Evaluation-while-drilling device and method for deep primary rock stress concentration area and storage medium

Abstract

The invention discloses a deep protolith stress concentration area while-drilling evaluation device and method and a storage medium, and belongs to the technical field of mine safety and disaster prevention and control. The device comprises a drill bit, an exploring tube and a drill rod, the exploring tube is arranged between the drill bit and the drill rod, an acoustic emission sensor, a torque sensor, a thrust sensor and a rotating speed sensor are integrated in the exploring tube, and near-drill-bit synchronous data collection is achieved. The method comprises the following steps: acquiring depth data while drilling; judging whether the coal rock property changes or not according to the acoustic emission signal, and adaptively selecting a stress evaluation model using pure drilling parameters or fusing acoustic emission characteristics and drilling parameters to obtain a single-hole stress profile; and integrating porous data in the working face, and carrying out spatial interpolation inversion and delineating a working face scale protolith stress concentration area. According to the method, continuous, real-time, near-source and multi-parameter fusion evaluation and visualization of the coal rock stress are realized, and efficient technical support is provided for advanced and accurate prevention and control of disasters such as rock burst.

Description

Technical Field

[0001] This invention belongs to the field of mine safety and disaster prevention technology, and specifically relates to a drilling evaluation device, method and storage medium for deep original rock stress concentration zones. Background Technology

[0002] As the depth of coal mining in my country continues to increase, the phenomenon of high ground stress in deep mines and stress concentration in the original rock caused by geological structures is becoming increasingly prominent, becoming a major factor inducing coal and rock gas dynamic disasters such as rockbursts and coal and gas outbursts. Therefore, accurate prediction and evaluation of deep original rock stress concentration zones are a key prerequisite for achieving advanced and precise disaster prevention and control.

[0003] Currently, the evaluation of deep original rock stress mainly relies on the following techniques: 1. Geological exploration and drilling sampling analysis method: Rock cores are obtained through surface or underground drilling, and rock mechanical parameters (such as compressive strength and elastic modulus) are tested in the laboratory. Combined with geological analysis, the distribution of in-situ stress is indirectly inferred. This method is a static point measurement method, with discrete data, long cycle time, and limited representativeness, which cannot meet the real-time evaluation needs of dynamic advancement of mining faces.

[0004] 2. Downhole Stress Relief and Stress Inversion Method: Stress gauges are installed in the roadway or borehole to measure local stress through casing stress relief, and then the regional stress is inverted using a geological model. This method is complex to operate, costly, and only involves point measurements; the inversion accuracy is limited by the model and the number of measurement points.

[0005] 3. Borehole imaging and video technology: This method uses optical or acoustic equipment to observe the borehole wall condition and qualitatively determine factors such as cracks and borehole collapse caused by stress concentration. However, this method is highly dependent on drilling conditions and cannot provide quantitative or continuous evaluation.

[0006] 4. Drilling Parameter Evaluation Methods: Parameters such as drilling pressure, torque, and rotational speed are monitored, and coal and rock properties or stress states are evaluated using empirical formulas. However, existing sensors are typically installed near the drilling rig, and the signals suffer severe attenuation and distortion after long-distance transmission through the drill pipe, failing to accurately reflect the coal and rock conditions ahead of the drill bit. More importantly, drilling parameters are simultaneously affected by the combined physical and mechanical properties of coal and rock, as well as geostress. Existing methods often assume uniform coal and rock properties and use only a few drilling parameters for stress evaluation, leading to poor reliability of evaluation results in complex formations with varying coal and rock properties.

[0007] In summary, existing technologies generally suffer from problems such as the inability to achieve continuous, real-time, and near-source monitoring of stress during drilling, the use of single evaluation parameters that do not consider the impact of changes in coal and rock properties, and the difficulty in making spatial visualization predictions at the working face scale. Summary of the Invention

[0008] The purpose of this invention is to propose a drilling evaluation device, method, and storage medium for deep in-situ stress concentration zones, so as to achieve continuous, real-time, near-source, and multi-parameter integrated evaluation of the stress state of coal and rock during drilling, and finally visualize and delineate the in-situ stress concentration zones at the working face scale, providing direct and efficient technical support for precise disaster prevention and control.

