Large fracture, fault plugging method

Abstract

The present application relates to the technical field of leak stopping in oil drilling, in particular to a method for stopping leakage of large cracks and faults, comprising the following steps: preparing a mixed filling material comprising first, second and third porous materials with different particle sizes; preparing the mixed filling material into a filling slurry with a volume-mass ratio of 25%-40%; lowering a drilling assembly to 5-10 m above the leakage layer, injecting the filling slurry, and raising the drilling assembly to 50-100 m above the liquid level of the filling slurry, and waiting for 1-2 hours; lowering the drilling assembly to the sand face, flushing sand at a rate of 5-15 L / s, flushing the remaining filling slurry into the leakage layer, and repeating the operation until the mixed filling material forms an effective throat in the leakage channel; and stopping leakage by using a bridging leak stopping slurry until the problem beyond the bridging leak stopping range is solved, and the leak stopping is completed. The present application adopts a leak stopping method of composite bridging and stopping process for the leakage channel of cracks or faults with an opening greater than 20 mm, and solves the problem of malignant leakage beyond the bridging leak stopping range.

Description

Technical Field

[0001] This invention relates to the field of plugging technology in oil drilling, specifically to a method for plugging large fractures and faults. Background Technology

[0002] Well leakage is a major problem restricting efficient drilling. In major oilfields, well leakage treatment accounts for over 50% of all complex and time-consuming incidents. While large fractures and fault-related severe leakage wells account for less than 25% of all leakage wells, the time and drilling fluid losses they cause both exceed 60% of the total leakage loss. Therefore, controlling large fractures and fault-related severe leakage is of paramount importance in plugging operations. Currently used plugging technologies mainly include bridging plugging and consolidation plugging. Bridging plugging requires the plugging material to bridge at the throat of the leakage channel, and the plugging material size must match the formation leakage channel size; typically, the bridging material particle size is less than 15mm. Consolidation plugging mainly presents problems related to retention and safety. Conventional consolidation plugging slurries are easily replaced or diluted by water within the leakage channel, making it difficult to form a continuous and effective consolidation plug within the leakage channel and wellbore. The success rate of sealing large cracks and faults is low, mainly because the leakage channels are too large. In particular, some cracks or faults with an opening greater than 20mm have long leakage channels that do not have obvious throats, and there is currently no efficient sealing method.

[0003] Literature review revealed that invention patent CN106281272B provides a bridging and plugging agent for fractured reservoirs and its preparation method. This bridging and plugging agent comprises bridging materials, calcium carbonate particles, bitumen powder, and acid-soluble fibers. It is suitable for plugging fractured leaks with a width of 1–5 mm, has a pressure resistance of up to 15 MPa, and an acid solubility rate exceeding 70%. Furthermore, after acid treatment, the non-acid-soluble rigid particles can prevent stress-sensitive damage to the reservoir, effectively protecting oil and gas reservoirs. However, this bridging and plugging agent is only applicable to fractured leaks with a width of 1–5 mm, limiting its application. Additionally, its bridging materials are quartz sand and / or ceramsite, which are spherical in shape and do not easily remain in the leak channels, making bridging difficult. Invention patent CN115806808A provides a bridging and plugging method that uses a bridging and plugging formula containing slag to form a primary sealing layer within the leak channel. An alkaline solution is then injected to activate the slag in the sealing layer, solidifying the entire sealing layer into a unified whole and improving its resistance to backflow. The sealing layer formed by this method has a backflow resistance greater than 6 MPa, which is significantly improved compared to the backflow resistance of sealing layers formed by conventional bridging methods. This invention primarily addresses the problems of backflow and re-leakage associated with conventional bridging methods. However, due to the limitations of conventional bridging principles, it can only solve leakage channels within 10 mm. Furthermore, the slag used in this invention is powder, and the principle employed is to activate its chemical properties with a strong alkali to achieve final consolidation. Currently, there are no directly reported technologies for sealing leakage channels in cracks or faults with an aperture greater than 20 mm using a composite bridging process. Summary of the Invention

[0004] Based on this, the present invention proposes a method for plugging large cracks and faults with leakage channels larger than 20 mm in size. The first step is to construct the throat of the large crack or fault leakage channel using a filling slurry composed of mineral materials with different particle sizes and porous properties. The second step is to seal the leakage channel using a bridging slurry.

[0005] According to a first aspect of the present invention, a method for sealing large cracks and faults is provided, comprising the following steps:

[0006] Prepare a mixed filling material comprising a first porous material, a second porous material, and a third porous material with different particle sizes;

[0007] The mixed filler material is formulated into a filler slurry with a volume-to-mass ratio of 25%-40%;

[0008] Lower the drill string assembly to 5-10m above the leaking layer, inject the filling slurry, pull the drill string to 50-100m above the filling slurry surface, and wait for 1-2 hours for plugging.

[0009] The drill string assembly is lowered to probe the sand surface, and sand is flushed at a rate of 5-15 L / s. All the remaining filling slurry is flushed into the leaking layer. The operation is repeated until the mixed filling material forms an effective throat in the leakage channel.

