Leaking stoppage and well killing method under ultra-deep layer overflow and leakage coexistence working condition

Abstract

The invention relates to a leaking stoppage and well killing method under an ultra-deep layer overflow and leakage coexistence working condition. According to the technical scheme, the method comprises the steps that firstly, the overflow strength and the leakage strength need to be accurately judged, the overflow strength is judged through well shut-in, if the casing pressure exceeds 3.5 MPa, the overflow strength is large, and if the leakage speed is larger than 20 m / h, the leakage strength is large; then, according to the leakage speed obtained through judgment and the specific working condition type, a corresponding leaking stoppage method is reasonably selected, positive circulation leaking stoppage is selected for the overflow and leakage working condition, and reverse circulation leaking stoppage is selected for the overflow and leakage working condition; then, an adaptive well killing method is selected according to the overflow strength, when the overflow strength is large, throttling circulation well killing is conducted after overflow and leakage are conducted through a pressing-back method, and throttling circulation well killing is conducted on the overflow and the leakage according to the leakage speed after leaking stoppage by selecting a proper chart. The method has the beneficial effects that the difference between the overflow leakage strength and the working condition type can be fully considered, the complex working condition with ultra-deep layer overflow leakage coexistence is effectively dealt with, the success rate of leaking stoppage and well killing is increased, and the safety risk and cost of drilling operation are reduced.

Description

Technical Field

[0001] The invention relates to the field of petroleum drilling engineering, and in particular to a leak plugging and well killing method under the condition of ultra-deep leakage coexisting. Background Art

[0002] With the continuous deepening of oil exploration and development, ultra-deep layers have gradually become important target areas. However, during ultra-deep drilling operations, complex conditions of coexistence of spills and leaks frequently occur, which brings great challenges to drilling work. At present, the treatment of coexistence of spills and leaks in multiple pressure systems at home and abroad mainly adopts controlled pressure drilling technology and plugging and well-killing technology. Controlled pressure drilling technology is a measure taken to prevent coexistence of spills and leaks. During the drilling process, it continuously adjusts and controls the wellbore pressure in the hope of achieving a state of near-balance with the formation pressure. However, since the essence of the coexistence of spills and leaks is that a single wellbore pressure is difficult to balance the formation pressure of multiple pressure systems, even if the wellbore pressure is continuously adjusted, it is difficult to achieve the balance of the formation pressure of the entire open hole section. Therefore, although this process can reduce the degree of coexistence of spills and leaks to a certain extent, it cannot efficiently solve this complex problem.

[0003] The plugging and well-killing technology is used to solve the complex working conditions of coexistence of spills and leaks. It combines the plugging and control capabilities of drilling fluid. However, the existing technology lacks targeted treatment strategies for different spill intensities and working conditions. In actual operations, when selecting plugging methods, it is often not possible to reasonably select appropriate technologies based on different leakage rates; when performing well-killing operations, it is also impossible to flexibly adopt effective well-killing methods based on the magnitude of the spill intensity, which leads to incomplete plugging and well-killing failures. The traditional methods have these problems mainly because of the insufficient understanding of the gas-liquid two-phase flow law in the wellbore under the working conditions of coexistence of ultra-deep spills, and the lack of full consideration of the differences in different spill intensities and working conditions. At the same time, the lack of a systematic and targeted treatment process makes it difficult to effectively respond to complex and changeable field conditions. These problems increase the safety risks of drilling operations, increase operating costs, and seriously restrict the efficient development of ultra-deep oil and gas resources. Therefore, there is an urgent need for a plugging and well-killing method that can fully consider the characteristics of the working conditions and effectively solve practical problems. Summary of the invention

[0004] The purpose of the present invention is to address the above-mentioned defects of the prior art and to provide a method for plugging leaks and killing wells under ultra-deep leakage coexisting working conditions, which can fully consider the differences in leakage intensity and working condition types, effectively cope with the complex working conditions of ultra-deep leakage coexisting, improve the success rate of plugging leaks and killing wells, and reduce the safety risks and costs of drilling operations.

