CN103305200A - Compound type hydrate inhibitor - Google Patents

Abstract

The invention belongs to the field of gas storage and transportation, and in particular relates to a composite gas hydrate inhibitor. The inhibitor is composed of polyvinyl caprolactam, alcohol or salt, and water, wherein each component is calculated by mass percentage, polyvinyl caprolactam accounts for 0.1%~0.5%, alcohol or salt accounts for 1%~5% , and the rest is water. The present invention adds certain salts or alcohols to the existing kinetic inhibitors, which can not only prolong the formation time of hydrates, but also reduce the formation amount of hydrates, greatly improving the inhibitory effect of kinetic inhibitors , so that the effect of the kinetic inhibitor is better, more stable, and the application range is wider.

Description

A compound hydrate inhibitor

technical field

The invention belongs to the field of gas storage and transportation, in particular to an additive for inhibiting the occurrence of hydrates in the gas storage and transportation process.

Background technique

During the extraction and transportation of oil and natural gas, various low-boiling hydrocarbon gases (such as methane, ethane, propane) and non-hydrocarbon gases (carbon dioxide, hydrogen sulfide) are easily Forms gas hydrates with water in petroleum fluids. Gas hydrate is a cage structure formed by water molecules connected by hydrogen bonds, and small gas molecules are surrounded in the cage structure by van der Waals force to form an ice-like compound. It gathers together under certain conditions and forms lumps. In severe cases, it will block equipment such as pipelines, wellbores, valves, and instruments. This poses a great threat to the production, storage and transportation of oil and gas industries, mainly in the following three aspects:

(1) Hydrate generated in the pipeline will block the pipeline, increase the pressure difference of the pipeline, damage the pipe fittings, etc.;

(2) The formation of hydrates in the porous media of formations will block oil and gas wells, reduce the porosity and relative permeability of oil and gas reservoirs, change the distribution of oil and gas in oil and gas reservoirs, and reduce the production of oil and gas wells;

(3) The formation of hydrate in the wellbore will block the wellbore, damage the internal components of the wellbore, reduce oil and gas production or even stop production.

Since Hammersdhmidt discovered that hydrates blocked natural gas pipelines in 1934, how to suppress the formation of hydrates during oil and gas production and transportation has become an urgent problem to be solved in the oil and gas industry.

The main conditions for the formation of natural gas hydrates are: (1) the water content of natural gas is in a saturated state, and the existence of liquid phase water is a necessary condition for the formation of hydrates; (2) high enough pressure and low enough temperature, different groups in natural gas The critical temperature for forming hydrates is the highest temperature at which hydrates of this component exist; (3) When the above conditions are met, the formation of hydrates also requires some auxiliary conditions, such as fluctuations in natural gas pressure, sudden changes in gas flow direction The resulting agitation, as well as the presence of seeds and so on.

Aiming at the conditions for hydrate formation, the most effective way to inhibit hydrate formation is to destroy its formation conditions. In general, hydrate prevention and control measures are to create conditions contrary to hydrate formation: high temperature, low pressure, removal (or reduce the water dew point). According to the research on the formation conditions of natural gas hydrate, the prevention and control measures of natural gas hydrate mainly include: heating method, dehydration method, depressurization control method, and adding chemical inhibitor method.

By heating the pipeline, the temperature of the system can be higher than the hydrate formation temperature under the system pressure, so as to avoid pipeline blockage. But the difficulty is that it is difficult to determine the location of the hydrate blockage, and once the hydrate is formed and then heat-treated, the hydrate will decompose and cause local high pressure, resulting in pipeline rupture. Dehydration technology eliminates the risk of hydrate formation by removing the water that causes hydrate formation, and is currently a preventive measure usually adopted before natural gas transmission. Dehydration of natural gas can significantly reduce the dew point of water. From a thermodynamic point of view, it means that the fugacity or activity of water is reduced, and the formation temperature of hydrate is significantly lowered, thereby eliminating the risk of hydrate formation during pipeline transportation. But the difficulty is that it is affected by the season and difficult to control, and the risk is relatively high.

Because in order to maintain a certain delivery capacity, the pressure of the pipeline generally cannot be lowered arbitrarily, so the pressure reduction control is only a method that can be realized in theory.

The method of adding chemical inhibitors has the advantages of simplicity, economy, and good effect, and is the most widely used method to prevent hydrate formation. In view of the serious harm of hydrates and the limitations of the other three hydrate control methods, it is of great significance to develop efficient hydrate inhibitors.

