Kilometer base rock mark drilling rescue method

Abstract

The invention belongs to the technical field of engineering geological drilling, and particularly relates to a kilometer base rock mark drilling rescue method which comprises the following steps: step 1, designing and optimizing a sidetrack track: selecting a sidetrack point, simulating and optimizing the track, and monitoring and regulating in real time; 2, the construction process is controlled, specifically, windowing is conducted, and a stable well track is built through an initial deflecting drilling tool combination; a drilling tool with a bent angle is combined with a measurement-while-drilling tool, so that a well track is subjected to angle increasing and / or direction twisting according to design, and the well track is accurately guided to an inlet of a target layer; after entering a target layer, carrying out real-time geosteering extension according to the logging while drilling data; a declining drilling tool combination is adopted, so that a well track is smoothly transited from a horizontal state to a well deviation angle of a design end point; aiming at drill jamming and drill burying accidents in ultra-deep bedrock standard construction, a sidetrack drilling technology, track optimization and a cement backfilling technology are combined, an oil field sidetrack drilling technology and bedrock standard high precision requirements are combined, and a targeted rescue process is provided.

Description

Technical Field

[0001] This invention belongs to the field of engineering geological leveling surveying, and specifically relates to a method for rescuing kilometer-long bedrock marker boreholes. Background Technology

[0002] Land subsidence is a complex, global, and multidisciplinary systemic problem. Research by the UNESCO Land Subsidence Working Group indicates that by 2040, land subsidence could affect approximately 19% of the global population. Its impact is widespread, threatening sustainable economic development and human life, and is the most significant geological hazard in plains areas, with the North China Plain being one of the most severely affected regions. Stable bedrock markers can serve as stable reference points for regional land subsidence leveling, offering advantages such as high accuracy and long-term stability. Bedrock markers must penetrate loose overburden layers and be embedded in stable bedrock. According to DZ / T0283-2015 "Specification for Land Subsidence Investigation and Monitoring," when the final borehole depth exceeds 500m, the final borehole apex angle must not exceed 2.0°. The difficulty of constructing bedrock markers increases with depth. To meet design and specification requirements for verticality, kilometer-level bedrock markers will utilize drilling-while-measuring, with the cumulative increase in the borehole apex angle not exceeding 0.2° for every 50m of drilling. The mudstone in the thick overburden above the bedrock has high viscosity and is easily expansive, making it prone to hydration during drilling, leading to wellbore instability and collapse. The softness and viscosity of the mudstone can prolong the effective drilling time of roller cone or PDC drill bits. Rock cuttings from broken mudstone cannot be circulated out after the drilling mud loses water, and when these cuttings accumulate to a certain extent, stuck drill bits or burial accidents are highly likely. Common methods for handling stuck drill bits or burial accidents include: reverse threading, reaming, casing washing, tappet retrieval, and blasting. The strong pulling method is suitable for initial minor stuck drill bits, but requires high drill bit strength and cannot resolve severe stuck drill bits caused by reduced diameter or collapse. The caustic soda soaking method is suitable for stuck drill bits caused by hydration and expansion (such as stuck drill bits in mudstone and shale). The slap impact method is effective for stuck drill bits with reduced diameter, but its effectiveness is limited for severe stuck drill bits or burial accidents caused by collapse. For serious stuck drill, stuck drill, and buried drill accidents that occur during benchmark drilling in bedrock with a cover layer exceeding 1500m, common methods for handling buried drill accidents are not very effective. Summary of the Invention

[0003] This invention addresses the stuck drill accident caused by drilling stoppage and inclination measurement during ultra-deep bedrock marker construction. It proposes a drilling rescue method integrating sidetracking technology, trajectory optimization, and cement backfilling. This method combines oilfield sidetracking technology with the high-precision requirements of bedrock markers, developing a targeted rescue process. Based on actual drilling data, it improves the anti-collision algorithm to achieve three-dimensional collision avoidance between the original borehole and the sidetracked borehole. Furthermore, it proposes a "segmented sealing + long curing time" strategy to ensure the stability of the sidetracking starting point, providing a practical case reference for handling stuck drill accidents during bedrock marker construction.

[0004] The objective of this invention is achieved as follows: A method for rescuing kilometer-long bedrock markers by drilling includes the following steps: Step 1: Side-drilling trajectory design and optimization S11 Side Drilling Point Selection: Backfill the borehole with cement grout to a depth of 700m-900m or more, and then perform side drilling after the grout has set. The side drilling point is set at 700m-800m. S12 trajectory simulation optimization: A three-dimensional trajectory model was established, and a trajectory scheme of "increasing inclination section + stabilizing inclination section + decreasing inclination section + preventing inclination section" was designed. Through simulation verification, the scheme can avoid the original wellbore stuck area. S13 Real-time Monitoring and Control: The monitoring system is activated, and a set of well inclination angle, azimuth angle and lithology data are collected at regular intervals and transmitted to the ground control system. If the well inclination angle is found to deviate from the design value during construction, the tool face angle of the directional drilling tool is immediately adjusted to correct the well inclination angle to the design range. Step 2: Construction Process Control S21, Window opening stage: Set the directional device at a predetermined depth on the original well casing, and use a window opening milling cone assembly to mill along the directional device to form a regular window; S22, Drilling stage: Using the initial directional drilling tool assembly, drill the initial new wellbore with low drilling pressure and low rotation speed to establish a stable wellbore trajectory; S23, Directional Drilling Stage: Using a drill string with bends and a measurement-while-drilling tool, the wellbore trajectory is increased inclination and / or azimuth is twisted according to the design through alternating operations of sliding drilling and composite drilling, precisely guiding it to the entrance of the target layer. S24, Horizontal section drilling stage: After entering the target layer, a rotary steering system or a low-angle second screw drill string is used, and real-time geological steering is performed based on logging-while-drilling data to maintain the well inclination angle within the range of 86° to 94°. S25, Drilling stage of deflection section: adopting a combination of deflection drill tools, mainly using composite drilling methods, to smoothly transition the wellbore trajectory from a horizontal state to the well inclination angle of the designed endpoint; S26, Mud Management Stage: Throughout the entire construction process, the performance of the drilling fluid is adjusted in real time. The adjustment of the drilling fluid performance includes maintaining its high rock carrying capacity, high lubricity, wellbore stability and reservoir protection characteristics, and removing harmful solid phases through solids control equipment.

