WO2018129920A1

WO2018129920A1 - Sample component for radial permeability test of rock having extra-low permeability and test method therefor

Info

Publication number: WO2018129920A1
Application number: PCT/CN2017/097704
Authority: WO
Inventors: 何柏; 谢凌志; 赵鹏; 任利; 张瑶
Original assignee: 四川大学
Priority date: 2017-01-12
Filing date: 2017-08-16
Publication date: 2018-07-19
Also published as: CN106841000B; CN106841000A

Abstract

A sample component and test method for radial permeability test of rock having extra-low permeability. The sample component comprises a cylindrical rock sample (3), and an upper adapter substitute (1) and a lower adapter substitute (2) both having a cylindrical main body structure. A cylindrical hole for providing a radial penetration channel for a permeable medium is processed at the center of the rock sample (3). A cylindrical boss (1-1) which is embedded and in fit with the cylindrical hole of the rock sample (3) is designed at the center of the bottom surface of the upper adapter substitute (1). A cylindrical convex ring (2-1) which is embedded and in fit with the cylindrical hole of the rock sample (3) is designed at the center of the top surface of the lower adapter substitute (2); a mounting hole (2-2) in fit with a lower pressing head is designed at the center of the bottom surface of the lower adapter substitute; and a permeable medium circulation hole penetrating the cylindrical convex ring (2-1) of the top surface from the mounting hole (2-2) is processed at the center of the lower adapter substitute. The sample component and the method can simply and effectively obtain the indoor permeability, especially the radial permeability, of the rock having extra-low permeability.

Description

Specimen component and test method for test test of radial permeability of ultra low permeability rock

Technical field

The invention belongs to the field of rock mechanical property testing, and particularly relates to a rock permeability testing test method.

Background technique

Permeability is an important characterization parameter for describing the ability of fluids to flow in porous media such as rock. It has a wide range of applications in energy extraction and storage, waste disposal, water conservancy engineering, environmental engineering and many other fields. At present, the indoor permeability test method (such as: steady state method, transient method, pore pressure oscillation method, etc.) generally adopts a cylindrical solid sample, and the osmotic medium penetrates from one end surface of the sample to the other end surface, using the formula (1) The axial permeability of the rock is calculated.

Where L is the height (m) of the cylindrical sample and A is the cross-sectional area (m ² ) of the sample.

In recent years, with the development of the economy, engineering activities such as unconventional oil and gas resources exploitation, CO ₂ geological storage, and salt rock energy reserves have become more frequent. However, this type of engineering activity faces a common problem, that is, the permeability of rock is extremely low. Because of the weak ability of such ultra-low permeability rock to allow fluid to pass through itself, the conventional experimental method for testing the permeability will face problems such as large time span and long time of the experimental measurement process, and due to the small system flow, the sensor The requirements are very high and it is often difficult to achieve accurate measurement and control. Therefore, the use of conventional methods to test the permeability characteristics of ultra-low permeability rock often brings great errors and difficulties to the experiment, and even the rock permeability characteristics cannot be measured. If the penetration test efficiency is improved by shortening the height of the sample and increasing the cross-sectional area of the sample, the sample will become a plate-like structure, which makes it difficult to couple with the stress level, and practice has shown that such a method improves the core. Penetration testing efficiency is not significant. On the other hand, many of the infiltration problems in engineering practice activities are three-dimensional diffusion flow processes. It is difficult to describe the permeability characteristics of the core in the axial direction. Therefore, how to obtain the permeability characteristics of ultra-low permeability rock cores, especially the radial permeability characteristics, is more important for the comprehensive study of the seepage law of ultra-low permeability rocks.

Summary of the invention

In view of the deficiencies of the prior art, a first object of the present invention is to provide a sample assembly for the ultra-low permeability rock radial permeability test for indoor permeability testing of ultra-low permeability rock, especially Radial Permeability Test; A second object of the present invention is to provide a test method based on the above-described sample assembly for the ultra-low permeability rock radial permeability test to obtain the ultra-low permeability rock radial penetration characteristics.

For the first object of the present invention, the present invention provides a sample assembly for testing the radial permeability of an ultra-low permeability rock, comprising a cylindrical rock sample, a top-up joint having a cylindrical structure and a lower portion. Conversion joint, the rock test The sample center is machined with a cylindrical hole for providing a radial permeation passage for the permeable medium, and a cylindrical boss embedded in the cylindrical hole of the rock sample is designed at the center of the bottom surface of the up-conversion joint; the top surface of the lower conversion joint is at the center The design has a cylindrical convex ring embedded with the cylindrical hole of the rock sample. The center of the bottom surface is designed with a matching hole for the lower pressing head, and the center is processed with an permeable medium circulation hole penetrating from the mounting hole to the cylindrical annular ring of the top surface.

