Method for measuring hydrogen index of natural gas by using nuclear magnetic resonance

Abstract

The invention provides a method for measuring the hydrogen content index of natural gas by using nuclear magnetic resonance, which comprises the following specific steps: injecting natural gas into a non-magnetic autoclave in a vacuum state to a pressure to be measured, then putting the non-magnetic autoclave into a nuclear magnetic resonance measurement chamber for detection, collecting a nuclear magnetic resonance T2 spectrum of the natural gas with the pressure to be measured, and calculating the hydrogen content index of the natural gas. Acquiring the spectral area Sg of the natural gas; s2, distilled water is injected into a non-magnetic autoclave with the interior in a vacuum state till the pressure to be measured, then the non-magnetic autoclave is placed into a nuclear magnetic resonance measurement chamber for detection, the collection parameters of a nuclear magnetic resonance device are the same as that of S2, the nuclear magnetic resonance T2 spectrum of the distilled water is collected, and the spectrum area Sw of the distilled water is obtained; the ratio of the spectral area Sg of the natural gas to the spectral area Sw of the distilled water is the hydrogen index HI of the natural gas with the pressure to be measured. According to the invention, the hydrogen index of the natural gas under different pressure conditions can be accurately measured, and a basis is provided for accurate evaluation of a natural gas reservoir by nuclear magnetic resonance logging.

Description

Technical Field

[0001] The invention belongs to the technical field of oil and gas reservoir exploration and development, and in particular belongs to a method for measuring the hydrogen index of natural gas by using nuclear magnetic resonance. Background Art

[0002] The hydrogen index (HI) is an inherent property of hydrogen-containing fluids, which is defined as the ratio of the number of hydrogen atoms per unit volume of fluid to the number of hydrogen atoms per unit volume of pure water under standard conditions. The hydrogen index is very important for NMR: in NMR well logging evaluation, the hydrogen index determines the value of the effective porosity of the formation, and the effective porosity is directly related to the reserves of the reservoir; in the field of NMR multiphase fluid measurement, the hydrogen index involves the calculation of the proportion of each phase component of the oil, water and gas mixed fluid, and its result directly affects the evaluation of the oil and gas production of oil and gas wells.

[0003] Natural gas, especially wet gas, often contains complex components such as hydrogen sulfide and nitrogen. Natural gas is highly compressible, and the density of natural gas under different pressure conditions varies greatly. Its hydrogen index is closely related to pressure. CN112083515B discloses a quantitative characterization of the mining effect of tight sandstone low-resistance reservoirs and a gas content evaluation method. This method uses gas logging data to calculate the total hydrogen index of gaseous hydrocarbons. However, although the information collected by logging is comprehensive, it still has many deficiencies in data accuracy and quality. There are shortcomings such as low online degree, poor logging data quality, and low reliability. The total hydrogen index of gaseous hydrocarbons estimated based on gas logging data is not reliable enough, and there is no device that can accurately measure the hydrogen index of natural gas under high pressure. Summary of the invention

[0004] In order to solve the problems existing in the prior art, the present invention provides a method for measuring the hydrogen index of natural gas using nuclear magnetic resonance, which can accurately measure the hydrogen index of natural gas under different pressure conditions and provide a basis for accurately evaluating natural gas reservoirs by nuclear magnetic resonance logging.

[0005] To achieve the above object, the present invention provides the following technical solution: a method for measuring the hydrogen index of natural gas using nuclear magnetic resonance, the specific steps are as follows:

[0006] S1 injects natural gas into a non-magnetic autoclave in a vacuum state to a pressure to be measured, then places the non-magnetic autoclave in a nuclear magnetic resonance measurement room for detection, collects the nuclear magnetic resonance T2 spectrum of the natural gas at the pressure to be measured, and obtains the spectrum area Sg of the natural gas;

[0007] S2 injects distilled water into a non-magnetic autoclave in a vacuum state to a pressure to be measured, and then places the non-magnetic autoclave into a nuclear magnetic resonance measurement room for detection. The acquisition parameters of the nuclear magnetic resonance device are the same as those of S2, and the nuclear magnetic resonance T2 spectrum of the distilled water is collected to obtain the spectrum area Sw of the distilled water;

[0008] The ratio of the spectrum area Sg of S3 natural gas to the spectrum area Sw of distilled water is the hydrogen index HI of the natural gas at the pressure to be measured.