[0005] Furthermore, in step S11, the cement slurry used is 325 cement slurry with a specific gravity of 1.6 g / cm3. The side drilling point is set at 700m, which can meet the standard design requirements. The stratum at this location is a thin layer of clay with fine sand, with a compressive strength of 35~40MPa, a porosity of <15%, and a stability that meets the requirements for side drilling.

[0006] Furthermore, in step S12, a three-dimensional trajectory model is established using Landmark software. The increasing inclination section is located at 700~730m, with the well inclination angle increasing from 0° to 1° and a length of 30m; the stabilizing inclination section is located at 730~900m, with the well inclination angle at 1° and a length of 170m; the decreasing inclination section is located at 900~950m, with the well inclination angle decreasing from 1° to 0.8° and a length of 50m; and the anti-inclination section is located below 950m. Through ABAQUS simulation verification, this scheme can avoid the original wellbore stuck area, with a minimum distance of 3.02m from underground obstacles and a trajectory deviation of <0.3m, meeting the anti-collision requirements.

[0007] Furthermore, in step S13, the monitoring system adopts a dual MWD+LWD system, which collects one set of well inclination angle, azimuth angle and lithology data every 5 minutes and transmits them to the ground control system. The response time is <10s. If the well inclination angle is found to deviate from the design value during construction, the tool face angle of the directional drilling tool is immediately adjusted to correct the well inclination angle to the design range.

[0008] Furthermore, in step S22, the initial directional drilling tool assembly adopts a structure of "Φ152.40mm HA136 drill bit + 1 drill collar + Φ89mm drill pipe", with the drilling pressure gradually increased from 5~10kN to 30kN and the rotation speed at 50r / min. Furthermore, in step S23, a 1.50° single-bend power drill is used, with a drilling pressure of 30~50kN and a pump pressure of 13~15MPa. A full measurement is performed every 9m of drilling, and the well inclination angle is adjusted by 0.3°~0.5° per drill. When the well inclination angle in the increased inclination section reaches 45°, a single drill is reamed once before connection to remove the cuttings bed. Furthermore, in step S24, the LWD system is connected, the drilling pressure is 30~40kN, the pump pressure is 17~18MPa, a short start-up and stop operation is performed every 80m of drilling, and lubricant is added to reduce the friction coefficient to 0.18, and the cuttings carrying rate reaches 92%. Furthermore, in step S25, the well inclination angle is gradually reduced to 0°, the drilling pressure is reduced to 20~30kN, the rotation speed is 55r / min, and the predetermined position of the bedrock layer is accurately reached with a depth error of only 0.3m; Furthermore, in step S26, a three-stage purification process is adopted throughout the process, the sand content of the mud is controlled at 0.3%~0.4%, the specific gravity is 25~1.35g / cm³, the viscosity is 28~32s, the water loss rate is <8mL / 30min, and there is no phenomenon of borehole wall collapse or drill cuttings accumulation.

[0009] The beneficial effects of this invention: This invention addresses the stuck drill accident caused by drilling stoppage and inclination measurement during ultra-deep bedrock marker construction. It proposes a borehole rescue method integrating sidetracking technology, trajectory optimization, and cement backfilling. By combining oilfield sidetracking technology with the high-precision requirements of bedrock markers, a targeted rescue process is developed. Based on actual drilling data, an anti-collision algorithm is improved to achieve three-dimensional spatial collision avoidance between the original borehole and the sidetracked borehole. A "segmented sealing + long curing time" strategy is proposed to ensure the stability of the sidetracking starting point, providing a practical case reference for handling stuck drill accidents during bedrock marker construction. Attached Figure Description

[0010] To more clearly illustrate the technical solutions of the embodiments of the present invention, the drawings used in the description of the embodiments of the present invention or the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0011] Figure 1 This is a schematic diagram of the bedrock marker structure in Example 1.

[0012] Figure 2 This is the actual drilling trajectory diagram from Example 1.

[0013] Figure 3 This is the side-drilling trajectory diagram designed in Example 1.

[0014] Figure 4 This is a coupled diagram of the actual drilling trajectory and the designed side-drilling trajectory in Example 1.

[0015] Figure 5 This is a diagram showing the center distance between the actual drilling trajectory and the designed side-drilling trajectory in Example 1.

[0016] Figure 6 This is a northward projection of the actual drilling trajectory and the designed side-drilling trajectory in Example 1.

[0017] Figure 7 This is an eastward projection of the actual drilling trajectory and the designed side-drilling trajectory in Example 1.

[0018] Figure 8 This is a horizontal projection diagram of the actual drilling trajectory and the designed side-drilling trajectory in Example 1.

[0019] Figure 9 This is a diagram showing the location relationship of the wellbore trajectory.