[0005] The present invention provides a method for plugging leaks and killing wells under the condition of coexistence of leaks in ultra-deep layers. The technical solution is: when ultra-deep drilling operations are faced with the complex condition of coexistence of leaks and leaks, (I) First, the overflow and leakage intensity must be accurately judged, including the following steps: 15 minutes after the well is shut in, if the casing pressure rises by more than 3.5MPa, the overflow intensity is determined to be large; if the casing pressure rises by less than 3.5MPa, the overflow intensity is determined to be small; at the same time, if the leakage rate is greater than 20m³ / h, the leakage intensity is determined to be large; if the leakage rate is less than or equal to 20m³ / h, the leakage intensity is determined to be small; (ii) According to the leakage rate and specific working condition type determined, a corresponding plugging method is reasonably selected. The plugging method selection steps include the following steps: if it is an overflow and leakage condition, a positive circulation plugging method is selected, that is, a plugging agent is pumped into the wellbore in a positive circulation manner so that the plugging agent first reaches the leakage layer at the bottom of the well, and then the well is shut down and the pressure is held to squeeze the plugging agent into the formation; if it is an overflow and leakage condition, a reverse circulation plugging method is selected, that is, a plugging agent is injected from the annulus so that the plugging agent first reaches the leakage layer at the top of the wellbore for plugging; (III) Select the appropriate well killing method according to the overflow intensity. The steps for determining the well killing method are as follows: When the overflow intensity is large, for the overflow and leakage conditions, the pressure back method is first used to increase the wellbore pressure and control the gas invasion speed. When the bottom hole pressure is greater than the formation pressure, it is converted to throttling circulation well killing. According to the leakage rate after plugging, the appropriate chart is selected to circulate the gas out of the wellbore; for the leakage and overflow conditions, according to the leakage rate after plugging, the appropriate chart is selected to perform throttling circulation well killing; When the overflow intensity is small, for both overflow and leakage and leakage and underflow conditions, throttling circulation well killing is directly adopted. According to the leakage rate after plugging, the throttling circulation critical well killing displacement chart is selected, the critical displacement is read, and throttling circulation well killing is carried out until the gas is discharged from the wellbore.

[0006] Preferably, the present invention further comprises the step of optimizing the particle size of the plugging material: Determine the fracture width range based on the on-site drilling fluid loss rate and the corresponding block loss data; Carry out plugging simulation under corresponding crack width conditions, obtain the relationship between crack length and crack width after crack bridging plugging under corresponding leakage rate, and determine the crack width at the plugging bridge position; The particle size of the plugging material is optimized based on the obtained seam width and the optimization principle of the particle size of the plugging material.

[0007] Preferably, for formation leakage with different leakage rates, the plugging method further includes the following: When the leakage rate is less than 10m³ / h, you can choose to continue drilling and use fine drill cuttings to build bridges to plug the leakage channel; or stop drilling, turn off the pump, lift the drill pipe above the suspected leakage formation, and treat the wellbore; or add drilling plugging materials to the drilling fluid in advance to increase the minimum critical crack width and achieve leakage prevention and plugging effects; When the loss rate is 10-20m³ / h, the viscosity coefficient, flow index and yield stress of the drilling fluid can be appropriately increased in the early stage of loss to reduce the wellbore pressure; or bridge plugging materials or high water loss plugging materials can be added to increase the maximum critical width of the crack or reduce the crack width to plug the leakage layer; When the loss rate is greater than 20m³ / h, curable plugging materials, gel plugging materials or water-absorbing / oil-absorbing polymer plugging materials need to be added in the early stage of loss; if plugging fails, composite plugging materials need to be used for plugging. The composite plugging materials include a combination of curable plugging materials and bridge plugging materials or gel plugging materials to reduce the crack width to below the minimum critical crack width, thereby achieving the effect of plugging the leakage layer.

[0008] Preferably, in the positive circulation plugging method: the plugging agent is mixed with the drilling fluid and pumped into the wellbore through the drill string, and the pump pressure and displacement changes are monitored during the pumping process. After the plugging agent reaches the leakage layer, the well is shut down and the pressure holding time is 30-60 minutes, and the pressure holding pressure value is gradually increased to 80%-90% slightly higher than the formation fracture pressure.

[0009] Preferably, in the reverse circulation plugging method, when injecting the plugging agent from the annulus, the displacement and pressure of the injection pump are adjusted so that the plugging agent is evenly distributed around the leaking layer, and after the injection is completed, appropriate pressure holding operation can be performed according to actual conditions.

[0010] Preferably, during the well-killing process using the pressure-back method, the pressure-back rate is controlled at 0.5-1 MPa / min, and the bottom hole pressure is increased to 10%-15% higher than the formation pressure.

[0011] Preferably, during the throttling circulation well killing process, the well killing fluid displacement and density are determined according to the selected chart and drilling fluid parameters, and the throttle valve opening is controlled to maintain the bottom hole pressure slightly higher than the formation pressure.

