Optimization design method for controlling leakage pressure rise of production pipe column

Abstract

The invention relates to an optimal design method for controlling leakage pressure rise of a production pipe column. The method comprises the steps that whether annulus liquid in an oil sleeve annulus of a target gas well leaks or not is determined; if the annulus liquid in the oil sleeve annulus of the target gas well does not leak, the depth of a leakage point of the production pipe column is determined; under the condition that the depth of the leakage point is determined, a first changing curve of the maximum pressure value of the oil sleeve annulus along with the annulus liquid density is determined; according to the pressure bearing capacity of an oil pipe head, a production pipe column, a production casing and a packer, a second changing curve of the maximum value of the pressure control range of the oil sleeve annulus along with the annulus liquid density is determined; and the annulus liquid density is optimized and determined according to the first change curve and the second change curve, so that the oil sleeve annulus pressure is reduced to be within a safety threshold value. The annular pressure of the oil sleeve can be reduced to be within the safety threshold value on the premise that a production pipe column is not replaced and a well is not overhauled, the pipe column leakage pressure rising phenomenon is effectively controlled, the phenomenon that the pressure bearing capacity of a shaft is exceeded is avoided, the control cost is reduced, and the maintenance period is shortened.

Description

Technical Field

[0001] The present application relates to the field of natural gas wellbore safety control, and in particular to an optimization design method for controlling the pressure rise of a production pipe column leakage. Background Art

[0002] With the rapid development of the national economy and the continuous improvement of environmental protection requirements, the consumption of natural gas has continued to increase, prompting the exploration and development of natural gas to advance into deep formations. At the same time, the supply and price of natural gas are greatly affected by the international situation and there is a seasonal peak in consumption. A large number of underground gas storage facilities need to be built to ensure the balance of supply and demand of natural gas. The production of natural gas depends on the wellbore and production string. The production string, also known as the oil pipe, is made of metal oil pipes connected by threads. As the production channel of natural gas from underground to the ground, the production string is subjected to complex loads and harsh temperature and pressure conditions. In some cases, it is accompanied by corrosive gases such as hydrogen sulfide and carbon dioxide. There will be various forms of leakage such as pipe wall corrosion perforation, stress cracking, coupling disengagement and thread seal failure, forming a gas-liquid interaction channel between the oil casing annulus and the oil pipe, which in turn causes the oil casing annulus pressure to rise, forming a leakage and pressure-increasing phenomenon in the production string.

[0003] The potential safety hazards caused by the leakage of production tubing are huge, especially when the annular pressure of the casing exceeds the bearing capacity of the wellbore. The potential safety hazards are mainly reflected in three aspects: first, the wellbore safety barrier is damaged. The high pressure of the annular pressure of the casing will cause accidents such as wellhead lifting, cement ring cracking and pipe column crushing; second, the flammable gas gathers in large quantities in the annular space, and there is a risk of leakage and fire; third, environmental pollution, natural gas will enter the shallow soil or groundwater along the leakage channel in the wellbore, and in some cases continue to release methane into the atmosphere, forming a source of greenhouse gas leakage. Therefore, when the production tubing leaks, effective measures need to be taken to reduce the annular pressure of the casing caused by the leakage to prevent the annular pressure of the casing from exceeding the bearing capacity of the wellbore.

[0004] However, the existing risk management of production tubing leakage is highly dependent on overhaul operations, which mainly rely on replacing the production tubing to control leakage pressure. The operation cost is high, and there are risks of tubing breakage, reservoir contamination and well control during the overhaul process. Chemical plugging faces the challenges of high temperature and high pressure, pipe wall contamination and lack of pressure barriers, making it difficult to achieve effective plugging.

[0005] Therefore, it is urgent to provide an optimized design method for controlling the leakage pressure of the production tubing string to solve the above-mentioned technical problems. Summary of the invention

[0006] The present application provides an optimized design method for controlling the pressure buildup due to leakage of a production string, which can reduce the casing annulus pressure to within a safe threshold without replacing the production string or overhauling the well, thereby effectively controlling the pressure buildup due to leakage of the production string and avoiding exceeding the pressure bearing capacity of the wellbore, thereby reducing the control cost and maintenance cycle, and achieving continuous high-intensity production of the gas well.

[0007] In a first aspect, the present application provides an optimization design method for controlling leakage pressure of a production tubing string, comprising the following steps:

[0008] Step 1: Determine whether the annular space liquid in the oil-casing annulus of the target gas well is lost; wherein the oil-casing annulus is composed of a tubing head, a production string, a production casing and a packer;

[0009] Step 2: If the annular space liquid in the oil casing annulus of the target gas well does not leak, then determine the leakage point depth of the production string;

[0010] Step 3: Under the condition of determining the depth of the leakage point, determine the first curve of the maximum pressure of the casing annulus and the change of the density of the annulus liquid;

[0011] Step 4: According to the pressure bearing capacity of the tubing head, production string, production casing and packer, determine the second curve of the maximum value of the pressure control range of the casing annulus as the density of the annulus liquid changes;

[0012] Step 5: Optimize and determine the annulus liquid density according to the change curve 1 and the change curve 2 to reduce the pressure of the oil casing annulus to within the safety threshold.

[0013] Preferably, the method of determining whether the annular liquid in the casing annulus of the target gas well has been lost comprises: based on the target gas well where the production string has leaked, determining whether the annular liquid has been lost by monitoring the annular liquid level in the casing annulus, and defining the annular liquid level fluctuation amplitude by dividing the difference between the maximum and minimum annular liquid level depths within a specific monitoring time by the maximum well depth; when the annular liquid level fluctuation amplitude does not exceed a threshold value within a specific time, it is considered that the annular liquid has not been lost; when the annular liquid level fluctuation amplitude exceeds a threshold value within a specific time, it is considered that the annular liquid has been lost.

[0014] Preferably, if the annular space liquid in the oil casing annulus of the target gas well does not leak, determining the leakage point depth of the production string includes:

[0015] Step 2.1: Obtain the pressure profile in the production string under shut-in conditions;

[0016] Step 2.2: Calculate and determine the pressure profile in the casing annulus based on the gas column and liquid column pressures;

[0017] Step 2.3: Based on the pressure difference between the pressure profile in the production string and the pressure profile in the casing annulus as the driving force of the leakage, the variation law of the maximum value of the casing annulus pressure with the depth of the leakage point is analyzed and determined to obtain the variation curve 3;

[0018] Step 2.4: According to the casing annulus pressure calculated under the shut-in condition, the leakage point depth corresponding to the pressure value on the variation curve 3 is the leakage point depth of the production string.

