Rock drilling efficiency evaluation method under in-situ stress recovery reconstruction
By using the in-situ stress recovery and reconstruction method, the particle size distribution of drill cuttings was collected and analyzed, and the mechanical specific energy (MSE) was calculated. This solved the problem of the difficulty in quantitatively evaluating the efficiency of deep drilling and enabled an accurate assessment of the drilling efficiency in deep rock.
Patent Information
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- XIAN UNIV OF TECH
- Filing Date
- 2026-01-06
- Publication Date
- 2026-04-21
AI Technical Summary
Existing technologies make it difficult to accurately quantify rock drilling efficiency during deep drilling, especially under in-situ stress recovery and reconstruction conditions, where the differences in drill cuttings size distribution and energy dissipation are not fully considered, making it difficult to quantitatively evaluate deep drilling efficiency.
The in-situ stress recovery and reconstruction method is adopted. Drill cuttings are collected and screened through drilling tests. The fracture angle and particle size distribution of the drill cuttings are calculated. The fractal dimension is obtained by fitting the curve using the fractal equation. The mechanical specific energy (MSE) is calculated by combining the cutting force and the drill cutting volume, so as to achieve a quantitative evaluation of rock drilling efficiency.
It provides a rock drilling efficiency evaluation index based on drill cuttings characteristics, which can truly reflect the drilling efficiency under complex in-situ stress environment at deep depths, and provides a theoretical basis for the prediction and optimization of deep drilling efficiency.
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Figure CN121903166A_ABST
Abstract
Description
Technical Field
[0001] This invention belongs to the field of rock drilling efficiency evaluation technology, and relates to a method for evaluating rock drilling efficiency under in-situ stress recovery and reconstruction. Background Technology
[0002] Deep drilling projects are typically conducted in environments coupled with high ground stress and strong disturbance, and the destructive characteristics of rock cuttings directly affect drilling efficiency. Accurately evaluating rock drilling efficiency under near-in-situ stress conditions is of great significance for revealing the fracture mechanism of deep rock masses and optimizing drilling parameters.
[0003] Existing studies are mostly based on conventional core sampling or laboratory mechanical tests. However, unloading damage is inevitable during traditional drilling, and stress release disturbs the initial stress state of the core, making it difficult for experimental results to accurately reflect the mechanical response of deep rock masses under actual drilling conditions. Especially during drilling, strong disturbances, rapid unloading, and complex fracturing mechanisms coexist, and drilling efficiency is mainly controlled by rock fracturing modes and energy utilization methods. Simply relying on strength and deformation parameters is insufficient to accurately characterize the efficiency level.
[0004] Some studies have simulated the stress state of deep rock masses under laboratory conditions through in-situ stress recovery and reconstruction experiments, and analyzed the drilling process and mechanical response. However, these methods mainly focus on overall energy consumption and macroscopic mechanical parameters, lacking a systematic characterization of drill cuttings particle size distribution and morphological characteristics, making it difficult to reveal the differences in energy dissipation under different fracture modes. Furthermore, under in-situ stress recovery and reconstruction conditions, the impact of drill cuttings retention, multiple breakages, and their effects on local stress states and drilling efficiency during auger drilling has not been fully considered, making it difficult to accurately and quantitatively evaluate deep drilling efficiency. Summary of the Invention
[0005] The purpose of this invention is to provide a method for evaluating rock drilling efficiency under in-situ stress recovery and reconstruction, which solves the problem that the efficiency of deep rock drilling is difficult to quantify accurately in the prior art.