[0012] Preferably, in the preferred step of the particle size of the plugging material: the statistical analysis method includes the analysis of the corresponding relationship between the historical leakage velocity and the fracture width, the two-dimensional axisymmetric model is constructed using ABAQUS software during the simulation process, the model parameters are set according to the actual formation conditions, and the cohesive unit is used to simulate the wellbore fracture leakage and plugging process.

[0013] Preferably, for formation leakage with different leakage rates, the plugging method further includes the following specific steps: When the leakage rate is less than 10m³ / h and drilling is continued, the change of leakage rate is observed after the drilling depth reaches 5-10 meters; when drilling is stopped and the pump is turned off, the drill pipe is lifted to 5-10 meters above the leakage layer, and the static observation time is 30-60 minutes; when the plugging material while drilling is added in advance, the amount of plugging material added is 3%-5% of the drilling fluid volume; When the loss rate is 10-20m³ / h and the drilling fluid performance is adjusted, the consistency coefficient is increased by 10%-20%, the flow index is adjusted to 0.5-0.7, and the yield stress is increased by 2-3Pa; the amount of bridge plugging material added is 5%-8% of the drilling fluid volume, and the amount of high water loss plugging material added is 3%-5%; When the loss rate is greater than 20m³ / h and curable plugging materials are added, the mixing ratio of curable plugging materials to drilling fluid is 1:3-1:5; when composite plugging materials are used for plugging, the appropriate combination is selected according to the formation fracture conditions and the composite plugging slurry is prepared in proportion.

[0014] Compared with the prior art, the beneficial effects of the present invention are as follows: 1. The present invention can quickly formulate the most appropriate plugging and well-killing strategies for different situations by accurately judging the intensity of the overflow. For example, after accurately judging the overflow intensity, for the working conditions of overflow and leakage, it is reasonable to arrange the first pressure back method and then throttling circulation well killing or direct throttling circulation well killing; for the working conditions of leakage and overflow, it is determined whether to directly throttle circulation well killing or select the throttling circulation well killing according to the leakage speed after plugging; this precise matching greatly improves the success rate of plugging and well killing, reduces the risk of failure caused by improper strategies, and ensures that in the complex ultra-deep overflow and leakage coexistence working conditions, each step of the operation can be targeted and effectively solve the problem; 2. Select appropriate plugging methods for different working conditions, such as the positive circulation plugging method for overflow and leakage and the reverse circulation plugging method for leakage and overflow, which can effectively avoid the risks caused by improper injection of plugging agents. In the well killing process, selecting the well killing method according to the overflow intensity can prevent dangerous situations such as blowouts caused by improper wellbore pressure control. At the same time, accurately judging the overflow intensity and reasonably selecting the plugging and well killing scheme can avoid excessive disturbance of the formation during the treatment process, reduce safety hazards such as formation collapse, and fully guarantee the safety of drilling operations; 3. Reasonable selection of plugging and well-killing methods, such as using the pressure-back method to quickly control the gas invasion speed and then converting to throttling circulation well-killing (overflow and underflow conditions) when the overflow intensity is large, and directly using the efficient throttling circulation well-killing method (two conditions) when the overflow intensity is small, can effectively shorten the processing time. In addition, the optimization of the particle size of the plugging material can make the plugging material play a role faster and better, reducing the plugging time. Overall, the optimization and coordination of each link significantly reduced the operation time and improved the drilling efficiency; 4. The present invention fully considers the complexity of the ultra-deep leakage coexistence conditions, including different leakage intensities, working condition types, formation characteristics and other factors. Through the judgment, selection and operation process of the system, it can flexibly deal with various complex situations, such as formation leakage treatment under different leakage rates, well killing response under different overflow intensities, etc., to ensure that in the complex and changeable ultra-deep environment, it always maintains effective plugging and well killing capabilities, providing a solid guarantee for the smooth progress of drilling operations; 5. The optimization of the particle size of the plugging material and the application of appropriate plugging methods can enable the plugging material to better fill the cracks, enhance the plugging effect of the formation, reduce the loss of formation fluids, and thus improve the stability of the formation. Stable formation conditions are conducive to the safety of subsequent drilling operations, reduce a series of problems caused by unstable formations, such as stuck drill and well wall collapse, and further ensure the smooth progress of the drilling project; 6. In the process of plugging and killing wells, reasonable selection of plugging agents, killing fluids and other resources according to different working conditions can avoid blind use and waste of resources. For example, appropriate plugging materials can be selected according to different leakage rates and formation conditions, and appropriate killing fluid density and displacement can be selected according to overflow intensity. This precise resource allocation not only improves the utilization efficiency of resources, but also ensures the best plugging and killing effects under limited resource conditions, providing support for the sustainable development of drilling operations. BRIEF DESCRIPTION OF THE DRAWINGS

