetermined length, ground throttling is performed.

[0017] Optionally, the predetermined length of the heat preservation tubing lowered into the well comprises the following steps:

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

[0019] obtaining a hydrate formation temperature after ground throttling and a wellhead temperature without hydrate formation according to the wellbore temperature-pressure coupling model;

[0020] fitting parameters of any one of the tubing assemblies for gas wells with the wellbore temperature-pressure coupling model to obtain a heat preservation tubing running length-wellhead temperature model;

[0021] inputting the wellhead temperature without hydrate formation into the heat preservation tubing 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] establishing a calculation formula of a wellbore total heat transfer coefficient:

[0024]

[0025] wherein, U is the wellbore total heat transfer coefficient; R1 is a convective heat transfer thermal resistance between produced fluid and an inner wall of the tubing, in units of (m2·℃) / W; R2 is a thermal conduction thermal resistance of the tubing, in units of (m2·℃) / W; R3 is a thermal conduction thermal resistance of the heat preservation layer, in units of (m2·℃) / W; R4 is an annulus medium radiation heat transfer thermal resistance, in units of (m2·℃) / W; R5 is an annulus medium convective heat transfer thermal resistance, in units of (m2·℃) / W; R6 is a casing thermal conduction thermal resistance, in units of (m2·℃) / W; R7 is a cement layer thermal conduction thermal resistance, in units of (m2·℃) / W;

[0026] introducing a formation thermal physical property spatial distribution according to the calculation formula of the wellbore total heat transfer coefficient to establish the wellbore temperature-pressure coupling model, the wellbore temperature-pressure coupling model satisfying the following calculation formula:

[0027]

[0028] wherein, θ is an angle between the wellbore and a horizontal plane; dz is a microelement along a length of a wellbore section; cp is a constant-pressure specific heat capacity, in units of J / (kg·℃); α v is a volume expansion coefficient, in units of K -1 ; r ins is an outer diameter of the heat preservation layer, in units of m; G is a produced fluid mass flow rate, in units of kg / s; Te is an original formation temperature, in units of ℃; Ke is a formation thermal conductivity coefficient at a position of the microelement, in units of W / (m·℃); f(t D) is a dimensionless temperature; Tm is a produced fluid temperature in the tubing, in units of ℃; Ti is an inner diameter of the tubing, in units of m; Km is a thermal conductivity coefficient of the produced fluid in the tubing, in units of W / (m·℃); vm is the average flow velocity of the produced fluid in the tubing, in m / s; λ is the Darcy friction factor; and ρm is the average density of the produced fluid, in kg / m 3 .

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

[0030] The oil pipe assembly for a gas well provided by the present application has the following advantages: the heat conduction coefficient of the heat preservation pipe is greatly reduced by the heat preservation sleeve, thereby reducing the heat loss of the wellbore and increasing the wellhead temperature to be higher than the hydrate formation temperature, so that the problem of hydrate formation after throttling and cooling on the ground of the gas well is prevented; the heat preservation pipe is detachably connected with the fixed pipe to provide a connection basis for the heat preservation pipe; the extension length of the heat preservation pipe is adjusted by the lifting mechanism, so that the wellhead temperature is adjusted; the extension length of the heat preservation pipe is compensated by the probe pipe, so that the whole oil pipe assembly can be deep into the deep part of the gas well to collect natural gas. BRIEF DESCRIPTION OF DRAWINGS

[0031] The accompanying drawings, which are included to provide a further understanding of the embodiments of the present application and are incorporated in and constitute a part of this application, illustrate embodiments of the present application and, together with the description, serve to explain the principles of the present application. In the drawings:

[0032] Figure 1 A schematic view of the oil pipe assembly for a gas well provided by the present application;

[0033] Figure 2 A side sectional view of the oil pipe assembly for a gas well provided by the present application;

[0034] Figure 3 A schematic view of the oil pipe assembly for a gas well provided by the present application when working;

[0035] Figure 4 A flow chart of the gas well hydrate prevention and treatment method provided by the present application;

[0036] Figure 5 A calculation flow chart of the numerical solution program of the pseudo-three-dimensional fracture propagation model of the gas well hydrate prevention and treatment method provided by the present application;

[0037] Figure 6 A seepage model diagram of the fracture of the gas well hydrate prevention and treatment method provided by the present application;

[0038] Figure 7 The wellbore temperature-pressure coupling model diagram of the hydrate prevention and treatment method of the gas well provided by the embodiment of the present application;

[0039] Figure 8 The heat preservation tubing running length-wellhead temperature model diagram of the hydrate prevention and treatment method of the gas well provided by the embodiment of the present application.

