A method for determining the minimum miscibility pressure of hydrocarbon gas and crude oil by using two-dimensional nuclear magnetic resonance

Abstract

The present invention relates to a method for measuring the minimum miscibility pressure of hydrocarbon gas and crude oil using two-dimensional nuclear magnetic resonance, comprising: (1) placing a sand-filled tube into a holder and placing the tube in a nuclear magnetic resonance instrument; (2) raising the temperature of the holder to the formation temperature; (3) setting a back pressure, injecting nitrogen into the sand-filled tube to pressurize it to the active oil bubble point pressure; displacing the nitrogen with active oil until the nitrogen used for pressure building is completely displaced; (4) displacing the active oil with hydrocarbon gas, and closing the holder outlet when hydrocarbon gas in the fluid at the outlet accounts for 30% of the pore volume; (5) injecting hydrocarbon gas into the sand-filled tube, pressurizing it step by step according to a preset pressure gradient, and testing the two-dimensional nuclear magnetic spectrum of the fluid in the sand-filled tube after each pressurization; (6) if the system changes from two phases to single phase at two adjacent pressure points, it indicates that the minimum miscibility pressure is in the interval corresponding to the two-phase pressure point and the single-phase pressure point. The present invention is low in cost and time-consuming, and can accurately and quickly measure the minimum miscibility pressure of an oil and gas system.

Description

Technical Field

[0001] The present invention belongs to the technical field of oil and gas field development, and in particular relates to a method for measuring the minimum miscibility pressure of oil and gas two phases based on two-dimensional nuclear magnetic fluid identification technology. Background Art

[0002] In the process of gas injection to enhance oil recovery, miscible flooding has a stronger potential for enhancing oil recovery than immiscible flooding. Accurately determining the minimum miscible pressure is of great significance in actual oilfield operations and in research on enhancing crude oil recovery by hydrocarbon gas injection.

[0003] Several existing traditional methods for measuring minimum miscibility pressure have problems such as being too time-consuming and complicated to operate. Therefore, in recent years, methods for rapidly measuring minimum miscibility pressure using nuclear magnetic resonance (NMR) have gradually gained more research and application. Some scholars have derived the minimum miscibility pressure based on the signal intensity change fitting of NMR imaging results (Zhao Yuechao, Zhu Ningjun, Song Yongchen, et al. Experimental system and method for determining the minimum miscibility pressure of oil and gas using MRI [J]. Laboratory Research and Exploration, 2015, (9): 16-20). The invention patent "A device and method for measuring the minimum miscibility pressure of oil and gas by integrated NMR and CT scanning" (CN110261266A) combines NMR imaging and CT imaging technology to achieve rapid measurement of minimum miscibility pressure. The above methods are all based on NMR imaging data. Some researchers have also derived the minimum miscibility pressure based on the relationship curves between proton density M0, longitudinal relaxation intensity 1 / T1, transverse relaxation intensity 1 / T2 and pressure changes (Chen Junlin. Research on MRI measurement of oil and gas diffusion coefficient and minimum miscibility pressure [D]. Dalian University of Technology, 2016). This method uses non-imaging nuclear magnetic resonance technology, but requires a certain data processing and fitting process.

[0004] Based on this, the present invention proposes a method for determining the minimum miscibility pressure of hydrocarbon gas and crude oil based on two-dimensional nuclear magnetic fluid identification technology. The method has low cost, short time consumption, intuitive data processing, and can accurately and quickly determine the minimum miscibility pressure of the oil and gas system. Summary of the Invention

[0005] The purpose of the present invention is to provide a method for determining the minimum miscibility pressure of hydrocarbon gas and crude oil using two-dimensional nuclear magnetic resonance. This method uses an SR-CPMG sequence to measure the T1-T2 two-dimensional spectrum of the fluid under target temperature and pressure conditions, identify the fluid phase characteristics, and determine the minimum miscibility pressure of the system based on the phase changes of the fluid at different pressures.

[0006] In order to achieve the above technical objectives, the present invention adopts the following technical solutions.