[0015] Figure 1 shows the schematic diagram of the seam length and width after bridging plugging at different leakage velocities; FIG2 is a schematic diagram of the simulation results of the well killing + throttling cycle by the pressure back method; FIG3 is a schematic diagram showing the characteristic curves of the seam length and seam width after bridging and plugging; FIG4 is a flow chart of plugging and well-killing treatment under the condition of coexistence of spills and leaks. DETAILED DESCRIPTION

[0016] The preferred embodiments of the present invention are described below in conjunction with the accompanying drawings. It should be understood that the preferred embodiments described herein are only used to illustrate and explain the present invention, and are not used to limit the present invention.

[0017] Embodiment 1, the present invention also provides a method for using a leak plugging and well killing method under the condition of ultra-deep leak coexistence, which comprises the following steps: Step 1: Preliminary judgment of leakage intensity: When leakage and spillage coexist at the drilling site, shut down the well immediately for 15 minutes and closely observe the changes in casing pressure. If the casing pressure rises by more than 3.5MPa, it is judged that the overflow intensity is large; otherwise, it is considered that the overflow intensity is small. At the same time, record the leakage rate. If the leakage rate is greater than 20m³ / h, it is judged that the leakage intensity is large; otherwise, it is judged that the leakage intensity is small. This step provides a basic judgment basis for subsequent work.

[0018] Step 2: Select the plugging method: Determine the plugging method according to the type of overflow condition. If it is an overflow and leakage condition, use the positive circulation plugging method, that is, use the positive circulation method to pump the plugging agent into the wellbore, so that the plugging agent first reaches the leakage layer at the bottom of the well, and then shut down the well to hold the pressure to squeeze the plugging agent into the formation to increase the pressure bearing capacity of the leakage formation; if it is an overflow and leakage condition, use the reverse circulation plugging method, inject the plugging agent from the annulus, and let it first reach the leakage layer at the top of the wellbore for plugging.

[0019] Step 3: Determine the range of crack width: Collect the on-site drilling fluid loss rate information, and combine it with the historical loss data of the Bozi block and other corresponding blocks, and use professional statistical analysis methods to accurately determine the current possible crack width range. This step is crucial for the subsequent selection of plugging materials.

[0020] Step 4: Conduct plugging simulation: Based on the determined crack width range, conduct plugging simulation experiments under corresponding conditions. With the help of ABAQUS software, cohesive units are used to simulate the wellbore crack leakage and plugging process, and the relationship between the crack length and crack width after crack bridging plugging under the corresponding leakage rate is deeply analyzed, so as to accurately determine the crack width at the plugging bridge position. Figure 1 .

[0021] Step 5: Optimize the particle size of the plugging material: Based on the crack width at the plugging bridge position obtained in the previous step, combined with the principle of optimizing the particle size of the plugging material, scientifically and rationally select the particle size of the plugging material. The plugging material with the appropriate particle size can better bridge and plug the cracks, thus improving the plugging effect.

[0022] Step 6. Decision on the well-killing method (when the overflow intensity is large): If the overflow intensity is large in the first step, for the overflow and leakage conditions, first use the pressure-back method to quickly increase the wellbore pressure and control the gas invasion rate in time. When the bottom hole pressure is greater than the formation pressure, the well-killing method is converted to throttling circulation well-killing. According to the actual leakage rate after plugging, select the appropriate chart to circulate and discharge the gas in the wellbore. For the leakage and overflow conditions, directly select the appropriate chart for throttling circulation well-killing according to the leakage rate after plugging. Figure 2 .

[0023] Step 7, decision on well killing method (when overflow intensity is small): If the overflow intensity is judged to be small in the first step, whether it is overflow or leakage, the throttling circulation well killing method is directly adopted. According to the leakage rate after plugging, select the corresponding throttling circulation critical well killing displacement chart, read the critical displacement corresponding to the well killing fluid parameters, and continue the throttling circulation well killing operation until all the gas in the wellbore is discharged. Figure 2 .

