Method for preparing rock test sample and method for testing rock

Abstract

The embodiment of the invention provides a method for preparing a rock test sample and a method for testing rock. The method comprises the following steps: acquiring bedrock elastic parameters and bedrock mechanical parameters of a to-be-tested fractured stratum; concrete is blended according to the bedrock elastic parameters and the bedrock mechanical parameters, and a concrete sample is obtained; manufacturing a crack surface mold according to the crack surface of the to-be-measured broken stratum base layer; and putting the concrete sample into the crack surface mold to obtain a test sample of the to-be-tested fractured stratum. According to the method, the three-dimensional rock sample for accurately representing the fracture surface roughness, the friction coefficient and the fracture of the fractured rock can be obtained.

Description

Technical Field

[0001] The present invention relates to the field of petroleum exploration, and in particular to a method for preparing a rock test sample and a method for testing rock. Background Art

[0002] With the large-scale advancement of deep and ultra-deep drilling projects, the collapse of wellbore walls and complex leakage in fractured formations during drilling have become increasingly prominent, seriously hindering the safe, efficient, and economical exploration and development of deep and ultra-deep oil and gas resources. There are two main methods for preparing conventional rock mechanics laboratory test samples: the first is to use a small drill bit or wire cutting to prepare cylindrical test samples, conduct rock mechanics experiments, and obtain the mechanical properties of the rock; the second is to use cement casting to prepare rock mechanics test samples, place smooth steel sheets in a mold according to a certain spatial arrangement, and pour cement into the mold to obtain indoor rock mechanics test samples, conduct rock mechanics experiments, and obtain the mechanical properties of the rock. In the first method, due to the high degree of fragmentation and poor integrity of the fractured rock, the rock mass is prone to disintegration and spalling during the drilling or wire cutting process with a small drill bit. The experimental samples obtained can no longer truly and effectively characterize the mechanical properties of the fractured formation rock, and cannot accurately reflect the fracture and failure laws of the fractured rock. The cracks in the rock mechanics test samples prepared by the second method are straight, and cannot characterize the surface roughness, friction coefficient and three-dimensional structure of the fracture surface of the broken rock. Summary of the Invention

[0003] The purpose of the embodiments of the present invention is to provide a method for preparing a rock test sample and a method for testing rock, which can obtain a three-dimensional rock sample that accurately characterizes the surface roughness, friction coefficient and cracks of a fractured rock fracture surface.

[0004] To achieve the above objectives, an embodiment of the present invention provides a method for preparing a rock test sample, the method comprising:

[0005] Obtaining bedrock elastic parameters and bedrock mechanical parameters of the fractured stratum to be tested;

[0006] mixing concrete according to the bedrock elastic parameters and the bedrock mechanical parameters to obtain a concrete sample;

[0007] Making a fracture surface mold according to the fracture surface of the fractured stratum base to be tested;

[0008] The concrete sample is placed in the fracture surface mold to obtain a test sample of the fractured stratum to be tested.

[0009] Optionally, the bedrock elastic parameters and bedrock mechanical parameters of the fractured stratum to be tested are obtained through a plunger sample mechanical experiment.

[0010] Optionally, the preparing concrete according to the bedrock elastic parameters and the bedrock mechanical parameters to obtain a concrete sample includes:

[0011] The proportions of water, ash, sand and gravel in the concrete are adjusted so that the elastic parameters and mechanical parameters of the concrete sample are consistent with the elastic parameters and mechanical parameters of the bedrock, respectively.

[0012] Optionally, the bedrock elastic parameters include static elastic modulus and static Poisson's ratio;

[0013] The bedrock mechanical parameters include uniaxial compressive strength.

[0014] Optionally, the sand-cement ratio and water-cement ratio of the concrete are calculated using the following formula:

[0015] UCS=257.325-61.3u-324.9v

[0016] E=35.506-10.234u-44.6v

[0017] Wherein, UCS is the uniaxial compressive strength,

[0018] E is the static elastic modulus,

[0019] u is the sand-to-cement ratio,

[0020] v is the water-cement ratio.

