Cement plug plugging method under oil-based drilling fluid condition and cement paste

Abstract

The invention discloses a cement plug plugging method under an oil-based drilling fluid condition and cement paste, and the method comprises the following steps: a drilling tool is put down to a well bottom or a leakage layer, and a pre-positioned spacer fluid is pumped at a first preset pumping displacement; cement paste is pumped with the second preset pump injection displacement; if the front spacer fluid flows out of the water hole of the drilling tool and starts to return upwards by a first preset height, drilling is conducted by one stand column height without stopping the pump; pumping the rear spacer fluid at a third preset pumping displacement; the drilling tool is kept immobile, and the drilling fluid is pumped with the fourth preset pumping displacement; judging whether the preposed spacer fluid flows out of the water hole of the drilling tool and begins to upwards return to the annulus or not; if yes, after the front spacer fluid upwards returns to the first preset height, the drill is pulled out by the height of one stand column without stopping the pump; if not, pulling out the hole to a second preset height above the cement surface; well closing and squeezing injection are conducted, and spacer fluid arranged in front of the bottom of the cement paste and cement paste with the sixth preset volume are squeezed into the leakage stratum; and according to the determined initial setting time of the cement paste, well shut-in squeezing injection is conducted with the preset squeezing injection displacement, and the total squeezing injection amount of the cement paste is determined.

Description

Technical Field

[0001] The invention relates to the technical field of oil and gas well drilling and completion, and in particular to a method for plugging leaks with cement under oil-based drilling fluid conditions and cement slurry. Background Art

[0002] With the continuous deepening of exploration and development, the engineering problems caused by complex geological conditions are increasing day by day. Among them, the leakage problem is the most prominent problem among all kinds of underground complexities because of its long treatment cycle and difficulty in plugging. Among the leakage problems, the leakage problem under oil-based drilling fluid conditions is the most difficult to solve.

[0003] Oil-based drilling fluid has the advantages of high temperature resistance, salt resistance, good well wall stability, good lubricity and little damage to oil and gas layers. It has been widely used as an important technical support for drilling deep wells, ultra-deep wells, high-angle directional wells, horizontal wells and water-sensitive complex formations at home and abroad, and has achieved significant results. According to statistics, oil-based drilling fluids are used in deep and ultra-deep drilling in the Tarim Basin, Sichuan Basin, Junggar Basin and Qaidam Basin in China. Oil-based drilling fluid systems are also used in the long horizontal section drilling of Sichuan and Chongqing shale gas and some tight oil and tight gas. While oil-based drilling fluid is widely used, it also has a certain impact on cementing construction, for example: ① Oil-based drilling fluid is easy to adhere to the well wall to form mud cake, and ordinary isolation fluid and flushing fluid are difficult to flush clean, so it is difficult to ensure the cleanliness of the wellbore before construction; ② Natural gas and other natural gas can be dissolved in oil-based drilling fluid. The natural gas that enters the oil-based drilling fluid will cause the gas-liquid volume ratio of the wellbore to increase rapidly during the migration to the upper well section, which means that it is difficult to ensure the stability of the whole process when cementing operations are carried out under oil-based drilling fluid conditions; ③ Oil-based drilling fluid has high viscosity, and it is easy to form an inverted rheological parameter with isolation fluid and cement slurry, resulting in serious mixing of different fluids during cementing construction, more slurry, limited strength development of cement stone, and poor interface bonding with the formation. The above influences often lead to low success rates of cement plugging and plugging when leakage occurs in the application of oil-based drilling fluid system, or even multiple constructions fail to meet the requirements, which seriously restricts the well construction cycle and affects the speed, quality and efficiency of drilling and completion.

[0004] At present, the measures to deal with the problems of low one-time success rate of cement plugging and difficulty in plugging leaking layers under oil-based drilling fluid conditions mainly include strengthening theoretical calculations to reasonably design the amount of cement slurry entering the well to control the height of the cement plug, introducing lipophilic admixtures into the cement slurry to improve interface bonding, and adding oil-based plugging materials or consolidation materials to the drilling fluid. Summary of the invention

[0005] In order to better achieve cement plugging and plugging leaks under oil-based drilling fluid conditions, the embodiments of the present application provide a cement plugging and plugging leak method and cement slurry under oil-based drilling fluid conditions.

[0006] In a first aspect, an embodiment of the present application provides a method for plugging leaks with cement under oil-based drilling fluid conditions, the method comprising:

[0007] Lower the drilling tool to the bottom of the well or the leaking layer, close the annular blowout preventer and try to squeeze the drilling fluid, squeeze in the first preset pumping amount of drilling fluid, and determine whether the leakage channel is unobstructed;

[0008] If yes, pump the pre-placed isolation liquid of the first preset density to the second preset pumping amount with the first preset pumping displacement;

[0009] Pumping cement slurry of a second preset density to a third preset pumping volume at a second preset pumping displacement;

[0010] According to the second preset pumping amount, the third preset pumping amount and the volume of the drilling tool, it is determined whether the front-placed isolation fluid will flow out of the drilling tool water hole and start to return to the annulus;

[0011] If so, after the front isolation fluid returns to the first preset height, the pump is continuously pumped up to drill a column height;

[0012] Pumping the rear-placed isolation liquid of the first preset density to a fourth preset pumping amount with a third preset pumping displacement;

[0013] Keeping the drilling tool stationary, pumping drilling fluid at a fourth preset pumping displacement to a fifth preset pumping displacement to displace cement slurry in the drilling tool;

[0014] According to the second preset pumping amount, the third preset pumping amount, the fourth preset pumping amount, the fifth preset pumping amount and the volume of the drilling tool, it is determined whether the front-placed isolation fluid will flow out of the drilling tool water hole and start to return to the annulus;

[0015] If so, after the front isolation fluid returns to the first preset height, the pump is continuously pumped up to drill a column height;

[0016] If not, start drilling to the second preset height above the cement surface;

[0017] Perform shut-in squeezing to squeeze the spacer fluid placed before the bottom of the cement slurry and the sixth preset volume of cement slurry into the leaking formation;

[0018] According to the determined initial setting time of the cement slurry, shut in the well and squeeze out the cement slurry at a preset squeezing displacement at the first preset time before the initial setting of the cement slurry, and judge whether the casing pressure value reaches the preset maximum casing pressure threshold value and the casing pressure value does not decrease when the pump is stopped;

[0019] If yes, stop squeezing and determine the total squeezing volume of cement slurry;

[0020] If not, the squeezing is stopped until the total squeezing amount of cement slurry reaches the first preset squeezing amount.

[0021] In one or some optional implementations of the embodiments of the present application, after stopping the squeezing, the well is shut down and a drilling plug is lowered after waiting for a preset length of time to obtain the pressure test results.

[0022] In one or some optional implementations of the embodiment of the present application, the first preset density of the isolation liquid is determined by the following method:

[0023] Obtain the formation pressure equivalent density, the preset reserved length of the cement plug, the construction leakage prevention and pressure stabilization conditions, and determine the first preset density of the pre-placed isolation fluid based on the balanced pressure theory; the first preset density ranges from 1.10 to 2.35 g / cm 3 ;

[0024] The second preset density of the cement slurry is determined by:

[0025] Obtain the formation pressure equivalent density, the preset reserved length of the cement plug, the anti-leakage condition and the pressure stability condition, and determine the second preset density of the cement slurry based on the balanced pressure theory; the range of the second preset density is 1.20-2.50 g / cm 3 .

[0026] In one or some optional implementations of the embodiments of the present application, the leakage prevention condition is a condition that the maximum dynamic equivalent of the design construction process is not greater than the pressure equivalent of the leaking layer; the pressure stability condition is a condition to ensure pressure stability throughout the entire process of injection and waiting for setting.

[0027] In one or some optional implementations of the embodiments of the present application, the cement slurry, based on the total mass of cement, further includes: a lightening agent of 0 to 75%, a weighting agent of 0 to 120%, a reinforcing material of 10 to 20%, a high-temperature reinforcing material of 0 to 30%, microsilica of 1 to 20%, an early strength agent of 0 to 3%, a fluid loss reducer of 1 to 3%, a dispersant of 1 to 2%, a fiber of 1 to 4%, and a retarder of 0 to 4%.

[0028] In one or some optional embodiments of the present application, the cement is Grade G oil well cement;

[0029] The lightening agent is a high-performance hollow glass microsphere with a density of 0.35 to 0.6 g / cm3 and a compressive strength of 12,000 to 15,000 psi;

[0030] The weighting agent is one or more of iron ore powder, micro manganese, and spherical high-density iron powder with a density of 4.2 to 7.2 g / cm3;

[0031] The reinforcing material is ultrafine cement;

[0032] The high temperature strengthening material is high performance silicon powder with a particle size of 200 to 1500 mesh and is only used after the temperature exceeds 100°C;

[0033] The early strength agent is at least one of sodium sulfate, calcium chloride, sodium chlorate and calcium formate;

[0034] The fluid loss reducer is at least one of a multi-polymer of 2-acrylamide-2-methylpropanesulfonic acid, N,N-dimethylacrylamide and unsaturated carboxylic acid;

[0035] The dispersant is a condensation product of formaldehyde and acetone or a polycarboxylic acid dispersant;

[0036] The fiber is at least one of sepiolite nanofiber and basalt mineral fiber;

[0037] The retarder is divided into low-temperature retarder and high-temperature retarder, wherein the low-temperature retarder is an organic acid and the high-temperature retarder is an acrylamide.

[0038] In one or some optional embodiments of the embodiments of the present application, the isolation fluid is based on the total mass of water and also includes: 2% to 5% suspending agent, 15% to 20% weighted flushing material, 4% to 5% flushing liquid, 8% to 10% oil-displacing flushing liquid, 6% to 10% anti-pollution agent, 0 to 300% weighting agent, 1% to 2% defoaming agent, and 1% to 2% antifoaming agent.

[0039] In one or some optional embodiments of the embodiments of the present application, the suspending agent is at least one of biopolymers and mineral powders;

[0040] The weighting material is a weighting material for cementing spacer fluid, and is composed of irregular prismatic ore powder;

[0041] The flushing fluid is a flushing fluid for fatty acid cementing isolation fluid;

[0042] The oil-displacing flushing fluid is an oil-displacing flushing fluid for a polyoxyethylene ether cementing isolation fluid;

[0043] The anti-pollution agent is at least one of organic salts and organic acids;

[0044] The weighting agent is at least one of barite, hematite and spinel.

