A process method for nitrogen injection and dissolution blocking of a salt well group immobile pipe column and application thereof

Abstract

The present application belongs to the technical field of salt mine water solution mining and cavity making and solution resistance, and particularly relates to a process method for nitrogen injection solution resistance of salt well group without moving pipe column. The method comprises the following steps: selecting movable pry-mounted or split type module to make and inject nitrogen; adopting the mode of injecting local wellbore volume nitrogen to inject gas from the production casing, and the gas injection amount is determined by the daily mining amount of the salt well and the gas compressibility coefficient; after the gas injection is completed, the anti-slip post-top replacement fluid is injected to delay the gas floating, and then clean water or brine and other well fluids are injected to rapidly displace the gas in the production casing into the solution cavity and play the role of top solution resistance. The present application can simplify the salt well gas injection process, reduce the operation links and the corresponding cost, greatly reduce the gas injection pressure and the construction safety risk, accelerate the gas displacement speed in the large size wellbore, improve the application adaptability of the salt well nitrogen injection solution resistance measures, and achieve the purpose of locally replacing the oil pad method and greatly reducing the solution resistance cost. The present application is also applicable to oil wells, water injection wells, geothermal wells or coal seam gas wells.

Description

Technical Field

[0001] This invention belongs to the technical field of salt mine water-soluble mining and cavity-making for dissolution prevention, specifically involving a process method for nitrogen gas injection for dissolution prevention in salt well groups without moving the tubing and its application. Background Technology

[0002] There are two methods for controlling dissolution in salt well groups: the air cushion method and the oil cushion method. In recent years, due to the high price of diesel fuel, the difficulty of oil-water separation, and environmental protection requirements, the air cushion method has shown a trend of replacing the oil cushion method.

[0003] Given that most saline well groups utilize a single-string injection and production method with production casing, implementing conventional nitrogen injection techniques in oilfields presents significant challenges: First, the injection process using a central tube, or the annular space between the central tube and the production casing, as a conduit increases operational steps and associated costs. Furthermore, the complex downhole conditions make it difficult to guarantee success rates and efficiency. Additionally, based on experience with saline well groups, downhole central tubes are prone to deformation and breakage, introducing significant variables and difficulties to subsequent injection, production, and maintenance. Second, single-wellbore gas injection with the production casing requires addressing the issue of gas stagnation caused by slippage within the large-diameter production casing; existing water displacement and blowout measures are neither effective nor economical. Third, for medium- and deep saline well groups, both of the above methods result in wellhead injection pressures approaching or exceeding the rated working pressure of the wellhead production tree under pure gas injection conditions, increasing safety risks and requiring additional safety measures and costs.

[0004] Therefore, the key to salt mines breaking free from the limitations of current gas injection technology, achieving the large-scale application of nitrogen injection technology, and replacing oil injection for dissolution inhibition lies in a simplified, low-risk process technology that eliminates the need for a central tube and uses existing production casing to implement gas injection with a stationary tubing string. Summary of the Invention

[0005] The technical problem to be solved by the present invention is to overcome the shortcomings of the prior art and provide a process method and its application for nitrogen gas injection for dissolution inhibition in salt well groups with the tubing stationary, in order to solve the technical problems of incompatibility of the gas cushion method described in the background art.

[0006] The technical solution of this invention to solve the above-mentioned technical problems is as follows: A process for nitrogen gas injection to inhibit dissolution in salt well groups without moving the tubing, comprising the following steps:

[0007] S1. Select a movable skid-mounted or split-type module to generate nitrogen, and inject nitrogen through the wellhead tree. The nitrogen injection pressure is determined according to the salt well production layer depth and the rated pressure of the wellhead tree. The nitrogen purity is not less than 95%.

[0008] S2. Nitrogen gas is injected into a local wellbore volume using the production casing as a single wellbore nitrogen injection section, which serves as a filling gas section. The injection volume is determined by the daily production volume of the salt well and the compressibility coefficient of the gas.

[0009] S3. Configure anti-slip post-displacement fluid and inject it into the production casing of the salt well group through the wellhead production tree to block or delay the nitrogen rise of the filling gas section.

