Foam lost circulation material, its application and method for treating shallow loss of oil and gas well

Abstract

The present application relates to the technical field of oil exploration, in particular to a kind of foam leak-stopper and its application and the method for treating oil and gas well superficial layer leakage.The foam leak-stopper includes: leak-stopper drilling fluid and foam cement slurry;The mass ratio of leak-stopper drilling fluid and foam cement slurry is 1:1-1:5.The foam leak-stopper provided by the present application has low density, low static column pressure in well after pumping, prevents foam cement slurry from leaking after cementing construction is completed, foam leak-stopper drilling fluid liquid level is high, and can simultaneously consolidate leakage layer near wellbore zone and full hole well wall.The cement stone formed after the foam leak-stopper and foam cement slurry provided by the present application are coagulated has low strength, and sweep plug is easy, which can shorten operation time.

Description

Technical Field

[0001] This invention relates to the field of petroleum exploration technology, specifically to a foam plugging agent, its application, and a method for controlling shallow surface leakage in oil and gas wells. Background Technology

[0002] In oil and gas well engineering, conventional cementing operations use cementing fluid to effectively seal the annular space between the casing string and the formation or outer casing, preventing reservoir damage and ensuring safe and efficient oil and gas production. In the drilling and completion of complex oil and gas wells, cementing is also a crucial means of addressing complex downhole conditions.

[0003] In wells with drilling fluid loss, the loss of drilling fluid will cause adverse effects such as drilling fluid waste, wellbore instability, and reservoir damage. Common methods include plugging with drilling fluid or pumping cement slurry to form a cement plug. This technology is effective for wells with low leakage rates, but for wells with large losses and low formation pressure, this method requires a very low drilling fluid density, which conventional cement slurry cannot meet. Furthermore, shallow surface losses can cause wellbore collapse and spalling. A series of measures, including plugging, cementing, retrieval, sidetracking, and well relocation, are implemented, but continuous spalling and stuck pipe occur downhole, leading to leakage, collapse, and inability to drill normally. For the complex situation of high-loss wells, another method is to run expansion pipes or similar tools into the well to plug the leakage point, but this method is costly, complex, and has unsatisfactory results.

[0004] In shallow, high-loss wells, the large volume of drilling fluid loss, sometimes even leading to fluid return failure, causes wellbore instability and collapse, severely impacting drilling safety and significantly increasing well construction time. The drilling fluid density is 1.0–1.1 g / cm³. 3 Conventional leak sealing methods are not feasible, and expansion pipe leak sealing technology is costly. There is an urgent need for a technical method that can solve the complex working conditions of shallow leakage. Summary of the Invention

[0005] The purpose of this invention is to overcome the drilling problems of shallow drilling fluid loss and wellbore collapse in the prior art, and to provide a foam plugging agent, its application and a method for controlling shallow leakage in oil and gas wells. The foam plugging agent can seal the leakage layer and the wellbore that has collapsed due to consolidation instability.

[0006] To achieve the above objectives, the first aspect of the present invention provides a foam plugging agent, which includes: plugging drilling fluid and foam cement slurry; wherein the mass ratio of the plugging drilling fluid to the foam cement slurry is 1:1 to 1:5.

[0007] A second aspect of the present invention provides the application of the foam plugging agent described herein in controlling shallow surface leakage in oil and gas wells.

[0008] A third aspect of the present invention provides a method for controlling shallow surface leakage in oil and gas wells, the method comprising:

[0009] The foam plugging agent described in this invention is delivered to the lost formation, displacing the original drilling fluid in the well and flowing down into the lost formation to plug the leak.

[0010] Through the above technical solution, the foam plugging agent provided by the present invention, when mixed with foam cement slurry in the plugging drilling fluid, can increase the viscosity of the plugging drilling fluid, reduce the density of the plugging drilling fluid, and increase the plugging effect.

[0011] The foam plugging agent provided by this invention has a low density and a low hydrostatic pressure in the well after pumping, which prevents the leakage of foam cement slurry after cementing operations. The high drilling fluid level of the foam plugging agent can simultaneously solidify the near-wellbore area of ​​the lost circulation zone and the entire wellbore wall. The cement stone formed after the foam plugging agent and foam cement slurry provided by this invention solidify has low strength, making it easy to clean and shortening the operation time.