[0007] A method for measuring the minimum miscibility pressure of hydrocarbon gas and crude oil using two-dimensional nuclear magnetic resonance comprises the following steps:

[0008] (1) The sand-filled tube is loaded into a holder and then placed in a nuclear magnetic resonance instrument. The inlet end of the holder is connected to an N2 intermediate container, a hydrocarbon gas (methane and ethane mixture) intermediate container, and a live oil intermediate container, respectively. The outlet end is connected to a back pressure valve. The holder is connected to a high-temperature circulation system. Pressure gauges are set at both ends. The nuclear magnetic resonance instrument is connected to a data processor.

[0009] (2) Turn on the high-temperature circulation system to raise the temperature of the holder to the formation temperature;

[0010] (3) Set the back pressure and inject N2 into the sand filling pipe to pressurize it to the oil bubble point pressure; then use oil to displace the N2. Every time 0.5PV of oil is displaced, the fluid composition at the holder outlet is detected by gas chromatography. When the outlet fluid is detected to contain no N2, it means that the N2 used for pressure building has been completely displaced.

[0011] (4) Adjust the pressure of the hydrocarbon gas intermediate container to ensure that the pressure of the hydrocarbon gas intermediate container is consistent with the pressure in the sand filling pipe, then use hydrocarbon gas to displace the live oil, collect the fluid at the outlet end, and close the clamp outlet when the hydrocarbon gas in the fluid at the outlet end accounts for 30% of the pore volume;

[0012] (5) Injecting hydrocarbon gas into the sand filling tube and gradually pressurizing it according to a preset pressure gradient. After each pressurization, the two-dimensional nuclear magnetic resonance spectrum of the fluid in the sand filling tube is tested. If the phase state at this time is measured to be oil and gas two-phase through two-dimensional nuclear magnetic resonance spectrum analysis, continue to inject hydrocarbon gas for pressurization;

[0013] (6) If the system changes from two phases to a single phase at two adjacent pressure points, it means that the minimum miscibility pressure is in the interval corresponding to the two-phase pressure point and the single-phase pressure point. The pressure is reduced to the middle pressure point of this interval, and the two-dimensional nuclear magnetic spectrum of the fluid in the sand-filled tube is tested and analyzed:

[0014] a. If it is a single phase, the minimum miscible pressure is in the range between the two-phase pressure point and the current pressure point.

[0015] b. If it is two-phase, the minimum miscible pressure is in the range between the current pressure point and the single-phase pressure point;

[0016] Repeat this step until the interval range is reduced to below 0.5 MPa. The midpoint pressure of this interval can be determined as the minimum miscibility pressure of hydrocarbon gas and crude oil.

[0017] Furthermore, in step (1), the sand-filled tube is a polytetrafluoroethylene tube filled with 80-mesh quartz sand, and 120-mesh ceramic filters are placed at both ends of the polytetrafluoroethylene tube to prevent the quartz sand from flowing.

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

[0019] (1) The present invention realizes the rapid testing of the minimum miscibility pressure of hydrocarbon gas and crude oil;

[0020] (2) Compared with the existing nuclear magnetic resonance imaging minimum miscibility pressure test method, the data processing based on two-dimensional nuclear magnetic resonance is more intuitive and less affected by human factors. BRIEF DESCRIPTION OF THE DRAWINGS

[0021] Figure 1 A diagram of a device for measuring the minimum miscible pressure of oil and gas using two-dimensional nuclear magnetic resonance.

[0022] Figure 2 This is the NMR test result diagram for unmixed phases.

[0023] Figure 3 This is the NMR test result diagram for miscible phases.

[0024] Figure 4 The experimental flow chart is shown in Figure 2.