[0006] The technical solution adopted in this invention is a method for evaluating rock drilling efficiency under in-situ stress recovery and reconstruction, which is implemented according to the following steps: Step 1: Perform in-situ stress recovery reconstruction on the rock sample, conduct drilling tests under these conditions, collect drill cuttings, and conduct sieve tests; Step 2: Based on the drilling parameters obtained in Step 1, obtain the cuttings fracture angle during the drilling process under the in-situ stress recovery and reconstruction condition, and calculate the cutting force; Step 3: Using the drill cuttings particle size distribution mass data obtained in Step 1, plot the fractal equation fitting curve, obtain the fractal dimension of the drill cuttings particle size, and calculate the drill cuttings volume; Step 4: Substitute the cutting force obtained in Step 2 and the drill cuttings volume obtained in Step 3 into the expression for the drilling efficiency evaluation index Mechanical Specific Energy (MSE) to obtain the MSE value based on the characteristics of the drill cuttings, and complete the quantitative evaluation of rock drilling efficiency under in-situ stress recovery and reconstruction conditions.
[0007] The beneficial effects of this invention are that it proposes a drilling efficiency evaluation index based on the characteristics of drill cuttings distribution, evaluates the rock drilling efficiency under in-situ stress recovery and reconstruction conditions, and provides a theoretical basis for the prediction and optimization of drilling efficiency under complex in-situ stress environments in deep locations. Attached Figure Description
[0008] Figure 1 This is a diagram of the stress loading path for in-situ stress recovery and reconstruction. Figure 2a The results are the fitting of cutting force and thrust for the brown-red sandstone in Example 1 under in-situ stress recovery and reconstruction and non-in-situ stress recovery and reconstruction conditions. Figure 2b The fitting results of cutting force and thrust for marble under in-situ stress recovery and reconstruction and non-in-situ stress recovery and reconstruction conditions in Example 2 are shown. Figure 2c The fitting results of cutting force and thrust for purple sandstone in Example 3 under in-situ stress recovery and reconstruction and non-in-situ stress recovery and reconstruction conditions; Figure 2d The fitting results of cutting force and thrust for granite under in-situ stress recovery and reconstruction and non-in-situ stress recovery and reconstruction conditions in Example 4 are shown. Figure 3a The fitting results of the fractal dimension of the brown-red sandstone in Example 1 under in-situ stress recovery and reconstruction and non-in-situ stress recovery and reconstruction conditions are shown. Figure 3b The fitting results of the fractal dimension of marble in Example 2 under in-situ stress recovery and reconstruction and non-in-situ stress recovery and reconstruction conditions; Figure 3c The fitting results of the fractal dimension of the purple sandstone in Example 3 under in-situ stress recovery and reconstruction and non-in-situ stress recovery and reconstruction conditions are shown. Figure 3d The fitting results of the fractal dimension of the granite in Example 4 under in-situ stress recovery and reconstruction and non-in-situ stress recovery and reconstruction conditions are shown. Figure 4 The mechanical specific energy (MSE) calculated using the method of this invention is compared with the mechanical specific energy (MSE) calculated using other methods. c The contrast between them; Figure 5 This describes the correspondence between the drilling efficiency evaluation index and the CI index determined based on the method of this invention. Detailed Implementation
[0009] The present invention will now be described in detail with reference to the accompanying drawings and specific embodiments.
[0010] The present invention provides a method for evaluating rock drilling efficiency under in-situ stress recovery and reconstruction, which is implemented according to the following steps: Step 1: In-situ stress recovery reconstruction is performed on the rock sample. Under these conditions, a drilling test is conducted using digital drilling equipment. Simultaneously, drill cuttings are collected and sieve analysis is performed. The specific process is as follows: First, in-situ stress recovery and reconstruction is performed on the rock sample: For a core at a given depth, the sample is placed in the confining pressure system of the digital drilling equipment, and a confining pressure corresponding to the target formation is applied while keeping the stress level constant; under the action of the confining pressure, the core deforms, which gradually weakens over time until it stabilizes, at which point the in-situ stress recovery and reconstruction is considered complete.
[0011] To study the deformation characteristics of deep rocks during stress recovery and reconstruction and to determine the appropriate stress maintenance time, an in-situ stress recovery and reconstruction pre-test was conducted before the formal test.
