A method and system for drilling

Abstract

The application relates to the technical field of mineral resource exploration and drilling, in particular to a drilling technology method and a matching system, which comprises the following steps: first, single-pipe hole forming and wall-securing section drilling, large-diameter single-pipe drilling tools are used to pass through the surface loose layer and are lowered into a surface casing for wall securing; second, rope coring and pipe-following section drilling, first-stage rope coring drilling tools are used to penetrate the loose sandstone stratum and are lowered into a PVC straight thread casing for pipe following and isolation of the upper loose sandstone; third, full-hole rope coring section drilling, second-stage rope coring drilling tools are used to combine with a PDC diamond drill bit and a tight anti-back-off drilling tool combination; mud solid control and circulation desanding, a three-stage separation of a vibrating screen, a desander and a desilter is used to control the solid phase content of drilling fluid. The matching system comprises a drilling tool combination module, a casing wall protection module, a hole bottom cutting module, an anti-falling connection module and a mud solid control and circulation system. The application has the effects of effectively solving the hole wall instability in the thick loose sandstone stratum and the high solid phase content of drilling fluid.

Description

Technical Field

[0001] This application relates to the technical field of mineral resource exploration and drilling, and in particular to a drilling technology method and supporting system. Background Technology

[0002] In the field of mineral resource exploration, core drilling is the most direct and reliable technical means of obtaining underground geological information and ore body samples. As exploration work progresses to deeper and more complex strata, the technical challenges faced by drilling operations are becoming increasingly prominent. Especially in the exploration of sandstone-type uranium deposits, boreholes need to successively traverse loose surface overburden, thick, weakly cemented sandstone strata, and deep ore-bearing target layers, making the geological conditions extremely complex.

[0003] Specifically, the loose surface layer has a loose structure and no self-stabilizing ability, making it extremely prone to borehole wall collapse; the thin, poorly cemented sandstone strata in the middle are thick and poorly cemented, and sand particles continuously peel off and mix into the drilling fluid during drilling, causing a sharp increase in the solid content of the drilling fluid, which not only aggravates drill bit wear but also increases the risk of accidents in the borehole; although the deep ore-bearing target layer is relatively intact, there are strict requirements for the core recovery rate, and wireline coring technology is required to improve efficiency.

[0004] Traditional drilling techniques typically employ a single drill string of uniform diameter to penetrate the entire borehole, or only run a single layer of surface casing at the borehole opening, lacking effective wall protection and isolation measures for the thick, loose sandstone formations in the middle. This leads to continuous collapse of loose sandstone during drilling, persistently high solids content in the drilling mud, and frequent accidents such as borehole narrowing, stuck drill bit, and drill string burial, severely impacting construction progress and drilling quality. Furthermore, traditional casing connections often use a clamp-type structure with raised steps on the outer wall, resulting in high frictional resistance during insertion and extraction in sand layers, easily causing casing breakage or formation disturbance. Simultaneously, conventional mud circulation systems lack efficient solids control capabilities, struggling to cope with the large amounts of cuttings generated by sandstone formations, leading to deterioration of drilling fluid performance and further exacerbating the complex conditions within the borehole.

[0005] Therefore, existing drilling techniques are ineffective in dealing with drilling through thick, loose sandstone formations. Summary of the Invention

[0006] To address the aforementioned problems, the purpose of this application is to provide a drilling technology method and supporting system.

[0007] Firstly, this application provides a drilling technology method, which adopts the following technical solution: Includes the following steps: Step S1, single-tube drilling and wall-stabilizing section drilling: use a single-tube drill with the first opening diameter to drill into the loose surface layer to the set depth, and then run in a surface casing of the corresponding diameter for wall stabilization. Step S2, Second-stage wireline coring and casing drilling: In the surface casing, a first-stage wireline coring drill with a diameter smaller than the first opening diameter is used to drill through the loose sandstone strata with poor cementation. During the drilling process, a PVC straight thread casing is simultaneously lowered into the casing until a relatively complete mudstone transition strata are reached. The PVC straight thread casing provides annulus reserves for the next drilling step and isolates the upper loose sandstone. Step S3, three-stage full-hole wireline coring section drilling: inside the PVC straight threaded casing, a second-stage wireline coring tool with a smaller diameter than the first-stage wireline coring tool is used, along with a PDC diamond drill bit and an anti-backlash tight-fitting drill bit combination, to perform wireline coring drilling in the mineral-bearing strata until the final hole is reached. Step S4, mud solids control circulation and sand removal: During the drilling process in steps S2 and S3, the drilling fluid containing a large amount of sandstone solid phase returned from the borehole is introduced into the surface mud solids control system for multi-stage physical separation to reduce the solid phase content of the drilling fluid. Then, the purified drilling fluid is pumped back into the borehole for circulation.

[0008] By adopting the above technical solution, the entire drilling operation is divided into three stages: the first stage, the second stage, and the third stage. The drill bit diameter decreases in each stage, forming a graded variable diameter borehole structure. In the first stage, a large-diameter single-tube drill bit is used to quickly penetrate the loose surface layer and run the surface casing, providing a stable borehole foundation for subsequent drilling. In the second stage, a wireline coring drill bit is used in conjunction with a PVC straight-thread casing, which is run in tandem to effectively isolate the thick loose sandstone strata in the middle, avoiding diameter reduction and stuck drill bit caused by its continuous collapse. At the same time, the inner cavity formed by the PVC casing provides sufficient annular space for the third stage. In the third stage, full-hole wireline coring is used under the protection of the PVC casing, which greatly improves the core recovery rate and drilling efficiency of the target mineralized layer. Mud solids control circulation desanding is carried out throughout the second and third stages. Through multi-stage physical separation, the solid content in the drilling fluid is continuously reduced, the drilling fluid performance is kept stable, and the probability of borehole accidents is reduced.

[0009] Optionally, in the step of synchronously lowering the PVC straight threaded sleeve in step S2, two adjacent PVC sleeves are connected and sealed by a flush straight thread. After the hole is closed in step S3, the PVC straight threaded sleeve is not subjected to a strong pulling operation to avoid damage to the pulling equipment caused by the loose sandstone strata "locking up".