[0010] S4. Well fluid is injected into the production casing through the wellhead tree. The injected fluid pushes the anti-slip post-displacement fluid downward until the filling gas section and the anti-slip post-displacement fluid are pushed into the solution cavity.

[0011] Furthermore, the anti-slip post-displacement fluid is modified starch or polyacrylamide, and the well fluid is clean water or brine.

[0012] Furthermore: In step S2, the volume of the nitrogen section is calculated according to the ideal gas law:

[0013] P1V1 / T1 = P2V2 / T2;

[0014] The transformation is: V1 = (P2V2T1) / (P1T2);

[0015] Where P1 is atmospheric pressure, 0.1 MPa;

[0016] V1 is the nitrogen injection volume under standard conditions, in Nm³. 3 ;

[0017] T1 is the temperature under standard conditions, 273.15K;

[0018] P2 is the pressure in the salt mine formation, in MPa;

[0019] T2 is the temperature of the salt mine layer, 273.15K;

[0020] V2 is the underground volume of nitrogen gas under the pressure of the salt mine mining layer, in Nm³. 3 ;

[0021] The ratio of V1 to V2 is the gas compressibility coefficient of the salt layer in which it is located.

[0022] Furthermore, V2 is determined by the daily output of the salt well.

[0023] Further: In step S3, the volume of the anti-slip post-displacement fluid is 0.5–2 m³. 3 The length is between 20 and 100 m, the viscosity is between 20 and 200 MPa·s, and the injection speed of the anti-slip post-displacement fluid is 15 to 30 m / s. 3 / h.

[0024] Further: In step S4, the injection pressure of the well fluid is not higher than the pressure of the nitrogen injection section in step S2, and the injection rate is 15-30 m / s. 3 / h, to meet the requirement of rapidly displacing gas from the wellbore within 1 to 2 hours, and to end the gas injection operation after the water injection pressure stabilizes at the daily production water injection pressure for 1 to 2 hours.

[0025] The present invention also provides an application of a process for nitrogen injection to inhibit dissolution in salt well groups with stationary tubing. The process for nitrogen injection to inhibit dissolution in salt well groups with stationary tubing, as described above, can also be applied to oil wells, water injection wells, geothermal wells, or coalbed methane wells.

[0026] The beneficial effects of this invention are:

[0027] 1. Firstly, this application uses the air cushion method instead of the oil cushion method, and the cost of the air cushion method is lower than that of the oil cushion method; moreover, the process mentioned in this application only requires the use of a fixed production casing and does not require the use of a central pipe, which reduces the complexity of the production process, significantly reduces the gas injection pressure and construction safety risks, accelerates the gas displacement efficiency in the wellbore, and improves the applicability of this process in saline well groups.

[0028] 2. In terms of cost, it can save on the relocation and operation costs of workover rigs, save on a series of expenses such as replacement of the central pipe and high-pressure wellhead production tree, and avoid subsequent operation problems of central pipe gas injection and injection-production. Attached Figure Description

[0029] To more clearly illustrate the specific embodiments of the present invention or the technical solutions in the prior art, the drawings used in the description of the specific embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are some embodiments of the present invention. For those skilled in the art, other drawings can be obtained from these drawings without creative effort.

[0030] Figure 1 A schematic diagram of the structure before construction of a process for nitrogen gas injection to inhibit dissolution in salt well groups without moving the tubing, as provided by the present invention;

[0031] Figure 2 This is a schematic diagram of the structure after the filling gas section is injected in a process method for nitrogen gas injection to inhibit dissolution in a salt well group with a stationary tubing provided by the present invention.

[0032] Figure 3 A schematic diagram of the structure after injecting anti-slipping displacement fluid in a process method for injecting nitrogen gas to inhibit dissolution in a salt well group with a stationary tubing string, as provided by the present invention.

[0033] Figure 4This is a schematic diagram of the structure after the injection fluid is injected in a process method for nitrogen gas injection to inhibit dissolution in a salt well group with a stationary tubing string, as provided by the present invention.