The above sample assembly for the ultra-low permeability rock radial permeability test has the same diameter of the up-conversion joint and the down-conversion joint as the diameter of the rock sample.

The sample assembly for the ultra-low permeability rock radial permeability test described above, the rock sample having an outer diameter of not less than 50 mm, preferably 50 to 100 mm, and an inner diameter of preferably 5 to 10 mm. The height of the rock sample is preferably 2 to 2.5 times its outer diameter.

The sample assembly for testing the radial permeability of the ultra-low permeability rock, the height of the main cylinder of the up-conversion joint is not less than 10 mm, preferably 10-20 mm, and the height of the boss on the bottom surface is not less than 5 mm, preferably 5 ~10mm, the diameter is smaller than the cylindrical hole at the center of the rock sample.

The sample test assembly for the radial permeability test of the ultra-low permeability rock, wherein the height of the main cylinder of the down-converting joint is not less than 50 mm, preferably 50-70 mm, and the depth of the mounting hole is not less than 20 mm, preferably 20-40 mm. The diameter of the mounting hole is preferably 20 to 40 mm. The height of the convex ring on the top surface of the down conversion joint is preferably not less than 5 mm, preferably 5 to 10 mm, and the outer diameter is smaller than the central cylindrical hole of the rock sample.

In view of the second object of the present invention, the present invention provides a test method based on the above-described sample assembly for the ultra-low permeability rock radial permeability test, comprising the following steps:

(1) Pre-infiltration pre-treatment work is carried out on ultra-low permeability rock samples. If the osmotic medium is liquid, the sample is subjected to liquid saturation pretreatment; if the osmotic medium is gas, the sample is subjected to drying pretreatment;

(2) Insert the convex ring on the bottom surface of the up-conversion joint and the convex ring on the top surface of the down-conversion joint into the central cylindrical hole of the rock sample, and apply the glue on the butt end face of the rock sample and the up-conversion joint and the down-conversion joint. The bonding agent is bonded and fixed to each other to prevent the leakage medium from leaking from the end surface of the sample during the experiment, and then the rock sample, the up-conversion joint and the down-conversion joint are integrally sealed with the sealed sample bag to prevent air. Water enters the sample and the sample is volatilized;

(3) The upper pressing head and the top of the up-conversion joint face each other, and the abutting surface is such that the permeated medium can be returned to the central hole of the upper pressing head, and then all the rock samples and all the up-conversion joints are covered with the permeation screen. And part of the upper pressing head, and then completely covered with the heat shrinkable film and penetrated the upper and lower joints of the permeation screen, and finally sealed the upper and lower ends of the heat shrinkable film with the sealing hoop to prevent the confining pressure during the experiment. The oil penetrates into the sample or the permeable medium leaks out;

(4) The upper pressing head is mounted on the testing machine, and the lower conversion joint is connected with the lower pressing head on the testing machine. After the whole permeation system is evacuated, the confining pressure and the axial pressure are increased to a predetermined value, so that the permeation medium penetrates the upstream and downstream pressures. reach P _0, 5 ~ 10 minutes, increasing the osmotic pressure upstream to P _i, osmotic downstream pressure P ₀ remains unchanged, on the permeate were measured, and the permeability of the downstream pressure variation with time.

The method for calculating the radial permeability of ultra-low permeability rock according to the invention:

The present invention satisfies the following assumptions during the experiment:

(1) Darcy's law is established during the infiltration process;

(2) The seepage gas is an ideal gas.

The permeability calculation formula described in the present invention is as follows:

P ₁ -P ₂ =(P _i -P ₀ )e ^-at (2)

Formula (2) is a variation of the pressure of the upstream and downstream pressure vessels of the permeation system with time in the method of the present invention, and the coefficient a in the formula (2) is related to the selected permeation medium, and when the permeation medium is a gas, (3) Calculate the permeability of the sample; when the osmotic medium is a liquid, the permeability of the sample can be calculated according to the formula (4).

