1. A method for testing the change of a water-drive pore structure of a loose rock core is characterized by comprising the following steps:

step 1: providing a loose core sample;

step 2: packaging the loose core sample in a core holder;

and step 3: heating the core sample to a required experiment temperature and enabling the core sample to reach a set annular pressure, vacuumizing the core sample and enabling the core sample to be saturated with water;

and 4, step 4: obtaining a first nuclear magnetic resonance T2 spectrum of the pore structure of the core sample by a nuclear magnetic resonance device;

and 5: carrying out constant-speed water displacement on saturated water in the core sample through a displacement pump, and obtaining a second nuclear magnetic resonance T2 spectrum of the pore structure of the core sample through the nuclear magnetic resonance device again after the injection amount of the displacement water reaches a set value;

step 6: calculating a percentage of water-flooding pore structure change of the core sample using the first and second nuclear magnetic resonance T2 and T2 spectra.

2. The method for testing the change of the water-drive pore structure of the loose core according to claim 1, wherein in the step 4, the parameters of the nuclear magnetic resonance device are set as follows: the sampling interval is 1-4 mus, the number of samples is 512-2048, the sampling time is 50-80 mus, the waiting time is 1-4s, the scanning times is 32-128, and the main frequency is 9.8 MHz.

3. The method for testing the change of the water-drive pore structure of the loose core according to claim 1, wherein in the step 5, the displacement speed of the displacement pump is 0.05ml/min-0.4ml/min, and the parameters of the nuclear magnetic resonance device are set as follows: the sampling interval is 1-4 mus, the number of samples is 12-2048, the sampling time is 50-80 mus, the waiting time is 1-4s, the scanning times is 32-128, and the main frequency is 9.8 MHz.

4. The method for testing the change of the water-drive pore structure of the loose core according to claim 1, wherein in the step 3, heating the core sample to a required experimental temperature comprises: and heating the core holder to the required experiment temperature through a constant-temperature oil bath circulating system, wherein a heating medium of the constant-temperature oil bath circulating system is fluorine-chlorine-carbon oil, and the heating medium and the core sample are isolated from each other.

5. The method for testing the change of the water-drive pore structure of the loose core according to claim 1, wherein in the step 3, a medium for applying annular pressure on the core sample is chlorofluorocarbon oil.

6. The method for testing the change of the water-flooding pore structure of the loose core according to claim 1, wherein in the step 3, the experimental temperature is 40-50 ℃.

7. The method for testing the change of the water-drive pore structure of the loose core according to claim 1, wherein in the step 3, the ring pressure is 2MPa to 4 MPa.

8. The method for testing the change of the water-drive pore structure of the loose core according to claim 1, wherein the material of the core holder is non-metal.

9. The utility model provides a loose rock core water drive pore structure changes testing arrangement which characterized in that includes:

a nuclear magnetic resonance device;

the core holder is arranged in a probe of the nuclear magnetic resonance device and used for packaging a core sample;

the core vacuumizing and pressurizing saturated water assembly is used for enabling the core sample to reach a state of full saturated water;

the water displacement component is used for injecting water injection quantity of a set value into the core sample;

the nuclear magnetic resonance device is used for obtaining a first nuclear magnetic resonance T2 spectrum when the core sample reaches a full saturated water state and a second nuclear magnetic resonance T2 spectrum when the water injection amount of the core sample is a set value;

and the processing module is used for calculating the percentage of the change of the water-flooding pore structure of the core sample through the first water nuclear magnetic resonance T2 spectrum and the second nuclear magnetic resonance T2 spectrum.

10. The testing device for testing water-drive pore structure change of the loose core according to claim 9, wherein the core vacuumizing and pressurizing saturated water assembly comprises a heating system, the heating system is a constant-temperature oil bath circulating system, a heating medium of the heating system is isolated from the core sample and/or the core vacuumizing and pressurizing saturated water assembly comprises a medium for applying annular pressure to the core sample, and the medium is chlorofluorocarbon oil.

Background

The sandstone oil and gas reservoir has high-permeability, medium-permeability, low-permeability and compact types, loose sandstone belongs to the high-permeability type, and the characterization method research on the water-drive pore structure change of the loose core has important significance on the evaluation of the water-drive pore structure change of the loose sandstone and the design of a development scheme.

