CN106872660A - A kind of deep water gas well surface shut-in stage gas hydrates growth simulation device - Google Patents

Abstract

The invention relates to a natural gas hydrate growth simulation device in the surface shut-in stage of a deep-water gas well. and computer terminals. The device can be used to simulate the growth of hydrates in the process of deep-water gas well testing on the ground during shut-in, and obtain the growth law of hydrates under different water content, temperature, pressure and other conditions, so as to study the "two openings and two closings" production system of deep-water gas well testing Feasibility, to provide a reference for the rational formulation of the work system.

Description

A device for simulating natural gas hydrate growth during surface shutdown of deep-water gas wells

technical field

The invention relates to the technical field of exploration and development of deep-water gas wells, in particular to a natural gas hydrate growth simulation device during the shut-in stage of deep-water gas well testing.

Background technique

Natural gas hydrate is a clathrate compound formed by natural gas and water at a low temperature above freezing point and a certain pressure. It looks like ice but has a different crystal structure from ice. Among them, water molecules form the main crystal network by means of hydrogen bonds, and the pores in the crystal lattice are filled with light hydrocarbons (methane, ethane, propane, isobutane) or non-light hydrocarbons (nitrogen, carbon dioxide, and hydrogen sulfide) molecules, the so-called guest molecule.

During the exploration and development of deep-water gas wells, methane hydrate with methane CH ₄ as the guest molecule is mainly formed. Its formation needs to go through two stages of nucleation and growth. After nucleation, the hydrate will continue to grow only when the conditions are suitable, otherwise the growth process will not continue. The suitable growth conditions are: the solution around the hydrate nucleus is in a supersaturated state, the surrounding environment has suitable low temperature and high pressure conditions and good heat dissipation conditions, and at the same time, the gas-liquid contact area is large enough to facilitate material transfer. Many studies at this stage have proved that the initial well opening stage and the well shut-in stage are the two stages with the greatest risk of hydrate formation and plugging during deepwater gas well testing.

At present, the testing work of deep-water gas wells is formulated from the perspective of avoiding hydrate formation, without considering the process of hydrate growth. However, in the actual test process, only when the hydrate grows to a certain extent will it affect the test work and bring great troubles to subsequent drilling and mining. Therefore, if a set of reasonable simulation methods and devices can be provided for hydrate growth during deep-water gas well shutdown, it will have certain reference significance for the formulation of testing work systems, which will help improve economic benefits and reduce safety hazards.

Contents of the invention

Aiming at the problems existing in the development of the above-mentioned deep-water gas wells, the present invention provides a hydrate growth simulation device during the shut-in phase of the deep-water gas well testing process. The device can be used to simulate the growth of hydrates in the process of deep-water gas well testing on the ground during shut-in, and obtain the growth law of hydrates under different water content, temperature, pressure and other conditions, so as to study the "two openings and two closings" production system of deep-water gas well testing Feasibility, to provide a reference for the rational formulation of the work system.

Technical scheme of the present invention is as follows:

A hydrate growth simulation device in the surface shut-in stage during deep-water gas well testing, which consists of a reaction column, a constant temperature control system, a natural gas gas supply system, a natural gas pressurization system, a liquid supply system, a drainage system, a parameter monitoring and data acquisition system and Composition of computer terminals; where:

The reaction column provides a place for the reaction of water and natural gas, and its lower end is respectively connected to the pipeline of the liquid supply system and the natural gas pressurization system; the natural gas pressurization system is connected to the pipeline of the natural gas supply system; the The upper end of the reaction column is connected to the drainage system pipeline;

The natural gas supply system is used to inject natural gas into the reaction column;

The natural gas pressurization system is used to pressurize the natural gas provided by the natural gas supply system, and to evacuate the reaction column;

The liquid supply system is used to inject liquid into the reaction column and maintain the liquid level in the reaction column;

The liquid discharge system is used to discharge natural gas and liquid after the reaction;

The constant temperature control system includes a local temperature control device arranged on the reaction column, a first temperature control tank with a built-in reaction column, and a second temperature control tank with a built-in liquid supply system and a natural gas supply system. tank; the constant temperature control system is used to control the temperature gradient and the overall temperature of the reaction column, and the temperature of the liquid supply system and the natural gas supply system;

The parameter monitoring and data acquisition system transmits the data to the computer terminal through the sensors arranged in each system to be tested.