If the volume of the upstream and downstream vessels (including the pipe volume) in the osmotic system is equal, ie (V ₁ =V ₂ =V), Equations (3) and (4) can be simplified as:

In the formula (2) to the formula (6):

k is the radial permeability (m ² ) of the sample, and P ₁ and P ₂ are the pressures (Pa) of the upstream and downstream pressure vessels in the permeation process respectively, and P _i and P ₀ are the upstream and downstream pressure vessels in the permeation process, respectively. Initial pressure (Pa),

The average pressure (Pa) of the upstream and downstream pressure vessels in the infiltration process, P _f is the final equilibrium pressure (Pa) of the infiltration system, and V ₁ and V ₂ are the volume of the upstream and downstream vessels (m ³ ) during the infiltration process, respectively. R ₁ and R ₂ are the inner radius and outer radius (m) of the rock sample, L is the height (m) of the rock sample, t is the experimental time (s), and μ is the viscosity coefficient of the permeable medium (Pa· s), β is the compressibility of the liquid (Pa ^-1 ).

In the above method, a filter paper is preferably placed on the joint surface of the upper head and the up-conversion joint to prevent small particles in the sample from blocking the permeation passage.

In the above method, the permeation screen may be selected from a wire mesh such as a wire mesh, a copper wire mesh or the like.

In the above method, an existing laboratory routine testing machine is used, and the indenter is used in the method of realizing a hydraulic fracturing experiment on a conventional rock mechanic test machine and a pressure device and a rock sample disclosed in the patent application No. 201610084533.1 Indenter.

In the above method, the penetration test under different confining pressures and the penetration test under full stress and strain conditions can be completed by changing the confining pressure or the axial pressure.

The osmotic medium selected in the method of the present invention may be a liquid or a gas, and the difference in the experiment process mainly has the following two points, one of which is that the pretreatment of the sample is different before performing the penetration test, if The osmotic medium is a liquid, and the sample is subjected to liquid saturation pretreatment; if the osmotic medium is a gas, the sample is subjected to a drying pretreatment. The second is that there are certain differences in the calculation formula of the permeability. Because of the small difference between each other, the gas permeation medium is taken as an example in the following patents unless otherwise specified.

The invention has the following beneficial effects:

1. The permeability test method and calculation formula of the present invention can effectively improve the permeability test efficiency. Compared with the conventional penetration test method, when the samples have the same diameter and height, the experimental method of the present invention can make the same time. The osmotic pressure decay rate is increased by at least an order of magnitude.

2. The invention can quantitatively analyze the permeability characteristics of ultra-low permeability rock under different stress states (especially the analysis of radial permeability characteristics), and can further understand complex seepage characteristics, for unconventional oil and gas resources exploitation and energy. Engineering practices such as storage are of great significance.

3. The conversion joints and samples of the invention are convenient for processing and manufacturing, and the experiment operation is simple, and is convenient for popularization and application.

DRAWINGS

Figure 1 is a schematic view showing the structure of the upper joint of the testing machine of the present invention.

2 is a schematic structural view of a down converter of the testing machine of the present invention.

Figure 3 is a cross-sectional view of a rock sample of the present invention.

Figure 4 is a schematic view showing the assembly of the tester adapter and the rock sample of the present invention.

Fig. 5 is a graph showing pressure versus time of the upstream and downstream vessels in Example 1.

Fig. 6 is a graph showing the calculation of the permeability in the embodiment.

In the figure, 1 - upconverter, 1-1 - boss, 2 - downconverter, 2-1 - convex ring, 2-2 - mounting hole, 3 - sample, 4 - permeate mesh, 5 - heat Shrink film, 6-adhesive, 7-sealing ferrule, 8-upper head.

detailed description

The method for testing the radial permeability of the ultra-low permeability rock and the conversion joint and the rock sample according to the present invention will be further described below by way of specific embodiments.

Example 1

The sample assembly for testing the radial permeability of ultra-low permeability rock, as shown in Figures 1-3, consists of a cylindrical rock sample 3, a top-up joint 1 and a down-converting joint 2 having a cylindrical structure. The rock sample center is processed with a cylindrical hole for providing a radial permeation passage for the osmotic medium, and a cylindrical boss 1-1 is embedded at the center of the bottom surface of the up-conversion joint with the cylindrical hole of the rock sample; The top of the top surface of the adapter is designed with a cylindrical convex ring 2-1 embedded in the cylindrical hole of the rock sample. The center of the bottom surface is designed to match the lower pressing head of the testing machine. The mounting hole 2-2, the lower conversion joint center processing There is an permeable medium flow hole penetrating from the mounting hole through the top cylindrical ring. The main body diameter of the up-conversion joint and the down-conversion joint is equal to the diameter of the rock sample. The rock sample is prepared by processing the collected shale outcrop through drilling, cutting, grinding and drilling.

