CN112304849A - Method for testing gas permeability of irregular-shaped loose rock sample - Google Patents
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- G—PHYSICS
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- G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
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- G01N1/28—Preparing specimens for investigation including physical details of (bio-)chemical methods covered elsewhere, e.g. G01N33/50, C12Q
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- G—PHYSICS
- G01—MEASURING; TESTING
- G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
- G01N1/00—Sampling; Preparing specimens for investigation
- G01N1/28—Preparing specimens for investigation including physical details of (bio-)chemical methods covered elsewhere, e.g. G01N33/50, C12Q
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Abstract
The invention discloses a method for testing gas permeability of an irregular loose rock sample, which comprises the following steps: selecting a rock core from the irregular loose rock sample; then removing the water of the selected core; shaping the core with the water removed and reinforcing the surface strength; then, sealing and additionally installing plugs with through holes at two horizontally opposite positions on the surface of the rock core; manufacturing a casting mould with an opening at the upper end, placing a core with plugs in an inner cavity of the casting mould, and respectively connecting the other ends of the two plugs with air pipes so that the other ends of the two air pipes extend out of the mould; then, casting the inner cavity of the mold by using foam, and forming a complete rock core after the foam is solidified; measuring gas permeability parameters of the prepared complete rock core; finally, the gas permeability and related parameters are determined. The method can efficiently measure the gas permeability of the gas reservoir irregular-shaped loose sandstone, and provides basic parameters for evaluation of similar reservoirs.
Description
Technical Field
The invention relates to the technical field of core analysis in the petroleum industry, in particular to a gas permeability testing method for a gas reservoir natural irregular loose sandstone rock sample.
Background
Loose sandstone is an important type of oil and gas reservoirs in China, plays an important role in the field of oil and gas energy, and loose sandstone gas reservoirs are also main objects for the research of geologists. Particularly, recently, along with the continuous deep exploration and development of natural gas reservoirs in Songliao basin, the natural rock cores of partial reservoirs are very loose, the rock cores taken from underground are extremely irregular in shape, different in shape and extremely easy to break, basic parameters such as gas permeability and the like are difficult to obtain by adopting a traditional method, and great inconvenience is brought to the reserve calculation and capacity evaluation of gas fields.
The core analysis is the basis of reservoir evaluation, and from laboratory research, the core analysis mainly comprises physical property analysis, oil saturation analysis, phase permeability experimental analysis and the like, so that the core analysis result is not only an important basis favorable for reservoir optimization, but also has general attention in relation to oil and gas resource evaluation.
At present, a sample is required to have a regular shape in core analysis, and generally, the sample is a small cylinder with the diameter of 2.54cm or 3.8cm and the end surface is flat according to the oil and gas industry standard GB/T29172-2012. At present, the loose sandstone is generally difficult to obtain a complete columnar core, so a core sand method is adopted for testing, and only approximate experimental results can be obtained; or crushing sandstone, selecting proper proportion and then bonding with adhesive for testing; or packing the loose regular columnar core by using filter paper and then washing oil. According to the method, due to the fact that the loose sandstone is few in cementing materials, a reservoir layer is loose, the problems of particle falling, cracking and the like are prone to occurring, and a plunger sample with the diameter of 2.5cm or 3.8cm cannot be prepared.
Therefore, how to measure parameters such as gas permeability and the like of the irregular-shaped loose gas reservoir sandstone core becomes a difficult problem in core analysis and reservoir evaluation.
Disclosure of Invention
The invention aims to provide a method for testing the gas permeability of an irregular-shaped loose rock sample, which can be used for efficiently testing the gas permeability of an irregular-shaped loose sandstone of a gas reservoir, is simple and practical to operate, has small error and provides basic parameters for evaluation of similar reservoirs.
In order to achieve the purpose, the invention provides a method for testing gas permeability of an irregular-shaped loose rock sample, which comprises the following steps:
(1) selecting a rock core from the irregular loose rock sample;
(2) removing water from the selected core;
(3) shaping the core with the water removed and reinforcing the surface strength;
(4) the plug with a through hole is hermetically and additionally arranged at two horizontally opposite positions on the surface of the rock core;
(5) manufacturing a casting mould with an opening at the upper end, placing the core with the plugs in the step (4) in an inner cavity of the casting mould, and respectively connecting the other ends of the two plugs with air pipes to enable the other ends of the two air pipes to extend out of the mould;
(6) casting the inner cavity of the mold by using foam, and forming a complete rock core after the foam is solidified;
(7) measuring gas permeability parameters of the complete rock core prepared in the step (6);
(8) gas permeability and related parameters are determined.