Through the mutual cooperation of the above-mentioned systems, the hydrate growth during the surface shut-in stage during the deep-water gas well test can be simulated to the greatest extent, so as to obtain the hydrate growth law under different water content, temperature, pressure and other conditions, which is conducive to the study of deep-water gas well testing. The feasibility of the "two openings and two closings" production system provides a reference for rationally formulating a work system.

The following is a detailed description of each system:

The reaction column includes two types: one is a reaction column made of stainless steel that can withstand a pressure of at least 30 MPa; the other is a visual reaction tube made of sapphire or high-strength glass that can withstand a pressure of at least 10 MPa column.

Flanges are installed at the upper and lower ends of the reaction column, and the flange plug at the lower end is provided with an interface, and the interface is respectively connected with the natural gas pressurization system and the liquid supply system.

Positions for installing various sensors are reserved on the reactor body of the reaction column. A camera is installed on the side of the visualized reaction column to shoot and record the growth of hydrate in the reaction column, and transmit the image information to the computer. The reaction column made of stainless steel measures the growth thickness of the hydrate layer through the hydrate thickness measurement sensor, and records the hydrate growth data through the computer. The reaction column mainly provides a place for hydrate formation, and the generated hydrate will adhere to the wall of the reaction column.

The constant temperature control system mainly includes two temperature control tanks and a local temperature control device arranged on the reaction column.

One of the temperature control tanks is used to adjust and control the temperature of water and natural gas injected into the reaction column, and the other is used to control the overall ambient temperature of the reaction column.

The local temperature control device is used to adjust the temperature of different positions in the reaction column to simulate the temperature field distribution in the test column during the deep water test, so as to control the growth rate of hydrate and the evaporation rate of water. The temperature distribution field is not a single increasing or decreasing temperature gradient, but is divided into two sections (that is, the temperature decreases from the sea level to the mud line, and the temperature increases from the mud line to the depth of the gas reservoir). The local temperature control device realizes the simulation of the temperature distribution field through two-stage temperature adjustment. First, the temperature of the overall column temperature of the reaction column is lowered through the temperature control tank, and then the local position of the column is heated to change the temperature field distribution of the column. , to simulate the actual situation on site. There may be different temperatures for unventilated reservoirs and different oceans. Therefore, the adjustable temperature range of the local temperature control device is between 0-90°C.

The natural gas supply system is used to inject experimental natural gas into the reaction column, mainly including a gas tank and an air inlet valve;

The natural gas pressurization system mainly includes a booster pump and a vacuum pump. The booster pump is used to boost the natural gas output from the natural gas supply system and adjust the reaction pressure in the reaction column. The gas output from the natural gas supply system is first pressurized by the booster pump of the natural gas booster system and then injected into the reaction column. The vacuum pump is used to evacuate the inside of the reaction column to a vacuum state before gas injection.

The liquid supply system mainly includes a liquid inlet valve, an electric pump and a water supply tank. The liquid supply system is used to provide liquid in the reaction column to maintain the liquid level in the reaction column.

The drainage system mainly includes a drainage valve and a drainage tank.

The parameter monitoring and data acquisition system mainly includes a gas flowmeter, a liquid flowmeter, a liquid temperature sensor, four temperature sensors, two gas pressure sensors, a hydrate layer ultrasonic thickness sensor, and a hygrometer. The parameter monitoring and data acquisition system is used to monitor the consumption of gas and liquid in the reaction column, the change of temperature, pressure and humidity, the thickness of the hydrate layer on the inner wall of the reaction column, the reaction time and other parameters, and collect and transmit them to the computer terminal.