[0034] Figure 5 This is a schematic diagram of the structure after the completion of the process of injecting nitrogen gas to inhibit dissolution in a salt well group without moving the tubing, as provided by the present invention.

[0035] Figure label:

[0036] 1-Rock layer; 2-Cap layer; 3-Salt layer; 4-Deposition cavity; 5-Production casing; 6-Wellhead Christmas tree; 7-Brine outlet; 8-Pre-flush fluid column; 9-Filling gas section; 10-Anti-slippage post-displacement fluid; 11-Injection fluid;

[0037] a-Injecting gas; b-Injecting water; c-Outflowing brine. Detailed Implementation

[0038] The embodiments of the technical solution of the present invention will now be described in detail with reference to the accompanying drawings. These embodiments are merely illustrative of the technical solution of the present invention and are therefore intended to limit the scope of protection of the present invention.

[0039] It should be noted that, unless otherwise stated, the technical or scientific terms used in this application should have the ordinary meaning as understood by one of ordinary skill in the art to which this invention pertains.

[0040] In the description of this application, it should be understood that the terms "center", "longitudinal", "lateral", "length", "width", "thickness", "upper", "lower", "front", "rear", "left", "right", "vertical", "horizontal", "top", "bottom", "inner", "outer", "clockwise", "counterclockwise", "axial", "radial", "circumferential", etc., indicating the orientation or positional relationship based on the orientation or positional relationship shown in the accompanying drawings, are only for the convenience of describing the present invention and simplifying the description, and are not intended to indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation, and therefore should not be construed as a limitation of the present invention.

[0041] Furthermore, the terms "first," "second," etc., are used for descriptive purposes only and should not be construed as indicating or implying relative importance or implicitly specifying the number of technical features indicated. In the description of this invention, "a plurality of" means two or more, unless otherwise explicitly defined.

[0042] In this application, unless otherwise expressly specified and limited, the terms "installation," "connection," "linking," and "fixing," etc., should be interpreted broadly. For example, they can refer to a fixed connection, a detachable connection, or an integral part; they can refer to a direct connection or an indirect connection through an intermediate medium; they can refer to the internal communication of two components or the interaction between two components. Those skilled in the art can understand the specific meaning of the above terms in this invention according to the specific circumstances.

[0043] In this application, unless otherwise expressly specified and limited, "above" or "below" the second feature can mean that the first feature is in direct contact with the second feature, or that the first feature is in indirect contact with the second feature through an intermediate medium. Furthermore, "above," "on top of," and "over" the second feature can mean that the first feature is directly above or diagonally above the second feature, or simply that the first feature is at a higher horizontal level than the second feature. "Below," "below," and "under" the second feature can mean that the first feature is directly below or diagonally below the second feature, or simply that the first feature is at a lower horizontal level than the second feature.

[0044] Example

[0045] like Figure 1 , Figure 2 , Figure 3 , Figure 4 and Figure 5 As shown, the present invention provides a process for nitrogen injection to inhibit dissolution in salt well groups with the tubing stationary, comprising the following steps:

[0046] Before construction, the selection of gas injection wells in salt well groups prioritizes wells with higher water injection rates, injecting nitrogen gas from the end with the higher water injection volume to inhibit dissolution. Based on the characteristics of salt mines, horizontal wells are typically selected for gas injection. During gas injection, the brine-end valve is opened to control the brine output and prevent abnormal accidents such as pressure loss or well blockage / sand blockage; simultaneously, precautions are taken to prevent gas from entering surface pipelines and processes.