In the prior art, documents in 1983, at the 01 st stage, Daqing petroleum geology and development research on pore structure parameter change after sandstone reservoir core water drive (flushing) "analyze core analysis data and mercury suppression data before and after water drive (flushing) of sandstone samples of various oil fields in the north of Daqing Changyuan and explain the change of the pore structure of the sandstone reservoir core in the water injection process by combining scanning electron microscope observation. The change of the water-flooding pore structure of the loose sandstone core, particularly the change of the pore structure characterized by the nuclear magnetic resonance technology is not reported.

Therefore, a method for conveniently testing the change of the water-drive pore structure of the loose rock core is expected to be used for evaluating the change of the water-drive pore structure of the loose sandstone.

Disclosure of Invention

The invention aims to provide a method and a device for testing the change of a water-drive pore structure of a loose core, which can test the change of the water-drive pore structure of the loose core and can be used for evaluating the change of the water-drive pore structure of loose sandstone.

In order to achieve the purpose, the invention provides a method for testing the change of a water-drive pore structure of a loose core, which comprises the following steps:

step 1: providing a loose core sample;

step 2: packaging the loose core sample in a core holder;

and step 3: heating the core sample to a required experiment temperature and enabling the core sample to reach a set annular pressure, vacuumizing the core sample and enabling the core sample to be saturated with water;

and 4, step 4: obtaining a first nuclear magnetic resonance T2 spectrum of the pore structure of the core sample by a nuclear magnetic resonance device;

and 5: carrying out constant-speed water displacement on saturated water in the core sample through a displacement pump, and obtaining a second nuclear magnetic resonance T2 spectrum of the pore structure of the core sample through the nuclear magnetic resonance device again after the injection amount of the displacement water reaches a set value;

step 6: calculating a percentage of water-flooding pore structure change of the core sample using the first and second nuclear magnetic resonance T2 and T2 spectra.

In an alternative, in the step 4, the parameters of the nuclear magnetic resonance apparatus are set as follows: the sampling interval is 1-4 mus, the number of samples is 512-2048, the sampling time is 50-80 mus, the waiting time is 1-4s, the scanning times is 32-128, and the main frequency is 9.8 MHz.

In an alternative scheme, in the step 5, the displacement speed of the displacement pump is 0.1ml/min, and the parameters of the nuclear magnetic resonance device are set as follows: the sampling interval is 1-4 mus, the number of samples is 512-2048, the sampling time is 50-80 mus, the waiting time is 1-4s, the scanning times is 32-128, and the main frequency is 9.8 MHz. According to a preferred embodiment of the present invention, in the step 3, heating the core sample to the required experiment temperature includes: and heating the core holder to the required experiment temperature through a constant-temperature oil bath circulating system, wherein a heating medium of the constant-temperature oil bath circulating system is fluorine-chlorine-carbon oil, and the heating medium and the core sample are isolated from each other.

According to a preferred embodiment of the present invention, in step 3, the medium for applying the ring pressure to the core sample is chlorofluorocarbon oil.

According to a specific embodiment of the present invention, in the step 3, the experimental temperature is 40 to 50 ℃.

According to a specific embodiment of the present invention, in the step 3, the ring pressure is 2MPa to 4 MPa.

Preferably, the material of the core holder is non-metallic.

The invention also provides a device for testing the change of the water-drive pore structure of the loose rock core, which comprises:

a nuclear magnetic resonance device;

the core holder is arranged in a probe of the nuclear magnetic resonance device and used for packaging a core sample;

the core vacuumizing and pressurizing saturated water assembly is used for enabling the core sample to reach a state of full saturated water;

the water displacement component is used for injecting water injection quantity of a set value into the core sample;

the nuclear magnetic resonance device is used for obtaining a first nuclear magnetic resonance T2 spectrum when the core sample reaches a full saturated water state and a second nuclear magnetic resonance T2 spectrum when the water injection amount of the core sample is a set value;

and the processing module is used for calculating the percentage of the change of the water-flooding pore structure of the core sample through the first water nuclear magnetic resonance T2 spectrum and the second nuclear magnetic resonance T2 spectrum.

