CN117189092B - Soft rock ground stress testing method based on drilling cuttings particle size distribution - Google Patents

Abstract

The present invention relates to a soft rock geostress testing method based on the particle size distribution of drill cuttings. The in-situ geostress of soft rock is calculated by combining the output energy of the drill rig, the amount of drill cuttings and the particle size distribution of drill cuttings during the drilling process. The test is divided into three parts: drill rig data monitoring and energy calculation, drill cuttings data monitoring and crushing energy calculation and geostress back calculation. The present invention is very suitable for coal mine production, and can effectively utilize gas extraction boreholes to achieve multiple uses of one hole and promote the informatization of drilling holes. The collected drill cuttings can be used for further analysis of the fine gas geological structure of mines in the future.

Description

A soft rock in-situ stress testing method based on drill cuttings particle size distribution

Technical Field

The invention relates to the technical field of rock and soil exploration and measurement, and in particular to a soft rock in-situ stress testing method based on drill cuttings particle size distribution.

Background technique

Geostress is a common geological parameter in mining production activities. The measurement and distribution inversion of geostress are of great significance to mining, underground space construction, and geological disaster prediction. Traditional geostress measurement methods include: core stress relief method, hydraulic fracturing method, strain recovery method, borehole collapse method, acoustic emission method, and a few pre-buried sensor test methods (such as optical fiber stress method) are highly dependent on sealing technology, and the repeatability of the test results is poor.

Most geostress measurement methods are only suitable for application in hard rock formations. Coal seams are weak layers in the formation, and their strength is lower than that of most formations. The properties of the lowest-strength mylonitic coal seams are similar to soil. Therefore, the geostress data of coal seams currently used in coal mining are mostly derived from the measurement results of the top and bottom rock formations, and there is still a lack of geostress test characterization methods suitable for soft rocks. Therefore, a geostress test method suitable for soft rocks is urgently needed.

Summary of the invention

The purpose of the present invention is to overcome the above-mentioned shortcomings and provide a soft rock in-situ stress testing method based on drill cuttings particle size distribution. The in-situ in-situ stress of soft rock is calculated by combining the drill rig output energy, the amount of drill cuttings and the particle size distribution of drill cuttings during the drilling process. The results can be used to guide coal mine safety production, for geological information characterization and disaster prediction, especially for the prediction of the risk of underground coal and rock dynamic disasters.

The object of the present invention is achieved in that:

A soft rock in-situ stress testing method based on drill cuttings particle size distribution includes the following contents:

Step 1: construct an upward through-layer drill hole with a diameter of Φ (unit: m) in the tunnel. When the drill hole enters the coal and rock layer to be measured, start collecting drill cuttings;

Step 2: Use sensors to collect the torque T (unit: N∙m) and speed _Nr (unit: r/min) of the drill pipe in real time. The effective power of the drilling rig during drilling is P= _TNr /9.549 (unit: W).

Step 3: Calculate the input energy W ₁ (unit J) of the drilling rig in the rock formation being measured. , where t is the time the drill rig spends drilling in the rock formation being measured;

The particle size distribution of the drill cuttings of the tested rock formation is obtained by using a screening and weighing device. The drill cuttings of the tested rock formation are placed in a multi-stage screening device. After screening, the mass of the drill cuttings on each screen is obtained in turn by using an electronic balance. The diameter of the screen hole of the nth screen is d _n , and the mass of the drill cuttings on the screen is M _n (unit: kg). Then, the surface area of the drill cuttings on the nth screen is S _n = 12M _n /(ρd _n +ρd _n-1 ), which is the apparent density of the drill cuttings (unit: kg/m ³ ). When n is 1, d _n-1 =2d ₁ ;

Step 5: Calculate the outer surface area of the drill cuttings on all the screens and add them up to obtain the total outer surface area of the drill cuttings S = S ₁ +S ₂ +∙∙∙S _n ;

Step 6: Take all the cuttings on the first screen and place them in the drop hammer crushing device;

Step 7: Check the gas tightness of the device, turn on the vacuum pump, evacuate for 24 hours, then fill the crushing device with high-pressure gas, the gas pressure is equal to the original gas pressure of the coal seam, let the gas be adsorbed in the constant temperature room for 24 hours, and replenish it in time after the pressure drops during this period to ensure that the gas pressure is always slightly greater than the original gas pressure of the coal seam;

Step 8: Use a drop hammer crushing device to impact the drill cuttings containing gas. The process refers to the Pu-type robustness coefficient measurement process. Let the drop hammer with a weight of m fall freely from a height h to impact the drill cuttings in the base. Repeat the drop hammer 3 to 5 times, and record the number of drops as a.