[0010] By adopting the above technical solutions, the casing installation process becomes smoother. After the borehole is completed, forceful pulling of the PVC casing is abandoned. This is because after the PVC casing has remained in the thick, loose sandstone strata for a long time, sand particles will tightly wrap around the casing wall, creating a "lock-in" effect. Forced pulling would not only easily cause the PVC casing to break off and remain inside the borehole, but could also damage the pulling equipment. PVC material is far less expensive than metal casing; leaving it inside the borehole as a permanent protective structure avoids the risks of pulling and simplifies the construction process, achieving a good balance between economy and safety.

[0011] Optionally, in step S3, the drilling parameters are dynamically adjusted based on the real-time formation characteristics encountered during drilling: When drilling into soft, loose, aeolian sandstone formations, drilling parameters that match low drilling pressure and high rotation speed should be used. When drilling into gravel or hard interlayer formations, drilling parameters that match high drilling pressure and low rotation speed are used to reduce impact damage to the cutting teeth of the PDC diamond drill bit.

[0012] By adopting the above technical solutions and dynamically adjusting drilling parameters according to formation characteristics, drilling efficiency can be ensured while effectively protecting the drill bit. In soft, loose, aeolian sandstone formations, low drilling pressure avoids the risk of stuck drill bit due to excessive bit infeed, while high rotational speed ensures sufficient cutting efficiency and cuttings removal capacity. In gravel-bearing or hard interlayer formations, high drilling pressure provides sufficient rock-breaking force, while low rotational speed reduces the impact frequency and energy when PDC cutting teeth collide with hard gravel, reducing cutting tooth breakage and abnormal wear, extending drill bit life, and reducing the number of tripping and tripping operations and construction costs caused by frequent drill bit replacements.

[0013] Optionally, in step S3, the bottom end of the second-stage wireline coring tool is connected to the PDC diamond drill bit with an increasing outer diameter, and a concentric reamer is connected to the upper part of the drill bit to improve the concentricity of the core column and the cuttings discharge velocity by reducing the annular gap between the drill bit and the borehole wall.

[0014] By adopting the above technical solution, the outer diameter gradient of the PDC diamond drill bit is increased, resulting in a hole diameter slightly larger than the outer diameter of the drill pipe, achieving a near-full-hole drilling effect. A concentric reamer is connected to the upper part of the drill bit to further refine the hole wall and ensure the drill string's centering within the hole. The effectively reduced annular space between the drill string and the hole wall makes the drill string operation more stable, reducing deviation and vibration, and improving the concentricity and integrity of the core column, thereby increasing core recovery rate. Furthermore, at the same mud pump rate, the reduced annular space significantly increases the upward flow velocity, facilitating the timely removal of cuttings from the bottom of the hole, reducing repeated grinding of cuttings at the bottom, protecting the drill bit, and improving the cleanliness of the bottom of the hole.

[0015] Optionally, the mud solids control circulation desanding step in step S4 specifically includes: the returned drilling fluid sequentially passes through a vibrating screen, a desander, and a desilter for three-stage solid-liquid separation, the separated rock cuttings and sand particles are discharged, and the purified drilling fluid with the required solid content is introduced into a storage tank to be pumped into the borehole.

[0016] By adopting the above technical solution, the vibrating screen, as the first-stage separation device, first removes larger-diameter rock cuttings; the desander, as the second-stage separation device, uses the principle of cyclone separation to separate medium-diameter sand particles; and the desilter, as the third-stage separation device, further removes fine-diameter muddy solids. This three-stage separation process refines the process step by step, effectively reducing the content of harmful solids in the drilling fluid to acceptable levels. This allows the purified drilling fluid to regain stable performance, avoiding problems such as increased drill string wear, abnormally high pump pressure, and deterioration of borehole cake quality caused by high solid content, thus ensuring the safety and efficiency of the entire drilling process.

[0017] Secondly, the supporting system provided in this application adopts the following technical solution: It includes a drill string assembly module, a casing wall protection module, a bottom hole cutting module, an anti-detachment connection module, and a mud solids control circulation system; The drill string assembly module includes a single-tube drill string, a first-stage wireline coring drill string, and a second-stage wireline coring drill string, with the outer diameter of each drill string decreasing in a gradient manner. The casing wall protection module includes a surface casing and a technical support pipe that is lowered into the loose sandstone strata. The technical support pipe is a PVC straight threaded casing that is spliced ​​together in multiple sections. The bottom hole cutting module is installed at the bottom of the second-stage wireline coring tool and includes a customized PDC diamond drill bit and a reamer assembly adapted to the outer diameter of the drill bit. The anti-loosening connection module is located at the drill pipe joint of the second-stage wireline coring tool and / or at the connection between the drill pipe and the bottom hole cutting module. It is configured as an anti-back-threading tight structure to lock the threads and prevent the drill tool from being uncoiled and falling off due to high torque. The inlet of the mud solids control circulation system is connected to the return slurry pipeline at the borehole opening, and the outlet is connected to the grouting pump inside the borehole. It includes a vibrating screen, a desander, a desilter, and a slurry storage tank connected in sequence by pipelines.

[0018] By adopting the above technical solutions, the gradient decreasing outer diameter design of the drill string assembly module ensures the rationality of the staged diameter change hole structure; the PVC straight threaded casing in the casing wall protection module provides an economical and efficient solution for isolating loose sandstone; the customized PDC diamond drill bit in the bottom hole cutting module, combined with the reamer, enables full-hole coring drilling; the anti-detachment connection module effectively prevents drill string backlash and detachment accidents in loose resistance formations; and the mud solids control circulation system continuously ensures the stability of drilling fluid quality. The systematic integration of each module standardizes and regulates the entire drilling operation process, significantly improving construction efficiency and safety levels.

[0019] Optionally, the anti-detachment connection module includes a male connector, a female connector, and an anti-reverse locking component; after the male connector is screwed into the female connector, the anti-reverse locking component mechanically interferes to block the reverse relative rotation of the male connector and the female connector, thereby preventing the drill bit from being back-locked and detached in loose resistance formations.

[0020] By adopting the above technical solution, once the male connector is screwed into the female connector and the set torque is reached, the anti-reverse locking component locks their relative positions through mechanical interference, preventing the possibility of reverse rotation. When drilling in loose sandstone formations, the torque experienced by the drill string fluctuates significantly, especially during tripping and when encountering resistance, which can easily generate reverse torque. Traditional threaded connections risk slippage and detachment under these conditions. The anti-reverse locking component fundamentally eliminates this hidden danger, ensuring the reliability of the drill string assembly connection under complex working conditions and avoiding retrieval accidents and project delays caused by drill string detachment.