[0045] In one or some optional implementations of the embodiment of the present application, judging whether the front spacer fluid will flow out of the drilling tool water hole and start to return to the annulus according to the second preset pumping amount, the third preset pumping amount and the volume of the drilling tool includes:

[0046] According to the second preset pumping amount, the third preset pumping amount and the volume of the drilling tool, it is determined whether the pumped cement slurry volume is greater than the volume of the drilling tool. If so, it is determined that the front-placed isolation fluid will flow out of the drilling tool water hole and start to return to the annulus.

[0047] In one or some optional implementations of the embodiment of the present application, judging whether the front spacer fluid will go out of the drilling tool water hole and start to return to the annulus according to the second preset pumping amount, the third preset pumping amount, the fourth preset pumping amount, the fifth preset pumping amount and the volume of the drilling tool includes:

[0048] According to the second preset pumping volume, the third preset pumping volume, the fourth preset pumping volume, the fifth preset pumping volume and the volume of the drill tool, it is determined whether the pumped cement slurry volume is greater than the volume of the drill tool. If so, it is determined that the front isolation fluid will exit the drill tool water hole and start to return to the annulus.

[0049] In one or some optional implementations of the embodiment of the present application, shutting in the well to squeeze out the bottoming front spacer fluid at the bottom of the cement slurry and the sixth preset volume of cement slurry into the lost formation includes:

[0050] The drilling fluid or clean water is used as the squeezing medium to carry out shut-in squeezing, and the spacer fluid placed before the bottom of the cement slurry and the sixth preset volume of cement slurry are squeezed into the leakage formation.

[0051] In one or some optional implementations of the embodiments of the present application, the initial setting time of the cement slurry is determined by the following method:

[0052] The initial setting test is carried out on the obtained bulk cement slurry sample to determine the initial setting time of the cement slurry.

[0053] In one or some optional implementations of the embodiment of the present application, the preset maximum casing pressure threshold is the minimum value of 80% of the internal pressure resistance of the upper casing and the fracture pressure value of the weak formation at the upper pipe shoe.

[0054] In a second aspect, an embodiment of the present application provides a cement slurry, comprising:

[0055] The cement slurry comprises, based on the total mass of cement, 0-75% of a lightening agent, 0-120% of a weighting agent, 10-20% of a reinforcing material, 0-30% of a high-temperature reinforcing material, 1-20% of microsilica, 0-3% of an early strength agent, 1-3% of a fluid loss reducing agent, 1-2% of a dispersant, 1-4% of a fiber, and 0-4% of a retarder.

[0056] In one or some optional embodiments of the present application, the cement is Grade G oil well cement;

[0057] The lightening agent is a high-performance hollow glass microsphere with a density of 0.35 to 0.6 g / cm3 and a compressive strength of 12,000 to 15,000 psi;

[0058] The weighting agent is one or more of iron ore powder, micro manganese, and spherical high-density iron powder with a density of 4.2 to 7.2 g / cm3;

[0059] The reinforcing material is ultrafine cement;

[0060] The high temperature strengthening material is high performance silicon powder with a particle size of 200 to 1500 mesh and is only used after the temperature exceeds 100°C;

[0061] The early strength agent is at least one of sodium sulfate, calcium chloride, sodium 6chlorate and calcium formate;

[0062] The fluid loss reducer is at least one of a multi-polymer of 2-acrylamide-2-methylpropanesulfonic acid, N,N-dimethylacrylamide and unsaturated carboxylic acid;

[0063] The dispersant is a condensation product of formaldehyde and acetone or a polycarboxylic acid dispersant;

[0064] The fiber is at least one of sepiolite nanofiber and basalt mineral fiber;

[0065] The retarder is divided into low-temperature retarder and high-temperature retarder, wherein the low-temperature retarder is an organic acid and the high-temperature retarder is an acrylamide.

[0066] The beneficial effects of the above technical solution provided by the embodiment of the present application include at least:

[0067] The method for plugging leaks with cement under oil-based drilling fluid conditions provided in the embodiment of the present application innovatively introduces new comprehensive cement plugging process technologies such as using oil-displacing anti-pollution isolation fluid as a base, squeezing and wetting and flushing the leaking channel in advance, and retaining part of the cement slurry in the leaking channel in advance, which has good effects on ensuring the quality of cement plugs and the bonding between cement and the leaking layer; and, a breakthrough waiting-for-setting squeezing and plugging technology is proposed, which can accurately control the initial setting time of the cement slurry, and shut in the well and squeeze again at the first preset time before the initial setting of the cement slurry until the cement slurry loses fluidity after the initial setting, then shut down the well and hold the pressure to wait for setting, so that the cement slurry with a certain structural strength can achieve a strong retention effect in the leaking channel, and can solidify to form a higher strength after the waiting-for-setting is completed, and the cement forms a good bonding with the leaking layer and the open hole section formation, truly realizing the plugging of the leaking layer. This method has a high one-time construction success rate and significant effects for solving problems such as low quality or even unsuccessful cement plugging caused by the use of oil-based drilling fluid, as well as leakage that cannot be effectively sealed. It reduces the overall cost, has good economy, can be promoted and applied on a large scale, does not require the use of any additional downhole tools and devices, and the cement slurry thickening time is adjustable and controllable, with high safety.

[0068] Other features and advantages of the present application will be described in the subsequent description, and partly become apparent from the description, or understood by practicing the present invention. The purpose and other advantages of the present application can be realized and obtained by the structures specifically pointed out in the written description, claims, and drawings.

[0069] The technical solution of the present application is further described in detail below through the accompanying drawings and embodiments. BRIEF DESCRIPTION OF THE DRAWINGS

[0070] The accompanying drawings are used to provide a further understanding of the present application and constitute a part of the specification. Together with the embodiments of the present application, they are used to explain the present application and do not constitute a limitation of the present application. In the accompanying drawings:

[0071] Figure 1 A schematic flow chart of a method for plugging leaks with cement under oil-based drilling fluid conditions provided in an embodiment of the present application;

[0072] Figure 2 A schematic diagram of the principle of a method for plugging leaks with cement under oil-based drilling fluid conditions provided in an embodiment of the present application. DETAILED DESCRIPTION

[0073] In the following description, specific details such as specific system structures, technologies, etc. are provided for the purpose of illustration rather than limitation, so as to provide a thorough understanding of the embodiments of the present application. However, it should be clear to those skilled in the art that the present application may also be implemented in other embodiments without these specific details. In other cases, detailed descriptions of well-known systems, devices, circuits, and methods are omitted to prevent unnecessary details from obstructing the description of the present application.

[0074] It should be understood that when used in the present specification and the appended claims, the term "comprising" indicates the presence of described features, wholes, steps, operations, elements and / or components, but does not exclude the presence or addition of one or more other features, wholes, steps, operations, elements, components and / or combinations thereof.

[0075] It should also be understood that the term “and / or” used in the specification and appended claims refers to any and all possible combinations of one or more of the associated listed items, and includes these combinations.

[0076] As used in the specification and appended claims of this application, the term "if" can be interpreted as "when" or "uponce" or "in response to determining" or "in response to detecting", depending on the context. Similarly, the phrase "if it is determined" or "if [described condition or event] is detected" can be interpreted as meaning "uponce it is determined" or "in response to determining" or "uponce [described condition or event] is detected" or "in response to detecting [described condition or event]", depending on the context.

[0077] In addition, in the description of the present application specification and the appended claims, the terms "first", "second", "third", etc. are only used to distinguish the descriptions and cannot be understood as indicating or implying relative importance.

[0078] References to "one embodiment" or "some embodiments" etc. described in the specification of this application mean that one or more embodiments of the present application include specific features, structures or characteristics described in conjunction with the embodiment. Therefore, the statements "in one embodiment", "in some embodiments", "in some other embodiments", "in some other embodiments", etc. that appear in different places in this specification do not necessarily refer to the same embodiment, but mean "one or more but not all embodiments", unless otherwise specifically emphasized in other ways. The terms "including", "comprising", "having" and their variations all mean "including but not limited to", unless otherwise specifically emphasized in other ways.

[0079] It should be understood that the size of the serial numbers of the steps in the following embodiments does not mean the order of execution. The execution order of each process should be determined by its function and internal logic, and should not constitute any limitation on the implementation process of the embodiments of the present application.

[0080] In order to illustrate the technical solution of the present application, a specific embodiment is provided below for illustration.

[0081] The inventors found that in the prior art, the measures to deal with the problems of low one-time success rate of cement plugging and difficulty in plugging leaking layers under oil-based drilling fluid conditions mainly include strengthening theoretical calculations to reasonably design the amount of cement slurry entering the well to control the height of the cement plug, introducing lipophilic admixtures into the cement slurry to improve interface bonding, and adding oil-based plugging materials or consolidation materials to the drilling fluid. However, the applicability of the above methods is relatively single, and more targeted measures are proposed only for a certain problem point under the conditions of oil-based drilling fluid, and it is impossible to effectively take into account all difficulties. Moreover, with the gradual deepening of exploration and development, there are more and more deep wells and ultra-deep wells. In the face of high temperature and high pressure conditions, it is even more difficult to use conventional plugging methods to deal with the problem of well leakage under the oil-based drilling fluid system.

[0082] In response to the above technical problems, the prior art discloses a variety of cement plugging and plugging methods. For example, CN105350940A discloses a cement plug quality control method, the core of which is to calculate the on-site control thickness of the cement plug, and can achieve cement plug thickness that meets the design requirements in general leaking wells. However, the density of the cement slurry used is only conventional density and has certain limitations, and it also does not specify what kind of drilling fluid system it is suitable for. CN110965959A discloses a cement plug method with controllable plug surface for cementing in formations prone to blowout and leakage. The core of the method is to determine the wellbore liquid column pressure through the reservoir pressure, and then determine the amount of fluid entering the well. This technology can ensure that the cement plug meets the design amount to a certain extent, but there are no targeted measures for the bonding of the cement plug with the formation, and it does not mention How to ensure the quality of cement plugs in case of oil-based drilling fluid; CN113999658A discloses a lipophilic cement slurry technology that can improve the sealing performance of oil-containing cementing interfaces. The core of the technology is to introduce anionic-nonionic surfactants into the cement slurry system to make the cement slurry lipophilic, thereby ensuring interface bonding, but there is no mention of plugging leaking layers under oil-based drilling fluid conditions; CN113897186A discloses an oil-based gel consolidation plugging system for oil-based drilling fluids suitable for malignant leaking formations. Oil-based gel and curable materials are added to the drilling fluid. As the formation temperature rises, the curing agent begins to participate in the polymerization reaction, causing the system to gradually consolidate to form strength and then plug the leaking layer, but the plugging pressure is not high and is only applicable to medium and low temperature conditions.