Preferably, the rock core selected in the step (1) is located at a position with balanced permeability on a loose rock sample, if the permeability and the length of the rock sample both meet research requirements, the rock sample is directly selected as the rock core, and if the permeability and the length of the rock sample do not meet the research requirements, the rock sample meeting the permeability requirements and the length requirements is cut along an axial position perpendicular to the rock sample as the rock core.
Preferably, the step (2) adopts a mode of putting the rock core into a thermostat and drying to remove water in the rock core.
Preferably, the specific operation of step (3) is: and putting the core to be measured in a metal basket with sieve pores on the surface, putting the core and the metal basket into the molten first paraffin, and taking out the core after soaking for a preset time to obtain the shaped core with the first paraffin layer on the surface.
Preferably, the glass fiber yarns are placed in a molten state of the first paraffin wax, so that the core is solidified to form a first paraffin layer with the glass fiber yarns after being taken out of the molten first paraffin wax.
Preferably, the first paraffin is paraffin wax number 52, and the core is soaked in the molten first paraffin for 25-30 seconds.
Preferably, in the step (4), a part of the first paraffin is scraped from the surface of the core wax-sealed by the first paraffin layer along two horizontally opposite positions vertical to the axis until the surface of the core is exposed, so that the shape of the two exposed core surfaces corresponds to the shape of one end of each of the two plugs, and then the two plugs are bonded to the exposed surface of the core by using the melted second paraffin.
Preferably, the second paraffin wax is semi-refined No. 64 paraffin wax.
Preferably, the casting mold is in a box shape with an open upper end, the wax-sealed core is arranged in the inner cavity of the mold, the distance between the wall of each inner cavity of the mold and the outer surface of the core is 80-100mm, and the other ends of the two plugs extend out of the mold respectively.
Preferably, the core is supported on the bottom surface of the inner cavity of the mold through a support, and the distance between the bottom surface of the core and the bottom surface of the inner cavity of the mold is 80-100 mm.
Preferably, the foaming liquid cast in the step (6) is injected upwards from the bottom of the inner cavity of the mold to the upper part of the inner cavity of the mold, and the complete processed core is formed after the foam is solidified.
Preferably, the gas permeability in step (7) is measured according to a national standard unsteady state method, and the formula is as follows:
the parametric measure of gas permeability is for the parameters in the above formula:
-a gas permeability of the gas,
；
-gas flow rate, mL/s;
-atmospheric pressure, atm;
-the end area of the core,
；
-viscosity of the gas, mPa · s;
-inlet end gas pressure, atm;
-outlet end gas pressure, atm.
By adopting the scheme, the method for testing the gas permeability of the irregular-shaped loose rock sample solves the problem that the rock core analysis cannot be carried out on the irregular-shaped loose rock sample at present, is unique, easy to operate, simple, convenient and practical, has small error, can accurately obtain basic parameters such as the gas permeability and the like, brings great convenience for reserve calculation and capacity evaluation of a gas field, and provides basic parameters for evaluation of similar reservoirs.
Drawings
FIG. 1 is a flow chart of the method for testing gas permeability of an irregular-shaped loose rock sample according to the invention;
FIG. 2 is a schematic diagram of the structure of a rock sample used in an embodiment of the testing method of the present invention;
FIG. 3 is a schematic view of a three-dimensional structure of a core selected according to an embodiment of the testing method of the present invention;
FIG. 4 is a schematic structural diagram of a core connection plug according to an embodiment of the testing method of the invention;
FIG. 5 is a schematic structural view of a core placed in a casting mold according to an embodiment of the testing method of the present invention;
fig. 6 is a schematic structural diagram of a core after casting according to an embodiment of the testing method of the present invention.
Detailed Description
The invention will be elucidated on the basis of an embodiment shown in the drawing. The embodiments disclosed herein are to be considered in all respects as illustrative and not restrictive. The scope of the present invention is not limited to the following description of the embodiments, but is defined only by the scope of the claims, and includes all modifications having the same meaning as and within the scope of the claims.
The method for testing the gas permeability of the irregular-shaped loose rock sample is described below by combining specific examples.
Referring to fig. 1, the method for testing gas permeability of the irregular loose rock sample comprises the following steps:
s101, selecting a rock core from an irregular loose rock sample: selecting a core section with strong representativeness from a rock sample as a core, wherein the core with strong representativeness is positioned at a part with balanced (moderate) permeability of the rock sample, the permeability of the core section is not too high or too low, if the permeability of the whole rock sample is moderate and the length of the core section also meets the research requirement, the rock sample can be directly used as the core, if the permeability distribution of the rock sample is unbalanced and the length of the rock sample also does not meet the research requirement, the core section meeting the permeability requirement and the length requirement can be intercepted along an axial part vertical to the rock sample as the core, and the representative core with the length of 4-5cm is intercepted from the rock sample.