[0024] Step 8. Targeted treatment for different leakage rates: Take different measures for different leakage rates. When the leakage rate is less than 10m³ / h, you can choose to continue drilling and rely on the accumulation of fine drill cuttings to build bridges to plug the leakage channel; or stop drilling, shut down the pump, lift the drill pipe above the suspected leakage formation, and treat the wellbore; you can also add drilling plugging materials to the drilling fluid in advance to prevent leakage. When the leakage rate is 10-20m³ / h, the viscosity coefficient, flow index and yield stress of the drilling fluid can be appropriately increased in the early stage of leakage to reduce the wellbore pressure; or add bridge plugging materials or high water loss plugging materials to plug the leakage layer. When the loss rate is greater than 20m³ / h, add curable plugging materials, gel plugging materials or water / oil absorbing polymer plugging materials in the early stage of loss; if plugging fails, use composite plugging materials (curable + bridge plug and / or gel, etc.) to reduce the crack width to below the minimum critical crack width, so as to achieve effective plugging of the leakage layer.

[0025] Embodiment 2, the present invention provides a method for plugging leaks and killing wells under the condition of ultra-deep leakage coexistence, specifically referring to Figure 4 : At the ultra-deep drilling site, when overflow and leakage coexist, the well is shut in immediately and maintained for 15 minutes. During this period, a dedicated person is arranged to closely observe the casing pressure gauge and accurately record the casing pressure rise value. If the casing pressure rises by more than 3.5MPa, the current working condition is judged to be a high overflow intensity according to the pre-set judgment standard; if the casing pressure rise does not exceed this value, it is judged to be a low overflow intensity. At the same time, professional flow monitoring equipment is used to accurately measure the leakage rate of drilling fluid. The measured leakage rate is compared with 20m³ / h. If the leakage rate is greater than 20m³ / h, the leakage intensity is determined to be high; if the leakage rate is less than or equal to 20m³ / h, the leakage intensity is determined to be low. For example, in an actual drilling operation, the casing pressure rose by 4MPa 15 minutes after the well was shut in, and the leakage rate reached 25m³ / h. According to the judgment standard, it can be determined that the working condition is a high overflow intensity and a high leakage intensity.

[0026] If it is determined to be an overflow and leak condition, start the positive circulation plugging operation process. First, fully mix the prepared plugging agent with the drilling fluid, and then use the drilling pump to pump the mixed liquid into the wellbore through the drill string in a positive circulation manner. During the pumping process, closely monitor the changes in pump pressure and displacement to ensure that the plugging agent can smoothly reach the leaking layer at the bottom of the well. When the plugging agent reaches the leaking layer, stop pumping, close the blowout preventer and perform pressure holding operation. According to the formation pressure and leakage situation, reasonably control the pressure holding time and pressure value. Generally, the pressure holding time can be controlled within 30-60 minutes, and the pressure value can be gradually increased to 80%-90% slightly higher than the formation fracture pressure, so that the plugging agent can be fully squeezed into the formation cracks to achieve plugging. If it is determined to be an overflow and leak condition, implement reverse circulation plugging operation. Inject the plugging agent from the annulus, and adjust the displacement and pressure of the injection pump to make the plugging agent flow downward along the annulus and preferentially reach the leaking layer at the top of the wellbore. During the injection process, the injection parameters should also be monitored in real time to ensure that the plugging agent is evenly distributed around the leaking layer. After the injection is completed, appropriate pressure holding operations can be performed according to the actual situation to enhance the plugging effect.

[0027] When it is necessary to optimize the particle size of the plugging material, first collect the detailed loss rate data of the on-site drilling fluid and the historical loss data of the block (such as the Bozi block), including the corresponding fracture width data under different loss rates in the past. Use statistical analysis methods to process the collected data to determine the fracture width range that may correspond to the current loss situation. For example, through the analysis of previous data in the Bozi block, it is found that when the loss rate is 2-3m³ / h, the fracture width is usually between 2-3mm, and this is used as a reference to determine the current fracture width range. Based on the determined fracture width range, a plugging simulation experiment is carried out. Using ABAQUS software, a two-dimensional axisymmetric model including the wellbore and formation is constructed, and the model parameters (such as model size, wellbore radius, Poisson's ratio, formation depth, initial pore pressure, etc., to simulate actual formation conditions) are set. In the simulation process, the cohesive unit is used to simulate the wellbore fracture loss and plugging process. By changing the simulation conditions (such as different plugging material particle size assumptions), the relationship between the fracture length and fracture width after fracture bridging and plugging is observed.

[0028] According to the simulation results, the crack width at the plugging bridge position is determined. For example, the simulation found that when the plugging material particle size is a certain value, a stable bridge is formed at a crack length of 20mm. At this time, the corresponding crack width is 2.65mm. This crack width is an important basis for the optimal plugging material particle size. According to the principle of optimizing the particle size of the plugging material (such as the particle size of the plugging material should be slightly larger than 1 / 3 - 1 / 2 of the crack width at the plugging bridge position), select the appropriate plugging material particle size, referring to Figure 3 .