[0012] In the preliminary test, a target confining pressure was applied to the rock sample and maintained for a certain period of time to ensure that the core returned to its original in-situ depth state, while the change of lateral deformation over time was continuously recorded; when the change of lateral deformation tended to stabilize, the rock sample was considered to have reached the target in-situ stress state; subsequently, the stress was released and the rock sample was placed in a cool and dry environment to simulate the stress release and environmental changes that occur during the extraction and transportation of deep rock cores to the laboratory.
[0013] Formal test: After the in-situ stress recovery and reconstruction is completed, the confining pressure is kept constant, and an axial load is applied to the rock sample to carry out the drilling test and obtain the drilling parameters under reconstruction conditions. During the drilling process, the drill cuttings generated are continuously collected by the drill cuttings collection device, and a sieving test is carried out after the drilling is completed to record the distribution quality data of drill cuttings in different particle size ranges, so as to provide experimental data for subsequent analysis of drill cuttings particle size distribution and morphology.
[0014] Step 2: Based on the drilling parameters obtained in Step 1, obtain the cuttings fracture angle during the drilling process under the in-situ stress recovery and reconstruction conditions. The cutting force was calculated. F t The value, specifically the process is as follows: Calculate the fracture angle of drill cuttings The expression is as follows: (1) in, It is the fracture angle of the drill cuttings. It is the drill bit inclination angle. It is the internal friction angle of the rock; calculate the cutting force including the size of the drill cuttings. F tThe expression is as follows: (2) in, k It is a constant related to the properties of rocks. t It is the tensile strength of the rock. d 0 is the height of the fault zone. ' is the friction angle between the drill bit and the rock.
[0015] Step 3: Using the drill cuttings particle size distribution mass data obtained in Step 1, plot the fractal equation fitting curve to obtain the fractal dimension of the drill cuttings particle size. D Calculate the volume of drill cuttings V dT The specific process is as follows: The fractal dimension of drill cuttings size can be obtained using the following expression. D : (3) in, M d For the diameter of the sieve opening d c The quality of drill cuttings, M dt The total mass of drill cuttings. d c It is the diameter of the sieve aperture. d cmax It is the maximum value of the sieve aperture diameter; K As a scaling factor, it is calculated by plotting ln( M d / M dt ) and ln( d c / d cmax The relationship diagram is based on the slope (3). -D The fractal dimension was derived. D fractal dimension D Used to characterize the degree of diamond chip breakage, the higher the value, the higher the proportion of fine diamond chips and the more complete the diamond breaking process.
[0016] Calculate the volume of drill cuttings generated during drilling. V dT The expression is: (4) in, V dT It is the volume of drill cuttings. c It is a proportionality constant related to the properties of the rock. n e It refers to the porosity of the rock.D It is the fractal dimension of the drill cuttings.
[0017] Step 4: Apply the cutting force obtained in Step 2 F t and the volume of drill cuttings obtained in step 3 V dT Substituting the expression for the drilling efficiency evaluation index Mechanical Specific Energy (MSE), the MSE value based on drill cuttings characteristics is calculated as follows: (5) in, d 'It is the drilling depth;' The MSE value of drill cuttings characteristics was used to quantitatively evaluate the rock drilling efficiency under in-situ stress recovery and reconstruction conditions.
[0018] Experimental verification: The following four examples verify the rock drilling efficiency evaluation method under in-situ stress recovery and reconstruction conditions described in this invention. Example 1 uses brownish-red sandstone, Example 2 uses marble, Example 3 uses purple sandstone, and Example 4 uses granite. Each example was conducted under in-situ stress recovery and reconstruction (SR) conditions and non-in-situ stress recovery and reconstruction (NSR) conditions, and comparative tests were carried out under different confining pressure conditions. The specific implementation process is as follows: Step 1: Perform in-situ stress recovery reconstruction on the sample, and conduct drilling tests using digital drilling equipment under these conditions, while collecting drill cuttings and conducting sieving tests. First, in-situ stress recovery reconstruction is performed on the rock sample: For a core at a given depth, the sample is placed in the confining pressure system of the digital drilling equipment, and a confining pressure corresponding to the target formation is applied while maintaining a constant stress level. Under the confining pressure, the core deforms, gradually weakening over time until it stabilizes; at this point, the in-situ stress recovery reconstruction is considered complete. The stress loading path for in-situ stress reconstruction is as follows: Figure 1 As shown.