[0019] Preferably, the step 2.1: obtaining the pressure profile in the production string under the shut-in condition comprises: closing the wellhead of the target gas well, recording the corresponding casing annulus pressure and the wellhead oil pressure, and then lowering a pressure gauge into the well to obtain the pressure profile in the production string;

[0020] Alternatively, the production string is segmented, the gas density in the segment is calculated based on the pressure and temperature, and then the pressure in the production string at the corresponding depth is calculated.

[0021] Preferably, the step of segmenting the production string, calculating the gas density in the segment according to the pressure and temperature, and then calculating the pressure in the production string at the corresponding depth comprises:

[0022] According to the PVT equation of the gas, the gas density is obtained, and the gas density can be described by the following formula:

[0023]

[0024] In the formula, ρ gi is the gas density of the i-th segment, g / cm 3 ;pt i is the pressure in the production string of the i-th segment, MPa; p s is the standard pressure, Pa; T s is the standard temperature, K; T ti is the temperature inside the production string of the i-th segment, i.e., the formation temperature, K; ρ gs is the standard density of the gas, g / cm 3 ; i is the segment number, dimensionless, i = 1, 2, 3...;

[0025] The temperature inside the production string of the i-th segment, that is, the formation temperature, is calculated using the following formula:

[0026] T ti =T t0 +g e ×i×H F (4)

[0027] Where, T t0 is the wellhead, K; g eis the geothermal gradient, K / 100m; H F is the segment length, m;

[0028] The pressure in the production string at the corresponding segment depth is calculated according to the gas density, as shown in the formula:

[0029] p ti+1 =p ti +10 -3 ×ρ gi ×g×H F (5)

[0030] In the formula, p ti+1 is the pressure in the production string of the i+1th segment, MPa; g is the acceleration of gravity, m / s 2 According to the above steps, the pressure inside the production string at the corresponding depth is calculated from the wellhead to the well bottom.

[0031] Preferably, the step 2.2: calculating the pressure profile in the casing annulus according to the gas column and liquid column pressures includes: calculating the gas density in the casing annulus. Since the length of the gas column in the casing annulus is short, the influence of the formation temperature on the gas density is no longer considered. The gas density in the casing annulus is expressed by the following formula:

[0032]

[0033] In the formula, ρ ga is the gas density in the casing annulus, g / cm 3 ; T ta is the wellhead temperature of the casing annulus, K;

[0034] According to the casing annulus pressure profile located above the casing annulus liquid level, it is only related to the annular gas column, and the casing annulus pressure profile located below the annular liquid level is affected by both the gas column and the liquid column pressure. The casing annulus pressure profile is calculated respectively, wherein, when calculating the profile, the casing annulus pressure is preset to be zero, which is expressed by the following formula:

[0035]

[0036] In the formula, H ta is the casing annulus depth, m; p ta Depth H ta The value of the casing annulus pressure profile, MPa; ρ ga is the gas density in the casing annulus, g / cm 3 , ρ L is the density of the annular liquid in the casing annulus, g / cm 3 ;pa casing annulus pressure, MPa.

[0037] Preferably, in step 2.3: based on the pressure difference between the pressure profile in the production tubing and the pressure profile in the casing annulus as the driving force for leakage, the maximum value of the casing annulus pressure is analyzed and determined as the variation law of the leakage point depth, and a variation curve 3 is obtained, including: according to the leakage driving force coming from the pressure difference on both sides of the leakage point, the pressure inside the leakage point depends on the pressure profile in the production tubing at the depth of the leakage point, and the pressure outside the leakage point depends on the pressure profile in the casing annulus at the depth of the leakage point, which is expressed by the following formula:

[0038]

[0039] In the formula, p ln Indicates the pressure inside the leak point, MPa; p lw Indicates the pressure outside the leakage point, MPa; H is the well depth, m; H L is the well depth of the leak point, m; p tL is the pressure value corresponding to the pressure profile in the production string at the depth of the leakage point, MPa; p taL is the pressure value corresponding to the casing annulus pressure profile at the depth of the leakage point, MPa;

[0040] After the production string leaks, the production string, the leak point and the casing annulus form a U-shaped tube. According to the U-shaped tube principle, when the casing annulus pressure reaches the maximum value, the pressure inside and outside the leak point are equal. The maximum casing annulus pressure corresponding to the leak points at different depths is determined and expressed by the following formula;

[0041] p anmax =p ln -p lw |H=H L (9)

[0042] In the formula, p anmax is the maximum value of casing annulus pressure, MPa;

[0043] According to the depth from the wellhead to the packer of the target gas well, the depth of the leakage point is changed, and according to the variation law of the maximum value of the casing annulus pressure with the depth of the leakage point, the variation curve 3 is obtained.

[0044] Preferably, the step 3: determining the maximum pressure of the casing annulus as the density of the annulus liquid changes curve 1 according to the determined leakage point depth, includes: when the leakage point depth is below the annulus liquid level, the pressure outside the leakage point is affected by the pressure of the annulus liquid column, and the pressure of the annulus liquid column is related to the density of the annulus liquid;

[0045] According to the known depth of the leakage point, the relationship between the maximum annular pressure caused by the leakage pressure and the annular liquid density is established and expressed by the following formula:

[0046] p amaxL =p lnL -10 -3 ×[(ρ ga ×g×H max )+ρ L ×g×(H LD -H max )] (11)

[0047] In the formula, p anmaxL To determine the maximum annular pressure of the casing at the depth of the actual leakage point of the gas well, MPa, ρ ga is the gas density in the casing annulus, g / cm3, ρ L is the density of the annular liquid in the casing annulus, g / cm3; p lnL is the pressure inside the leakage point when the leakage point depth is known to be HL, MPa; according to the density of the annular space liquid, the maximum pressure of the casing annulus is obtained as the density of the annular space liquid changes.