[0047] S1. Select a movable skid-mounted or split-type module for nitrogen production and inject nitrogen through the wellhead production tree 6; S2. Use a method of injecting nitrogen into a local wellbore volume, and inject gas into a single wellbore through the production casing 5. The injection volume is determined by the daily production volume of the salt well and the gas compressibility coefficient, such as the production depth of the salt well group, the rated pressure of the wellhead production tree 6, and the filling volume and pressure of the filling gas section 9. Taking the two forms of integrated skid-mounted and split-type modules of existing nitrogen production and injection equipment as a reference, and based on the on-site gas injection operation conditions and the need for flexible nitrogen injection and dissolution prevention in a large area of ​​the mining area, select a movable split-type nitrogen production and injection module that is more suitable for passage and access to the site and the limited space of the field well site. Typically, the system is divided into three modules: nitrogen production, nitrogen injection, and power generation. These modules can be transported to the well site separately by trailer. Nitrogen production and injection are performed using movable, split-type nitrogen production and injection modules, and the nitrogen is injected into the filling gas section 9. The filling gas section 9 partially fills the production casing 5. Furthermore, based on the daily injection and production intensity of the salt well group and the overall mine production plan, the required amount of dissolved nitrogen gas and nitrogen production capacity is typically estimated based on two factors: the current oil cushion's normal dissolution rate (oil content per 10,000 cubic meters) and the expansion of the top space of the solution cavity. The difference in protection between the oil cushion and the gas cushion is also considered. The downhole gas volume is selected as a multiple of the oil cushion's oil consumption, thus determining the daily required dissolved nitrogen gas consumption and nitrogen production capacity range for the salt well group. Typically, this ranges from 300 to 800 Nm³. 3 A nitrogen production range of [number] h can cover the daily usage of soluble nitrogen in a single well group in a salt mine. Furthermore, based on existing corrosion research, the purity of the injected nitrogen is no less than 95%.

[0048] S3. Configure anti-slippage post-displacement fluid 10, which is injected into the production casing 5 of the salt well group from the wellhead production tree 6 through the ground high-pressure manifold via a pump truck, in order to seal or block the filling gas section 9.

[0049] S4. Water or brine or other injection fluid 11 is injected into the production casing 5 through the wellhead production tree 6. The injection fluid 11 pushes the anti-slip post-displacement fluid 10 downward until the filling gas section 9 and the anti-slip post-displacement fluid 10 are completely pushed into the solution cavity 4. After entering the solution cavity 4, nitrogen gas automatically floats to the top of the solution cavity 4 and plays a role in inhibiting dissolution.

[0050] Then, continue injecting the injection fluid 11 until the injection pressure stabilizes at the daily production injection pressure for 1 to 2 hours, and then end the gas injection operation.

[0051] The typical geological structure of a salt well group consists of a rock layer 1, a caprock 2, and a salt mineral layer 3 from top to bottom. The salt mineral layer 3 contains a solution cavity 4. In this process, the salt well group with the best water injection performance is selected based on the principle of injecting water. Nitrogen gas is injected from the side with the largest water injection volume to inhibit dissolution. Then, a filling gas section 9 is injected into the production casing 5, and the filling gas section 9 occupies part of the volume of the production casing 5. Then, a gel-like, high-viscosity anti-slip post-displacement fluid 10 is used as a seal, acting like a piston. Finally, well fluid 11 is injected on top of the anti-slip post-displacement fluid 10, pushing the anti-slip post-displacement fluid 10, the filling gas section 9, and the pre-filled fluid column 8 in the original wellbore into the solution cavity 4. The anti-slip post-displacement fluid 10 will be diluted or degraded after entering the solution cavity for a certain period of time. The filling gas section 9 will spread on the top of the solution cavity 4 and form a barrier layer, playing a role in inhibiting the upward dissolution of the solution cavity 4.

[0052] Since the production casing 5 is only partially filled with gas, the gas injection pressure is less than the gas injection pressure required to completely fill the production casing 5 with gas, thereby significantly reducing the gas injection pressure and safety risks during construction. In the large-size production casing 5 without a central tube, the post-placed anti-slip displacement fluid 10 blocks and delays the slippage of the filling gas section 9 during the displacement process, acting like a piston to accelerate the displacement efficiency of the gas in the casing and the construction speed, thus improving the adaptability of this technology in salt well groups.