As an alternative, the core vacuumizing and pressurizing saturated water assembly comprises a heating system, the heating system is a constant-temperature oil bath circulating system, a heating medium of the heating system is isolated from the core sample, and/or the core vacuumizing and pressurizing saturated water assembly comprises a medium for pressurizing the core sample by ring pressing, and the medium is chlorofluorocarbon oil.

The invention has the beneficial effects that:

the invention provides a method for testing water-drive pore structure change of a loose core, which comprises the steps of obtaining a first nuclear magnetic resonance T2 spectrum of a core sample in a saturated water state by using a nuclear magnetic resonance device; and a second nuclear magnetic resonance T2 spectrum of the pore structure of the core sample after the injection amount of the displacement water reaches a set value. And calculating the percentage of the change of the water-drive pore structure of the core sample by using the first nuclear magnetic resonance T2 spectrum and the second nuclear magnetic resonance T2 spectrum, and the method can be used for evaluating the change of the water-drive pore structure of the loose sandstone.

The present invention has other features and advantages which will be apparent from or are set forth in detail in the accompanying drawings and the following detailed description, which are incorporated herein, and which together serve to explain certain principles of the invention.

Drawings

The above and other objects, features and advantages of the present invention will become more apparent by describing in more detail exemplary embodiments thereof with reference to the attached drawings.

Fig. 1 shows a first nmr T2 spectrum and a second nmr T2 spectrum of a method for testing changes in the water-flooding pore structure of a loose core, according to an embodiment of the invention.

Fig. 2 shows a schematic diagram of a testing device for water-drive pore structure change of a loose core.

Detailed Description

The present invention will be described in more detail below. While the present invention provides preferred embodiments, it should be understood that the present invention may be embodied in various forms and should not be limited by the embodiments set forth herein. Rather, these embodiments are provided so that this disclosure will be thorough and complete, and will fully convey the scope of the invention to those skilled in the art.

In the description of the present invention, it should be noted that the terms "center", "upper", "lower", "left", "right", "vertical", "horizontal", "inner", "outer", etc., indicate orientations or positional relationships based on the orientations or positional relationships shown in the drawings, and are only for convenience of description and simplicity of description, but do not indicate or imply that the device or element being referred to must have a particular orientation, be constructed and operated in a particular orientation, and thus, should not be construed as limiting the present invention.

In the description of the present invention, it should be noted that, unless otherwise explicitly specified or limited, the terms "mounted," "connected," and "connected" are to be construed broadly, e.g., as meaning either a fixed connection, a removable connection, or an integral connection; may be mechanically coupled, may be directly coupled, or may be indirectly coupled through an intermediary. The specific meanings of the above terms in the present invention can be understood in specific cases to those skilled in the art.

Example 1

The method for testing the change of the water-drive pore structure of the loose core comprises the following steps:

step 1: providing a loose core sample;

step 2: packaging the loose core sample in a core holder;

and step 3: heating the core sample to a required experiment temperature and enabling the core sample to reach a set annular pressure, vacuumizing the core sample and enabling the core sample to be saturated with water;

and 4, step 4: obtaining a first nuclear magnetic resonance T2 spectrum of the pore structure of the core sample by a nuclear magnetic resonance device;

and 5: carrying out constant-speed water displacement on saturated water in the core sample through a displacement pump, and obtaining a second nuclear magnetic resonance T2 spectrum of the pore structure of the core sample through the nuclear magnetic resonance device again after the injection amount of the displacement water reaches a set value;

step 6: calculating a percentage of water-flooding pore structure change of the core sample using the first and second nuclear magnetic resonance T2 and T2 spectra.

Specifically, the test method of the present invention comprises 6 steps.

Step 1, providing a loose core sample, preferably, the core sample is cylindrical, and the diameter and the length can be set according to the experiment requirement. The core sample can be obtained by drilling, and the core sample is subjected to necessary cleaning treatment before testing, such as drying after being washed by an alcohol benzene solvent.

And 2, packaging the loose core sample in a core holder, wherein the core holder is a sealed cavity, two circular end faces of the core sample are exposed in the cavity, and the core holder is made of nonmetal in the preferred scheme.