In order to achieve an effective hydrate suppression effect in actual formation, the method of adding a sufficient amount of chemical additives is often used to increase the equilibrium formation pressure of hydrates (higher than the operating pressure of the pipeline), or reduce the equilibrium formation temperature of hydrates (lower than The operating temperature of the pipeline), in order to inhibit the formation of hydrates, change the thermodynamic conditions of hydrate formation, crystallization rate or aggregation form, to achieve the purpose of maintaining fluid flow, the types of hydrate inhibitors are mainly divided into thermodynamic inhibitors, dynamic Chemical inhibitors and antipolymerization agents, traditional thermodynamic inhibitors such as alcohols such as methanol and ethylene glycol, or electrolytes can change the equilibrium conditions of hydrates, but when using thermodynamic inhibitors, the addition amount is large, and the concentration (mass fraction) in aqueous solution is generally It needs to reach 10%-60%, and some even reach 50%, the cost is high, and the loss of inhibitor is also large, which will bring environmental pollution problems. The antipolymerization agent can make it difficult for the generated gas hydrate to coalesce into agglomerates, and it can work in the case of closed pipelines or large subcooling, but there are limitations, and it only works when oil and water exist at the same time. Therefore, since the 1990s, scholars at home and abroad began to study low-dose kinetic inhibitors to replace the use of thermodynamic inhibitors. Kinetic inhibitors inhibit or delay the growth time of hydrates, thereby inhibiting the formation of hydrates without affecting the thermodynamic conditions of hydrate formation. However, kinetic inhibitors are greatly affected by the degree of subcooling. At present, the highest applicable supercooling degree for kinetic inhibitors is only 10-12°C. At higher supercooling degrees, the inhibitory activity is low, so they must be combined with thermodynamic inhibitors. It is economical and effective to use. In view of the above reasons, and on the basis of fully considering the advantages and disadvantages of various natural gas hydrate inhibitor methods, the present invention proposes a method for preparing a composite hydrate inhibitor.

Contents of the invention

The purpose of the present invention is to provide a high-efficiency compound hydrate inhibitor preparation method with low investment cost, economical operation and no limitation of subcooling degree.

To achieve the above object, the present invention adopts the following technical solutions:

A composite gas hydrate inhibitor, composed of kinetic inhibitor, alcohol or salt, and water, wherein each component is calculated by mass percentage, kinetic inhibitor accounts for 0.1% to 0.5%, alcohol or salt accounts for 1% ~5%, the rest is water. .

Wherein, kinetic inhibitor selects polyvinyl caprolactam (PVCap) for use.

Salts are potassium acetate and potassium nitrate.

Alcohols select ethylene glycol for use.

Beneficial effects of the present invention:

(1) Good effect: Kinetic inhibitors can only prolong the formation time of hydrate, but cannot reduce the amount of hydrate formation. However, the present invention inhibits hydrate formation from two aspects of hydrate formation kinetics and thermodynamics. In addition to being able to Prolonging the formation time of hydrates can also change the phase equilibrium point of hydrates and reduce the amount of hydrates formed.

(2) Wider application: The problems faced by kinetic inhibitors in the application are low inhibitory activity, greater influence from the external environment, poor versatility, and limited application. Because the effect of compound inhibitors is greatly improved, and it is also It can reduce the formation of hydrate, so it is more stable and more versatile.

(3) Lower cost, more economical and environmentally friendly: the additives selected in the present invention are some cheap, easily available and low-corrosion salts and alcohols, and the addition amount is not large, and the amount of kinetic inhibitors after compounding will be reduced. This will greatly reduce the cost of suppressing hydrate formation in the oil and gas industry.

The present invention adds certain salts or alcohols to the existing kinetic inhibitors, which can not only prolong the formation time of hydrates, but also reduce the formation amount of hydrates, greatly improving the inhibitory effect of kinetic inhibitors , so that the effect of the kinetic inhibitor is better, more stable, and the application range is wider.

Description of drawings

Figure 1 is a flow chart of the hydrate formation experimental device

1. High-pressure gas cylinder; 2. Pressure regulating valve; 3. Mass flow meter; 4. Check valve; 5. Gate valve; 6. Vacuum pump; 7. Pressure and temperature transmitter; 8. Circulation tank; 9. Constant temperature water bath ; 10, reactor; 11, data acquisition system; 12, computer; 13, photoelectric lens.

Detailed ways

The present invention will be further described in detail below, but the embodiments of the present invention are not limited thereto.

The experimental device that the present invention adopts is as shown in Figure 1, by high-pressure cylinder 1; Regulator valve 2; Mass flowmeter 3; Check valve 4; Gate valve 5; Vacuum pump 6; ; constant temperature water bath 9; reactor 10; data acquisition system 11; computer 12 and other components. The high-pressure gas cylinder 1 is used as the gas source, adjusted to an appropriate pressure through the pressure regulating valve 2, and the mass flow meter 3 is used to measure the consumption of natural gas. The temperature and pressure in the reactor 10 are monitored by a pressure and temperature transmitter 7 . The liquid temperature in the constant temperature water bath 9 is controlled by the circulation tank 8, thereby adjusting the temperature in the reaction kettle. The data is collected by the data acquisition system 11 and the computer 12, and the hydrate formation status in the reactor is monitored through the photoelectric lens 13. Vacuum pump 6 is used for sucking liquid in the reactor. The working pressure of the system is 0-30MPa, and the temperature range is -10℃-25℃.

Specific preparation process:

1) Use the vacuum pump 6 to vacuumize the reactor 10 and the piping system, and the vacuuming time is 40-50min.

2) In order to get rid of the air in the reactor 10 and the pipeline system as much as possible, replace them twice with the test gas, and then evacuate them again.