[0053] Based on the above technical solution, the anti-slip post-displacement fluid 10 is a thickening substance such as modified starch or polyacrylamide. The anti-slip post-displacement fluid 10 is prepared on-site into a gel slug or a high-viscosity fluid. The anti-slip post-displacement fluid 10 needs to undergo compatibility testing to ensure it does not react adversely with the liquids in the production casing 5, the solution cavity 4, or the surrounding formation. The well fluid 11 is clean water or brine; this helps to control production costs.

[0054] Based on the above technical solution, in step S2, the calculation method for the amount of nitrogen gas used in the nitrogen section follows the ideal gas law:

[0055] P1V1 / T1 = P2V2 / T2;

[0056] The transformation is: V1 = (P2V2T1) / (P1T2);

[0057] Where P1 is atmospheric pressure, 0.1 MPa;

[0058] V1 is the nitrogen injection volume under standard conditions, in Nm³. 3 ;

[0059] T1 is the temperature under standard conditions, 273.15K;

[0060] P2 is the pressure in the salt mine formation, in MPa;

[0061] T2 is the temperature of the salt mine layer, 273.15K;

[0062] V2 is the underground volume under the pressure of the salt mine mining layer, in Nm³. 3 ;

[0063] The ratio of V1 to V2 is the gas compressibility coefficient of the salt layer in which it is located.

[0064] The value of V2, the daily underground nitrogen gas insulation volume of the salt well group, is estimated based on the daily production volume and the oil content per 10,000 cubic meters of the aforementioned top space expansion of the solution cavity 4 and the normal insulation oil content. The downhole gas cushion volume is selected as a multiple of the oil volume used for oil cushion insulation. In addition, considering the number of wells and the interval sequence for nitrogen injection in the salt mine, and maintaining a certain control margin, the single injection volume corresponding to the surface gas injection needs to be multiplied by V1 by the number of days of the interval.

[0065] The nitrogen injection volume V1 is designed to be 300–800 Nm³. 3 With a nitrogen production and injection capacity of [number] h, nitrogen can be completely injected into the production casing in one go within a few hours, with a volume of 0.3 to 0.7 times the wellbore volume of the production casing 5. According to the pressure formula, the maximum gas injection pressure at the wellhead can be reduced to approximately 40% to 60% of the rated pressure of the wellhead production tree 6 (the specific pressure depends on the density of the returned solution).

[0066] Based on the above technical solution, in step S3, the volume of the anti-slip post-displacement fluid 10 is 0.5–2 m³. 3 The length is between 20 and 100 m, the viscosity is between 20 and 200 MPa·s, and the injection speed of the anti-slip post-displacement fluid 10 is 15 to 30 m / s. 3 / h.

[0067] The amount of anti-slip displacement fluid 10 used is determined based on factors such as well depth, inner diameter of production casing 5, gas volume in production casing 5, slippage rate, and water injection rate. After being injected into production casing 5, it forms a certain length and number of slugs to block or slow down the rise of gas in filling gas section 9.

[0068] Based on the above technical solution, in step S4, the injection pressure of the well fluid 11 is not higher than the pressure of the nitrogen injection section in step S2, and the injection rate is 15-30 m / s. 3 / h, to meet the requirement of rapidly displacing gas from the wellbore within 1 to 2 hours, and to end the gas injection operation after the water injection pressure stabilizes at the daily production water injection pressure for 1 to 2 hours.

[0069] Under the premise of simplicity, the pre-filled liquid column 8 and the post-filled well fluid 11 that fill the casing 5 can be made of high-density fluids such as brine, which can produce greater liquid column pressure and reduce gas injection pressure.

[0070] The specific parameter calculation example is as follows:

[0071] For example, consider a salt well group with a burial depth of 2000m, a formation temperature of 80℃, using N80, 7” API casing, a 250mm wellhead, a discharge rate of 20-40m³ / h, and a brine specific gravity of 1.2:

[0072] (1) According to the aforementioned formula, the compression ratio of the surface gas injection volume to the gas volume of the formation is approximately 209.

[0073] (2) Based on the daily extraction rate of 20-40 m3 / h for salt well groups, the underground nitrogen gas insulation volume V2 is taken as 5-10 m3, then the single gas injection volume V1 of the surface gas injection is in the range of 1050-2100 m3; the nitrogen gas insulation cycle is 3-5 days / time, and the gas content of the brine reaches 10.4-69.4.