Dimensions: The height of the main cylinder of the up-conversion joint is 10mm, the outer diameter is 50mm, the height of the upper boss is 5mm, the diameter of the upper boss is 5mm; the height of the main cylinder of the down-conversion joint is 50mm, the outer diameter is 50mm, concave The groove depth is 25 mm, the groove has a diameter of 20 mm, and the lower boss of the down-conversion joint has a height of 5 mm and a diameter of 5 mm. The height of the rock sample is L = 100 mm, the inner radius of the rock sample is R ₁ = 5 mm, and the outer radius R ₂ = 50 mm.

The test method for the ultra-low permeability rock radial permeability test based on the above test machine adapter rock sample, the steps are as follows:

(1) Drying pretreatment of the ultra-low permeability rock test with nitrogen as the osmotic medium;

(2) Insert the convex ring on the bottom surface of the up-conversion joint and the convex ring on the top surface of the down-conversion joint into the central cylindrical hole of the rock sample, and apply the glue on the butt end face of the rock sample and the up-conversion joint and the down-conversion joint. The bonding agent is bonded and fixed to each other to prevent the leakage medium from leaking from the end surface of the sample during the experiment, and then the rock sample, the up-conversion joint and the down-conversion joint are integrally sealed with the sealed sample bag to prevent air. The moisture enters the sample and the sample is volatilized, and the sample is allowed to stand after sealing, so that the adhesive fully exerts the bonding effect;

(3) After at least 24 hours, remove the sealed sample and the test machine adapter, place the upper head on the top of the up-conversion joint, face the top, and place on the mating surface of the upper and upper adapters. A layer of filter paper to prevent small particles in the sample from clogging the infiltrated pipe, and then covering all the rock samples, all up-converting joints, and some upper indenters with a permeate wire mesh, and the permeate mesh is at least 2 mm above the up-conversion joint, The permeate screen does not touch the lower conversion joint, and the permeation screen is fixed by the shrink film coating. The height of the coating is sufficient to completely cover the permeated screen and beyond the upper and lower joints, and then the heat shrinkage is fixed by the sealing hoop. The upper and lower ends of the membrane prevent the penetration of the pressurized oil into the sample during the experiment;

(4) Install the upper pressing head on the testing machine, connect the lower conversion joint with the lower pressing head on the testing machine, and after vacuuming the whole permeation system, increase the confining pressure to 3 MPa, the axial pressure to 3 MPa, and open the gas cylinder to make the infiltration upstream and downstream. after the pressure reaches P ₀ = 0.2MPa, 5-10 minutes, increasing the osmotic pressure upstream to P _i = 2.2MPa, osmotic downstream pressure P ₀ remains unchanged, were measured on the permeate, the downstream pressure vessel pressure variation with time;

(6) After the test, the sample and the adapter are removed from the test machine, and the bonded sample and the adapter are baked in an electric furnace until the failure is removed, and the adapter is cleaned for subsequent use in repeated tests.

The change law of the pressure of the upper and lower pressure vessels with time is shown in Fig. 5. Firstly, according to the change law of the pressure of the upstream and downstream pressure vessels with time,

In the present embodiment, the volume of the upper and lower containers (including the pipe volume) is equal to the slope of the time t, that is, (V ₁ = V ₂ = V), so the radial permeability k of the sample is calculated according to the formula (5).

After the completion of the permeability test, after half an hour, the permeability was tested again under this condition to ensure the repeatability of the experiment. The permeability of the sample was measured twice at 2.084×10 ^-19 and 2.062×10 ^-19 , respectively, and had good repeatability.