[0010] The sealing process is completed when bridging grout is used to plug leaks beyond the scope of bridging.

[0011] According to an embodiment of the present invention, the first porous material is volcanic rock particles and / or slag particles with a particle size of 1-3 mm;

[0012] The second porous material is volcanic rock particles and / or slag particles with a particle size of 3-5 mm;

[0013] The third porous material is volcanic rock particles and / or slag particles with a particle size of 5-8 mm.

[0014] The porosity of the first porous material, the second porous material, and the third porous material is 15-45%.

[0015] According to an embodiment of the present invention, the filling slurry comprises well slurry and mixed filling material in a volume ratio of 3:1;

[0016] The density of the well slurry is 1.72 g / cm³. 3 ;

[0017] The mass ratio of the first porous material, the second porous material, and the third porous material in the mixed filler material is 1:2:1.

[0018] According to an embodiment of the present invention, the step of flushing all the remaining filler grout into the drain layer includes: injecting 10-15m of filler grout each time. 3 Repeat the operation multiple times until the mineral material forms an effective throat in the leakage channel.

[0019] According to an embodiment of the present invention, the effective throat has the characteristics of both throttling and non-blocking, creating conditions for subsequent bridging materials to bridge within the leakage channel.

[0020] According to an embodiment of the present invention, the drilling fluid circulation tank for preparing the filling slurry should have a volume not exceeding 20m³. 3 It can be completely isolated from other circulating tanks, the drilling fluid pump can be directly filled with water, the weight pump can be directly fed with materials, and the agitator is intact.

[0021] According to an embodiment of the present invention, the bridging sealant comprises materials with a density of 1.15 g / cm³. 3 Well slurry and mixed nutshell materials of different particle sizes;

[0022] The mixed shell material includes shell material with a particle size of 1-3 mm, shell material with a particle size of 3-5 mm, shell material with a particle size of 5-8 mm, and shell material with a particle size of 10-15 mm.

[0023] The bridging and sealing slurry also includes sepiolite wool with a particle size of 3-6 mm, sawdust and cottonseed with a particle size of 0.5-1 mm, and polypropylene fiber.

[0024] According to an embodiment of the present invention, the method for preparing the bridge plugging grout includes: in a container with a total volume of 60m³ 3 Pour 40m into the circulating tank. 3 Well slurry, density 1.15 g / cm³ 3 Adjust the viscosity of the funnel to 68s, and add the mixed nut shell material, sepiolite wool, sawdust, cottonseed and polypropylene fiber in sequence according to the formula. Keep the stirrer and weight pump running continuously during the preparation.

[0025] According to an embodiment of the present invention, the filling slurry is prepared in a volume of 20m³. 3 Pour 15m into the circulating tank. 3 The well slurry density was increased to 1.72 g / cm³. 3 Adjust the viscosity of the funnel to 88s, and add the first porous material, the second porous material and the third porous material in sequence according to the formula. Keep the stirrer and the weight pump running continuously during the preparation.

[0026] According to an embodiment of the present invention, the step of lowering the drill string assembly to 5-10m above the leaking layer, injecting the filling slurry, pulling the drill string to 50-100m above the filling slurry surface, and waiting for plugging to occur for 1-2 hours includes:

[0027] The drill string assembly was lowered to the bottom of the well, and the pump was started at a displacement of 2m³ / h. 3 Circulate for 10 minutes at a rate of / min, and no slurry returns to the wellhead;

[0028] Pump in the filling slurry and allow it to stand still for plugging: Pull the drill string assembly to a depth of 5-10m above the leaking zone, using a drilling fluid pump at a displacement of 1.5m³ / min. 3 Pumping filling slurry at a speed of / min, with no slurry return throughout the process; monitoring the annular fluid level, pulling the drill string to 50-100m above the filling slurry level, and waiting for plugging to proceed for 1-2 hours;

[0029] Drill down to the leaking layer. If there is no residual volcanic rock in the wellbore, repeat the above steps of pumping in filling slurry and waiting for the blockage to occur until the drill string assembly encounters resistance when drilling down to the leaking layer.

[0030] According to an embodiment of the present invention, the sealing process using bridging grout until the problem exceeds the scope of bridging sealing is completed includes:

[0031] The drill string assembly is pulled up to 5-10m above the leaky zone, using a drilling fluid pump at a displacement of 1m³ / min. 3 / min, pump in the bridging and plugging slurry;

[0032] Drill to a depth of 50-100m above the grout level, wait 6 hours for plugging, then drill down in sections to circulate the bridging grout until it reaches the bottom. Gradually increase the flow rate to 45L / s for circulation without leakage, and the plugging is successful.

[0033] According to an embodiment of the present invention, the step of lowering the drill string assembly to probe the sand surface, flushing the sand at a small displacement (5-15 L / s), flushing all the remaining filling slurry into the leakage layer, and repeating the operation until the mixed filling material forms an effective throat in the leakage channel, further includes:

[0034] If the leakage rate decreases after the bridging grout enters the leakage layer, it indicates that the mixed filling material has formed an effective throat in the leakage channel. Based on the sealing effect, the filling can be repeated or the bridging grout can be adjusted for another sealing attempt.