[0021] Optionally, the sand-cement ratio and water-cement ratio of the concrete are calculated using the following formula:

[0022] UCS=257.325-61.3u-324.9v

[0023] μ=0.5-0.167u-0.3v

[0024] Wherein, UCS is the uniaxial compressive strength, μ is the static Poisson's ratio, u is the sand-cement ratio, and v is the water-cement ratio.

[0025] Optionally, the method further includes: verifying the test sample, including: comparing the test sample with the fracture surface friction coefficient of the fractured stratum to be tested, and if the difference in the fracture surface friction coefficients of the two exceeds an allowable range, adjusting the prepared concrete and remaking the test sample.

[0026] Optionally, the method for making the crack surface mold is 3D printing.

[0027] On the other hand, the present invention also provides a method for testing rocks, which comprises performing rock parameter testing on a test sample obtained by the above-mentioned method for preparing a rock test sample to obtain test parameters of the rock.

[0028] Optionally, the rock parameter testing method includes: true triaxial rock mechanics parameter testing, direct shear test testing;

[0029] The test parameters include: elastic modulus, Poisson's ratio, compressive strength, cohesion, internal friction angle, and shear strength.

[0030] The present invention provides a method for preparing a rock test sample, comprising: obtaining bedrock elastic parameters and bedrock mechanical parameters of a fractured formation to be tested; mixing concrete based on the bedrock elastic parameters and the bedrock mechanical parameters to obtain a concrete sample; creating a fracture surface mold based on the fracture surface of the base layer of the fractured formation to be tested; and placing the concrete sample into the fracture surface mold to obtain a test sample of the fractured formation to be tested. This method configures test samples based on the bedrock elastic parameters and bedrock mechanical parameters, significantly improving the scientific validity of rock mechanics test results in fractured formations.

[0031] Other features and advantages of the embodiments of the present invention will be described in detail in the subsequent detailed description. BRIEF DESCRIPTION OF THE DRAWINGS

[0032] The accompanying drawings are used to provide a further understanding of the embodiments of the present invention and constitute a part of the specification. Together with the following detailed description, they are used to explain the embodiments of the present invention, but do not constitute a limitation of the embodiments of the present invention. In the accompanying drawings:

[0033] Figure 1 It is a schematic flow chart of a method for preparing a rock test sample according to the present invention;

[0034] Figure 2 It is a schematic flow chart of a specific embodiment of a method for preparing a rock test sample according to the present invention;

[0035] Figure 3 Schematic diagram of a fractured stratum bedrock test sample of the present invention;

[0036] Figure 4 Schematic diagram of the 3D printed crack printing mold and square mold of the present invention;

[0037] Figure 5 is a schematic diagram of a direct shear test block sample of the present invention;

[0038] Figure 6 Schematic diagram of an experimental block sample containing a single crack according to the present invention. DETAILED DESCRIPTION

[0039] The following describes the specific implementation of the embodiment of the present invention in detail with reference to the accompanying drawings. It should be understood that the specific implementation described herein is only used to illustrate and explain the embodiment of the present invention and is not used to limit the embodiment of the present invention.

[0040] Example 1

[0041] Figure 1 FIG. 1 is a flow chart of a method for preparing a rock test sample according to the present invention, as shown in FIG. Figure 1 As shown, a method for preparing a rock test sample of the present invention includes: step S101 is to obtain bedrock elastic parameters and bedrock mechanical parameters of the fractured stratum to be tested. Preferably, the bedrock elastic parameters and bedrock mechanical parameters of the fractured stratum to be tested are obtained through a plunger sample mechanical test.

[0042] Specifically, the bedrock elastic parameters include static elastic modulus and static Poisson's ratio; the bedrock mechanical parameters include uniaxial compressive strength. The elastic modulus is the stress under uniaxial stress state divided by the strain in that direction. The static elastic modulus is to apply a constant tensile (or compressive) stress on the sample and measure its elastic deformation; or to apply a constant bending stress on the sample and measure its elastic bending deflection, and calculate the elastic modulus based on the stress and strain. Poisson's ratio refers to the ratio of the transverse normal strain to the axial normal strain when the material is under unidirectional tension or compression, also called the transverse deformation coefficient. It is an elastic constant that reflects the transverse deformation of the material. The static Poisson's ratio is the Poisson's ratio under static conditions. The uniaxial compressive strength of rock refers to the ultimate destructive strength obtained when the sample is compressed in only one direction, that is, the rock sample is placed between the upper and lower plates of a press and pressurized until the sample is crushed to obtain the pressure strength value.

