Novel method for preventing and treating hydrate in tight gas shaft

Abstract

The invention relates to a novel method for preventing and treating tight gas shaft hydrates. The method comprises the following steps: (1) injecting methanol: when the temperature of a wellhead is reduced to 13 DEG C, starting to inject methanol at the position of a wellhead sleeve (1) in advance, firstly dismounting a pressure gauge at the position of the sleeve (1), then installing a methanol injection pipeline, and starting a methanol injection pump to inject methanol; the injection amount of the methanol is 10%-15% of the daily water yield in percentage by mass; (2) the methanol is continuously injected for 24 hours, when the designed injection amount is completed, a methanol injection pipeline is disassembled, and then a pressure gauge is installed at the position of the sleeve (1); (3) the filling temperature is normal temperature, the pressure is the pressure of a gas well casing and is 10-12MPa generally, and (4) production halt is not needed in the filling process. After the method is adopted for unblocking, continuous production and stable operation of the tight gas wells are realized.

Description

Technical Field

[0001] This invention relates to the field of oil and gas production technology, and in particular to a new method for preventing hydrates in tight gas wells, which is used to improve natural gas recovery rate. Background Technology

[0002] During gas production, the conditions for hydrate formation in the wellbore are: the presence of free water, high pressure, low temperature, and fluid disturbance. Once hydrates form in the wellbore, they can cause wellbore blockage, reduced gas well production, damage to internal wellbore components, and even well shutdown. Dynamic data from tight gas wells indicate that gas well production node parameters are in high-risk zones for hydrate formation (e.g., ...). Figure 1 As shown in the image, wellbore hydrate freezing is prone to occur. The locations where hydrate freezing occurs are as follows: Figure 2 As shown, this caused the gas well to be unable to produce normally.

[0003] Hydrates forming in the wellbore not only pose serious threats to gas well production but also create difficulties for well management. The main hazards of hydrates are as follows: ① Hydrates forming on the tubing perimeter turn smooth tubing walls into rough ones, causing some of the mixed fluid to slip off the wall as it passes through. ② Hydrates form a loose, mesh-like plug on the tubing wall. During the lifting process, gas passes through this loose plug, while some liquid slips off upon contact, leading to an accumulation of liquid at the bottom of the well. ③ Hydrates form a dense plug inside the tubing, such as… Figure 3 - Figure 5 As shown, the oil pipe section is completely blocked, making the gas well unable to produce.

[0004] Theoretically, hydrates are loose, snow-like substances that melt upon contact with methanol, making methanol an effective "enemy" of hydrates. However, in practice, unblocking these hydrates is time-consuming, labor-intensive, and ineffective, indicating that wellbore freezing is not simply caused by hydrates, but rather by a more severe "ice blockage." As the freezing time of the gas well increases, the ice content in the blockage increases, and the effectiveness of methanol treatment gradually decreases.

[0005] Ice blockage: This is a phenomenon caused by the freezing of free water inside the wellbore due to excessively low temperatures. It is more stable and denser than hydrates. Its formation mechanism differs significantly from that of natural gas hydrates: ice is formed by hydrogen bonds in its molecules, while hydrates are formed by van der Waals forces. Melting ice at 0°C requires 0.335 kJ of heat, while decomposing natural gas hydrates requires 0.15 kJ of heat. Therefore, ice blockage is a more difficult phenomenon to manage than hydrate blockage. Summary of the Invention

[0006] To address the technical problems existing in the background art, this invention provides a novel method for preventing and controlling hydrates in tight gas wells. After unblocking using this method, these tight gas wells achieve continuous production and stable operation.

[0007] The technical solution provided by this invention is: A novel method for preventing hydrate buildup in tight gas wells includes the following steps: (1) Add methanol: When the wellhead temperature drops to 13℃, start adding methanol in advance at the wellhead casing (1). First, remove the pressure gauge at the casing (1), then install the methanol injection pipeline, and start the methanol injection pump to inject methanol. The amount of methanol added is 10% to 15% of the daily water production, calculated as a percentage by mass.

[0008] (2) The methanol injection time is 24 hours of continuous injection. When the designed injection volume is completed, the methanol injection pipeline is removed and the pressure gauge is installed at the position of the casing (1).

[0009] (3) The injection temperature is normal temperature, and the pressure is the gas well casing pressure, which is generally 10-12 MPa.

[0010] (4) No production stoppage is required during the injection process. Gas wells produce through tubing. Due to gravity difference, methanol will fall to the bottom of the casing well. The bottoms of the oil and casing wells are connected. The methanol added to the casing mixes with the production gas flow at the bottom of the well. During the gas flow production process, methanol and natural gas are mixed together and transported from the bottom of the well to the wellhead through the production tubing.

[0011] The beneficial effects of this invention are as follows: The conventional approach to unblocking existing gas wells is "unblock when it's blocked," but in actual production, the unblocking effect is not significant. Pre-emptive methanol injection becomes a necessary means to prevent natural gas hydrate freezing and further ice blockage. In the later stages of tight gas well production, the wellbore hydrate formation temperature is 12℃. When the wellhead temperature drops to 13℃, methanol injection begins in advance. This pre-emptive methanol injection embodies the principle of prevention being better than cure. Attached Figure Description

[0012] Appendix Figure 1 It is a curve showing the formation of hydrates in tight gas wells.