Step 9: Calculate the total energy E = mgha (unit J) input by the drop hammer, put the drill cuttings in the base into the screening device, repeat steps 4 and 5, and the surface area of the drill cuttings after the drop hammer is crushed is S';

Step 10: Calculate and obtain the crushing surface energy consumption γ=E/S' (unit: J/m ² ) of the soft rock layer under the condition of falling hammer. The crushing surface energy consumption under drilling condition is linearly related to the surface energy consumption under falling hammer condition. The ratio is ξ. Then the crushing surface energy consumption under drilling condition is γ=ξE/S'.

Step 11: Calculate the total energy consumed by rock crushing during drilling, W ₂ =γS;

Step 12: Calculate the rock crushing energy W ₃ =W ₂ -W ₁ provided by the ground stress during the drilling process;

Step 13: Divide the crushing energy provided by the ground stress into two parts, namely, the deformation energy W _3,2 of the drilled rock cuttings under the in-situ condition and the work W _3,1 done by the formation on the drilled rock cuttings. Assuming the borehole to be in plane strain condition, the work done by the formation on the borehole in the infinite hydrostatic pressure environment is W _3,1 =2π(1+ν)p ² Φ ² L/(3E _Y ), and the in-situ deformation energy of the drilled rock mass in the borehole is W _3,2 =3π(1-2ν)p ² Φ ² L/(8E _Y ), where E _Y and ν are Young's modulus (unit Pa) and Poisson's ratio of the measured rock formation, p is the in-situ ground stress of the measured rock formation (unit Pa), and L is the length of the borehole in the measured rock formation (unit m);

Step 14: Based on W _3,1 +W _3,2 =W ₂ -W ₁ , the formulas in the above steps are combined to obtain the calculation method of the ground stress of the measured rock layer:

.

Furthermore, in step one, a drilling rig is set in the tunnel, a drilling rig torque and speed monitoring device is provided on the drilling rig, and the drill rod of the drilling rig penetrates upward into the coal rock layer to be measured.

Furthermore, in step three, the screening and weighing device includes a screening system and a weighing system. The screening system may adopt a multi-stage screening device, and the weighing system may adopt an electronic balance.

Furthermore, in step six, the drop hammer crushing device includes a gas sealing device, a drop hammer and a drop hammer protection tube, drill cuttings with a particle size greater than _d1 are placed at the bottom of the drop hammer protection tube, a liftable drop hammer is arranged inside the drop hammer protection tube, a gas sealing device is arranged on the top surface of the drop hammer protection tube, and the top of the drop hammer protection tube is connected to a gas source.

Furthermore, in step six, the drop hammer protection cylinder is also connected to a gas pressure gauge and a vacuum pump respectively.

Furthermore, in step eight, a 2.4 kg drop hammer is allowed to fall freely from a height of 0.6 m to impact the drill cuttings in the base. The drop hammer is repeated 3 to 5 times, and the number of drops is recorded as a.

Furthermore, in step ten, in order to improve the accuracy of the test results, experimental tests and verifications are carried out separately for different rock formations to be tested.

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

The geostress testing method of the present invention has looser requirements on rock hardness and is suitable for soft rocks, especially coal seams.

The geostress testing method proposed in the present invention is very suitable for coal mine production. It can effectively utilize gas extraction boreholes to achieve multiple uses of one hole and promote the informatization of drilling holes. The collected drill cuttings can be used for further analysis of the fine gas geological structure of mines in the future. At the same time, the geostress measurement method proposed in the present invention is relatively simple and can be divided into three modules: drilling energy calculation - crushing energy calculation - geostress energy calculation. It is expected that a fully automated underground geostress measurement device while drilling will be developed based on this method to promote the development of intelligent mine disaster warning analysis.