[0025] Figure 1 In: 1, 24, 25, 26 - ISCO injection pump; 2 - hydrocarbon gas intermediate container; 3 - N2 intermediate container; 4, 5, 6, 7, 14, 17 - valves; 8 - live oil intermediate container; 9 - nuclear magnetic resonance apparatus; 10 - high-temperature circulation system; 11 - core holder; 12 - polytetrafluoroethylene tube; 13 - quartz sand; 15 - pressure gauge; 16 - back pressure valve; 18 - back pressure pump; 19 - drain tank; 20 - data processor; 21 - hydraulic oil valve; 22 - circulation pump; 23 - fluorinated liquid; 24 - ceramic filter. DETAILED DESCRIPTION

[0026] The present invention will be further described below with reference to the accompanying drawings.

[0027] The nuclear magnetic resonance equipment used in this invention mainly consists of a computer, a radio frequency module, a gradient module, etc. The magnet type is a permanent magnet, the magnetic field strength is 0.3±0.05T, the instrument main frequency is 12.8MHz, and the probe coil diameter is 150mm.

[0028] A device for measuring the minimum miscible pressure of oil and gas using a nuclear magnetic resonance instrument, such as Figure 1 As shown, the filled quartz sand 13 is located in a polytetrafluoroethylene tube 12, ceramic filters 24 are placed at both ends of the polytetrafluoroethylene tube, placed in a holder 11, and then placed in a nuclear magnetic resonance instrument 9. The inlet end of the holder is respectively connected to the N2 intermediate container 3, the hydrocarbon gas intermediate container 2 and the live oil intermediate container 8, and the outlet end is connected to the back pressure valve 16. The N2 intermediate container, the hydrocarbon gas intermediate container and the live oil intermediate container are respectively connected to the injection pumps 24, 1, and 26. The back pressure valve is connected to the back pressure pump 18. The holder is connected to the high-temperature circulation system 10. Pressure gauges 15 are set at both ends. The nuclear magnetic resonance instrument is connected to the data processor 20.

[0029] Method for determining the minimum miscibility pressure of hydrocarbon oil and gas using two-dimensional nuclear magnetic resonance technology (detailed process see Figure 4 ), specifically including the following steps:

[0030] (1) Calibrate and clean various instruments;

[0031] (2) Connect the sand-filled tube to the nuclear magnetic test system, close valves 4 and 6, open valves 5 and 7, turn on the ISCO pump, and use N2 to perform a pressure test on the entire experimental device to detect leaks. Maintain a pressure of 2 MPa for 12 hours. If there is no obvious change in pressure, the system can be considered to be leak-free and the experiment can be continued.

[0032] (3) Turn on the injection pump 25 and the circulation pump 22 to circulate the fluorinated liquid 23 and raise the core holder temperature to 56°C;

[0033] (4) Start the back pressure pump 18, open valve 17, and set the back pressure to 8 MPa. Start the ISCO pump and inject N2 into the sand filling pipe to pressurize it to the bubble point pressure of the live oil, 8 MPa; then close valve 5, open valve 6, and start the ISCO pump to inject live oil to displace the N2. Every time 0.5 PV of live oil is displaced, the fluid composition at the holder outlet is detected by gas chromatography. When it is detected that the fluid at the outlet does not contain N2, the N2 used for pressure building has been completely displaced;

[0034] (5) Adjust the pressure of the hydrocarbon gas intermediate container to keep it consistent with the live oil pressure in the sand filling pipe. Then close valve 6, open valve 4, start the ISCO pump, inject hydrocarbon gas to displace the live oil, collect the fluid at the outlet, and when the hydrocarbon gas at the outlet reaches 30% of the pore volume calculated by the volume coefficient, close the clamp outlet.