[0083] The prior art represented by the above patents has achieved certain results in solving the problem of cement plugging and plugging leaks in oil-based drilling fluids, but its adaptability is relatively single and it is not possible to simultaneously achieve the goals of cement plugging and plugging leaking layers. Based on this, in order to ensure that cement plugs can be quickly plugged and plugged successfully under the oil-based drilling fluid system, a cement plugging and plugging technology under oil-based drilling fluid conditions with strong pertinence, good adaptability, safety, high efficiency, economy and wide coverage has been developed. After further research and development, the inventor made this application to provide a cement plugging and plugging method under oil-based drilling fluid conditions.

[0084] Embodiment 1

[0085] The present application provides a method for plugging leaks with cement under oil-based drilling fluid conditions. Figure 1 As shown, the method includes:

[0086] S101: lower the drilling tool to the bottom of the well or the leaking layer, close the annular blowout preventer and try to squeeze the drilling fluid, squeeze in the first preset pumping amount of drilling fluid, and determine whether the leakage channel is unobstructed. If yes, execute S102; if not, execute step S115.

[0087] In the embodiment of the present application, the oil-based drilling fluid conditions include a full oil drilling fluid system and an oil-in-water drilling fluid system, with a density range of 1.10 to 2.35 g / cm 3 , temperature range 30~200℃, cement plug is cement-based working fluid system, density range 1.20~2.50g / cm 3 , temperature range 30~200℃. The technical principle of the method provided in the embodiment of the present application is: comprehensively consider the pressure bearing capacity of the leaking layer, the density of the drilling fluid, the design height of the cement plug and the cement injection volume, and apply the balanced pressure method to reasonably design the density of the isolation fluid, the density of the cement slurry and the displacement of the cement, to ensure that no leakage occurs during the construction process or to minimize the leakage, and at the same time ensure the pressure stability during the injection and waiting process to prevent the formation fluid from rushing up. Figure 2 As shown in the figure, it is a principle diagram of the cement plugging method under the condition of oil-based drilling fluid. The method is performed in the order from left to right in the figure: ① During the construction process of pumping drilling fluid to replace cement slurry (i.e., injection replacement), when the high-efficiency oil-displacing anti-pollution front-placed isolation fluid returns 100 to 150 meters out of the drill pipe, the drill tool is continuously pumped up (i.e., drilling) by a column height, so that part of the front-placed isolation fluid forms a bottoming effect at the bottom of the cement slurry to avoid direct contact between the bottom of the cement slurry and the drilling fluid, and also prepares for the subsequent early wetting and flushing of the leakage channel; ② It is designed that the cement surface in the drill pipe is 100 to 150 meters higher than the cement surface outside the pipe at the end of injection replacement, to ensure that no slurry is mixed during the drilling process, to ensure the quality of the cement plug, and to create conditions for the formation of a pure cement plug; ③ After the drilling is completed, the well is immediately shut in for squeezing and injection to remove the front-placed isolation fluid and 3 to 5 meters of the bottom-placed isolation fluid. 3 The cement slurry is squeezed into the leakage channel in advance, with the aim of making the pre-placed isolation fluid wet and flush the adherent oil film in the leakage channel, creating favorable conditions for the cement slurry to finally stay and consolidate in the leakage channel, and at the same time, it can play the role of pre-staying part of the cement slurry in the leakage channel; ④ Based on the initial setting data of the large-scale cement slurry on site, the well is shut down and squeezed again 3 hours before the initial setting of the cement slurry, and the cement slurry with a certain structural force is squeezed into the leakage layer, so that the pure cement can stay strongly in the leakage channel and consolidate to form a higher strength. At the same time, the pressure is held down and the setting is waited for, so as to improve the strength development of the cement stone and the interface bonding quality with the formation, so as to meet the goal of quickly resuming the next operation.

[0088] The above technical principle overcomes the problems that often occur when cement plugging and plugging leaks using the existing conventional method under oil-based drilling fluid conditions, such as serious cement slurry mixing, low cement plug quality, and poor or even ineffective cement solidification of the leakage channel, and avoids unfavorable situations such as failure to achieve the expected effect after cement plugging, failure to effectively plug the leakage layer, and inability to continue subsequent construction, which affects the well construction cycle. It solves the problem of poor quality and low strength of cement plugs and ineffective plugging of leakage layers after conventional cement plugging under oil-based drilling fluid conditions, and the technology has many advantages such as high success rate after one-time construction and guaranteed safety of actual on-site implementation.

[0089] In the embodiment of the present application, based on the above technical principle, a method for plugging leaks with cement under oil-based drilling fluid conditions is implemented. In step S101, the drill is lowered to the bottom of the well or the leaking layer, the annular blowout preventer is closed to try to squeeze out the drilling fluid, and the first preset pumping amount of drilling fluid is squeezed in to determine whether the leaking channel is unobstructed. The range of the first preset pumping amount is set according to the actual situation, for example, it can be set to 3 to 5m 3 .

[0090] S102: Pumping the pre-placed isolation fluid of the first preset density to a second preset pumping volume with a first preset pumping displacement.

[0091] In the embodiment of the present application, before executing S102, the first preset density of the isolation liquid is determined in the following manner:

[0092] Obtain the formation pressure equivalent density, the preset reserved length of the cement plug, the construction leakage prevention and pressure stabilization conditions, and determine the first preset density of the pre-placed isolation fluid based on the balanced pressure theory; the first preset density ranges from 1.10 to 2.35 g / cm 3 .

[0093] In the embodiment of the present application, the leakage prevention condition is a condition that the maximum dynamic equivalent of the design construction process is not greater than the pressure equivalent of the leaking layer; the pressure stability condition is a condition to ensure pressure stability throughout the entire process of injection and waiting for setting.

[0094] In the embodiment of the present application, it is necessary to first take the equivalent pressure density of the formation (i.e. the leaking layer) obtained as the basis, comprehensively consider the reserved length of the cement plug design, the conditions of leak prevention and pressure stability during the construction process, and calculate the reasonable isolation fluid density and cement slurry density through the balanced pressure theory. Among them, the balanced pressure theory calculation is the balance between the liquid column pressure composed of all types of liquids in the wellbore and the formation pressure. The parameters involved include the density, height and formation pressure coefficient of different liquids, etc. The formula involved is the liquid column pressure calculation formula. The specific implementation method of the balanced pressure theory calculation can refer to the detailed description in the prior art and is not specifically limited here.

[0095] In the embodiment of the present application, when it is determined by step S101 that the leakage channel is blocked, step S115 is executed to stop pumping; when it is determined by step S101 that the leakage channel is unblocked, step S102 is executed to pump the pre-placed first preset density isolation fluid to the second preset pumping volume with the first preset pumping displacement. The range of the first preset pumping displacement is set according to the actual situation, for example, it can be set to 1.2 to 1.5 m 3 / min; the first preset density range is set to 1.10 ~ 2.35g / cm 3 .

[0096] In the embodiment of the present application, the isolation liquid is based on the total mass of water (in percentage) as the standard, and also includes: suspending agent 2% to 5%, weighted flushing material 15% to 20%, flushing liquid 4% to 5%, oil-displacing flushing liquid 8% to 10%, anti-pollution agent 6% to 10%, weighting agent 0 to 300%, defoaming agent 1% to 2%, and antifoaming agent 1% to 2%.

[0097] In the embodiment of the present application, the suspending agent is 2% to 5%, the weighted flushing material is 15% to 20%, the flushing liquid is 4% to 5%, the oil displacement type flushing liquid is 8% to 10%, the anti-pollution agent is 6% to 10%, the weighting agent is 0 to 300%, the defoaming agent is 1% to 2%, and the antifoaming agent is 1% to 2%, which specifically includes:

[0098] The suspending agent is at least one of biopolymers and mineral powders;

[0099] The weighting material is a weighting material for cementing spacer fluid, and is composed of irregular prismatic ore powder;

[0100] The flushing fluid is a flushing fluid for fatty acid cementing isolation fluid;

[0101] The oil-displacing flushing fluid is an oil-displacing flushing fluid for a polyoxyethylene ether cementing isolation fluid;

[0102] The anti-pollution agent is at least one of organic salts and organic acids;

[0103] The weighting agent is at least one of barite, hematite and spinel.

[0104] In the embodiment of the present application, the formula of the isolation liquid of the first preset density is: water + 2% to 5% suspending agent (DRY-S1 / DRY-S2) + 15% to 20% weighted flushing material DRW-2S + 4% to 5% flushing liquid DRY-1L + 8% to 10% oil-displacing flushing liquid DRY-2L + 6% to 10% anti-pollution agent DRP-1L + 0 to 300% weighting agent (baryte or iron ore powder) + 1% to 2% defoaming agent (DRX-1L) + 1% to 2% antifoaming agent (DRX-2L). Among them, the suspending agent is composed of one or two of biopolymers and mineral powders, polymers such as polyethylene oxide, polyethylene glycol and carboxymethyl starch, and mineral powders such as organic bentonite and kaolin; the weighting material is the weighting material for cementing prefluid, which is composed of irregular prismatic mineral powders; the flushing fluid is a flushing fluid for fatty acid cementing prefluid; the oil-displacing flushing fluid is an oil-displacing flushing fluid for polyoxyethylene ether cementing prefluid; the anti-pollution agent is one or more of organic salts and organic acids, organic salts such as sodium tartrate and sodium benzoate, and organic acids such as carboxylic acids and sulfonic acids; the weighting agent is one or more of barite, hematite and spinel.

[0105] S103: Pumping cement slurry of a second preset density to a third preset pumping volume at a second preset pumping displacement.

[0106] In the embodiment of the present application, before executing S103, the second preset density of the cement slurry is determined in the following manner:

[0107] Obtain the formation pressure equivalent density, the preset reserved length of the cement plug, the anti-leakage condition and the pressure stability condition, and determine the second preset density of the cement slurry based on the balanced pressure theory; the range of the second preset density is 1.20-2.50 g / cm 3 .

[0108] In the embodiment of the present application, the leakage prevention condition is a condition that the maximum dynamic equivalent of the design construction process is not greater than the pressure equivalent of the leaking layer; the pressure stability condition is a condition to ensure pressure stability throughout the entire process of injection and waiting for setting.

[0109] In the embodiment of the present application, after executing step S102, that is, after the pumping of the first preset density of the spacer liquid is completed, the cement slurry of the second preset density is pumped at the second preset pumping displacement, wherein the range of the second preset pumping displacement is set according to the actual situation, for example, it can be set to 1.0~1.8m 3 / min, the compressive strength of cement slurry is 24h>14MPa and 48h>24MPa, which can inhibit the strength decline of cement paste under high temperature.