All pipeline connection methods in the present invention adopt anti-high pressure stainless steel pipelines.

The present invention further provides a method for judging the risk degree of hydrate formation by using the above simulation device: in the reaction column, hydrate grows in a wall-attached manner and gradually thickens in the form of a hydrate layer. The hydrate layer grows preferentially at the simulated mud line in the pipe string, and the growth rate of hydrate adheres to the wall at different parts of the pipe string. If the hydrate layer grows and completely blocks the wellbore during the well shut-in time, the surface well shut-in method is not suitable under the temperature and pressure conditions, and the number of well shut-in and shut-in should be reduced as much as possible, and hydrate suppression measures should be taken according to the actual situation. If the hydrate layer has formed to a certain thickness but has not blocked the entire pipe string, it can be judged whether there is a risk of blockage according to the situation after the well is opened again. The specific judgment method is as follows:

Assuming that the wall hydrate thickness is d, the radius of the gas flow section here is R=(L-2d)/2, and the gas flow velocity is:

In the formula, L is the wellbore diameter, m; Q is the gas flow rate, m ³ /d.

Then the resultant force on the wall surface hydrate particles is:

F＝F _f -Gcosθ-F _c

Substituting gravity, drag force, etc. into

When the hydrate particles are in the critical state of force balance, the resultant force F=0, then

At this time, the radius of the gas flow section is:

Hydrate thickness at this time

When R>r, it indicates that as the gas flow area decreases, the gas flow rate in the wellbore increases and the corresponding drag force increases when the well is opened again and the production rate is constant.

When R<r, it indicates that the drag force cannot carry the hydrate to the wellhead under the production rate of the well, and blockage will be formed in the wellbore.

The technical effect of the scheme of the present invention is:

(1) Use a dual temperature control system, including a temperature control tank and a local temperature control device to simulate the temperature field distribution in the wellbore during well shut-in, so that the temperature of the hydrate formation area and the evaporation area of the bottom water in the reaction column can be separated to the greatest extent. The actual situation of using surface shut-in in the field test work;

(2) The present invention designs two kinds of reaction strings, which are suitable for simulating the growth of ground well shut-in hydrate under different pressure conditions. Using the visualization column under low pressure conditions can directly observe the attachment position of the hydrate on the reaction column. At the same time, the two reaction columns can measure the gas phase and liquid phase flow pressure changes through the data acquisition system, calculate the consumption of gas phase and liquid phase during the growth process of hydrate formation, and combine the value of the hydrate layer thickness sensor to obtain the hydrate The growth rate under the experimental conditions has a guiding effect on the field test work;

(3) The present invention combines the distribution of gas and water with the growth of hydrates during well shut-in, and affects the speed of water vapor diffusion by changing the height of the liquid level in the reaction pipe string and the temperature of the reaction pipe string at the liquid accumulation place; According to the risk of hydrate formation under different liquid level heights and temperatures, it is proposed whether hydrate suppression measures should be taken for different gas reservoir temperatures and liquid accumulation heights during field test work.

Description of drawings

Fig. 1 is a schematic diagram of the growth of hydrates on the surface of deep-water gas well testing during shut-in.

Fig. 2 is a schematic diagram of hydrate growth when the gas in the test string of a deep-water gas well is the continuous phase.

Fig. 3 is a schematic diagram of hydrate growth formed by droplets in the test string of a deep-water gas well.

Fig. 4 is a block diagram of the working principle of the ground shut-in hydrate growth simulation device for deep-water gas well testing.

Fig. 5 is a system diagram of the ground well shut-in hydrate growth simulation device for water and gas well testing.

Fig. 6 is a structural diagram of a pressure-resistant reaction column.