[0043] Step S102 is to mix concrete according to the bedrock elastic parameters and the bedrock mechanical parameters to obtain a concrete sample.

[0044] According to a specific embodiment, the preparing concrete according to the bedrock elastic parameters and the bedrock mechanical parameters to obtain the concrete sample includes: adjusting the ratio of water, lime, sand and gravel in the concrete so that the elastic parameters and mechanical parameters of the concrete sample are consistent with the bedrock elastic parameters and bedrock mechanical parameters, respectively.

[0045] The sand-cement ratio and water-cement ratio of the concrete are calculated by the following formula:

[0046] UCS=257.325-61.3u-324.9v

[0047] E=35.506-10.234u-44.6v

[0048] Wherein, UCS is the uniaxial compressive strength, E is the static elastic modulus, u is the sand-cement ratio, and v is the water-cement ratio.

[0049] Alternatively, the sand-cement ratio and water-cement ratio of the concrete can be calculated using the following formula:

[0050] UCS=257.325-61.3u-324.9v

[0051] μ=0.5-0.167u-0.3v

[0052] Wherein, UCS is the uniaxial compressive strength, μ is the static Poisson's ratio, u is the sand-cement ratio, and v is the water-cement ratio.

[0053] Step S103 is to make a fracture surface mold according to the fracture surface of the fractured stratum base to be tested. Preferably, the method of making the fracture surface mold is 3D printing.

[0054] A single fracture surface is 3D-printed as a fracture surface printing mold. This fracture surface printing mold is made by crushing the stratum. Samples prepared using this mold align with the morphology of the crushed stratum. The fracture surface printing mold printed by the 3D printer is scanned using a laser scanner to obtain point cloud data of the fracture surface. This point cloud data is processed to obtain an STL file of the single fracture surface in the crushed rock. Using 3D printing technology, the STL file is configured for printing, and the printing material is selected. The single fracture surface is then printed to serve as the fracture surface printing mold.

[0055] Step S104 is to place the concrete sample into the crack surface mold to obtain the test sample of the fractured stratum to be tested. The crack surface mold is used to print the crack surface structure on the direct shear test sample to prepare an intermediate test block sample containing a single crack.

[0056] The direct shear test cube sample is prepared by adding cement, sand, water, and a certain amount of defoaming agent to a mixing barrel in a water-cement-sand ratio that reflects the mechanical strength of the fractured bedrock. The raw materials are poured into a square mold in multiple batches until all the raw materials are poured into the mold, completing the casting of the direct shear test cube sample.

[0057] The present invention clarifies the requirements for indicators such as the mechanical strength of bedrock, the three-dimensional structure of cracks, and the similarity of the friction coefficient of the crack surface, and realizes the real and scientific characterization of the mechanical properties and fracture failure laws of rocks in broken formations only through rock mechanics experimental tests, thereby improving the scientificity and accuracy of the experimental test results of rock mechanics in broken formations.

[0058] Example 2

[0059] Figure 2 FIG. 1 is a flow chart of a specific embodiment of a method for preparing a rock test sample according to the present invention. Figure 2 As shown, the method includes the following steps:

[0060] Step 1 is to obtain the elastic parameters (static elastic modulus and static Poisson's ratio) and mechanical strength (uniaxial compressive strength) of the broken formation bedrock using conventional plunger sample mechanical experimental methods.

[0061] The plunger sample mechanical experiment is conducted on a plunger rock sample. The plunger rock sample typically refers to a cylindrical rock sample with a diameter of 25.4mm-45mm and a length of 25.4mm-50mm. These rock samples are characterized by a small diameter and volume, a regular shape, ease of drilling, and two parallel end faces. These rock samples are easy to process and have clear geometric concepts. Through mechanical experiments on the plunger rock sample, mechanical parameters of the plunger rock sample can be obtained, including static elastic modulus, static Poisson's ratio, and uniaxial compressive strength.