[0110] In the embodiment of the present application, the cement slurry, based on the total mass of cement (in percentage), also includes: a lightening agent of 0 to 75%, a weighting agent of 0 to 120%, a reinforcing material of 10 to 20%, a high-temperature reinforcing material of 0 to 30%, microsilica of 1 to 20%, an early strength agent of 0 to 3%, a fluid loss reducer of 1 to 3%, a dispersant of 1 to 2%, a fiber of 1 to 4%, and a retarder of 0 to 4%.

[0111] In the embodiment of the present application, the lightening agent is 0-75%, the weighting agent is 0-120%, the reinforcing material is 10-20%, the high temperature reinforcing material is 0-30%, the microsilicon is 1-20%, the early strength agent is 0-3%, the fluid loss reducer is 1-3%, the dispersant is 1-2%, the fiber is 1-4%, and the retarder is 0-4%, specifically including:

[0112] The cement is Grade G oil well cement;

[0113] The lightening agent is a high-performance hollow glass microsphere with a density of 0.35 to 0.6 g / cm3 and a compressive strength of 12,000 to 15,000 psi;

[0114] The weighting agent is one or more of iron ore powder, micro manganese, and spherical high-density iron powder with a density of 4.2 to 7.2 g / cm3;

[0115] The reinforcing material is ultrafine cement;

[0116] The high temperature strengthening material is high performance silicon powder with a particle size of 200 to 1500 mesh and is only used after the temperature exceeds 100°C;

[0117] The early strength agent is at least one of sodium sulfate, calcium chloride, sodium chlorate and calcium formate;

[0118] The fluid loss reducer is at least one of a multi-polymer of 2-acrylamide-2-methylpropanesulfonic acid, N,N-dimethylacrylamide and unsaturated carboxylic acid;

[0119] The dispersant is a condensation product of formaldehyde and acetone or a polycarboxylic acid dispersant;

[0120] The fiber is at least one of sepiolite nanofiber and basalt mineral fiber;

[0121] The retarder is divided into low-temperature retarder and high-temperature retarder, wherein the low-temperature retarder is an organic acid and the high-temperature retarder is an acrylamide.

[0122] In the embodiment of the present application, the formula of pumping cement slurry is cement + 0-75% lightening agent (glass beads) + 0-120% weighting agent (iron powder) + 10-20% reinforcing material DRB-1S + 0-30% high temperature reinforcing material DRB-2S + 1-20% microsilicon + 0-3% early strength agent (DRA-1S / DRA-2S / DRA-3S) + 1-3% fluid loss reducer DRF-1S + 1-2% dispersant DRS-1S + 1-4% fiber + 0-4% retarder (DRH-1L / DRH-2L) + water. The cement slurry is pumped according to the second preset pumping displacement. During the process of pumping cement slurry, it should be ensured that the density reaches the design requirement value, that is, reaches the range of the second preset density, which is set to 1.20-2.50 g / cm 3 .

[0123] S104: Based on the second preset pumping amount, the third preset pumping amount and the volume of the drilling tool, determine whether the pre-placed spacer fluid will flow out of the drilling tool water hole and start to return to the annulus. If so, execute step S105; if not, execute step S106.

[0124] In the above step S104, judging whether the front spacer fluid will flow out of the drilling tool water hole and start to return to the annulus according to the second preset pumping amount, the third preset pumping amount and the volume of the drilling tool specifically includes:

[0125] According to the second preset pumping amount, the third preset pumping amount and the volume of the drilling tool, it is determined whether the pumped cement slurry volume is greater than the volume of the drilling tool. If so, it is determined that the front-placed isolation fluid will flow out of the drilling tool water hole and start to return to the annulus.

[0126] In the embodiment of the present application, during the execution of step S103, according to the second preset pumping amount and the third preset pumping amount, i.e., the pre-placed isolation fluid pumping amount and the cement slurry pumping amount, and the volume of the drill tool, it is calculated whether the pre-placed isolation fluid will come out of the drill tool water hole and start to return to the annulus during the execution of step S103. The standard for judging whether the pre-placed isolation fluid will come out of the drill tool water hole during the process of pumping cement slurry is that if the amount of cement slurry pumped is greater than the volume of the drill tool, the pre-placed fluid will come out of the drill tool and start to return during the process of pumping cement slurry. If the drill tool water hole comes out, step S105 is executed, and after the pre-placed isolation fluid returns to the first preset height, the pumping is continued to drill a column height; if there is no drill tool water hole, S105 is not executed, and step S106 is directly entered. Among them, the first preset height range is set according to the actual situation, for example, it can be set to 100~150m.

[0127] S105: After the front isolation fluid returns to the first preset height, the pump is continuously pumped to drill a column height.

[0128] In the embodiment of the present application, the above step S105 is only executed after it is determined that the front spacer fluid will come out of the drilling tool and start to return during the execution of step S104. If it is determined in step S104 that the front spacer fluid does not come out of the drilling tool water hole, this step S105 is not executed. Among them, the specific value of a column height is determined according to actual conditions.

[0129] S106: Pumping the rear-placed isolation liquid of the first preset density to a fourth preset pumping volume with a third preset pumping displacement.

[0130] In the embodiment of the present application, if it is determined that the front spacer fluid has not flowed out of the drilling tool water hole during the execution of step S104, step S106 is directly executed, that is, after the cement slurry is pumped in step S103, the rear spacer fluid is pumped at the third preset pumping displacement. The rear spacer fluid has the same formula as the front spacer fluid and the same density as the first preset density. The third preset pumping displacement range is set according to the actual situation, for example, it can be set to 3 to 5m 3 ; The fourth preset pumping amount is obtained according to the actual situation.

[0131] S107: Keep the drilling tool stationary, and pump drilling fluid at the fourth preset pumping displacement to the fifth preset pumping displacement to displace the cement slurry in the drilling tool.

[0132] In the embodiment of the present application, after executing step S106, that is, after the pumping of the post-placed isolation fluid is completed, the drill bit is kept stationary, and drilling fluid is pumped with the fourth preset pumping displacement to replace the cement slurry in the drill bit. The slurry replacement displacement (that is, the fourth preset pumping displacement of the drilling fluid) satisfies the annulus return speed greater than 1m / s. The slurry replacement volume must be strictly executed in accordance with the design requirements, and the fifth preset pumping volume is obtained according to actual conditions.

[0133] S108: According to the second preset pumping amount, the third preset pumping amount, the fourth preset pumping amount, the fifth preset pumping amount and the volume of the drilling tool, determine whether the pre-placed isolation fluid will flow out of the drilling tool water hole and start to return to the annulus. If yes, execute step S109; if no, execute step S110.

[0134] In the embodiment of the present application, judging whether the front spacer fluid will go out of the drilling tool water hole and start to return to the annulus according to the second preset pumping amount, the third preset pumping amount, the fourth preset pumping amount, the fifth preset pumping amount and the volume of the drilling tool specifically includes:

[0135] According to the second preset pumping volume, the third preset pumping volume, the fourth preset pumping volume, the fifth preset pumping volume and the volume of the drill tool, it is determined whether the pumped cement slurry volume is greater than the volume of the drill tool. If so, it is determined that the front isolation fluid will exit the drill tool water hole and start to return to the annulus.

[0136] In the embodiment of the present application, during the execution of step S107, according to the second preset pumping amount, the third preset pumping amount, the fourth preset pumping amount, the fifth preset pumping amount and the volume of the drill tool, it is determined whether the front-placed spacer fluid will come out of the drill tool water hole and start to return to the annulus by judging whether the pumped cement slurry amount is greater than the volume of the drill tool. When the pumped cement slurry amount is greater than the volume of the drill tool, it is determined that the front-placed spacer fluid will come out of the drill tool water hole and start to return to the annulus; when the pumped cement slurry amount is less than the volume of the drill tool, it is determined that the front-placed spacer fluid will not come out of the drill tool water hole.

[0137] S109: After the front isolation fluid returns to the first preset height, the pump is continuously pumped to drill a column height.

[0138] In the embodiment of the present application, during the execution of step S108, after it is determined that the pre-placed isolation fluid has exited the drilling tool water hole and has begun to return to the first preset height, the above step S109 is executed to immediately start drilling a column height without stopping the pump. The first preset height range is set according to actual conditions, for example, it can be set to 100-150m.

[0139] S110: Drilling to a second preset height above the cement surface.

[0140] In the embodiment of the present application, during the execution of step S108, after it is determined that the pre-placed isolation fluid will not flow out of the drilling tool water hole, the above step S110 is executed, and after the pumping of drilling fluid to replace the cement slurry in the drilling tool is completed, the drill is immediately pulled out to a second preset height above the cement surface. The second preset height range is set according to actual conditions, for example, it can be set to 100 to 300 meters.

[0141] It should be noted that before executing step S110, the slurry column structure in the drill bit and the annulus after the slurry replacement is completed should be designed in advance to ensure that the cement surface in the drill bit is 100 to 150 meters higher than the cement surface outside the pipe, so that no slurry mixing is generated during the drilling process, creating favorable conditions for forming a pure cement plug.

[0142] S111: shut in the well and squeeze out the spacer fluid placed before the bottom of the cement slurry and the sixth preset volume of cement slurry into the leakage formation.

[0143] In the above step S111, shutting in the well to squeeze out the spacer fluid at the bottom of the cement slurry and the sixth preset volume of cement slurry into the leakage formation specifically includes:

[0144] The drilling fluid or clean water is used as the squeezing medium to carry out shut-in squeezing, and the spacer fluid placed before the bottom of the cement slurry and the sixth preset volume of cement slurry are squeezed into the leakage formation.

[0145] In the embodiment of the present application, after executing step S110, that is, after the drilling is completed, step S111 is immediately executed to implement shut-in squeezing, so that all the pre-placed spacer fluid at the bottom of the cement slurry and the sixth preset volume of cement slurry are squeezed into the lost formation in advance. Among them, the squeezing medium used for squeezing can be one of drilling fluid or clean water; the sixth preset volume range is set according to the actual situation, for example, it can be set to 3 to 5m 3 .

[0146] S112: According to the determined initial setting time of cement slurry, shut in the well and perform squeezing injection at a preset squeezing displacement at the first preset time before the initial setting of cement slurry, and judge whether the casing pressure value reaches the preset maximum casing pressure threshold and the casing pressure value does not decrease when the pump is stopped. If yes, execute step S113; if no, execute step S114.

[0147] In the above step S112, the initial setting time of the cement slurry is determined specifically in the following manner:

[0148] The initial setting test is carried out on the obtained bulk cement slurry sample to determine the initial setting time of the cement slurry.