[0019] To investigate the deformation characteristics of deep rocks during stress recovery and reconstruction and to determine the appropriate stress maintenance time, a preliminary test was conducted before the formal test. In the preliminary test, a target confining pressure was applied to the sample and maintained for a certain period to ensure the core recovered to its original in-situ depth state, while the lateral deformation over time was continuously recorded. When the lateral deformation stabilized, the sample was considered to have reached the target in-situ stress state. Subsequently, the stress was released, and the sample was placed in a cool, dry environment to simulate the stress release and environmental changes that occur during the extraction and transportation of deep rock cores to the laboratory.
[0020] After in-situ stress recovery and reconstruction, the confining pressure was kept constant, and an axial load was applied to the sample to conduct a drilling test and obtain the drilling parameters under reconstruction conditions. During the drilling process, the drill cuttings generated were continuously collected by a drill cuttings collection device, and a sieving test was conducted after drilling was completed to record the mass of drill cuttings with different particle size ranges, providing experimental data for subsequent analysis of drill cuttings particle size distribution and morphology.
[0021] Step 2: Based on the drilling parameters obtained in Step 1, obtain the cuttings fracture angle during drilling under in-situ stress reconstruction conditions. Calculate cutting force F t value; Drill cuttings fracture angle The expression is as follows: (1) Calculate the cutting force including the size of the drill chips. F t expression: (2) in, It is the fracture angle of the drill cuttings. It is the drill bit inclination angle. It is the internal friction angle of the rock. k It is a constant related to the properties of rocks. t It is the tensile strength of the rock. ' is the angle of friction between the drill bit and the rock. d 0 represents the height of the fault zone.
[0022] Reference Figure 2a , Figure 2b , Figure 2c , Figure 2d The figures show the fitting results of cutting force and thrust for the four types of samples selected in the above embodiments under in-situ stress recovery and reconstruction and non-in-situ stress recovery and reconstruction conditions. The results show that the fitting results obtained by the method of the present invention are good, and both cutting force and thrust exhibit stage-like variation characteristics.
[0023] Step 3: Using the drill cuttings particle size distribution mass data obtained in Step 1, plot the fractal equation fitting curve, obtain the fractal dimension of the drill cuttings particle size, and calculate the drill cuttings volume; The fractal dimension expression for drill cuttings particle size is: (3) in, M d For the diameter of the sieve opening d c The quality of drill cuttings, M dt This represents the total mass of drill cuttings. KAs a scaling factor, it is calculated by plotting ln( M d / M dt ) and ln( d c / d cmax The relationship diagram is based on the slope (3). -D ) to obtain the fractal dimension D fractal dimension D Used to characterize the degree of diamond chip breakage, the higher the value, the higher the proportion of fine diamond chips and the more complete the diamond breaking process.
[0024] The volume of drill cuttings generated during drilling. V dT The expression is: (4) in, V dT It is the volume of drill cuttings. c It is a proportionality constant related to the properties of the rock. n e It refers to the porosity of the rock. D It is the fractal dimension of the drill cuttings. d cmax It is the maximum value of the sieve aperture diameter.
[0025] Reference Figure 3a , Figure 3b , Figure 3c , Figure 3d Tables 1 and 2 show the fitting results of the fractal equations for the four types of samples selected in the above embodiments under in-situ stress recovery and reconstruction conditions and non-in-situ stress recovery and reconstruction conditions, respectively. The results in the figures and tables show that the fitting obtained by the method of the present invention is good, and the drill cuttings particle size distribution follows bifractal characteristics. In Table 1, K 3c It is the stress level. K 3c Defined as the ratio of confining pressure to uniaxial compressive strength. D 1 is the fractal dimension of small-diameter drill cuttings. D 2 is the fractal dimension of large-diameter drill cuttings.