[0020] Figure 10 This is the center distance diagram in Example 1.

[0021] Figure 11 This is the horizontal projection diagram in Example 1.

[0022] Explanation of reference numerals in the attached figures: 1. Marker head; 2. Secondary marker head; 3. Anthracene oil; 4. Clean water; 5. Clay cementing section; 6. Marker rod; 7. Cement cementing section; 8. Marker rod centralizer; 9. Protective pipe centralizer; 10. Protective pipe; 11. Drill wall; 12. Protective pipe tray; 13. Marker bottom embedded section; 14. Pipe shoe. Detailed Implementation

[0023] To make the technical means, creative features, objectives, and effects of this invention readily understandable, the invention is further illustrated below with reference to specific embodiments. Unless otherwise specified, the operating methods, equipment, and raw materials used in the following embodiments are all conventional operating methods. The invention will be further described below with reference to the embodiments.

[0024] Example 1 1. Basic Project Information 1.1. Project Overview Located in Yanjin County, Henan Province, the project involves constructing a ground settlement monitoring network with a bedrock marker group in the northeast corner of the county's People's Park. This network will enable real-time monitoring and transmission of indicators such as soil deformation, groundwater level, and pore water pressure, thus establishing a ground settlement monitoring network system. The site includes 16 marker wells: 1 bedrock marker, 8 layer markers, 4 groundwater level monitoring wells, and 3 pore water pressure monitoring wells.

[0025] 1.2 Stratigraphic Conditions

[0026] The project area belongs to the North China stratigraphic region. The strata, from top to bottom, consist of the Quaternary Holocene (Qh, 12.5m), Upper Pleistocene (Qp3, 66.0m), Middle Pleistocene (Qp2, 91m), and Lower Pleistocene (Qp1, 129.2m), and the Neogene Pliocene (N2, 495m) and Miocene (N1, not penetrated). The target bedrock stratum for benchmarking is located in the Guantao Formation sandstone at the bottom of the Miocene.

[0027] 1.3 Bedrock Marker Design Scheme like Figure 1As shown, the bedrock marker body mainly consists of five parts: a protective pipe, a marker rod, a stabilizer, a marker head (observation marker point), and a marker base. The designed borehole depth is 1865m. Drilling is conducted in three sections: the first section has a diameter of 450mm and a depth of 0–204m; the second section has a diameter of 311mm and a depth of 204–1866m; and the third section has a diameter of 152mm and a depth of 1866–1876m. The marker base must penetrate more than 5m into stable bedrock (sandstone layer), and the protective pipe must penetrate more than 2m into stable bedrock or stable strata to ensure the measuring marker rod is not disturbed. The annular gap between the borehole wall and the protective pipe is controlled between 65 and 150mm. The borehole is vertical. For every 50m of drilling, the borehole apex angle increases by no more than 0.2°, with the final apex angle not exceeding 1.0°. The borehole depth is corrected every 100m of drilling, and the depth deviation should not exceed ±0.5‰. The outer and inner protective casings of the bedrock markers are both N80 standard oil casings. The marker poles are also N80 standard oil casings with a pagoda-shaped structure, and their length is divided according to the 95-90 rule. The protective casings have a double-layer structure: the outer protective casing has an outer diameter of Φ339.7mm, a wall thickness of 9.65mm, and a depth of 0~204m; the inner protective casing has an outer diameter of Φ177.8mm and a wall thickness of 8.05mm. The marker poles have a "three-tower" structure, with dimensions from bottom to top: Φ89×6.45mm, Φ73×5.51mm, and Φ60×4.83mm.

[0028] 1.4 Construction and Accident Occurrence of Bedrock Markers 1.4.1 Construction status of bedrock markers The ZJ-20 type oil drilling rig was selected for bedrock benchmark drilling. The drill pipe specifications were Φ127mm and Φ114mm, the drill collar specifications were Φ203mm, and the drill bit specifications were Φ450mm, Φ311.1mm, Φ152mm, and φ215.9mm. After the first drilling operation was completed, a 204m long protective casing with an outer diameter of Φ339.7mm and a wall thickness of 9.65mm was run in and cemented. After cementing, a φ215.9mm PDC drill bit + non-magnetic drill collar + φ172mm screw rod + φ114mm drill pipe, along with a drilling rig, was used for the second drilling operation. The plan was to drill to the target formation and then use a Φ311.1mm drill bit for borehole enlargement. Drilling was stopped every 50m to measure and record parameters such as borehole inclination and azimuth.

[0029] 1.4.2 The process of "drill sticking and getting stuck" During the second drilling phase, routine inclination surveys were conducted at a depth of 1659m. After drilling was stopped, the measured depth was 1647.63m, with an inclination angle of 0.04° and an azimuth angle of 1647.54°. After the inclination survey was completed, drilling resumed. It was found that the mud pump was circulating normally, but the drill string could not be raised or lowered, and it could not rotate continuously. Multiple drilling attempts were made, but the situation did not improve. It was initially determined that a "stuck drill string" accident had occurred.

[0030] At the time of the accident, the extruded rock fragments were dark red and brownish-red mudstone, with a small amount of grayish-white and white conglomerate, in flaky form, corresponding to mudstone interbedded with thin layers of fine sand.