[0009] To achieve the above objectives, the present invention adopts the following technical solution: A drilling evaluation device for deep in-situ stress concentration zones includes a drill bit, a probe, and a drill pipe, wherein the probe is disposed between the drill bit and the drill pipe; the probe contains: The sensor unit is used to collect data on the process of the drill bit cutting coal and rock. The sensor unit includes at least an acoustic emission sensor, a torque sensor, a thrust sensor, and a speed sensor. A signal processing and storage unit, electrically connected to the sensor unit, is used to receive, process, and store the data collected by the sensor unit; A power supply unit provides power to the sensor unit and the signal processing and storage unit. The probe is configured to enter and exit the borehole together with the drill bit and drill rod.

[0010] Furthermore, the probe is provided with threaded interfaces at both ends for connecting the drill bit and / or drill rod.

[0011] A method for evaluating deep in-situ stress concentration zones while drilling, employing the aforementioned deep in-situ stress concentration zone evaluation device, includes the following steps: S1, Drilling data collection; During the process of the drill bit cutting coal and rock, the device is used to simultaneously collect acoustic emission signals, torque, thrust and rotational speed data when drilling to different depths; S2, Single-hole stress evaluation; Based on the data collected in step S1, evaluate the changes in coal and rock stress along the single-hole drilling path; S3, Inversion of stress zone on working surface; By integrating the single-hole coal and rock stress evaluation results from multiple boreholes within the working face, and through spatial analysis, the original rock stress concentration zone of the entire working face is inverted and delineated.

[0012] Furthermore, S2 specifically includes: S21. Based on the characteristic parameters of the acoustic emission signal, determine whether the physical and mechanical properties of the coal and rock in the current drilling section have changed; S22. If the physical and mechanical properties of coal and rock have not changed, then establish a first stress evaluation model with torque, thrust, and rotational speed as independent variables, and calculate the relative stress change Fn1 on the drilling path. S23. If the physical and mechanical properties of coal and rock change, a second stress evaluation model is established with acoustic emission signal characteristic parameters, torque, thrust, and rotational speed as independent variables, and the relative stress change Fn2 on the drilling path is calculated. S24. Obtain the stress profile diagram that varies along the borehole depth.

[0013] Furthermore, the characteristic parameters of acoustic emission signals include one or more of amplitude, energy, ring count, and frequency.

[0014] Furthermore, S21 specifically includes: A coal-rock strength model is established with acoustic emission signal characteristic parameters as independent variables, and the coal-rock strength F of the current drilling section is calculated. s Among them, the physical and mechanical properties of coal and rock specifically include the coal and rock strength F. s ; The coal and rock strength model is: F s =f(a1*Ae1, a2*Ae2, a3*Ae3); Where Ae1, Ae2, and Ae3 are characteristic parameters of the acoustic emission signal, and a1, a2, and a3 are model coefficients.

[0015] Furthermore, the first stress evaluation model is: Fn1 = f(b1*T, b2*I, b3*R); Where T is torque, I is thrust, R is rotational speed, and b1, b2, and b3 are model coefficients; The second stress evaluation model is: Fn2 = f(c1*Ae1, c2*Ae2, c3*Ae3, c4*T, c5*I, c6*R); Where Ae1, Ae2, and Ae3 are characteristic parameters of acoustic emission signals, T is torque, I is thrust, R is rotational speed, and c1 to c6 are model coefficients.

[0016] Furthermore, S3 specifically includes: The stress profile data obtained from each borehole evaluation is used as spatial discrete points. Kriging interpolation or inverse distance weighting is used for spatial interpolation to generate a continuous stress change field distribution map within the working face area. Based on the preset stress change threshold, the area exceeding the threshold is delineated from the distribution map as the original rock stress concentration area.

[0017] Furthermore, S4 is included after S3: verifying the delineated stress concentration zone of the original rock using borehole radar or geological exploration data.

[0018] A computer-readable storage medium having a program stored thereon, which, when executed by a processor, implements the drilling evaluation method for deep in-situ stress concentration zones as described above.

