Novel method for preventing natural gas gathering and transportation freezing blockage

Abstract

A novel method for preventing natural gas gathering and transportation freezing blockage comprises the following steps that (1) firstly, gas-liquid mixed fluid at a well head is subjected to basic phase separation through a separator, gas enters a gas channel, and liquid drops are separated out through rectification and gravity settling; liquid enters the liquid space, bubbles are separated out, and meanwhile, under the gravity condition, gas flows out of the gas outlet after liquid drops are removed through the mist catcher before the gas leaves the separator; (2) after the gas leaves the separator, methanol is continuously added in a dropwise manner, the mass percent concentration of the added methanol is 15-20%, and the addition amount of the methanol is related to the saturated water content in the natural gas; and (3) a filling mode: filling from the rear end of the separator, and continuously filling for 24 hours. By adopting the method, the problem of freezing blockage is solved, normal production of the gas well is prevented from being influenced by freezing blockage, and the gas production efficiency is improved.

Description

Technical Field

[0001] This method relates to the technical field of enhanced oil recovery in gas fields. More specifically, it relates to a new method for preventing freezing and blockage in natural gas gathering and transportation. Background Art

[0002] In response to the problems that occur during the production process of gas wells, innovative treatment countermeasures need to be developed to reduce the production cost of gas production. The main problems are as follows: First, the produced water volume of the put-into-production gas wells is large. Coupled with the long gathering pipeline and large frictional resistance, the backpressure at the wellhead is high, affecting the productivity of the gas wells. The flowing temperature at the wellhead of the gas wells is low, resulting in easy freezing and blockage of the gathering pipelines and low well-opening rate. Second, the pressure at the wellhead of the gas wells is high. When opening the well, it is necessary to vent and carry geothermal heat, but due to safety and environmental protection requirements, the wellhead venting operation cannot be carried out. The temperature at the wellhead is low, and the fluid temperature in the gathering pipeline is even lower, resulting in freezing and blockage of the gathering pipelines and difficult well opening. Third, the failure rate of the electric heating tapes on the gathering pipelines of gas wells is high. Normal gas production cannot be carried out in winter, and freezing and blockage problems occur frequently, seriously affecting the normal production of gas wells. Summary of the Invention

[0003] The purpose of the present invention is to provide a new method for preventing freezing and blockage in natural gas gathering and transportation, solve the problems existing in the current background art, and improve the gas production efficiency.

[0004] The technical solution provided by the present invention is: A new method for preventing freezing and blockage in natural gas gathering and transportation includes the following steps:

[0005] (1), First, the gas-liquid mixed fluid at the wellhead first undergoes basic phase separation through a separator. The gas enters the gas channel, and through rectification and gravity sedimentation, liquid droplets are separated; the liquid enters the liquid space, and bubbles are separated. At the same time, under the condition of gravity, the gas flows out from the gas outlet after removing liquid droplets through a mist eliminator before leaving the separator.

[0006] (2), After the gas leaves the separator, methanol is continuously added drop by drop. The mass percentage concentration of methanol addition is 15% - 20%, and the addition amount of methanol is related to the saturated water content in natural gas.

[0007] The saturated water content in natural gas is determined by the following formula:

[0008]

[0009] In the formula: W - saturated water content, kg / m 3 ;

[0010] T - absolute temperature of natural gas fluid, K;

[0011] P - absolute pressure of natural gas fluid, MPa.

[0012] Set the saturated water content of natural gas at the inlet of the gas production pipeline as Wr and at the outlet as Wc. Then, the maximum amount of condensate water generated during the flow of natural gas in the gas production pipeline: Q n = W r - W c ;

[0013] (3) Injection method: Inject from the back end of the separator and carry out continuous 24-hour injection.

[0014] The pressure after the first section of the separator is controlled at 6 - 8 MPa, the temperature is controlled at 25 - 30 °C, the pressure after the second section is controlled at 2.5 - 3.0 MPa, and the outlet temperature of natural gas is controlled at 25 - 30 °C.

[0015] The injection concentration of the methanol is the percentage of the mass of methanol in the mass of the maximum condensate water.

[0016] The beneficial effects of the present invention are as follows: 1. A calculation formula for predicting the amount of condensate water is established and verified on-site, and the error is controlled within 5%, which can meet the working requirements. 2. Through indoor experiments, the injection concentration of methanol is mastered, and the temperature drop of hydrate is determined. Through indoor high-pressure reactor experiments, the hydrate formation temperature under different pressure conditions is determined, and finally the influence of methanol concentration on the temperature drop of hydrate is obtained to guide the on-site injection work. Description of the Drawings

[0017] Figure 1 It is the curve of the saturated water content of natural gas of the present invention changing with temperature. Specific Embodiments

[0018] In order to make the technical problems, technical solutions and beneficial effects to be solved by the present invention clearer, the present invention will be further described in detail below with reference to the drawings and embodiments. It should be understood that the specific embodiments described herein are only used to explain the present invention and are not used to limit the present invention.

[0019] A new method for preventing freezing and blockage in natural gas gathering and transportation includes the following steps:

[0020] Step 1. First, the gas-liquid mixed fluid at the wellhead first undergoes basic phase separation in the separator. The gas enters the gas channel, and through rectification and gravity sedimentation, liquid droplets are separated; the liquid enters the liquid space, and gas bubbles are separated. At the same time, under the condition of gravity, the gas flows out from the gas outlet after removing liquid droplets through the mist eliminator before leaving the separator. At this time, the natural gas at the outlet of the separator contains no free water but only saturated water, and the condition for forming hydrate blockage no longer exists near the wellhead. However, during the long-distance gathering and transportation of the gas production pipeline, due to the relatively low temperature of the buried pipeline, some condensate water will be generated, and at this time, the condition for forming hydrate exists. For the above reasons, continuous drip feeding of medicine is required to prevent the condensate water from forming hydrate with natural gas and causing blockage of the gas production pipeline.