In the picture:

1. Reaction column; 2. Constant temperature control system; 2-a, temperature control tank; 2-b, temperature control tank; 3. Flange plug; 4. Gas flow meter; 5. Air valve; 6. Booster Pump; 7. Gas tank; 8. Inlet valve; 9. Water supply tank; 10. Liquid flowmeter; 11. Electric pump; 12. Vacuum pump; 13. Drain valve; 14. Drain tank; 15. Computer; 16. Hydration Layer thickness measurement sensor; 17. Intake temperature sensor; 18. Intake pressure sensor; 19. Liquid temperature sensor; 20. Local temperature control device; 21. Temperature sensor in the reaction column; 22. Hygrometer; 23. Gas Pressure sensor; 24. Fluid injection port; 25. Temperature sensor installation interface; 26. Pressure sensor installation interface; 27. Fluid outlet; 28. Hygrometer sensor installation interface; 29. Local temperature control device for pipe string; 30. Camera; 31. The installation interface of the hydrate thickness ultrasonic sensor.

detailed description

The following examples are used to illustrate the present invention, but are not intended to limit the scope of the present invention.

Fig. 2 is a schematic diagram of hydrate growth during the surface shut-in stage of deep-water gas well testing, and a growth characteristic model of "splashing water and freezing" was established for the growth of hydrate in the test string. In the shut-in stage of deep-water gas well testing, the gas phase in the test string is a continuous phase, and water vapor molecules are dissolved in the gas phase, and a small amount of small liquid droplets are also entrained in the gas phase. After the ground well is shut in, the liquid phase on the inner wall of the test string mainly exists in the form of a liquid film. Since the shut-in fluid does not flow, the liquid film will gradually slide down to the bottom of the well under the action of gravity. The water vapor in the wellbore is moving freely and randomly, and some of the water vapor molecules migrate to the liquid film on the wall of the test pipe string during the movement. Since the nucleation of hydrate is heterogeneous nucleation, it occurs in the gas At the liquid interface, hydrates will nucleate and grow at the surface of the liquid film on the test tube wall, where water vapor and methane are consumed. Due to the consumption of water vapor, there is a concentration difference in the wellbore. Under the action of the concentration difference, the water at the bottom of the well will evaporate water molecules, and these water vapor molecules will diffuse upward to the hydrate formation area to continue to promote the growth of hydrate. The hydrate layer is a membrane-like structure with pores, the gas phase and the liquid phase diffuse and contact through the pores, and the hydrate continues to grow. With the growth of hydrate, the pores will gradually become smaller until they are completely filled with hydrate. At this time, the gas phase and the liquid phase are separated, and further nucleation and growth cannot occur. If there is still a liquid film on the inner wall of the test string, the liquid film will migrate further downward under the action of gravity, and finally only the hydrate layer will be left attached to the inner wall of the test string.

Fig. 3 is a schematic diagram of hydrate growth formed by droplets in the test string of a deep-water gas well. In the shut-in stage, in addition to the water vapor molecules dissolved in the gas phase, there are also some small amount of mist droplets. These mist-like liquid droplets fully contact with gas phase molecules in the wellbore. First, a very thin hydrate film will be formed at the contact interface between gas and liquid droplets. The hydrate film has a structure with pores, and gas phase molecules and liquid phase molecules pass through the pores. The liquid in the membrane is continuously consumed, the hydrate membrane becomes thicker gradually, and the hydrate grows. For smaller droplets, hydrate particles will eventually form, and the hydrate particles will slide down under the action of gravity, and may stagnate and adhere to the inner wall of the test string when they contact the well wall. For larger droplets, the hydrate film is thicker in the late growth stage, which hinders the diffusion of liquid and gas phase molecules, so the growth rate in the later stage is slow, and hydrate particles containing liquid inside will eventually be formed.

Fig. 4 is a system diagram of the hydrate growth simulation device for deep-water gas well testing. The following descriptions are given for the hydrate growth simulation experiment steps of the invention during the deep-water test ground shut-in period (the reaction column adopts a pressure-resistant 10MPa visual reaction column):

(1) Pretreatment reaction column: after testing the sealing performance of the reaction column, flush the reaction column. The pretreated reaction column is connected with other devices and the sealing condition of the pipeline connection is checked. At this time, all valves are closed.