[0048] Preferably, the step 4: determining the second curve of the maximum value of the pressure control range of the casing annulus as the density of the annulus liquid changes according to the pressure bearing capacity of the tubing head, the production tubing string, the production casing and the packer, comprises: based on the maximum value of the pressure control range of the casing annulus, the pressure bearing capacity of the tubing head, the production tubing string, the production casing and the packer needs to be guaranteed, and the pressure bearing capacity of the tubing head, the production tubing string, the production casing and the packer is calculated respectively to determine the maximum value of the pressure control range of the casing annulus; wherein the maximum value of the pressure control range of the casing annulus determined by the tubing head is 80% of its rated pressure bearing capacity, which is expressed by the following formula:

[0049] p 1 =0.8×p 额 (12)

[0050] In the formula, p 1 The maximum value of the casing annulus pressure control range determined by the tubing head, MPa; p 额 is the rated pressure resistance of the tubing head, MPa;

[0051] The maximum value of the pressure control range of the casing annulus determined by the production string is the anti-external collapse strength of the production string under the conditions of well opening and well closing, which is expressed by the following formula:

[0052]

[0053] In the formula, p 2 The maximum value of the casing annulus pressure control range determined by the production string, MPa; p 挤is the minimum collapse strength of the production string in the gas well, MPa; S 2 is the safety factor against external collapse, dimensionless; p t2 is the pressure inside the tubing string corresponding to the depth where the minimum anti-external collapse strength of the production string is, MPa; h 2 The depth of the minimum anti-external collapse strength of the production string, m;

[0054] The maximum value of the control range of the casing annulus pressure determined by the production casing is the internal pressure resistance of the production casing, which is expressed by the following formula:

[0055]

[0056] In the formula, p 3 The maximum value of the casing annulus pressure control range determined by the production casing, MPa; p 内 is the minimum internal pressure strength of the production casing, MPa; S 3 is the safety factor of the production casing against internal pressure, dimensionless; p b is the pressure value of annulus B, MPa; ρ b is the equivalent brine density of annulus B, g / cm 3 ;h 3 is the depth of the minimum internal pressure strength of the production casing, m;

[0057] The maximum value of the pressure control range of the casing annulus determined by the packer is the limit of the packer setting pressure, which is expressed by the following formula:

[0058] p 4 =p 封 +p 下 -10 -3 ρ L gh 4 (15)

[0059] In the formula, p 4 is the maximum value of the casing annulus pressure control range determined by the packer, MPa; p 封 is the packer setting working pressure difference, MPa; p 下 is the pressure at the lower end of the packer, MPa; h 4 is the depth from the annulus protection fluid level to the packer, m;

[0060] The maximum value of the pressure control range of the casing annulus is obtained according to the minimum value of the maximum values ​​of the pressure control range of the casing annulus determined by the tubing head, the production string, the production casing and the packer, and is expressed by the following formula;

[0061] Δp aA =min(p 1 , p 2 , p3 , p 4 ) (16)

[0062] Where △pa A is the maximum value of the pressure control range of the casing annulus, MPa;

[0063] According to the transformation of the annular space liquid density, a second curve of the maximum value of the pressure control range of the casing annular space and the change of the annular space liquid density is obtained.

[0064] Preferably, the step 5: optimizing and determining the annular space liquid density according to the change curve 1 and the change curve 2 to reduce the pressure of the casing annular space to within the safety threshold, comprises: drawing a change curve 1 of the maximum pressure of the casing annular space along with the change curve of the annular space liquid density, and a change curve 2 of the maximum pressure control range of the casing annular space along with the change curve of the annular space liquid density in the same coordinates;

[0065] When the casing annulus pressure is less than the casing annulus force control range, the corresponding annulus liquid density is the required optimized annulus liquid density value;

[0066] When the density value does not exist or is too large, the depth of the annular liquid surface is increased, and then the above steps 2 to 5 are repeated to redetermine the annular liquid density.

[0067] This application has at least the following advantages:

[0068] (1) Effectively control the leakage and pressure-increasing phenomenon of the production string without moving the production string and avoiding major repairs, so as to avoid exceeding the pressure bearing capacity of the wellbore, thereby reducing the control cost and maintenance cycle, and achieving continuous high-intensity production of the gas well;

[0069] (2) No additional equipment is required, and the production string does not need to be lifted for overhaul. The cost is low, the effect lasts for a long time, and the annular pressure will not rise repeatedly;

[0070] (3) It has a wide range of applications and is suitable for gas storage injection and production wells and high-pressure gas wells. BRIEF DESCRIPTION OF THE DRAWINGS

[0071] Figure 1 A schematic diagram showing a wellbore structure in one embodiment;

[0072] Figure 2 A schematic diagram of the steps of an optimization design method for controlling the pressure rise of a production tubing column leakage in one embodiment;

[0073] Figure 3 A curve showing the maximum pressure of the casing annulus as a function of the depth of the leak point in one embodiment - a schematic diagram of locating the leak point;

[0074] Figure 4A schematic diagram of optimizing the density value of annular space liquid in one embodiment;

[0075] Figure 5 FIG. 4 is a schematic structural diagram of a computer device in one embodiment.

[0076] Figure numerals: 1, formation; 2, cement ring; 3, production casing; 4, production tubing string; 5, packer; 6, reservoir; 7, wellhead; 8, annulus liquid; 9, annulus gas; 10, casing annulus liquid level. DETAILED DESCRIPTION

[0077] The present application is further described in detail below in conjunction with the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are only used to explain the present application and are not used to limit the present application.

[0078] It should be noted that the terms used herein are only for describing specific embodiments and are not intended to limit the exemplary embodiments according to the present application. As used herein, unless the context clearly indicates otherwise, the singular form also means

[0079] The figures include plural forms, and further, it should be understood that when the terms “include” and / or “comprise” are used in this specification, they indicate the presence of features, steps, operations, devices, components and / or their combinations.

[0080] To make the purpose, technical scheme and advantages of the embodiments of the present application clearer, the embodiments of the present application will be described in detail below in conjunction with the accompanying drawings. However, it will be appreciated by those skilled in the art that in the embodiments of the present application, many technical details are proposed in order to enable the reader to better understand the present application. However, even without these technical details and various changes and modifications based on the following embodiments, the technical scheme claimed in the present application can also be implemented. The markings of the following embodiments are for convenience of description and should not constitute any limitation to the specific implementation of the present application. The various embodiments can be combined with each other and quoted from each other without contradiction.