[0035] As can be seen from the above technical solution, the method for sealing large cracks and faults provided by the present invention has the following beneficial effects:

[0036] This invention proposes a method for plugging leaks in large cracks and faults with leakage channels larger than 20 mm. The first step involves selecting porous mineral materials, crushing them into different particle sizes (1-3 mm, 3-5 mm, 5-8 mm), and using them as filler materials. These materials are then transported into the leakage channel using drilling fluid, where they slowly deposit under gravity, gradually accumulating to form a throat with a certain curvature. This process throttles the flow without blocking it, creating conditions for subsequent bridging materials to form a bridge within the leakage channel. The second step involves using bridging slurry for sealing, addressing severe leakage problems that exceed the scope of bridging slurry application. Detailed Implementation

[0037] To make the objectives, technical solutions, and advantages of the present invention clearer, the present invention will be further described in detail below with reference to specific embodiments.

[0038] According to a first aspect of the present invention, a method for sealing large cracks and faults is provided, comprising the following steps:

[0039] Prepare a mixed filling material comprising a first porous material, a second porous material, and a third porous material with different particle sizes;

[0040] The mixed filler materials are formulated into a filler slurry with a volume-to-mass ratio of 25%-40%;

[0041] Lower the drill string assembly to 5-10m above the leaking layer, inject filling grout, pull the drill string to 50-100m above the filling grout surface, and wait for 1-2 hours for plugging.

[0042] The drill string assembly is lowered to explore the sand surface, and sand is flushed at a rate of 5-15 L / s. All the remaining filler slurry is flushed into the leaking layer. The operation is repeated until the mixed filler material forms an effective throat in the leakage channel.

[0043] The sealing process is completed when bridging grout is used to plug leaks beyond the scope of bridging.

[0044] According to an embodiment of the present invention, the first porous material is volcanic rock particles and / or slag particles with a particle size of 1-3 mm;

[0045] The second porous material is volcanic rock particles and / or slag particles with a particle size of 3-5 mm;

[0046] The third porous material is volcanic rock particles and / or slag particles with a particle size of 5-8 mm;

[0047] The porosity of the first, second, and third porous materials is 15-45%.

[0048] According to an embodiment of the present invention, the filling slurry comprises well slurry and mixed filling material in a volume ratio of 3:1;

[0049] The density of the well slurry was 1.72 g / cm³. 3 ;

[0050] The mass ratio of the first porous material, the second porous material, and the third porous material in the mixed filler material is 1:2:1.

[0051] According to an embodiment of the present invention, flushing all remaining filler grout into the perforated layer includes: injecting 10-15m³ of filler grout each time. 3 Repeat the operation multiple times until the mineral material forms an effective throat in the leakage channel.

[0052] According to an embodiment of the present invention, the drill assembly is a smooth drill rod or a milling joint + smooth drill rod.

[0053] According to an embodiment of the present invention, the bridging and sealing grout comprises materials with a density of 1.15 g / cm³. 3 Well slurry and mixed nutshell materials of different particle sizes;

[0054] The mixed nutshell materials include nutshell materials with a particle size of 1-3 mm, nutshell materials with a particle size of 3-5 mm, nutshell materials with a particle size of 5-8 mm, and nutshell materials with a particle size of 10-15 mm.

[0055] The bridging and sealing grout also includes sepiolite wool with a particle size of 3-6 mm, sawdust and cottonseed with a particle size of 0.5-1 mm, and polypropylene fiber.

[0056] According to an embodiment of the present invention, the method for preparing the bridge plugging grout includes: pouring 40m³ of grout into a circulating tank with a total volume of 60m³.3 Well slurry, density 1.15 g / cm³ 3 Adjust the viscosity of the funnel to 68s, and add the mixed nut shell material, sepiolite wool, sawdust, cottonseed and polypropylene fiber in sequence according to the formula. Keep the stirrer and weight pump running continuously during the preparation.

[0057] According to an embodiment of the present invention, the filling slurry is prepared in a volume of 20m³. 3 Pour 15m into the circulating tank. 3 The well slurry density was increased to 1.72 g / cm³. 3 Adjust the viscosity of the funnel to 88s, and add the first porous material, the second porous material and the third porous material in sequence according to the formula. Keep the stirrer and the weight pump running continuously during the preparation.