[0040] Markings in the drawings and corresponding component names:

[0041] 10 - fixed tubing; 11 - safety valve; 20 - heat preservation tubing; 21 - heat preservation sleeve; 211 - first half hoop; 212 - second half hoop; 213 - fixing piece; 214 - support along; 22 - heat preservation layer; 30 - probe tubing. DETAILED DESCRIPTION

[0042] In order to make the purpose, technical scheme and advantages of the present application clearer, the present application is further described in detail below in combination with embodiments and drawings. The illustrative embodiments of the present application and the description thereof are only used to explain the present application and do not limit the present application.

[0043] Please refer to Figures 1 to 3 The embodiment provides a tubing assembly for a gas well, which comprises a lifting mechanism, a fixed tubing 10 connected to the lifting mechanism, the fixed tubing 10 being vertically arranged, the lifting mechanism being capable of lifting the fixed tubing 10 in the axial direction, and a safety valve 11 arranged on the fixed tubing 10; a heat preservation tubing 20, which is coaxially and detachably connected to the fixed tubing 10, and is covered with a heat preservation sleeve 21; and a probe tubing 30, which is coaxially and detachably connected to the heat preservation tubing 20 away from the fixed tubing 10.

[0044] The oil pipe assembly for gas well provided by the present application is characterized in that the heat preservation oil pipe 20 is provided and is covered with a heat preservation sleeve 21 to greatly reduce the heat conductivity coefficient thereof, thereby reducing the heat loss of the well bore, increasing the well head temperature, and making the well head temperature higher than the hydrate formation temperature, so as to prevent the problem of hydrate formation after the gas well ground throttling and temperature reduction; on this basis, the fixed oil pipe 10 is provided and is detachably connected with the heat preservation oil pipe 20, so as to provide a connection basis for the heat preservation oil pipe 20; further, the lifting mechanism is provided and is connected with the fixed oil pipe 10, so that the heat preservation oil pipe 20 can be indirectly driven to extend along the well by the lifting mechanism, so as to adjust the extension length of the heat preservation oil pipe 20 and thereby adjust the well head temperature; on this basis, the probe oil pipe 30 is provided, so as to compensate the length of the heat preservation oil pipe 20 and make the whole oil pipe assembly capable of extending to the deep part of the gas well to collect natural gas. Through the cooperation of the above components, the oil pipe assembly for gas well can solve the problem of hydrate formation after throttling, so as to replace the two measures of water jacket furnace ground heating and water hydrate inhibitor, thereby directly avoiding the problems of the two measures.

[0045] It should be noted that the lifting mechanism can be any lifting mechanism for oil pipe in the prior art, and the connection mode is generally the embracing embedding type, which is convenient for the oil pipe to be buckled and unbuckled.

[0046] Preferably, in order to facilitate the buckling and unbuckling, the fixed oil pipe 10, the heat preservation oil pipe 20 and the probe oil pipe 30 are coaxially detachably connected by threads.

[0047] In order to further explain the specific structure of the heat preservation sleeve 21, the heat preservation sleeve 21 comprises a first half hoop 211, a second half hoop 212 and a plurality of fixing members 213, the first half hoop 211 and the second half hoop 212 can embrace to form the heat preservation sleeve 21, and the fixing members 213 can maintain the embracing state of the first half hoop 211 and the second half hoop 212.

[0048] Through the above arrangement, the heat preservation sleeve 21 is assembled in an embracing manner, which does not affect the butt joint of the two ends of the heat preservation oil pipe 20 and is convenient for arranging other heat preservation materials between the outer wall of the heat preservation oil pipe 20 and the inner wall of the heat preservation sleeve 21.

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

[0050] Through the above arrangement, the first half hoop 211 and the second half hoop after embracing are fixed by sleeving and clamping, which is convenient for installation.

[0051] Preferably, in order to limit the installation position of the fastener 213 and prevent it from sliding unnecessarily along the axial direction of the heat-insulating oil pipe 20, the heat-insulating sleeve 21 includes a pair of the fasteners 213; the outer diameters of the two ends of the first clamp 211 and the second clamp 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 fastener 213 matches and fits the outer diameters of the two ends of the first clamp 211 and the second clamp 212 in the length direction, and the fastener 213 fits against the support edge 214.