The testing method of the present invention is simple, especially for coal mine engineering, does not require the addition of new equipment and new processes, reduces testing costs, and makes more full use of the original boreholes in the coal mine. The present invention utilizes the dense gas extraction boreholes to obtain detailed ground stress distribution data.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic diagram of the through-layer drilling construction and drilling rig characteristic parameter collection scheme of the present invention.

FIG. 2 is a schematic diagram of a test solution for the amount of drill cuttings and the distribution of drill cuttings particle size according to the present invention.

FIG3 is a schematic diagram of a surface energy consumption test scheme for crushing gas-containing drill cuttings according to the present invention.

FIG. 4 is a schematic diagram of the in-situ stress calculation principle based on the hydrostatic pressure environment and elasticity theory of the present invention.

in:

Tested coal and rock layer 1, drill rod 2, tunnel 3, drilling rig torque and speed monitoring device 4, drilling rig 5, drill cuttings 6, screening system 7, weighing system 8, gas sealing device 9, drop hammer 10, drill cuttings with particle size greater than d1 11, drop hammer protection tube 12, gas pressure gauge 13, vacuum pump 14, gas source 15.

Detailed ways

In order to better understand the technical solution of the present invention, the following will be described in detail in conjunction with the relevant illustrations. It should be understood that the following specific embodiments are not intended to limit the specific implementation of the technical solution of the present invention, and are only implementations that can be adopted by the technical solution of the present invention. It should be noted that the description of the positional relationship of each component in this article, such as component A being located above component B, is based on the description of the relative positions of the components in the illustration, and is not intended to limit the actual positional relationship of the components.

Example

Referring to Figures 1 to 4, Figure 1 shows a schematic diagram of the through-layer drilling construction and drilling rig characteristic parameter collection scheme of this embodiment. As shown in the figure, a soft rock geostress testing method based on drill cuttings particle size distribution of the present invention, in underground engineering, in order to avoid the influence of the stress change zone near the rock wall on the measurement results, the geostress test drilling hole should be a through-layer drilling hole, preferably an upward hole, and the test is divided into three parts: drilling rig data monitoring and energy calculation, cuttings data monitoring and crushing energy calculation, and geostress back calculation, which specifically includes the following steps:

Step 1, as shown in FIG1 , a drilling rig 5 is arranged in the tunnel 3, and a drilling rig torque and speed monitoring device 4 is arranged on the drilling rig 5. The drill rod 2 of the drilling rig 5 penetrates upward into the coal and rock layer 1 to be measured, and an upward through-layer drill hole with a diameter of Φ (unit m) is constructed in the tunnel. When the drill hole enters the rock layer to be measured, the drill cuttings 6 are collected;

Step 2: Use sensors to collect the torque T (unit: N∙m) and speed _Nr (unit: r/min) of the drill pipe in real time. The effective power of the drilling rig during drilling is P = _TNr /9.549 (unit: W).

Step 3: Calculate the input energy W ₁ (unit J) of the drilling rig in the rock formation being measured. , where t is the time the drill rig spends drilling in the rock formation being measured;

Referring to FIG2 , a screening and weighing device is used to obtain the particle size distribution of the drill cuttings of the rock formation being tested. The screening and weighing device includes a screening system 7 and a weighing system 8. The screening system 7 may use a multi-stage screening device, and the weighing system 8 may use an electronic balance.

Put the drill cuttings of the rock formation to be tested into a multi-stage screening device. After screening, use an electronic balance to obtain the mass of the drill cuttings on each screen in turn. Let the diameter of the screen hole of the nth screen be _dn , and the mass of the drill cuttings on the screen be _Mn (unit: kg). Then the surface area of the drill cuttings on the nth screen is _Sn = _12Mn /( _ρdn +ρdn _-1 ), which is the apparent density of the drill cuttings (unit: kg/ ^m3 ). When n is 1, _dn-1 = _2d1 ;

Step 5: Calculate the outer surface area of the drill cuttings on all the screens and add them up to obtain the total outer surface area of the drill cuttings S = S ₁ +S ₂ +∙∙∙S _n ;

Step six: Take all the drill cuttings on the first screen and put them into the crushing device; see Figure 3, the crushing device includes a gas sealing device 9, a drop hammer 10 and a drop hammer protection tube 12, and the drill cuttings 11 with a particle size greater than _d1 are placed at the bottom of the drop hammer protection tube 12. A liftable drop hammer 10 is arranged inside the drop hammer protection tube 12, and a gas sealing device 9 is arranged on the top surface of the drop hammer protection tube 12. The top of the drop hammer protection tube 12 is connected to a gas source 15, and the drop hammer protection tube 12 is also connected to a gas pressure gauge 13 and a vacuum pump 14 respectively.