[0058] According to an embodiment of the present invention, the drill string assembly is lowered to 5-10m above the leaking layer, filling slurry is injected, and the drill string is pulled up to 50-100m above the filling slurry surface, and then left to stand for 1-2 hours to plug the leak, including:

[0059] The drill string assembly was lowered to the bottom of the well, and the pump was started at a displacement of 2m³ / h. 3 Circulate for 10 minutes at a rate of / min, and no slurry returns to the wellhead;

[0060] Pump in filler slurry and allow to stand still for plugging: Pull the drill string up to 5-10m above the leaking zone, and use a drilling fluid pump at a displacement of 1.5m³ / h. 3 Pumping filling slurry at a speed of / min, with no slurry return throughout the process; monitoring the annular fluid level, pulling the drill string to 50-100m above the filling slurry level, and waiting for plugging to proceed for 1-2 hours;

[0061] Drill down to the leaking formation. If there is no residual volcanic rock in the wellbore, repeat the above steps of pumping in filling slurry and waiting for the plug to be plugged until the drill string assembly encounters resistance when drilling down to the leaking formation.

[0062] According to an embodiment of the present invention, bridging sealant is used for sealing until the problem is resolved beyond the scope of bridging sealant, at which point the sealant is complete, including:

[0063] Pull the drill string assembly to a depth of 5-10m above the leaky zone, using a drilling fluid pump at a displacement of 1m³ / min. 3 / min, pump in bridging and plugging grout;

[0064] Drill to a depth of 50-100m above the grout level, wait 6 hours for plugging, then drill down in sections to circulate and drain the bridging grout, flushing to the bottom. Gradually increase the flow rate to 45L / s with no leakage, and the plugging is successful.

[0065] According to an embodiment of the present invention, the drill string assembly is lowered to probe the sand surface, and sand is flushed at a small flow rate (5-15 L / s) to flush all the remaining filler slurry into the leaking layer. This operation is repeated until the mixed filler material forms an effective throat in the leakage channel. The method also includes:

[0066] A test plugging was performed using bridging grout. If the leakage rate decreased after the bridging grout entered the leakage layer, it indicates that the mixed filling material has formed an effective throat in the leakage channel. Depending on the plugging effect, the filling can be repeated or the bridging grout can be adjusted for another plugging.

[0067] The technical solution of the present invention will be described in detail below through preferred embodiments. It should be noted that the specific embodiments in the following text are for illustrative purposes only and are not intended to limit the present invention.

[0068] Example 1

[0069] A certain well, with a second-stage wellbore diameter of 311.1 mm and a surface casing shoe depth of 508 m, experienced a loss of return at a depth of 1632.5 m, resulting in a 0.2 m drain. The lithology is limestone, and the drilling fluid density is 1.15 g / cm³. 3 The annular fluid level was monitored at 182m. Based on geological data analysis, it was determined that a large fracture might have been encountered during drilling. The drill string was pulled out, and a milling head joint and a clean drill rod were installed. 40m of 35.2% bridging grout was pumped in to plug the leak. 3 Formula: Well slurry + 5% nutshell (1-3mm) + 7.5% nutshell (3-5mm) + 10% nutshell (5-8mm) + 5% nutshell (10-15mm) + 2.5% sepiolite fiber (3-6mm) + 2.5% sawdust (0.5-1mm) + 2.5% cottonseed + 0.2% polypropylene fiber (8mm); 12m of slurry replacement 3 No slurry returned during the entire process, and the monitored annular liquid level remained at 185m. The on-site decision was to first use volcanic rock to prepare a filling slurry to construct a throat within the leakage channel, and then proceed with bridging and sealing the leak.

[0070] 1. Preparation of sealing grout:

[0071] Filler grout preparation: In a total volume of 20m³ 3 Pour 15m into the circulating tank. 3 The well slurry density was increased to 1.72 g / cm³. 3 Adjust the viscosity of the funnel to 88s, add the filler materials in sequence according to the formula, and keep the stirrer and weight pump running continuously during the preparation.

[0072] Formula: 15m 3 Well slurry (density 1.72 g / cm³) 3 ) + 1t volcanic rock (1-3mm) + 2t volcanic rock (3-5mm) + 1t volcanic rock (5-8mm);

[0073] Bridge plugging grout preparation: In a total volume of 60m³ 3 Pour 40m into the circulating tank. 3 Well slurry, density 1.15 g / cm³ 3Adjust the viscosity of the funnel to 68s, add the bridging material in sequence according to the formula, and keep the stirrer and weight pump running continuously during the preparation.

[0074] Formula: 40m 3 Well slurry (density 1.15 g / cm³) 3 )+2t nutshells (1-3mm)+3t nutshells (3-5mm)+4t nutshells (5-8mm)+2t nutshells (10-15mm)+1t sepiolite fiber (3-6mm)+1t sawdust (0.5-1mm)+1t cottonseed+0.08t polypropylene fiber (8mm).