[0012] In specific applications: This invention has a foam sealant density of 0.8–1.0 g / cm³. 3 It is equal to or lower than the density of pure water by 1.0 g / cm³. 3 The advantages of this method are that the drilling fluid density used in shallow drilling is 1.0-1.1 g / cm³. 3 The occurrence of drilling fluid loss indicates that the formation's pressure-bearing capacity is less than the equivalent density of 1.0 g / cm³. 3 The foam-filled cement slurry of the present invention meets this condition: the hydrostatic pressure at the bottom of the well is low, ensuring that the foam-filled cement slurry does not leak or only partially leaks into the well. The foam-filled cement slurry partially enters the formation and forms cement stone of a certain strength in the well and the lost layer, thereby achieving the purpose of sealing the lost layer.

[0013] Conventional drilling fluids used alone as plugging agents have a density higher than that of water and cannot be lower than 1.0 g / cm³. 3 The drawback of this method is that, for formations with high conventional pressure bearing capacity, the plugging drilling fluid can plug the leakage fractures after entering the formation and prevent further leakage. However, for shallow formations with wide fractures, high leakage velocities, and low pressure bearing capacity, the plugging drilling fluid can completely leak into the formation under the high fluid column pressure inside the well, thus failing to achieve the desired plugging effect.

[0014] Conventional use of conventional cement grout alone as a sealant has the drawback of high density; conventional low-density cement grout only reaches a density of 1.4–1.9 g / cm³. 3The density is still much higher than that of clean water. For shallow, low-density drilling fluid loss-of-return oil and gas wells, the high density of cement slurry causes the bottom hole pressure to be much higher than the pressure-bearing capacity of the loss-of-return formation. Under the action of hydrostatic pressure difference, it completely enters the loss zone and is flushed into the formation by the fluid in the loss zone. It cannot form cement stone near the wellbore and cannot seal the loss zone. Attached Figure Description

[0015] Figure 1 This is a schematic diagram of the method for treating shallow surface leakage in oil and gas wells provided by a preferred embodiment of the present invention.

[0016] Explanation of reference numerals in the attached figures

[0017] 1. Cement mortar hopper; 2. Slurry mixing tank; 3. Cementing truck; 4. Foamed cement slurry mixing skid; 5. Nitrogen; 6. Leakage plugging material; 7. Leakage plugging drilling fluid mixing tank; 8. Cement head; 9. Drill pipe; 10. Wellbore; 11. Lost zone; 12. Wellhead equipment. Detailed Implementation

[0018] The endpoints and any values ​​of the ranges disclosed herein are not limited to the precise ranges or values, and these ranges or values ​​should be understood to include values ​​close to these ranges or values. For numerical ranges, the endpoint values ​​of the various ranges, the endpoint values ​​of the various ranges and individual point values, and individual point values ​​can be combined with each other to obtain one or more new numerical ranges, which should be considered as specifically disclosed herein.

[0019] In this invention, the shallow layer refers to the strata shallower than 1000m.

[0020] The first aspect of the present invention provides a foam plugging agent, which includes: plugging drilling fluid and foam cement slurry; wherein the mass ratio of the plugging drilling fluid to the foam cement slurry is 1:1 to 1:5.

[0021] According to a preferred embodiment of the present invention, the mass ratio of the plugging drilling fluid to the foamed cement slurry is 1:1 to 1:3.

[0022] According to a preferred embodiment of the present invention, the density of the foam sealant is 0.8-1.2 g / cm³. 3 Preferably, it is 0.8-1.0 g / cm³. 3 .

[0023] According to a preferred embodiment of the present invention, the plastic viscosity of the foam sealant is 100-180 mPa·s.

[0024] According to a preferred embodiment of the present invention, the density of the plugging drilling fluid is 1.2-1.5 g / cm³. 3 .

[0025] According to a preferred embodiment of the present invention, the density of the foamed cement slurry is 0.7-1.2 g / cm³. 3 .

[0026] According to a preferred embodiment of the present invention, the thickening time of the foamed cement slurry is 80-150 min.

[0027] The foamed cement slurry contains: cement slurry base, foaming agent, foam stabilizer and nitrogen; preferably, the cement slurry base contains 64-78% by weight of oil well G-grade pure cement, 1-4% by weight of silica fume and 21-35% by weight of slurry mixing water.

[0028] According to a preferred embodiment of the present invention, the foamed cement slurry comprises 98.8-99.2% by weight of cement slurry base, 0.4-0.6% by weight of foaming agent, and 0.4-0.6% by weight of foam stabilizer, based on 100% by weight.