Step 7: Check the gas tightness of the device, turn on the vacuum pump, evacuate for 24 hours, then fill the crushing device with high-pressure gas, the gas pressure is equal to the original gas pressure of the coal seam, let the gas be adsorbed in the constant temperature room for 24 hours, and replenish it in time after the pressure drops during this period to ensure that the gas pressure is always slightly greater than the original gas pressure of the coal seam;

Step 8: Use a drop hammer crushing device to impact the drill cuttings containing gas. The process refers to the Pu-type solidity coefficient measurement process, that is, let a 2.4kg drop hammer fall freely from a height of 0.6m to impact the drill cuttings in the base. Repeat the drop hammer 3 to 5 times, and record the number of drops as a.

Step 9: Calculate the total energy input by the drop hammer E = 14.1a (unit J), put the drill cuttings in the base into the screening device in Figure 2, repeat steps 4 and 5, and the surface area of the drill cuttings after the drop hammer is crushed is S';

Step 10: Calculate the crushing surface energy consumption γ=E/S' (unit J/m ² ) of the soft rock layer under the condition of drop hammer. The crushing surface energy consumption under drilling conditions is linearly related to the surface energy consumption under the condition of drop hammer. The ratio is ξ. Then the crushing surface energy consumption under drilling conditions is γ=ξE/S'. To improve the accuracy of the test results, it is best to conduct separate experimental tests and verifications for different rock layers under test.

Step 11: Calculate the total energy consumed by rock crushing during drilling, W ₂ =γS;

Step 12: Calculate the rock crushing energy W ₃ =W ₂ -W ₁ provided by the ground stress during the drilling process;

Step 13: Divide the crushing energy provided by the ground stress into two parts, namely, the deformation energy W _3,2 of the drilled rock cuttings under the in-situ condition and the work W _3,1 done by the formation on the drilled rock cuttings, as shown in FIG4 . Assuming the borehole to be in plane strain condition, according to the elastic mechanics theory: the work done by the formation on the borehole in the infinite hydrostatic pressure environment is W _3,1 =2π(1+ν)p ² Φ ² L/(3E _Y ), and the in-situ deformation energy of the drilled rock mass in the borehole is W _3,2 =3π(1-2ν)p ² Φ ² L/(8E _Y ), where E _Y and ν are Young's modulus (unit Pa) and Poisson's ratio of the measured rock formation, p is the in-situ ground stress of the measured rock formation (unit Pa), and L is the length of the borehole in the measured rock formation (unit m);

Step 14: Based on W _3,1 +W _3,2 =W ₂ -W ₁ , the formulas in the above steps are combined to obtain the calculation method of the ground stress of the measured rock layer:

.

In this embodiment, there is a prerequisite when applying it: _W1 cannot be much greater than _W3 , that is, the drilling rig energy should be at the same order of magnitude as the ground stress energy, or the drilling rig energy should be less than _the ground stress energy, so as to avoid _W2≈W1 (which will cause a large error range of ground stress energy or even a negative value). Therefore, when using the above method to measure ground stress, the drilling rig power should be reduced as much as possible while ensuring drillability, or this method should be applied in deep rock formations.

In this embodiment, when multiple boreholes are constructed in the same rock formation to measure ground stress, steps 6 to 10 do not need to be repeated multiple times. When it is ensured that the physical properties of the rock formation do not change much (the rock formation being measured within the same geological unit), the surface energy consumption measurement only needs to be carried out once.

In this embodiment, when constructing multiple boreholes to measure geostress, the borehole spacing should be large enough (more than twice the width of the borehole pressure relief zone, which can be obtained based on numerical simulation) to avoid the impact of the drilling construction on the geostress measurement results of adjacent boreholes.