[0052] With the above settings, the installation position of the fastener 213 is restricted to both ends of the insulation sleeve 21 in the axial direction. The first clamp 211 and the second clamp 212 are clamped from both ends, which facilitates installation. The insertion depth of the fastener 213 is limited by the support 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] To further improve the insulation performance of the insulated oil pipe 20 and the insulation sleeve 21, and to further limit the fixing member 213, 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 protruding oil pipe 30 are provided with internal threads, and the fixing member 213 is clamped between the support edge 214 and the corresponding end of the fixed oil pipe 10 or the protruding oil pipe 30.

[0054] With the above settings, when the heat-insulating oil pipe 20 is connected to the fixed oil pipe 10 and the protruding oil pipe 30, the two ends of the heat-insulating sleeve 21 in the length direction are screwed into the fixed oil pipe 10 and the protruding oil pipe 30, which increases the contact area of ​​the sealing surface of the connection end, further improving the heat insulation performance of the heat-insulating oil pipe 20. In addition, the end faces of the fixed oil pipe 10 and the protruding oil pipe 30 can press the fixing member 213 tightly, completely limiting the fixing member 213, making the structure more stable.

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

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

[0057] S0, gas well production capacity forecast;

[0058] S1, obtaining a preset length of the heat preservation tubing to be lowered;

[0059] S2, after the heat preservation tubing 20 of any one of the tubing assemblies for gas wells is lowered into the well by the preset length, ground throttling is performed.

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

[0061] S01, establishing a quasi-three-dimensional acid-etched fracture extension model;

[0062] Specifically, gas well reservoir reconstruction is an effective means to improve gas well production, and currently, reservoir reconstruction is carried out before gas well production. The productivity after gas well reconstruction is an important parameter affecting the depth of heat preservation tubing to be lowered, affecting the heat preservation effect and economy. Based on the existing two-dimensional acid fracturing model, only the flow of fluid along the length direction of the fracture and the diffusion mass transfer along the fracture wall are considered, and the flow of acid in the height direction of the fracture and the change of acid concentration with time are ignored. When the reservoir longitudinal heterogeneity is obvious, the simulation result is often inaccurate. In view of the problem that the etching degree of acid-etched fracture changes over time, a quasi-three-dimensional acid fracturing fracture extension model considering acid etching-acid loss is established by using Newton iteration method, which improves the prediction accuracy of acid-etched fracture shape;

[0063] Four basic equations constituting the quasi-three-dimensional fracture extension model are obtained, which are as follows:

[0064] (1) continuity equation:

[0065]

[0066] (2) fluid pressure drop equation:

[0067]

[0068] (3) fracture width equation:

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

[0070] (4) fracture height control equation:

[0071]

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

[0073]

[0074] First, assume that the injection time is t, and the fracture length is L fThe crack is divided into several elements along its length. The standard fourth-order Runge-Kutta method is used to solve the crack height control equation. The height h(x,t) and displacement q(x,t) of each element section are solved using initial and boundary conditions. The net crack pressure p(x,t) and crack width w(x,t) are then calculated. The flow rate to the crack opening is used as a criterion for the next iteration. Finally, L is calculated using volume conservation. f (t). Assuming the crack length L... f And calculate L f (t) is compared until the given accuracy requirement is met. Calculations show that this method has good convergence and fast computational efficiency. The computation flowchart is as follows. Figure 5 As shown;

[0075] Based on the above derivation, a numerical solution program for a pseudo-three-dimensional crack propagation model was developed using Matlab software, and calculations were performed for the case where the stress in the crack bottom layer and the cap layer is symmetrical.

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

[0077] Specifically, based on the trilinear principle, a production capacity prediction model for low-permeability gas reservoirs was established, considering the effects of fracture morphology, stress sensitivity, slippage effect, and high-speed non-Darcy flow in the fractures. The gas flow from the reservoir to the fracture opening is considered to consist of two parts: first, the radial flow within the reservoir matrix, including radial flow at the fracture tip and linear flow on both sides of the fracture; second, the flow within the fracture from the fracture tip to the bottom of the well. The fracture flow model is shown in the figure below. Figure 6 As shown;

[0078] The flow equations between the crack mesh and the matrix, and between the crack meshes, are as follows:

[0079]

[0080] The model is solved using an iterative method from the end of the fracture to the fracture opening. The outflow of the grid block at the fracture opening, Q1, is the fracture production, i.e., the production after fracturing.