[0029] According to a preferred embodiment of the present invention, the method for preparing the foamed cement slurry includes: adding cement slurry base, foaming agent, and foam stabilizer into a mixing skid and mixing with nitrogen gas to form foamed cement slurry.

[0030] In this invention, there is no particular limitation on the type of foaming agent. Conventional foaming agents in the art can be used in this invention. Preferably, the foaming agent is selected from at least one of sodium fatty alcohol polyoxyethylene ether sulfate, cocamidopropyl betaine, and sodium α-alkenyl sulfonate.

[0031] In this invention, there is no particular limitation on the type of foam stabilizer. Conventional foam stabilizers in the art can be used in this invention. Preferably, the foam stabilizer is selected from at least one of hydroxyethyl cellulose, hydroxyethyl methyl cellulose and xanthan gum.

[0032] The method for preparing the foamed cement slurry includes: adding cement slurry base, foaming agent, and foam stabilizer into a foamed cement slurry foaming device and mixing with nitrogen gas to form foamed cement slurry.

[0033] According to a preferred embodiment of the present invention, the plugging drilling fluid contains drilling fluid and plugging material; the mass ratio of drilling fluid to plugging material is 100:15-100:35.

[0034] According to a preferred embodiment of the present invention, the drilling fluid is selected from at least one of low-solids polymer drilling fluid, freshwater drilling fluid, brine drilling fluid, and mixed oil drilling fluid.

[0035] According to a preferred embodiment of the present invention, the sealing material is selected from at least one of walnut shells, limestone, rubber granules, asphalt, fibers, and peanut shells.

[0036] A second aspect of the present invention provides the application of the foam plugging agent described herein in controlling shallow surface leakage in oil and gas wells.

[0037] A third aspect of the present invention provides a method for controlling shallow surface leakage in oil and gas wells, the method comprising:

[0038] The foam plugging agent described in this invention is delivered to the lost formation, displacing the original drilling fluid in the well and flowing down into the lost formation to plug the leak.

[0039] According to a preferred embodiment of the present invention, the method includes the following steps:

[0040] (1) Wellhead preparation: First, stop drilling, raise downhole tools (such as drill pipes) to the wellhead, close the wellhead, and surface fluids can enter the well through the drill pipes;

[0041] (2) Prepare the plugging drilling fluid and continuously pump the plugging drilling fluid to the cement head through a high-pressure pipeline;

[0042] (3) Prepare foamed cement slurry using a foamed cement slurry foaming device and deliver it to the cement head;

[0043] (4) The foamed cement slurry and the plugging drilling fluid are mixed in the cement head pipeline to form the foam plugging agent, which is then transported to the lost formation. The foam plugging agent displaces the original drilling fluid in the well and flows down into the lost formation.

[0044] (5) After the foam plugging agent is delivered, stop delivering the plugging drilling fluid and continue delivering the foam cement slurry. The foam cement slurry will displace the foam plugging agent and continue to flow into the lost circulation zone in the well.

[0045] (6) After the foamed cement slurry is delivered, the well is closed and allowed to solidify. After the cement slurry solidifies, the well is opened and the plug is removed. The drill bit reaches the bottom of the well, and the shallow surface leakage treatment construction is completed.

[0046] The wellhead preparation scheme provided in step (1) of this invention involves raising the drill pipe to the wellhead, removing the drill string at the bottom of the drill pipe, leaving 20m-30m of the drill pipe in the well, and closing the wellhead annulus. Surface fluid enters the drill pipe and the well only through the pipeline connected to the drill pipe.

[0047] The plugging drilling fluid provided in step (2) of this invention includes plugging drilling fluids with various properties used on site, and the density of the plugging drilling fluid can be adjusted according to the working conditions at the bottom of the well.

[0048] In step (3) of this invention, cement slurry base is first prepared (for example, cement slurry base is continuously prepared on a cement truck). According to the actual working conditions in the well, a certain proportion of water loss reducer, retarder, dispersant, etc. can be added to the cement slurry base to adjust the performance of the cement slurry base and meet the cementing construction requirements. The density of the cement slurry base is designed according to the conditions in the well.