[0074] (3) With the selected nitrogen production and injection equipment capacity of 300-800 Nm3 / h, the pure nitrogen injection time is 1.2-7 hours.

[0075] (4) Then, the injection pressure at the wellhead in the production casing for a single injection of 1050-2100 m3 on the surface is 10-12 MPa, which is 40-48% of the rated pressure of 25 MPa at the wellhead of the 250 well.

[0076] Implementation of nitrogen displacement process with no tubing in salt well groups:

[0077] 1. After nitrogen injection into the single wellbore is completed, an anti-slippage post-displacement fluid 10 slug is injected. The anti-slippage post-displacement fluid 10 is composed of modified starch or polyacrylamide and is prepared on-site into a gel slug or a high-viscosity fluid. The anti-slippage post-displacement fluid 10 must undergo compatibility testing to ensure it does not react adversely with the liquids in the production casing 5, the solution cavity 4, or the surrounding formation.

[0078] 2. The dosage of the anti-slip displacement fluid 10 is determined based on factors such as well depth, inner diameter of the production casing 5, gas volume in the wellbore, slippage velocity, and water injection rate. Typically, the volume of the anti-slip displacement fluid 10 is 0.5–2 m³. 3 The slugs are 20 to 100 m long and 20 to 200 mPa·s in viscosity. After being injected into the wellbore, they form slugs of a certain length and number to block or slow down the rise of gas.

[0079] 3. The injection of anti-slip post-displacement fluid 10 is carried out by a mobile high-pressure pump truck, sequentially injecting anti-slip post-displacement fluid 10 and clean water through a ground high-pressure manifold. Figure 3 The injection / water injection rate is 15-30m / s. 3 / h, the water injection pressure is not higher than the gas injection pressure, which meets the requirement of rapidly displacing the gas out of the wellbore within 1 to 2 hours.

[0080] 4. To further reduce the injection pressure, the pre-liquid column 8 and post-liquid column of the gas can use high-density fluids such as on-site brine.

[0081] 5. In accordance with relevant petroleum industry standards and requirements, the gas injection operation shall be terminated 1-2 hours after the water injection pressure has stabilized at the normal production water injection pressure. Figure 4 ).

[0082] The above steps complete the construction process of nitrogen injection for dissolution inhibition in a salt well group.

[0083] The present invention also provides an application of a process for nitrogen injection to inhibit dissolution in salt well groups with stationary tubing. Such process can also be applied to oil wells, water injection wells, geothermal wells or coalbed methane wells.

[0084] Furthermore, the application of a nitrogen injection process for dissolution inhibition in salt well groups with stationary tubing in salt mines can create a regular, periodic, and intermittent alternating dynamic dissolution inhibition mode, achieving comprehensive dissolution inhibition protection for multiple salt well groups in salt mines. This mode includes three technical aspects:

[0085] Firstly, based on the overall deployment of the salt mine and the injection and production intensity of individual wells, nitrogen production and injection parameters are selected and determined, including the number of injection wells per day, interval time, nitrogen injection volume, and injection time. For example, based on the capacity of the selected nitrogen production and injection equipment, the total amount of nitrogen injected per well for solution inhibition, the implementation time of nitrogen injection per well, the number of wells that can be injected with nitrogen per day, and the nitrogen injection cycle period are determined based on the number of feasible salt well groups and the number of wells injected per day, etc.

[0086] Secondly, considering the different requirements for dissolution inhibition in salt well groups at different production stages, for salt well groups with smaller solution cavities in the early stages of production, the proportion of the gas cushion equivalent to the normal dissolution inhibition oil cushion volume can be reduced; for salt well groups with larger solution cavities in the middle stages of production, the proportion of the gas cushion equivalent to the normal dissolution inhibition oil cushion volume can be increased. The operation of the dynamic dissolution inhibition mode can be optimized by utilizing the combination of gas injection arrangements for the well groups.