[0075] 2. Construction process and results:

[0076] The first step is to inject replacement filler slurry. Lower the drill pipe to the bottom of the well and start the pump at a flow rate of 2m³ / h. 3 Circulate for 10 minutes at a rate of 1 / min. If no mud returns to the wellhead, pull out the drill string to 1625m and use a drilling fluid pump at a displacement of 1m³ / min. 3 Pump grout at a rate of 15m / min. 3 15m of pulp replacement 3 No slurry return occurred throughout the entire process. The annular fluid level was monitored at 183m. The drill string was pulled out to 1200m, then allowed to stand still for 1 hour before being lowered to 1632.5m. No residual volcanic rock was found in the wellbore. 20m of slurry was prepared again according to the formula. 3 Fill with slurry, pull out the drill string to 1625m, and use a drilling fluid pump at a displacement of 1m³ / h. 3 / min, pumping in 15m 3 Filling grout, replacement grout 15m 3 No slurry returned during the entire process. The annular fluid level was monitored at 181m. The drill string was pulled out to 1200m and left to stand still for 1 hour to plug the blockage. When the drill string was lowered to 1632m, it encountered resistance. The pump was started and the bottom of the well was flushed at a rate of 10-15L / s until all the remaining volcanic rock in the wellbore entered the leakage channel. The drill string was lowered to 1632.5m to verify that the wellbore was unobstructed.

[0077] The second step is bridging and plugging the leak. Drilling is initiated to 1625m, using a drilling fluid pump at a displacement of 1m³ / min. 3 / min, pumping grout into the bridge plugging section for 40m 3 (Pump in 38m of plugging grout) 3 (Wellhead return), 12m of slurry was replaced. 3 During the slurry replacement process, 8m of slurry returned from the wellhead. 3 The drilling was started at 1200m, and the grout was left to stand still for 6 hours before being plugged. The grout was then drained in sections and circulated to drain the leaking slurry. The slurry was flushed to the bottom and the flow rate was gradually increased to 45L / s. There was no leakage during circulation, and the leak was successfully plugged.

[0078] Example 2

[0079] A certain well, with a second-stage wellbore diameter of 444.5 mm and a surface casing shoe depth of 199 m, experienced a loss of return at a depth of 608 m, resulting in a 0.5 m drain failure. The lithology is sandstone, and the drilling fluid density is 1.08 g / cm³. 3 The annular fluid level was monitored at 87m. Based on geological data analysis, it was determined that a fault may have been encountered during drilling. The on-site decision was made to first construct a throat within the leakage channel using volcanic rock-based filling grout, followed by bridging and sealing the leak.

[0080] 1. Preparation of sealing grout:

[0081] Filler grout preparation: In a container with a total volume of 15m³ 3 Pour 10m into the circulating tank. 3 The well slurry density was increased to 1.7 g / cm³. 3 Adjust the viscosity of the funnel to 84s, add the filling materials in sequence according to the formula, and keep the stirrer and weight pump running continuously during the preparation.

[0082] Formula: 10m 3 Well slurry (density 1.7 g / cm³) 3 ) + 1t volcanic rock (1-3mm) + 1t volcanic rock (3-5mm) + 2t volcanic rock (5-8mm);

[0083] Bridge plugging grout preparation: In a total volume of 60m³ 3 Pour 50m into the circulating tank. 3 Well slurry, density 1.08 g / cm³ 3 Adjust the viscosity of the funnel to 71s, add the bridging material in sequence according to the formula, and keep the stirrer and weight pump running continuously during the preparation.

[0084] Formula: 50m 3 Well slurry (density 1.08 g / cm³) 3 )+3t nutshells (3-5mm)+4t nutshells (5-8mm)+3t nutshells (10-15mm)+1t sepiolite fiber (3-6mm)+4t rubber granules (5-8mm)+2t cottonseed+1t mica sheet (5-8mm)+0.1t polypropylene fiber (8mm).

[0085] 2. Construction process and results:

[0086] The first step is to inject replacement filler slurry. Lower the drill pipe to the bottom of the well and start the pump at a flow rate of 2m³ / h. 3 Circulate for 10 minutes at a rate of 1.5 m³ / min. If no mud returns to the wellhead, pull out the drill string to 601 m and use a drilling fluid pump at a displacement of 1.5 m³ / min. 3 Pump grout at a rate of 10m / min. 3 6m of pulp replacement 3No slurry return occurred throughout the entire process. The annular fluid level was monitored at 81m. The drill string was pulled out to 302m, then allowed to stand still for 1 hour before being lowered to 608m. No residual volcanic rock was found in the wellbore. 15m of slurry was prepared again according to the formula. 3 Fill with slurry, pull out the drill string to 601m, and use a drilling fluid pump at a displacement of 1.5m³ / h. 3 / min, pumping in 10m 3 Filling grout, replacement grout 6m 3 No slurry return occurred throughout the entire process. The annular fluid level was monitored at 78m. Drilling was pulled out to 302m, and a 1-hour standby period was observed before drilling down to 608m. No residual volcanic rock was found in the wellbore. 15m³ of filling slurry was prepared again according to the formula, and drilling was pulled out to 601m. A drilling fluid pump was used at a displacement of 1.5m³. 3 / min, pumping in 10m 3 Filling grout, replacement grout 6m 3 No slurry returned during the entire process. The annular fluid level was monitored at 79m. The drill string was pulled out to 302m and left to stand still for 1 hour to plug the blockage. When the drill string was lowered to 606.5m, it encountered resistance. The pump was started and the bottom of the well was flushed at a rate of 15-20L / s until all the remaining volcanic rock in the wellbore entered the leakage channel. The drill string was lowered to 608m to verify that the wellbore was unobstructed.