[0081] Please refer to Figure 1As shown, the wellbore serves as a channel for oil and gas production and carbon energy injection / extraction. The wellbore structure generally includes a production casing 3 arranged in a wellhead 7. The lower end of the production casing 3 is inserted into the reservoir 6. The space formed between the production casing 3 and the formation 1 (the side wall of the wellhead 7) is the casing annulus. The casing annulus is filled with a cement ring 2. The cement ring 2 plays a role in fixing the production casing 3, preventing the production casing 3 from corrosion and preventing the fluids of different layers from communicating with each other to achieve a cementing effect. A production string 4 is arranged in the middle position of the production casing 3. The area enclosed by the production string 4 and the production casing 3 is the oil-casing annulus. The oil-casing annulus is filled with annular space liquid 8 and annular space gas 9. The interface between the annular space liquid 8 and the annular space gas 9 is the oil-casing annular space liquid level 10. A packer 5 is arranged at the bottom of the production casing 3. The lower end of the production string 4 passes through the packer 5. It can be understood that the oil-casing annulus consists of a tubing head, a production casing 3, a production string 4 and a packer 5.

[0082] Please refer to Figure 2 As shown, the present application provides an optimization design method for controlling the pressure rise of a production string leakage, comprising the following steps:

[0083] S201: Determine whether annular space liquid in the oil-casing annulus of the target gas well is lost; wherein the oil-casing annulus is composed of a tubing head, a production string, a production casing and a packer;

[0084] S202: If the annular space liquid in the oil casing annulus of the target gas well has not been lost, determining the leakage point depth of the production string;

[0085] S203: Determine a curve 1 of the maximum pressure of the casing annulus as the density of the annulus liquid changes according to the determined depth of the leakage point;

[0086] S204: according to the pressure bearing capacity of the tubing head, the production string, the production casing and the packer, determine the second curve of the maximum value of the pressure control range of the casing annulus as the density of the annulus liquid changes;

[0087] S205: Optimizing and determining the annulus liquid density according to the change curve 1 and the change curve 2 to reduce the pressure of the oil casing annulus to within a safety threshold.

[0088] In the embodiment of the present application, the density of the annular space liquid in the casing annulus is optimized, and the casing annulus pressure is then reduced to within the safety threshold, thereby effectively controlling the safety risks caused by the leakage and pressure rise of the production string. More importantly, the leakage and pressure rise of the production string are effectively controlled without moving the production string and avoiding major repairs, avoiding exceeding the pressure bearing capacity of the wellbore, thereby reducing the management and control costs and maintenance cycle, and achieving continuous high-intensity production of the gas well.

[0089] The following is a detailed description of each step:

[0090] S201: Determine whether annular space liquid in the oil-casing annulus of the target gas well is lost; wherein the oil-casing annulus is composed of a tubing head, a production string, a production casing and a packer;

[0091] In this embodiment, it should be noted that it is first necessary to determine whether the annular liquid in the oil casing annulus of the target gas well has been lost, so as to determine the applicability of the optimization design method of the present application. Specifically, for the target gas well with a leak in the production string, the annular liquid level in the oil casing annulus is monitored to determine whether the annular liquid has been lost, wherein the monitoring method may be but is not limited to acoustic liquid level monitoring, etc. The annular liquid level fluctuation amplitude is defined as: the difference between the maximum and minimum annular liquid level depths monitored within a specific time divided by the maximum well depth, wherein the specific time may be but is not limited to 24 hours, and the monitoring frequency may be but is not limited to 12 hours, but the total number of monitoring times within the specific monitoring time should not be less than 2 times, which is expressed by the following formula (1):

[0092]

[0093] In the formula, F 1 is the fluctuation amplitude of the annular liquid level, dimensionless; H max is the maximum depth of the annular liquid level, m; H min is the minimum depth of the annulus liquid level, m; H W is the maximum well depth, m;

[0094] When the fluctuation amplitude of the annular liquid level within a specific time does not exceed the threshold, it is considered that the annular liquid has not been lost; when the fluctuation amplitude of the annular liquid level within a specific time exceeds the threshold, it is considered that the annular liquid has been lost. The threshold may be, but is not limited to, 0.01.

[0095] Because the present application controls the pressure buildup due to leakage of the production tubing by optimizing the density of the annular liquid, the control effect will be weakened when the annular liquid leaks. Therefore, the optimization design method provided by the present application is not suitable for situations where the annular liquid leaks. When the annular liquid has not leaked, the optimization design scheme provided by the present application can be used to control the pressure buildup due to leakage of the production tubing.

[0096]

[0097] Where F is the threshold for judging whether the method is applicable and is dimensionless.

[0098] S202: If the annular space liquid in the oil casing annulus of the target gas well has not been lost, determining the leakage point depth of the production string; specifically including:

[0099] S202.1: Obtain the pressure profile in the production string under shut-in conditions;

[0100] S202.2: Calculate the pressure profile in the casing annulus based on the gas column and liquid column pressure;

[0101] S202.3: Based on the pressure difference between the pressure profile in the production string and the pressure profile in the casing annulus as the driving force of the leakage, determine the variation law of the maximum value of the casing annulus pressure with the depth of the leakage point, and obtain variation curve 3;

[0102] S202.4: Based on the casing annulus pressure calculated under the shut-in condition, the leakage point depth corresponding to the pressure value on the variation curve 3 is the leakage point depth of the production string.