[0087] Thirdly, by combining routine, small-scale, rotating gas injections as short-term cycles with large-scale, concentrated gas injections in salt well groups that meet high-pressure injection conditions as long-term cycles, both dynamic dissolution inhibition during daily operations and the need for sudden, concentrated gas injections can be addressed. This allows for more comprehensive dissolution inhibition measures for salt well groups. Furthermore, taking the implementation of two salt well groups as an example, the utilization efficiency of nitrogen production and injection equipment can be increased from 6% to 23%, enhancing the value of these equipment.

[0088] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, and not to limit them; although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some or all of the technical features; and these modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of the present invention.

Claims

1. A process for nitrogen injection to inhibit dissolution in salt well groups with the tubing stationary, characterized in that, Includes the following steps: S1. Select a movable skid-mounted or split-type module to generate nitrogen, and inject nitrogen through the wellhead tree. The nitrogen injection pressure is determined according to the salt well production layer depth and the rated pressure of the wellhead tree. The nitrogen purity is not less than 95%. S2. Nitrogen gas is injected into a local wellbore volume using the production casing as a single wellbore nitrogen injection section, which serves as a filling gas section. The injection volume is determined by the daily production volume of the salt well and the compressibility coefficient of the gas. S3. Configure anti-slip post-displacement fluid and inject it into the production casing of the salt well group through the wellhead production tree to block or delay the nitrogen rise of the filling gas section. S4. Well fluid is injected into the production casing through the wellhead tree. The injected fluid pushes the anti-slip post-displacement fluid downward until the filling gas section and the anti-slip post-displacement fluid are pushed into the solution cavity.

2. The process for nitrogen injection to inhibit dissolution in salt well groups with a stationary tubing as described in claim 1, characterized in that, The anti-slip post-displacement fluid is modified starch or polyacrylamide, and the well fluid is clean water or brine.

3. The process for nitrogen injection to inhibit dissolution in salt well groups with a stationary tubing as described in claim 1, characterized in that, In step S2, the volume of the nitrogen section is calculated according to the ideal gas law: P1V1 / T1 = P2V2 / T2; The transformation is: V1 = (P2V2T1) / (P1T2); Where P1 is atmospheric pressure, 0.1 MPa; V1 is the nitrogen injection volume under standard conditions, in Nm³. 3 ; T1 is the temperature under standard conditions, 273.15K; P2 is the pressure in the salt mine formation, in MPa; T2 is the temperature of the salt mine layer, 273.15K; V2 is the underground volume of nitrogen gas under the pressure of the salt mine mining layer, in Nm³. 3 ; The ratio of V1 to V2 is the gas compressibility coefficient of the salt layer in which it is located.

4. The process for nitrogen injection to inhibit dissolution in salt well groups with a stationary tubing as described in claim 3, characterized in that, V2 is determined by the daily output of salt wells.

5. The process for nitrogen injection to inhibit dissolution in salt well groups with stationary tubing according to claim 1, characterized in that, In step S3, the volume of the anti-slip post-displacement fluid is 0.5–2 m³. 3 The length is between 20 and 100 m, the viscosity is between 20 and 200 MPa·s, and the injection speed of the anti-slip post-displacement fluid is 15 to 30 m / s. 3 / h.

6. The process for nitrogen injection to inhibit dissolution in salt well groups with a stationary tubing as described in claim 3, characterized in that, In step S4, the injection pressure of the well fluid is not higher than the pressure of the nitrogen injection section in step S2, and the injection rate is 15-30 m / s. 3 / h, to meet the requirement of rapidly displacing gas from the wellbore within 1 to 2 hours, and to end the gas injection operation after the water injection pressure stabilizes at the daily production water injection pressure for 1 to 2 hours.

7. The application of a process for nitrogen gas injection to inhibit dissolution in salt well groups with the tubing stationary, characterized in that, The process of nitrogen injection for dissolution inhibition in salt well groups with stationary tubing as described in claim 1 can also be applied to oil wells, water injection wells, geothermal wells, or coalbed methane wells.

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