(2) Treatment of the reaction column: use the vacuum pump 12 to evacuate the inside of the reaction column to a vacuum state, and turn off the vacuum pump 12 .

(3) Temperature control: Use the temperature control tank 2-a to control the temperature of the reaction column 1 to the temperature at the seabed mud line during the test, and use the temperature control tank 2-b to adjust the temperature in the gas tank 7 and the water supply tank 9 to Temperature conditions in the gas reservoir during the test. Adjusting the local temperature control device 20 increases the temperature of the reaction string, changes the temperature distribution in the reaction string, and simulates the temperature field of the test string during the deep-water gas well test.

(4) Inject the experimental liquid: open the liquid inlet valve 8, observe the liquid level through the visual reaction column, use the electric pump 11 to pump the required experimental liquid into the reaction column to the specified height, and close the liquid inlet valve 8 and the electric pump 11.

(5) Inject test gas: open the intake valve 5 and the booster pump 6, supply gas to the reaction column and pressurize, monitor the pressure in the reaction column through the gas pressure sensor 23 in the reaction column, when the reaction tube When the experimental pressure is reached in the column, the inlet valve 5 and the booster pump 6 are closed, and the pressure in the reaction column is monitored. If it can be kept stable for a period of time, the next operation can be carried out.

(6) Shooting and recording: After the operation of adjusting the experimental temperature is completed, turn on the camera to shoot and record the hydrate formation area in the reactor.

(7) Hydrate growth process: Start timing at the same time as shooting, and observe the growth of the hydrate layer according to the data transmitted from the hydrate layer thickness measurement sensor 16 to the computer 15 and the images captured by the camera.

(8) Drainage and exhaust: after the specified time of the experiment is reached, the discharge valve 13 is opened to release the gas in the reaction column, and the liquid inlet valve 5 is opened to drain the remaining water at the bottom of the reaction column into the water supply tank 9 . Remove the flange plug 3 on the reaction column 1, and observe the growth of the hydrate layer in the reaction column.

(9) Working condition of parameter detection and data acquisition and processing system: gas flow meter 4 monitors the gas flow injected into the reaction column; liquid flow meter 10 monitors the liquid flow injected into the reaction column; inlet temperature sensor 17 monitors the injection reaction tube The gas temperature in the column provides a temperature reference for the local temperature control device; the liquid temperature sensor 19 monitors the temperature of the liquid injected into the reaction column by the reaction tube and provides a temperature reference for the temperature control device; the gas pressure sensor 23 in the column monitors the temperature in the reaction column The pressure level provides reference for the pressurization system; the temperature sensor 21 in the column monitors the temperature in the column during the reaction process and provides a reference for the local temperature control device; the hygrometer 22 monitors the change of water content in the reaction column during the hydrate growth process The hydrate layer thickness sensor 16 monitors the growth thickness change of the hydrate layer during the hydrate growth process. All the sensors in the system monitor the parameters and transmit the collected data to the computer for quantitative analysis of hydrate growth. Through the collected parameters and their changing trends, in-depth quantitative research on the hydrate growth process can be carried out, so as to provide a reference for the formulation of the working system of the deep-water gas well testing process.

The experimental procedure of using a pressure-resistant 30MPa reaction column is basically the same as that of using a pressure-resistant 10MPa reaction column. Since the pressure-resistant 30MPa reaction column is invisible, step (7) can be omitted.

Figure 6 is the structural diagram of the reaction column in the system diagram. Before the experiment, gas is introduced into the reaction column to check the tightness between the reaction column and the flange plug. After confirming that the sealing performance is good, it is connected with Device connection for other systems. The pressure-resistant 10MPa visual reactor has the same structure as the pressure-resistant 30MPa reactor, but the difference is that the visual reactor can directly record the hydrate growth process through the naked eye or a camera, and the non-visual reactor needs to use materials with higher pressure resistance. Hydrate growth can only be monitored with ultrasonic sensors.