[0021] Optionally, in the bottom hole cutting module, the customized PDC diamond drill bit is an impregnated wireline coring drill bit, and its lip bottom surface is provided with PDC teeth to optimize the cutting area. The reamer assembly is a detachable structure sleeved on the upper part of the drill bit.

[0022] By adopting the above technical solution, the wear resistance of the impregnated drill bit is combined with the high-efficiency cutting performance of the PDC cutting teeth, ensuring both rapid drilling efficiency in sandstone formations and extending the drill bit's service life. The reamer assembly adopts a detachable structure that fits onto the upper part of the drill bit, facilitating replacement and adjustment according to different hole diameter requirements and formation conditions. This improves the applicability and flexibility of the bottom hole cutting module. Simultaneously, the detachable structure facilitates individual replacement and maintenance after wear, reducing overall operating costs.

[0023] Optionally, the two ends of the PVC straight threaded sleeve are respectively provided with matching straight external threads and straight internal threads. After connection, the outer wall surface and the inner wall surface of the PVC straight threaded sleeve are flush and without external protrusion steps, so as to reduce the side wall friction resistance when the pipe is lowered into the sand layer.

[0024] By adopting the above technical solution, the PVC straight-threaded casing features a structure where straight external threads and straight internal threads are machined at both ends of the casing wall, respectively. After connection, the outer and inner wall surfaces are flush, eliminating the protruding steps at the joints of traditional clamp-type casings. When running the casing in thick, loose sandstone formations, the flush outer wall surface significantly reduces the sidewall friction resistance between the casing and the sand layer, making the casing run smoother, reducing the required downforce, and preventing the casing from bending or breaking due to excessive resistance. The flush inner wall surface ensures the unobstructed flow of the casing's internal cavity, providing an unobstructed passage for the three-section drilling tool and avoiding interference from the internal protruding steps during drill string tripping.

[0025] In summary, this application includes at least one of the following beneficial technical effects: 1. By using the first, second, and third stage variable diameter drilling process, combined with the synchronous lowering of PVC straight thread follow pipe into the isolated loose sandstone strata, the technical problems of borehole wall instability and frequent collapse and diameter reduction in the thick loose sandstone strata are systematically solved, enabling drilling to safely and efficiently traverse complex strata to reach the target mineral-bearing layer. 2. By using full-line coring drilling combined with customized PDC diamond drill bits and anti-backlash tight-fitting drill string combinations, the core recovery rate and drilling efficiency of ore-bearing strata were significantly improved, the incidence of in-hole accidents was reduced, and the overall construction cost was lowered, while ensuring the safety of drill string connections. 3. By using a mud solids control circulation system to separate the returned drilling fluid in three stages—vibrating screen, desander, and desilter—the solid content of the drilling fluid during drilling in sandstone formations is effectively controlled, maintaining the long-term stability of the drilling fluid performance, reducing drilling fluid consumption and waste emissions, and achieving both economic and environmental benefits. Attached Figure Description

[0026] Figure 1 This is a schematic diagram of the overall process flow of drilling technology methods; Figure 2 This is a schematic diagram of the overall structural layout of the drilling support system; Figure 3 This is a schematic diagram of the graded variable diameter structure of the bore. Figure 4 This is a partially enlarged schematic diagram of the PVC straight thread sleeve connection structure; Figure 5 This is a cross-sectional view of the hole bottom cutting module structure; Figure 6 This is a cross-sectional view of the anti-detachment connection module structure; Figure 7 This is a schematic diagram of the mud solids control circulation system. In the picture, 1. Single-tube drill string; 2. Surface casing; 3. First-stage wireline coring drill string; 4. PVC straight thread sleeve, 41. straight external thread, 42. straight internal thread; 5. Second-stage wireline coring tool; 6. PDC diamond drill bit; 61. PDC tooth set; 7. Reamer assembly; 8. Anti-detachment connection module; 81. Male connector; 82. Female connector; 83. Anti-reverse locking component; 9. Slurry solids control circulation system; 91. Vibrating screen; 92. Sand remover; 93. Desliming device; 94. Slurry storage tank. 10. Mud pump; 11. Orifice return pipeline; 12. Surface loose layer; 13. Loose sandstone stratum; 14. Mudstone transition stratum; 15. Ore-bearing target layer. Detailed Implementation

[0027] The following is in conjunction with the appendix Figure 1 -Appendix Figure 7 This application will be described in further detail below.

[0028] Example 1: A drilling technique, comprising the following steps: Step S1: Drilling of the single-tube borehole and solid-wall section.

[0029] Reference Figure 1 and Figure 3 A single-tube drill string 1 with an outer diameter of Φ170mm was used to drill through the loose surface layer 12. The loose surface layer 12 is usually a Quaternary overburden layer, mainly composed of unconsolidated sand, gravel, and clay, with a thickness generally ranging from several meters to tens of meters. Due to the loose structure and lack of self-stabilizing ability of this layer, the large-diameter single-tube drill string 1 can quickly penetrate this layer and form a regular borehole wall.

[0030] After drilling reaches the set depth (i.e., a certain distance after penetrating the loose surface layer 12 and entering the relatively stable lower rock layer), drilling is stopped, and the single-tube drill string 1 is retrieved. Then, a surface casing 2, matching the borehole diameter, is lowered. In this embodiment, the outer diameter of the surface casing 2 is Φ168mm, and it is made of steel. After the surface casing 2 is lowered into place, cement slurry is injected into the annulus between the casing and the borehole wall for cementing. After the cement slurry solidifies, a stable borehole foundation is formed, which supports the weight of subsequent drill strings, prevents borehole collapse, and provides a sealed channel for drilling fluid circulation.

[0031] In the specific construction of step S1, the single-tube drill bit 1 uses a conventional alloy drill bit, and the drilling parameters can be adjusted according to the specific lithology of the loose surface layer 12. For loose sandy soil layers, a medium drill pressure (e.g., 3-5 kN) and a medium rotation speed (e.g., 80-120 rpm) are used; for layers with more gravel, the drill pressure is appropriately increased (e.g., 5-8 kN) and the rotation speed is reduced (e.g., 60-80 rpm) to avoid impact damage to the drill bit alloy blades. During drilling, an appropriate mud circulation volume must be maintained to ensure timely removal of rock cuttings and prevent pump blockage or drill bit jamming caused by rock cuttings accumulation.