[0031] 1.5 Emergency rescue measures and cause analysis after "drill sticking and jamming" 1.5.1 Emergency rescue measures taken The general procedure for handling a stuck drill bit accident includes: using the drill rig winch for strong pulling, soaking with a release agent, using a milling machine to release the stuck bit, and using a vibratory pipe puller to pull it out. After determining that an accident has occurred, the following rescue measures were immediately taken based on the situation at the scene: (1) Try to pull hard

[0032] After an initial assessment that the drill string was stuck, the operators immediately started the winch to attempt to forcefully pull and move the drill string to free it. The winch's maximum pulling force was 1200kN (80% of the drill string's safety limit). After lifting the drill string 3m, it became stuck again. Multiple attempts were made, but it was still impossible to pull it out. Considering the elastic deformation of the drill string, the analysis concluded that the lifting distance was caused by the deformation of the drill string, and that forceful pulling was ineffective in freeing it.

[0033] (2) First soaking in caustic soda solution

[0034] Considering the drilling strata consisted of mudstone interbedded with thin layers of fine sand, an emergency caustic soda solution (pH=12) of 4.2 m³ was prepared using readily available on-site reagents and pumped into the borehole for soaking as a rescue operation. The soaking depth calculation formula is as follows: In the formula V 溶液 R is the volume of caustic soda solution injected into the orifice. 钻头 R is the drill bit radius. 钻具 Where is the radius of the drill bit.

[0035] The initial immersion depth in the caustic soda solution was 159.08 m. After 10 hours, another attempt was made to forcefully pull the object out of the jam, but there was no obvious sign of loosening.

[0036] (3) Second soaking in caustic soda solution

[0037] The initial immersion depth with the caustic soda solution was limited, so a new caustic soda solution was prepared and brought in. 48 hours later, a second 39 m³ caustic soda solution with pH=12 was prepared and pumped into the borehole using a mud pump. The total immersion depth reached 1636.3 m. After 10 hours, another attempt was made to forcefully pull the stuck material out, but there was still no significant loosening. (4) Vibration rescue using shock absorbers Soaking in caustic soda solution had little effect, so a vibratory pulling method was attempted. After 72 hours, a vibrator arrived, was installed, and vibratory action was taken along with a winch pull, but the pulling effect was still minimal.

[0038] (5) High-strength steel wire rope under high tension 96 hours later, the winch was replaced with a higher strength steel wire rope, and another strong pull was used to try to untangle it. The pulling force was close to the rated limit of the winch, but it still did not loosen. The forced pull rescue failed.

[0039] (6) Maintain mud circulation After the high-strength steel wire rope failed to be pulled free, the mud pump continued to work to ensure that the mud in the well could continue to circulate, and continued to try to pull and move the drill string, while waiting for the next rescue measures.

[0040] (7) Milling and unwinding card 144 hours later, the reverse-threaded drill bit arrived. Using a reverse-clamp milling technique to unstick the drill bit, the reverse drill bit was successfully retrieved at a depth of 855m on the first attempt. The reverse-threaded drill bit was lowered again, and after thread alignment, an attempt was made to reverse it. However, the drill bit quickly jammed, the torque increased dramatically, and mud circulation could not be established. It was determined that the drill bit was stuck at this depth. To prevent the reverse-threaded drill bit from sticking to the drill string, it was decided to rotate it clockwise to retrieve the reverse-threaded drill rod.

[0041] 1.5.2 Accident Cause Analysis Even after a stuck drill bit incident, mud circulation can still be established. The stuck drill bit type is determined to be "adhesive stuck drill bit." Mud is squeezed out from between the drill bit and the borehole wall, and mud cake seals the gap between the drill bit and the borehole wall, causing the drill bit to adhere to the borehole wall, resulting in an adhesive stuck drill bit incident. The drill bit was located in a clay layer at the depth of the incident. During the incident handling process, mud circulation was not timely, and water filtered out from the mud entered the clay layer. The mudstone absorbed water and expanded, causing the drill bit to become stuck with a reduced diameter.

[0042] An expert team was organized to conduct a comprehensive assessment of the current situation of the accident. They concluded that the probability of successfully rescuing the stuck drill using existing measures was low, given the urgency of the project schedule. Therefore, an alternative solution was needed.

[0043] 2. Side-drilling rescue plan

[0044] To ensure the completion of the construction task, considering the current situation of the accident, the overall schedule, economic factors, and safety, it was decided to attempt to introduce sidetracking technology from the oil drilling field into the rescue and handling of this accident. The key to the sidetracking scheme is to design the sidetracking trajectory based on the previous actual drilling trajectory, ensuring that the process well tip angle and the final well tip angle meet the technical requirements, and that the designed sidetracking trajectory does not collide with the actual drilling trajectory.

[0045] 2.1 Actual drilling trajectory (1) Actual drilling trajectory data The actual drilling trajectory before the accident is shown in Table 1. It can be seen that in the early stage, for every 50m of drilling, the well top angle increased by no more than 0.2°, and the cumulative well top angle was less than 1°, which met the technical requirements.

[0046] Table 1. Actual Drilling Trajectory Data

[0047] (2) Trajectory data calculation The minimum curvature method is used to convert the well depth (MD), inclination angle (INC), and azimuth angle (AZI) to obtain the three-dimensional X, Y, and Z coordinates, thereby drawing the wellbore trajectory diagram.

[0048] ① Calculate the average well inclination angle and azimuth angle variation

[0049] ② Calculate the scaling factor RF

[0050] When β=0 (straight section of the well), RF=1.

[0051] ③ Calculate coordinate increments ④ Calculate three-dimensional coordinates

[0052]

[0053] ⑤ Actual drilling trajectory diagram as shown Figure 2 As shown.