[0049] In step (3) of the present invention, the cement slurry base is pumped to the inlet of the foam cement slurry foaming device (e.g., foam cement slurry mixing skid). In the foam cement slurry foaming device, nitrogen gas, foaming agent and foam stabilizer are injected into the cement slurry base to form foam cement slurry, which is then transported to the cement head through the outlet of the foam cement slurry foaming device.

[0050] In step (5) of this invention, the density of the foamed cement slurry is lower than that of the foamed plugging agent, and the density of the foamed cement slurry is lower than that of the drilling fluid when leakage begins in the well. The pressure of the liquid column of the foamed cement slurry in the well is lower than that of the formation pressure of the leakage layer, so as to ensure that the foamed cement slurry does not continue to leak after the well is shut in.

[0051] According to a preferred embodiment of the present invention, in steps (4) and (5), when conveying the foam plugging agent and foam cement slurry, the fluid flow rate must meet the requirement that the foam plugging agent and foam cement slurry flow in the well in the form of plug flow.

[0052] According to a preferred embodiment of the present invention, in step (5), when conveying foamed cement slurry, the discharge rate of foamed cement slurry is controlled after the top of the foamed plugging drilling fluid reaches the lost circulation layer.

[0053] According to a preferred embodiment of the present invention, in step (5), the thickening time of the prepared foamed cement slurry needs to be accurately designed to shorten the thickening time of the foamed cement slurry.

[0054] According to a preferred embodiment of the present invention, in step (5), the volume of the prepared foamed cement slurry is greater than the volume inside the wellbore, so that the wellbore is still filled with foamed cement slurry after the foamed cement slurry enters the lost formation, and the foamed cement slurry solidifies into cement stone of a certain strength in the wellbore and near the lost formation.

[0055] According to one embodiment of the present invention, the present invention provides a schematic flowchart of a method for treating shallow surface leakage in oil and gas wells, as shown below. Figure 1 As shown, the method includes:

[0056] (1) Preparation of foamed cement slurry: cement ash and slurry mixing water are stored in cement ash tank 1 and slurry mixing water tank 2 respectively.

[0057] (2) Preparation of drilling fluid for plugging: Drilling fluid and plugging materials are stored in drilling fluid pool and plugging material warehouse 6, respectively.

[0058] (3) First stop drilling, lift the bottom of drill pipe 9 down into the well to a distance of 20m to 30m from the wellhead device 12, close the wellhead annulus, connect cement head 8 to the top of drill pipe 9, connect cementing pipeline and drilling fluid pipeline, and at this time the surface fluid can be injected into the well through drill pipe 9;

[0059] (4) The plugging material 6 and the original conventional drilling fluid are mixed in the plugging drilling fluid mixing tank 7 to form a plugging drilling fluid, which is then pumped to the cement head 8;

[0060] (5) Cement ash and grouting water are transported to cementing truck 3 through pipelines, and cement ash and grouting water are mixed in proportion to form cement slurry base slurry of designed density and pumped into foam cement slurry mixing skid 4.

[0061] (6) High-pressure nitrogen 5 is delivered to the foamed cement slurry mixing skid 4 through the pipeline, and forms foamed cement slurry with cement slurry base slurry in the foamed cement slurry mixing skid 4, and is pumped to the cement head 8.

[0062] (7) Foamed cement slurry is mixed with plugging drilling fluid to form foam plugging agent, which is continuously injected into the well under pump pressure;

[0063] (8) The pumping rate of foam plugging agent shall be pumped according to the design rate. After the design rate is reached, the injection of plugging drilling fluid shall be stopped. At this time, only foam cement slurry shall be injected.

[0064] (9) Foamed cement slurry is continuously injected into the well, and the discharge rate of foamed cement slurry is adjusted according to the design.

[0065] (10) During the injection of foamed cement slurry, the pump pressure at the wellhead shall be continuously monitored. When the design wellhead pressure or the design foamed cement slurry injection volume is reached, the injection of foamed cement slurry shall be stopped.

[0066] (11) After stopping the injection of foamed cement slurry, the cementing truck pumps the designed volume of clean water into the casing head through the pipeline to ensure that there is no foamed cement slurry inside or outside the drill pipe.

[0067] (12) Close the well and wait for the foamed cement slurry to solidify and reach a certain strength. Then open the well and use the drill pipe to sweep the plug to the bottom of the well. The shallow surface leakage control construction is completed.

[0068] The present invention will be described in detail below through embodiments.