[0032] Step S2: Second-line wireline coring and drilling of the casing section.

[0033] Reference Figure 1 and Figure 3 Drilling is carried out inside the surface casing 2 using a first-stage wireline coring tool 3 with an outer diameter of Φ122mm. The diameter of the first-stage wireline coring tool 3 is smaller than the borehole diameter of Φ170mm, allowing it to pass smoothly through the inner cavity of the surface casing 2 and begin drilling.

[0034] The main strata drilled during the second phase were loose sandstone strata 13. This stratum is poorly cemented sandstone, mainly composed of aeolian sandstone, with local thin layers of mudstone and gravel layers. The characteristics of this stratum are: weak cementation between sand grains, making it extremely easy to peel off and disintegrate during drilling; large stratum thickness, usually reaching tens or even hundreds of meters; and short borehole wall self-stabilization time, with significant diameter reduction occurring within hours after drilling stops.

[0035] During drilling, PVC straight threaded casing 4 is simultaneously lowered into the borehole. The specific operating procedure is as follows: after each run of the first-stage wireline coring tool 3 (usually 1.5-3m), the inner casing is retrieved and the core is extracted using a wireline retrieval device. Subsequently, PVC straight threaded casing 4 is sequentially inserted from the borehole opening and lowered along with the drilling. The outer diameter of the PVC straight threaded casing 4 is Φ140mm, which allows it to be smoothly lowered into the Φ170mm borehole formed in the first drilling operation.

[0036] Reference Figure 4The connection method between two adjacent PVC straight threaded sleeves 4 is as follows: one end of each PVC sleeve is machined with a straight external thread 41, and the other end is machined with a matching straight internal thread 42. During connection, the straight external thread 41 end of the previous PVC sleeve is screwed into the straight internal thread 42 end of the next PVC sleeve. After tightening, the outer and inner walls of both sleeves are flush, without any protruding steps or clamping structures. This flush straight thread connection structure has the following advantages: First, the outer wall surface is smooth after connection, resulting in low sidewall friction resistance when the casing is lowered into the loose sandstone stratum 13, reducing the required downforce; second, the inner wall surface is smooth, providing an unobstructed passage for the trip drill bit; third, the straight thread connection has good sealing performance, effectively preventing sand particles and groundwater in the loose sandstone stratum 13 from seeping into the casing through the connection gap.

[0037] The PVC straight threaded casing 4 continues to be lowered until it reaches the mudstone transition stratum 14 beneath the loose sandstone stratum 13. The mudstone transition stratum 14 is relatively intact mudstone or silty mudstone, possessing a certain degree of self-stabilizing ability, and can serve as the bottom support layer for the PVC casing. At this point, the PVC straight threaded casing 4 has completely isolated and sealed off the entire upper loose sandstone stratum 13, providing a stable borehole environment for the third drilling stage.

[0038] In this embodiment, after the hole is closed in step S3, no forceful pulling operation is performed on the PVC straight threaded sleeve 4. This is because after the PVC straight threaded sleeve 4 has been placed in the loose sandstone stratum 13 for a long time, the surrounding sand particles tightly wrap around the sleeve wall under the action of formation pressure and mud pressure difference, forming a significant "lock-in" effect. If forcibly pulled out, on the one hand, the tensile strength of the PVC sleeve is limited, and it is easy to break at weak points and remain in the hole, causing difficult-to-handle hole accidents; on the other hand, the forceful pulling process may cause the isolated loose sandstone stratum 13 to collapse again, contaminating the hole. PVC material is inexpensive, and leaving it in the hole will not cause significant economic losses, while it can also continue to play an isolation role as a permanent protective structure.

[0039] Step S3: Drill the core section of the three-hole full-eye rope.

[0040] Reference Figure 1 , Figure 3 and Figure 5 Inside the PVC straight threaded casing 4, a second-stage wireline coring tool 5 with an outer diameter of Φ110mm is used, along with a customized PDC diamond drill bit 6 and an anti-backlash tight-fitting drill tool combination, to perform wireline coring drilling in the ore-bearing target layer 15 until the final hole is reached.

[0041] The ore-bearing target layer 15 is typically a uranium-bearing sandstone layer, mainly composed of medium- to fine-grained sandstone, with localized argillaceous interlayers and gravel layers. This layer is the core target layer for drilling operations, and strict requirements are placed on the core recovery rate and quality. Typically, a core recovery rate of no less than 80% is required, and no less than 95% for key layers.

[0042] Reference Figure 5 The bottom end of the second-stage wireline coring tool 5 is connected to a PDC diamond drill bit 6 with an increasing outer diameter. In this embodiment, the outer diameter of the PDC diamond drill bit 6 is configured as Φ110+1mm (i.e., Φ111mm), +2mm (i.e., Φ112mm), or +3mm (i.e., Φ113mm), which can be selected according to specific formation conditions and coring requirements. The PDC diamond drill bit 6 is an impregnated wireline coring drill bit, and its lip bottom surface is provided with PDC teeth 61 with optimized cutting area design. The impregnated matrix gives the drill bit good wear resistance, while the PDC teeth 61 provide efficient cutting capability. The combination of the two allows the drill bit to drill quickly in sandstone formations and has a long service life.

[0043] A reamer assembly 7 is connected to the upper part of the PDC diamond drill bit 6. The reamer assembly 7 is a detachable structure, fitted onto the drill bit body at the top via threads or snap-fit. The outer diameter of the reamer assembly 7 is the same as or slightly smaller than the outer diameter of the PDC diamond drill bit 6. Its functions are: firstly, to refine and enlarge the hole wall drilled by the drill bit, eliminating any irregularities or slight diameter reductions; secondly, to provide centering and stabilization, ensuring the concentricity of the drill bit within the hole, thereby improving the concentricity and integrity of the core column. The detachable design of the reamer assembly 7 allows for easy replacement based on wear, without requiring the replacement of the entire drill bit assembly.