[0054] 2.2 Side-drilling trajectory design (1) Selection of side drilling points During the rescue phase, 855m of drill string was removed. To ensure that the borehole apex angle and the final borehole apex angle meet the technical requirements, the side-drilling trajectory point was selected in the 700-730m well depth section. The 730-900m section was reserved as a stabilizing section, the 900-950m section as a deflection section, and the depth below 950m as a normal anti-deviation section.

[0055] (2) Trajectory design The actual drilled wellbore has an azimuth range of 241.9°-279.0° at a depth of 700m-730m, with a designed sidetrack azimuth of 147.75°. The maximum inclination in the stabilizing section is 1°. In the decreasing section, the inclination will decrease to 0.8° at 950m, and then gradually decrease to 0°. The minimum separation distance between the actual drilling trajectory and the designed sidetrack trajectory is set to meet the following conditions:

[0056] Table 2 Side Drilling Trajectory Design Data Table

[0057] Design the side-drilling trajectory diagram as follows: Figure 3 As shown.

[0058] 3.3 Collision Avoidance Analysis Interpolation was used to calculate the center distance between the actual drilling trajectory and the designed sidetracking trajectory under constant depth conditions, and a safety threshold was set. Distance ≤ 3m: high collision risk; 3m < distance ≤ 5m: medium risk; 5m < distance: safe. Figure 10 As can be seen, from the stabilizing section to the decreasing section and then back to the stabilizing section, the center distance between the actual drilling trajectory and the designed side-drilling trajectory gradually increases, reaching 5 meters at a depth of 858.78m, which is within the safe threshold range. This ensures that the side-drilling will not collide with any remaining drilling tools or casing in the original borehole, thus avoiding secondary accidents.

[0059] Table 3 Center Distance of Actual Drilling Trajectory and Designed Side-Drilling Trajectory under Iso-Depth Conditions

[0060] The coupling between the actual drilling trajectory and the designed side-drilling trajectory is as follows: Figure 4 As shown.

[0061] The center distance between the actual drilling trajectory and the designed side-drilling trajectory is as follows: Figure 5 As shown.

[0062] The northward projection diagram of the actual drilling trajectory and the designed side-drilling trajectory is shown below. Figure 6 As shown.

[0063] The eastward projection diagram of the actual drilling trajectory and the designed side-drilling trajectory is shown below. Figure 7 As shown.

[0064] Horizontal projection diagram of actual drilling trajectory and designed side-drilling trajectory as shown in the figure Figure 8 As shown.

[0065] Wellbore trajectory location relationship diagram as follows Figure 9 As shown.

[0066] 3. Wellbore stability analysis and sidetracking safety assessment based on numerical simulation 3.1 Establishing the Model and Boundary Conditions To assess the stability of the wellbore and the safety of the wellbore trajectory during sidetracking, a three-dimensional axisymmetric formation model was established using finite element method (FEM) software. The model's vertical range is 0–1660 m, and its radial range is 0–20 m, simulating the main lithological distribution of the formation where the borehole is located. The model uses C3D8 eight-node three-dimensional solid elements to obtain the spatial distribution of stress and deformation around the wellbore.

[0067] The model is constrained at the bottom (Ux=Uy=Uz=0), radially constrained on the sides (Ur=0), and has a free boundary at the top to reflect the natural surface condition. The wellbore radius is designed to be Φ215.9 mm, and the well diameter is 0.108 m. The in-situ stress follows a linear distribution law, with the vertical principal stress increasing linearly with depth, taking a gradient of 22 MPa / km, and the lateral stress coefficient K0=0.7. The borehole pressure is applied based on the hydrostatic pressure distribution calculated according to the drilling mud density of 1.25 g / cm³.

[0068] To ensure computational accuracy, the mesh was refined near the well wall, with a minimum element size of approximately 0.1 m, while larger meshes (0.5–1 m) were used in areas further away from the well wall. The total number of elements in the model mesh was approximately 85,000.

[0069] 3.2 Material constitutive model and parameter setting To accurately reflect the nonlinear mechanical properties of strata, the Drucker–Prager yield criterion was used to simulate the plasticity of soil and rock masses. This model can effectively describe the strain softening characteristics of soil and rock media under shear failure.

[0070] Table 4. Stratigraphic parameters for each region were determined based on measured data from the Yanjin area and typical empirical values ​​from North China.

[0071] Based on the parameter transformation relationship of the Drucker–Prager model:

[0072] The equivalent yield parameters β and d of each stratum are calculated and used for ABAQUS material input.

[0073] 3.3 Operating Conditions and Load Settings To comprehensively analyze the stability of the wellbore at different operational stages, three typical operating conditions were set up: Table 5 Operating Conditions

[0074] The loading method is as follows: Borehole pressure: Based on a mud density of 1.25 g / cm³, the pressure at the bottom of the well is approximately 20.4 MPa. In-situ stress in the formation: Vertical principal stress , Horizontal principal stress ; Side-drilling disturbance load: Local tangential shear stress is applied at a depth of 700 m to simulate drill bit disturbance and contact with the wellbore.

[0075] 3.4 Numerical Simulation Results and Analysis 3.4.1 Principal Stress Distribution Simulation results show that the principal stress near the wellbore exhibits a clear circumferential concentration characteristic. Under drilling shutdown conditions, the maximum principal stress on the outer side of the wellbore is approximately 36 MPa, while the formation stress at greater distances tends to be uniformly distributed. When the mud pressure decreases, the circumferential tensile stress on the wellbore increases significantly, and if the mud density is insufficient, it may cause local wellbore collapse.