[0149] In the embodiment of the present application, the initial setting of cement slurry is the time when the cement slurry starts to lose its fluidity. Before construction, the cement slurry initial setting test will be carried out with the on-site large sample ash and on-site potion. According to the initial and final setting test of the on-site large sample cement slurry, the accurate initial setting time of the cement slurry is determined, and the cement slurry with a preset squeezing displacement is shut in and squeezed at the first preset time before the initial setting of the cement slurry. Among them, the first preset time is set according to the actual situation, for example, it can be set to 3h; the preset squeezing displacement is set according to the actual situation, for example, it can be set to 1.5~3L / s; the total squeezing volume of cement slurry, that is, the amount of cement slurry squeezed for the first time after the slurry replacement is completed, should not exceed the first preset squeezing volume, wherein the range of the first preset squeezing volume is set according to the actual situation.

[0150] In the embodiment of the present application, during the execution of step S112, the casing pressure value cannot exceed the preset maximum casing pressure threshold, and it is determined whether the casing pressure value reaches the preset maximum casing pressure threshold and the casing pressure value does not decrease when the pump is stopped. If so, step S113 is executed; if not, step S114 is executed.

[0151] In the embodiment of the present application, the preset maximum casing pressure threshold is the minimum value between 80% of the internal pressure resistance of the upper casing and the fracture pressure value of the weak formation at the upper pipe shoe.

[0152] S113: Stop squeezing and determine the total squeezing volume of cement slurry.

[0153] In the embodiment of the present application, when executing step S112, it is determined whether the casing pressure value reaches the preset maximum casing pressure threshold and the casing pressure value does not decrease when the pump is stopped. If the casing pressure value is close to the maximum value during the injection process and the casing pressure value does not decrease when the pump is stopped, the injection is stopped in advance, and the actual amount of cement slurry injected into the leaking layer is counted, that is, the total amount of cement slurry injected.

[0154] S114: Stop squeezing until the total squeezed amount of cement slurry reaches a first preset squeezed amount.

[0155] S115: Stop squeezing.

[0156] In the embodiment of the present application, when executing step S112, it is determined whether the casing pressure value reaches the preset maximum casing pressure threshold and the casing pressure value does not decrease when the pump is stopped. If the casing pressure value is not close to the maximum value or the casing pressure value decreases when the pump is stopped during the injection process, the cement slurry is continued to be injected until the total amount of cement slurry injected reaches the first preset amount.

[0157] In the embodiment of the present application, after executing step S112, the well is shut down and the cement plug is drilled and a pressure test is performed to verify the quality of the cement plug and the pressure bearing capacity of the leaking layer after plugging. The specific time for shutting down and waiting for cement slurry is determined according to the density of cement slurry, which is 1.20-1.75 g / cm 3 When the solidification time is 48 hours, the density is 1.75~1.85g / cm 3 or 2.00~2.50g / cm 3 When solidified for 36 hours, the density is 1.85~2.00g / cm 3 When solidified, wait for 24 hours.

[0158] The inventors implemented cement plugging or plugging for different wells under oil-based drilling fluid conditions according to conventional methods, and obtained the following comparative examples 1 to 4. In addition, according to the cement plugging or plugging method under oil-based drilling fluid conditions of the present application, cement plugging or plugging was implemented under the same conditions for comparison, and the following embodiments 1 to 3 were obtained. The complete implementation process and results are as follows:

[0159] In a specific comparative example, hereinafter referred to as comparative example 1, the conventional cement plugging method was used under oil-based drilling fluid conditions, and the process and results of the side drilling cement plug application in the Lu 203H123-X1 well of the southern Sichuan shale gas well were as follows:

[0160] 1) The well is a horizontal well converted from a vertical well, with an artificial bottom depth of 3850m. Before sidetracking, cement plugs need to be injected in the 3500-3800m section to meet the needs of later sidetracking operations. The drilling fluid system is an oil-based drilling fluid with a density of 2.18g / cm 3 ;

[0161] 2) Use the conventional cement plugging method to carry out construction. After the drilling tool is lowered to a well depth of 3800m, start the pump to circulate the water hole;

[0162] 3) Cement truck pumps the front isolation fluid for 5m 3 The density of the front isolation fluid is 2.20g / cm 3 , displacement is 1.8m 3 / min; followed by pumping slurry water 2.9m 3 The density of the slurry water is 1.02g / cm 3 , displacement is 0.6m 3 / min;

[0163] 4) The cement truck pump density is 2.30g / cm 3 15m of cement slurry 3 , displacement is 0.7m 3 / min. Cement slurry formula: Jiahua G-grade oil well cement + 100% weighting agent + 1% microsilica + 2.5% fluid loss additive + 1.2% dispersant + 73% water. The cement slurry performance results are shown in Table 1;

[0164] 5) Mud pump replaces drilling fluid 26m 3 , the drilling fluid density is 2.18g / cm 3 , displacement is 1.05m 3 / min; pump replaces weighted drilling fluid 10m 3 , the density of the weighted drilling fluid is 2.35g / cm 3 , displacement is 0.9m 3 / min;

[0165] 6) After the slurry replacement is completed, the drill is immediately pulled up to 2981m to circulate the drilling fluid to ensure the safety of the operation;

[0166] 7) After waiting for setting for 48 hours, drill the plug, and after finding the plug surface, pressurize it to 15T, with a compression distance of 1.3m. After 1 minute, the pressure drops sharply to 5T. Then, pressurize it to 15T for the second time, with a compression distance of 1.36m. After 1 minute, the pressure drops sharply to 5T again. The cement chips returned by the drill plug are like "debris" and break into pieces when squeezed.

[0167] The above comparative example 1 shows that when the conventional cement plug method is used, the cement plug is prone to problems such as poor quality, poor bonding with the formation and low strength, and the formed cement plug cannot meet the subsequent side drilling construction requirements.

[0168] In a specific comparative example, hereinafter referred to as comparative example 2, after adjusting the density and performance of cement slurry, the conventional cement plugging method was again applied under the condition of oil-based drilling fluid, and the process and results of the side drilling cement plug application in the Lu 203H123-X1 well of the southern Sichuan shale gas well were as follows:

[0169] 1) Cement truck pumps 12m of pre-placed isolation fluid 3 The density of the front isolation fluid is 1.94g / cm 3 , displacement is 1m 3 / min; followed by pumping slurry water 1m 3 The density of the slurry water is 1.02g / cm 3 , displacement is 0.6m 3 / min;

[0170] 2) The cement truck pump density is 1.98g / cm 3 13m of cement slurry 3 , displacement is 0.8m 3 / min. Cement slurry formula: Jiahua G-grade oil well cement + 18% weighting agent + 2% microsilica + 2.5% fluid loss additive + 1.2% dispersant + 63% water. The cement slurry performance results are shown in Table 1;

[0171] 3) Mud pump replaces drilling fluid 21.3m 3 , the drilling fluid density is 2.18g / cm 3 , displacement is 0.9m 3 / min; pump replaces weighted drilling fluid 10m 3 , the density of the weighted drilling fluid is 2.40g / cm 3 , displacement is 0.9m 3 / min;

[0172] 4) After the slurry replacement is completed, the drill is immediately pulled up to 3400m to circulate the drilling fluid to ensure the safety of the operation;

[0173] 5) After pressurizing and waiting for solidification for 48 hours, the plug was drilled and the plug surface was found to be 3460m. The pressure was increased to 10T and the pressure did not drop. However, after the plug was drilled to 3600m, the total hydrocarbon content was measured to rise to 58.2879%, and the drilling time was accelerated.

[0174] The above comparative example 2 shows that in order to solve the problems of cement plug strength and bonding, the amount of pre-placed isolation fluid was increased and the density of cement slurry was reduced. The conventional cement plug construction method was applied again. Although the cement plug was improved in strength and bonding, it was not pressed firmly throughout the whole process, resulting in the existence of crossflow channels in the cement plug. The cement plug construction failed again, indicating that only a single aspect was considered without comprehensive targeted measures, and the success rate of cement plug construction under oil-based drilling fluid conditions was low.

[0175] In a specific comparative example, hereinafter referred to as comparative example 3, the conventional cementing plugging method was used to carry out the plugging application process and results of the deep shale gas well Yang 101H65-X1 well as follows:

[0176] 1) The main leaking layer of the well is located at 2860m, ​​the geological stratification is the Qixia Formation, and the drilling fluid system has a density of 2.15g / cm 3 The oil-based drilling fluid was lost at the wellhead after circulation, and the density of the oil-based drilling fluid was reduced to 1.95g / cm 3 , the displacement dropped to 15L / s, and the return was seen at the wellhead;

[0177] 2) Use a combination of plugging slurry and cement slurry to plug leaks. Prepare 15m of plugging slurry in advance before construction. 3 The plugging slurry density is 2.15g / cm 3 , the concentration is 30%, the plugging slurry formula is: 10% while drilling + 10% single seal + 5% compound + 3% walnut shell + 2% cottonseed shell, and the φ127mm×wall thickness 9.19mm drill pipe is lowered to the well depth of 2870m;

[0178] 3) Mud pump injects plugging slurry for 15m 3 , the plugging slurry displacement is 0.9m 3 / min; Pump the front isolation fluid 2.3m 3 The density of the front isolation fluid is 2.05g / cm 3 , displacement is 0.9m 3 / min;

[0179] 4) Cement truck pumps cement slurry for 10m 3 , cement slurry density is 2.10g / cm 3 , displacement is 0.9m 3 / min. Cement slurry formula: Jiahua G-grade oil well cement + 90% weighting agent + 2% microsilica + 2.5% fluid loss additive + 1.2% dispersant + 59% water. The cement slurry performance results are shown in Table 1;

[0180] 5) Mud pump replaces drilling fluid 28m 3 , the drilling fluid density is 1.95g / cm 3 , displacement is 1.2m 3 / min;

[0181] 6) After the slurry replacement is completed, the drill is immediately started to 2460m to ensure the safety of the construction;

[0182] 7) After the drilling is completed, the pressure is held and squeezed to squeeze in 4m of drilling fluid 3 , the maximum casing pressure is 7.5MPa, and the pressure is reduced to 5MPa after solidification under pressure;

[0183] 8) After the setting is completed, drill the plug and drain the water intermittently during the drilling process. After the plug is drilled to 2860m, ​​the leakage will resume again, with a maximum leakage rate of 10m 3 / h.