S102, removing water of the selected core: generally, a gas reservoir rock sample contains a certain amount of moisture, the rock core is placed in a constant temperature box to be dried, and the moisture in the rock core is dried at the temperature of 50-60 ℃ to ensure the data accuracy in the permeability measurement.
S103, shaping the core with the water removed and reinforcing the surface strength: the specific operation is as follows: placing the core 1 (refer to fig. 2 and 3) with the moisture removed in the step S102 in a metal basket with a sieve pore on the surface, then placing the metal basket and the core 1 together into the first molten paraffin with the glass fiber filaments inside for soaking for a predetermined time, and taking out, specifically: adding first paraffin into a container, wherein the container of the embodiment adopts a stainless steel basin with the volume of 5L, the first paraffin adopts solid paraffin with the volume of No. 52, placing the basin on an electric furnace for heating to melt the first paraffin, then the core 1 together with the metal basket is put into the melted first paraffin solution for 25-30 seconds, during this time, glass fiber strands having a diameter of about 50 μm and a length of 3 to 5mm were added to the molten paraffin solution, and as shown in FIG. 4, the surface of the core 1 after being taken out had a first paraffin layer 2 in which the glass fiber strands were mixed, and the glass fiber strands served as ribs to further strengthen the surface of the core 1, thus, the loose core 1 is fixed into a shape with certain strength, the impact resistance strength of the core 1 with the first paraffin layer 2 on the surface is improved compared with that of the naked core, and the soaking time of the core 1 in the molten first paraffin solution and the data of the depth of the first paraffin soaked in the core 1 are given in the following table 1. The result shows that the core 1 is soaked in the first paraffin solution for 30 seconds, the depth of the first paraffin soaked on the surface of the core 1 is 1.56mm, the requirement of the surface strength of the core is met, the core is placed in a container with a calibrated volume and filled with water, and the volume V of the core can be calculated according to the discharged water amount and the thickness of the first paraffin layer 2 on the surface of the core 1.
TABLE 1
| Soaking time in |
5 | 10 | 20 | 30 | 45 | 60 |
| Depth of immersion, mm | 0.55 | 0.92 | 1.19 | 1.56 | 1.84 | 2.03 |
S104, referring to fig. 4, installing plugs with through holes in two horizontally opposite positions on the surface of the rock core in a sealing mode: the specific operation is as follows: scraping a first paraffin layer with the size of 20mm multiplied by 40mm respectively on the outer side surface of a core 1 wax-sealed by a first paraffin layer 2 along two horizontally opposite parts vertical to an axis till the surface of the core 1 is exposed, simultaneously exposing pores of the core, wherein the shape of the surface of the two exposed cores 1 corresponds to the shape of one end of each of two plugs 3, namely, the plug 3 in the embodiment adopts a cuboid plug 3 with the cross section of 20mm multiplied by 40mm made of organic glass material, one end of the plug 3 is fixed with a 140-mesh stainless steel screen with the diameter of 20mm multiplied by 40mm, then the end of the plug 3 is pasted on the exposed core surface, a circle between the plug 3 and the core 1 is coated with melted second paraffin for sealing, so that the two plugs 3 are sealed and fixed on the surface of the core 1 scraping the first paraffin layer, the second paraffin adopts semi-refined No. 64 paraffin with high melting point, and thus the plug installation is completed, and the other end of the plug 3 is screwed with a metal evacuating nozzle 4.
S105, manufacturing a casting mold with an open upper end, and referring to fig. 5, the mold 5 is a box shape with an open upper end, the mold 5 in this embodiment is a rectangular parallelepiped with an open upper end made of a wood board, and the dimensions of the mold are as follows: the distance between the wall of each inner cavity of the mold 5 and the outer surface of the wax-sealed core is 80-100mm, and the core 1 is supported on the bottom surface of the inner cavity of the mold 5 through the two brackets 6, so that the distance between the bottom surface of the core 1 and the bottom wall of the inner cavity of the mold 5 is 80-100 mm. The two brackets 6 support the rock core, so that subsequent foam can be poured to the bottom of the rock core conveniently. The evacuating nozzles 4 on the two plugs 3 are respectively communicated with one ends of the two air pipes 7 through rubber pipes, and the other ends of the two air pipes 7 extend out of the mold 5, so that the air pipes 7 can be prevented from being blocked during pouring.