[0087] The second step is bridging and plugging the leak. Drilling is initiated to 605m, using a drilling fluid pump at a displacement of 1.5m³ / min. 3 / min, pumping 50m of bridge plugging grout 3 (Pump in 41m of plugging grout) 3 (When the wellhead returns), 5m of slurry is replaced. 3 During the slurry replacement process, 2.4m of slurry returned from the wellhead. 3 The drill was pulled up to 210m and left to stand still for 6 hours to plug the leak. The drill was then lowered into sections to circulate and drain the leaking slurry. The slurry was flushed to the bottom and the flow rate was gradually increased to 55L / s. There was no leakage during circulation, and the leak was successfully plugged.

[0088] Example 3

[0089] A certain well, with a second-stage wellbore diameter of 311.1 mm and a surface casing shoe depth of 502 m, experienced a loss of return at 1231.6 m, resulting in a 0.17 m loss of circulation. The lithology is limestone, and the drilling fluid density is 1.14 g / cm³. 3 The annular fluid level was monitored at 142m. Based on geological data analysis, it was determined that a large fracture might have been encountered during drilling. The drill string was pulled out, and a milling head joint and a clean drill rod were installed. 40m of 33.2% bridging grout was pumped in to plug the leak. 3 Formula: Well slurry + 5% nutshell (1-3mm) + 7.5% nutshell (3-5mm) + 9% nutshell (5-8mm) + 4% nutshell (10-15mm) + 2.5% sepiolite fiber (3-6mm) + 2.5% sawdust (0.5-1mm) + 2.5% cottonseed + 0.2% polypropylene fiber (8mm); 12m of slurry replacement 3No slurry returned during the entire process, and the monitored annular liquid level remained at 135m. The on-site decision was to first construct a throat within the leakage channel using slag-based filling slurry, followed by bridging and sealing.

[0090] 1. Preparation of sealing grout:

[0091] Filler grout preparation: In a total volume of 20m³ 3 Pour 15m into the circulating tank. 3 The well slurry density was increased to 1.75 g / cm³. 3 Adjust the viscosity of the funnel to 87s, add the filling materials in sequence according to the formula, and keep the stirrer and weight pump running continuously during the preparation.

[0092] Formula: 15m 3 Well slurry (density 1.72 g / cm³) 3 )+1.5t slag (1-3mm)+1.5t slag (3-5mm)+1t slag (5-8mm);

[0093] Bridge plugging grout preparation: In a total volume of 60m³ 3 Pour 40m into the circulating tank. 3 Well slurry, density 1.14 g / cm³ 3 Adjust the viscosity of the funnel to 65s, add the bridging material in sequence according to the formula, and keep the stirrer and weight pump running continuously during the preparation.

[0094] Formula: 40m 3 Well slurry (density 1.14 g / cm³) 3 )+2t nutshells (1-3mm)+4t nutshells (3-5mm)+3t nutshells (5-8mm)+1t nutshells (10-15mm)+1t sepiolite fiber (3-6mm)+1t sawdust (0.5-1mm)+1t cottonseed+0.08t polypropylene fiber (8mm).

[0095] 2. Construction process and results:

[0096] The first step is to inject replacement filler slurry. Lower the drill pipe to the bottom of the well and start the pump at a flow rate of 2m³ / h. 3 Circulate for 10 minutes at a rate of 1 / min. If no mud returns to the wellhead, pull out the drill string to 1225m and use a drilling fluid pump at a displacement of 1m³ / min. 3 Pump grout at a rate of 15m / min. 3 15m of pulp replacement 3 No slurry return occurred throughout the entire process. The annular fluid level was monitored at 136m. Drilling was pulled out to 900m, then allowed to stand still for 1 hour before drilling down to 1231.6m. No residual volcanic rock was found in the wellbore. 20m of slurry was prepared again according to the formula. 3 Fill with slurry, pull out the drill string to 1225m, and use a drilling fluid pump at a displacement of 1m³ / h. 3 / min, pumping in 15m3 Filling grout, replacement grout 15m 3 No slurry returned during the entire process. The annular fluid level was monitored at 133m. The drill string was pulled out to 900m and left to stand still for 1 hour to plug the blockage. When the drill string was lowered to 1230.8m, it encountered resistance. The pump was started and the bottom of the well was flushed at a rate of 10-15L / s until all the remaining volcanic rock in the wellbore entered the leakage channel. The drill string was lowered to 1231.6m to verify that the wellbore was unobstructed.

[0097] The second step is bridging and plugging the leak. Drilling is initiated to 1225m, using a drilling fluid pump at a displacement of 1m³ / min. 3 / min, pumping grout into the bridge plugging section for 40m 3 (Pump in 32m of plugging grout) 3 (When the wellhead returns), 10m of slurry is replaced. 3 During the slurry replacement process, 6.4m of slurry returned from the wellhead. 3 The drilling was started at 708m, and the grout was left to stand still for 8 hours before being plugged. The grout was then drained in sections and circulated to drain the leaking slurry. The slurry was flushed to the bottom and the flow rate was gradually increased to 45L / s. There was no leakage during circulation, and the leak was successfully plugged.