[0029] If the overflow intensity is large: For the overflow and leakage conditions, the pressure back method is used first. Rapidly adjust the throttle valve to increase the wellbore back pressure, so that the bottom hole pressure rises rapidly and the invasion speed of the formation gas into the wellbore is controlled. During the pressure back process, closely monitor the changes in casing pressure, vertical pressure and bottom hole pressure, and reasonably control the pressure back speed and pressure increase value according to the formation pressure and gas invasion. Generally, the pressure back speed can be controlled at 0.5-1MPa / min, and the bottom hole pressure is increased to 10%-15% slightly higher than the formation pressure. When the bottom hole pressure is greater than the formation pressure, stop the pressure back method and switch to throttling circulation well killing. According to the actual loss rate after plugging, select the appropriate chart from the pre-established well killing chart (such as the chart based on the relationship between the loss rate and the well killing fluid displacement and density) to determine the displacement and density of the well killing fluid. Then, start the drilling pump, pump the well killing fluid into the wellbore at the selected displacement and density, perform throttling circulation well killing, and circulate and discharge the gas in the wellbore.

[0030] For the up-leakage and down-flow conditions, according to the leakage rate after plugging, directly select the appropriate chart from the well-killing chart, determine the parameters of the well-killing fluid, and then perform the throttling circulation well-killing operation. During the throttling circulation well-killing process, the throttle valve opening must be strictly controlled to keep the bottom hole pressure slightly higher than the formation pressure to prevent the formation gas from invading the wellbore again.

[0031] If the overflow intensity is small: Regardless of the overflow and leakage or the leakage and overflow conditions, the throttling circulation well killing method is directly adopted. First, according to the leakage rate after plugging, the corresponding throttling circulation critical well killing displacement chart is selected. By measuring the density, viscosity and other parameters of the drilling fluid, the critical displacement value is read from the chart. Then, the drilling pump is started, and the well killing fluid is pumped into the wellbore at a value slightly higher than the critical displacement. At the same time, the throttling valve is adjusted to control the bottom hole pressure to be slightly higher than the formation pressure, and the throttling circulation well killing is performed until all the gas in the wellbore is discharged.

[0032] When the leakage rate is less than 10m³ / h: If you choose to continue drilling, keep the drilling parameters stable and closely observe the return of drilling fluid. As drilling proceeds, fine drill cuttings in the formation will gradually enter the leakage channel and accumulate in the cracks to bridge. According to past experience and on-site monitoring, after drilling to a certain depth (such as 5-10 meters), the leakage rate may gradually decrease or even stop, achieving the purpose of plugging the leakage channel.

[0033] If you choose to stop drilling and shut down the pump, slowly lift the drill pipe to the suspected leakage formation, and ensure that the bottom of the drill pipe is at least 5-10 meters above the leakage layer. Stop the drilling pump to make the liquid in the wellbore still and observe whether the leakage is automatically eliminated. If the leakage stops within a certain period of time (such as 30-60 minutes), normal drilling can be resumed; if the leakage still does not stop, other plugging measures can be considered.

[0034] If you choose to add the plugging material while drilling in advance, add an appropriate amount of plugging agent while drilling to the drilling fluid according to the formation characteristics and leakage prediction (for example, the amount can be estimated based on 3% - 5% of the drilling fluid volume). During the drilling process, the plugging agent while drilling enters the formation with the drilling fluid, fills the cracks, increases the minimum critical crack width, and achieves the effect of leak prevention and plugging.

[0035] When the leakage rate is 10 - 20m³ / h: In the early stage of leakage, adjust the drilling fluid performance. By adding thickeners (such as sodium carboxymethyl cellulose, etc.), changing flow pattern modifiers (such as adding appropriate amounts of polymers) and increasing yield stress additives (such as bentonite, etc.) to the drilling fluid, the viscosity coefficient, flow pattern index and yield stress of the drilling fluid can be increased. According to field tests and experience, the viscosity coefficient is generally increased by 10% -20%, the flow pattern index is adjusted to 0.5 - 0.7, and the yield stress is increased by 2 - 3Pa to reduce the wellbore pressure and reduce the leakage of drilling fluid.

[0036] At the same time, bridge plugging materials or high water loss plugging materials can be added. Bridge plugging materials (such as fiber plugging materials) or high water loss plugging materials (such as diatomaceous earth, etc.) are added to the drilling fluid in a certain proportion (such as bridge plugging materials can account for 5%-8% of the drilling fluid volume, and high water loss plugging materials can account for 3%-5%), and then pumped into the wellbore after sufficient mixing. The bridge plugging material forms a bridge plug structure in the leakage channel, and the high water loss plugging material quickly loses water under the action of pressure difference to form a filter cake, which together seals the leakage layer.