And 3, heating the core sample to the required experiment temperature and enabling the core sample to reach the set annular pressure, vacuumizing the core sample and enabling the core sample to be saturated with water. In one embodiment, heating the core sample to a desired experimental temperature comprises: and heating the core holder to the required experiment temperature through a constant-temperature oil bath circulating system, wherein a heating medium of the constant-temperature oil bath circulating system is fluorine-chlorine-carbon oil, and the heating medium and the core sample are isolated from each other. In an alternative embodiment, the experimental temperature is 40-50 ℃. The two circular ends of the core sample correspond to the inlet and the outlet of the core holder respectively. And the inlet and the outlet of the core holder are used for connecting a core vacuumizing and pressurizing saturated water assembly and are used for vacuumizing and pressurizing a core sample to treat the saturated water. And the periphery of the side surface of the core sample is wrapped with a medium material layer for applying annular pressure on the core sample. In an alternative embodiment, the medium for applying the ring pressure to the core sample is chlorofluorocarbon oil. The fluorine-chlorine-carbon oil does not have nuclear magnetic resonance signals, and the interference on the signals of the rock core sample is eliminated. The ring pressure range is 2MPa-4 MPa.

And 4, after the core sample is saturated with water, acquiring a first nuclear magnetic resonance T2 spectrum of the pore structure of the core sample by using a nuclear magnetic resonance device. In the step, the parameter setting range of the nuclear magnetic resonance device is as follows: the sampling interval is 1-4 mus, the number of samples is 512-2048, the sampling time is 50-80 mus, the waiting time is 1-4s, the scanning times is 32-128, and the main frequency is 9.8 MHz. And 5, performing constant-speed water displacement on the saturated water in the core sample through a displacement pump, and obtaining a second nuclear magnetic resonance T2 spectrum of the pore structure of the core sample through the nuclear magnetic resonance device again after the injection amount of the displacement water reaches a set value. In one embodiment, the displacement speed of the displacement pump is 0.05ml/min-0.4ml/min, and the parameter setting range of the nuclear magnetic resonance device is as follows: the sampling interval is 1-4 mus, the number of samples is 512-2048, the sampling time is 50-80 mus, the waiting time is 1-4s, the scanning times is 32-128, and the main frequency is 9.8 MHz. And 6, calculating the percentage of the change of the water-flooding pore structure of the core sample by using the first nuclear magnetic resonance T2 spectrum and the second nuclear magnetic resonance T2 spectrum. Percent (%) change in water-flooding pores is the area of water contained in the changed pores/initial state of saturated water T2 spectrum area.

The invention provides a method for testing water-drive pore structure change of a loose core, which comprises the steps of obtaining a first nuclear magnetic resonance T2 spectrum of a core sample in a saturated water state by using a nuclear magnetic resonance device; and a second nuclear magnetic resonance T2 spectrum of the pore structure of the core sample after the injection amount of the displacement water reaches a set value. And calculating the percentage of the change of the water-drive pore structure of the core sample by using the first nuclear magnetic resonance T2 spectrum and the second nuclear magnetic resonance T2 spectrum, and the method can be used for evaluating the change of the water-drive pore structure of the loose sandstone.

The following is a description of a specific example.

1) Sampling and sample preparation

A cylindrical loose core sample with the diameter of 2.5 cm and the length of 7 cm is selected for the experiment.

2) Core packaging

And (3) loading the loose core sample into a nonmetal core holder for packaging, and then placing the nonmetal core holder into a nuclear magnetic equipment probe to connect a pipeline.

3) Conditions of the experiment

And heating the loose rock core to the required temperature according to the experimental condition, and keeping the temperature stable, wherein the experimental temperature is 45 ℃. The heating adopts a constant temperature oil bath circulating system, the heating medium is fluorine-chlorine-carbon oil, and the heating medium is not contacted with the rock core sample. The fluorine-chlorine-carbon oil is a non-nuclear magnetic resonance signal, so that the interference on the core sample signal is eliminated, and meanwhile, the fluorine-chlorine-carbon oil and the fluorine oil are used for adding an annular pressure medium around the core sample. The experimental ring pressure is 4 MPa. After the temperature and the annular pressure are stable, after vacuumizing for 24 hours (the vacuum degree is 10-6mbar), saturated water is used for scanning the loose rock core sample in the rock core holder by utilizing a nuclear magnetic resonance device, wherein nuclear magnetic resonance parameters are set as follows: the sampling interval is 2 mus, the sampling number is 2048, the sampling time is 60 mus, the waiting time is 2s, the scanning times are 64, the main frequency is 9.8MHz, and a first nuclear magnetic resonance T2 spectrum after the core is saturated with water is obtained as an initial state (as shown in figure 1).