[0035] (6) Start the ISCO pump to inject hydrocarbon gas for step-by-step pressurization. Set the pressure gradient to 2 MPa each time. The pressure at this time is 10 MPa, slightly higher than the bubble point pressure. Through two-dimensional nuclear magnetic spectrum analysis, it is measured that the phase state at this time is oil and gas. The test results are as follows: Figure 2 As shown, two signals can be detected, indicating that the oil and ethane mixture are not miscible, and hydrocarbon gas injection is continued for pressurization;

[0036] (7) When the pressure increased from 14 MPa to 16 MPa, the system changed from two phases to a single phase, indicating that the minimum miscibility pressure is in the range of 14 MPa to 16 MPa;

[0037] (8) When the pressure is reduced to the middle pressure point of 15MPa in this range, it is still two-phase, indicating that the minimum miscible pressure is between 15MPa and 16MPa; when the pressure is further reduced to 15.5MPa, it becomes a single phase, indicating that the minimum miscible pressure is between 15MPa and 15.5MPa. The test results are as follows Figure 3As shown, only one signal can be detected, indicating that the oil and hydrocarbon gas are miscible. The minimum miscible pressure can be determined to be the midpoint of the interval, 15.25 MPa, and this pressure is identified as the minimum miscible pressure of the system.

[0038] (9) Close the valve at the ISCO pump, slowly release the pressure in the sand filling pipe to atmospheric pressure, and clean the sand filling pipe.

Claims

1. A method for measuring the minimum miscibility pressure of hydrocarbon gas and crude oil using two-dimensional nuclear magnetic resonance, comprising the following steps: (1) The sand-filled tube is loaded into a holder and then placed in a nuclear magnetic resonance instrument. The inlet end of the holder is connected to an N2 intermediate container, a hydrocarbon gas intermediate container, and a live oil intermediate container, respectively. The outlet end is connected to a back pressure valve. The holder is connected to a high-temperature circulation system. Pressure gauges are provided at both ends. The nuclear magnetic resonance instrument is connected to a data processor. (2) Turn on the high-temperature circulation system to raise the temperature of the holder to the formation temperature; (3) Set the back pressure and inject N2 into the sand filling pipe to pressurize it to the oil bubble point pressure; then use oil to displace the N2. Every time 0.5PV of oil is displaced, the fluid composition at the holder outlet is detected by gas chromatography. When the outlet fluid is detected to contain no N2, it means that the N2 used for pressure building has been completely displaced. (4) Adjust the pressure of the hydrocarbon gas intermediate container to ensure that the pressure of the hydrocarbon gas intermediate container is consistent with the pressure in the sand filling pipe, then use hydrocarbon gas to displace the live oil, collect the fluid at the outlet end, and close the clamp outlet when the hydrocarbon gas in the fluid at the outlet end accounts for 30% of the pore volume; (5) Injecting hydrocarbon gas into the sand filling tube and gradually pressurizing it according to a preset pressure gradient. After each pressurization, the two-dimensional nuclear magnetic resonance spectrum of the fluid in the sand filling tube is tested. If two signals are detected through two-dimensional nuclear magnetic resonance spectrum analysis, the phase state at this time is oil and gas, and the hydrocarbon gas injection is continued for pressurization; (6) If the system changes from two phases to a single phase at two adjacent pressure points, it means that the minimum miscibility pressure is in the interval corresponding to the two-phase pressure point and the single-phase pressure point.

2. The method for measuring the minimum miscibility pressure of hydrocarbon gas and crude oil using two-dimensional nuclear magnetic resonance according to claim 1, characterized in that: In step (1), the sand-filled tube is a polytetrafluoroethylene tube filled with 80-mesh quartz sand, and 120-mesh ceramic filters are placed at both ends of the polytetrafluoroethylene tube to prevent the quartz sand from flowing.

3. The method for measuring the minimum miscibility pressure of hydrocarbon gas and crude oil using two-dimensional nuclear magnetic resonance according to claim 1, characterized in that: In step (6), the pressure is reduced to the middle pressure point between the two-phase pressure point and the single-phase pressure point, and the two-dimensional nuclear magnetic spectrum of the fluid in the sand-filled tube is tested and analyzed: a. If it is a single phase, the minimum miscible pressure is in the range between the two-phase pressure point and the current pressure point. b. If it is two-phase, the minimum miscible pressure is in the range between the current pressure point and the single-phase pressure point; Repeat this step until the interval is reduced to below 0.5 MPa. The midpoint pressure of this interval is the minimum miscibility pressure of hydrocarbon gas and crude oil.

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