[0069] Example 1

[0070] (1) Take 800g of pure cement and 24g of silica to form 824g of cement ash. Mix the cement ash and grouting water at a mass ratio of 100:44 to form a cement slurry base (density 1.88g / cm³). 3 The cement slurry base was pumped into the foamed cement slurry mixing skid, and 7.1g of foaming agent (cocamidopropyl betaine) and 4.7g of foam stabilizer (hydroxyethyl cellulose) were added to the skid. Nitrogen gas was then introduced, and the mixture was stirred to obtain a foam density of 1.0g / cm³. 3 Foamed cement slurry, thickening time 92 minutes;

[0071] (2) A conventional drilling fluid (low-solids polymer drilling fluid, wherein the weight ratio of water, organic cationic polymer, nitrohumic acid and polyvinyl alcohol is 100:1.5:0.5:0.5) is mixed with a plugging material (walnut shell and asphalt particles in a mass ratio of 2:1) at a mass ratio of 100:25 to obtain a plugging drilling fluid (density 1.15 g / cm³). 3 );

[0072] (3) Mix the foamed cement slurry from step (1) and the plugging drilling fluid from step (2) at a mass ratio of 1:1 to obtain a foam plugging agent (density 0.90 g / cm³). 3 The plastic viscosity is 142 mPa·s.

[0073] Example 2

[0074] (1) Take 800g of pure cement and 24g of microsilica to form 824g of cement ash. Mix the cement ash and grouting water at a mass ratio of 100:52 to form a cement slurry base (density 1.80g / cm³). 3 The cement slurry base was pumped into the foamed cement slurry mixing skid, and 7.5g of foaming agent (sodium fatty alcohol polyoxyethylene ether sulfate) and 5.0g of foam stabilizer (hydroxyethyl methyl cellulose) were added to the skid. Nitrogen gas was then introduced, and the mixture was stirred to obtain a foamed cement slurry with a viscosity of 0.8g / cm³. 3 The foamed cement slurry thickened in 142 minutes.

[0075] (2) A plugging drilling fluid (density 1.2 g / cm³) is prepared by mixing conventional freshwater drilling fluid (clean water) with plugging material (limestone and peanut shells in a mass ratio of 3:1) at a mass ratio of 100:30. 3 );

[0076] (3) Mix the foamed cement slurry from step (1) and the plugging drilling fluid from step (2) at a mass ratio of 2:1 to obtain a foam plugging agent (density 0.92 g / cm³). 3 The plastic viscosity is 132 mPa·s.

[0077] Example 3

[0078] (1) Take 800g of pure cement and 24g of microsilica to form 824g of cement ash. Mix the cement ash and grouting water at a mass ratio of 100:48 to form a cement slurry base (density 1.83g / cm³). 3 The cement slurry base was pumped into the foamed cement slurry mixing skid, and 7.3g of foaming agent (sodium α-alkenyl sulfonate) and 4.9g of foam stabilizer (hydroxyethyl cellulose) were added to the skid. Nitrogen gas was then introduced, and the mixture was stirred to obtain a foamed cement slurry with a viscosity of 0.9g / cm³. 3 The foamed cement slurry thickened in 121 minutes.

[0079] (2) A conventional drilling fluid (composed of 0.2% xanthan gum, 4% bitumen, 20% sodium chloride, and 0.2% anionic cellulose) was mixed with a plugging material (walnut shells and limestone in a mass ratio of 3:1) at a mass ratio of 100:35 to obtain a plugging drilling fluid (density 1.28 g / cm³). 3 );

[0080] (3) Mix the foamed cement slurry from step (1) and the plugging drilling fluid from step (2) at a mass ratio of 1:2 to obtain a foam plugging agent (density 0.95 g / cm³). 3 (Plastic viscosity is 110 mPa·s).