[0009] Furthermore, the vacuum degree in the non-magnetic autoclave is less than 100Pa.

[0010] Furthermore, the non-magnetic autoclave is made of corundum ceramics.

[0011] Furthermore, the pressure to be measured is determined according to the formation depth.

[0012] Furthermore, the dimensions of the non-magnetic autoclave match those of the NMR measurement chamber.

[0013] Furthermore, the non-magnetic autoclave comprises a non-magnetic autoclave body, a non-magnetic autoclave cap is sealed on the top of the non-magnetic autoclave body, a fluid injection hole is penetrated in the middle of the non-magnetic autoclave cap, the inlet of the fluid injection hole is connected with a metal pipeline, a valve is arranged on the inlet of the metal pipeline, and the non-magnetic autoclave body and the non-magnetic autoclave cap are both made of corundum ceramics.

[0014] Furthermore, the non-magnetic autoclave body is threadedly connected to the non-magnetic autoclave cap.

[0015] Furthermore, a groove is engraved in the middle of the lower end of the non-magnetic autoclave cap at a distance of 0 to 10 mm from the lower bottom surface, and an O-type rubber ring is installed in the groove to seal the non-magnetic autoclave body and the non-magnetic autoclave cap.

[0016] Furthermore, the O-type rubber ring is made of fluorinated rubber.

[0017] Furthermore, the diameter of the fluid injection hole is 2 mm.

[0018] Compared with the prior art, the present invention has at least the following beneficial effects:

[0019] The invention provides a method for measuring the hydrogen index of natural gas by applying nuclear magnetic resonance. A non-magnetic autoclave is used as a container for measuring the nuclear magnetic resonance T2 spectrum of natural gas. The T2 spectrum of natural gas under different pressure conditions is first measured, and then the T2 spectrum of water under the same pressure condition is measured as a standard. The hydrogen index is calculated by using the ratio of the envelope areas of the T2 spectra of natural gas and water. The hydrogen index of natural gas under different pressure conditions can be measured, and a basis is provided for accurately evaluating natural gas reservoirs by nuclear magnetic resonance logging.

[0020] Furthermore, the non-magnetic autoclave of the present invention is made of corundum ceramics. Compared with autoclaves made of conventional materials, the non-magnetic autoclave of the present invention does not generate nuclear magnetic resonance signals, thereby effectively highlighting the nuclear magnetic signals of natural gas and distilled water, and realizing accurate measurement of the hydrogen index of natural gas under different pressure conditions. BRIEF DESCRIPTION OF THE DRAWINGS

[0021] Figure 1 The figure is a flow chart of the method of the present invention.

[0022] Figure 2 This is a diagram of a non-magnetic high-pressure autoclave device.

[0023] Figure 3 Schematic diagram of measuring natural gas nuclear magnetic T2 spectrum using a non-magnetic autoclave.

[0024] Figure 4 This is the NMR T2 spectrum of natural gas and distilled water at a pressure of 10MPa.

[0025] In the attached drawings: 1- non-magnetic autoclave body; 2- non-magnetic autoclave cap; 3- O-type rubber ring; 4- fluid injection hole; 5- M8 threaded interface; 6- metal pipeline; 7- high-pressure valve; 8- magnet box; 9- data connection line; 10- radio frequency device; 11- computer. DETAILED DESCRIPTION

[0026] The present invention will be further described below in conjunction with the accompanying drawings and specific embodiments.