[0062] The elastic modulus is the stress under unidirectional stress divided by the strain in that direction. The static elastic modulus is to apply a constant tensile (or compressive) stress to the sample and measure its elastic deformation; or to apply a constant bending stress to the sample and measure its elastic bending deflection, and calculate the elastic modulus based on the stress and strain. Poisson's ratio refers to the ratio of the transverse normal strain to the axial normal strain when the material is under unidirectional tension or compression, also called the transverse deformation coefficient. It is an elastic constant that reflects the transverse deformation of the material. The static Poisson's ratio is the Poisson's ratio under static conditions. The uniaxial compressive strength of rock refers to the ultimate destructive strength obtained when the sample is compressed in only one direction, that is, the rock sample is placed between the upper and lower platens of a press and pressurized until the sample is crushed to obtain the pressure strength value.

[0063] Step 2 involves preparing mixed slurries with varying water-lime-sand-gravel ratios and using a specialized mold casting method to prepare fractured bedrock test samples. The elastic parameters (static elastic modulus and static Poisson's ratio) and mechanical strength (uniaxial compressive strength) of the test samples with varying ratios are then determined. The test samples prepared using this specialized mold casting method maintain consistent elastic and mechanical parameter ratios.

[0064] The step of preparing concrete according to the bedrock elastic parameters and the bedrock mechanical parameters to obtain a concrete sample includes: adjusting the ratio of water, ash, sand and gravel in the concrete so that the elastic parameters and mechanical parameters of the concrete sample are consistent with the bedrock elastic parameters and bedrock mechanical parameters, respectively.

[0065] The sand-cement ratio and water-cement ratio of the concrete are calculated by the following formula:

[0066] UCS=257.325-61.3u-324.9v

[0067] E=35.506-10.234u-44.6v

[0068] Wherein, UCS is the uniaxial compressive strength, E is the static elastic modulus, u is the sand-cement ratio, and v is the water-cement ratio.

[0069] Alternatively, the sand-cement ratio and water-cement ratio of the concrete can be calculated using the following formula:

[0070] UCS=257.325-61.3u-324.9v

[0071] μ=0.5-0.167u-0.3v

[0072] Wherein, UCS is the uniaxial compressive strength, μ is the static Poisson's ratio, u is the sand-cement ratio, and v is the water-cement ratio.

[0073] According to a specific embodiment, Figure 3 As shown, the fractured stratum bedrock test sample is prepared by mixing a mixed slurry with different water-cement-sand ratios, where the water, ash, and ash in the sand and gravel are cement, using a special mold preparation method, and a conventional plunger sample mechanical experiment is carried out to obtain the elastic parameters (static elastic modulus and static Poisson's ratio) and mechanical strength (uniaxial compressive strength) of the test samples with different configuration ratios.

[0074] The water-cement-sand ratio can be:

[0075] Cement: sand: water = 2.5:1.5:1;

[0076] Cement: sand: water = 2.5:2:1;

[0077] Cement: sand: water = 2.5:2.5:1.

[0078] The types of cement include, but are not limited to, silicate 42.5 cement (compressive strength of 42.5 MPa), sulfoaluminate 62.5 cement (compressive strength of 62.5 MPa), aluminate 72.5 cement (compressive strength of 72.5 MPa), etc. The types of sand and gravel include, but are not limited to, quartz sand, river sand, etc.

[0079] Step 3: Based on the bedrock mechanical parameters (static elastic modulus, static Poisson's ratio and uniaxial compressive strength), determine the water-cement-sand ratio that can characterize the mechanical strength of the bedrock of the fractured stratum.

[0080] Step 4: Use a laser scanner to obtain a single fracture surface in the broken rock, and then use 3D printing to print the single fracture surface as a fracture surface printing mold. The fracture surface printing mold is a fracture surface mold made by breaking the formation. The sample prepared using this mold is consistent with the morphology of the broken formation.

[0081] Specifically, such as Figure 4As shown, the fracture surface mold printed by the 3D printer is scanned by a laser scanner to obtain point cloud data of the fracture surface. This point cloud data is processed to obtain an STL file of a single fracture surface in the crushed rock. Using 3D printing technology, the STL file of the fracture surface is set up for printing, and the printing material is selected to print the single fracture surface, which serves as the fracture surface mold.