3) Pour the prepared aqueous solutions of compound inhibitors of different concentrations into the reactor 10, stir for 3-5 minutes, and pre-cool to a certain temperature.

4) Open the one-way valve 4, fill the high-pressure experiment gas into the reactor 10, and maintain the pressure of the reaction system at the pressure required for the experiment through the pressure regulating valve 2.

5) Set the experimental temperature and start the temperature control system of the experimental device. The reactor 10 is cooled by the circulation tank 8 until the temperature in the reactor 10 reaches the set temperature.

6) Conduct hydrate formation experiments.

The composition of the selected composite inhibitor is as follows: the mass of the aqueous solution is 200g, the mass concentration of polyvinyl caprolactam (PVCap) added is between 0.1% and 0.5%, and the mass percentage of added salts or alcohols is between 1% and 5%. See Table 1. The experimental steps are the same as above. Three concentrations of PVCap are mixed with three salts or alcohols of different concentrations, and the inhibition time and pressure drop obtained through experiments are compared to screen out the optimal concentration ratio of the compound inhibitor.

Table 1 Compound inhibitor preparation concentration

Comparative example (pure water)

The conditions for the start of the reaction are 2°C and a pressure of 5MPa, and the equilibrium pressure of the methane hydrate formed at 2°C is 4.6MPa. The experimental steps are the same as above. When the temperature in the reactor is cooled to 2°C, feed methane (purity 99.99%) gas to make the pressure in the reactor reach 5Mpa, start stirring to keep it at 500rmp, because methane dissolves in water, the pressure drops slightly, when the pressure When it reaches 3.4MPa, the reaction reaches equilibrium, and the amount of methane gas consumed is reflected by the pressure drop. The induction time required for the hydrate formation of pure water under the above conditions is 45min, the reaction completion time is 157min, and the pressure drop in the reaction is 0.7MPa.

Example 1

0.1% PVCap and 1% ethylene glycol compound, the experimental procedure is the same as above, the results show that the induction time is 65min, the reaction completion time is 180min, the pressure drop of methane gas is 0.6MPa, and its inhibition performance is more obvious than that of pure water.

Example 2

0.1% PVCap and 3% ethylene glycol compounded, the experimental procedure is the same as above, the results show that the induction time is 78min, the reaction completion time is 200min, the pressure drop of methane gas is 0.5MPa, and its inhibition performance is significantly improved.

Example 3

0.1% PVCap and 5% ethylene glycol were compounded, the experimental procedure was the same as above, the results showed that the induction time was 85min, the reaction completion time was 215min, the pressure drop of methane gas was 0.45MPa, and the inhibition performance was significantly improved.

Example 4

0.3% PVCap and 1% ethylene glycol compounded, the experimental procedure is the same as above, the results show that the induction time is 90min, the reaction completion time is 225min, the pressure drop of methane gas is 0.35MPa, and its inhibition performance is significantly improved.

Example 5

0.3% PVCap and 3% ethylene glycol compound, the experimental procedure is the same as above, the results show that the induction time is 105min, the reaction completion time is 245min, the pressure drop of methane gas is 0.35MPa, and its inhibition performance is significantly improved.

Example 6

0.3% PVCap and 5% ethylene glycol compounded, the experimental procedure is the same as above, the results show that the induction time is 120min, the reaction completion time is 276min, the pressure drop of methane gas is 0.3MPa, and its inhibition performance is significantly improved.

Example 7

0.5% PVCap and 1% ethylene glycol compound, the experimental procedure is the same as above, the results show that the induction time is 127min, the reaction completion time is 289min, the pressure drop of methane gas is 0.32MPa, and its inhibition performance is significantly improved.

Example 8

0.5% PVCap and 3% ethylene glycol compound, the experimental procedure is the same as above, the results show that the induction time is 135min, the reaction completion time is 334min, the pressure drop of methane gas is 0.25MPa, and its inhibition performance is significantly improved.

Example 9

0.5% PVCap and 5% ethylene glycol compound, the experimental procedure is the same as above, the results show that the induction time is 156min, the reaction completion time is 377min, the pressure drop of methane gas is 0.2MPa, and its inhibition performance is significantly improved.

From the above examples, it can be concluded that the combination of 0.1%-0.5% PVCap and 1%-5% ethylene glycol has an obvious inhibitory effect on the formation of gas hydrate, and the combination of 0.5% PVCap and 5% ethylene glycol has the best inhibitory effect. good. Similarly, the compounding of potassium acetate and potassium nitrate with PVCap in the same concentration range also has obvious inhibitory effect on the formation of hydrate.

Claims (2)

1. a compound gas hydrate inhibitor is characterized in that being made up of Vinylcaprolactam homopolymer, alcohol or salt and water, wherein each component by mass percentage, Vinylcaprolactam homopolymer accounts for 0.1% ~ 0.5%, alcohol or salt account for 1% ~ 5%, all the other are water.

2. according to the described compound gas hydrate inhibitor of claim, it is characterized in that alcohols is ethylene glycol, salt is Potassium ethanoate or saltpetre.

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