[0103] The following is a detailed description. In this embodiment, it should be noted that for gas wells applicable to the optimization design method of the present application, the first step is to determine the depth of the leakage point, mainly by drawing a curve of the maximum annular pressure changing with the depth of the leakage point. To draw the change curve, it is first necessary to determine the pressure profile in the production string and the casing annulus pressure profile under the shut-in condition. Specifically, close the wellhead of the target gas well, and record the corresponding casing annulus pressure and wellhead oil pressure. Then, lower a pressure gauge into the well to obtain the pressure profile in the production string; or, if a pressure gauge is not available, the pressure profile in the production string at the corresponding depth can be obtained by calculation. First, the production string is segmented. The segment length can be, but is not limited to, 1m. Then, based on the pressure and temperature, the gas density in the segment is calculated, and then the pressure in the production string at the corresponding depth is calculated. According to the PVT equation of the gas, the gas density is obtained, which can be expressed as:

[0104]

[0105] In the formula, ρ gi is the gas density of the i-th segment, g / cm3; p ti is the pressure in the production string of the i-th segment, MPa; p s is the standard pressure, Pa; Ts is the standard temperature, K; T ti is the temperature inside the production string of the i-th segment, i.e., the formation temperature, K; ρ gs is the standard density of the gas, g / cm3; i is the segment number, dimensionless, i=1, 2, 3...;

[0106] The temperature inside the production string of the i-th segment, that is, the formation temperature, is calculated using the following formula:

[0107] T ti =T t0 +g e ×i×H F (4)

[0108] Where, T t0is the wellhead, K; g e is the geothermal gradient, K / 100m; H F is the segment length, m;

[0109] The pressure in the production string at the corresponding segment depth is calculated based on the gas density as shown in the formula:

[0110] p ti+1 =p ti +10 -3 ×ρ gi ×g×H F (5)

[0111] In the formula, p ti+1 is the pressure in the production string of the i+1th segment, MPa; g is the acceleration of gravity, m / s 2 ;

[0112] According to the above formulas (3) to (5), the pressure profile in the production string at the corresponding depth can be obtained by calculating from the wellhead to the well bottom.

[0113] After obtaining the pressure profile in the production string, the casing annulus pressure profile is calculated. When the casing annulus pressure is zero, the casing annulus pressure profile is affected by the gas column and liquid column pressure. First, the gas density in the casing annulus is calculated. Because the length of the gas column in the casing annulus is short, the influence of the formation temperature on the gas density is no longer considered. The gas density in the casing annulus is as shown in the formula:

[0114]

[0115] In the formula, ρ ga is the gas density in the casing annulus, g / cm 3 ; T ta is the wellhead temperature of the casing annulus, K;

[0116] According to the casing annulus pressure profile located above the casing annulus liquid level, it is only related to the annular gas column, and the casing annulus pressure profile located below the annular liquid level is affected by both the gas column and the liquid column pressure. The casing annulus pressure profile is calculated respectively, wherein, when calculating the profile, the casing annulus pressure is preset to be zero, which is expressed by the following formula:

[0117]

[0118] In the formula, H ta is the casing annulus depth, m; p ta is the casing annulus pressure profile value at depth Hta, MPa; ρ ga is the gas density in the casing annulus, g / cm 3 ρ Lis the density of the annular liquid in the casing annulus, g / cm 3 .

[0119] After obtaining the pressure profiles in the production string and the casing annulus, the maximum pressure of the casing annulus is analyzed as the depth of the leak point changes. The driving force of the leak comes from the pressure difference on both sides of the leak point. The pressure inside the leak point depends on the pressure profile in the production string at the depth of the leak point. The pressure outside the leak point depends on the pressure profile of the casing annulus at the depth of the leak point, which is expressed by the following formula:

[0120]

[0121] In the formula, pl n Indicates the pressure inside the leak point, MPa; pl w Indicates the pressure outside the leakage point, MPa; H is the well depth, m; H L is the well depth of the leak point, m; pt L is the pressure value corresponding to the pressure profile in the production string at the depth of the leak point, MPa; pta L is the pressure value corresponding to the casing annulus pressure profile at the depth of the leakage point, MPa;

[0122] After the production string leaks, the production string, the leak point and the casing annulus form a U-shaped tube. According to the U-shaped tube principle, when the casing annulus pressure reaches the maximum value, the pressure inside and outside the leak point are equal. The maximum casing annulus pressure corresponding to the leak points at different depths is determined and expressed by the following formula;

[0123] p anmax =p 1n -p 1w |H=H L (9)

[0124] In the formula, p anmax is the maximum value of casing annulus pressure, MPa;

[0125] According to the depth from the wellhead to the bottom packer of the target gas well, the depth of the leakage point is changed to obtain the variation law of the maximum value of the casing annulus pressure with the depth of the leakage point, and the variation curve is plotted to obtain the variation curve 3.

[0126] According to the above recorded casing annulus pressure under shut-in conditions, the depth of the leakage point corresponding to the pressure value on the curve is the actual depth of the leakage point of the gas well production string, which is expressed by the following formula:

[0127] H LD =H L1 |p anmax =p as (10)

[0128] In the formula, H LD is the depth of the actual leakage point of the gas well, m; pa s is the casing annulus pressure recorded after shutting in the well, MPa; H L1 The depth of the leakage point corresponding to the casing annulus pressure under the shut-in condition of the leakage point, m.

[0129] S203: Determine a curve 1 of the maximum pressure of the casing annulus as the density of the annulus liquid changes according to the determined depth of the leakage point;

[0130] In this embodiment, it should be noted that, according to the depth of the leak point, the maximum pressure of the casing annulus changes with the density of the annular liquid under the condition of a fixed depth leak point. When the depth of the leak point is below the annular liquid surface, the pressure outside the leak point is affected by the pressure of the annular liquid column, and the pressure of the annular liquid column is related to the density of the annular liquid; under the condition that the depth of the leak point is known, the relationship between the maximum annular pressure caused by the leakage pressure and the density of the annular liquid can be established, which is expressed by the following formula:

[0131] p amaxL =p lnL -10 -3 ×[(ρ ga ×g×H max )+ρ L ×g×(H LD -H max )] (11)

[0132] Where panmax L is the maximum value of the casing annulus pressure under the condition of the depth of the actual leakage point of the gas well, MPa, ρ ga is the gas density in the casing annulus, g / cm3, ρ L is the density of the annular liquid in the casing annulus, g / cm3;

[0133] By changing the density of the annular space liquid, the maximum pressure curve of the casing annular space as the density of the annular space liquid changes can be obtained.