[0082] The processing of point cloud data includes, but is not limited to, filtering, noise reduction, denoising, and point cloud smoothing. The 3D printing settings include, but are not limited to, print thickness, print speed, and support generation. The 3D printing materials include, but are not limited to, nylon, rigid photosensitive resin, and ABS-like photosensitive resin.

[0083] Step 5: Prepare a direct shear test block sample of 50 mm long × 50 mm wide × 25 mm high based on the water-cement sand ratio.

[0084] The direct shear test is a test used in geotechnical engineering to find out the shear strength of soil. The specific steps are: take a soil sample and put it into a shear box, fix the upper box, and allow the lower box to slide in the horizontal direction. First, apply vertical pressure, and then apply horizontal shear force to the lower box of the shear box step by step until the sample is sheared. Generally, 4-5 samples are taken and different vertical pressures are applied to each of them to repeat the test. This test is a common method for measuring the shear strength of soil because it is simple and easy to perform.

[0085] Step 6: Use a crack surface mold to print the crack surface structure on the direct shear test sample to prepare a single crack test block sample. Preferably, after curing the sample for 28 days, the sample is polished to complete the preparation of the single crack test block sample.

[0086] Step 7: Conduct direct shear experiments to obtain the friction coefficients of the direct shear test cube samples and the crack surfaces of real crushed rocks, respectively, to ensure the accuracy of the friction coefficients of the crack surfaces of the test cube samples.

[0087] The direct shear test is a common method for determining the shear strength of soil. Four specimens are usually subjected to different vertical pressures and horizontal shear forces are applied to shear them. The shear stress at failure is measured, and then the shear strength index of the soil (internal friction angle φ and cohesion c) is determined according to Coulomb's law.

[0088] like Figure 5 As shown, the direct shear test cube sample is prepared by adding cement, sand, water, and a certain amount of defoaming agent in a water-cement-sand ratio that can characterize the mechanical strength of the fractured stratum bedrock into a mixing barrel to obtain the raw materials required for casting. The casting raw materials are poured into the square mold in multiple times until all the raw materials are poured into the square mold, completing the casting of the direct shear test cube sample. Figure 6 shown.

[0089] The present invention provides a method for preparing a rock test sample, comprising: obtaining bedrock elastic parameters and bedrock mechanical parameters of a fractured formation to be tested; mixing concrete based on the bedrock elastic parameters and the bedrock mechanical parameters to obtain a concrete sample; creating a fracture surface mold based on the fracture surface of the base layer of the fractured formation to be tested; and placing the concrete sample into the fracture surface mold to obtain a test sample of the fractured formation to be tested. This method configures test samples based on the bedrock elastic parameters and bedrock mechanical parameters, significantly improving the scientific validity of rock mechanics test results in fractured formations.

[0090] Example 3

[0091] On the other hand, the present invention also proposes a method for testing rocks, which includes performing rock parameter testing on the test sample obtained by the method for preparing the rock test sample described above to obtain the test parameters of the rock. The rock parameter testing method includes: true triaxial rock mechanics parameter testing and direct shear test testing. The test parameters include: elastic modulus, Poisson's ratio, compressive strength, cohesion, internal friction angle, and shear strength. This method is based on the method for preparing the fractured rock mechanics experimental test sample based on the similarity between the mechanical strength of the bedrock and the friction coefficient of the fracture surface, clarifies the requirements for indicators such as the mechanical strength of the bedrock, the three-dimensional structure of the fracture and the similarity between the friction coefficient of the fracture surface, and realizes that the rock mechanics experimental test can truly and scientifically characterize the mechanical properties and fracture failure laws of the fractured formation rock, thereby improving the scientific nature of the fractured formation rock mechanics experimental test results.

[0092] The present invention provides a method for preparing a rock test sample, comprising: obtaining bedrock elastic parameters and bedrock mechanical parameters of a fractured formation to be tested; mixing concrete based on the bedrock elastic parameters and the bedrock mechanical parameters to obtain a concrete sample; creating a fracture surface mold based on the fracture surface of the base layer of the fractured formation to be tested; and placing the concrete sample into the fracture surface mold to obtain a test sample of the fractured formation to be tested. This method configures test samples based on the bedrock elastic parameters and bedrock mechanical parameters, significantly improving the scientific validity of rock mechanics test results in fractured formations.