[0019] The drilling evaluation device, method, and storage medium for deep in-situ stress concentration zones provided by this invention overcome the problems of discrete evaluation processes, delays, poor representativeness, and lack of comprehensive consideration of coal and rock properties and stress effects in existing technologies. It achieves continuous, real-time, near-source, and multi-parameter fusion evaluation of the stress state of deep coal and rock, and ultimately realizes the visual identification and delineation of in-situ stress concentration zones at the working face scale. This provides direct and efficient technical support for the advanced and precise prevention and control of disasters such as rockbursts and coal and gas outbursts. Its technical effects are mainly reflected in the following aspects: 1. By integrating a probe between the drill bit and drill pipe, multiple types of sensors, including acoustic emission, torque, thrust, and rotational speed sensors, are placed close to the drill bit, enabling synchronous data acquisition "near the drill bit." This design minimizes signal attenuation and distortion during long-distance drill pipe transmission, ensuring that the acquired parameters such as torque, thrust, and acoustic emission accurately and sensitively reflect the interaction between the coal and rock and stress in front of the drill bit, laying a reliable data foundation for subsequent accurate evaluation.

[0020] 2. An innovative evaluation method combining dynamic identification of coal and rock properties with adaptive selection of stress evaluation models is proposed. By analyzing characteristic parameters such as amplitude and energy of acoustic emission signals in real time, the method dynamically determines whether the physical and mechanical properties of coal and rock (such as strength) change during drilling. In the homogeneous stage of coal and rock properties, a first stress evaluation model based on torque, thrust, and rotational speed is constructed to directly reflect stress changes. In the stage of coal and rock property changes, a second stress evaluation model integrating acoustic emission characteristic parameters and drilling parameters is constructed, effectively eliminating the interference of lithological changes on drilling parameters, thereby achieving independent and accurate evaluation of in-situ stress changes. This method breaks through the limitations of traditional methods that rely on only a few drilling parameters and assume constant lithology, significantly improving the reliability and accuracy of stress evaluation in complex strata.

[0021] 3. This invention achieves spatial expansion and visualization from single-hole "line" evaluation to working-face "surface" evaluation. Based on continuous stress profile data obtained from multiple boreholes, and using spatial analysis methods such as Kriging interpolation, the continuous stress change field across the entire working face can be inferred, and the stress concentration zone of the original rock can be automatically delineated based on threshold values. This allows hidden stress anomaly areas to be displayed intuitively and quantitatively, elevating traditional point-like, discrete understanding to spatial visualization and prediction at the working face scale, greatly facilitating engineers' overall grasp and location of disaster risk areas.

[0022] In summary, this invention, through innovative device structure, near-source acquisition of multi-source information, intelligent adaptation of the evaluation model, and the comprehensive application of spatial analysis and visualization technologies, has formed a drilling evaluation system integrating data acquisition, real-time processing, precise analysis, and result visualization. Its ultimate effect lies in its ability to efficiently, continuously, and accurately identify and delineate the stress concentration zones in the original rock of deep mining faces. This provides a direct and scientific basis for formulating targeted stress relief and enhanced support measures for disaster prevention, and has significant practical application value for ensuring the safe and efficient mining of deep mines. Attached Figure Description

[0023] Figure 1 This is a schematic diagram of the drilling evaluation device for deep in-situ stress concentration zones according to an embodiment of the present invention; Figure 2 This is a flowchart of the deep in-situ stress concentration zone evaluation method according to an embodiment of the present invention; Explanation of reference numerals in the attached figures: 1. Drill bit, 2. Probe tube, 3. Drill rod, 4. Sensor unit, 5. Signal processing and storage unit, 6. Power supply unit. Detailed Implementation

[0024] The present invention will be further described in detail below with reference to the accompanying drawings and specific embodiments: Example 1 like Figure 1 As shown in the figure, this embodiment proposes a drilling evaluation device for deep in-situ stress concentration zones, including a drill bit 1, a probe 2, and a drill rod 3. The probe 2 has threaded interfaces at both ends, which are threadedly connected to the drill bit 1 and the drill rod 3. The probe 2 is configured to enter and exit the borehole along with the drill bit 1 and the drill rod 3.

[0025] The probe 2 is equipped with a sensor unit 4, a signal processing and storage unit 5, and a power supply unit 6.