[0134] S204: according to the pressure bearing capacity of the tubing head, the production string, the production casing and the packer, determine the second curve of the maximum value of the pressure control range of the casing annulus as the density of the annulus liquid changes;

[0135] In this implementation, it should be noted that the maximum value of the pressure control range of the casing annulus is determined by the curve 2 with the change of the annulus liquid density. First, the maximum value of the pressure control range of the casing annulus needs to ensure the pressure bearing capacity of the tubing head, production string, production casing and packer; among them, the maximum value of the pressure control range of the casing annulus determined by the tubing head is 80% of its rated pressure bearing capacity, which is expressed by the following formula:

[0136] p 1 =0.8×p 额 (12)

[0137] In the formula, p 1 is the maximum value of the casing annulus pressure control range determined by the tubing head, MPa; p is the rated pressure resistance of the tubing head, MPa;

[0138] The maximum value of the pressure control range of the casing annulus determined by the production string mainly considers the anti-external collapse strength of the production string under the conditions of well opening and well closing, which is expressed by the following formula:

[0139]

[0140] In the formula, p 2 is the maximum value of the casing annulus pressure control range determined by the production string, MPa; p squeeze is the minimum anti-external collapse strength of the production string in the gas well, MPa; S 2 is the safety factor against external collapse, dimensionless; p t2 is the pressure inside the oil pipe string corresponding to the depth where the production pipe string has the minimum anti-external collapse strength, MPa; h 2 The depth of the minimum anti-external collapse strength of the production string, m;

[0141] The maximum control range of the casing annulus pressure determined by the production casing mainly considers the casing's internal pressure resistance, which is expressed by the following formula:

[0142]

[0143] In the formula, p 3 is the maximum value of the casing annulus pressure control range determined by the production casing, MPa; p is the minimum internal pressure strength of the production casing, MPa; S 3 is the safety factor of the production casing against internal pressure, dimensionless; p b is the pressure value of annulus B, MPa; ρ b is the equivalent brine density of annulus B, g / cm 3 ;h 3 is the depth of the minimum internal pressure strength of the production casing, m;

[0144] The maximum value of the pressure control range of the casing annulus determined by the packer mainly considers the limitation of the packer setting pressure and is expressed by the following formula:

[0145] p 4 =p 封 +p 下 -10 -3 ρ L gh 4 (15)

[0146] In the formula, p 4 is the maximum value of the casing annulus pressure control range determined by the packer, MPa; p 封 is the packer setting working pressure difference, MPa; p 下 is the pressure at the lower end of the packer, MPa; h 4 is the depth from the annulus protection fluid level to the packer, m;

[0147] The maximum value of the pressure control range of the casing annulus is the minimum value of the maximum value of the pressure control range of the casing annulus determined by the tubing head, production string, production casing and packer, and is expressed by the following formula;

[0148] Δp aA =min(p 1 , p 2 , p 3 , p 4 ) (16)

[0149] In the formula, △p aA is the maximum value of the pressure control range of the casing annulus, MPa;

[0150] By changing the annular space liquid density, we can obtain the second curve of the maximum value of the pressure control range of the casing annular space as the annular space liquid density changes.

[0151] Please refer to Figure 3 , Figure 4 As shown, S205: optimizing and determining the annulus liquid density according to the change curve 1 and the change curve 2 to reduce the pressure of the oil casing annulus to within the safety threshold.

[0152] In this embodiment, it should be noted that within the same coordinate system, a curve 1 showing the maximum value of the casing annulus pressure changing with the annulus liquid density and a curve 2 showing the maximum value of the casing annulus pressure control range changing with the annulus liquid density are drawn; when the casing annulus pressure is less than the casing annulus force control range, the corresponding annulus liquid density is the required optimized annulus liquid density value; when the density value does not exist or is too large, the annulus liquid level depth is increased, and then the above steps S202 to S205 are repeated to redetermine the annulus liquid density.

[0153] like Figure 5 , is a block diagram of a computer device according to an embodiment of the present application. The computer device is intended to represent various forms of digital computers or mobile devices. The digital computer may include a desktop computer, a portable computer, a workbench, a personal digital assistant, a server, a mainframe computer, and other suitable computers. The mobile device may include a tablet computer, a smart phone, a wearable device, etc.

[0154] like Figure 5 As shown, the device 600 includes a computing unit 601, a ROM 602, a RAM 603, a bus 604, and an input / output (I / O) interface 605, and the computing unit 601, ROM 602 and RAM 603 are connected to each other through the bus 604. The input / output (I / O) interface 605 is also connected to the bus 604.

[0155] The computing unit 601 can perform various processes in the method embodiment of the present application according to the computer instructions stored in the read-only memory (ROM) 602 or the computer instructions loaded from the storage unit 608 to the random access memory (RAM) 603. The computing unit 601 can be various general and / or special processing components with processing and computing capabilities. The computing unit 601 may include, but is not limited to, a central processing unit (CPU), a graphics processing unit (GPU), various dedicated artificial intelligence (AI) computing chips, various computing units running machine learning model algorithms, digital signal processors (DSPs), and any appropriate processors, controllers, microcontrollers, etc. In some embodiments, the method provided in the embodiment of the present application can be implemented as a computer software program, which is tangibly contained in a computer-readable storage medium, such as a storage unit 608.

[0156] RAM 603 may also store various programs and data required for the operation of device 600. Part or all of a computer program may be loaded and / or installed on device 600 via ROM 602 and / or communication unit 609.

[0157] The input unit 606, output unit 607, storage unit 608 and communication unit 609 in the device 600 can be connected to the I / O interface 605. The input unit 606 can be, for example, a keyboard, a mouse, a touch screen, a microphone, etc. The output unit 607 can be, for example, a display, a speaker, an indicator light, etc. The device 600 can exchange information, data, etc. with other devices through the communication unit 609.

[0158] It should be noted that the device may also include other components necessary for normal operation, or may only include components necessary for implementing the solution of the present application, rather than all the components shown in the figure.

[0159] Various implementations of the systems and techniques described herein can be realized in digital electronic circuit systems, integrated circuit systems, field programmable gate arrays (FPGAs), application specific integrated circuits (ASICs), application specific standard products (ASSPs), systems on chips (SOCs), load programmable logic devices (CPLDs), computer hardware, firmware, software, and / or combinations thereof.

[0160] The computer instructions for implementing the method of the present application can be written in any combination of one or more programming languages. These computer instructions can be provided to the computing unit 601, so that when the computer instructions are executed by the computing unit 601 such as a processor, the steps involved in the method embodiment of the present application are executed.

