CN102495090A - Device and method for low-temperature high-pressure nuclear magnetic resonance imaging of natural gas hydrate - Google Patents

Abstract

A low-temperature and high-pressure nuclear magnetic resonance imaging device and method for natural gas hydrate, which belong to the technical fields of basic physical property research of natural gas hydrate and hydrate exploitation technology. The device includes an end cap, an inner tube, a vacuum outer tube, a circulating fluid inlet and outlet, a sealing ring, a filter screen, and a head; the head and the inner tube form a closed space, which is the test area of the MRI system ;The space formed by the vacuum outer tube, the inner tube and the end caps at both ends is used for circulating fluid to control the reaction temperature; except for the filter screen and sealing ring, all parts are made of non-metallic polyamide-imide material ;The device is vertically placed in the imaging probe of the nuclear magnetic resonance imager, the design pressure is 0-40MPa, and the design temperature is -20-180℃, which can be used to study the hydrate formation and decomposition characteristics of natural gas hydrate under various storage conditions; It uses few magnetic materials and is resistant to high pressure, without any influence on the nuclear magnetic resonance system. It has a compact structure and is easy to use.

Description

Low temperature and high pressure nuclear magnetic resonance imaging device and method of natural gas hydrate

technical field

The invention relates to a low-temperature and high-pressure nuclear magnetic resonance imaging device and method for natural gas hydrate, and belongs to the technical fields of research on basic physical properties of natural gas hydrate and hydrate mining technology.

Background technique

As a new energy source, natural gas hydrate has attracted worldwide attention. Modeling and experimental studies on gas hydrates have been extensively carried out around the world. Since gas hydrates are mainly distributed in permafrost and the seabed, the cost of field research is very high. Now the research is mainly carried out in the laboratory to simulate the state of real gas hydrate reservoirs.

For experimental research, the research methods mainly include traditional, optical, ultrasonic, electrical, CT and nuclear magnetic resonance imaging techniques. Among them, the traditional technology is to directly observe the formation and decomposition of natural gas hydrate. The cost is relatively low, but only qualitative analysis can be done, and the obtained data is inaccurate. Optical research mainly uses the change of light transmittance or optical photography to determine the formation and decomposition of hydrate , this method has relatively high requirements for the reactor, which needs to be pressure-resistant and transparent, and the reaction matrix must also be transparent; ultrasonic technology is based on the measured acoustic parameters, such as sound velocity, frequency, attenuation, etc., to reflect the natural gas hydrate reservoir. Various physical property information (porosity, saturation, permeability, etc.), but this method cannot intuitively observe the formation and decomposition of hydrate; electrical technology detects some electrical properties of the reaction medium (such as resistance, dielectric Constants, etc.) to determine the formation and decomposition of hydrates. This method has high requirements for hydrate samples, and this method is not perfect. It can only qualitatively determine the formation and decomposition of hydrates, and cannot be quantitatively measured; CT technology uses X-rays Scan a certain thickness of the sample to determine the formation and decomposition of hydrates due to the different absorption rates of gas, water, hydrate, ice and porous media to X-rays. However, CT technology can only scan the sample in two dimensions. Moreover, since the porous media is also imaged, the porous media has a serious impact on the observation of natural gas hydrate; nuclear magnetic resonance imaging (MRI) is a relatively new research method, which is made of atomic nuclei with a magnetic moment under the action of a high-intensity magnetic field. It can absorb electromagnetic radiation of appropriate frequency, and the chemical environment of atomic nuclei in different molecules is different, there will be different resonance frequencies, resulting in different resonance spectra, so as to intuitively measure various characteristics of natural gas hydrate (including porosity, saturation, Permeability, flow field, temperature field, etc.), this method can carry out quantitative three-dimensional visualization measurement inside the sample, can accurately reflect the properties of various fluids in porous media, and exclude the influence of the medium skeleton. The requirements are relatively high, and it needs to be non-magnetic, high-voltage resistant and have a certain operating temperature range.

In order to overcome various deficiencies of the existing testing methods, the present invention provides a low-temperature and high-pressure nuclear magnetic resonance imaging device for natural gas hydrate, which can conveniently use nuclear magnetic resonance imaging technology to carry out three-dimensional visualized physical simulation research on natural gas hydrate, and the obtained test The image can be quantitatively analyzed, and parameters such as the porosity of the porous medium, the permeability and saturation of the gas hydrate in the porous medium, the flow field when it is generated and decomposed, and the temperature field can be obtained.

Contents of the invention

The invention provides a low-temperature and high-pressure nuclear magnetic resonance imaging device and method for natural gas hydrate. The device is vertically placed in the imaging probe of the nuclear magnetic resonance imager, and can perform hydrate formation and decomposition characteristics of natural gas hydrate under various storage conditions. Research; the device uses less magnetic material and is high-voltage resistant, has no effect on the nuclear magnetic resonance system, is compact in structure, and is easy to use.