In this embodiment, gas has an important influence on the mechanical behavior and crushing properties of the coal body. Refer to "Coal Mechanics". In order to further eliminate the influence of gas on the calculation results of ground stress, the Young's modulus and Poisson's ratio of the gas-containing coal rock mass should be used when calculating the ground stress energy _W3 .

working principle:

Soft rock has strong viscoelasticity, and its structure continues to flow until it reaches equilibrium during a long geological process. The in-situ stress approaches the hydrostatic state. Many scholars assume that the in-situ stress of coal seams is hydrostatic pressure, see "Coal and Gas Outburst". Therefore, the in-situ stress measurement of soft rock does not require accurate characterization of the three-dimensional stress, but only requires an estimate of the reasonable hydrostatic pressure. In rock crushing engineering, the particle size distribution produced after rock crushing is related to the input energy, and the energy consumption of rock crushing is proportional to the added surface area of the fragments. According to the existing empirical model, the energy consumed in the crushing process can be calculated based on the particle size distribution of the rock after crushing.

During the drilling process, the energy for rock crushing comes from the sum of the in-situ deformation energy provided by the geostress and the input energy of the drilling rig, that is, rock crushing energy consumption = geostress energy + drilling rig energy. Obviously, for the same drilling rig (assuming that the drilling rig energy is approximately constant), the more the drill cuttings are crushed, the larger the amount of drill cuttings will be, and the more energy will be consumed for rock crushing, which can be inferred that the geostress here is greater.

More precisely, if the torque and speed of the drill can be monitored in real time, the drill energy can be further obtained, and the rock crushing energy consumption can be obtained based on the amount of drill cuttings and the distribution of drill cuttings particle size. According to the above analysis, the geostress energy will be accurately calculated. Under hydrostatic pressure, the relationship between geostress energy and geostress can be analyzed by elastic mechanics. In summary, the geostress value of soft rock can be obtained by combining the characteristic data of the drill and drill cuttings with the theoretical calculation model.

There are a large number of layer-transmitting boreholes arranged underground in coal mines. These boreholes are usually only used for gas pressure measurement, extraction and calibration. If the data from these boreholes are utilized, the geostress distribution of the entire production space will be obtained, which is of great significance to the safe production of coal mines.

The above are only specific application examples of the present invention and do not constitute any limitation on the protection scope of the present invention. Any technical solution formed by equivalent transformation or equivalent replacement shall fall within the protection scope of the present invention.

Claims (7)

1. The soft rock ground stress testing method based on the drill cuttings particle size distribution is characterized by comprising the following steps of:

firstly, constructing an upward through-layer drilling hole with the diameter phi in a roadway, wherein the unit of phi is m, and when the drilling hole enters a coal stratum to be tested, collecting drill cuttings;

step two, collecting torque T and rotation speed N of the drill rod in real time by utilizing a sensor _r Units of T N ∙ m, N _r The effective power in the drilling process of the drilling machine is P=TN _r 9.549, P being in W;

step three, calculating the input energy W of the drilling machine in the rock stratum to be tested ₁ ，W ₁ Is represented by the unit J of (2),wherein t is the drilling time of the drilling machine in the rock stratum to be tested;

step four, obtaining the particle size distribution of the rock stratum drilling cuttings to be tested by adopting a screening weighing device, putting the rock stratum drilling cuttings to be tested into a multi-stage screening device, after screening is finished, sequentially obtaining the quality of the drilling cuttings on each screen by using an electronic balance, and recording the diameter of the screen hole of the nth screen as d _n The mass of the drilling cuttings on the sieve is M _n ，M _n In kg, the outer surface area of the drill cuttings on the nth screen is S _n = 12M _n /(ρd _n +ρd _n-1 ) The apparent density of drill cuttings is expressed in kg/m ³ When n is 1, d _n-1 =2d ₁ ；

Step five: calculating the external surface area of the drill cuttings on all the screens, and accumulating to obtain the total external surface area S=S of the drill cuttings ₁ +S ₂ +∙∙∙S _n ；