[0081] Field Application 1

[0082] Well A was designed to reach a depth of 716m at the surface. Significant leakage occurred when drilling reached 580m, with a leakage rate of 80m / s. 3 Drilling continued at 611m, where a loss of return occurred, and the drilling fluid level was measured at 208m downhole. The loss was plugged using conventional cement plugging methods, with a cement slurry density of 1.80 g / cm³. 3 The pressure was far greater than the bearing capacity of the downhole lost circulation zone. Conventional cement slurry resulted in severe leakage, plugging failure, and drilling fluid continued to fail to return. Foam plugging agent was used to treat the shallow surface leakage in this well. The specific implementation process is as follows:

[0083] (1) After drilling is completed, lift the drill pipe to the wellhead, unload the drill bit, and lower the drill pipe to 32m downhole;

[0084] (2) Connect the cement head to the top of the drill pipe and connect the pipeline;

[0085] (3) Cement ash and grouting water are piped into the cement truck, where they are mixed to a density of 1.40 g / cm³. 3 The cement slurry base is pumped into the foamed cement slurry mixing skid;

[0086] (4) Foamed cement slurry is mixed in the mixing skid by adding foaming agent, foam stabilizer, and filling with nitrogen to form a density of 0.7 g / cm³. 3 The foamed cement slurry is pumped to the cement head;

[0087] (5) Add conventional drilling fluid (composed of 0.2% xanthan gum, 4% bitumen, 20% sodium chloride, and 0.2% anionic cellulose) and plugging material (limestone and peanut shells in a 3:1 mass ratio) to the drilling fluid pool to prepare a solution with a density of 1.0–1.1 g / cm³. 3 The plugging drilling fluid was pumped to the cement head;

[0088] (6) Foamed cement slurry and plugging drilling fluid (flow ratio 1:3) are mixed at the cement head to form a mixture with a density of 0.8–0.9 g / cm³. 3A foam plugging agent with a plastic viscosity of 145 Pa·s was continuously pumped in, along with foam cement slurry and plugging drilling fluid. The foam plugging agent was continuously pushed into the well, with a discharge rate of 0.4 m³. 3 / min;

[0089] (7) Foam sealant pumping rate: 15m 3 Then stop injecting plugging drilling fluid and continue injecting 0.7 g / cm³. 3 The foamed cement slurry has a discharge rate of 1.0 m³. 3 / min;

[0090] (8) The foamed cement grout injection volume reaches 65m 3 Subsequently, the pump pressure of the foamed cement slurry injection pump gradually increased from 1.8 MPa to 2.5 MPa, indicating that the leakage at the bottom of the well had been significantly sealed. Foamed cement slurry injection was then stopped, and the cementing truck injected 2m³ of slurry into the cementing pipeline. 3 Clear water;

[0091] (9) After the water injection was completed, the well was closed and allowed to solidify for 48 hours. Then, the well was opened and the plug was removed, and drilling continued to 850m. The shallow layer treatment was completed, and the effect was significant, ensuring the smooth progress of subsequent drilling.

[0092] Field Application 2

[0093] Well B was designed to reach a depth of 716m at the surface. Significant leakage occurred when drilling reached 580m, with a leakage rate of 80m / s. 3 Drilling continued at 611m, where a loss of return occurred, and the drilling fluid level was measured at 208m downhole. The loss was plugged using conventional cement plugging (cement slurry density 1.60 g / cm³). 3 The pressure loss was far greater than the bearing capacity of the downhole lost circulation zone. Conventional cement slurry resulted in severe leakage, leading to plugging failure and continued drilling fluid loss. Foam-filled drilling fluid was then used to treat the shallow surface leakage in this well.

[0094] The specific implementation process is as follows:

[0095] (1) After drilling is completed, lift the drill pipe to the wellhead, unload the drill bit, and lower the drill pipe to 32m downhole;

[0096] (2) Connect the cement head to the top of the drill pipe and connect the pipeline;

[0097] (3) Cement ash and grouting water are piped into the cement truck, where they are mixed to a density of 1.40 g / cm³. 3 The cement slurry base is pumped into the foamed cement slurry mixing skid;

[0098] (4) Foamed cement slurry is mixed in the mixing skid by adding foaming agent, foam stabilizer, and filling with nitrogen to form a density of 0.7 g / cm³. 3 The foamed cement slurry is pumped to the cement head;

[0099] (5) Add conventional drilling fluid and plugging material to the drilling fluid pool to prepare a solution with a density of 1.0–1.1 g / cm³. 3 The plugging drilling fluid was pumped to the cement head;

[0100] (6) Foamed cement slurry and plugging drilling fluid (flow ratio 1:3) are mixed at the cement head to form a mixture with a density of 0.85–0.95 g / cm³. 3 A foam plugging agent with a plastic viscosity of 123 Pa·s was continuously pumped in, along with foam cement slurry and plugging drilling fluid. The foam plugging agent was continuously pushed into the well, with a discharge rate of 0.4 m³. 3 / min;