The technical solution adopted by the present invention to solve technical problems is:

A low-temperature and high-pressure nuclear magnetic resonance imaging device for natural gas hydrate, including an end cover, an inner tube, a vacuum outer tube, a circulating fluid inlet and outlet, a sealing ring, a filter screen, and a head. The upper and lower heads and the inner tube form a closed space. The head has a sealing ring, which can effectively seal with the inner tube. The formed sealed space is the test area of the MRI system; this test area can be added Various substances involved in the formation of natural gas hydrate, such as water, gas, solution and porous media; porous media refers to materials such as glass beads, quartz sand or clay; the upper and lower end caps and the inner pipe are firmly combined by threads, and Press the heads at both ends, so that the inner tube can withstand high pressure; the upper and lower ends of the head are equipped with filter screens, which can effectively block the movement of various added solids; vacuum outer tube, inner tube and end caps at both ends The formed space is used for the circulation of circulating fluid to control the reaction temperature. The circulation enters from the inlet of the circulating fluid at the lower end and flows out from the outlet of the circulating fluid at the upper end; the vacuum outer tube is designed to effectively block the heat conduction of the circulating fluid to the outside of the tube;

Except for the rubber ring and filter screen, all are made of non-magnetic, non-metallic polyamide-imide material.

After the natural gas hydrate low-temperature and high-pressure nuclear magnetic resonance imaging device is loaded with the substances required for the natural gas hydrate reaction, it is placed in the nuclear magnetic resonance imaging system, and the reaction conditions are met by controlling its temperature and pressure, and the nuclear magnetic resonance imaging device is used for detection at the same time. The data of porosity, gas hydrate saturation and growth structure, flow field and temperature field during formation and decomposition are obtained by quantitative analysis of the image.

The beneficial effect of the present invention is that after the gas hydrate low temperature and high pressure nuclear magnetic resonance imaging device is filled with the substances required for the reaction, the temperature and pressure of the entire system are controlled by the temperature and pressure control system to meet the production conditions of natural gas hydrate, and Putting it into the nuclear magnetic resonance imaging system for quantitative measurement can obtain data such as the porosity and permeability of porous media, the saturation of natural gas hydrate, and the flow field and temperature field when it is generated and decomposed. The design pressure of this low-temperature and high-pressure nuclear magnetic resonance imaging device is 0-40Mpa, and the design temperature is -20-180°C, which can fully meet the environmental conditions under various storage conditions of natural gas hydrate; because the minimum operating temperature of the coil probe of the nuclear magnetic resonance imaging system is 10°C, so in order to prevent the normal use of the nuclear magnetic resonance imaging device, the outer tube of the simulated porous media device is designed with a vacuum barrier, which well blocks the heat conduction between the outer wall of the device and the nuclear magnetic coil coil probe, and achieves a good heat insulation effect , to protect the probe; a full set of simulated porous media devices are made of polyamide-imide materials, non-magnetic and meet the requirements of high pressure, compact structure, and easy to use.

Description of drawings

The present invention will be further described below in conjunction with the accompanying drawings and embodiments.

Fig. 1 is a schematic diagram of a structure diagram of a device for simulating porous media.

Fig. 2 is a B-B sectional structure diagram of Fig. 3 .

Fig. 3 is a cross-sectional structure diagram along line A-A of Fig. 1 .

In the figure, 1 upper head; 2 circulating fluid outlet; 3 upper end cover; 4 upper filter; 5 vacuum outer tube; 6 inner tube; 7 reactant; 8 lower filter; 9 sealing ring; Lower end cover; 12 circulating fluid inlets.

Detailed ways

Figures 1, 2, and 3 show a high-pressure and low-temperature NMR imaging device for natural gas hydrate. The device adopts two sealing heads 1, 9 and the inner pipe 6 to form a closed space; the sealing head has a sealing ring 9; it can effectively seal with the inner pipe 6; various water, various reactants 7 such as gas, solution and porous medium; the upper filter screen 4 and the lower filter screen 8 can effectively block the movement of various added solids on the head; the inner threads of the upper end cover 3 and the lower end cover 11 and The inner tube 6 is firmly combined; and the upper head 1 and the lower head 10 are pressed; this makes the inner tube withstand high pressure; the space formed by the vacuum jacket 6, the inner tube 5, the upper end cover 3, and the lower end cover 11 is used for circulating fluid Circulation to control the reaction temperature; the circulating fluid enters from the circulating fluid inlet 12 at the lower end; flows out from the circulating fluid outlet 2 at the upper end; the circulating fluid inlets and outlets 2 and 12 are symmetrically provided with spare inlets and outlets; if you want to control the circulating fluid more accurately Temperature; a temperature sensor can be inserted at an alternate inlet and outlet location to measure temperature.