[0098] Example 4

[0099] A certain well, with a second-stage wellbore diameter of 215.9 mm and a surface casing shoe depth of 401 m, experienced a loss of return at a depth of 812 m, resulting in a 0.32 m drain failure. The lithology is sandstone, and the drilling fluid density is 1.12 g / cm³. 3 The annular fluid level was monitored at 182m. Based on geological data analysis, it was determined that a fault might have been encountered during drilling. The on-site decision was made to first construct a throat within the leakage channel using a filling grout made of volcanic rock and slag, followed by bridging and sealing the leak.

[0100] 1. Preparation of sealing grout:

[0101] Filler grout preparation: In a container with a total volume of 15m³ 3 Pour 10m into the circulating tank. 3 The well slurry density was increased to 1.7 g / cm³. 3 Adjust the viscosity of the funnel to 86s, add the filler materials in sequence according to the formula, and keep the stirrer and weight pump running continuously during the preparation.

[0102] Formula: 10m 3 Well slurry (density 1.7 g / cm³) 3 ) + 1t volcanic rock (1-3mm) + 1t volcanic rock (3-5mm) + 1.5t slag (5-8mm);

[0103] Bridge plugging grout preparation: In a total volume of 60m³ 3 Pour 40m into the circulating tank. 3 Well slurry, density 1.12 g / cm³ 3Adjust the viscosity of the funnel to 68s, add the bridging material in sequence according to the formula, and keep the stirrer and weight pump running continuously during the preparation.

[0104] Formula: 40m 3 Well slurry (density 1.12 g / cm³) 3 ) + 2t nutshells (3-5mm) + 2.5t nutshells (5-8mm) + 2t nutshells (10-15mm) + 1t sepiolite fiber (3-6mm) + 3t rubber granules (5-8mm) + 1.5t cottonseed + 1t mica sheet (5-8mm) + 0.1t polypropylene fiber (8mm).

[0105] 2. Construction process and results:

[0106] The first step is to inject replacement filler slurry. Lower the drill pipe to the bottom of the well and start the pump at a flow rate of 2m³ / h. 3 Circulate for 10 minutes at a rate of 1.5 m / min. If no mud returns to the wellhead, pull out the drill string to 805 m and use a drilling fluid pump at a displacement of 1.5 m / min. 3 Pump grout at a rate of 10m / min. 3 8m of pulp replacement 3 No slurry return occurred throughout the entire process. The annular fluid level was monitored at 179m. The drill string was pulled out to 502m, then allowed to stand still for 1 hour before being lowered to 812m. No residual volcanic rock was found in the wellbore. 15m of slurry was prepared again according to the formula. 3 Fill with slurry, pull out the drill string to 805m, and use a drilling fluid pump at a displacement of 2m³ / h. 3 Circulate at a rate of 1.5 m³ / min for 10 minutes. If no slurry returns to the wellhead, then discharge at a rate of 1.5 m³ / min. 3 Pump grout at a rate of 10m / min. 3 8m of pulp replacement 3 No slurry returned during the entire process. The annular fluid level was monitored at 178m. The drill string was pulled out to 502m and left to stand still for 1 hour to plug the blockage. When the drill string was lowered to 811.1m, it encountered resistance. The pump was started and the bottom of the well was flushed at a rate of 15-20L / s until all the remaining volcanic rock in the wellbore entered the leakage channel. The drill string was lowered to 812m to verify that the wellbore was unobstructed.

[0107] The second step is bridging and plugging the leak. Drilling is initiated to 805m, using a drilling fluid pump at a displacement of 1.5m³ / h. 3 / min, pumping grout into the bridge plugging section for 40m 3 (Pump in 28m of plugging grout) 3 (When the wellhead returns), 5m of slurry is replaced. 3 During the slurry replacement process, 3.2m of slurry returned from the wellhead. 3 The drill was pulled up to 388m and held stationary for 6 hours to plug the leak. The drill was then lowered into sections to circulate and drain the leaking slurry. The slurry was flushed to the bottom and the flow rate was gradually increased to 42L / s. There was no leakage during circulation, and the leak was successfully plugged.

[0108] The specific embodiments described above further illustrate the purpose, technical solution, and beneficial effects of the present invention. It should be understood that the above descriptions are merely specific embodiments of the present invention and are 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 sealing large cracks and faults, characterized in that, Includes the following steps: Prepare a mixed filling material comprising a first porous material, a second porous material, and a third porous material with different particle sizes; The mixed filler material is formulated into a filler slurry with a volume-to-mass ratio of 25%-40%; Lower the drill string assembly to 5-10m above the leaking layer, inject the filling slurry, pull the drill string to 50-100m above the filling slurry surface, and wait for 1-2 hours for plugging. The drill string assembly is lowered to probe the sand surface, and sand is flushed at a rate of 5-15 L / s. All the remaining filling slurry is flushed into the leaking layer. The operation is repeated until the mixed filling material forms an effective throat in the leakage channel. The sealing process is completed when bridging grout is used to plug leaks beyond the scope of bridging.