[0093] The above describes in detail the optional implementation methods of the embodiments of the present invention in conjunction with the accompanying drawings. However, the embodiments of the present invention are not limited to the specific details in the above implementation methods. Within the technical concept of the embodiments of the present invention, various simple modifications can be made to the technical solutions of the embodiments of the present invention, and these simple modifications all fall within the scope of protection of the embodiments of the present invention.

[0094] It should also be noted that the various specific technical features described in the above specific embodiments can be combined in any appropriate manner without contradiction. To avoid unnecessary repetition, the embodiments of the present invention will not further describe various possible combinations.

[0095] Those skilled in the art will appreciate that all or part of the steps in the above-mentioned embodiments can be implemented by instructing the relevant hardware through a program, which is stored in a storage medium and includes a number of instructions for causing a single-chip microcomputer, chip, or processor to execute all or part of the steps in the methods described in the various embodiments of the present application. The aforementioned storage medium includes various media that can store program code, such as a USB flash drive, a mobile hard disk, a read-only memory (ROM), a random access memory (RAM), a magnetic disk, or an optical disk.

[0096] In addition, various implementations of the embodiments of the present invention may be arbitrarily combined, and as long as they do not violate the concept of the embodiments of the present invention, they should also be regarded as the contents disclosed in the embodiments of the present invention.

Claims

1. A method for preparing a rock test sample, characterized in that: The method includes: Obtaining bedrock elastic parameters and bedrock mechanical parameters of the fractured stratum to be tested; mixing concrete according to the bedrock elastic parameters and the bedrock mechanical parameters to obtain a concrete sample; Making a fracture surface mold according to the fracture surface of the fractured stratum base to be tested; The concrete sample is placed in the fracture surface mold to obtain a test sample of the fractured stratum to be tested.

2. The method according to claim 1, characterized in that The bedrock elastic parameters and bedrock mechanical parameters of the fractured stratum to be tested are obtained through a plunger sample mechanical experiment.

3. The method according to claim 1, characterized in that The step of preparing concrete according to the bedrock elastic parameters and the bedrock mechanical parameters to obtain a concrete sample includes: The proportions of water, ash, sand and gravel in the concrete are adjusted so that the elastic parameters and mechanical parameters of the concrete sample are consistent with the elastic parameters and mechanical parameters of the bedrock, respectively.

4. The method according to claim 1 or 3, characterized in that The bedrock elastic parameters include static elastic modulus and static Poisson's ratio; The bedrock mechanical parameters include uniaxial compressive strength.

5. The method according to claim 4, characterized in that The sand-cement ratio and water-cement ratio of the concrete are calculated by the following formula: UCS=257.325-61.3u-324.9v E=35.506-10.234u-44.6v Wherein, UCS is the uniaxial compressive strength, E is the static elastic modulus, u is the sand-to-cement ratio, v is the water-cement ratio.

6. The method according to claim 4, characterized in that The sand-cement ratio and water-cement ratio of the concrete are calculated by the following formula: UCS=257.325-61.3u-324.9v μ=0.5-0.167u-0.3v Wherein, UCS is the uniaxial compressive strength, μ is the static Poisson's ratio, u is the sand-to-cement ratio, v is the water-cement ratio.

7. The method according to claim 1, characterized in that The method further includes: Verifying the test sample includes comparing the test sample with a fracture surface friction coefficient of the fractured stratum to be tested, and if the difference in the fracture surface friction coefficients of the two exceeds an allowable range, adjusting the prepared concrete and remaking the test sample.

8. The method according to claim 1, characterized in that The method for making the crack surface mold is 3D printing.

9. A method for testing rocks, characterized in that: The method comprises performing rock parameter testing on a test sample obtained by the method for preparing a rock test sample according to any one of claims 1 to 8 to obtain the test parameters of the rock.

10. The method according to claim 9, characterized in that The rock parameter testing method includes: true triaxial rock mechanics parameter testing and direct shear test testing; The test parameters include: elastic modulus, Poisson's ratio, compressive strength, cohesion, internal friction angle, and shear strength.

Images