[0027] like Figure 1 As shown, the present invention provides a method for measuring the hydrogen index of natural gas by using nuclear magnetic resonance. The definition of hydrogen index refers to the ratio of the hydrogen content of the test sample to the hydrogen content of water under the same conditions, and the envelope area of ​​the nuclear magnetic resonance T2 spectrum represents the hydrogen content. Therefore, the hydrogen index of natural gas can be accurately measured by using nuclear magnetic resonance. The hydrogen index of natural gas under different pressure conditions is different. Combining the pressure vessel with nuclear magnetic resonance detection can realize the measurement of the hydrogen index of natural gas under different pressure conditions. The specific steps are as follows:

[0028] S1 injects natural gas into a non-magnetic autoclave in a vacuum state to a pressure to be measured, and the vacuum degree is within 100Pa;

[0029] S2 places the non-magnetic autoclave of S1 into a nuclear magnetic resonance measurement room for detection, collects the nuclear magnetic resonance T2 spectrum of the natural gas under the pressure to be measured, and obtains the spectrum area Sg of the natural gas;

[0030] S3 injecting distilled water into a non-magnetic autoclave in a vacuum state to a pressure to be measured;

[0031] S4 places the non-magnetic autoclave of S3 into a nuclear magnetic resonance measurement room for detection. The acquisition parameters of the nuclear magnetic resonance device are the same as those of S2. The nuclear magnetic resonance T2 spectrum of distilled water is collected to obtain the spectrum area Sw of distilled water.

[0032] S5 calculates the hydrogen index HI of the natural gas at the pressure to be measured based on the spectrum area Sg of the natural gas and the spectrum area Sw of distilled water, specifically:

[0033] HI=Sg / Sw.

[0034] Preferably, the autoclave is a non-magnetic autoclave made of corundum ceramics. The tensile strength of corundum ceramics is higher than 160 MPa, which is close to the strength of 316 stainless steel. The non-magnetic autoclave does not generate nuclear magnetic resonance signals and can effectively highlight the nuclear magnetic resonance signals of natural gas and distilled water.

[0035] Preferably, the maximum pressure resistance of the non-magnetic autoclave is 200 MPa, and the safe working pressure reaches 70 MPa (equivalent to the formation pressure at a formation depth of 7,000 meters), which can meet the current formation pressure requirements of oil and gas wells of various depths.

[0036] Preferably, the test pressure is determined according to the formation depth.

[0037] like Figure 2 As shown, the present invention proposes a new non-magnetic autoclave based on the nuclear magnetic detection environment, which not only has a certain pressure resistance performance, but is also suitable for the existing nuclear magnetic detection environment. Specifically, it includes a non-magnetic autoclave body 1, a non-magnetic autoclave cap 2, an O-type rubber ring 3, a fluid injection hole 4, an M8 threaded interface 5, a metal pipeline 6 and a valve 7, wherein:

[0038] A non-magnetic autoclave cap 2 is arranged on the top of the non-magnetic autoclave body 1, and the non-magnetic autoclave cap 2 is sealed with the non-magnetic autoclave body 1 through an O-type rubber ring 3. A fluid injection hole 4 is arranged through the middle of the non-magnetic autoclave cap 2, and the inlet of the fluid injection hole 4 is connected with a metal pipeline 6 through an M8 threaded interface 5. The inlet of the metal pipeline 6 is provided with a valve 7 connected with a standard M8 pressure ring and a pressure cap.

[0039] Preferably, the non-magnetic autoclave body 1 has a diameter of 45 mm, a wall thickness of 10 mm, and a height of 150 mm;

[0040] Preferably, the inner wall of the upper end of the non-magnetic autoclave body 1 is engraved with an internal thread with a specification of M25*2 and a thread length of 50 mm, which is used for threaded connection with the non-magnetic autoclave cap 2 .

[0041] Preferably, the non-magnetic autoclave cap 2 has a diameter of 25 mm and a height of 80 mm;

[0042] Preferably, the lower end of the non-magnetic autoclave cap 2 is engraved with an external thread at a position 10mm-60mm away from the lower bottom surface, with a specification of M25*2 and a thread length of 50mm.

[0043] Preferably, a groove is engraved in the middle of the section of the lower end of the non-magnetic autoclave cap 2 0 to 10 mm away from the lower bottom surface, with a width of 2 mm and a depth of 1.5 mm;

[0044] Preferably, the O-shaped rubber ring 3 is installed in the above-mentioned groove, and the inner diameter of the O-shaped rubber ring 3 is 22 mm and the cross-sectional diameter is 1.8 mm;

[0045] Preferably, the diameter of the fluid injection hole 4 is 2 mm.