[0021] Step 2. Calculation of the maximum condensate water volume:

[0022] The saturated water content in natural gas is determined by the following formula:

[0023]

[0024] In the formula: W—the saturated water content, kg / m 3 ;

[0025] T—the absolute temperature of the natural gas fluid, K;

[0026] P—the absolute pressure of the natural gas fluid, MPa.

[0027] Assume that the saturated water content of natural gas at the inlet of the gas production pipeline is Wr and that at the outlet is Wc. Then, the maximum condensate water volume Q generated during the flow of natural gas in the gas production pipeline: n = W r - W c .

[0028] The saturated water content of natural gas increases with the decrease of pressure. However, under the conditions of high-pressure gathering and transportation, the change amplitude is not significant; the saturated water content of natural gas decreases with the decrease of temperature, and the influence of temperature on the saturated water content of natural gas is greater than that of pressure. Therefore, when natural gas flows in the gas production pipeline, since the pressure at the inlet of the gas production pipeline is close to that at the outlet, the condensate water volume is mainly determined by the temperature difference between the inlet and the outlet. The curve of the saturated water content of natural gas changing with temperature is as Figure 1 shown.

[0029] Step 3. After the gas leaves the separator, methanol is continuously added drop by drop. Methanol can effectively remove the hydrate blockage, but if too much is added, it is easy to form liquid accumulation, affecting the gas well production capacity. According to the table of the relationship between methanol concentration and the temperature drop of hydrate production, the preferred mass percentage concentration of methanol injection is 15% - 20%. The injection concentration of the methanol is the percentage of the mass of methanol in the mass of the maximum condensate water.

[0030] --Table 1 Table of the relationship between methanol concentration and the temperature drop of hydrate production

[0031]

[0032]

[0033] Step 4. Injection method: Inject from the back end of the separator. In order to improve the prevention and control effect, continuous injection for 24 hours is adopted, which can remove the less blocked form of hydrate and make full use of methanol.

[0034] Step 5: The temperature and pressure of natural gas have a great influence on the gas-liquid separation efficiency. Therefore, during operation, parameters such as the temperature and pressure of natural gas in the separator should be strictly controlled. For Well CP2, the daily gas production is controlled at about 50,000 m³, the pressure after the first stage is controlled at 6 - 8 MPa, the temperature is controlled at 25 - 30 °C, the pressure after the second stage is controlled at 2.5 - 3.0 MPa, and the outlet temperature of natural gas is controlled at 25 - 30 °C.

[0035] Under the condition of ensuring the external transportation conditions, improve the separation effect to ensure that there is no free water in the natural gas at the separator outlet. Through calculation, after long-distance gas gathering and transportation through the gas pipeline, for Well CP2, according to the saturated water content calculation formula in natural gas, when the outlet pressure of natural gas is 2.5 - 3.0 MPa and the outlet temperature is 25 - 30 °C, the saturated water content in every 10,000 m³ of natural gas is 50 - 60 kg. After long-distance pipeline transportation, due to the cooling effect of the earth's geothermal temperature on the natural gas temperature, when entering the station, the pressure drops to 2.8 - 2.9 MPa and the temperature drops to 0 - 3 °C. At this time, there is almost no saturated water in the natural gas. Therefore, 50 - 60 kg of condensate water can be generated during the transportation of 10,000 m³ of natural gas. When transporting 50,000 m³ of natural gas, 250 - 300 kg of condensate water will be generated, and 40 - 50 kg of methanol needs to be continuously injected to achieve stable external transportation.

Claims

1. A new method for preventing freezing and blocking of natural gas gathering and transportation, characterized by: The following steps are involved: (1) First, the gas-liquid mixed fluid at the wellhead is separated by the separator. The gas enters the gas channel and separates the liquid droplets through rectification and gravity sedimentation. The liquid enters the liquid space and separates the bubbles. At the same time, under gravity conditions, the gas passes through the mist collector to remove the liquid droplets before leaving the separator and then flows out from the gas outlet. (2) After the gas leaves the separator, methanol is continuously added dropwise, with the concentration of methanol added being 15% to 20% by mass. The amount of methanol added is related to the saturated water content in the natural gas; The saturated water content in natural gas is determined by the following formula: Where: W—saturated water content, kg / m 3 ; T—absolute temperature of natural gas fluid, K; P—absolute pressure of natural gas fluid, MPa. Assuming the saturated water content of natural gas at the inlet of the gas pipeline is Wr, and that at the outlet is Wc, the maximum amount of condensate water generated by natural gas during the flow of the gas pipeline is: Q n =W r -W c ; (3) Filling method: Inject from the rear end of the separator and fill continuously for 24 hours.

2. The new method for preventing freezing and blocking of natural gas gathering and transportation according to claim 1 is characterized in that: The pressure after the first section of the separator is controlled at 6-8 MPa and the temperature is controlled at 25-30°C. The pressure after the second section is controlled at 2.5-3.0 MPa and the natural gas outlet temperature is controlled at 25-30°C.

3. According to claim 1, it is characterized in that: The filling concentration of methanol is the percentage of the mass of methanol to the maximum mass of condensate water.

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