[0161] The computer-readable storage medium provided in the present application may be a tangible medium that may contain or store computer instructions for executing the steps involved in the method embodiments of the present application. The computer-readable storage medium may include, but is not limited to, electronic, magnetic, optical, electromagnetic, and other forms of storage media.

[0162] The above specific implementations do not constitute a limitation on the protection scope of this application. It should be understood by those skilled in the art that various modifications, combinations, sub-combinations and substitutions can be made according to design requirements and other factors. Any modifications, equivalent substitutions and improvements made within the spirit and principles of this application should be included in the protection scope of this application.

Claims

1. An optimization design method for controlling the pressure rise due to leakage of a production tubing, characterized in that: The following steps are involved: Step 1: Determine whether the annular space liquid in the oil-casing annulus of the target gas well is lost; wherein the oil-casing annulus is composed of a tubing head, a production string, a production casing and a packer; Step 2: If the annular space liquid in the oil casing annulus of the target gas well does not leak, then determine the leakage point depth of the production string; Step 3: Under the condition of determining the depth of the leakage point, determine the first curve of the maximum pressure of the casing annulus and the change of the density of the annulus liquid; Step 4: According to the pressure bearing capacity of the tubing head, production string, production casing and packer, determine the second curve of the maximum value of the pressure control range of the casing annulus as the density of the annulus liquid changes; Step 5: Optimize and determine the annulus liquid density according to the change curve 1 and the change curve 2 to reduce the pressure of the oil casing annulus to within the safety threshold.

2. The optimization design method for controlling the pressure rise due to leakage of a production tubing according to claim 1, characterized in that: The step of determining whether the annular space liquid in the casing annulus of the target gas well has been lost comprises: Based on the target gas well where the production string leaks, the annular liquid level in the casing annulus is monitored to determine whether the annular liquid is leaking; The annular liquid level fluctuation amplitude is defined by dividing the difference between the maximum and minimum annular liquid level depths within a specific monitoring period by the maximum well depth; When the fluctuation amplitude of the annular space liquid level does not exceed the threshold value within a specific time, it is considered that the annular space liquid has not been lost; When the annular space liquid level fluctuation amplitude exceeds a threshold value within a specific time, it is considered that the annular space liquid is lost.

3. The optimization design method for controlling the pressure rise due to leakage of a production tubing according to claim 1, characterized in that: If the annular space liquid in the oil casing annulus of the target gas well does not leak, determining the leakage point depth of the production string includes: Step 2.1: Obtain the pressure profile in the production string under shut-in conditions; Step 2.2: Calculate the pressure profile in the casing annulus based on the gas column and liquid column pressures; Step 2.3: Based on the pressure difference between the pressure profile in the production string and the pressure profile in the casing annulus as the driving force of the leakage, the variation law of the maximum value of the casing annulus pressure with the depth of the leakage point is analyzed and determined to obtain the variation curve 3; Step 2.4: According to the casing annulus pressure calculated under the shut-in condition, the leakage point depth corresponding to the pressure value on the variation curve 3 is the leakage point depth of the production string.

4. The optimization design method for controlling the pressure rise due to leakage of a production tubing according to claim 3, characterized in that: The step 2.1: obtaining the pressure profile in the production string under the shut-in condition, comprises: closing the wellhead of the target gas well, recording the corresponding casing annulus pressure and the wellhead oil pressure, and then lowering a pressure gauge into the well to obtain the pressure profile in the production string; or, The production string is divided into sections, and the gas density in the sections is calculated based on the pressure and temperature, and then the pressure in the production string at the corresponding depth is calculated.

5. The optimization design method for controlling the pressure rise due to leakage of a production tubing according to claim 4, characterized in that: The production string is segmented, and the gas density in the segment is calculated according to the pressure and temperature, and then the pressure in the production string at the corresponding depth is calculated, including: According to the PVT equation of the gas, the gas density is obtained, and the gas density can be described by the following formula: In the formula, ρ gi is the gas density of the i-th segment, g / cm 3 , p ti is the pressure in the production string of the i-th segment, MPa, p s is the standard pressure, Pa; T s is the standard temperature, K, T ti is the temperature in the production string of the i-th segment, i.e., the formation temperature, K, ρ gs is the standard density of the gas, g / cm 3 , i is the segment number, dimensionless, i = 1, 2, 3...; The temperature inside the production string of the i-th segment, that is, the formation temperature, is calculated using the following formula: T ti =T t0 +g e ×i×H F (4), Where, T t0 is the wellhead, K, g e is the geothermal gradient, K / 100m, H F is the segment length, m; The pressure in the production string at the corresponding segment depth is calculated according to the gas density, as shown in the formula: p ti+1 =p ti +10 -3 ×ρ gi ×g×H F (5), In the formula, p ti+1 is the pressure in the production string of the i+1th segment, MPa; g is the acceleration of gravity, m / s 2 ; According to the above steps, the pressure in the production string at the corresponding depth is calculated from the wellhead to the well bottom.

6. The optimization design method for controlling the pressure rise due to leakage of a production tubing according to claim 3, characterized in that: The step 2.2: calculating the pressure profile in the casing annulus according to the gas column and liquid column pressures, comprises: The gas density in the casing annulus is calculated. Since the length of the gas column in the casing annulus is short, the influence of the formation temperature on the gas density is no longer considered. The gas density in the casing annulus is expressed by the following formula: In the formula, ρ ga is the gas density in the casing annulus, g / cm 3 , T ta is the wellhead temperature of the casing annulus, K; According to the casing annulus pressure profile located above the casing annulus liquid level, it is only related to the annular gas column, and the casing annulus pressure profile located below the annular liquid level is affected by both the gas column and the liquid column pressure. The casing annulus pressure profile is calculated respectively, wherein, when calculating the profile, the casing annulus pressure is preset to be zero, which is expressed by the following formula: In the formula, H ta is the casing annulus depth, m, p ta Depth H ta The value of the casing annulus pressure profile, MPa, ρ ga is the gas density in the casing annulus, g / cm 3 , ρ L is the density of the annular liquid in the casing annulus, g / cm 3 ;p a Casing annulus pressure, MPa.