[0046] Preferably, the non-magnetic autoclave body 1 is made of corundum ceramics, the main component of which is Al2O3.

[0047] Furthermore, the non-magnetic autoclave cap 2 is made of corundum ceramics, the main component of which is Al2O3.

[0048] Furthermore, the O-type rubber ring 3 is made of fluorinated rubber.

[0049] Example

[0050] The method and device of the present invention are used to measure the hydrogen index of methane gas (CH4) under the conditions of temperature 25°C and pressure 10MPa. The operation method includes the following steps:

[0051] S1. Install the non-magnetic autoclave cap 2 on the threaded connection port of the non-magnetic autoclave body 1 and tighten the non-magnetic autoclave cap 2. Connect the vacuum pump to the valve 7, evacuate the autoclave for 5 minutes, then close the valve 7 and disconnect the vacuum pump;

[0052] S2. Connect the methane gas source to valve 7, open the valve and inject methane gas into the kettle to a pressure of 10 MPa, then close the valve and disconnect the gas source;

[0053] S3, placing the non-magnetic autoclave after methane gas injection into the nuclear magnetic resonance measurement room ( Figure 3 );

[0054] S4. Set the acquisition parameters of the nuclear magnetic resonance device:

[0055] The RF pulse frequency is 12.534MHz;

[0056] The sampling frequency is 200KHz;

[0057] The sampling delay is 0.05ms;

[0058] The pulse width is divided into 90° pulse width (P1=6.8μs) and 180° pulse width (P2=10.8μs);

[0059] The waiting time is 10000ms;

[0060] The echo time is 0.8ms;

[0061] The number of echoes is 2048;

[0062] The cumulative number is 10;

[0063] S5. Adjust the parameters and collect the NMR T2 spectrum of methane gas at a pressure of 10 MPa;

[0064] S6. After the collection is completed, take out the non-magnetic autoclave, connect valve 7 to the exhaust gas collection device, slowly open the valve, and after unloading the pressure, disconnect valve 7 from the exhaust gas collection device.

[0065] S7, unscrew the non-magnetic autoclave cap 2, add distilled water into the autoclave, open the valve 7, install and slowly tighten the non-magnetic autoclave cap 2, and discharge the excess distilled water in the autoclave through the valve 7.

[0066] S8, connect valve 7 to a constant speed and constant pressure pump, inject distilled water into the kettle to a pressure of 10 MPa, close valve 7, and disconnect the valve from the constant speed and constant pressure pump;

[0067] S9, place the non-magnetic autoclave 1 device into the NMR measurement room, and continue to collect the NMR T2 spectrum of distilled water using the same parameters ( Figure 4 );

[0068] S10. Export the T2 spectrum measurement data of methane gas and distilled water, open it in EXCEL, and obtain that the spectrum area of ​​natural gas is 4315.59, and the spectrum area of ​​distilled water is 14002.52.

[0069] Then the hydrogen index HI of natural gas at a pressure of 10MPa is:

[0070] HI=2110 / 14002=0.151.

[0071] Comparative Example

[0072] According to the definition of hydrogen index, the hydrogen index of methane (CH4), the main component of natural gas, is calculated at a temperature of 25°C and a pressure of 10MPa.

[0073] It is known that at a temperature of 25°C and a pressure of 10 MPa, the density of methane (CH4) gas is g 71.7kg / m 3 , the density of water (H2O) under the same conditions is ρ w About 1000kg / m 3 .

[0074] The hydrogen index is equal to the ratio of the number of hydrogen nuclei contained in the substance to the number of hydrogen nuclei contained in the same volume of fresh water. Under this condition, the hydrogen index of methane gas is approximately:

[0075] H g =2.13ρ g / ρ w =0.153.