[0037] As a preferred solution of the present invention, when the loss rate is greater than 20m³ / h: in the early stage of loss, a curable plugging material, a gel plugging material or a water-absorbing / oil-absorbing polymer plugging material is added. For example, a curable plugging material (such as a cement slurry plugging material) can be mixed with drilling fluid in a certain ratio (such as 1:3-1:5) and then pumped into the loss layer. The curable plugging material solidifies within a certain period of time to form a high-strength plugging layer; the gel plugging material (such as an acrylamide gel plugging agent) can be adjusted in concentration according to the loss situation and then pumped in to form a gel plug in the crack; the water-absorbing / oil-absorbing polymer plugging material (such as a water-absorbing resin plugging agent) absorbs water and expands after contacting the formation fluid to fill the crack.

[0038] If plugging fails, composite plugging materials are used for secondary plugging. According to the formation fracture conditions and leakage characteristics, select a suitable composite plugging material combination (such as curable plugging material + bridge plugging material + gel plugging material, etc.). For example, the curable plugging material (such as cement slurry plugging material) is mixed with the drilling fluid in a certain ratio (such as 1:3 - 1:5) and pumped into the formation. After it is initially solidified, a mixture of bridge plug plugging material (such as mica flakes) and gel plugging material (such as acrylamide gel plugging agent) compounded in a certain ratio (such as 1:5) is pumped in to reduce the fracture width to below the minimum critical fracture width, achieving effective plugging.

[0039] The above are only some preferred embodiments of the present invention. Any person skilled in the art may modify the above technical solutions or modify them into equivalent technical solutions. Therefore, the corresponding simple modifications or equivalent transformations made according to the technical solutions of the present invention shall fall within the scope of protection claimed by the present invention.

Claims

1. A method for plugging leaks and killing wells under the condition of ultra-deep leakage coexisting, characterized in that: When ultra-deep drilling operations face complex conditions of spills and leaks, (I) First, the overflow and leakage intensity must be accurately judged, including the following steps: 15 minutes after the well is shut in, if the casing pressure rises by more than 3.5MPa, the overflow intensity is determined to be large; if the casing pressure rises by less than 3.5MPa, the overflow intensity is determined to be small; at the same time, if the leakage rate is greater than 20m³ / h, the leakage intensity is determined to be large; if the leakage rate is less than or equal to 20m³ / h, the leakage intensity is determined to be small; (ii) According to the leakage rate and specific working condition type determined, a corresponding plugging method is reasonably selected. The plugging method selection steps include the following steps: if it is an overflow and leakage condition, a positive circulation plugging method is selected, that is, a plugging agent is pumped into the wellbore in a positive circulation manner so that the plugging agent first reaches the leakage layer at the bottom of the well, and then the well is shut down and the pressure is held to squeeze the plugging agent into the formation; if it is an overflow and leakage condition, a reverse circulation plugging method is selected, that is, a plugging agent is injected from the annulus so that the plugging agent first reaches the leakage layer at the top of the wellbore for plugging; (III) Select the appropriate well killing method according to the overflow intensity. The steps for determining the well killing method are as follows: When the overflow intensity is large, for the overflow and leakage conditions, the pressure back method is first used to increase the wellbore pressure and control the gas invasion speed. When the bottom hole pressure is greater than the formation pressure, it is converted to throttling circulation well killing. According to the leakage rate after plugging, the appropriate chart is selected to circulate the gas out of the wellbore; for the leakage and overflow conditions, according to the leakage rate after plugging, the appropriate chart is selected to perform throttling circulation well killing; When the overflow intensity is small, for both overflow and leakage and leakage and underflow conditions, throttling circulation well killing is directly adopted. According to the leakage rate after plugging, the throttling circulation critical well killing displacement chart is selected, the critical displacement is read, and throttling circulation well killing is carried out until the gas is discharged from the wellbore.

2. The method for plugging leaks and killing wells under the condition of coexistence of ultra-deep leakage according to claim 1, characterized in that: The steps of optimizing the particle size of the plugging material are also included: Determine the fracture width range based on the on-site drilling fluid loss rate and the corresponding block loss data; Carry out plugging simulation under corresponding crack width conditions, obtain the relationship between crack length and crack width after crack bridging plugging under corresponding leakage rate, and determine the crack width at the plugging bridge position; The particle size of the plugging material is optimized based on the obtained seam width and the optimization principle of the particle size of the plugging material.