S106, casting the inner cavity of the mold 5 by using foam, and curing the foam to form a complete core: the specific operation is as follows: preparing a polyurethane foaming machine and a foaming agent, starting the foaming machine, extending a foam outlet nozzle of the foaming machine to the bottom of the core, injecting a casting foaming liquid from the bottom of an inner cavity of the mold 5 upwards to the upper part of the inner cavity of the mold 4, and curing foam to obtain a complete treated core 8 (shown in figure 6).
S107, measuring gas permeability parameters of the complete core prepared in the step S106: the specific measurement is as follows: the gas flow measurement is carried out on the complete processed core 8 by adopting a national standard GB/T29172-2012 method, the measurement pressure is less than 0.1MPa, the phenomenon that foam is sealed and broken due to large pressure is avoided, measurement results of atmospheric pressure, inlet end gas pressure, outlet end gas pressure, gas flow and gas viscosity are recorded, the volume V of the core 1 can be calculated according to the water quantity discharged from the core and placed in a quantitative container described in the section S103, the axial length L of the core 1 is measured, and the volume V and the axial length L are substituted into a cylindrical (approximate) volume formula: v = π r2L, to find the radius r of the circle (approximation) of the core 1, and then to bring it into the area of the circle equation: a = π r2The size of A can be determined.
S108, determining gas permeability and related parameters: substituting the data results of each parameter measured in step S107 into the formula:
and calculating the gas permeability. Under the condition that the sealing of the core is not damaged and the condition that the temperature is lower than 35 ℃ (the melting temperature of the first paraffin and the second paraffin), the saturated water of the core 1 can be further pumped out, the water porosity of the core 1 can be obtained according to the mass difference before and after the saturated water, and the core flow experiment can also be carried out.
If the core with the measured gas permeability is not subjected to other tests, the whole core can be placed into a constant temperature box, the core is heated to 60-70 ℃ and is kept at the constant temperature for 30-40 minutes, after the second paraffin and the first paraffin layer on the surface of the core 1 are molten, the foam can be cut open, and the core is taken out.
Examples
Selecting two cores on the same rock sample, wherein one core is a cylinder with a regular shape, the other core is a semi-cylindrical rock sample with an irregular shape and a semicircular cross section, and performing permeability measurement on the cores with two different shapes on the same rock sample as follows:
1. selecting a core from a regular cylindrical core, manually grinding the selected core into the regular cylindrical core with the diameter of 25mm and the length of 50mm, uniformly mixing the quick epoxy resin glue and the curing agent in proportion, and quickly bonding a commercially available circular stainless steel core cover with the diameter of 25mm to the end surface of the ground core to bond the periphery of the end surface of the core and the periphery of the core cover together without gaps. After the epoxy resin is cured, smearing the exposed part of the rock core with a mixed solution of rapid epoxy resin and a curing agent until the rock core is completely sealed, testing the rock core under the pressure of 0.1MPa without leakage, completing the preparation of the rock core which is relatively regular, and accessing the rock core sealed by the epoxy resin into a gas permeability testing process to measure the gas permeability. The results are shown in Table 2 for core number T-01.
TABLE 2 gas permeability comparison table for testing regular shape core and irregular shape core
2. According to the steps of the testing method, a gas reservoir core is firstly split from the middle of a semicylindrical core with irregular shape and is cut into the length of 50mm, then the steps S102-S108 are adopted, a gas permeability testing process is accessed in the steps S107 and S108, the gas permeability is measured, the gas permeability is calculated according to the calculation method of national standard GB/T29172-2012, and the calculation result is shown in the core number T-02 of the table 2.
The experimental results prove that: the permeability error between the gas permeability of the irregular core and the gas permeability of the regular core is 4.2%, and the requirement that the gas permeability is less than 5% allowed by the industry is basically met.
The core after the permeability measurement can be used for removing the paraffin layer on the surface by heating and then performing other related analysis.
Other embodiments of the invention will be apparent to those skilled in the art from consideration of the specification and practice of the invention disclosed herein. This application is intended to cover any variations, uses, or adaptations of the invention following, in general, the principles of the invention and including such departures from the present disclosure as come within known or customary practice within the art to which the invention pertains. It is intended that the specification and examples be considered as exemplary only, with a true scope and spirit of the invention being indicated by the following claims.