[0044] By increasing the outer diameter gradient design of the PDC diamond drill bit 6 and cooperating with the reamer assembly 7, the annular space clearance between the drill bit and the borehole wall is effectively reduced, achieving the desired drilling effect. The reduced annular space clearance brings two technical advantages: First, under the same mud pump volume, the upward flow velocity within the annulus is significantly increased, allowing cuttings to be carried out of the bottom of the borehole in a timely manner, reducing cuttings deposition and repeated grinding at the bottom of the borehole, improving borehole cleanliness, and thus improving drilling efficiency and core quality; second, the drill bit operates more stably, with reduced deviation and vibration, and the drill bit's working condition is more uniform, which helps extend the drill bit's life.

[0045] Reference Figure 6At the drill pipe joint of the second-stage wireline coring tool 5 and at the connection between the drill pipe and the bottom-of-hole cutting module, an anti-detachment connection module 8 is installed, configured as an anti-backlash tight-fitting structure. The anti-detachment connection module 8 includes a male connector 81, a female connector 82, and an anti-reverse locking element 83. After the male connector 81 is screwed into the female connector 82, the anti-reverse locking element 83 prevents the reverse relative rotation between the male connector 81 and the female connector 82 through mechanical interference. The anti-reverse locking element 83 can adopt various structural forms such as pin type, snap ring type, or bolt locking type, as long as it can reliably achieve mechanical interference to prevent reverse rotation.

[0046] When drilling through loose sandstone strata 13, the drill string experiences uneven resistance and significant torque fluctuations. Especially when encountering gravel interlayers or localized narrowing, the drill string may momentarily experience large reverse torques. Traditional standard threaded connections risk unraveling under these conditions, potentially leading to the drill string detaching and falling to the bottom of the hole, causing complex retrieval accidents. The anti-detachment connection module 8 fundamentally eliminates this hidden danger, ensuring the reliable connection of the drill string assembly throughout the entire drilling process.

[0047] During the drilling process in step S3, the drilling parameters are dynamically adjusted based on the real-time formation characteristics encountered. Specifically: When drilling into soft, loose, aeolian sandstone formations, the rock strata have poor cementation, low strength, and are prone to sand grain detachment. In this case, a parameter combination that matches low drill pressure (e.g., 2-4 kN) with high drilling speed (e.g., 150-250 rpm) is used. Low drill pressure avoids the risk of stuck drill bit and core breakage caused by excessive drill bit infeed, while high drilling speed ensures sufficient cutting efficiency and linear velocity, enabling the PDC tooth 61 to efficiently cut soft sandstone by shearing. At the same time, the high annular backflow velocity brought about by high drilling speed helps to promptly remove a large amount of detached sand grains.

[0048] When drilling into gravel-bearing or hard interlayer formations, where the rock strata contain relatively hard gravel or well-cemented hard interlayers, a parameter combination matching high drill pressure (e.g., 6-10 kN) and low drilling speed (e.g., 60-100 rpm) is used. High drill pressure provides sufficient axial force to crush and break the hard gravel, while low drilling speed significantly reduces the impact frequency and single impact energy when the PDC cutting teeth 61 collide with the hard gravel, reducing the risk of PDC cutting tooth breakage and abnormal wear, and effectively extending the drill bit's service life.

[0049] Drilling continues until the designed final depth is reached. After the final depth is reached, subsequent work such as logging and sampling is carried out.

[0050] Step S4: Slurry solids control circulation for sand removal.

[0051] Reference Figure 1 and Figure 7During the drilling process in steps S2 and S3, as the drilling continues into the loose sandstone strata 13 and the sandstone layers within the ore-bearing target layer 15, a large amount of rock cuttings and sand particles are returned from the wellhead with the drilling fluid, causing the solid content of the drilling fluid to continuously increase. If effective solid phase control is not implemented, key performance indicators of the drilling fluid, such as density, viscosity, and filtration loss, will deviate from the design range, leading to a series of in-hole problems.

[0052] Therefore, the drilling fluid containing a large amount of sandstone solid phase returned from the wellhead is introduced into the surface mud solid control circulation system 9 through the wellhead return pipeline 11 for multi-stage physical separation to reduce the solid phase content of the drilling fluid.

[0053] The working process of mud solids control circulation system 9 is as follows: First-stage separation – Vibrating screen 91: The returning drilling fluid first passes through vibrating screen 91. Vibrating screen 91 uses a high-frequency vibrating screen to screen the drilling fluid, separating larger rock cuttings (typically larger than 74μm) from the drilling fluid. The separated coarse rock cuttings slide down the screen surface to the waste collection area for discharge, while the drilling fluid that has passed through the screen flows into the mud tank below vibrating screen 91. The mesh size of vibrating screen 91 can be selected and adjusted according to the particle size distribution of the formation rock cuttings to achieve the best separation effect.

[0054] Second-stage separation – Desander 92: The drilling fluid, initially purified by the vibrating screen 91, is pumped from the mud tank to the desander 92. The desander 92 utilizes the principle of cyclone separation, generating a high-speed rotating centrifugal force field within the cyclone chamber. This force throws larger sand particles (typically larger than 44 μm) from the drilling fluid against the cyclone chamber wall and out through the underflow outlet. After treatment by the desander 92, medium and coarse sand particles in the drilling fluid are further removed.

[0055] The third stage of separation—desluber 93: The drilling fluid treated by desander 92 continues into desilber 93. Desilber 93 also uses the principle of cyclone separation, but its cyclone chamber diameter is smaller and its rotation speed is higher, enabling it to separate finer particles of mud solids (typically particles larger than 15-25 μm). After treatment by desilber 93, the content of harmful solids in the drilling fluid is reduced to acceptable levels.

[0056] After the three-stage separation process described above, the purified drilling fluid is temporarily stored in a mud storage tank 94. The mud storage tank 94 has a certain volume, which can buffer and store the purified drilling fluid. Bentonite, polymers, and other treatment agents can be added to the mud storage tank 94 as needed to adjust the drilling fluid's properties. Subsequently, the drilling fluid that meets the required performance standards in the mud storage tank 94 is pumped back into the borehole for circulation using a mud pump 10.