The steps of using the above-mentioned gas hydrate high-pressure and low-temperature nuclear magnetic resonance imaging device are as follows:

The first step: complete the preparation of simulated porous media. Open the upper end cover 3 and the upper head 1, add the glass beads, quartz sand or clay required for the specific working conditions in the inner tube 6, and compact it to ensure that the gas, water or solution required for the reaction will still remain after injection. It can be kept stable; plug the upper head 1 and then install the upper end cover 3 and tighten it; the space filled with fillers formed between the two heads and the inner pipe is used as a simulated porous medium.

The second step: the device is loaded into the nuclear magnetic resonance imaging system. The space formed by the inner tube 6, the vacuum jacket 5 and the upper and lower end caps is used for the flow of circulating fluid; the circulating fluid inlet 12 is connected to the outlet of the constant temperature circulation tank; the circulating fluid outlet is connected to the inlet of the constant temperature circulation tank; a circulation is formed to control the inner tube temperature; the upper head 1 and the lower head 10 are externally connected to pipelines to provide reactants needed for the reaction; such as gas, water or solution, etc., and finally fixed in the imaging probe of the nuclear magnetic resonance imager.

Step 3: Carry out the formation and decomposition of natural gas hydrate. First use the vacuum pump to evacuate the inner tube of the device; then use the injection pump to inject the reactants required for the reaction; use the back pressure system to control the pressure in the inner tube 6 to reach the set pressure value; control the temperature of the constant temperature circulation tank to meet The need for the formation and decomposition of natural gas hydrate; the in-situ three-dimensional visualization and quantitative testing of the entire natural gas hydrate formation and decomposition process is carried out using nuclear magnetic resonance imaging.

Claims (5)

1. gas hydrate NMR imaging device, this NMR imaging device comprises end cap, interior pipe, vacuum outer tube, circulating fluid import and export, O-ring seal, filter screen, end socket; It is characterized in that upper cover, low head and interior pipe have been formed the space of a sealing, end socket has O-ring seal, and the seal cavity of formation is the test zone of MRI system; This test zone adds the material that various participation gas hydrate generate; Upper end cover, bottom end cover and interior pipe pass through the screw thread strong bonded, and push down the two ends end socket; End socket all is provided with filter screen in two ends up and down; The space that vacuum outer tube, interior pipe and two ends end cap are formed is used for circulation fluid circulates and controls temperature of reaction, and circulation gets into from the circulating fluid import of lower end, flows out from the circulating fluid outlet of upper end.

2. a kind of gas hydrate NMR imaging device according to claim 1 is characterized in that, except that rubber ring and filter screen, all the nonmetallic materials polyamide-imides material by no magnetic forms.

3. a kind of gas hydrate NMR imaging device according to claim 1 is characterized in that, described test zone adds the material that various participation gas hydrate generate, and comprises water, gas, solution and porous medium.

4. a kind of gas hydrate NMR imaging device according to claim 3 is characterized in that described porous medium is meant beaded glass, silica sand or clay.

5. utilize the method for the arbitrary said gas hydrate NMR imaging device of claim 1-5, it is characterized in that following steps,

The first step; Accomplish the preparation of simulation porous medium: open upper end end cap and upper cover, inwardly add the required material of setting of concrete operating mode in the pipe, guarantee that the required gas of reaction, water or solution still can keep stable after injecting; Refill the upper end end cap beyond the Great Wall behind the upper cover, screw; The space of the full filler of the filling of being formed between two end sockets and the interior pipe is as the simulation porous medium;

Second step; With this device MRI system of packing into: interior pipe, vacuum jacket and up and down the space formed of two end cap be used for flowing of circulating fluid; The circulating fluid import connects the outlet of constant temperature circulation groove; The circulating fluid outlet connects the inlet of constant temperature circulation groove; Form a circulation and control interior pipe temperature; Upper cover, the external pipeline of low head provide reaction required reactant, are fixed at last within the imaging probe of NMR imaging instrument;

The 3rd step; Carry out gas hydrate and generate decomposition: utilize vacuum pump will install interior pipe earlier and vacuumize; Utilize injection pump to inject the required reactant of reaction again; Utilize back pressure system to control the pressure in the interior pipe, reach setup pressure value; The temperature of control constant temperature circulation groove satisfies gas hydrate and generates the needs that decompose; Utilize NMR imaging instrument that whole gas hydrate are generated decomposable process and carry out the visual quantitative test of in-situ three-dimensional.

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