[0026] Table 1. Fractal Dimension of Drill Cutting Particle Size D 1 and D 2. Comparison of data
[0027] Step 4: The cutting forces obtained in Step 2 and Step 3 F t and drill cuttings volume V dTSubstituting the mechanical specific energy (MSE) expression into the drilling efficiency evaluation index, the MSE value based on drill cuttings characteristics is calculated to quantitatively evaluate the rock drilling efficiency under in-situ stress reconstruction conditions.
[0028] (5) in, d 'It refers to the drilling depth.'
[0029] Substitute the fractal dimension of the drill cuttings obtained in step 3 into the mechanical specific energy (MSE) expression in step 4 (formula (5)) to calculate the drilling efficiency index under drilling conditions.
[0030] Based on the work done by the cutting force and thrust during drilling, and the volume of rock destroyed during drilling, the following calculations are made: MSE c , MSE c The expression is: (6) in, MSE c For mechanical specific energy, W For drilling work, V The volume of rock destroyed during drilling.
[0031] Theoretical calculations MSE c A comparative analysis was performed with the MSE obtained using the method of this invention. (Refer to...) Figure 4 The results show the MSE comparison of brown-red sandstone, marble, purple sandstone, and granite selected in the four embodiments above under in-situ stress reconstruction and non-in-situ stress reconstruction conditions. The results show that drilling efficiency decreases after in-situ stress reconstruction. The drilling efficiency ranking of the four embodiments is: brown-red sandstone > marble > purple sandstone > granite. For different lithologies and stress conditions, the experimental data points are generally distributed around the reference line y=x, indicating that the results of the two MSE calculation methods are basically consistent, thus verifying the accuracy and reliability of the rock drilling efficiency evaluation method under in-situ stress recovery reconstruction proposed in this invention.
[0032] A drilling efficiency evaluation index (CI index) is introduced to characterize drilling efficiency. The CI index is compared and analyzed with the mechanical specific energy (MSE) evaluation index based on drill cuttings characteristics proposed in this invention to study their correspondence under different lithological and stress conditions. (Refer to...) Figure 4The above embodiments describe the relationship between MSE and CI index for brownish-red sandstone, marble, purple sandstone, and granite selected under in-situ stress reconstruction and non-in-situ stress reconstruction conditions. The results show an exponential relationship between the CI index and the MSE drilling efficiency evaluation index proposed in this invention, with a correlation coefficient of 80%. This further verifies the applicability and reliability of the drilling efficiency evaluation method proposed in this invention under in-situ stress recovery and reconstruction conditions.
[0033] The drilling efficiency evaluation index, Mechanical Specific Energy (MSE), proposed in this invention is calculated based on drill cuttings generated under in-situ stress recovery and reconstruction conditions. The relevant parameters can be obtained simply by collecting and analyzing the drill cuttings generated during the drilling process, offering advantages such as ease of acquisition and strong experimental operability. This index can accurately reflect the fracture mode and energy dissipation characteristics of deep rock masses under in-situ stress recovery and reconstruction conditions, thereby achieving an accurate evaluation of drilling efficiency under complex stress environments at depth.
Claims
1. A method for evaluating rock drilling efficiency under in-situ stress recovery and reconstruction, characterized in that, Follow these steps: Step 1: Perform in-situ stress recovery reconstruction on the rock sample, conduct drilling tests under these conditions, collect drill cuttings, and conduct sieving tests; Step 2: Based on the drilling parameters obtained in Step 1, obtain the cuttings fracture angle during the drilling process under the in-situ stress recovery and reconstruction condition, and calculate the cutting force; Step 3: Using the drill cuttings particle size distribution mass data obtained in Step 1, plot the fractal equation fitting curve, obtain the fractal dimension of the drill cuttings particle size, and calculate the drill cuttings volume; Step 4: Substitute the cutting force obtained in Step 2 and the drill cuttings volume obtained in Step 3 into the expression for the drilling efficiency evaluation index Mechanical Specific Energy (MSE) to obtain the MSE value based on the characteristics of the drill cuttings, and complete the quantitative evaluation of rock drilling efficiency under in-situ stress recovery and reconstruction conditions.