[0057] Solids control and desandering are integrated throughout the second and third drilling phases, forming a closed-loop cycle of "drilling—slurry return—solids control purification—re-injection." This continuous solids control keeps the drilling fluid at its optimal performance, effectively preventing problems such as accelerated drill string wear, abnormal pump pressure increases, and deterioration of borehole cake quality caused by high solids content. Simultaneously, the closed-loop circulation significantly reduces the amount of freshly prepared drilling fluid and the discharge of waste drilling fluid, resulting in significant economic and environmental benefits.

[0058] The implementation principle of this application embodiment is as follows: a systematic graded variable diameter drilling method is formed through a four-step coordinated process: first, large-diameter single-tube borehole solidification; second, wireline coring combined with PVC straight-thread casing to isolate loose sandstone; third, full-hole wireline coring for efficient drilling into the ore-bearing target layer; and fourth, continuous mud solids control and circulation for sand removal. This method, tailored to the geological characteristics of areas covered by thick, loose sandstone strata, organically integrates several key technologies, including borehole stability control, drilling fluid solids management, efficient coring, and safe drilling. This enables drilling to safely and efficiently traverse complex loose strata and obtain high-quality cores from the ore-bearing target layer, achieving a comprehensive effect of improving construction efficiency, reducing accident rates, and controlling costs.

[0059] Example 2: This example discloses a drilling support system for implementing the method described in Example 1, including a drill string assembly module, a casing wall protection module, a bottom hole cutting module, an anti-detachment connection module 8, and a mud solids control circulation system 9.

[0060] Specifically, refer to Figure 2 and Figure 3 The drill string assembly module includes a single-tube drill string 1, a first-stage wireline coring drill string 3, and a second-stage wireline coring drill string 5. The outer diameter of each drill string decreases in a gradient to adapt to the graded diameter hole structure.

[0061] The single-tube drill bit 1 has an outer diameter of Φ170mm and is used to drill into the loose surface layer 12 to form a single borehole. The single-tube drill bit 1 is composed of a conventional alloy drill bit and a standard drill rod.

[0062] The first-stage wireline coring tool 3 has an outer diameter of Φ122mm and is used to drill into loose sandstone formations 13 within the surface casing 2. The first-stage wireline coring tool 3 employs a standard wireline coring system, including an outer casing assembly, an inner casing assembly, a retrieval tool, and a winch. The advantage of the wireline coring system is that it eliminates the need to raise and lower the drill pipe during coring; the inner casing can be pulled out of the borehole via a wire rope for coring and replacement, significantly improving drilling efficiency.

[0063] The second-stage wireline coring tool 5 has an outer diameter of Φ110mm and is used to drill into the ore-bearing target layer 15 inside the PVC straight thread casing 4. The second-stage wireline coring tool 5 also uses a wireline coring system, but its diameter is smaller than that of the second-stage tool, and it works with the bottom-cutting module to achieve full-hole coring.

[0064] The outer diameter gradient of each drilling tool is as follows: Φ170mm (first stage) → Φ122mm (second stage) → Φ110mm (third stage), which ensures the rationality of the hole structure with graded diameter changes, and the drilling tools at each stage can pass smoothly and work within the hole diameter or casing formed in the previous stage.

[0065] Specifically, refer to Figure 2 , Figure 3 and Figure 4 The casing wall protection module includes the surface casing 2 and the technical casing.

[0066] Surface casing 2 is a steel casing with an outer diameter of Φ168mm, which is lowered into a Φ170mm borehole formed in the well, leaving a 2mm annulus between it and the borehole wall for cementing. The main functions of surface casing 2 are to fix the borehole section, prevent the collapse of the loose surface layer 12, support the weight of subsequent drilling tools, and provide a sealing for drilling fluid circulation.

[0067] The technical casing is a multi-segment spliced ​​PVC straight threaded casing 4 with an outer diameter of Φ140mm. The PVC straight threaded casing 4 is simultaneously lowered into the loose sandstone stratum 13 during the second drilling operation until it reaches the mudstone transition stratum 14.

[0068] Reference Figure 4 Each PVC straight threaded sleeve 4 has a straight external thread 41 machined on one end of its tube wall and a matching straight internal thread 42 machined on the other end. The machining accuracy of the straight thread meets the sealing requirements, and the connection is tight after the threads are screwed on. The outer and inner wall surfaces of the connected PVC straight threaded sleeve 4 are flush and transitioned without any external or internal protrusions.

[0069] PVC material possesses the following characteristics suitable for technical casing installation: firstly, it is lightweight, facilitating on-site handling and operation; secondly, it is corrosion-resistant, unaffected by drilling fluid and groundwater; thirdly, it is inexpensive, causing no significant economic loss when placed in the borehole; and fourthly, it has a certain degree of flexibility, allowing it to adapt to minor changes in borehole diameter during casing installation without becoming brittle. The wall thickness of the PVC straight thread casing 4 has been calculated to withstand the lateral pressure of the loose sandstone formation 13 without crushing or deforming, while its inner diameter meets the space requirements for the smooth passage of the Φ110mm three-section drilling tool and the circulation of drilling fluid.

[0070] Specifically, refer to Figure 5The bottom hole cutting module is installed at the bottom of the second-stage wireline coring tool 5, and includes a customized PDC diamond drill bit 6 and a reamer assembly 7 adapted to its outer diameter.

[0071] The customized PDC diamond drill bit 6 is a plugged wireline coring drill bit. Its matrix is ​​manufactured using a plugged diamond process, resulting in excellent wear resistance. The drill bit features PDC tooth rows 61 with optimized cutting area design on the lip surface. These PDC tooth rows 61 are made of polycrystalline diamond composite sheets, offering extremely high cutting efficiency. The optimized arrangement of the PDC tooth rows 61 on the lip surface ensures that each tooth has a uniform cutting area and consistent depth of cut, preventing uneven wear and core deviation caused by localized over-cutting.

[0072] The customized PDC diamond drill bit 6 can be configured with an outer diameter of Φ111mm (+1mm), Φ112mm (+2mm), or Φ113mm (+3mm), which is a gradient increase of 1-3mm from the standard outer diameter of the second-stage wireline coring tool 5 (Φ110mm). This gradient increase in outer diameter results in a hole diameter slightly larger than the drill pipe's outer diameter, creating a drilling effect. The specific choice of +1mm, +2mm, or +3mm depends on the lithology, hardness, and integrity of the target layer: for harder and more intact sandstone layers, +1mm or +2mm can be used to achieve a tighter, full-hole effect; for strata with more gravel or well-developed bedding, +2mm or +3mm is preferable to allow for a slightly larger annular space to ensure smooth cuttings removal.