[0184] The above comparative example 3 shows that the composite plugging method of plugging slurry + cement slurry, under the condition of oil-based drilling fluid, not only the plugging of the leaking layer is ineffective, the cement slurry is not well solidified or even fails to solidify in the leakage channel, and the quality of the cement plug is also very poor, the drill plug has intermittent emptying phenomenon, and the drilling pressure cannot be increased. It proves that the conventional cement plugging method is almost ineffective in plugging oil-based drilling fluid wellbore.

[0185] In a specific comparative example, hereinafter referred to as comparative example 4, the plugging method of the oil-based gel consolidation plugging agent was applied to the deep shale gas well Yang 101H65-X1, and the process and effect of the plugging application were as follows:

[0186] 1) For the leaking well in comparative example 3, after multiple cementing plugging methods failed, an oil-based gel consolidation plugging agent was used to plug the leak again;

[0187] 2) Prepare 15m of oil-based gel consolidation plugging slurry before construction 3 , the plugging slurry density is 2.10g / cm 3 , concentration is 50%, plugging slurry formula: 30% slurry-making organic bentonite + 20% gel + 15% curing agent;

[0188] 3) Mud pump pump oil-based gel consolidation plugging agent 15m 3 , displacement is 0.9m 3 / min;

[0189] 4) Mud pump replaces drilling fluid 28m 3 , the drilling fluid density is 1.95g / cm 3 , displacement is 1.2m 3 / min;

[0190] 5) After the slurry replacement is completed, the drill is immediately pulled up to 2300m to ensure construction safety;

[0191] 6) After the drilling is completed, wait for 8 hours, and then drill the plug after the consolidation plug solidifies. 3 / min circulation without leakage, gradually circulate to increase the density of drilling fluid, the density of drilling fluid increases from 1.95g / cm3 Increase to 2.05g / cm 3 When , the leakage occurs again.

[0192] The above-mentioned comparative example 4 shows that the application of oil-based gel consolidation plugging agent to plug leaks can solidify at the wall of the leaking layer to achieve preliminary plugging, but the consolidation strength of the consolidation plugging agent is not high, and it fails to enter the leakage channel to achieve filling and plugging of the cracks, resulting in low pressure after plugging the leaking layer. After increasing the density of the drilling fluid, it is easy to leak again, and it cannot meet the subsequent drilling requirements. It proves that the conventional cement plugging method has almost no effect on plugging oil-based drilling fluid wells. It should be noted that the plugging construction implemented by using oil-based gel consolidation plugging agent does not belong to the category of cement-based plugging, and the relevant parameters cannot be compared. Therefore, the relevant parameter content of comparative example 4 is not shown in Table 1. This comparative example shows that oil-based condensation and consolidation is currently also a way of plugging, but the success rate is low.

[0193] In a specific embodiment of the present application, hereinafter referred to as Example 1, the cement plugging plugging method under the oil-based drilling fluid conditions of the present application is applied to the process and results of the side drilling cement plug application in the Lu 203H123-X1 well of the southern Sichuan shale gas well are as follows:

[0194] 1) The well was converted from a straight well to a horizontal well. Later, the side drilling needed to inject side drilling cement plugs, which required high strength and good bonding of the cement plugs. The drilling fluid system of the well was oil-based drilling fluid with a density of 2.18 g / cm 3 Before the application of the cement plugging and plugging technology under the oil-based drilling fluid conditions of the present invention, the conventional cement plugging method had been used for construction twice, and the quality of the cement plugs did not meet the standards and could not meet the subsequent sidetracking construction, resulting in a loss of 46 days of work time;

[0195] 2) The cement plugging method under the oil-based drilling fluid conditions of the present application is used to carry out cement plugging construction, and the design adopts the low injection method to lower the drilling tool to a well depth of 3880m;

[0196] 3) In order to improve the displacement and flushing effect of the oil-based drilling fluid residue adhering to the well wall, the mud pump pumps 11m of high-efficiency oil-displacing anti-pollution front-end isolation fluid. 3 The density of the front isolation fluid is 2.20g / cm 3 , displacement is 1m 3 / min. Isolation fluid formula: water + 5% suspension agent DRY-S3 + 20% weighted flushing material DRW-2S + 4% flushing fluid DRY-1L + 10% oil-displacing flushing fluid DRY-2L + 10% anti-pollution agent DRP-1L + 300% barite + 2% defoaming agent DRX-1L + 2% antifoaming agent DRX-2L;

[0197] 4) To further enhance the flushing effect on the well wall, use a cement truck to pump 7m of grouting water.3 The density of the slurry is 1.02g / cm 3 , displacement is 1m 3 / min;

[0198] 5) The cement truck pump density is 2.26g / cm 3 15m of cement slurry 3 , displacement is 1.1m 3 / min. Cement slurry formula: cement + 120% iron ore powder + 10% reinforcing material DRB-1S + 30% high temperature reinforcing material DRB-2S + 1% microsilica + 3% fluid loss reducer DRF-1S + 2% dispersant DRS-1S + 1% basalt fiber + 4% retarder DRH-2L + water. The cement slurry performance results are shown in Table 1;

[0199] 6) Mud pump pumps the rear isolation fluid 3m 3 The density of the rear isolation fluid is 2.20g / cm 3 , displacement is 0.6m 3 / min, the formula is the same as the front isolation fluid. 3 When the isolation fluid starts to flow upward from the drilling tool water hole, the drilling tool is immediately pumped up to about a column height of 26m without stopping after the isolation fluid flows upward for 100m, ensuring that the bottom of the cement plug does not directly contact the drilling fluid, creating conditions for the formation of a pure cement plug.

[0200] 7) Mud pump replaces drilling fluid 31m 3 , the drilling fluid density is 2.18g / cm 3 , displacement is 1.5m 3 / min. After the slurry replacement is completed, the cement surface inside the drill bit is 150m higher than the outside of the pipe to avoid slurry mixing during the drilling process;

[0201] 8) After the slurry replacement is completed, the well is immediately opened and the drilling is started to 3300m, 200m above the cement surface to ensure construction safety;

[0202] 9) After circulating and removing the slurry, shut down the well and hold the pressure to 3MPa, and wait for solidification under pressure;

[0203] 10) After waiting for 48 hours to solidify, the drilling plug was lowered to a plug surface of 3410 m. The drilling pressure was increased to 15 T without decreasing, and the plug was drilled to 3600 m. During the entire drilling process, the cement plugs were solid plugs, no emptying occurred, and no aftereffects occurred. The side drilling operation was successfully implemented.

[0204] The above-mentioned Example 1 illustrates that after the cement plugging construction is implemented using the cement plugging method under the oil-based drilling fluid conditions of the present application, the cement plug has high strength and is well bonded to the formation, and the leakage prevention and stabilization are in place during the construction and waiting for setting process.

[0205] In a specific embodiment of the present application, hereinafter referred to as Example 2, the cement plugging method under the oil-based drilling fluid conditions of the present application is applied to the deep shale gas well Yang 101H65-X1 well, and the process and effect of plugging are as follows:

[0206] 1) The main leaking layer of the well is located at 2860m, ​​the geological stratification is Qixia Formation, and the drilling fluid system is oil-based drilling fluid with a density of 2.15g / cm 3 After the leakage occurred, the circulation wellhead was lost, and the pressure equivalent density of the leakage layer was 1.95g / cm 3 Before the application of the present invention's cement plugging and plugging technology under the oil-based drilling fluid conditions, 5 plugging slurry plugging, 7 conventional cement plugging and 1 oil-based consolidating agent plugging had been used. After multiple plugging methods, although the circulation could be re-established, the pressure increase was limited and leakage occurred again, making it impossible to continue drilling. The cumulative loss of oil-based drilling fluid was 212m 3 , loss of working time 40 days;

[0207] 2) Based on the calculation of the equivalent density of the leaky layer and the equilibrium pressure, the design adopted the low injection method and lowered the drilling tool to a well depth of 2900m;

[0208] 3) In order to improve the displacement and flushing effect of the oil-based drilling fluid residue adhering to the well wall, the mud pump pumps 10m of high-efficiency oil displacement anti-pollution front spacer fluid. 3 The density of the front isolation fluid is 1.90g / cm 3 , displacement is 0.5m 3 / min. Pre-insulating fluid formula: water + 2% suspension agent DRY-S3 + 15% weighted flushing material DRW-2S + 4% flushing fluid DRY-1L + 10% oil-displacing flushing fluid DRY-2L + 8% anti-pollution agent DRP-1L + 190% barite + 1% defoaming agent DRX-1L + 1% antifoaming agent DRX-2L;

[0209] 4) The cement truck pump density is 1.95g / cm 3 18m of cement slurry 3 , displacement is 1m 3 / min. Cement slurry formula: cement + 20% reinforcing material DRB-1S + 1% microsilica + 3% early strength agent DRA-2S + 2% fluid loss agent DRF-1S + 2% dispersant DRS-1S + 4% sepiolite fiber + 3% retarder DRH-2L + water. The cement slurry performance results are shown in Table 1;

[0210] 5) Pump cement slurry 15.5m 3 When the front-placed isolation fluid begins to flow back up from the water hole of the drilling tool, the drilling tool will be immediately lifted up by about a column height without stopping the pump after the front-placed isolation fluid flows back up 100m, so that the isolation fluid can form a bottom cushion at the bottom of the cement plug.

[0211] 6) After the cement slurry is pumped, the mud pump pumps the rear isolation fluid for 3m 3 The density of the rear isolation fluid is 1.90g / cm 3 , displacement is 0.5m 3 / min, the formula is the same as the previous isolation fluid;

[0212] 7) Mud pump replaces drilling fluid 26m 3 , the drilling fluid density is 1.90g / cm 3 , displacement is 1.5m 3 / min. After the slurry replacement is completed, the cement surface inside the drill bit is 100m higher than the outside of the pipe to avoid slurry mixing during the drilling process;

[0213] 8) There was no leakage during the entire construction process. The drill was immediately started after the slurry replacement was completed, and the drilling was started to 2200m to ensure construction safety;

[0214] 9) After drilling is completed, shut down the well immediately and squeeze out all the bottom spacer fluid and 3m 3 Cement slurry is squeezed into the leaking layer in advance; the oil film in the leaking channel is wetted and flushed, and part of the cement is filled into the leaking channel in advance;

[0215] 10) According to the initial setting test data of the cement slurry on site, the well was shut down and the drilling fluid was squeezed again 3 hours before the initial setting of the cement slurry, and a total of 10m 3 , the casing pressure rose to a maximum of 12.6MPa and then stabilized at 10MPa, the pump was stopped and the well was shut down to wait for solidification;

[0216] 11) After 24 hours of waiting for setting, drill the plug and drill to 2900m, with a maximum displacement of 1.8m 3 / min circulation without leakage, and the wellhead is pressurized to perform formation pressure test.