Claims

a sample assembly for testing a radial permeability of an ultra-low permeability rock, comprising: a cylindrical rock sample (3), a top-conversion joint (1) and a down-conversion joint (2) having a cylindrical body structure, The rock sample center is processed with a cylindrical hole for providing a radial permeation passage for the permeate medium, and a cylindrical boss (1-1) embedded in the cylindrical hole of the rock sample is designed at the center of the bottom surface of the up-conversion joint; The center of the top surface of the conversion joint is designed with a cylindrical convex ring (2-1) embedded in the cylindrical hole of the rock sample, and the center of the bottom surface is designed with a mounting hole (2-2) matching the lower pressing head, the center An permeable medium flow hole is formed through the cylindrical annular ring passing through the mounting hole from the mounting hole.
A sample assembly for testing a radial permeability of an ultra-low permeability rock according to claim 1, wherein the diameters of the up-conversion joint and the down-conversion joint are equal to the diameter of the rock sample.
A sample assembly for testing a radial permeability of a particularly low permeability rock according to claim 1, wherein said rock sample has an outer diameter of 50 to 100 mm and an inner diameter of 5 to 10 mm.
A sample assembly for testing a radial permeability of a particularly low permeability rock according to claim 3, wherein the rock sample has a height of from 2 to 2.5 times its outer diameter.
A sample assembly for testing a radial permeability of an ultra-low permeability rock according to any one of claims 1 to 4, characterized in that the height of the main cylinder of the up-conversion joint is 10-20 mm, and the height of the boss on the bottom surface It is 5 to 10 mm in diameter and smaller than the cylindrical hole at the center of the rock sample.
The sample test assembly for testing the radial permeability of a particularly low permeability rock according to any one of claims 1 to 4, characterized in that the height of the main cylinder of the down conversion joint is 50 to 70 mm, and the depth of the mounting hole is 20 to 40mm, the diameter of the mounting hole is 20~40mm.
The sample assembly for testing the radial permeability of a particularly low permeability rock according to claim 6, wherein the height of the convex ring (2-1) on the top surface of the down conversion joint is 5 to 10 mm, and the outer diameter is smaller than the rock test. Sample center cylindrical hole.
A test method for a sample assembly for testing a radial permeability of a particularly low permeability rock according to claim 1, comprising the steps of:

(1) Pre-treatment work is carried out on the ultra-low permeability rock test before infiltration. If the osmotic medium is liquid, the sample is subjected to liquid saturation pretreatment; if the osmotic medium is gas, the sample is subjected to drying pretreatment;

(2) Insert the convex ring on the bottom surface of the up-conversion joint and the convex ring on the top surface of the down-conversion joint into the central cylindrical hole of the rock sample, and apply the glue on the butt end face of the rock sample and the up-conversion joint and the down-conversion joint. The bonding agent is bonded and fixed to each other to prevent the leakage medium from leaking from the end surface of the sample during the experiment, and then the rock sample, the up-conversion joint and the down-conversion joint are integrally sealed with the sealed sample bag to prevent air. Moisture in moisture entering the sample or sample;

(3) The upper pressing head and the top of the up-conversion joint face each other, and the abutting surface is capable of returning the permeated medium to the upper pressing head In the heart hole, the entire rock sample, all the up-conversion joints and part of the upper head are covered with a permeate screen, and then the permeated screen is completely covered with a heat shrinkable film and beyond the upper and lower joints of the permeate screen. Finally, the upper and lower ends of the heat shrinkable film are sealed by a sealing ferrule to prevent the surrounding oil from penetrating into the sample or the permeable medium during the experiment;

(4) The upper pressing head is mounted on the testing machine, and the lower conversion joint is connected with the lower pressing head on the testing machine. After the whole permeation system is evacuated, the confining pressure and the axial pressure are increased to a predetermined value, so that the permeation medium penetrates the upstream and downstream pressures. reach P 0, 5-10 minutes later, increasing the osmotic pressure upstream to P i, osmotic downstream pressure P 0 remains unchanged, on the permeate were measured, and the permeability of the downstream pressure variation with time.
The ultra-low permeability rock radial permeability test test method according to claim 8, characterized in that, when calculating the permeability, the pressure law of the upstream and downstream pressure vessels of the permeation system changes with time P 1 - P 2 =(P i -P 0 )e -at calculates the coefficient a,

When the osmotic medium is a gas, the permeability is calculated according to the following formula:

When the osmotic medium is a liquid, the permeability is calculated according to the following formula:

In the above formula, k is the radial permeability (m 2 ) of the sample, and P 1 and P 2 are the pressures (Pa) of the upstream and downstream pressure vessels in the permeation process, respectively, and V 1 and V 2 are respectively in the permeation process. , downstream container volume (m 3 ), R 1 , R 2 are the inner radius and outer radius (m) of the rock sample, L is the height of the rock sample (m), t is the experimental time (s), μ is The viscosity coefficient (Pa·s) of the permeable medium, and β is the compression coefficient (Pa -1 ) of the liquid.
The ultra low permeability rock radial permeability test test method according to claim 8, characterized in that a filter paper is placed on the joint surface of the upper indenter and the upconversion joint.