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

[0082] S11. Establish a wellbore temperature-pressure coupling model;

[0083] S12. Based on the wellbore temperature-pressure coupling model, obtain the hydrate formation temperature after surface throttling and the wellhead temperature at which no hydrate is formed;

[0084] S13. Fit any of the above parameters of the tubing assembly used in gas wells to the wellbore temperature-pressure coupling model to obtain the insulated tubing length-wellhead temperature model.

[0085] S14, the hydrate is not generated wellhead temperature into the length of the heat preservation tubing model, get the preset length.

[0086] Further optionally, the establishment 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, and each link in the fluid lifting process is quantified and integrated, and the calculation formula of the total heat transfer coefficient of the wellbore based on the outer diameter of the heat preservation layer is established:

[0088]

[0089] Wherein: U is the total heat transfer coefficient of the wellbore; R1 is the convective heat transfer resistance between the produced fluid and the inner wall of the tubing, with the unit of (m2·℃) / W; R2 is the thermal resistance of the tubing, with the unit of (m2·℃) / W; R3 is the thermal resistance of the heat preservation layer, with the unit of (m2·℃) / W; R4 is the radiation heat transfer resistance of the annulus medium, with the unit of (m2·℃) / W; R5 is the convective heat transfer resistance of the annulus medium, with the unit of (m2·℃) / W; R6 is the thermal resistance of the casing, with the unit of (m2·℃) / W; R7 is the thermal resistance of the cement layer, with the unit of (m2·℃) / W;

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

[0091]

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

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

[0094] S131, given different production, using wellbore temperature-pressure coupling model to predict wellhead temperature and pressure, taking wellbore and ground flow as a unified production system, according to the predicted wellhead temperature and pressure, combining with the pressure transmission, using graphical method or empirical formula method to predict the hydrate formation temperature after ground throttling and the wellhead temperature without hydrate formation, specifically as shown in the following table: Figure 7

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

[0096] S141, set different lengths of heat preservation tubing and ordinary tubing combination, given production parameters, using wellbore temperature-pressure coupling model to calculate wellhead temperature. When the wellhead temperature is higher than the hydrate formation temperature, the ground does not generate hydrate, that is, the minimum length of the heat preservation tubing is determined, as shown in the following table:

[0097] Hydrate formation temperature corresponding to different wellhead pressure

[0098]

[0099] It should be noted that the heat preservation tubing length-wellhead temperature model is as shown in Figure 8

[0100] The above specific embodiments further illustrate the purpose, technical solutions and beneficial effects of the present application. It should be understood that the above description is only a specific embodiment of the present application and is not used to limit the protection scope of the present application. Any modification, equivalent replacement, improvement, etc. within the spirit and principles of the present application should be included in the protection scope of the present application.​​