Step six: taking all drill cuttings on a first screen, and putting the drill cuttings into a drop hammer crushing device;

step seven: checking the gas tightness of the device, starting a vacuum pump, vacuumizing for 24 hours, and then filling high-pressure gas into the crushing device, wherein the gas pressure is equal to the in-situ gas pressure of the coal seam, so that the gas is adsorbed in a constant temperature chamber for 24 hours, and timely supplementing after the pressure is reduced during the period, so that the gas pressure is ensured to be slightly higher than the in-situ gas pressure of the coal seam all the time;

step eight: the method comprises the steps of (1) impacting drill cuttings containing gas by using a drop hammer breaking device, wherein in the process of measuring a common firmness coefficient, a drop hammer with a weight m freely drops from a height h to impact the drill cuttings in a base, repeating the drop hammer for 3-5 times, and recording the drop hammer times as a;

step nine: calculating the total energy E=mgha, unit J of E, putting the drill cuttings fragments in the base into a screening device, and repeating the fourth and fifth steps to obtain the external surface area S' of the drill cuttings after breaking by the drop hammer;

step ten: calculating to obtain the breaking surface energy consumption gamma=E/S' gamma of the tested soft rock stratum under the drop hammer condition ² The energy consumption of the crushing surface under the drilling condition and the surface energy consumption under the drop hammer condition are in a linear relation, and the ratio is zeta, so that the energy consumption of the crushing surface under the drilling condition is gamma=zeta E/S';

step eleven: calculating the total energy W consumed by rock breaking during the drilling process ₂ =γS；

Step twelve: calculating the rock breaking energy W provided by ground stress in the drilling process ₃ =W ₂ -W ₁ ；

Step thirteen: dividing the crushing energy provided by the ground stress into two parts, namely the deformation energy W of the drilled rock fragments under the in-situ condition _3，2 And the work W performed by the stratum on the drilled rock debris _3，1 Assuming the borehole as a plane strain condition, wherein the work done by the infinite hydrostatic pressure environment stratum on the borehole is W _3，1 =2π(1+ν)p ² Φ ² L/(3E _Y ) The in-situ deformation energy of the rock mass drilled in the drill hole is W _3，2 =3π(1-2ν)p ² Φ ² L/(8E _Y ) Wherein E is _Y And v is Young's modulus and Poisson's ratio of the rock stratum to be tested, p is in-situ stress of the rock stratum to be tested, E _Y The units of v, p are Pa, L is the length of a borehole in the rock stratum to be tested, and the unit of L is m;

step fourteen: according to W _3，1 +W _3，2 =W ₂ -W ₁ And (3) combining the formulas in the steps to obtain a ground stress calculation method of the rock stratum to be tested:

。

2. the soft rock crustal stress test method based on drill cuttings particle size distribution according to claim 1, wherein: in the first step, a drilling machine is arranged in the roadway, a drilling machine torque and rotation speed monitoring device is arranged on the drilling machine, and a drilling rod of the drilling machine penetrates upwards into a coal rock stratum to be tested.

3. The soft rock crustal stress test method based on drill cuttings particle size distribution according to claim 1, wherein: and step three, the screening and weighing device comprises a screening system and a weighing system, wherein the screening system adopts a multi-stage screening device, and the weighing system adopts an electronic balance.

4. The soft rock crustal stress test method based on drill cuttings particle size distribution according to claim 1, wherein: in the sixth step, the drop hammer breaking device comprises a gas sealing device, a drop hammer and a drop hammer protection cylinder, and the particle size is larger than d ₁ The drill cuttings of the drill are placed at the bottom of a drop hammer protection cylinder, a lifting drop hammer is arranged in the drop hammer protection cylinder, and the top surface of the drop hammer protection cylinderThe top of the drop hammer protection cylinder is connected with a gas source.

5. The soft rock crustal stress testing method based on the particle size distribution of drill cuttings according to claim 4, wherein: in the sixth step, the drop hammer protection cylinder is also respectively connected with a gas pressure gauge and a vacuum pump.

6. The soft rock crustal stress test method based on drill cuttings particle size distribution according to claim 1, wherein: and step eight, freely falling a drop hammer with the weight of 2.4kg from the height of 0.6m, impacting drill cuttings in the base, repeating the drop hammer for 3-5 times, and recording the drop hammer times as a.

7. The soft rock crustal stress test method based on drill cuttings particle size distribution according to claim 1, wherein: in step ten, in order to improve the precision of the test result, experimental tests and verification are carried out on different rock strata, wherein xi is independent.