[0076] It can be seen from the comparative examples and comparative examples that the present invention uses a non-magnetic autoclave as a container for measuring the nuclear magnetic resonance T2 spectrum of methane gas, firstly measures the T2 spectrum of methane gas under the pressure condition to be measured, and then measures the T2 spectrum of water under the same pressure condition as a standard, and compares it with the T2 spectrum of methane gas. The hydrogen index obtained by the area ratio is consistent with the hydrogen index result calculated theoretically for methane gas. This shows that the method of the present invention can accurately measure the hydrogen index of natural gas under different pressure conditions, and provide a basis for accurately evaluating natural gas reservoirs by nuclear magnetic resonance logging.

[0077] It should be emphasized that the embodiments described in the present invention are illustrative rather than restrictive. Therefore, the present invention includes but is not limited to the embodiments described in the specific implementation manner. Any other implementation manners derived by those skilled in the art based on the technical solution of the present invention also fall within the scope of protection of the present invention.

Claims

1. A method for measuring the hydrogen index of natural gas using nuclear magnetic resonance, characterized in that: The specific steps are as follows: S1 injects natural gas into a non-magnetic autoclave in a vacuum state to a pressure to be measured, then places the non-magnetic autoclave in a nuclear magnetic resonance measurement room for detection, collects the nuclear magnetic resonance T2 spectrum of the natural gas at the pressure to be measured, and obtains the spectrum area Sg of the natural gas; S2 injects distilled water into a non-magnetic autoclave in a vacuum state to a pressure to be measured, and then places the non-magnetic autoclave into a nuclear magnetic resonance measurement room for detection. The acquisition parameters of the nuclear magnetic resonance device are the same as those of S2, and the nuclear magnetic resonance T2 spectrum of the distilled water is collected to obtain the spectrum area Sw of the distilled water; The ratio of the spectrum area Sg of S3 natural gas to the spectrum area Sw of distilled water is the hydrogen index HI of the natural gas at the pressure to be measured.

2. The method for measuring the hydrogen index of natural gas using nuclear magnetic resonance according to claim 1, characterized in that: The vacuum degree in the non-magnetic autoclave is less than 100 Pa.

3. The method for measuring the hydrogen index of natural gas using nuclear magnetic resonance according to claim 1, characterized in that: The non-magnetic high-pressure autoclave is made of corundum ceramics.

4. The method for measuring the hydrogen index of natural gas using nuclear magnetic resonance according to claim 1, characterized in that: The pressure to be measured is determined according to the formation depth.

5. The method for measuring the hydrogen index of natural gas using nuclear magnetic resonance according to claim 1, characterized in that: The dimensions of the non-magnetic autoclave match the NMR measurement chamber.

6. The method for measuring the hydrogen index of natural gas using nuclear magnetic resonance according to claim 1, characterized in that: The non-magnetic autoclave comprises a non-magnetic autoclave body (1), a non-magnetic autoclave cap (2) is sealed on the top of the non-magnetic autoclave body (1), a fluid injection hole (4) is provided through the middle of the non-magnetic autoclave cap (2), the inlet of the fluid injection hole (4) is connected to a metal pipeline (6), and a valve (7) is provided at the inlet of the metal pipeline (6), and the non-magnetic autoclave body (1) and the non-magnetic autoclave cap (2) are both made of corundum ceramics.

7. The method for measuring the hydrogen index of natural gas using nuclear magnetic resonance according to claim 6, characterized in that: The non-magnetic autoclave body (1) is threadedly connected to the non-magnetic autoclave cap (2).

8. The method for measuring the hydrogen index of natural gas using nuclear magnetic resonance according to claim 6, characterized in that: A groove is engraved in the middle of the lower end of the non-magnetic autoclave cap (2) at a distance of 0 to 10 mm from the lower bottom surface, and an O-type rubber ring (3) is installed in the groove to seal the non-magnetic autoclave body (1) and the non-magnetic autoclave cap (2).

9. The method for measuring the hydrogen index of natural gas using nuclear magnetic resonance according to claim 8, characterized in that: The O-type rubber ring (3) is made of fluorinated rubber.

10. The method for measuring the hydrogen index of natural gas using nuclear magnetic resonance according to claim 6, characterized in that: The diameter of the fluid injection hole (4) is 2 mm.

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