[0073] The reamer assembly 7 is a detachable structure, fitted onto the drill bit body above the PDC diamond drill bit 6 via a threaded connection or a snap-fit ​​mechanism. The outer circumferential surface of the reamer assembly 7 is inlaid with carbide blocks or diamond composite sheets, providing the ability to dress the hole wall and enlarge the hole. The outer diameter of the reamer assembly 7 is matched to the outer diameter of the PDC diamond drill bit 6. Its main functions include: dressing the hole wall drilled by the drill bit, eliminating irregular shapes; providing centering guidance for the drill bit within the hole, maintaining drill bit concentricity; and enlarging narrowed sections during drill bit lifting, reducing the risk of obstruction in subsequent drill runs. The detachable design of the reamer assembly 7 allows for individual replacement based on wear levels without disassembling the entire bottom hole cutting module.

[0074] Specifically, refer to Figure 6 The anti-detachment connection module 8 is located at the drill pipe joint of the second-stage wireline coring tool 5 and / or at the connection between the drill pipe and the bottom hole cutting module. It is configured as an anti-back-thread tight-fitting structure to lock the threads and prevent the drill tool from being uncoiled and detached due to high torque.

[0075] The anti-detachment connection module 8 includes a male connector 81, a female connector 82, and an anti-retrace locking component 83. The male connector 81 and the female connector 82 are respectively machined on the ends of two adjacent drill rod sections or on the connection end face between the drill rod and the bottom hole cutting module, and are connected by standard threads. After the male connector 81 is screwed into the female connector 82 and tightened to the set torque, the anti-retrace locking component 83 is installed in place.

[0076] The anti-reverse locking element 83 works by mechanically interfering with the reverse relative rotation between the male connector 81 and the female connector 82. Specifically, the anti-reverse locking element 83 can adopt one or more of the following structural forms: (1) Pin locking type: Corresponding pin holes are provided on the mating surfaces of male connector 81 and female connector 82. After male connector 81 is screwed into place, locking pins are passed through the corresponding pin holes of both and fixed. The shear strength of the pins is sufficient to resist the reverse torque.

[0077] (2) Snap ring locking type: A ring groove is provided on the outer circumferential surface of the female connector 82. After the male connector 81 is screwed into place, the elastic snap ring is snapped into the ring groove. The end of the snap ring forms axial interference with the end face of the male connector 81, preventing the male connector 81 from retracting in the opposite direction.

[0078] (3) Bolt locking type: Radial bolt holes are provided at the connection between male connector 81 and female connector 82. After screwing into place, locking bolts are screwed in, and the end of the bolt is pressed against the mating surface to form friction locking.

[0079] Regardless of the specific structural form adopted, the anti-reverse locking component 83 can form a reliable mechanical interference lock after the male connector 81 and the female connector 82 are screwed into place, effectively preventing the drill bit from being pulled back and falling off due to torque fluctuations in loose resistance formations.

[0080] Specifically, refer to Figure 7 The inlet of the mud solids circulation system 9 is connected to the borehole opening through the return mud pipe 11, and the outlet is connected to the mud pump 10 through a pipe. The mud pump 10 pumps the purified drilling fluid back into the borehole for circulation.

[0081] The mud solids control circulation system 9 includes a vibrating screen 91, a desander 92, a desilter 93, and a slurry storage tank 94 connected in sequence by pipelines.

[0082] Vibrating screen 91 is a high-frequency vibrating screen, located at the very front of the mud solids circulation system 9, receiving sand-laden drilling fluid from the wellhead return pipe 11. Vibrating screen 91 is equipped with multiple replaceable screens, the mesh size of which can be selected according to the formation cuttings particle size. Through high-frequency vibration, the vibrating screen 91 causes the drilling fluid to flow through the screen into the mud tank below, while cuttings particles larger than the screen mesh size are trapped on the screen surface and slide down along the vibration direction to the waste collection area for discharge.

[0083] The desander 92 is located downstream of the vibrating screen 91 and is connected to the mud tank below the vibrating screen 91 via a pipeline. The desander 92 includes a sand pump and a hydrocyclone assembly. The sand pump pumps the drilling fluid, which has been preliminarily purified by the vibrating screen 91, to the hydrocyclone assembly, which uses the principle of centrifugal separation to separate and discharge sand particles with a diameter greater than approximately 44 μm in the drilling fluid.

[0084] The desilter 93 is located downstream of the desander 92 and is connected to the outlet end of the desander 92 via a pipeline. The desilter 93 also includes a pump and a hydrocyclone assembly, but its hydrocyclones have a smaller diameter (usually around 100 mm) and a higher rotation speed, enabling it to separate finer solid particles with a diameter greater than approximately 15-25 μm.

[0085] The slurry storage tank 94 is located downstream of the desilter 93 and receives the qualified drilling fluid after three-stage separation and purification. The slurry storage tank 94 has sufficient volume for buffer storage, and a stirring device can be installed inside to maintain the homogeneity of the drilling fluid. Drilling fluid performance testing and chemical addition can also be performed at the slurry storage tank 94 as needed to ensure that the various performance indicators of the drilling fluid pumped into the borehole meet the requirements.

[0086] The mud pump 10 is located downstream of the mud storage tank 94. It draws purified drilling fluid from the mud storage tank 94 through pipelines and pumps it into the borehole at a set pump rate and pressure, completing a complete closed-loop cycle of "drilling cuttings generated in the borehole → sand-bearing drilling fluid returned from the borehole opening → coarse screening by vibrating screen → sand removal by desander → mud removal by desilter → storage and preparation in the mud storage tank → re-injection into the borehole by mud pump".

[0087] The implementation principle of this application embodiment is as follows: a complete drilling system is formed through the systematic integration and coordinated operation of five major modules: drill string assembly module, casing wall protection module, bottom hole cutting module, anti-detachment connection module, and mud solids control circulation system. The drill string assembly module provides a graded decreasing drill string sequence with varying diameters; the casing wall protection module solves the wall protection problems of the loose surface layer and the middle loose sandstone strata through surface casing and PVC straight threaded casing, respectively; the bottom hole cutting module achieves efficient full-hole coring through customized PDC diamond drill bits and reamer assemblies; the anti-detachment connection module ensures the reliability of drill string connections under complex working conditions; and the mud solids control circulation system continuously controls the drilling fluid solids content to maintain stability. Each module has a clear function and compatible interfaces, jointly supporting the implementation of the graded variable diameter drilling method described in Embodiment 1, enabling drilling operations in areas covered by thick loose sandstone strata to be completed safely, efficiently, and economically.