[0101] (7) Foam sealant pumping rate: 15m 3 Then stop injecting plugging drilling fluid and continue injecting 0.7 g / cm³. 3 The foamed cement slurry has a discharge rate of 1.0 m³. 3 / min;

[0102] (8) The foamed cement grout injection volume reaches 65m 3 Subsequently, the pump pressure of the foamed cement slurry injection pump gradually increased from 1.8 MPa to 2.5 MPa, indicating that the leakage at the bottom of the well had been significantly sealed. Foamed cement slurry injection was then stopped, and the cementing truck injected 2m³ of slurry into the cementing pipeline. 3 Clear water;

[0103] After the water injection was completed, the well was closed and allowed to solidify for 48 hours. Then, the well was reopened, the plug was removed, and drilling continued to 850m. The shallow layer treatment was completed, and the effect was significant, ensuring the smooth progress of subsequent drilling.

[0104] The preferred embodiments of the present invention have been described in detail above; however, the present invention is not limited thereto. Within the scope of the inventive concept, various simple modifications can be made to the technical solutions of the present invention, including combinations of various technical features in any other suitable manner. These simple modifications and combinations should also be considered as the content disclosed in the present invention and are all within the protection scope of the present invention.

[0105] Field Application 2

[0106] Well C has a surface depth of 852m and a drilling fluid density of 1.05g / cm³. 3 Significant leakage occurred at a depth of 646m, with a leakage rate reaching 114m / s. 3 / h, drilling continued to 677m when a loss of return occurred, and the formation's bearing capacity was below 1.05g / cm³. 3The drilling fluid level was tested at 190m downhole. Positive leakage was plugged using a plugging drilling fluid (the plugging material consisted of walnut shells, asphalt, and fiber in a 1:1:0.2 ratio, mixed with the well's drilling fluid at a ratio of plugging material:drilling fluid = 30:100, with a density of 1.10 g / cm³). 3 The drilling fluid used for plugging (whose density exceeded the pressure-bearing capacity of the downhole lost circulation zone) failed to return, resulting in plugging failure. Foam-filled drilling fluid was then used to treat the shallow surface lost circulation in this well.

[0107] The specific implementation process is as follows:

[0108] (1) After drilling is completed, lift the drill pipe to the wellhead, unload the drill bit, and lower the drill pipe to 100m downhole;

[0109] (2) Connect the cement head to the top of the drill pipe and connect the pipeline;

[0110] (3) Cement ash and grouting water are piped into the cement truck, where they are mixed to a density of 1.35 g / cm³. 3 The cement slurry base is pumped into the foamed cement slurry mixing skid;

[0111] (4) Foamed cement slurry is mixed in the mixing skid by adding foaming agent, foam stabilizer, and filling with nitrogen to form a density of 0.78 g / cm³. 3 The foamed cement slurry is pumped to the cement head;

[0112] (5) Add conventional drilling fluid and plugging material to the drilling fluid pool to prepare a solution with a density of 1.05–1.08 g / cm³. 3 The plugging drilling fluid was pumped to the cement head;

[0113] (6) Foamed cement slurry and plugging drilling fluid (flow ratio 1:3) are mixed at the cement head to form a mixture with a density of 0.80–0.92 g / cm³. 3 A foam plugging agent with a plastic viscosity of 160 Pa·s was continuously pumped in, along with foam cement slurry and plugging drilling fluid. The foam plugging agent was continuously pushed into the well, with a discharge rate of 0.5 m³. 3 / min;

[0114] (7) Foam sealant pumping rate: 15m 3 Then stop injecting plugging drilling fluid and continue injecting 0.78 g / cm³. 3 The foamed cement slurry has a discharge rate of 0.8m³. 3 / min;

[0115] (8) The foamed cement grout injection volume reached 88m³. 3 Subsequently, the pressure of the foamed cement slurry pump gradually increased from 1.2 MPa to 4.4 MPa, indicating that the leakage at the bottom of the well had been significantly sealed. Foamed cement slurry injection was then stopped, and the cementing truck injected 2m³ of slurry into the cementing pipeline.3 Clear water;

[0116] After the water injection was completed, the well was closed and allowed to solidify for 48 hours. Then, the well was reopened, the plug was removed, and drilling continued to 850m. The shallow layer treatment was completed, and the effect was significant, ensuring the smooth progress of subsequent drilling.