[0217] The results of Example 2 above show that the pressure equivalent density of the leaking layer at 2860m is 1.95g / cm 3 Increased to 2.16g / cm 3 , meeting the requirements for resuming drilling.

[0218] In a specific embodiment of the present application, hereinafter referred to as Example 3, the process and effect of plugging the deep shale gas well Lu 203H123-X5 well by using the cement plugging method under the oil-based drilling fluid conditions of the present application are as follows:

[0219] 1) The main leaking layer of the well is located at 2936-3033m, the geological stratification is the Qixia Formation, and the drilling fluid system has a density of 1.98g / cm 3Oil-based drilling fluid. Before the application of the present invention's oil-based drilling fluid, cement plugging and plugging technology, 8 conventional cementing methods have been used to plug leaks, but no significant effect was achieved. Each time the plugging was completed, the leak occurred again, and drilling could not be continued. The total loss of oil-based drilling fluid was 49m 3 , 13 days of lost work time;

[0220] 2) Combined with the calculation of the equivalent density and equilibrium pressure of the leaky layer, the design adopted the low injection method and lowered the drilling tool to a well depth of 3060m;

[0221] 3) In order to improve the displacement and flushing effect of the oil-based drilling fluid residue adhering to the well wall, the mud pump pumps 8m of high-efficiency oil displacement anti-pollution front spacer fluid 3 The density of the front isolation fluid is 1.90g / cm 3 , displacement is 1m 3 / min. Pre-insulating fluid formula: water + 2% suspension agent DRY-S1 + 15% weighting material DRW-2S + 4% flushing fluid DRY-1L + 10% oil-displacing flushing fluid DRY-2L + 6% anti-pollution agent DRP-1L + 190% barite + 1% defoaming agent DRX-1L + 1% antifoaming agent DRX-2L;

[0222] 4) The cement truck pump density is 1.90g / cm 3 16m of cement slurry 3 , displacement is 1m 3 / min. Cement slurry formula: cement + 20% reinforcing material DRB-1S + 3% microsilica + 3% early strength agent DRA-3S + 2% fluid loss agent DRF-1S + 2% dispersant DRS-1S + 4% basalt fiber + 2.5% retarder DRH-2L + water. The cement slurry performance results are shown in Table 1;

[0223] 5) After the cement slurry is pumped, the mud pump pumps the rear isolation fluid for 3m 3 , density is 1.90g / cm 3 , displacement is 1m 3 / min, the formula is the same as the previous isolation fluid;

[0224] 6) Mud pump replaces drilling fluid 28.4m 3 , the drilling fluid density is 1.90g / cm 3 , displacement is 1.5m 3 / min. After the slurry replacement is completed, the cement surface inside the drill bit is 100m higher than the outside of the pipe to avoid slurry mixing during the drilling process;

[0225] 7) Pump 5.5m of drilling fluid 3When the front-placed isolation fluid begins to flow back up from the water hole of the drilling tool, the drilling tool will be immediately lifted up by about a column height without stopping the pump after the front-placed isolation fluid flows back up 100m, so that the isolation fluid can form a bottom cushion at the bottom of the cement plug.

[0226] 8) There was no leakage during the entire construction process. The drill was immediately started after the slurry replacement was completed, and the drilling was started to 2460m to ensure construction safety;

[0227] 9) After drilling is completed, shut down the well immediately and squeeze out all the bottom spacer fluid and 3m 3 The cement slurry is squeezed into the leaking layer in advance to wet and flush the oil film in the leaking channel and fill part of the cement into the leaking channel in advance;

[0228] 10) According to the initial setting test data of the cement slurry on site, squeeze and inject again 3 hours before the initial setting of the cement slurry, and squeeze and inject cement slurry into the leaking layer for a total of 11m 3 , the casing pressure rose to a maximum of 10.5MPa and then stabilized at 7.2MPa, the pump was stopped and the well was shut down to wait for solidification;

[0229] 11) After 24 hours of waiting for setting, drill the plug to 3060m, with a maximum displacement of 1.5m 3 / min circulation without leakage, and the wellhead is pressurized to perform formation pressure test.

[0230] The results of Example 3 above show that the pressure equivalent density of the leaking layer at 2936-3033m is 1.90g / cm 3 Increased to 2.25g / cm 3 , meeting the requirements for resuming drilling.

[0231] Table 1 Summary of cement slurry properties

[0232] project Example 1 Example 2 Example 3 Comparative Example 1 Comparative Example 2 Comparative Example 3 Density, g / cm3 2.26 1.95 1.90 2.30 1.98 2.10 Thickening time, min 290 245 220 300 290 240 Sedimentation stability, g / cm3 0.04 0.01 0.01 0.09 0.07 0.08 Free liquid, % 0 0 0 0.3 0.2 0.2 API water loss, mL 48 40 40 67 58 60 24h compressive strength, MPa 12 18 19 3 7 6 48h compressive strength, MPa 26 35 37 17 21 20

[0233] As shown in Table 1, combined with the parameter comparison of Comparative Examples 1 to 3 and Examples 1 to 3, it can be seen that Comparative Examples 1 to 3 are plugging construction examples using cement slurry + conventional process, and Examples 1 to 3 are plugging construction examples using high-performance cement slurry + improved process. First of all, in terms of cement slurry itself, the cement slurry in the examples is better than the cement slurry in the comparative examples in terms of sedimentation stability, water loss, free liquid control and compressive strength; secondly, innovation and optimization have been carried out in the plugging process, such as the oil-displacing spacer fluid is pumped up to the height of a column after returning 100 to 150 meters from the drill pipe, and squeezed immediately after the slurry replacement is completed, and squeezed again 3 hours before the initial setting of the cement slurry. High-performance cement slurry and innovative processes jointly ensure the success of the plugging construction. In the cement plugging method under oil-based drilling fluid conditions of the present application, the multi-density high-strength cement slurry system developed has outstanding advantages in properties such as sedimentation stability, free liquid control, API water loss and compressive strength. Especially in terms of compressive strength, the compressive strength of the high-strength cement slurry system far exceeds that of ordinary cement slurry.

[0234] From the above comparison results, it can be seen that the cement plugging and plugging method under oil-based drilling fluid conditions of the present application overcomes the shortcomings and defects of conventional plugging and plugging methods such as cement plugging, plugging slurry plugging and oil-based consolidating agent plugging under oil-based drilling fluid systems, and has the advantages of strong pertinence, wide applicability, high success rate and high safety. It has outstanding results in ensuring the quality of cement plugs, cement consolidation strength, leakage channel filling and solidification bonding, proving that this method has good effects on cement plugging and plugging under oil-based drilling fluid systems.

[0235] In the embodiments of the present application, the cement plugging and plugging method under the oil-based drilling fluid conditions of the present application has the following advantages compared with the conventional cement plugging and plugging methods:

[0236] 1) The balanced pressure method is used in a refined way. Based on the equivalent density of the leaking layer, the density, dosage and annular slurry column structure of the fluid entering the well are reasonably designed to achieve leakage prevention and pressure stabilization during cementing construction, avoiding the problems of "the more you inject, the more you leak", poor quality of cement plugs after waiting for setting, poor bonding and the existence of crossflow channels that occurred in the past when conventional cement plugs were used;

[0237] 2) Innovatively introduced new comprehensive cement plugging technology such as oil displacement anti-pollution isolation fluid padding, early squeeze wetting and flushing of leakage channels, and early retention of some cement slurry in leakage channels. It has a good effect on ensuring the quality of cement plugs and the bonding of cement and leakage layer;

[0238] 3) Developed a multi-density high-strength cement slurry system with a cement slurry density range of 1.20 to 2.50 g / cm 3, 48h cement stone strength is 14~50MPa, the density of cement plug is expanded from conventional density to full density range, improving the adaptability and success rate;

[0239] 4) A breakthrough technology of waiting for setting and squeezing is proposed. The initial setting time of cement slurry is precisely controlled, and the well is shut down and squeezed again 3 hours before the initial setting of cement slurry until the cement slurry loses fluidity after initial setting, and then the well is shut down and pressure is held to wait for setting. This allows the cement slurry with a certain structural strength to achieve a strong retention effect in the leakage channel and solidify to form a high strength after the waiting for setting is completed. The cement forms a good bond with the leakage layer and the open hole section formation, truly achieving the plugging of the leakage layer;

[0240] 5) Cement plugging and plugging technology under oil-based drilling fluid conditions. For the problems of low quality or even failure of cement plugging and ineffective plugging of leakage caused by the use of oil-based drilling fluid, a number of targeted measures and process technologies have been proposed, with a high one-time construction success rate and significant results;

[0241] 6) The cement plugging method under the oil-based drilling fluid conditions of the present application mainly uses cement and various admixtures. Compared with other plugging methods, the overall cost is low and the economy is good, and it can be promoted and applied on a large scale;

[0242] 7) The cement plugging method under oil-based drilling fluid conditions of the present application does not use any additional downhole tools and devices, the cement slurry thickening time is adjustable and controllable, and the safety is high.

[0243] Embodiment 2

[0244] Based on the same inventive concept, the embodiment of the present application further provides a cement slurry, including:

[0245] The cement slurry comprises, based on the total mass of cement (in percentage), 0-75% of a lightening agent, 0-120% of a weighting agent, 10-20% of a reinforcing material, 0-30% of a high-temperature reinforcing material, 1-20% of microsilica, 0-3% of an early strength agent, 1-3% of a fluid loss reducing agent, 1-2% of a dispersant, 1-4% of a fiber, and 0-4% of a retarder.

[0246] In a specific embodiment, the cement slurry further comprises:

[0247] The cement is Grade G oil well cement;

[0248] The lightening agent is a high-performance hollow glass microsphere with a density of 0.35 to 0.6 g / cm3 and a compressive strength of 12,000 to 15,000 psi;

[0249] The weighting agent is one or more of iron ore powder, micro manganese, and spherical high-density iron powder with a density of 4.2 to 7.2 g / cm3;

[0250] The reinforcing material is ultrafine cement;

[0251] The high temperature strengthening material is high performance silicon powder with a particle size of 200 to 1500 mesh and is only used after the temperature exceeds 100°C;

[0252] The early strength agent is at least one of sodium sulfate, calcium chloride, sodium chlorate and calcium formate;

[0253] The fluid loss reducer is at least one of a multi-polymer of 2-acrylamide-2-methylpropanesulfonic acid, N,N-dimethylacrylamide and unsaturated carboxylic acid;

[0254] The dispersant is a condensation product of formaldehyde and acetone or a polycarboxylic acid dispersant;

[0255] The fiber is at least one of sepiolite nanofiber and basalt mineral fiber;

[0256] The retarder is divided into low-temperature retarder and high-temperature retarder, wherein the low-temperature retarder is an organic acid and the high-temperature retarder is an acrylamide.