[0026] Sensor unit 4 (sensor compartment) is used to collect data on the process of drill bit 1 cutting coal and rock. Sensor unit 4 encapsulates an acoustic emission sensor, a torque sensor, a thrust sensor, and a speed sensor. The acoustic emission sensor is used to collect the acoustic emission signals generated by drill bit 1 during the process of drill bit 1 cutting coal and rock. The torque sensor is used to collect the torque of drill bit 1 and drill rod 3 during the process of drill bit 1 cutting coal and rock. The thrust sensor is used to collect the axial thrust of drill bit 1 and drill rod 3 during the process of drill bit 1 cutting coal and rock. The speed sensor is used to collect the rotational speed of drill bit 1 and drill rod 3 during the process of drill bit 1 cutting coal and rock.

[0027] Sensor unit 4 is arranged between drill bit 1 and drill rod 3 so that each sensor is as close as possible to the position of drill bit 1, so as to minimize the signal transmission loss and interference in drill rod 3 and ensure that the collected data is "near drill bit" data that reflects the true state of coal and rock in front of drill bit 1.

[0028] The signal processing and storage unit 5 (circuit board) includes a preamplifier, an analog-to-digital converter, a microprocessor, and a memory chip, and is responsible for conditioning, acquiring, compressing, and storing sensor signals. The signal processing and storage unit 5 is electrically connected to the sensor unit 4, and is used to receive, process, and store the data acquired by the sensor unit 4.

[0029] Power supply unit 6 is a high-capacity intrinsically safe lithium battery pack, which powers sensor unit 4 and signal processing and storage unit 5.

[0030] Example 2 like Figure 1 , Figure 2 As shown, this embodiment proposes a method for evaluating deep in-situ stress concentration zones during drilling, employing the deep in-situ stress concentration zone evaluation device from Embodiment 2 above, and includes the following steps: S1, Drilling data collection; During the drilling of the gas drainage borehole, the device is activated, and all sensors begin collecting data, recording synchronously at a preset sampling frequency and drilling depth. While drill bit 1 cuts through coal and rock, the device synchronously collects acoustic emission signals, torque, thrust, and rotational speed data at different drilling depths throughout the entire borehole depth. After drilling is completed, the drill string 2 is withdrawn, and the stored data is exported to an explosion-proof tablet PC via a USB interface connected to the signal processing and storage unit 5.

[0031] S2, Single-hole stress evaluation; Based on the data collected in step S1, evaluate the changes in coal and rock stress along the single-hole drilling path.

[0032] S21. Based on the characteristic parameters of the acoustic emission signal, which include one or more of amplitude, energy, ring count, and frequency, determine whether the physical and mechanical properties of the coal and rock in the current drilling section have changed. The characteristic parameters of the acoustic emission signal reflect the physical and mechanical properties of the coal and rock (such as strength). By analyzing the changes in the characteristic parameters of the acoustic emission signal along the hole depth, determine whether the physical and mechanical properties of the coal and rock have changed during drilling.

[0033] S21 specifically includes: A coal-rock strength model is established with acoustic emission signal characteristic parameters as independent variables, and the coal-rock strength F of the current drilling section is calculated. s Among them, the physical and mechanical properties of coal and rock specifically include the coal and rock strength F. s .

[0034] The coal and rock strength model is: F s =f(a1*Ae1, a2*Ae2, a3*Ae3); Where Ae1, Ae2, and Ae3 are characteristic parameters of the acoustic emission signal, and a1, a2, and a3 are model coefficients.

[0035] S22. If the physical and mechanical properties of the coal and rock do not change, the changes in drilling parameters (torque, thrust, and rotational speed) reflect stress changes. Therefore, a first stress evaluation model with torque, thrust, and rotational speed as independent variables is established to calculate the relative stress change Fn1 on the drilling path.

[0036] The first stress evaluation model is: Fn1 = f(b1*T, b2*I, b3*R); Where T is torque, I is thrust, R is rotational speed, and b1, b2, and b3 are model coefficients.

[0037] S23. If the physical and mechanical properties of coal and rock change, it is necessary to separate the influence of the changes in the physical and mechanical properties of coal and rock on the drilling parameters. Then, a second stress evaluation model is established with acoustic emission signal characteristic parameters, torque, thrust, and rotational speed as independent variables, and the relative stress change Fn2 on the drilling path is calculated.

[0038] The second stress evaluation model is: Fn2 = f(c1*Ae1, c2*Ae2, c3*Ae3, c4*T, c5*I, c6*R); Where Ae1, Ae2, and Ae3 are characteristic parameters of acoustic emission signals, T is torque, I is thrust, R is rotational speed, and c1 to c6 are model coefficients.