[0117] The preferred embodiments of the present invention have been described in detail above; however, the present invention is not limited thereto. Within the scope of the inventive concept, various simple modifications can be made to the technical solutions of the present invention, including combinations of various technical features in any other suitable manner. These simple modifications and combinations should also be considered as the content disclosed in the present invention and are all within the protection scope of the present invention.

Claims

1. A foam sealant, characterized in that, The plugging agent comprises: plugging drilling fluid and foamed cement slurry; the mass ratio of the plugging drilling fluid to the foamed cement slurry is 1:1-1:5; The foamed cement slurry contains: cement slurry base, foaming agent, foam stabilizer and nitrogen; the cement slurry base contains 64%-78% by weight of oil well grade G pure cement, 1%-4% by weight of silica fume and 21%-35% by weight of slurry mixing water; based on 100% by weight of the foamed cement slurry, it contains 98.8%-99.2% by weight of cement slurry base, 0.4%-0.6% by weight of foaming agent and 0.4%-0.6% by weight of foam stabilizer.

2. The foam sealant according to claim 1, wherein, The mass ratio of the plugging drilling fluid to the foamed cement slurry is 1:1-1:3; and / or The density of the foam sealant is 0.8-1.2 g / cm³. 3 ; and / or The plastic viscosity of the foam sealant is 100-180 mPa·s.

3. The foam sealant according to claim 2, wherein, The density of the foam sealant is 0.8-1.0 g / cm³. 3 .

4. The sealing agent according to claim 1, wherein, The density of the plugging drilling fluid is 1.2-1.5 g / cm³. 3 .

5. The sealing agent according to any one of claims 1-4, wherein, The density of the foamed cement slurry is 0.7-1.2 g / cm³. 3 ; and / or The thickening time of foamed cement slurry is 80-150 minutes.

6. The sealing agent according to any one of claims 1-4, wherein, The foaming agent is selected from at least one of sodium fatty alcohol polyoxyethylene ether sulfate, cocamidopropyl betaine, and sodium α-alkenyl sulfonate; The foam stabilizer is selected from at least one of hydroxyethyl cellulose, hydroxyethyl methyl cellulose and xanthan gum.

7. The sealing agent according to any one of claims 1-4, wherein, The method for preparing the foamed cement slurry includes: adding cement slurry base, foaming agent, and foam stabilizer into a foamed cement slurry foaming device and mixing with nitrogen gas to form foamed cement slurry.

8. The sealing agent according to any one of claims 1-4, wherein, The plugging drilling fluid contains drilling fluid and plugging material; the mass ratio of drilling fluid to plugging material is 100:15-100:

35. The drilling fluid is selected from at least one of low-solids polymer drilling fluid, freshwater drilling fluid, brine drilling fluid, and oil-mixed drilling fluid; and / or The sealing material is selected from at least one of walnut shells, limestone, rubber granules, asphalt, fibers, and peanut shells.

9. The application of the foam plugging agent according to any one of claims 1-8 in controlling shallow surface leakage in oil and gas wells.

10. A method for controlling shallow surface leakage in oil and gas wells, characterized in that, The method includes: The foam plugging agent according to any one of claims 1-8 is delivered to the lost formation to displace the original drilling fluid in the well and enter the lost formation to plug the leak.

11. The method according to claim 10, wherein, The method includes the following steps: (1) Wellhead preparation: First, stop drilling, raise the downhole tools to the wellhead, close the wellhead, and surface fluid can enter the well through the drill pipe; (2) Prepare the plugging drilling fluid and continuously pump the plugging drilling fluid to the cement head through a high-pressure pipeline; (3) Prepare foamed cement slurry using a foamed cement slurry foaming device and deliver it to the cement head; (4) The foam cement slurry and the plugging drilling fluid are mixed in the cement head pipeline to form the foam plugging agent, which is then transported to the lost formation. The foam plugging agent displaces the original drilling fluid in the well and flows down into the lost formation. (5) After the foam plugging agent is delivered, stop delivering the plugging drilling fluid and continue delivering the foam cement slurry. The foam cement slurry will displace the foam plugging agent and continue to flow into the lost circulation zone in the well. (6) After the foamed cement slurry is delivered, the well is closed and left to set. After the cement slurry has solidified, the well is opened and the plug is removed. The drill bit reaches the bottom of the well, and the shallow surface leakage treatment construction is completed.

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