[0076] 3.4.2 Distribution of the plastic zone Under side-drilling disturbance conditions, an elliptical plastic zone with a thickness of approximately 0.5 m appeared on the outer edge of the wellbore near 700 m. The plastic zone was mainly concentrated at the intersection of the side-drilling directional section and the old borehole trajectory, but it did not penetrate the wellbore, indicating that the wellbore was generally in a safe state.

[0077] 3.4.3 Displacement Contour Map The maximum radial deformation of the wellbore was approximately 1.1 mm, occurring during the mud pressure reduction phase. The deformation increased slowly with depth, with the bottom displacement slightly higher than the mid-section. This deformation was within acceptable limits and did not trigger shear failure.

[0078] 3.4.4 Safety Factor Analysis Calculate the wellbore safety factor based on the circumferential stress σθ, the borehole pressure pm, and the shear strength τc:

[0079] The results show: During normal drilling, Fs = 2.1; When drilling is stopped and inclination is measured, Fs = 1.35; During the side-drilling disturbance stage, Fs=1.68.

[0080] This indicates that the wellbore remained safe at each stage, and the safety margin in the sidetracking section was sufficient.

[0081] 3.5 Security Assessment and Optimization Recommendations Based on the numerical simulation and field results, the following insights and suggestions can be drawn:

[0082] (1) Wellbore stress characteristics In deep formations, the principal stress concentration in the wellbore is significant, with the circumferential stress being much greater than the radial stress, which is a key factor controlling wellbore stability.

[0083] (2) Stability of side drilling points Simulations show that the stress distribution at the 700 m side-drilling point is uniform, the plastic zone has not been fully formed, and the conditions for side-drilling are met.

[0084] (3) Mud density control When the mud density is below 1.20 g / cm³, the tensile stress on the wellbore increases rapidly. The density should be maintained between 1.25 and 1.30 g / cm³ to maintain pressure balance within the borehole.

[0085] (4) Control parameters of the inclined plane formation process It is recommended to control the drilling pressure to ≤80kN, the pump pressure to ≤5 MPa, and the build-up rate to ≤1.0° / 30 m in order to avoid a sudden increase in wellbore disturbance stress.

[0086] (5) Safety margin for side drilling The fact that the wellbore safety factor remained above 1.5 during sidetracking indicates that the process parameters were designed reasonably and can be promoted and applied in subsequent deep drilling operations.

[0087] 4. Analysis of the implementation and effects of side-drilling 4.1 Construction process control (1) Window opening stage: Due to the formation hardness of 35~40MPa and the cementing quality qualification rate of 92%, the ground anchor directional device is used for window opening. The fixed position error of the directional device is 0.08°. The window is opened by a special milling cone (cutting speed 0.3m / h). The window diameter deviation is ±2mm, the regularity is 98%, and there is no casing damage. (2) Drilling stage: Initial drilling (1649 - 1669m): The structure of “Φ152.40mmHA136 drill bit + 1 drill collar + Φ89mm drill rod” was adopted. The drilling pressure was gradually increased from 5~10kN to 30kN, the rotation speed was 50r / min, and the window was successfully passed without any obstruction. (3) Directional drilling (1669~1789m): Use a 1.50° single-bend power drill, drill pressure 30~50kN, pump pressure 13~15MPa, perform a full measurement every 9m of drilling, adjust the well inclination angle by 0.3°~0.5° / section, when the well inclination angle of the increased section reaches 45°, perform a single-section reaming once (reaming speed 0.5m / min) to remove the cuttings bed (thickness <30mm); (4) Horizontal section drilling (1789~1845m): Connect to LWD system, drill pressure 30~40kN, pump pressure 17~18MPa, perform short start-up and stop operation every 80m, add lubricant (addition amount 0.8%) to reduce the friction coefficient to 0.18, and the cuttings carrying rate to 92%; (5) Drilling in the deflection section (1845~1865m): Gradually reduce the well inclination angle to 0°, reduce the drilling pressure to 20~30kN, and the rotation speed to 55r / min, accurately reach the predetermined position of the bedrock layer, with a depth error of only 0.3m; (6) Mud control: The entire process adopts a three-level purification process, the sand content of the mud is controlled at 0.3%~0.4%, the specific gravity is 1.25~1.35g / cm³, the viscosity is 28~32s, the water loss rate is <8mL / 30min, and there is no hole wall collapse or drill cuttings accumulation.

[0088] A dual MWD + LWD system was activated, collecting one set of well inclination angle, azimuth angle, and lithology data every 5 minutes and transmitting them to the surface control system (response time <10s). During construction, a deviation of 0.8° from the design value was found at 1680m. The tool face angle of the directional drilling tool was immediately adjusted by 3°, and the well inclination angle was corrected to the design range within 20 minutes. The total number of trajectory adjustments was only 3, with an adjustment accuracy of ±0.1°. Figure 2 and Figure 3 .

[0089] 4.2 Side-drilling Implementation Process and Key Technical Measures

[0090] (1) Wellbore backfilling and directional drilling preparation For the section below 700m of the original borehole, P.O42.5 ordinary silicate cement grout was used for backfilling. The actual drilled borehole diameter was 215.9mm, and calculations showed that 6m³ of cement grout could backfill to a height of 163.7m. The cement grout sealing procedure was as follows: a φ114mm drill rod was lowered to a depth of 855m, cement grout was pumped into the borehole, and then the grout was replaced with clean water. After the grout replacement was completed, the drill rod was pulled up, and the cement grout was allowed to set for 72 hours. Considering the cement grout residue on the borehole wall and the actual borehole size, the sealing section was expected to be located between 695m and 855m in depth.

[0091] (2) Control of side drilling process parameters

[0092] Directional drilling was performed at 700 m using a directional bending screw and a measurement while drilling (MWD) system.