Claims

1. A method for preventing and controlling gas well hydrates, characterized in that, Includes a tubing assembly for a gas well, the tubing assembly comprising: A lifting mechanism is connected to a fixed oil pipe (10), the fixed oil pipe (10) is vertically arranged, the lifting mechanism can make the fixed oil pipe (10) move up and down along the axis, and the fixed oil pipe (10) is equipped with a safety valve (11). Insulated oil pipe (20), the insulated oil pipe (20) is coaxially and detachably connected to the fixed oil pipe (10), and the insulated oil pipe (20) is covered with an insulation sleeve (21). An inserting oil pipe (30) is provided, wherein the inserting oil pipe (30) is coaxially and detachably connected to the end of the heat-insulating oil pipe (20) away from the fixed oil pipe (10); Includes the following steps: The preset length of the insulated oil pipe (20) is obtained; After the insulated oil pipe (20) is lowered into the well to the preset length, surface throttling is implemented; The process of obtaining the preset length of the insulated oil pipe (20) includes the following steps: Establish a wellbore temperature-pressure coupling model; Based on the wellbore temperature-pressure coupling model, the hydrate formation temperature after surface throttling and the wellhead temperature at which hydrates do not form are obtained. The parameters of the tubing assembly are fitted with the wellbore temperature-pressure coupling model to obtain the insulated tubing (20) running length-wellhead temperature model; The wellhead temperature at which no hydrate is generated is introduced into the length-wellhead temperature model of the insulated tubing (20) to obtain the preset length; The establishment of the wellbore temperature-pressure coupling model includes the following steps: Establish the formula for calculating the overall heat transfer coefficient of the wellbore: ； in: U is the overall heat transfer coefficient of the wellbore; R1 is the convective heat transfer resistance between the product fluid and the inner wall of the tubing, with units of (m2·℃) / W; R2 is the thermal resistance of the oil pipe, expressed in (m2·℃) / W; R3 is the thermal resistance of the insulation layer, with units of (m2·℃) / W; R4 is the thermal resistance of the annular medium for radiative heat transfer, with units of (m2·℃) / W; R5 is the thermal resistance of the annular medium for convective heat transfer, with units of (m2·℃) / W; R6 is the thermal resistance of the bushing, with units of (m2·℃) / W; R7 is the thermal resistance of the cement layer, expressed in (m2·℃) / W. Based on the calculation formula for the overall heat transfer coefficient of the wellbore, and introducing the spatial distribution of formation thermal properties, a temperature-pressure coupling model for the wellbore is established. This temperature-pressure coupling model satisfies the following calculation formula: ； in: θ is the angle between the well shaft and the horizontal plane; dz is a infinitesimal element taken along the length of the wellbore; cp is the specific heat capacity at constant pressure, expressed in J / (kg·℃). α v The volumetric expansion coefficient is expressed in K. -1 ; r ins This refers to the outer diameter of the insulation layer, in meters (m). G represents the product liquid mass flow rate, in kg / s; Te represents the original formation temperature, in °C. Ke is the thermal conductivity of the formation at the location of the micro-element, with units of W / (m·℃); f(t D) is the dimensionless temperature; Tm is the temperature of the produced fluid inside the tubing, in °C. Ti is the inner diameter of the oil pipe, in meters (m). Km is the thermal conductivity of the fluid produced in the tubing, expressed in W / (m·℃). ν m The average flow velocity of the produced fluid inside the tubing is expressed in m / s. λ is the Darcy friction coefficient; ρm is the average density of the product liquid, in kg / m³. 3 ; p is the wellbore pressure, in MPa; T represents the wellbore temperature, measured in °C. g is the acceleration due to gravity, and its unit is m / s². 2 .

2. The method for preventing gas well hydrates according to claim 1, characterized in that, The fixed oil pipe (10), the heat-insulating oil pipe (20), and the probing oil pipe (30) are detachably connected by a threaded coaxial connection.

3. The method for preventing gas well hydrates according to claim 1, characterized in that, The insulation sleeve (21) includes a first half-hoop (211), a second half-hoop (212) and several fasteners (213). The first half-hoop (211) and the second half-hoop (212) can be joined together to form the insulation sleeve (21), and the fasteners (213) can maintain the joined state of the first half-hoop (211) and the second half-hoop (212).

4. The method for preventing gas well hydrates according to claim 3, characterized in that, The fastener (213) is annular and is fitted around the first half-hoop (211) and the second half-hoop (212) that are wrapped together.

5. The method for preventing gas well hydrates according to claim 4, characterized in that, The insulation sleeve (21) includes a pair of the fasteners (213); The outer diameters at both ends of the first half-hoop (211) and the second half-hoop (212) in the length direction are smaller than the outer diameter of the middle part, so that support edges (214) are formed at both ends respectively. The inner diameter of the fastener (213) matches and is fitted with the outer diameters of the two ends of the first half hoop (211) and the second half hoop (212) along their length direction. The fastener (213) is in contact with the support edge (214).

6. The method for preventing gas well hydrates according to claim 5, characterized in that, The outer walls of the first half-hoop (211) and the second half-hoop (212) in the length direction are provided with external threads, and the corresponding ends of the fixed oil pipe (10) and the probing oil pipe (30) are provided with internal threads. The fixing member (213) is clamped between the support edge (214) and the corresponding end of the fixed oil pipe (10) or the probing oil pipe (30).

7. The method for preventing gas well hydrates according to any one of claims 1-6, characterized in that, An insulation layer (22) is sandwiched between the insulation sleeve (21) and the insulation oil pipe (20). The insulation layer (22) is evenly applied to the outer wall of the insulation oil pipe (20) and compacted by the insulation sleeve (21). The materials of the insulation layer (22) include any one or more combinations of aerogel felt, microporous calcium silicate, titanium ceramic insulation board, aluminum silicate fiber blanket, plate aerogel and aerogel coating.

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