[0088] The embodiments described in this specific implementation are preferred embodiments of this application and are not intended to limit the scope of protection of this application. Identical components are represented by the same reference numerals. Therefore, all equivalent changes made to the structure, shape, and principle of this application should be covered within the scope of protection of this application.

Claims

1. A drilling technique, characterized in that, Includes the following steps: Step S1, drilling of the single-tube borehole and solidification section: using a single-tube drill bit (1) with the first borehole diameter to drill into the loose surface layer (12) to the set depth, and then inserting a surface casing (2) with the corresponding diameter to solidify the wall. Step S2, second-stage wireline coring and casing section drilling: In the surface casing (2), a first-stage wireline coring tool (3) with a diameter smaller than the first opening diameter is used to drill through the loose sandstone strata (13) with poor cementation. During the drilling process, a PVC straight thread casing (4) is simultaneously lowered into the casing until a relatively complete mudstone transition strata (14) is reached. The PVC straight thread casing (4) provides annular reserves for the next drilling step and isolates the upper loose sandstone. Step S3, three-way full-hole wireline coring section drilling: inside the PVC straight threaded sleeve (4), a second-stage wireline coring tool (5) with a diameter smaller than the first-stage wireline coring tool (3) is used, along with a PDC diamond drill bit (6) and an anti-backlash tight-fitting drill bit combination, to perform wireline coring drilling in the mineral-bearing strata until the final hole is reached. Step S4, mud solids control circulation and sand removal: During the drilling process in steps S2 and S3, the drilling fluid containing a large amount of sandstone solid phase returned from the borehole is introduced into the surface mud solids control system for multi-stage physical separation to reduce the solid phase content of the drilling fluid. Then, the purified drilling fluid is pumped back into the borehole for circulation.

2. The drilling technique method according to claim 1, characterized in that, In step S2, the PVC straight threaded sleeve (4) is inserted synchronously. The two adjacent PVC sleeves are connected and sealed by a flush straight thread. After the hole is closed in step S3, the PVC straight threaded sleeve (4) is not pulled out forcefully to avoid damage to the pipe pulling equipment caused by the loose sandstone strata (13) "locking up".

3. The drilling technique method according to claim 1, characterized in that, In step S3, drilling parameters are dynamically adjusted based on the real-time formation characteristics encountered during drilling: When drilling into soft, loose, aeolian sandstone formations, drilling parameters that match low drilling pressure and high rotation speed should be used. When drilling into gravel or hard interlayer formations, high drilling pressure and low rotation speed are used to reduce the impact damage to the cutting teeth of the PDC diamond drill bit (6).

4. The drilling technique method according to claim 1, characterized in that, In step S3, the bottom end of the second-stage wireline coring tool (5) is connected to the PDC diamond drill bit (6) with an increasing outer diameter, and a concentric reamer is connected to the upper part of the drill bit. By reducing the annular gap between the drill bit and the borehole wall, the concentricity of the core column and the cuttings discharge velocity are improved.

5. The drilling technique method according to claim 1, characterized in that, The mud solids control circulation desanding step described in step S4 specifically includes: the returned drilling fluid passes through a vibrating screen (91), a desander (92) and a mud desander (93) in sequence for three-stage solid-liquid separation, the separated rock cuttings and sand particles are discharged, and the drilling fluid with the purified solid content meeting the standard is introduced into the slurry tank (94) to be pumped into the borehole.

6. A drilling support system for implementing the method according to any one of claims 1-5, characterized in that, It includes a drill string assembly module, a casing wall protection module, a bottom hole cutting module, an anti-detachment connection module (8), and a mud solids control circulation system (9). The drill assembly module includes a single-tube drill (1), a first-stage wireline coring drill (3), and a second-stage wireline coring drill (5), with the outer diameter of each drill decreasing in a gradient. The casing wall module includes a surface casing (2) and a technical support pipe that is inserted into the loose sandstone stratum (13). The technical support pipe is a PVC straight threaded casing (4) spliced ​​together from multiple sections. The bottom cutting module is installed at the bottom of the second-stage wireline coring tool (5) and includes a customized PDC diamond drill bit (6) and a reamer assembly (7) adapted to the outer diameter of the drill bit. The anti-loosening connection module (8) is set at the drill rod joint of the second-stage wireline coring tool (5) and / or at the connection between the drill rod and the bottom hole cutting module. It is configured as an anti-back-threading tight structure to lock the threads and prevent the drill tool from being uncoiled and falling off due to high torque. The inlet end of the mud solids control circulation system (9) is connected to the slurry return pipeline (11) at the borehole opening, and the outlet end is connected to the grouting pump in the borehole. It includes a vibrating screen (91), a desander (92), a mud remover (93), and a slurry storage tank (94) connected in sequence by pipelines.

7. The supporting system according to claim 6, characterized in that, The anti-detachment connection module (8) includes a male connector (81), a female connector (82), and an anti-reverse locking component (83). After the male connector (81) is screwed into the female connector (82), the anti-reverse locking component (83) mechanically interferes to block the reverse relative rotation of the male connector (81) and the female connector (82), thereby preventing the drill bit from being derailed and detached in loose resistance formations.

8. The supporting system according to claim 6, characterized in that, In the bottom hole cutting module, the customized PDC diamond drill bit (6) is a wire-insulated coring drill bit with PDC teeth (61) on its lip bottom surface to optimize the cutting area. The reamer assembly (7) is a detachable structure sleeved on the upper part of the drill bit.

9. The supporting system according to claim 6, characterized in that, The PVC straight threaded sleeve (4) has matching straight threaded external thread (41) and straight threaded internal thread (42) at both ends of the pipe wall. The outer wall surface and the inner wall surface of the connected PVC straight threaded sleeve (4) are flush and without any protruding steps, so as to reduce the side wall friction resistance when the pipe is lowered into the sand layer.

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