[0093] (3) Drill string optimization combination The drilling tools used are a φ215.9mm PDC drill bit + non-magnetic drill collar + φ172mm screw + φ114mm drill pipe.

[0094] During drilling, closely monitor the changes in various parameters such as the weight gauge, pump pressure gauge, and torque; collect rock cuttings once every 0.5m of drilling and confirm whether they contain iron filings.

[0095] 4.3 Monitoring of Sidetracking Process and Wellbore Stability Wellbore stability was assessed by real-time monitoring of bottom hole torque, pump pressure, wellhead discharge rate, and slurry return rate. Results showed that:

[0096] (1) The torque changes smoothly The torque remained within the range of 3.5 to 4.2 kN·m in the 700–1200 m section, without any sticking or sudden changes, indicating that the wellbore did not collapse or the drill string friction did not increase.

[0097] (2) Pump pressure and return slurry stability Pump pressure fluctuations were less than 0.3 MPa, slurry return was stable, and there was no significant leakage; this indicates that the pressure inside the borehole remained balanced and no leakage channels appeared on the well wall.

[0098] (3) The well wall has a good shape. By comparing the logging-while-drilling gamma ray curve with the borehole diameter curve, it was found that the borehole diameter change rate was <3%, indicating that no significant plastic expansion occurred in the borehole wall.

[0099] (4) The stress response of the side drilling section is reasonable Compared with the numerical simulation results above, the measured radial deformation of the well wall in the field was about 0.9 mm, while the simulation result was 1.1 mm, with an error of <20%, which verifies the reliability of the model prediction.

[0100] 4.4 Results of Side Drilling Completion and Marking Results The side-drilling operation lasted 7 days, reaching the designed depth of 1864.30m. Subsequent construction steps include:

[0101] (1) A 2m core was taken using a φ215.9mm core drill bit. The lithology was mainly mudstone, sandy mudstone and fine-grained sandstone. The structure was relatively complete. The core was columnar and short columnar, and the lithology was good.

[0102] (2) Use a Φ311.1mm PDC drill bit + φ172mm screw + 1 Φ203mm non-magnetic drill collar (9m long) + 2 Φ177.8mm drill collars (18m long) + Φ114mm drill rod + Φ133mm active drill rod to enlarge the hole and run in a φ177.8mm oil casing.

[0103] (3) For the section from 240 to 1866.3m, cement slurry with a water-cement ratio of 0.5, ordinary Portland cement P.O42.5, and a density of 1.71 g / cm³ was used for cementing. The amount of cement slurry used was about 73 m³. Cementing was carried out by pumping with a cementing truck. After the cement slurry was injected, the slurry was replaced and pressed at 15 MPa. The well was then shut in and allowed to set. Subsequently, the upper annulus section was backfilled with clay balls for cementing.

[0104] (4) After cementing, a Ф152mm roller cone bit was used to clean the cement plug to 1866.30m, and drilling continued to 1874m. Then, a 152mm diameter core drilling tool was used to verify the final borehole layer. The core depth was 1874.0-1876.0m. The core was a thin layer of purplish-red sandstone interbedded with mudstone in the Guantao Formation (N1g). The benchmark layer was reached, and the benchmark bottom rod and centralizer were installed. The benchmark bottom was fixed with 0.09mm3 of P.042.5 ordinary silicate cement slurry.

[0105] Post-drilling logging data showed that the wellbore trajectory deviation was less than 1.2°, and the sidetracking trajectory matched the design curve well. The wellbore was smooth, with no collapse or diameter reduction. Downhole sonic, gamma, and resistivity logging results indicated that the formation in the sidetracked section was intact, and mud loss was low, meeting design expectations.

[0106] 4.5 Comparison and Analysis of Numerical Simulation Results and Field Verification To verify the rationality of the numerical simulation, the simulation results were compared and analyzed with the field data.

[0107] Table 6 Comparison of Simulated and Measured Data

[0108] The comparison results show that the Drucker-Prager formation model established by the finite element software can accurately reflect the stress state and stability variation of the wellbore. The model predictions are highly consistent with the field monitoring results, indicating that the sidetracking parameter design is reasonable and the construction risks are controllable.

[0109] This embodiment addresses a drill sticking accident during the construction of an 1865 m ultra-deep bedrock benchmark in Yanjin County. A successful rescue was achieved using sidetracking technology, validating its adaptability under complex bedrock conditions. Numerical simulation based on ABAQUS revealed the stress distribution and plastic zone evolution characteristics of the wellbore, indicating good wellbore stability near the sidetracking point. Formation numerical analysis using the Drucker–Prager model showed that the maximum radial deformation of the wellbore was approximately 1.1 mm, with a safety factor consistently higher than 1.5, demonstrating the safety and controllability of the sidetracking process. The engineering practice and simulation results mutually corroborate each other, providing a replicable technical approach for rescue operations in ultra-deep bedrock drilling accidents.

[0110] This embodiment analyzes the failure mechanism of traditional unblocking measures (forced pulling, caustic soda soaking, and shock jacking) through a case study of a drilling accident in a 1865m deep bedrock benchmark borehole. It proposes a segmented treatment scheme: "reverse-threaded drill bit milling unblocking + trajectory anti-collision analysis + cement-sealed side-drilling." By reverse-threading the drill bit and removing 855m of the drill bit, combined with 3D trajectory optimization design and 700m of cement backfilling and curing, accurate drilling to the target stratum was successfully achieved after side-drilling (trajectory deviation <0.5°), shortening the construction period by approximately 30 days. This provides an innovative approach for cross-domain technology transfer in the handling of complex deep-hole accidents.