2. The method for sealing large cracks and faults according to claim 1, characterized in that, The first porous material is volcanic rock particles and / or slag particles with a particle size of 1-3 mm; The second porous material is volcanic rock particles and / or slag particles with a particle size of 3-5 mm; The third porous material is volcanic rock particles and / or slag particles with a particle size of 5-8 mm. The porosity of the first porous material, the second porous material, and the third porous material is 15-45%.

3. The method for sealing large cracks and faults according to claim 1, characterized in that, The filling slurry comprises well slurry and mixed filling material in a volume ratio of 3:1; The density of the well slurry is 1.72 g / cm³. 3 ; The mass ratio of the first porous material, the second porous material, and the third porous material in the mixed filler material is 1:2:

1.

4. The method for sealing large cracks and faults according to claim 1, characterized in that, The step of flushing all the remaining filler grout into the drain layer includes: injecting 10-15m of filler grout each time. 3 Repeat the operation multiple times until the mineral material forms an effective throat in the leakage channel.

5. The method for sealing large cracks and faults according to claim 1, characterized in that, The bridging and sealing grout has a density of 1.15 g / cm³. 3 Well slurry and mixed nutshell materials of different particle sizes; The mixed shell material includes shell material with a particle size of 1-3 mm, shell material with a particle size of 3-5 mm, shell material with a particle size of 5-8 mm, and shell material with a particle size of 10-15 mm. The bridging and sealing slurry also includes sepiolite wool with a particle size of 3-6 mm, sawdust and cottonseed with a particle size of 0.5-1 mm, and polypropylene fiber.

6. The method for sealing large cracks and faults according to claim 5, characterized in that, The method for preparing the bridge plugging grout includes: in a container with a total volume of 60m³ 3 Pour 40m into the circulating tank. 3 Well slurry, density 1.15 g / cm³ 3 Adjust the viscosity of the funnel to 68s, and add the mixed nut shell material, sepiolite wool, sawdust, cottonseed and polypropylene fiber in sequence according to the formula. Keep the stirrer and weight pump running continuously during the preparation.

7. The method for sealing large cracks and faults according to claim 3, characterized in that, The filling grout is prepared in a total volume of 20m³. 3 Pour 15m into the circulating tank. 3 The well slurry density was increased to 1.72 g / cm³. 3 Adjust the viscosity of the funnel to 88s, and add the first porous material, the second porous material and the third porous material in sequence according to the formula. Keep the stirrer and the weight pump running continuously during the preparation.

8. The method for sealing large cracks and faults according to claim 1, characterized in that, The process of lowering the drill string assembly to 5-10m above the leaking layer, injecting the filling slurry, pulling the drill string to 50-100m above the filling slurry surface, and then allowing it to stand still for 1-2 hours to plug the leak includes: The drill string assembly was lowered to the bottom of the well, and the pump was started at a displacement of 2m³ / h. 3 Circulate for 10 minutes at a rate of / min, and no slurry returns to the wellhead; Pump in the filling slurry and allow it to stand still for plugging: Pull the drill string assembly to a depth of 5-10m above the leaking zone, using a drilling fluid pump at a displacement of 1.5m³ / min. 3 Pumping filling slurry at a speed of / min, with no slurry return throughout the process; monitoring the annular fluid level, pulling the drill string to 50-100m above the filling slurry level, and waiting for plugging to proceed for 1-2 hours; Drill down to the leaking layer. If there is no residual volcanic rock in the wellbore, repeat the above steps of pumping in filling slurry and waiting for the blockage to occur until the drill string assembly encounters resistance when drilling down to the leaking layer.

9. The method for sealing large cracks and faults according to claim 1, characterized in that, The process of using bridging sealant to seal leaks continues until the problem exceeds the scope of bridging sealant application, at which point the sealing is complete. include:. The drill string assembly is pulled up to 5-10m above the leaky zone, using a drilling fluid pump at a displacement of 1m³ / min. 3 / min, pump in the bridging and plugging slurry; Drill to a depth of 50-100m above the grout level, wait 6 hours for plugging, then drill down in sections to circulate the bridging grout until it reaches the bottom. Gradually increase the flow rate to 45L / s for circulation without leakage, and the plugging is successful.

10. The method for sealing large cracks and faults according to claim 1, characterized in that, The process of lowering the drill string assembly to probe the sand surface, flushing the sand at a small displacement (5-15 L / s), and flushing all the remaining filler slurry into the leakage layer, repeating the operation until the mixed filler material forms an effective throat in the leakage channel, also includes: If the leakage rate decreases after the bridging grout enters the leakage layer, it indicates that the mixed filling material has formed an effective throat in the leakage channel. Based on the sealing effect, the filling can be repeated or the bridging grout can be adjusted for another sealing attempt.