It is to be understood that the present invention is not limited to the embodiment methods, structures, and precise structures shown in the drawings, which have been described above, and that various modifications and changes may be made without departing from the scope thereof. The scope of the invention is limited only by the appended claims.
Claims (12)
1. A method for testing gas permeability of an irregular loose rock sample is characterized by comprising the following steps:
(1) selecting a rock core from the irregular loose rock sample;
(2) removing water from the selected core;
(3) shaping the core with the water removed and reinforcing the surface strength;
(4) the plug with a through hole is hermetically and additionally arranged at two horizontally opposite positions on the surface of the rock core;
(5) manufacturing a casting mould with an opening at the upper end, placing the core with the plugs in the step (4) in an inner cavity of the casting mould, and respectively connecting the other ends of the two plugs with air pipes to enable the other ends of the two air pipes to extend out of the mould;
(6) casting the inner cavity of the mold by using foam, and forming a complete rock core after the foam is solidified;
(7) measuring gas permeability parameters of the complete rock core prepared in the step (6);
(8) gas permeability and related parameters are determined.
2. The method for testing the gas permeability of the irregular-shaped loose rock sample according to claim 1, wherein the rock core selected in the step (1) is located at a position with balanced permeability on the loose rock sample, if the permeability and the length of the rock sample both meet research requirements, the rock sample is directly selected as the rock core, and if the permeability and the length of the rock sample do not meet the research requirements, the rock sample meeting the permeability and the length requirements is intercepted along an axial position perpendicular to the rock sample and is taken as the rock core.
3. The method for testing gas permeability of the irregular-shaped loose rock sample according to claim 1, wherein the step (2) is carried out in a manner that the core is placed in a thermostat and dried to remove water in the core.
4. The method for testing gas permeability of an irregularly-shaped loose rock sample according to claim 1, wherein the specific operation of the step (3) is as follows: and putting the core to be measured in a metal basket with sieve pores on the surface, putting the core and the metal basket into the molten first paraffin, and taking out the core after soaking for a preset time to obtain the shaped core with the first paraffin layer on the surface.
5. The method for testing gas permeability of an irregularly-shaped unconsolidated rock sample as claimed in claim 4, wherein the glass fiber strands are placed under the first paraffin wax in a molten state, and the core is solidified to form a first paraffin layer having the glass fiber strands after being taken out of the molten first paraffin wax.
6. The method for testing gas permeability of an irregularly-shaped unconsolidated rock sample as claimed in claim 4, wherein the first paraffin wax is paraffin wax number 52, and the core is soaked in the melted first paraffin wax for 25-30 seconds.
7. The method for testing gas permeability of an irregular-shaped unconsolidated rock sample according to claim 4, wherein in the step (4), partial first paraffin is respectively scraped from the surface of the core, which is wax-sealed by the first paraffin layer, along two horizontally opposite parts vertical to the axis until the surface of the core is exposed, so that the shapes of the two exposed core surfaces correspond to the shapes of one ends of the two plugs, and then the two plugs are bonded to the exposed surface of the core by using the molten second paraffin.
8. The method for testing gas permeability of an irregularly-shaped unconsolidated rock sample of claim 7, wherein the second paraffin wax is semi-refined paraffin wax number 64.
9. The method for testing the gas permeability of the irregular loose rock sample according to claim 1, wherein the casting mold is in a box shape with an open upper end, the wax-sealed rock core is arranged in the inner cavity of the mold, the distance from the wall of each inner cavity of the mold to the outer surface of the rock core is 80-100mm, and the other ends of the two plugs respectively extend out of the mold.
10. The method for testing gas permeability of an irregular-shaped loose rock sample according to claim 9, wherein the core is supported on the bottom surface of the inner cavity of the mold through a support, and the distance between the bottom surface of the core and the bottom surface of the inner cavity of the mold is ensured to be 80-100 mm.
11. The method for testing gas permeability of an irregular-shaped loose rock sample according to claim 1, wherein the foaming liquid cast in the step (6) is injected upwards from the bottom of the inner cavity of the mold to the upper part of the inner cavity of the mold, and a complete treated core is formed after the foam is solidified.
12. The method for testing gas permeability of irregular-shaped loose rock samples according to claim 1, wherein the gas permeability in the step (7) is measured according to a national standard unsteady state method, which is characterized in thatThe formula is as follows:
the parametric measure of gas permeability is for the parameters in the above formula:
-a gas permeability of the gas,
；
-gas flow rate, mL/s;
-atmospheric pressure, atm;
-the end area of the core,
；
-viscosity of the gas, mPa · s;
-inlet end gas pressure, atm;
-outlet end gas pressure, atm.
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