And setting the displacement pump speed to be 0.1ml/min according to the experimental conditions, starting the core constant-speed water flooding experiment, and after the water flooding injection amount reaches 8 PV. And starting the nuclear magnetic resonance device again, and scanning the loose rock core sample, wherein the nuclear magnetic resonance parameters are set as follows: the sampling interval is 2 mus, the sampling number is 2048, the sampling time is 60 mus, the waiting time is 2s, the scanning times are 64, the main frequency is 9.8MHz, and a core water flooding second nuclear magnetic resonance T2 spectrum (shown in figure 1) is obtained.

4) Characterization method for water flooding pore structure change

Referring to fig. 1, the obtained first nuclear magnetic resonance T2 spectrum and second nuclear magnetic resonance T2 spectrum are used to characterize the core water-flooding pore structure change. The abscissa of the T2 spectrum represents the size of the pore size of the different pores of the core, and the ordinate represents the amount of water contained in the different pores. In the figure, the first nuclear magnetic resonance T2 spectrum of saturated water shows that water in the core sample is mainly distributed in pores between A and B (0.003um-29um), the second nuclear magnetic resonance T2 spectrum shows that water in the core sample is mainly distributed in pores between A and C (0.003um-387um), and the comparison of the first nuclear magnetic resonance T2 spectrum and the second nuclear magnetic resonance T2 spectrum shows that the water flooding pore structure of the core sample is in a variation range between B and C (29um-387um), and the area of a shaded part in the figure is the water amount contained in the variation of the water flooding pores. Using the formula: the percent (%) of the water flooding pore change is the area of the amount of water contained in the changed pores/the spectrum area of the saturated water initial state T2, and the percent of the water flooding pore change is calculated to be 8.1%.

Example 2

The embodiment discloses a loose rock core water drive pore structure changes's testing arrangement, refer to fig. 2, and this testing arrangement includes:

a nuclear magnetic resonance apparatus 1;

the core holder 2 is arranged in a probe 5 of the nuclear magnetic resonance device 1, and the core holder 2 is used for packaging a core sample 8;

the core vacuumizing and pressurizing saturated water assembly is used for enabling the core sample to reach a state of full saturated water;

the water displacement component is used for injecting water injection quantity of a set value into the core sample;

the nuclear magnetic resonance device is used for obtaining a first nuclear magnetic resonance T2 spectrum when the core sample reaches a full saturated water state and a second nuclear magnetic resonance T2 spectrum when the water injection amount of the core sample is a set value;

and the processing module is used for calculating the percentage of the change of the water-flooding pore structure of the core sample through the first water nuclear magnetic resonance T2 spectrum and the second nuclear magnetic resonance T2 spectrum.

It should be noted that the core vacuumizing and pressurizing saturated water assembly and the water displacement assembly are prior art, and specific structures are not described herein.

In an optional embodiment, the core vacuumizing and pressurizing saturated water assembly comprises a heating system, the heating system is a constant-temperature oil bath circulating system, a heating medium of the heating system is isolated from the core sample, and/or the core vacuumizing and pressurizing saturated water assembly comprises a medium for pressurizing the core sample by annular pressure, and the medium is chlorofluorocarbon oil.

The device is used for testing the change of the water-drive pore structure of the loose rock core, and a nuclear magnetic resonance device is used for obtaining a first nuclear magnetic resonance T2 spectrum of the rock core sample in a saturated water state; and a second nuclear magnetic resonance T2 spectrum of the pore structure of the core sample after the injection amount of the displacement water reaches a set value. And calculating the percentage of the change of the water-drive pore structure of the core sample by using the first nuclear magnetic resonance T2 spectrum and the second nuclear magnetic resonance T2 spectrum, and the method can be used for evaluating the change of the water-drive pore structure of the loose sandstone. Test methods refer to example 1.

Having described embodiments of the present invention, the foregoing description is intended to be exemplary, not exhaustive, and not limited to the embodiments disclosed. Many modifications and variations will be apparent to those of ordinary skill in the art without departing from the scope and spirit of the described embodiments.