7. The optimization design method for controlling the pressure rise due to leakage of a production tubing according to claim 3, characterized in that: The step 2.3: based on the pressure difference between the pressure profile in the production string and the pressure profile in the casing annulus as the driving force of the leakage, the variation law of the maximum value of the casing annulus pressure with the depth of the leakage point is analyzed and determined to obtain the variation curve 3, including: The driving force of leakage comes from the pressure difference on both sides of the leakage point. The pressure inside the leakage point depends on the pressure profile inside the production string at the depth of the leakage point. The pressure outside the leakage point depends on the pressure profile of the casing annulus at the depth of the leakage point, which is expressed by the following formula: In the formula, p ln Indicates the pressure inside the leak point, MPa, p lw Indicates the pressure outside the leak point, MPa, H is the well depth, m, H L is the well depth of the leak point, m, p tL is the pressure value corresponding to the pressure profile in the production string at the depth of the leak point, MPa, p tal is the pressure value corresponding to the casing annulus pressure profile at the depth of the leakage point, MPa; After the production string leaks, the production string, the leak point and the casing annulus form a U-shaped tube. According to the U-shaped tube principle, when the casing annulus pressure reaches the maximum value, the pressure inside and outside the leak point are equal. The maximum casing annulus pressure corresponding to the leak points at different depths is determined and expressed by the following formula; p anmax =p ln -p 1w |H=H L (9), In the formula, p anmax is the maximum value of casing annulus pressure, MPa; According to the depth from the wellhead to the packer of the target gas well, the depth of the leakage point is changed, and the variation law of the maximum value of the casing annulus pressure with the depth of the leakage point is analyzed to obtain the variation curve 3.

8. The optimization design method for controlling the pressure rise due to leakage of a production tubing according to claim 1, characterized in that: The step 3: determining the maximum pressure of the casing annulus as the density of the annulus liquid changes curve 1 according to the determined leakage point depth, including: When the depth of the leakage point is below the annular liquid surface, the pressure outside the leakage point is affected by the pressure of the annular liquid column, and the pressure of the annular liquid column is related to the density of the annular liquid. According to the known depth of the leakage point, the relationship between the maximum annular pressure caused by the leakage pressure and the annular liquid density is established and expressed by the following formula: p amaxL =p lnL -10 -3 ×[(ρ ga ×g×H max )+r L ×g×(H LD -H max )] (11), In the formula, p anmaxL is the maximum value of the casing annulus pressure under the condition of the depth of the actual leakage point of the gas well, MPa, ρ ga is the gas density in the casing annulus, g / cm3, ρ L is the density of the annular liquid in the casing annulus, g / cm3; According to the density of the annular space liquid being changed, a curve 1 showing the maximum pressure of the casing annular space as the density of the annular space liquid changes is obtained.

9. The optimization design method for controlling the pressure rise due to leakage of a production tubing according to claim 1, characterized in that: Step 4: Determine the second curve of the maximum value of the pressure control range of the casing annulus as the density of the annulus liquid changes according to the pressure bearing capacity of the tubing head, the production string, the production casing and the packer, including: Based on the maximum value of the pressure control range of the casing annulus, it is necessary to ensure the pressure bearing capacity of the tubing head, tubing, production casing and packer, and the pressure bearing capacity of the tubing head, production tubing, production casing and packer are calculated respectively to determine the maximum value of the pressure control range of the casing annulus; wherein, the maximum value of the pressure control range of the casing annulus determined by the tubing head is 80% of its rated pressure bearing capacity, which is expressed by the following formula: β＝0.8×p 额 (12) Where p1 is the maximum value of the casing annulus pressure control range determined by the tubing head, MPa, p 额 is the rated pressure resistance of the tubing head, MPa; The maximum value of the pressure control range of the casing annulus determined by the tubing is the anti-external collapse strength of the tubing under the conditions of well opening and well shut-in, which is expressed by the following formula: Where p2 is the maximum value of the casing annulus pressure control range determined by the tubing, MPa, p 挤 is the minimum anti-external collapse strength of the oil pipe in the gas well, MPa, S2 is the anti-external collapse safety factor, dimensionless, p t2 is the pressure in the tubing string corresponding to the depth of the minimum anti-external collapse strength of the tubing, MPa, and h2 is the depth of the minimum anti-external collapse strength of the tubing, m; The maximum value of the control range of the casing annulus pressure determined by the production casing is the internal pressure resistance of the production casing, which is expressed by the following formula: Where p3 is the maximum value of the casing annulus pressure control range determined by the production casing, MPa, p 内 is the minimum internal pressure strength of the production casing, MPa, S3 is the safety factor of the production casing against internal pressure, dimensionless, p b is the pressure value of annulus B, MPa, ρ b is the equivalent brine density of annulus B, g / cm 3 ; h3 is the depth of the minimum internal pressure resistance of the production casing, m; The maximum value of the pressure control range of the casing annulus determined by the packer is the limit of the packer setting pressure, which is expressed by the following formula: p4=p 封 +p 下 -10 -3 r L gh4 (15) Where p4 is the maximum value of the casing annulus pressure control range determined by the packer, MPa, p 封 is the packer setting working pressure difference, MPa, p 下 is the pressure at the lower end of the packer, MPa, h4 is the depth from the annulus protection fluid level to the packer, m; The maximum value of the pressure control range of the casing annulus is obtained according to the minimum value of the maximum values ​​of the pressure control range of the casing annulus determined by the tubing head, the production string, the production casing and the packer, and is expressed by the following formula; Δp aA =min(p1,p2,p3,p4) (16) In the formula, △p aA is the maximum value of the pressure control range of the casing annulus, MPa; According to the transformation of the annular space liquid density, a second curve of the maximum value of the pressure control range of the casing annular space and the change of the annular space liquid density is obtained.

10. The optimization design method for controlling the pressure rise due to leakage of a production tubing according to claim 1, characterized in that: The step 5: optimizing and determining the annular space liquid density according to the change curve 1 and the change curve 2 to reduce the pressure of the oil casing annulus to within the safety threshold, including: Draw a first curve of the maximum pressure of the casing annulus changing with the density of the annulus liquid and a second curve of the maximum pressure control range of the casing annulus changing with the density of the annulus liquid in the same coordinates; When the casing annulus pressure is less than the casing annulus force control range, the corresponding annulus liquid density is the required optimized annulus liquid density value; When the density value does not exist or is too large, the depth of the annular liquid surface is increased, and then the above steps 2 to 5 are repeated to redetermine the annular liquid density.

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