[0257] The specific formula of the cement slurry provided in the embodiment of the present invention can refer to the detailed description of the cement plugging method under oil-based drilling fluid conditions in the above-mentioned embodiment 1, and will not be repeated here.

[0258] It should be noted that the above-mentioned embodiments are only used to express the technical solutions of the present invention, and the description thereof is relatively specific and detailed, but it cannot be understood as limiting the patent scope of the present invention. It should be pointed out that the present invention is described in detail with reference to the aforementioned embodiments. For ordinary technicians in this field, they can still modify the technical solutions recorded in the aforementioned embodiments, or replace part or all of the technical features therein with equivalents. However, these modifications or replacements do not make the essence of the corresponding technical solutions deviate from the scope of the technical solutions of the embodiments of the present invention.

[0259] The preferred embodiments of the present invention are described in detail above. However, the present invention is not limited to the specific details in the above embodiments. Within the technical concept of the present invention, a variety of simple modifications can be made to the technical solution of the present invention, and these simple modifications all belong to the protection scope of the present invention.

[0260] It should also be noted that the various specific technical features described in the above specific embodiments can be combined in any suitable manner without contradiction. In order to avoid unnecessary repetition, the present invention will not further describe various possible combinations.

Claims

1. A method for plugging leaks with cement under oil-based drilling fluid conditions, characterized in that: include: Lower the drilling tool to the bottom of the well or the leaking layer, close the annular blowout preventer and try to squeeze out the drilling fluid, squeeze in the first preset pumping amount of drilling fluid, and determine whether the leakage channel is unobstructed; If yes, pump the pre-placed isolation liquid of the first preset density to a second preset pumping amount with the first preset pumping displacement; Pumping cement slurry of a second preset density to a third preset pumping amount at a second preset pumping displacement; According to the second preset pumping amount, the third preset pumping amount and the volume of the drilling tool, it is determined whether the front-placed isolation fluid will flow out of the drilling tool water hole and start to return to the annulus; If so, after the front isolation fluid returns to the first preset height, the pump is continuously pumped to drill a column height; Pumping the rear-placed isolation liquid of the first preset density to a fourth preset pumping amount with a third preset pumping displacement; Keeping the drilling tool stationary, pumping drilling fluid at a fourth preset pumping displacement to a fifth preset pumping displacement to displace cement slurry in the drilling tool; According to the second preset pumping amount, the third preset pumping amount, the fourth preset pumping amount, the fifth preset pumping amount and the volume of the drilling tool, it is determined whether the front-placed isolation fluid will flow out of the drilling tool water hole and start to return to the annulus; If so, after the front isolation fluid returns to the first preset height, the pump is continuously pumped to drill a column height; If not, start drilling to the second preset height above the cement surface; Perform shut-in squeezing to squeeze the spacer fluid placed before the bottom of the cement slurry and the sixth preset volume of cement slurry into the leaking formation; According to the determined initial setting time of the cement slurry, shut in the well and squeeze out the cement slurry at a preset squeezing displacement at the first preset time before the initial setting of the cement slurry, and judge whether the casing pressure value reaches the preset maximum casing pressure threshold value and the casing pressure value does not decrease when the pump is stopped; If yes, stop squeezing and determine the total squeezing volume of cement slurry; If not, the squeezing is stopped until the total squeezing amount of cement slurry reaches the first preset squeezing amount.

2. The method according to claim 1, characterized in that After stopping the squeezing and injection, the well is shut down and the drilling plug is lowered after waiting for a preset time to obtain the pressure test results.

3. The method according to claim 1, characterized in that The first preset density of the isolation fluid is determined by: Obtain the formation pressure equivalent density, the preset reserved length of the cement plug, the construction leakage prevention and pressure stabilization conditions, and determine the first preset density of the pre-placed isolation fluid based on the balanced pressure theory; the first preset density ranges from 1.10 to 2.35 g / cm 3 ; The second preset density of the cement slurry is determined by: Obtain the formation pressure equivalent density, the preset reserved length of the cement plug, the anti-leakage condition and the pressure stability condition, and determine the second preset density of the cement slurry based on the balanced pressure theory; the range of the second preset density is 1.20-2.50 g / cm 3 .

4. The method according to claim 3, characterized in that The leakage prevention condition is that the maximum dynamic equivalent of the design construction process is not greater than the pressure equivalent of the leaking layer; the pressure stability condition is to ensure pressure stability during the entire process of injection and waiting for setting.

5. The method according to claim 1, characterized in that The cement slurry, based on the total mass of cement, also includes: 0-75% lightener, 0-120% weighting agent, 10-20% reinforcing material, 0-30% high-temperature reinforcing material, 1%-20% microsilica, 0-3% early strength agent, 1%-3% fluid loss reducer, 1%-2% dispersant, 1%-4% fiber, and 0-4% retarder.

6. The method according to claim 5, characterized in that The cement is Grade G oil well cement; The lightening agent has a density of 0.35 to 0.6 g / cm 3 High-performance hollow glass microspheres with a compressive strength of 12,000 to 15,000 psi; The weighting agent has a density of 4.2 to 7.2 g / cm 3 One or more of iron ore powder, micro manganese, and spherical high-density iron powder; The reinforcing material is ultrafine cement; The high temperature strengthening material is high performance silicon powder with a particle size of 200 to 1500 mesh and is only used after the temperature exceeds 100°C; The early strength agent is at least one of sodium sulfate, calcium chloride, sodium chlorate and calcium formate; The fluid loss reducer is at least one of a multi-polymer of 2-acrylamide-2-methylpropanesulfonic acid, N,N-dimethylacrylamide and unsaturated carboxylic acid; The dispersant is a condensation product of formaldehyde and acetone or a polycarboxylic acid dispersant; The fiber is at least one of sepiolite nanofiber and basalt mineral fiber; The retarder is divided into low-temperature retarder and high-temperature retarder, wherein the low-temperature retarder is an organic acid and the high-temperature retarder is an acrylamide.

7. The method according to claim 1, characterized in that The isolation liquid is based on the total mass of water and also includes: 2% to 5% suspending agent, 15% to 20% weighted flushing material, 4% to 5% flushing liquid, 8% to 10% oil-displacing flushing liquid, 6% to 10% anti-pollution agent, 0% to 300% weighting agent, 1% to 2% defoaming agent, and 1% to 2% antifoaming agent.

8. The method according to claim 7, characterized in that The suspending agent is at least one of biopolymers and mineral powders; The weighting material is a weighting material for cementing spacer fluid, and is composed of irregular prismatic ore powder; The flushing fluid is a flushing fluid for fatty acid cementing isolation fluid; The oil-displacing flushing fluid is an oil-displacing flushing fluid for a polyoxyethylene ether cementing isolation fluid; The anti-pollution agent is at least one of organic salts and organic acids; The weighting agent is at least one of barite, hematite and spinel.

9. The method according to claim 1, characterized in that The step of judging whether the front-placed spacer fluid will flow out of the drilling tool water hole and start to return to the annulus according to the second preset pumping amount, the third preset pumping amount and the volume of the drilling tool comprises: According to the second preset pumping amount, the third preset pumping amount and the volume of the drilling tool, it is determined whether the pumped cement slurry volume is greater than the volume of the drilling tool. If so, it is determined that the front-placed isolation fluid will flow out of the drilling tool water hole and start to return to the annulus.

10. The method according to claim 1, characterized in that The step of judging whether the front spacer fluid will flow out of the drilling tool water hole and start to return to the annulus according to the second preset pumping amount, the third preset pumping amount, the fourth preset pumping amount, the fifth preset pumping amount and the volume of the drilling tool comprises: According to the second preset pumping volume, the third preset pumping volume, the fourth preset pumping volume, the fifth preset pumping volume and the volume of the drill tool, it is determined whether the pumped cement slurry volume is greater than the volume of the drill tool. If so, it is determined that the front isolation fluid will exit the drill tool water hole and start to return to the annulus.

11. The method according to claim 1, characterized in that The shut-in squeezing method is to squeeze the spacer fluid placed before the bottom of the cement slurry and the sixth preset volume of cement slurry into the leakage formation, including: The drilling fluid or clean water is used as the squeezing medium to carry out shut-in squeezing, and the spacer fluid placed before the bottom of the cement slurry and the sixth preset volume of cement slurry are squeezed into the leakage formation.

12. The method according to claim 1, characterized in that The initial setting time of cement paste is determined by: The initial setting test is carried out on the obtained bulk cement slurry sample to determine the initial setting time of the cement slurry.

13. The method according to claim 1, characterized in that The preset maximum casing pressure threshold is the minimum value of 80% of the internal pressure resistance of the upper casing and the fracture pressure value of the weak formation at the upper pipe shoe.

14. A cement slurry, characterized in that: The cement slurry comprises, based on the total mass of cement (in percentage), 0-75% of a lightening agent, 0-120% of a weighting agent, 10-20% of a reinforcing material, 0-30% of a high-temperature reinforcing material, 1-20% of microsilica, 0-3% of an early strength agent, 1-3% of a fluid loss reducing agent, 1-2% of a dispersant, 1-4% of a fiber, and 0-4% of a retarder.

15. The cement slurry according to claim 14, characterized in that The cement is Grade G oil well cement; The lightening agent has a density of 0.35 to 0.6 g / cm 3 High-performance hollow glass microspheres with a compressive strength of 12,000 to 15,000 psi; The weighting agent has a density of 4.2 to 7.2 g / cm 3 One or more of iron ore powder, micro manganese, and spherical high-density iron powder; The reinforcing material is ultrafine cement; The high temperature strengthening material is high performance silicon powder with a particle size of 200 to 1500 mesh and is only used after the temperature exceeds 100°C; The early strength agent is at least one of sodium sulfate, calcium chloride, sodium chlorate and calcium formate; The fluid loss reducer is at least one of a multi-polymer of 2-acrylamide-2-methylpropanesulfonic acid, N,N-dimethylacrylamide and unsaturated carboxylic acid; The dispersant is a condensation product of formaldehyde and acetone or a polycarboxylic acid dispersant; The fiber is at least one of sepiolite nanofiber and basalt mineral fiber; The retarder is divided into low-temperature retarder and high-temperature retarder, wherein the low-temperature retarder is an organic acid and the high-temperature retarder is an acrylamide.

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