[0039] The model coefficients a1 to a3, b1 to b3, and c1 to c6 were obtained through laboratory simulations of borehole tests on coal and rock with different stresses and intensities.

[0040] S24. Obtain the stress profile diagram that varies along the borehole depth.

[0041] In this embodiment, the data from S1 is read, the acoustic emission signal characteristic parameters are imported into the coal and rock strength model, and the coal and rock strength F of the current drilling section is calculated. s Determine the coal and rock strength F in the 0-80m section. s No change was observed in the coal and rock strength F in the 80m to 85m section. s Increase (e.g., from soft coal to hard coal or gangue).

[0042] The physical and mechanical properties of the coal and rock in the 0-80m section remained unchanged (coal and rock strength F). s(No change) The relative stress change Fn1 was calculated using a pre-calibrated first stress evaluation model (e.g., Fn1=0.05*T+0.1*I - 0.02*R). It was found that the Fn1 value in the 55-65m segment was consistently high, indicating the existence of a stress increase zone.

[0043] The physical and mechanical properties of coal and rock change in the 80-85m section (coal and rock strength F). s The relative stress change Fn2 was calculated using the second stress evaluation model (increased). The results show that even after deducting the increase in torque caused by lithological hardening, the Fn2 value in this segment is still at a normal level, indicating that there is no abnormal stress concentration.

[0044] A "depth-relative stress value" profile was generated for the borehole, marking the 55-65m range as the stress anomaly section.

[0045] S3, Inversion of stress zone on working surface; By integrating the single-hole coal and rock stress evaluation results of all multiple boreholes within the working face, and through spatial analysis, the original rock stress concentration zone of the entire working face is inverted and delineated.

[0046] S3 specifically includes: The stress profile data (depth-stress value) obtained from each borehole evaluation is used as spatial discrete points. Spatial interpolation is performed using Kriging interpolation or inverse distance weighting to generate a continuous stress change field distribution map within the working face area. Based on a preset stress change threshold, the area exceeding the threshold is delineated from the distribution map as the original rock stress concentration zone.

[0047] In this embodiment, data acquisition and analysis were completed for all (e.g., 50) extraction boreholes within the working face, resulting in 50 stress profiles. The spatial coordinates (X, Y, Z) and stress anomaly values ​​of all identified stress anomaly points (e.g., the midpoint depth and average stress value of the anomaly segment) were imported into a Geographic Information System (GIS) or specialized geological software. Kriging interpolation was used to generate a stress anomaly isosurface map of the entire coal seam in the working face. A threshold of 1.5 times the average stress value was set, and areas exceeding this threshold on the isosurface map were colored and marked as "original rock stress concentration zones." The results showed that the concentration zone was located in the central-eastern part of the working face, coinciding with the location of a known concealed small fault.

[0048] S4. By using structural information detected by borehole radar or geological exploration data to verify the delineated stress concentration zone of the original rock, the development of fractures in the area was confirmed, thus improving the accuracy of prediction.

[0049] Based on this, the coal mine formulated measures to strengthen the pressure relief boreholes and gas extraction in the area, achieving targeted disaster prevention and control.

[0050] Example 3 This embodiment 3 describes a computer-readable storage medium storing a program that, when executed by a processor, is used to implement the steps of the deep in-situ stress concentration zone evaluation method as described in embodiment 2 above.

[0051] The computer-readable storage medium can be an internal storage unit of any device or apparatus with data processing capabilities, such as a hard disk or memory, or an external storage device of any device with data processing capabilities, such as a plug-in hard disk, smart media card (SMC), SD card, flash card, etc.

[0052] The present invention has now been described in detail with reference to the accompanying drawings. Based on the above description, those skilled in the art should have a clear understanding of the present invention. Of course, the above description is merely a preferred embodiment of the present invention, and the present invention is not limited to the embodiments listed above. It should be noted that any equivalent substitutions or obvious modifications made by those skilled in the art under the guidance of this specification fall within the scope of this specification and should be protected by the present invention.