2. The method for evaluating rock drilling efficiency under in-situ stress recovery and reconstruction according to claim 1, characterized in that, In step 1, in-situ stress recovery reconstruction is performed on the rock sample. The specific process is as follows: For a core sample at a given depth, the sample is placed in the confining pressure system of the digital drilling equipment, and a confining pressure corresponding to the target formation is applied while maintaining a constant stress level. Under the action of the confining pressure, the core sample deforms, which gradually weakens over time until it stabilizes. At this point, the in-situ stress recovery and reconstruction is considered complete.
3. The method for evaluating rock drilling efficiency under in-situ stress recovery and reconstruction according to claim 1, characterized in that, In step 1, a drilling test is conducted using digital drilling equipment, and drill cuttings are collected and screened to identify deformation characteristics during stress recovery and reconstruction and determine the appropriate stress holding time. The specific process is as follows: In the preliminary test, a target confining pressure was applied to the rock sample and maintained for a certain period of time to ensure that the core returned to its original in-situ depth state, while the change of lateral deformation over time was continuously recorded; when the change of lateral deformation tended to stabilize, the rock sample was considered to have reached the target in-situ stress state; subsequently, the stress was released and the rock sample was placed in a cool and dry environment to simulate the stress release and environmental changes that occur during the extraction and transportation of deep rock cores to the laboratory. Formal test: After the in-situ stress recovery and reconstruction is completed, the confining pressure is kept constant, and an axial load is applied to the rock sample to carry out the drilling test and obtain the drilling parameters under reconstruction conditions. During the drilling process, the drill cuttings generated are continuously collected, and a sieving test is carried out after the drilling is completed to record the distribution quality data of drill cuttings in different particle size ranges.
4. The method for evaluating rock drilling efficiency under in-situ stress recovery and reconstruction according to claim 1, characterized in that, In step 2, the fracture angle of the drill cuttings is calculated. The expression is as follows: （1） in, It is the fracture angle of the drill cuttings. It is the drill bit tilt angle. It is the internal friction angle of the rock.
5. The method for evaluating rock drilling efficiency under in-situ stress recovery and reconstruction according to claim 1, characterized in that, In step 2, the cutting force, including the size of the drill chips, is calculated. F t The expression is as follows: （2） in, k It is a constant related to the properties of rocks. t It is the tensile strength of the rock. d 0 is the height of the fault zone. ' is the angle of friction between the drill bit and the rock.
6. The method for evaluating rock drilling efficiency under in-situ stress recovery and reconstruction according to claim 1, characterized in that, In step 3, the fractal dimension of the drill cuttings particle size is obtained using the following expression. D : （3） in, M d For the diameter of the sieve opening d c The quality of drill cuttings, M dt The total mass of drill cuttings. d c It is the diameter of the sieve aperture. d cmax It is the maximum value of the sieve aperture diameter; K As a scaling factor, it is calculated by plotting ln( M d / M dt ) and ln( d c / d cmax The relationship diagram is based on the slope (3). -D The fractal dimension was derived. D .
7. The method for evaluating rock drilling efficiency under in-situ stress recovery and reconstruction according to claim 1, characterized in that, In step 3, the volume of drill cuttings generated during the drilling process is calculated. V dT The expression is: （4） in, V dT It is the volume of drill cuttings. c It is a proportionality constant related to the properties of the rock. n e It refers to the porosity of the rock. D It is the fractal dimension of the drill cuttings.
8. The method for evaluating rock drilling efficiency under in-situ stress recovery and reconstruction according to claim 1, characterized in that, In step 4, the MSE value based on drill cuttings characteristics is calculated, as shown in the following expression: （5） in, d 'It refers to the drilling depth.'