3. The method for plugging leaks and killing wells under the condition of coexistence of ultra-deep leakage according to claim 1, characterized in that: For formation leakage with different leakage rates, the plugging methods also include the following: When the leakage rate is less than 10m³ / h, you can choose to continue drilling and use fine drill cuttings to build bridges to plug the leakage channel; or stop drilling, turn off the pump, lift the drill pipe above the suspected leakage formation, and treat the wellbore; or add drilling plugging materials to the drilling fluid in advance to increase the minimum critical crack width and achieve leakage prevention and plugging effects; When the loss rate is 10-20m³ / h, the viscosity coefficient, flow index and yield stress of the drilling fluid can be appropriately increased in the early stage of loss to reduce the wellbore pressure; or bridge plugging materials or high water loss plugging materials can be added to increase the maximum critical width of the crack or reduce the crack width to plug the leakage layer; When the loss rate is greater than 20m³ / h, curable plugging materials, gel plugging materials or water-absorbing / oil-absorbing polymer plugging materials need to be added in the early stage of loss; if plugging fails, composite plugging materials need to be used for plugging. The composite plugging materials include a combination of curable plugging materials and bridge plugging materials or gel plugging materials to reduce the crack width to below the minimum critical crack width, thereby achieving the effect of plugging the leakage layer.

4. The method for plugging leaks and killing wells under the condition of ultra-deep leakage coexisting according to claim 1, characterized in that: In the positive circulation plugging method: the plugging agent is mixed with the drilling fluid and pumped into the wellbore through the drill string. The pump pressure and displacement changes are monitored during the pumping process. After the plugging agent reaches the leaking layer, the well is shut down and the pressure is held for 30-60 minutes. The holding pressure value is gradually increased to 80%-90% slightly higher than the formation fracture pressure.

5. The method for plugging leaks and killing wells under the condition of coexistence of ultra-deep leakage according to claim 1, characterized in that: In the reverse circulation plugging method, when injecting the plugging agent from the annulus, the displacement and pressure of the injection pump are adjusted so that the plugging agent is evenly distributed around the leaking layer. After the injection is completed, appropriate pressure holding operation can be performed according to the actual situation.

6. The method for plugging leaks and killing wells under the condition of coexistence of ultra-deep leakage according to claim 1, characterized in that: During the pressure-back well killing process, the pressure-back speed is controlled at 0.5-1MPa / min, raising the bottom hole pressure to 10%-15% higher than the formation pressure.

7. The method for plugging leaks and killing wells under the condition of ultra-deep leakage coexisting according to claim 1, characterized in that: During the throttling circulation well killing process, the well killing fluid displacement and density are determined according to the selected chart and drilling fluid parameters, and the throttle valve opening is controlled to keep the bottom hole pressure slightly higher than the formation pressure.

8. The method for plugging leaks and killing wells under the condition of coexistence of ultra-deep leakage according to claim 2, characterized in that: In the step of optimizing the particle size of the plugging material: the statistical analysis method includes the analysis of the corresponding relationship between the historical leakage velocity and the fracture width. During the simulation process, ABAQUS software is used to construct a two-dimensional axisymmetric model. The model parameters are set according to the actual formation conditions. Cohesive units are used to simulate the wellbore fracture leakage and plugging process.

9. The method for plugging leaks and killing wells under the condition of coexistence of ultra-deep leakage according to claim 3, characterized in that: For formation leakage with different leakage rates, the plugging method also includes the following specific steps: When the leakage rate is less than 10m³ / h and drilling is continued, the change of leakage rate is observed after the drilling depth reaches 5-10 meters; when drilling is stopped and the pump is turned off, the drill pipe is lifted to 5-10 meters above the leakage layer, and the static observation time is 30-60 minutes; when the plugging material while drilling is added in advance, the amount of plugging material added is 3%-5% of the drilling fluid volume; When the loss rate is 10-20m³ / h and the drilling fluid performance is adjusted, the consistency coefficient is increased by 10%-20%, the flow index is adjusted to 0.5-0.7, and the yield stress is increased by 2-3Pa; the amount of bridge plugging material added is 5%-8% of the drilling fluid volume, and the amount of high water loss plugging material added is 3%-5%; When the loss rate is greater than 20m³ / h and curable plugging materials are added, the mixing ratio of curable plugging materials to drilling fluid is 1:3-1:5; when composite plugging materials are used for plugging, the appropriate combination is selected according to the formation fracture conditions and the composite plugging slurry is prepared in proportion.

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