Claims

1. A drilling evaluation device for deep in-situ stress concentration zones, characterized in that, It includes a drill bit, a probe tube, and a drill rod, wherein the probe tube is disposed between the drill bit and the drill rod; the probe tube contains: The sensor unit is used to collect data on the process of the drill bit cutting coal and rock. The sensor unit includes at least an acoustic emission sensor, a torque sensor, a thrust sensor, and a speed sensor. A signal processing and storage unit, electrically connected to the sensor unit, is used to receive, process, and store the data collected by the sensor unit; A power supply unit provides power to the sensor unit and the signal processing and storage unit. The probe is configured to enter and exit the borehole together with the drill bit and drill rod.

2. The deep in-situ stress concentration zone evaluation device according to claim 1, characterized in that, The probe is provided with threaded interfaces at both ends for connecting the drill bit and / or drill rod.

3. A method for evaluating deep in-situ stress concentration zones while drilling, employing the deep in-situ stress concentration zone evaluation device as described in claim 1 or 2, characterized in that, Includes the following steps: S1, Drilling data collection; During the process of the drill bit cutting coal and rock, the device is used to simultaneously collect acoustic emission signals, torque, thrust and rotational speed data when drilling to different depths; S2, Single-hole stress evaluation; Based on the data collected in step S1, evaluate the changes in coal and rock stress along the single-hole drilling path; S3, Inversion of stress zone on working surface; By integrating the single-hole coal and rock stress evaluation results from multiple boreholes within the working face, and through spatial analysis, the original rock stress concentration zone of the entire working face is inverted and delineated.

4. The method for evaluating deep in-situ stress concentration zones during drilling according to claim 3, characterized in that, S2 specifically includes: S21. Based on the characteristic parameters of the acoustic emission signal, determine whether the physical and mechanical properties of the coal and rock in the current drilling section have changed; S22. If the physical and mechanical properties of the coal and rock have not changed, then establish a first stress evaluation model with torque, thrust, and rotational speed as independent variables, and calculate the relative stress change Fn1 on the drilling path. S23. If the physical and mechanical properties of coal and rock change, a second stress evaluation model is established with acoustic emission signal characteristic parameters, torque, thrust, and rotational speed as independent variables, and the relative stress change Fn2 on the drilling path is calculated. S24. Obtain the stress profile diagram that varies along the borehole depth.

5. The method for evaluating deep in-situ stress concentration zones during drilling according to claim 4, characterized in that, The characteristic parameters of acoustic emission signals include one or more of the following: amplitude, energy, ring count, and frequency.

6. The method for evaluating deep in-situ stress concentration zones during drilling according to claim 4, characterized in that, S21 specifically includes: A coal-rock strength model is established with acoustic emission signal characteristic parameters as independent variables, and the coal-rock strength F of the current drilling section is calculated. s Among them, the physical and mechanical properties of coal and rock specifically include the coal and rock strength F. s ; The coal and rock strength model is: F s =f(a1*Ae1, a2*Ae2, a3*Ae3); Where Ae1, Ae2, and Ae3 are characteristic parameters of the acoustic emission signal, and a1, a2, and a3 are model coefficients.

7. The method for evaluating deep in-situ stress concentration zones during drilling according to claim 4, characterized in that, The first stress evaluation model is: Fn1 = f(b1*T, b2*I, b3*R); Where T is torque, I is thrust, R is rotational speed, and b1, b2, and b3 are model coefficients; The second stress evaluation model is: Fn2 = f(c1*Ae1, c2*Ae2, c3*Ae3, c4*T, c5*I, c6*R); Where Ae1, Ae2, and Ae3 are characteristic parameters of acoustic emission signals, T is torque, I is thrust, R is rotational speed, and c1 to c6 are model coefficients.

8. The method for evaluating deep in-situ stress concentration zones during drilling according to claim 4, characterized in that, S3 specifically includes: The stress profile data obtained from each borehole evaluation is used as spatial discrete points. Kriging interpolation or inverse distance weighting is used for spatial interpolation to generate a continuous stress change field distribution map within the working face area. Based on the preset stress change threshold, the area exceeding the threshold is delineated from the distribution map as the original rock stress concentration area.

9. The method for evaluating deep in-situ stress concentration zones during drilling according to claim 3, characterized in that, S3 is followed by S4: using borehole radar or geological exploration data to verify the delineated stress concentration zone in the original rock.

10. A computer-readable storage medium having a program stored thereon, characterized in that, When the program is executed by the processor, it implements the method for evaluating deep in-situ stress concentration zones as described in any one of claims 3 to 9.

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