Although the present invention has been described in detail with general descriptions and specific embodiments above, it is obvious to those skilled in the art that some modifications or improvements can be made on the basis of the present invention. Therefore, the modifications or improvements made on the basis of not departing from the spirit of the present invention all belong to the protection scope of the present invention.

Claims (7)

1. a kind of deep water gas well surface shut-in stage gas hydrates growth simulation device, it is characterised in that by reaction tubing string, Thermostatic control system, natural gas supply system, natural gas boosting system, liquid-supplying system, excretory system, parameter monitoring and data are adopted Collecting system and terminal are constituted；Wherein：

It is described reaction tubing string be that water and natural solid/liquid/gas reactions provide place, its lower end respectively with the liquid-supplying system, the natural gas Pressure charging system pipeline is connected；

The natural gas boosting system is connected with the natural gas supply system pipeline；

The upper end of the reaction tubing string is connected with the excretory system tubes；

The thermostatic control system includes the partial temperature control device, the built-in reaction tubing string that are arranged on the reaction tubing string Second temperature controlling groove of the first temperature controlling groove and the built-in liquid-supplying system and the natural gas supply system；

The parameter monitoring and data collecting system transfer data to computer by being arranged at the sensor of each examining system Terminal.

2. deep water gas well surface shut-in stage gas hydrates growth simulation device according to claim 1, its feature It is that the reaction tubing string is divided to two kinds：A kind of is that use can bear the reaction that the stainless steel material of at least 30MPa pressure is made Tubing string；Another kind is that use can bear the visualization reaction that the sapphire or high strength glass of at least 10MPa pressure are made Tubing string.

3. deep water gas well surface shut-in stage gas hydrates growth simulation device according to claim 1 and 2, it is special Levy and be, the partial temperature control device in the thermostatic control system adjusts temperature range between 0-90 DEG C.

4. according to any described deep water gas well surface shut-in stage gas hydrates growth simulation devices of claim 1-3, Characterized in that, the natural gas supply system includes a gas tank and an intake valve, for real to injection in reaction tubing string Test natural gas gas；

The natural gas boosting system includes a booster pump and a vavuum pump；The booster pump comes from described for supercharging The natural gas of natural gas supply system output simultaneously adjusts reaction pressure in reaction tubing string.

5. according to any described deep water gas well surface shut-in stage gas hydrates growth simulation devices of claim 1-4, Characterized in that, the liquid-supplying system includes liquid feed valve, an electrodynamic pump and a water supply tank；For in reaction tubing string Liquid level in liquid and maintenance reaction tubing string is provided.

6. according to any described deep water gas well surface shut-in stage gas hydrates growth simulation devices of claim 1-5, Characterized in that, the parameter monitoring and data collecting system include gas flowmeter, fluid flowmeter, a liquid Temperature sensor, four temperature sensors, two gas pressure sensors, hydrate layer ultrasonic thickness sensor, One hygrometer；For monitoring gas and liquid-consumed situation, temperature, pressure humidity situation of change, reaction tubing string in reaction tubing string The thickness of hydrate layer on inwall, reaction time and collection is transferred to terminal.

7. a kind of any analogue means of utilization claim 1-6 judges the method that gas hydrates form degree of risk： Hydrate is grown in reaction tubing string with adherent manner, and the progressive additive in the form of hydrate layer；

If within the closed-in time, hydrate layer grows and thoroughly blocks pit shaft, then under the conditions of the temperature, pressure, be not suitable for using Surface shut-in form, should reduce switch well number of times, and hydrate braking measure is taken according to actual conditions；

If hydrate layer forms certain thickness but not yet blocks whole tubing string, judged whether according to the situation after driving a well again Constitute and block risk.