[0111] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A method for drilling a rescue hole in a kilometer of bedrock, characterized in that, The method comprises the following steps: Step 1: Sidetracking trajectory design and optimization S11: Sidetracking point selection: cement slurry is backfilled to 700-900 m, and after the cement slurry is set, sidetracking is performed, and the sidetracking point is determined at 700-800 m; S12: Trajectory simulation optimization: a three-dimensional trajectory model is established, a trajectory scheme of "build-up section + stable section + drop-off section + anti-inclination section" is designed, and the scheme can avoid the sticking area of the original wellbore through simulation verification; S13: Real-time monitoring and control: the monitoring system is started, and every interval of time, a group of hole inclination, azimuth, and lithology data is collected and transmitted to the ground control system; if the hole inclination deviates from the design value during construction, the tool face angle of the directional drilling tool is immediately adjusted to correct the hole inclination to the design range; Step 2: Construction process control S21: Window opening stage: the whipstock is set at the predetermined depth of the original casing, and the window milling cone combination is used to mill along the whipstock to form a regular window; S22: Drilling stage: the initial build-up drilling tool combination is used to drill out the initial new wellbore at low drilling pressure and low rotation speed to establish a stable wellbore track; S23: Directional drilling stage: the drilling tool with a bend is combined with the measurement while drilling tool, and the sliding drilling and the composite drilling are alternately operated to make the wellbore trajectory increase in inclination and / or twist the azimuth according to the design and accurately guide to the target layer entrance; S24: Horizontal section drilling stage: after entering the target layer, the rotary steering system or the low-angle second screw drilling tool is used, and the real-time geosteering is performed according to the logging while drilling data to keep the hole inclination in the range of 86° to 94° to extend; S25: Drop-off section drilling stage: the drop-off drilling tool combination is used to make the wellbore trajectory smoothly transition from the horizontal state to the design end point hole inclination in the composite drilling mode; S26: Mud control stage: during the whole construction process, the drilling fluid performance is real-time controlled, the control of the drilling fluid performance includes maintaining the high cuttings-carrying property, high lubricity, wellbore stability, and reservoir protection characteristics, and the harmful solid phase is removed through the solid control equipment.

2. A method of kilometer rock marker drilling rescue according to claim 1, characterized in that, In the step S11, the cement slurry adopts 325 cement slurry with a specific gravity of 1.6 g / cm3, and the sidetracking point is determined at 700 m, which can meet the design requirements, the stratum at this position is a thin layer of clay and fine sand, the compressive strength reaches 35-40 MPa, the porosity is less than 15%, and the stability meets the sidetracking requirements.

3. A method of drilling a rescue hole in a kilometer of rock according to claim 1, characterized in that, In the step S12, the Landmark software is used to establish a three-dimensional trajectory model, wherein the build-up section is located at 700-730 m, the hole inclination is increased from 0° to 1°, and the length is 30 m; the stable section is located at 730-900 m, the hole inclination is 1°, and the length is 170 m; the drop-off section is located at 900-950 m, the hole inclination is decreased from 1° to 0.8°, and the length is 50 m; the anti-inclination section is located below 950 m, and the scheme can avoid the sticking area of the original wellbore through ABAQUS simulation verification, the minimum distance from the underground obstacle is 3.02 m, the trajectory deviation is less than 0.3 m, and the anti-collision requirements are met.

4. The method according to claim 1, wherein, In step S13, the monitoring system adopts MWD+LWD dual system, collects a set of inclination, azimuth and lithology data every 5 minutes, and transmits them to the ground control system, with a response time of less than 10 seconds. If the inclination deviates from the designed value during construction, the tool face angle of the directional drilling tool is immediately adjusted to correct the inclination to the designed range.

5. The method according to claim 1, wherein, In step S22, the initial build-up tool combination adopts the structure of "Φ152.40mm HA136 bit+1 column drill collar+Φ89mm drill pipe", the drilling pressure is gradually increased from 5~10kN to 30kN, and the rotating speed is 50r / min.

6. A method of kilometer base rock marker drilling rescue according to claim 1, characterized in that, In step S23, a 1.50° single bend power drill is enabled, the drilling pressure is 30~50kN, the pump pressure is 13~15MPa, a full measurement is performed every 9m of drilling, the inclination adjustment range is 0.3°~0.5° / root, and when the inclination of the build-up section reaches 45°, a single eye is drawn once before a single drill pipe is connected, and the rock debris bed is removed.

7. A method of drilling a rescue hole in a kilometer of rock according to claim 1, characterized in that, In step S24, the LWD system is connected, the drilling pressure is 30~40kN, the pump pressure is 17~18MPa, a short tripping operation is performed every 80m of drilling, the lubricant is added to reduce the friction coefficient to 0.18, and the rock debris carrying rate reaches 92%.

8. A method of kilometer bedrock marker drilling rescue according to claim 1, characterized in that, In step S25, the inclination is gradually reduced to 0°, the drilling pressure is reduced to 20~30kN, the rotating speed is 55r / min, the predetermined position of the bedrock layer is accurately reached, and the depth error is only 0.3m.

9. The method according to claim 1, wherein, In step S26, a three-stage purification process is used throughout the process, the sand content of the mud is controlled at 0.3%~0.4%, the specific gravity is 25~1.35g / cm³, the viscosity is 28~32s, the water loss rate is less than 8mL / 30min, and there is no hole wall collapse and drill cuttings accumulation phenomenon.

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