[0013] Appendix Figure 2 This is a schematic diagram showing the location of hydrate formation in a tight gas well.

[0014] Appendix Figure 3 This is a schematic diagram of hydrates adhering to the inner wall of a well.

[0015] Appendix Figure 4 This is a schematic diagram of hydrates forming a non-dense plug inside the wellbore.

[0016] Appendix Figure 5 This is a schematic diagram of hydrates forming a dense plug inside the wellbore.

[0017] Appendix Figure 6It is a graph showing the critical pressure and temperature curves for gas well hydrate production.

[0018] Appendix Figure 7 This is a schematic diagram of methanol being added to the wellhead casing.

[0019] Appendix Figure 8 This is a comparison chart of the production status of well S207 before and after.

[0020] Appendix Figure 9 This is a schematic diagram of the methanol injection interface at the wellhead gas production tree. Detailed Implementation

[0021] The present invention will be further described below with reference to the accompanying drawings and examples: Example 1: Taking well S207 as an example A new method for preventing hydrates in tight gas wells includes the following steps: (1) Methanol injection: When the wellhead temperature drops to 13℃, start injecting methanol in advance at the wellhead casing 1 position, such as Figure 7 and Figure 9 As shown, first remove the pressure gauge at casing 1, then install the methanol injection pipeline and start the methanol injection pump to inject methanol; the amount of methanol injected is 150 kg; the position of the gate valve pressure gauge connector 2 is mainly used to deal with the oil pipe being frozen and blocked, and to unblock it when the oil pipe is frozen and production cannot proceed normally; the position of the pressure gauge connector 3 at the oil casing connection point in the wellhead production process is mainly used to deal with the freezing problem of the gas production pipeline. The wellbore hydrate formation temperature is 12℃ (e.g., Figure 6 As shown in the diagram, pre-injection of methanol embodies the principle of prevention over cure. Instead of the traditional "plugging and unplugging" method of injecting methanol, it is injected from the casing at the wellhead. This allows the methanol to reach the bottom of the well via the annulus and then be carried upwards by the gas flow from the bottom of the tubing directly to the hydrate site, ensuring full utilization of the methanol and efficiently disrupting hydrate formation.

[0022] Methanol is a double-edged sword. It can effectively prevent hydrate freezing and blockage, but excessive addition can easily lead to liquid accumulation. Field practice has shown that the optimal hydrate formation temperature is 5℃, corresponding to a methanol injection concentration of 10%–15%. The daily water production of the gas well can be determined by monitoring its production dynamics. Multiplying this by the injection concentration of 10%–15% gives the daily methanol injection amount. Table 1 below shows the relationship between methanol concentration and hydrate production temperature. Table 1 Relationship between methanol concentration and hydrate production temperature drop

[0023] (2) Methanol injection time is 24 hours of continuous injection; when the designed injection volume is completed, the methanol injection pipeline is removed and the pressure gauge is installed at the position of sleeve 1.

[0024] (3) Methanol is injected through the casing, which does not affect the normal production of tight gas wells, and can also "silently" remove the blockage of hydrates. Due to the gravity difference, methanol will fall to the bottom of the well. During the gas production process, methanol and natural gas are mixed together and transported from the bottom of the well to the wellhead so that methanol can be fully utilized.

[0025] Field tests at Well S207 revealed frequent wellbore freezing and blockage, rendering normal production impossible. Using the method described in this application, 150 kg of methanol was injected daily from the casing when the wellhead temperature dropped to 13°C to prevent hydrate formation in the wellbore. This method enabled continuous production and stable operation of these tight gas wells. Water sample analysis showed a methanol concentration of 17%, meeting the 5°C temperature drop requirement. Before methanol injection optimization, frequent freezing and blockage prevented continuous production; after optimization, the gas wells achieved continuous production, increasing daily gas production by 12,000 cubic meters, with stable production. Figure 8 The water sample moisture content test results are shown in Table 2 below.

[0026] Table 2: Moisture Content Analysis of Water Sample from Well S207

Claims

1. A novel method for preventing hydrate buildup in tight gas wells, comprising the following steps: (1) Add methanol: When the wellhead temperature drops to 13℃, start adding methanol in advance at the wellhead casing (1). First, remove the pressure gauge at the casing (1), then install the methanol injection pipeline, and start the methanol injection pump to inject methanol. The amount of methanol added is 10% to 15% of the daily water production, calculated by mass percentage. (2) Methanol injection is carried out continuously for 24 hours. (3) The injection temperature is room temperature, and the pressure is the gas well casing pressure, which is 10-12 MPa; (4) No production stoppage is required during the injection process. Gas wells produce through tubing. Due to gravity difference, methanol will fall to the bottom of the casing well. The bottoms of the oil and casing wells are connected. The methanol added to the casing mixes with the production gas flow at the bottom of the well. During the gas flow production process, methanol and natural gas are mixed together and transported from the bottom of the well to the wellhead through the production tubing.

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